JP4853299B2 - Mass of clathrate hydrate, formation method thereof, heat storage method, heat storage device - Google Patents

Description

The present invention relates to a clathrate hydrate mass formed by accumulating clathrate hydrate produced by cooling an aqueous solution containing a clathrate hydrate-forming substance, and a method for forming the same. Lumps of clathrate hydrate can be used as a component of a latent heat storage body, for example, in heat utilization fields such as air conditioning and heat storage and heat dissipation, and other energy-related fields, and in particular, latent heat that forms the core part of a stationary heat storage device Suitable for heat storage.
Moreover, this invention relates to the thermal storage method and thermal storage apparatus using the clathrate hydrate used for an air conditioning, a cooling device, etc.
In this specification, the following terms have the following meanings.
(I) “Block” means an object having an outer shape as one aggregate, and there is no limitation on the shape as long as it is visually distinguishable from surrounding objects, unless otherwise specified. The sharpness of the outline, internal structure, strength, hardness, viscosity, density, composition, etc. are not limited.
(Ii) “Offshore” refers to the direction in which an aqueous solution is present with reference to the heat exchange surface in a state where the heat exchange surface is present in the aqueous solution.

The latent heat storage material generated from the solution cooled by the heat exchange with the cold heat source is accumulated on the surface of the heat exchange surface where the heat exchange with the cold heat source occurs or from the surface toward the offshore of the solution. What has come to have an outer shape has a technical value as a latent heat storage body.
A typical example of a technology constructed with this value in mind is the ice heat storage technology. Ice heat storage technology generates ice by cooling ice-making liquid contained in a tank with a refrigerant through a heat exchanger installed in the tank, and this is formed on the surface of the heat exchange surface or on the surface thereof. It is a technology for achieving effective use of energy by forming ice blocks by accumulating or growing from the surface toward the liquid offshore, using the ice blocks as a latent heat storage body, and using it in a heat storage air conditioning system (Patent Document 1).

In addition to ice, latent heat storage materials are known. For example, clathrate hydrate (Patent Document 2).
The clathrate hydrate is produced by cooling an aqueous solution containing a clathrate hydrate-generating substance by heat exchange with a cold heat source. The clathrate hydrate becomes a lump when accumulated on the surface of the heat exchange surface where heat exchange with the cold heat source occurs or from the surface toward the offshore of the aqueous solution. Since these properties are similar to the properties of ice, which is the basis of the above-mentioned ice heat storage technology, ice and clathrate hydrate (or ice-making liquid and clathrate hydrate-generating substances are added in the ice heat storage technology. It can be expected that the technology to be referred to as clathrate hydrate heat storage technology will be constructed without difficulty if it is simply replaced with an aqueous solution containing it, but it is not so simple when actually considered for use in a heat storage system.

The most serious problem in the construction of clathrate hydrate heat storage technology is that clathrate hydrate has lower thermal conductivity than ice. For this reason, an aqueous solution containing the clathrate hydrate forming substance is cooled by heat exchange with a cold heat source to produce clathrate hydrate, and heat exchange with the cold heat source takes place on or from the surface of the heat exchange surface. In the process of accumulating toward the offshore of the aqueous solution, it is difficult for cold heat to be transmitted through the clathrate hydrate from the heat exchange surface toward the offshore of the aqueous solution, and the formation of new clathrate hydrate toward the offshore of the aqueous solution It takes a long time, and as a result, it is difficult to grow larger as a massive clathrate hydrate.
It is difficult for the clathrate hydrate to grow into a large lump body, which means that the heat storage amount that can store heat reaches a peak. For this reason, clathrate hydrate accumulated on or from the surface of the heat exchange surface where heat exchange with the cold heat source takes place using physical (mechanical) or thermal means. Attempts have been made to repeatedly promote the formation and agglomeration of clathrate hydrates by exfoliating the lump from the surface and dispersing it in a solution to form a slurry, thereby exposing the heat exchange surface (patent) Document 3 and Patent document 4). In this case, the slurry is used as a heat storage agent (or heat storage material).
However, the amount of heat storage per unit volume (heat storage density) is higher than the clathrate hydrate mass formed by the accumulation of clathrate hydrate on the heat exchange surface compared to the clathrate hydrate slurry. Is bigger. In this sense, it can be said that it is originally desirable to use a clathrate hydrate mass as a heat storage agent (or heat storage material).

Therefore, in order to establish clathrate hydrate heat storage technology that can be used for actual heat storage air conditioning systems, etc., in the ice heat storage technology, clathrate hydrate (or ice making liquid instead of ice) is used. It is not enough to use a simple contrivance of using an aqueous solution containing a clathrate hydrate-producing substance. The low thermal conductivity of clathrate hydrate can be overcome by some means, and the clathrate hydrate Special measures are needed to store more latent heat in the body.

Here, as a technique for facilitating the conduction of heat when the latent heat storage material is generated from a solution, for example, there is the following.
(A) A method in which expanded graphite is mixed in a solid-liquid phase change material as a heat conductive aid (Patent Document 5).
(B) A carbon fiber having thermal conductivity is oriented on the heat transfer tube surface, or fins or wires made of a material having high thermal conductivity are provided (Patent Document 6).

  In addition to improving the thermal conductivity of clathrate hydrate, as a technique for increasing the heat storage amount of clathrate hydrate, for example, as a technique using eutectic with ice, clathrate hydrate There are clathrate hydrates produced in the process of cooling the aqueous solution containing the product substance, and ice is produced by further cooling, and a mixed slurry of clathrate hydrate and ice is used as the main agent of the heat storage agent ( Patent Document 7).

Japanese Patent Laid-Open No. 7-294076 Japanese Patent No. 3641362 JP 2000-111123 A JP 2000-205775 A Japanese Patent Laid-Open No. 2004-149796 JP 2000-55578 A JP 2001-280875 A

  As a method for improving the thermal conductivity of clathrate hydrate, the above-mentioned methods (A) and (B) are based on the addition of another auxiliary material to the heat storage agent or the addition of a heat exchanger member. Therefore, it is necessary to make the structure complicated, and the material cost and the processing cost increase, resulting in an overall increase in cost. Moreover, the space occupation of the added member causes a problem that the volume of the heat storage agent and thus the heat storage amount per unit volume is reduced.

  In addition, as a technique for increasing the heat storage amount of clathrate hydrate, the technique of Patent Document 7 using a eutectic with ice is used for the clathrate hydrate produced on the heat exchange surface by heat exchange each time the clathrate hydrate is produced. Remove and repeat the generation and removal of clathrate hydrate on the newly exposed heat exchange surface and store it in a separate heat storage tank to store cold heat and further generate ice to increase the amount of heat storage It is a technique. Therefore, the thermal conductivity of the clathrate hydrate mass accumulated on the surface of the heat exchange surface or from the surface toward the offshore of the aqueous solution cannot be improved. Problems caused by low thermal conductivity cannot be solved.

  The present invention has been made in view of the above points, and in a massive body of clathrate hydrate produced by heat exchange between an aqueous solution containing a clathrate hydrate-generating substance and a cold heat source, latent heat storage properties are provided. Establish clathrate hydrate storage technology that overcomes the low thermal conductivity of clathrate hydrate as a material, enables more latent heat storage, and can withstand use in actual heat storage air conditioning systems, etc. The purpose is to provide technology that contributes to

The present invention made in order to achieve the above object has the following configuration.
(1) A clathrate hydrate mass according to the first aspect of the present invention is a clathrate hydrate mass obtained by cooling an aqueous solution containing a clathrate hydrate-forming substance. The freezing point of the clathrate hydrate is higher than 0 ° C., and is obtained by cooling the aqueous solution below the eutectic point of clathrate hydrate and ice.

(2) A clathrate hydrate mass according to the second embodiment of the present invention is a clathrate water produced by cooling an aqueous solution containing a clathrate hydrate-producing substance by heat exchange with a cold heat source. The sum is a clump of clathrate hydrate accumulated on or from the surface of the heat exchange surface where heat exchange with the cold heat source occurs toward the offshore of the aqueous solution, The freezing point of the hydrate is higher than 0 ° C., and it is obtained by cooling the aqueous solution below the eutectic point of clathrate hydrate and ice.

(3) The clumps of clathrate hydrate according to the third aspect of the present invention are those according to the second aspect of the present invention, wherein the clathrate hydrates are further away from the heat exchange surface toward the offshore of the aqueous solution. The volume ratio or the weight ratio of the clathrate hydrate in the lump is reduced.

(4) The clathrate hydrate body according to the fourth embodiment of the present invention is the refrigerant in which the cold heat source is passed through the heat transfer tube in the second and third embodiments, and the heat The exchange surface is the outer surface of the heat transfer tube, and the clathrate hydrate lump is accumulated around the heat transfer tube to form a substantially coaxial sheath or substantially cylindrical outer shape.

(5) The clumps of clathrate hydrate according to the fifth embodiment of the present invention are the clathrate hydrates according to the first to fourth embodiments, wherein the clathrate hydrate has a freezing point higher than 0 ° C. and 20 The temperature is lower than ° C., and ice is present inside the clathrate hydrate lump, and the proportion of ice is 26% by weight or less.

(6) A clathrate hydrate mass according to the sixth aspect of the present invention is the clathrate hydrate formation in an aqueous solution in any one of the first to fifth aspects. The concentration of the substance is characterized by being higher than the concentration that gives the eutectic point of clathrate hydrate and water and lower than the concentration that gives the harmonic melting point.

(7) In the method for forming a clathrate hydrate mass according to the seventh aspect of the present invention, the aqueous solution containing the clathrate hydrate-forming substance is cooled by heat exchange with a cold heat source so that the freezing point is 0. A method of forming a clathrate hydrate mass by generating clathrate hydrate higher than ° C. and accumulating on the surface of the heat exchange surface or from the surface toward the offshore of the aqueous solution. It has the process of adjusting the temperature of a cold heat source to below the eutectic point of clathrate hydrate and ice.

(8) In the method for forming a clathrate hydrate lump according to the eighth aspect of the present invention, the aqueous solution containing the clathrate hydrate-forming substance is cooled by heat exchange with a cold heat source so that the freezing point is 0. A method of forming a clathrate hydrate mass by generating clathrate hydrate higher than ° C. and accumulating on the surface of the heat exchange surface or from the surface toward the offshore of the aqueous solution, It has a step of adjusting the temperature of the cold heat source below the eutectic point of clathrate hydrate and ice and adjusting the heat flow for cooling the aqueous solution to 0.6 kW / m ² or more. . Here, the heat flow refers to the amount of cooling heat per unit surface area of the heat exchange surface.

(9) In the heat storage method according to the ninth aspect of the present invention, the aqueous solution containing the clathrate hydrate-generating substance is cooled below the eutectic point of clathrate hydrate and ice by heat exchange with a cold heat source. By doing so, a mass of clathrate hydrate having a freezing point higher than 0 ° C. is formed to store heat.

(10) A heat storage device according to a tenth aspect of the present invention supplies an aqueous solution containing a clathrate hydrate-generating substance and a heat storage tank including a heat exchanger, and supplies a refrigerant as a cold heat source to the heat exchanger. The aqueous solution containing the clathrate hydrate forming substance in the refrigerator and the heat storage tank is cooled to below the eutectic point of clathrate hydrate and ice by heat exchange with a cold heat source, and the freezing point is 0 ° C. And a control means for controlling the temperature of the cold source so as to form a higher mass of clathrate hydrate.

In the clathrate hydrate mass according to the present invention, its thermal conductivity is relatively high. This is because the cooling action of the cold heat source extends to the offshore farther away from the heat exchange surface, and the formation and accumulation of clathrate hydrate proceeds from the farther offshore aqueous solution. It means that it becomes easy. In short, even if the thermal conductivity of the clathrate hydrate itself is low, the overall mass of clathrate hydrate in the process of formation is improved so that more latent heat can be stored. become. As a result, more latent heat is stored in the finally obtained clathrate hydrate mass.
The mechanism and principle of the relatively high thermal conductivity of the clathrate hydrate lump according to the present invention are as follows: the eutectic of ice and clathrate hydrate or ice inside the lump as described later. It can be inferred that it is caused by the fact that it is generated and exists.

  Therefore, according to the present invention, the thermal conductivity of clathrate hydrate formed as a mass is improved by a relatively low-cost method that eliminates complexity without introducing new materials and components. And the latent heat storage amount can be increased. And this is the clathrate hydrate heat storage that can improve the efficiency (COP) of the refrigeration cycle by improving the partial load factor in the refrigerator connected to the cold heat source such as cooling the refrigerant, and can withstand actual use Contribute to the establishment of technology.

The above effects are not limited to the first and second embodiments of the present invention, but are common to the present invention. In addition to this, the effects (including unique effects) corresponding to the embodiments of the present invention are as follows. It is as follows.
That is, in the clumps of clathrate hydrate according to the third embodiment of the present invention, the volume ratio or the weight ratio of the clathrate hydrate decreases as it moves away from the sea. This is because the eutectic of ice and clathrate hydrate and the ice itself are formed inside the lump, and the existence of the ice increases the thermal conductivity. It means that the volume ratio or weight ratio of ice in the lump is increased, and that its thermal conductivity does not increase or decrease.
When cold heat is conducted from the heat exchange surface toward the clathrate hydrate mass offshore, it tends to become harder to cool as it moves further offshore, but the thermal conductivity of the mass tends toward offshore. As the distance increases, the volume ratio or weight ratio of ice increases, and its thermal conductivity does not increase or decrease, so cold heat is easily conducted, and the portion of the lump that is offshore, and thus the aqueous solution that is offshore. Also, the cold heat from the heat exchange surface is conducted smoothly.
Therefore, according to the 3rd form of this invention, the production | generation and accumulation | storage of clathrate hydrate become easy also from the aqueous solution which is offshore, and the lump of clathrate hydrate which can heat-store much latent heat is implement | achieved. be able to.

  In the fourth embodiment of the present invention, the cold heat source is a refrigerant passed through the heat transfer tube, the heat exchange surface is the outer surface of the heat transfer tube, and the clathrate hydrate mass accumulates around the heat transfer tube. Thus, an outer shape of a substantially coaxial sheath shape or a substantially cylindrical shape is formed. A typical example of an existing apparatus that employs such a heat transfer tube is an ice heat storage apparatus. As described above, the ice heat storage technology can not be directly converted to the clathrate hydrate heat storage technology, but if the clathrate hydrate block according to the fourth aspect of the present invention is used, the existing ice heat storage technology can be used. The rationality that it is possible to divert part of the device to produce it is created, and it becomes easy to update the equipment, equipment, etc. design and hydrate heat storage. Equipment can be used effectively and costs can be reduced.

  According to the fifth aspect of the present invention, the freezing point of the clathrate hydrate is higher than 0 ° C. and lower than 20 ° C., and the proportion of ice in the clathrate hydrate lump is 26% by weight or less. From this, it is possible to realize a clathrate hydrate mass without lowering the efficiency (COP) of the refrigeration cycle of the refrigerator.

In the clathrate hydrate mass according to the sixth aspect of the present invention, the concentration of the clathrate hydrate-forming substance in the aqueous solution is higher than the concentration that provides the eutectic point of the clathrate hydrate and water. Higher and lower than the concentration that gives a harmonic melting point. Therefore, the aqueous solution in which the clathrate hydrate agglomerates are formed inevitably passes through a solid-liquid mixed phase comprising the clathrate hydrate solid and the aqueous solution in the process of being cooled by heat exchange with the cold heat source. The concentration range of the clathrate hydrate-forming substance. Therefore, according to this form, in the lump in the formation process, the cooling action of the cold source extends to the offshore farther from the heat exchange surface, and the clathrate hydrate is also removed from the aqueous solution farther offshore. The utility and result (the effect of the present invention) that the generation and accumulation are easy to proceed are more remarkably and suitably expressed.
In addition, the block body which concerns on this form is formed from the aqueous solution of a density | concentration lower than a harmonic density | concentration. This means that the mass can be formed with a relatively small amount of clathrate hydrate-generating substance. Therefore, the agglomerate is inexpensive and suitable for clathrate hydrate heat storage technology that can withstand actual use.

  In the seventh aspect of the present invention, since the step of adjusting the temperature of the cold heat source to be equal to or lower than the eutectic point of the clathrate hydrate and ice, the envelope according to the first to sixth aspects is provided. A hydrated body mass can be formed.

In an eighth aspect of the present invention, the step of adjusting the temperature of the cold heat source to be equal to or lower than the eutectic point of clathrate hydrate and ice and adjusting the heat flow for cooling the aqueous solution to 0.6 kW / m ² or higher. Since it has it, it can implement | achieve the formation method suitable for forming the lump of the clathrate hydrate which concerns on the 1st thru | or 6th form.

  This is because the eutectic of ice and clathrate hydrate or the ice itself is formed inside the clumps of clathrate hydrate, and the presence thereof is the cause of increased thermal conductivity. According to the seventh or eighth form, it becomes easy to introduce ice into the lump body at least in the form of eutectic with clathrate hydrate, the overall heat conductivity is improved, and more latent heat is obtained. In other words, it is possible to form a lump that can store heat.

In the ninth aspect of the present invention, heat can be stored by the massive body by forming the massive body of clathrate hydrate according to the first to sixth aspects. As a result, the thermal conductivity of the clathrate hydrate in the formation process is improved as a whole, and more latent heat can be stored.
Therefore, according to the present invention, the thermal conductivity of clathrate hydrate formed as a mass is improved by a relatively low-cost method that eliminates complexity without introducing new materials and components. Thus, the latent heat storage amount can be increased.

  In the 10th form of this invention, the thermal storage apparatus which can form the lump body of the clathrate hydrate which concerns on the 1st thru | or 6th form, and can store heat | fever can be implement | achieved, As mentioned above, latent heat storage The amount can be increased. Therefore, in a refrigerator connected to a cold heat source such as cooling the refrigerant, it is possible to improve the efficiency (COP) of the refrigeration cycle by improving the partial load factor.

The phenomenon that the thermal conductivity of the clumps of clathrate hydrate according to the present invention is relatively high is supported by measured values as will be described later, but the cause is relatively within the lump. It can be reasonably inferred and explained that ice with high thermal conductivity is formed. Details are as follows.
The following description also serves as a part of the basic principle and examples of the present invention.

<Principle of clathrate hydrate and ice formation>
(A) About clathrate hydrate formation curve In a regenerative air conditioning system, generally, the higher the refrigerant evaporation temperature of the refrigeration cycle, the higher the efficiency (COP) of the refrigeration cycle and the more energy saving. In such a heat storage type air conditioning system, a heat storage agent having a freezing point higher than 0 ° C. and lower than 20 ° C. is suitable.
For example, tetra n-butyl ammonium salt, tri n-butyl n pentyl ammonium salt, tetra iso-amyl ammonium salt, tetra n-butyl phosphonium salt, triiso-amyl sulfonium salt disclosed in Patent Document 2 A typical example is clathrate hydrate produced by cooling an aqueous solution.

FIG. 5 shows the concentration of an aqueous solution of tetra n-butylammonium bromide (hereinafter sometimes referred to as “TBAB”), which is one of the tetra n-butylammonium salts, and the clathrate hydrate formation temperature. The vertical axis represents the clathrate hydrate formation temperature (° C.), and the horizontal axis represents the aqueous solution concentration (% by weight).
In FIG. 5, the harmonic melting point means that the composition before and after the phase change from the aqueous solution (liquid phase) to the hydrate (solid phase) does not change when the aqueous solution of the hydrate-generating substance is cooled to produce the hydrate. The temperature of the case (eg, producing a hydrate with the same concentration as the hydrate-generating substance concentration in the original aqueous solution). In the present specification, the concentration that provides the harmonic melting point is referred to as the harmonic concentration. In other words, in the phase diagram where the vertical axis is clathrate hydrate formation temperature and the horizontal axis is aqueous solution concentration (hereinafter sometimes referred to as “hydrate formation curve”), the maximum point is called the harmonic melting point. The concentration giving the harmonic melting point (harmonic concentration) is about 40% by weight (point H in FIG. 5).

  In addition, the clathrate hydrate formation curve of the clathrate hydrate generating substances (particularly quaternary ammonium salts) other than TBAB is qualitatively the same as that of TBAB. The following explanation is given as a representative of the substance. Other data are also related to TBAB, but the explanation according to the principle of the present invention does not change qualitatively for clathrate hydrate-generating substances (particularly quaternary ammonium salts) other than TBAB.

(B) Relationship between the aqueous solution concentration and the clathrate hydrate formation temperature when the aqueous solution containing the clathrate hydrate-forming substance is slowly cooled while stirring and mixing When the aqueous solution with the TBAB concentration is a harmonic concentration is cooled Hydrate begins to form at the harmonic melting point, and the temperature is constant at this melting temperature until all of the aqueous solution is hydrated. Similarly, melting occurs at this constant melting temperature. In addition, the amount of latent heat at the time of solidification and melting of the hydrate is maximized at the harmonic concentration.
On the other hand, when an aqueous solution having a TBAB concentration lower than the harmonic concentration is cooled, the clathrate hydrate formation characteristics shown in FIG. 6 are exhibited.

FIG. 6 is a graph showing changes in aqueous solution concentration and clathrate hydrate formation temperature when an aqueous solution containing TBAB having a concentration of 30% by weight is in an initial state and is slowly cooled while being stirred and mixed.
When the aqueous solution in the initial state is cooled from the point S at a temperature of 15 ° C., the supercooling phenomenon in which the temperature of the aqueous solution becomes the point A, that is, the clathrate hydrate formation temperature at a concentration of 30% by weight or lower than the point A Through this, TBAB clathrate hydrate begins to form.
When the concentration of TBAB is less than the concentration that gives a harmonic melting point, the formation of clathrate hydrate causes the TBAB to be incorporated into the clathrate hydrate and the concentration of TBAB in the aqueous solution decreases. Therefore, according to the clathrate hydrate formation, the clathrate hydrate formation temperature in the mixture of the aqueous solution and clathrate hydrate decreases in the direction of the arrow to follow the clathrate hydrate formation curve. go. When the concentration of TBAB reaches about 5% by weight, the eutectic point with ice (point B: about −0.5 ° C.) is reached. At this stage, clathrate hydrate and ice eutectics begin to form. When the aqueous solution containing the clathrate hydrate-forming substance is cooled, no ice is produced until the temperature reaches the eutectic point with ice, only clathrate hydrate is produced, and after the eutectic point is reached. Ice is also produced.

  The above are general characteristics regarding clathrate hydrate formation when an aqueous solution containing a clathrate hydrate-forming substance is cooled.

(C) Regarding the relationship between the method of cooling an aqueous solution containing an clathrate hydrate-forming substance and the formation of clathrate hydrates Hereinafter, an aqueous solution containing an clathrate hydrate-forming substance (hereinafter sometimes referred to as “aqueous solution”) ), The clathrate hydrate is accumulated on or from the surface of the heat exchange surface toward the offshore of the aqueous solution without peeling off the clathrate hydrate from the heat exchange surface. This will be described based on the result of the experiment to be formed. In this case as well, it goes without saying that the clathrate hydrate generation behavior along the clathrate hydrate generation curve of FIG. 6 is shown.

(A) When the aqueous solution is slowly cooled from the point S in FIG. 6 with the heat exchange surface temperature higher than the eutectic point B, the cooling heat quantity (heat flow) per unit surface area of the heat exchange surface is about 0.6 kW / m, for example. ^{When the} temperature is gradually cooled from the point S in FIG. 6 by making it smaller than ² , the clathrate hydrate is formed through heat exchange after reaching the point A on the clathrate hydrate formation curve, which accumulates and forms a lump. It reaches a point T on average, but no ice is formed.
In this case, since the heat exchange surface is covered with clathrate hydrate, new clathrate hydrate is generated by cooling by heat conduction through the clathrate hydrate already present. . Since the clathrate hydrate has low thermal conductivity, the cold heat that should be transmitted from the heat exchange surface does not reach the offshore of the aqueous solution as the clathrate hydrate is formed, and the growth of the massive clathrate hydrate It reaches the peak, and a sufficient amount of clathrate hydrate does not accumulate, and the heat storage density, which should be high originally, cannot be used for heat storage (by the way, heat exchange surface temperature is cooled to a temperature higher than the eutectic point B for heat exchange. It is the cold storage technique of Patent Documents 3 and 4 that the clathrate hydrate is generated on the surface and removed by physical (mechanical) or thermal means. Ice is formed when the temperature is lowered below point B. Therefore, every time the clathrate hydrate is formed along the clathrate hydrate formation curve, the clathrate hydrate is removed from the heat exchange surface and accumulated in a separate heat storage tank. The clathrate hydrate slurry that had been mixed with ice is used as a mixed slurry on the heat load side. Is cold storage technique of Patent Document 7 of that).

(A) When the aqueous solution is rapidly cooled from the point S by setting the heat exchange surface temperature to a temperature equal to or lower than the eutectic point B. Unlike (a) above, the heat flow is set to about 0.6 kW / m ² or more. When rapidly cooling from the point S of 6, the aqueous solution reaches the point A on the clathrate hydrate formation curve, and thereafter, clathrate hydrate is formed through heat exchange, and further, this accumulates and grows into a lump. . At that time, since the temperature is not higher than the eutectic point B on the heat exchange surface, an eutectic of clathrate hydrate and ice is formed.
On the other hand, in the nucleation of clathrate hydrate using tetrahydrofuran as a guest molecule, the clathrate hydrate is cooled to about −6 ° C., ie, below the eutectic point of the clathrate hydrate and ice. Precursor phenomenon that ice nucleation occurs before hydrate nucleation has been confirmed (Harazaki, Tsukamoto: “Ice nucleation as precursor of hydrate crystallization”, Journal of the Japanese Association of Crystal Growth, Vol.30, No.3,
p. 133)
Considering these, the following model can be set for improving the thermal conductivity due to the presence of ice inside the clathrate hydrate mass.
That is, the clathrate hydrate crystals produced have a so-called dendritic structure in the form of tree branches, and crystals are formed radially from the heat exchange surface. Under the cooling condition in which the aqueous solution is rapidly cooled to a temperature below the eutectic point, the clathrate hydrate and ice co-crystallize from the aqueous solution inside the structure in which the clathrate hydrate crystals are entangled in a radial pattern. As a result, the clathrate hydrate in which ice is dispersed grows in a lump shape. At this time, in addition to the ice growth at the molecular level called eutectic, ice particles are formed in the aqueous solution surrounded by the clathrate hydrate crystals, and also locally on part of the heat exchange surface. In some cases, ice crystals may be formed. Thus, the presence of ice dispersed in the clathrate hydrate that grows in a lump shape improves the thermal conductivity by the amount of the ice, thereby improving the thermal conductivity. Thereby, the cooling action of the cold heat source extends to the offshore farther from the heat exchange surface, and the formation and accumulation of clathrate hydrate are also facilitated from the aqueous solution farther offshore.

  If the above model is valid, even if the thermal conductivity of the clathrate hydrate itself is low, the overall mass of clathrate hydrate in the process of formation is improved and more latent heat is obtained. As a result, more latent heat is stored in the clathrate hydrate lump that is finally produced.

(D) Appropriateness of the model For example, an aqueous solution of tetra n-butylammonium bromide having an initial aqueous solution concentration of 30% by weight was cooled to the eutectic point below the eutectic point with ice. When 10% by weight is averagely distributed in the mass (invention) and when the heat exchange surface is cooled at a temperature higher than the eutectic point with ice and no ice is present in the clathrate hydrate mass FIG. 7 shows the result of comparing the time-dependent change in the amount of heat storage with (conventional) by calculating the heat storage amount of only the clathrate hydrate, excluding the heat storage amount of the ice itself in the clumps of clathrate hydrate. This is shown in the graph. In the graph of FIG. 7, the vertical axis indicates the heat storage amount ratio with the maximum heat storage amount of the present invention being 1, and the horizontal axis indicates the heat storage required time ratio with the time required to reach the maximum heat storage amount of the present invention being 1. Yes. As shown in the graph of FIG. 7, the heat storage amount when ice is present in the clathrate hydrate lump is increased by about 20% compared to the case where heat is stored only with the conventional clathrate hydrate. I understood that. It shows that the thermal conductivity of the clathrate hydrate mass is improved by the ice present inside the clathrate hydrate mass.

Next, a clump of clathrate hydrate was actually formed, and the heat passage rate at that time was measured. The measuring device is as shown in FIG. 8. The heat transfer pipe 63 and the heat storage material 65 are accommodated in the heat storage tank 61, and the refrigerant is circulated and supplied to the heat transfer tube 63 by the refrigerant circulation device 67. An average value of measured values of T1 to T5), a refrigerant temperature (measured values of thermometers T6 and T7), and a refrigerant circulation flow rate are measured. The heat storage material 65 uses an aqueous solution of tetra-n-butylammonium bromide (TBAB) having an initial aqueous solution concentration of 30% by weight, and changes the cooling temperature and heat flow (cooling heat amount per unit surface area of the heat transfer tube) to exchange heat. And the heat passage rate was calculated. The cooling temperature is the average value of the refrigerant temperature at the inlet and outlet of the heat transfer tube, and is the same temperature as the average value of the surface temperature of the heat transfer tube. The amount of exchange heat and the heat transfer rate are determined by the following formula.
Exchange heat [kW] = (heat transfer tube outlet refrigerant temperature [K]-heat transfer tube inlet refrigerant temperature [K]) x refrigerant flow rate [kg / s] x refrigerant specific heat [kJ / kgK]
Heat passage rate [kW / m ² K] = exchange heat quantity [kW] / {heat transfer tube surface area [m ² ] · (heat storage material temperature [K] −average refrigerant temperature from heat transfer tube inlet to outlet
[K])}
When the cooling temperature is set to a temperature lower than −0.5 ° C., which is the eutectic point of TBAB and ice (Examples 1 to 6), and when the cooling temperature is set to a temperature higher than −0.5 ° C. (comparison) The heat transfer rates of Examples 1 and 2) were determined, and the difference in heat transfer rate was determined based on the heat transfer rate of Comparative Example 1 as shown in Table 1.

From the results shown in Table 1, the following technical matters were confirmed.
(1) When the aqueous solution is cooled below the eutectic point of clathrate hydrate and ice, the heat transfer rate is increased as compared with the case where the aqueous solution is cooled to a temperature higher than the eutectic point. That is, the thermal conductivity of the mass formed by accumulating clathrate hydrate generated from the aqueous solution increases.
(2) In order to increase the thermal conductivity or heat storage amount of the clathrate hydrate mass, when cooling the aqueous solution below the eutectic point of clathrate hydrate and ice, the heat flow is 0.6 kW / m. ^Two or more are preferable.
(3) In order to increase the thermal conductivity or heat storage amount of the clathrate hydrate mass, it is preferable that the clathrate hydrate and ice be below the eutectic point of ice and cooled at a lower temperature.
In addition, in the so-called static type heat storage method in which there is no forced convection of the heat storage material inside the heat storage tank as in this measurement experiment, the influence of the heat conductivity of the heat storage material is dominant on the heat storage efficiency. Therefore, by implementing the technical matters (1), (2), and (3) above, the thermal conductivity of the clathrate hydrate body of the heat storage material can be increased, and the heat storage efficiency can be increased.

Further, in Examples 1 and 2 in Table 1, after the aqueous solution was cooled to produce a clathrate hydrate mass, this was immediately lifted to cut the mass, and a portion near the heat exchange surface When the cross section was observed with a magnifying glass, crystals different from the columnar clathrate hydrate crystals could be observed. Such crystals cannot be observed in the case of Comparative Examples 1 and 2, and cannot be considered other than ice from the viewpoint of the composition of the aqueous solution and the cooling temperature.
On the other hand, in Examples 3 to 6, it was not possible to observe crystals different from the columnar clathrate hydrate crystals in the vicinity of the heat exchange surface by the method as described above. As shown, an increase in heat transmittance was confirmed. Although ice and ghost crystals could not be confirmed, it is difficult to think that ice does not exist from the cooling temperature of the aqueous solution. Conversely, if ice is present, the increase in heat transmittance can be explained.

  From the above results, the above model that the thermal conductivity is improved by the presence of ice inside the clathrate hydrate lump is reasonable, and according to this model, at least the basis of the present invention. It can be said that the principle can be explained.

(E) Related matter (a) In any case of Examples 1 to 6, after the aqueous solution was cooled to produce a clathrate hydrate mass, it was immediately lifted to incise the mass, When a portion (outer edge portion or a portion close to it) separated from the vicinity of the heat exchange surface to the offshore side was collected and the cross section was observed with a magnifying glass, a crystal that seemed to be ice as described above could be observed. This can be explained as follows based on the above model.
That is, when the aqueous solution is cooled by heat exchange with a cold heat source, clathrate hydrate having a freezing point higher than that of ice is generated in the process before the ice, and the surface of the heat exchange surface or the surface thereof As a result of accumulation of the aqueous solution toward the offshore, the concentration of clathrate hydrate-forming substance in the aqueous solution decreases toward the offshore. On the other hand, in the process of forming a clathrate hydrate mass, ice is encapsulated inside the mass, so that the clathrate water in the aqueous solution is equivalent to the amount of water used for the ice production. The concentration of the sum product increases. However, the concentration of clathrate hydrate-forming substance in the aqueous solution decreases as it goes offshore due to the formation and accumulation of clathrate hydrate. The concentration of clathrate hydrate-forming substance in the aqueous solution decreases as it goes offshore. Therefore, in the clathrate hydrate mass, the volume ratio or weight ratio occupied by clathrate hydrate decreases and the volume ratio or weight ratio that ice occupies as it moves further offshore as long as the effect of cooling reaches. Will increase. As a result, in these measurement examples, it can be explained that ice (a crystal considered) was observed in a portion near the outer edge of the lump.
However, regardless of whether this explanation is valid or not, in Examples 1 to 6, it is possible to realize a clathrate hydrate mass that can further increase the thermal conductivity and store more latent heat. As shown in FIG.

(B) In measurement examples 3 to 6, the transparent material could not be observed in the vicinity of the heat exchange surface by the method described above, but the portion separated from the vicinity of the heat exchange surface to the offshore side (outer edge portion) The fact that this was able to be observed from (or a part close to it) means that the volume ratio or the weight ratio of ice is higher as the distance to the offshore side increases.

<Heat storage air conditioning system>
FIG. 1 is a diagram for explaining the configuration of a heat storage type air conditioning system according to an embodiment of the present invention. In the heat storage type air conditioning system of the present embodiment, each component device constituting each of the heat source device A, the air conditioning load device B, and the heat storage device C is connected by a refrigerant pipe, and the refrigerant flow path is switched in the middle of the refrigerant pipe. The refrigeration cycle circuit is configured by connecting with the on-off valves 51, 53, and 55.
The heat source device A includes a compressor 1 that pressurizes the refrigerant, and an outdoor heat exchanger 2 that performs heat exchange between the outside air and the refrigerant in the refrigeration cycle.
The air conditioning load device B is installed indoors and depressurizes the refrigerant flowing into the indoor heat exchangers 4a and 4b and the indoor heat exchangers 4a and 4b that exchange heat between the indoor air and the refrigerant in the refrigeration cycle. The second decompression devices 5a and 5b are provided.

Furthermore, the heat storage device C heat-exchanges the heat storage tank 7 storing the heat storage agent, the heat storage agent 9 made of an aqueous solution containing a hydrate-generating substance stored in the heat storage tank 7, the heat storage agent 9 and the refrigerant of the refrigeration cycle. The heat storage heat exchanger 11, the first pressure reducing device 12 that reduces the pressure of the refrigerant sent to the heat storage heat exchanger 11, the thermometer 13 that measures the temperature of the heat storage agent, and the heat storage that measures the amount of heat stored in the heat storage agent 9. The detection value of the calorimeter 15 and the heat storage calorimeter 15 is input to calculate the heat flow measurement value, the heat flow detection calculation device 17 that outputs to the controller 21 described later, and the measurement value of the thermometer 13 is input to control the heat flow The heat flow target value calculation device 19 for calculating the value, the heat flow target value calculated by the heat flow target value calculation device 19 and the heat flow measurement value calculated by the heat flow detection calculation device 17 are input, and these heat flow target value and heat flow measurement value are input. The control signal is calculated so that this deviation becomes zero. The has an adjustment gauge 21 to be outputted to the first pressure reducing device 12.
The thermometer 13 for measuring the temperature of the heat storage agent measures the temperature of the heat storage agent at a plurality of locations in the heat storage tank 7 and calculates the average value or some determination process to obtain a representative value, a specific location in the heat storage tank 7 The temperature is appropriately selected from those for measuring the temperature of the heat storage agent (for example, at the bottom or at the bottom).
The operation of the heat storage device C is managed by a computer (not shown), and at least some functions of the heat flow detection calculation device 17 and the heat flow target calculation device 19 are realized by execution of a computer program.

The heat storage agent 9 is adjusted so that the concentration of the hydrate-generating substance in the aqueous solution is less than the harmonic concentration.
The heat storage meter 15 is a measuring device that can measure the heat storage amount by using a thermometer, a level meter, a solution concentration meter or the like alone or in combination.
The heat flow detection calculation device 17 calculates the average heat flow for the last minute based on the heat transfer area of the heat storage heat exchanger 11 stored in advance and the input value from the heat storage meter 15 to obtain the first pressure reduction. A heat flow measurement value for feedback control of the device 12 is used. The heat flow detection calculation device also has a function of integrating the heat storage amount per minute measured by the heat storage meter 15, and can output a stop signal for the heat storage operation when the planned heat storage amount is reached. is there.
The heat flow target value calculation device 19 stores information on the initial aqueous solution concentration and the relationship between the aqueous solution concentration and the clathrate hydrate formation temperature shown in FIG. Then, the heat flow target value calculation device 19 inputs the measured value of the thermometer 13, and stores heat based on the relationship between the input value and the previously stored aqueous solution concentration and clathrate hydrate generation temperature shown in FIG. It is determined whether or not the temperature of the agent is the clathrate hydrate generation start temperature, and based on this determination, a heat flow target value for feedback control of the first decompression device 12 is output to the controller 21.

The operation method of the heat storage type air conditioning system of the present embodiment configured as described above will be described separately for a heat storage operation method for storing heat and a heat storage-based cooling operation method using heat storage.
<Heat storage operation method>
During the heat storage operation, the on-off valves 51 and 53 are closed and the on-off valve 55 is open.
The refrigerant compressed by the compressor 1 is cooled and condensed by heat exchange with air in the outdoor heat exchanger 2. The cooled refrigerant is decompressed by the first decompression device 12 and evaporated by the heat storage heat exchanger 11, and at this time, the heat storage agent 9 is cooled to store the cold energy. The evaporated refrigerant returns to the compressor 1 and repeats this cycle. Hereinafter, in this heat storage operation, an example of a specific operation control method for growing clathrate hydrate in which ice is distributed from an aqueous solution containing a hydrate-generating substance into a lump will be described.

The temperature of the heat storage agent 9 in the heat storage tank 7 is measured by a thermometer 13 provided in the heat storage tank 7, and the measured temperature value is input to the heat flow target value calculation device 19. The heat flow target value calculation device 19 determines whether or not the temperature of the heat storage agent 9 is the clathrate hydrate generation start temperature, and when the temperature of the heat storage agent 9 is lower than the clathrate hydrate generation start temperature. The clathrate hydrate is generated and reaches an equilibrium state, and waits until the temperature of the heat storage agent 9 becomes equal to or higher than the clathrate hydrate generation start temperature.
On the other hand, if the heat flow target value calculation device 19 determines that the temperature of the heat storage agent is equal to or higher than the clathrate hydrate generation temperature, the heat flow target value for feedback control of the first decompression device 12 is, for example, 1.0 kW. / M ² is input to the controller 21.

Next, the amount of heat stored per minute is measured by the heat storage meter 15 and input to the heat flow detection calculation device 17. The heat flow detection calculation device 17 calculates the average heat flow for the last minute based on the input heat storage amount measurement value and the heat transfer area of the heat storage heat exchanger 11 stored in advance, and calculates the first heat flow. This is input to the controller 21 as a heat flow measurement value for feedback control of the decompression device 12.
The controller 21 calculates a deviation between the heat flow target value input from the heat flow target value calculation device 19 and the heat flow measurement value input from the heat flow detection calculation device 17 so that the deviation becomes 0, that is, heat flow measurement. A control signal is output to the first pressure reducing device 12 so that the value becomes 1.0 kW / m ² which is the heat flow target value. The first pressure reducing device 12 receives a control signal input from the controller 21 and controls the expansion ratio of the refrigerant by controlling the opening of the pressure reducing valve, and the refrigerant introduced into the heat storage heat exchanger 11. The evaporation temperature and heat flow are adjusted.
And by controlling in this way, the evaporation temperature of the refrigerant, that is, the temperature of the heat exchange surface of the heat storage heat exchanger 11 is controlled to be equal to or lower than the eutectic point of the clathrate hydrate and ice. The clathrate hydrate rapidly cooled below the eutectic point of the clathrate hydrate and ice, and as described in the explanation of the principle, the clathrate hydrate in which the ice is dispersed further on the surface of the heat storage heat exchanger 11 Grows in a lump from its surface to the offshore.
Moreover, a control signal is also output to the compressor 1 so that the heat flow measurement value becomes 1.0 kW / m ² which is the heat flow target value, and the compressor capacity control and the first decompression device control are linked. Thus, it is possible to easily control the heat flow while keeping the evaporation temperature of the refrigerant introduced into the heat storage heat exchanger 11 below the eutectic temperature.
Needless to say, the superheat degree control of the decompression device and the capacity control of the compressor are performed in a normal refrigeration system in consideration of the stability of the heat storage air conditioning system.

FIG. 2 is a diagram schematically showing the heat storage tank 7 shown in FIG. 1, and a clathrate hydrate lump is formed around the heat storage heat exchanger (heat transfer tube) 11 installed in the heat storage tank 7. It shows the state being done. FIG. 3 is an enlarged view showing a cross section taken along the line AA in FIG. In FIG. 2, as an example of the arrangement of the heat storage heat exchanger (heat transfer tube), the meandering in the vertical direction is shown. However, the arrangement is not limited to this. For example, the heat exchanger is arranged so as to meander in the horizontal direction. May be.
As shown in FIGS. 2 and 3, the massive clathrate hydrate produced by cooling an aqueous solution having a concentration lower than the harmonic concentration of clathrate hydrate has a substantially coaxial sheath shape and a substantially cylindrical shape around the heat transfer tube. Is formed.

The clumps of clathrate hydrate have higher thermal conductivity and a larger amount of heat storage than when the aqueous solution is not cooled below the eutectic point of clathrate hydrate and ice. (Based on the above model) This is because ice is formed inside the lump, and as a result, ice with high thermal conductivity is dispersed in the solid phase of clathrate hydrate with low thermal conductivity. (The heat conductivity is improved by the amount of ice, and the amount of heat storage is also increased. It is assumed that ice functions as a heat conduction aid and fins, and also functions as a latent heat storage agent.) . Therefore, heat transfer characteristics are improved without adding a new auxiliary material that increases the thermal conductivity in the thermal storage agent or a member that increases the thermal conductivity, and the amount of heat storage per unit volume is increased at low cost. Can be achieved.
In addition, the volume ratio of clathrate hydrate in the clathrate hydrate lump decreases in the clathrate hydrate lump as the distance from the heat transfer tube 11 increases. (Based on the above model) This is because clathrate hydrate with a freezing point higher than ice is produced before ice in the process of being cooled by heat exchange with a cold source, on the surface of the heat exchange surface or As a result of accumulation from the surface toward the offshore of the aqueous solution, the concentration of clathrate hydrate-forming substance in the aqueous solution decreases toward the offshore.
The volume ratio or the weight ratio of the clathrate hydrate in the mass of the clathrate hydrate decreases as it moves further offshore, and the volume ratio or weight ratio of the ice in the mass increases accordingly. By doing so, the thermal conductivity of the clathrate hydrate mass increases as it moves further offshore. When cold heat is conducted from the heat exchange surface toward the offshore of the clathrate hydrate mass, it tends to become harder to cool as it moves away to the offshore, but the heat conduction of the clathrate hydrate mass Since the property becomes higher as it moves further offshore, cold heat is easily conducted, and cold heat from the heat exchange surface is smoothly conducted even offshore of the clathrate hydrate lump.

  The higher the ice inclusion ratio in the clathrate hydrate mass, the better the heat transfer characteristics, but the efficiency of the refrigeration cycle (COP) decreases accordingly. Therefore, the ice inclusion ratio is limited to a range that does not sacrifice the refrigeration cycle COP.

Fig. 4 shows the relationship between the COP (heat storage COP ratio) normalized by setting the heat storage COP of the conventional ice heat storage air conditioning system to 1 and the ice inclusion ratio based on experiments, and is shown in a graph. The horizontal axis represents the ice inclusion ratio (% by weight), and the left vertical axis represents the COP ratio during heat storage. In FIG. 4, the right vertical axis represents the heat transfer performance improvement ratio normalized by assuming that the heat passage rate is 1 when the ice inclusion rate is 0%.
The heat transfer rate is the amount of exchange heat supplied from the refrigerant, the surface area of the heat transfer tube, and the difference between the heat storage agent temperature and the refrigerant temperature (specifically, the heat storage agent temperature in the heat storage tank-the refrigerant from the heat transfer tube inlet to the outlet). Based on the average temperature), the following formula was used.
Heat passage rate = exchange heat quantity ÷ heat transfer tube surface area ÷ (heat storage agent temperature in heat storage tank – average refrigerant temperature from heat transfer tube inlet to outlet)

  As can be seen from the graph of FIG. 4, the heat transfer rate increases with an increase in the ice inclusion ratio and the heat transfer performance improvement ratio increases, but the COP ratio during heat storage decreases with an increase in the ice inclusion ratio. The COP ratio at the time of heat storage is 1, and the ice inclusion ratio that is equivalent to the ice heat storage air conditioning system is 26%. For this reason, the inclusion ratio of ice for securing the COP or higher during heat storage of the conventional ice heat storage air conditioning system to improve the heat transfer is preferably 26% by weight or less.

In addition, what is necessary is just to adjust the aqueous solution density | concentration of the clathrate hydrate production | generation substance in order to make the inclusion ratio of the ice in a clathrate hydrate lump to 26 weight% or less. Increasing the concentration of clathrate hydrate-generating substance reduces the ice inclusion ratio, and decreasing the inclusion hydrate-generating substance concentration increases the ice inclusion ratio. The inclusion ratio of ice in the clathrate hydrate mass can be set to a predetermined value by adjusting the concentration of the clathrate hydrate-generating substance to a predetermined concentration.
It is also possible to adjust the inclusion ratio of ice in the clathrate hydrate mass by adjusting the temperature of the heat exchange surface, that is, the evaporation temperature of the refrigerant and the heat flow.

<Cooling operation method using heat storage>
In the regenerative cooling operation, the on-off valves 51 and 55 are closed, the on-off valve 53 is opened, and the first pressure reducing device 12 is fully opened. The refrigerant compressed by the compressor 1 is cooled and condensed by heat exchange with air in the outdoor heat exchanger 2. The first decompression device 12 is in a fully opened state, and the refrigerant flows through the heat storage heat exchanger 11 without being decompressed. The refrigerant flowing through the heat storage heat exchanger 11 is further cooled by the heat storage agent 9 and enters a supercooled state. The supercooled refrigerant is decompressed by the second decompression devices 5a and 5b and evaporated by the indoor heat exchangers 4a and 4b. At this time, the air is cooled and air-conditioning is performed. The evaporated refrigerant returns to the compressor 1 and repeats this cycle.
This regenerative cooling operation is completed when the regenerative air conditioning system determines that there is no remaining heat storage in the heat storage tank. Subsequent cooling air-conditioning is performed by opening the on-off valve 51 and closing the first pressure reducing device 12 so that the refrigerant bypasses the heat storage tank 7.

In the heat storage air conditioning system shown in FIG. 1, the heat transfer characteristics when the heat transfer tube surface temperature was stored below the eutectic point of clathrate hydrate and ice were stored at a temperature higher than the eutectic point. The superiority of storing heat below the eutectic point was verified by comparing with the heat transfer characteristics of the case. In addition, tetra n butyl ammonium bromide aqueous solution was used as a heat storage agent.
The heat transfer characteristics were evaluated by the ratio of change in heat passage rate with respect to the heat storage amount obtained from the exchange heat amount. The graph of FIG. 9 shows the heat passage rate change ratio with respect to the heat storage amount. In FIG. 9, the horizontal axis indicates the amount of heat storage (kJ), and the vertical axis indicates the heat passage rate change ratio.

The heat passage rate change ratio refers to a change in the heat passage rate over time with reference to the heat passage rate when clathrate hydrate starts to form on the surface of the heat transfer tube. The exchange heat amount, the heat storage amount, the heat passage rate, and the heat passage rate change ratio can be obtained by the following equations.
Exchange heat quantity = (heat transfer tube outlet specific enthalpy-heat transfer tube inlet specific enthalpy) x refrigerant flow rate The refrigerant specific enthalpy is obtained by measuring the temperature or pressure of the refrigerant flowing into and out of the heat transfer tube.
・ Heat storage amount = Exchange heat amount × Heat storage time ・ Heat passage rate = Exchange heat amount ÷ Heat transfer tube surface area ÷ (Heat storage agent temperature in the heat storage tank-Refrigerant average temperature from heat transfer tube inlet to outlet)
・ Heat passage rate change ratio = Heat passage rate at every measurement ÷ Heat passage rate when hydrate begins to form

As shown in FIG. 9, in both cases where heat is stored below the eutectic point and when heat is stored at a temperature higher than the eutectic point, cooling proceeds and hydrate is accumulated from the heat transfer tube surface toward the offshore. As the amount of stored heat increases, the heat passage rate decreases and the heat passage rate change ratio gradually decreases.
However, in the graph of FIG. 9, when the heat is stored below the eutectic point, the decrease in the heat passage rate change ratio is less than when the heat is stored at a temperature higher than the eutectic point. It is clearly shown that the heat passage rate is 10-20% higher than when heat is stored. This proves that the heat transfer performance is excellent when heat is stored below the eutectic point.

Note that the determination method and feedback control contents in the heat flow target calculation device 19 shown in the above heat storage operation method are merely examples, and these contents can be arbitrarily determined and changed by modifying the computer program. it can.
For example, the cooling profile of the tetra-n-butylammonium bromide aqueous solution shown in the hydrate formation curve of FIG. 6 can be set as follows. When the aqueous solution concentration of the clathrate hydrate-forming substance is 25% by weight or more and less than the harmonic melting point concentration, 0 when the temperature of the aqueous solution is equal to or higher than the temperature on the hydrate formation curve corresponding to the concentration. Control the evaporation temperature of the refrigerant so that the aqueous solution is cooled with a heat flow of .8 kW / m ² or more, and when the temperature of the aqueous solution is lower than the temperature on the hydrate formation curve, Then, the evaporating temperature of the refrigerant is controlled so that the aqueous solution is cooled with a heat flow of 0.6 kW / m ² or more.
When the aqueous solution concentration is 15 wt% or more and less than 25 wt%, when the temperature of the aqueous solution is equal to or higher than the temperature on the hydrate formation curve corresponding to the concentration, a heat flow of 1.0 kW / m ² or more When the temperature of the aqueous solution is lower than the temperature on the hydrate formation curve, after the temperature on the hydrate formation curve is reached, 0.7 kW / The evaporation temperature of the refrigerant is controlled so as to cool the aqueous solution with a heat flow of m ² or more.
When the aqueous solution concentration is less than 15% by weight and larger than the eutectic point concentration, the temperature of the aqueous solution does not depend on whether it is higher or lower than the temperature on the hydrate formation curve corresponding to the concentration, and is generally 0.9 kW / m. ^The refrigerant evaporating temperature is controlled so as to cool the aqueous solution with ^two or more heat flows.
The reason why the heat flow is set small when the aqueous solution concentration is 25% by weight or more is to reduce waste of energy in consideration of the fact that the aqueous solution viscosity is large and heat transfer is difficult when the aqueous solution concentration is large. .

The above is an example of an aqueous solution of tetra-n-butylammonium bromide, but other clathrate hydrate-forming substances having similar hydrate-formation curves also correspond to the aqueous solution concentration of the clathrate hydrate-formation substance. In addition, in accordance with whether the temperature of the aqueous solution is higher than or lower than the temperature on the hydrate formation curve corresponding to the concentration of the aqueous solution, the heat flow is similarly stepped at 0.6 kW / m ² or higher. The evaporation temperature of the refrigerant can be controlled so as to cool the aqueous solution instead.

Further, the temperature of the heat exchange surface, that is, the evaporation temperature profile of the refrigerant or the cooling profile of the aqueous solution is first formed on the heat exchange surface, for example, the concentration of the aqueous solution, the shape of the heat storage tank 7, the arrangement of the heat transfer tubes in the heat storage tank 7. The amount and thickness of the clathrate hydrate, the area and distribution of the heat exchange surface covered by the clathrate hydrate, the distribution and amount of ice inside the clathrate hydrate mass in the formation process, etc. It can be determined in consideration.
For example, (1) heat exchange surface for a certain time at a temperature slightly lower than the clathrate hydrate formation temperature corresponding to the concentration of the aqueous solution (for example, 5 ° C if the clathrate hydrate formation temperature is 10 ° C) After maintaining the temperature, the heat exchange surface temperature is lowered at a high speed. (2) The heat exchange surface temperature is slowed down to an intermediate target temperature at which the temperature of the aqueous solution is lower than the clathrate hydrate formation temperature corresponding to the concentration. (3) Raise and lower the heat exchange surface temperature so that the temperature of the aqueous solution fluctuates across the temperature of the eutectic point of ice and clathrate hydrate. , Etc. temperature profiles can be used.

  Further, the temperature of the heat exchange surface, that is, the evaporation temperature profile of the refrigerant or the cooling profile of the aqueous solution can be set as follows. That is, after the start of cooling of the aqueous solution, until the supercooling is released and clathrate hydrate begins to be formed, the clathrate hydrate is cooled so that the temperature of the heat exchange surface becomes equal to or higher than the eutectic point. After starting to form, cooling is performed so that the temperature of the heat exchange surface is equal to or lower than the eutectic point. Here, the supercooling means a state in which the clathrate hydrate is not formed and the aqueous solution state is maintained even when the temperature of the clathrate hydrate-forming substance aqueous solution is lower than the freezing point.

According to the cooling profile of the aqueous solution as described above, the clathrate hydrate or clathrate hydrate and ice eutectic are not formed on the heat exchange surface until clathrate hydrate starts to form. The aqueous solution is cooled from the exchange surface, and the entire aqueous solution in the heat storage tank is cooled in a supercooled state. In this case, there is no clathrate hydrate or clathrate hydrate and ice eutectic with low heat transfer compared to the aqueous solution on the heat exchange surface, so the heat transfer rate from the heat exchange surface to the aqueous solution is large and efficient. The aqueous solution in the entire heat storage tank can be cooled well. In addition, since the refrigerant is supplied with the evaporating temperature of the refrigerant equal to or higher than the eutectic point, the COP of the refrigeration cycle can be increased, resulting in energy saving.
In addition, after the clathrate hydrate has started to form, by cooling so that the temperature of the heat exchange surface is below the eutectic point, an eutectic of clathrate hydrate and ice is produced on the heat exchange surface. It is possible to store heat by forming a clump of clathrate hydrate while suppressing a decrease in heat transfer.

  In addition, as a specific method for realizing the cooling profile of the aqueous solution as described above, by measuring the temperature of the aqueous solution in the heat storage tank, supercooling is released and clathrate hydrate begins to be generated, and the aqueous solution temperature is balanced. The temperature of the heat exchange surface may be determined to be changed from an operation for cooling the eutectic point to the eutectic point or lower to an operation for cooling to the eutectic point or lower. In order to change the temperature of the heat exchange surface, that is, the evaporation temperature of the refrigerant in this way, the operation of lowering the pressure and temperature of the refrigerant and lowering the number of revolutions of the compressor should be performed by adjusting the opening of the pressure reducing valve. Good.

Moreover, you may make it cool so that the temperature of a heat exchange surface may become below a eutectic point simultaneously with the start of a thermal storage operation.
In this case, a refrigerant thermometer for measuring the temperature of the refrigerant is provided downstream of the first pressure reducing device 12, and the measured refrigerant temperature is input to the controller 21, so that the heat storage agent is simultaneously with the start of the heat storage operation. Regardless of the measured value of the thermometer 13 that measures the temperature of the refrigerant, the controller 21 adjusts the temperature of the refrigerant evaporated in the heat storage heat exchanger 6 to be equal to or lower than the eutectic point of clathrate hydrate and ice. Control the first decompressor 12

It is a figure explaining the structure of the thermal storage type air conditioning system which concerns on one embodiment of this invention. It is a figure which shows typically the thermal storage tank which concerns on one embodiment of this invention. It is an enlarged view of the arrow AA cross section of FIG. It is the graph which computed the relationship between the inclusion ratio of the ice and COP which normalized the COP at the time of thermal storage of the conventional ice thermal storage air conditioning system as 1, and COP. It is a graph which shows the relationship between the aqueous solution density | concentration of the tetra n-butylammonium bromide (TBAB), and the clathrate hydrate formation temperature. It is a graph which shows the change of the aqueous solution density | concentration and clathrate hydrate formation temperature when the aqueous solution of 30 weight% containing TBAB is made into an initial state, and this is gently cooled, stirring and mixing. It is explanatory drawing explaining the effect of this invention, when initial stage aqueous solution density | concentration is 30 weight% and it assumed that ice distributed 10 weight% in clathrate hydrate on average, it is an analytical analysis of the heat storage amount with time. It is a graph which shows the result evaluated. It is explanatory drawing of the apparatus used in order to confirm the effect of this invention. It is explanatory drawing explaining the effect of this invention, and is a graph which shows the heat-passage rate change ratio with respect to the amount of heat storage about the Example and comparative example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Compressor, 2 Outdoor heat exchanger, 4a, 4b Indoor heat exchanger, 5a, 5b 2nd decompression device, 7 Thermal storage tank, 9 Thermal storage agent, 11 Thermal storage heat exchanger, 12 1st decompression device, 13 thermometer, 15 heat storage quantity meter, 17 heat flow detection calculation device, 19 heat flow target value calculation device, 21 controller, 51, 53, 55 on-off valve.

Claims (7)

A clathrate hydrate mass obtained by cooling an aqueous solution containing a clathrate hydrate-forming substance, wherein the clathrate hydrate has a freezing point higher than 0 ° C., and the aqueous solution is clathrated and hydrated A clathrate hydrate mass obtained by cooling below the eutectic point of an object and ice. The clathrate hydrate produced by cooling the aqueous solution containing the clathrate hydrate-generating substance by heat exchange with a cold heat source is on or on the surface of the heat exchange surface where heat exchange with the cold heat source occurs. A clathrate hydrate mass accumulated from the surface toward the offshore of the aqueous solution, the freezing point of the clathrate hydrate being higher than 0 ° C., the aqueous solution being clathrate hydrate and ice A clathrate hydrate mass obtained by cooling below the eutectic point. The cold heat source is a refrigerant passed through the heat transfer tube, the heat exchange surface is an outer surface of the heat transfer tube, and the clathrate hydrate lump is accumulated around the heat transfer tube to be substantially coaxial sheath The mass of clathrate hydrate according to claim 2, wherein the clathrate hydrate has a cylindrical or substantially cylindrical outer shape. An aqueous solution containing a clathrate hydrate-forming substance is cooled by heat exchange with a cold heat source to produce a clathrate hydrate having a freezing point higher than 0 ° C., and the aqueous solution on or from the surface of the heat exchange surface A method of forming a mass of the clathrate hydrate by accumulating toward the offshore of
A method for forming a clathrate hydrate lump comprising adjusting the temperature of the cold heat source to be equal to or lower than the eutectic point of clathrate hydrate and ice. An aqueous solution containing a clathrate hydrate-forming substance is cooled by heat exchange with a cold heat source to produce a clathrate hydrate having a freezing point higher than 0 ° C., and the aqueous solution on or from the surface of the heat exchange surface A method of forming a mass of the clathrate hydrate by accumulating toward the offshore of
The clathrate water comprising the steps of adjusting the temperature of the cold heat source to be equal to or lower than the eutectic point of clathrate hydrate and ice, and adjusting the heat flow for cooling the aqueous solution to 0.6 kW / m ² or more. A method for forming a lump of a Japanese product. By cooling the aqueous solution containing the clathrate hydrate-forming substance to a temperature below the eutectic point of clathrate hydrate and ice by heat exchange with a cold heat source, the clathrate hydrate having a freezing point higher than 0 ° C. A heat storage method characterized by forming a lump and storing heat. A heat storage tank comprising an aqueous solution containing a clathrate hydrate-generating substance and a heat exchanger, a refrigerator for supplying a refrigerant as a cold heat source to the heat exchanger, and a clathrate hydrate-generating substance in the heat storage tank Is cooled to below the eutectic point of clathrate hydrate and ice by heat exchange with a cold heat source to form a clathrate hydrate mass having a freezing point higher than 0 ° C. A heat storage device comprising control means for controlling the temperature of the source.

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