JP2753742B2 - Magnetic fluid, tube sealed with the magnetic fluid, and method for preventing snow accumulation using heat pipe or heat siphon constituted by the tube - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a magnetic fluid in which a change in magnetization is extremely sensitive to a change in temperature, a tube in which the magnetic fluid is sealed, a heat pipe constituted by the tube, The present invention relates to a method for preventing snow accumulation using a heat siphon.

<Conventional technology> A magnetic fluid is a dispersion of extremely fine ferromagnetic particles with a particle diameter of about 10 nm that is stably dispersed in an organic solvent or water. Since no coagulation and sedimentation occurs, the liquid itself behaves as if it has ferromagnetism.

For the production of the above-described magnetic fluid, for example, a basic salt of an unsaturated fatty acid such as oleic acid is added to an aqueous suspension of a ferromagnetic metal oxide such as a wet synthesized magnetite, and fine particles of the ferromagnetic metal oxide are added. A method for producing a base magnetic fluid as an oil-based magnetic fluid by adsorbing and aggregating unsaturated fatty acid ions and dispersing this aggregate in oils (Japanese Patent Publication No. 53-17118). The obtained aggregate is placed in water, and a water-based magnetic fluid is produced by adding an anionic or nonionic surfactant having 9 or more carbon atoms in the hydrocarbon chain to obtain a water-based magnetic fluid (particularly, Japanese Patent Publication No. 54-40069) is known.

The magnetic fluid manufacturing method described above is offered as a high-quality product, and the fields of application of magnetic fluid are expanding to rotating shaft seals, specific gravity difference sorting, various dampers, acceleration sensors, tilt sensors, etc. Have been.

On the other hand, magnetic fluids that are dispersions of ferromagnetic fine particles include
If the temperature is lower than the specific Curie temperature, the oxidation tends to decrease as the temperature increases. As a system utilizing this property, a conversion system from thermal energy to kinetic energy has been proposed. This is a system in which, for example, when a magnetic field is applied to a closed channel having a temperature difference, a magnetic fluid in the channel receives a non-equilibrium force and circulates spontaneously.

In this system, it has been clarified that the driving force of the magnetic fluid is proportional to the magnetization change rate of the magnetic fluid at two points having a temperature difference. However, such a system generally has the heat resistance of the magnetic fluid itself. Because the magnetic fluid is used near room temperature, it is necessary that the magnetization of the magnetic fluid near room temperature has large temperature dependence.

In the above-mentioned system, the temperature dependency of magnetization is too low for a magnetic fluid containing magnetite as a magnetic powder as obtained from the above-described manufacturing method, so that it cannot be used.

Therefore, as a ferrite having a large magnetization change rate that can be used in the above-described system, Japanese Patent Application Laid-Open No.
Japanese Patent Application Publication No. JP-A-2005-64139 proposes a magnetic fluid using manganese zinc (Mn-Zn) ferrite as a magnetic powder.

<Problems to be Solved by the Invention> However, the conventional magnetite having a Curie point of 400 ° C. or higher, or a magnetic fluid containing Mn-Zn ferrite as a magnetic powder has insufficient temperature dependence of magnetization. ,
FIG. 1 is a curve showing the relationship between magnetization and temperature of a kerosene-based magnetic fluid in which magnetite is dispersed (hereinafter, referred to as thermomagnetic curve). FIG. 2 is a graph showing heat measured by separating only magnetite powder from the magnetic fluid. As can be clearly seen from the graph, the magnetization change rate Δσ of the magnetite powder in a magnetic field of 4 × 10 ⁵ A / m at 0 ° C. and 100 ° C. was only 0.03.
It's just T.

The temperature dependence of the magnetization of the magnetite dispersed kerosene-based magnetic fluid, by applying a magnetic field of 3.2 × 10 ⁵ A / m, in the range of ^{0~100 ℃, 3 × 10 -4 T} / ℃ It's just that.

Further, when the Mn-Zn ferrite is made into fine particles having a particle size of about 10 nm, and the fine particles are used as a magnetic powder to prepare a magnetic fluid, the same conditions (3.2 × 10 ⁵ A / m magnetic field, 0 to 100 ° C.) The temperature dependence of the magnetization in the range was only about 1 × 10 ⁻³ T / ° C.

Therefore, conventional magnetic fluids cannot be used for the above-described energy conversion system, and therefore have a very large temperature dependence of magnetization near room temperature and a large absolute value of magnetization, that is, a so-called magnetic fluid. There has been a strong demand for warm magnetic fluids.

<Means for solving the problems> The present invention has been proposed in view of the above, a large number of wet ferrites are synthesized, and as a result of detailed examination, calcium ions are added during wet synthesis of zinc ferrite. In the prepared Mn-Ca-Zn ferrite, Fe-Ca-Zn ferrite, Co-Ca-Zn ferrite, Ni-Ca-Zn ferrite, Cu-Ca-Zn ferrite, Mg-Ca-Zn ferrite The composition ratio of wet ferrite whose magnetization change rate around room temperature shows an extremely large value is found, and the above wet ferrite is coated with a surfactant, and a magnetic fluid dispersed in an organic solvent or water as a magnetic powder. The present invention relates to a sealed tube, and a method for preventing snow accumulation using a heat pipe or heat siphon formed of the tube.

The wet ferrite used in the present invention has a composition formula of (MeO) _X · (CaO) _Y · (ZnO) _Z · Fe ₂ O ₃ It is represented by

In addition, this wet ferrite shows an extremely large magnetization change rate Δσ at 0 to 100 ° C., and the present inventors have found that the Curie point increases as the Ca ²⁺ ion in the Mg-Mn ferrite increases. The inventor completed the invention after intense research inspired by the decline.

The thermomagnetic curves (−50) of each of the wet ferrite described above and the mixed zinc-based ferrite containing no Ca as a comparative example.
To 100 ° C., a ^{3.2 × 10 5 A / m)} , is shown in FIG. 3, the addition of Ca ²⁺ ions, not only the magnetization of the mixed zinc ferrite is increased significantly even if the temperature dependence of magnetization Is growing. In particular, Co _0.3 Ca _0.1 Zn _0.6 Fe ₂ O ₄ ((CoO) _0.3 · (CaO) _0.1 · (ZeO) _0.6
Fe ₂ O ₃ ) shows extremely large temperature dependence of magnetization, and shows a high value as high as 2.1 × 10 ⁻³ T / ° C. at room temperature.

FIG. 4 shows a three-component composition diagram of Ni—Ca—Zn ferrite as an example showing the relationship between the numerical value of the temperature dependence of magnetization and the composition ratio as described above. The numerical values in FIG. ⁴ represent the temperature dependence of the magnetization at 0 ° C. (× 10 ⁻⁴ T / ° C.), and the values in parentheses indicate the magnetization (× 10 ⁴ A / m) in a magnetic field of 3.2 × 10 ⁵ A / m. ^-2 T). White circles indicate the mixing ratio at the time of preparation, and black circles indicate the composition ratio after synthesis.

As apparent from FIG. 4, the obtained Ni—Ca—Zn ferrite became a solid solution in which the composition ratio of Ca ²⁺ ions was smaller than the mixing ratio of the first solution in the coprecipitation.

Further, in FIG. 4, since the magnetization and the ratio range in which the temperature dependence of the magnetization is particularly excellent are shown by dotted lines, the reaction is carried out at a molar ratio of approximately Ni: Ca: Zn = 2: 2: 6. It can be seen that the magnetization at 0 ° C. and the Ni—Ca—Zn ferrite having a large temperature dependence of the magnetization can be obtained.

For the wet ferrites other than the above-mentioned Ni-Ca-Zn-based ferrites, the magnetization and temperature dependence of the magnetization were measured. As a result, an effective composition ratio range (in the dotted line) was obtained as shown in FIG. Was done.

The wet ferrite described above exhibited a spinel structure by X-ray diffraction, and had a lattice constant of about 0.84 nm.

In order to stably disperse the wet ferrite in an organic solvent or water to form a magnetic fluid, it is necessary to produce fine particles having a particle diameter of about 15 nm or less. It has been found that the wet ferrite in the range of the ratio can be easily made into fine particles of 15 nm or less.

As described above, wet ferrite having high magnetization and temperature dependence of magnetization is pH 10 to 14, preferably pH 12 to 14.
13. Since it can be manufactured under normal pressure under coprecipitation conditions at a temperature of 80 to 100 ° C., it can be supplied inexpensively and in large quantities without requiring a special reactor.

After coating the wet ferrite with a surfactant such as an unsaturated fatty acid ion and dispersing it in a conventionally used organic solvent such as kerosene or water, it has a large temperature dependency of magnetization, In addition, the magnetic fluid of the present invention having large magnetization can be manufactured.

In addition, the magnetic fluid of the present invention requires a special method for producing a magnetic powder by coating the surface of wet ferrite fine particles with a surfactant and dispersing the magnetic powder in an organic solvent or water. Not
It can be easily manufactured using a conventionally known method.

The present invention also includes a tube which is partially filled with or filled with the above-described magnetic fluid and is sealed, and a method for preventing snowfall using a heat pipe or heat siphon constituted by the tube.

This snow accumulation prevention method is to form a heat pipe by making the tube sealed with the magnetic fluid into a straight tube or a bent shape, or to form a heat siphon by endless, and put this heat pipe or heat siphon underground It is buried. In this case, the upper part of the heat pipe or heat tube should be close to the ground surface, and the lower part should be underground.
It is located at about 18 m, and a magnetic field gradient is formed by making a permanent magnet desired in the middle of the height. It is desirable to use a tube made of a material having excellent thermal conductivity for the heat pipe and the heat siphon, but the tube near the permanent magnet needs to be non-magnetic.

When a heat pipe or heat siphon is buried in the ground in this way, if there is a temperature difference between the upper tube near the ground surface and the lower tube under the ground, the magnetization of the magnetic fluid in the high temperature part will be low, Since the magnetization of the magnetic fluid in the low-temperature portion is large, the low-temperature magnetic fluid with a high magnetization is attracted to the magnetic field, and the high-temperature magnetic fluid with a low magnetization is discharged from the magnetic field, causing the flow of the magnetic fluid, and the heat pipe,
The action as a heat siphon occurs.

The underground temperature is almost constant regardless of the season when the depth is 7m or less, and is almost equal to the average temperature in the local area.
It is about 10-14 ° C.

However, the temperature on the ground surface is -16 during snowfall or freezing.
Since the temperature is about 0 ° C., a temperature difference of at least 10 ° C. and a maximum of 30 ° C. occurs between the upper part and the lower part of a heat pipe or heat siphon buried under the ground under snowy or freezing weather conditions.

In the magnetic fluid of the present invention sealed in a heat siphon buried underground, if the above-mentioned temperature range and temperature difference occur, the rate of magnetization change is large as shown in FIG. It can circulate and transport underground thermal energy to the ground surface to prevent snow and freezing. Moreover, since the temperature dependence of magnetization is almost linear in the above-mentioned temperature range, the larger the temperature difference is, that is, the amount of heat transport increases in proportion to the decrease in the temperature of the ground surface, the higher the temperature difference. Even if there is a sudden temperature house, the temperature near the ground surface can be kept constant at all times.

When the temperature of the ground surface is low and the temperature of the ground is relatively low, such as in a cold region, the lower part of the tube must be buried deep in the ground. And, when sufficient kinetic energy to circulate the magnetic fluid cannot be obtained by enlarging the upper part, in the magnetic fluid of the composition of the present invention, the solvent is vaporized with a low boiling point like a fluorocarbon solvent or hexane. Effective liquid is effective. In this case, instead of using a heat siphon in which a tube sealed with a magnetic fluid is made endless, the tube is buried in the ground using a heat pipe having an inverted L-shape, and the magnetic fluid is filled in the heat pipe. Instead of being filled, it may be sealed at the bottom.

In a normal heat pipe, vaporization of liquid occurs on the inner surface of the pipe, which is a heat transfer surface. However, when air bubbles are generated on the inner wall of the pipe, heat conduction to the liquid is hindered. However, when using a heat pipe or heat siphon with a tube in which the magnetic fluid of the present invention is sealed and applying a magnetic field with a permanent magnet facing the lower part, convection of the magnetic fluid is promoted by the magnetic field, and the convection is heat transfer. In the vicinity of the surface, ascending flow is brought to the liquid, bubbles are prevented from being generated on the inner wall of the tube, and the heat transfer effect is not hindered.

(Effects of the Invention) As described above, the present invention is to coat a mixed zinc-based wet ferrite having the above composition ratio with a surfactant and use it as a magnetic powder. The fluid has an extremely large magnetization as compared with a conventional magnetic fluid, and has an extremely large magnetization change rate near room temperature.

Further, since the magnetic fluid of the present invention does not require a special manufacturing process, it can be manufactured easily and at low cost, and can be supplied in a large amount.

Therefore, the magnetic fluid of the present invention is expected to greatly contribute to the realization of the system by using it in, for example, the above-described energy conversion system, heat pipe, heat siphon, and the like. Further, at the time of snowfall, snow falling on the ground surface can be melted, and even if snow accumulates, it can be melted, so that it is possible to reliably prevent snow accumulation.

(Example) Hereinafter, an example of the present invention will be described.

Example 1 (Preparation of Temperature-Sensitive Ferrite) Nickel chloride (or manganese chloride, ferrous chloride, cobalt chloride, copper chloride, magnesium chloride), calcium chloride, zinc chloride and ferric chloride, each containing 0.1% of ferrite.
A 5 mol / aqueous solution and a 6N aqueous sodium hydroxide solution were prepared, and in 200 ml of the above aqueous sodium hydroxide solution, with stirring, 40 ml of an aqueous nickel chloride solution, 40 ml of an aqueous calcium chloride solution, 120 ml of an aqueous zinc chloride solution, A precipitate is formed by adding 400 ml of a mixed solution of a metal salt of an aqueous iron solution. At this time, sodium hydroxide is sequentially added so that the pH value is maintained at about 13 as needed.

The suspension of the precipitate formed as described above is kept at 90 to 100 ° C. or higher while stirring, and aging is performed for 1 hour.

The suspension obtained in this manner is washed repeatedly until there is no Ca ²⁺ ion in the washing solution by repeating the inclined washing, dried at 70 ° C., and then pulverized in a mortar, as shown below. Various measurements were performed.

(Structural analysis by X-ray diffraction): The obtained sample shows a spinel phase as a result of X-ray diffraction,
It was presumed that the crystal structure of spinel ferrite was adopted.

(Measurement of particle diameter by electron microscope and BET method): When the particle diameter was estimated based on the particle diameter by electron microscope and the specific surface area value by BET method, the values of both were almost the same, and the particle diameter of 10 to 11 nm It was found to have.

(Measurement of magnetic properties by magnetic balance): FIG. 6 shows a magnetization curve of the sample, and FIG. 7 shows a thermomagnetic curve of the sample.

Example 2 (Preparation of Kerosene-Based Magnetic Fluid) 100 g / 85 ml of a sodium oleate aqueous solution was added to the ferrite suspension obtained by the same method as in Example 1 after the inclined washing, and the liquid temperature was reduced to 80 ° C. The adsorption reaction was performed for 30 minutes while keeping the temperature. Next, 1N hydrochloric acid was added to adjust the pH to pH 7 to 5, the suspended matter was condensed, and the aggregate was filtered on filter paper, washed with water to remove the electrolyte and excess oleic acid, and then dehydrated to form a cake. obtain. After air-drying the above dehydrated cake,
Pour into 50 ml of kerosene, stir vigorously while gradually increasing the temperature, and stop heating and stirring when the residual water evaporates and the liquid temperature reaches 120 ° C.

The dispersion obtained as described above is subjected to a maximum magnetic field of 3 × 10 ⁵ A
/ m, a magnetic field gradient of 4 × 10 ⁶ A / m ² for 3 hours, and a small amount of precipitate was removed to obtain a kerosene-based magnetic fluid.

 FIG. 8 shows a thermomagnetic curve of the magnetic fluid.

Example 3 (Preparation of a water-based magnetic fluid) To a oleic acid-adsorbed and dehydrated cake of magnetic powder obtained in the same manner as in Example 2, 20 g of sodium dodecylbenzenesulfonate and 50 g of water were added, and the mixture was stirred to obtain a uniform mixture. A dispersion was obtained.

The dispersion obtained as described above is subjected to a maximum magnetic field of 3 × 10 ⁵ A
/ m, a magnetic field gradient of 4 × 10 ⁶ A / m ² for 3 hours to obtain a water-based magnetic fluid by removing a small amount of precipitate.

Table 1 shows the measured solution properties and magnetic properties of the kerosene-based and water-based magnetic fluids prepared from Examples 2 and 3 described above.

Permanent magnets 2 and 2 were placed in the middle of a heat siphon (FIG. 9) 1 in which a tube a sealed by filling with a magnetic fluid produced in Examples 2 and 3 and having a closed circuit was used. C. and the movement of the magnetic fluid was observed.

The above-described closed circuit heat siphon 1 is used as an example of a mechanism for converting heat energy into kinetic energy, and the tube a forming the closed circuit has an inner diameter 1c.
m, via corners A, B, C, D (AB = C
D = 65 cm, AD = BC = 20 cm). Further, since the tube a is immersed in the cooling tank 3 between BC and immersed in the heating tank 4 between AD, a copper tube with a copper plate is used between BC and AD, and other tubes between AB and Acrylic tubes were used between the CDs to prevent heat conduction through the tube walls.

The cooling bath 3 is, for example, an ice bath 5 containing an ice block therein as shown in FIG. 10. The tube a is kept at 0 ° C. (273 K) between BC, and the heating bath 4 is, for example, a constant temperature water bath ( (Not shown), tube a is placed between AD and 20 ° C
(273K).

Then, a permanent magnet 2, 2 having a thickness of 2.5 cm and an area of 5 cm × 2 cm is placed in D
When the N-pole and S-pole were installed in a position near (at a distance of 5 cm from D) at an angle of 30 ° and opposed to each other, the maximum magnetic field at the center between the magnetic poles was 2,260 (Oe).

The flow rate of the magnetic fluid in the heat siphon 1 can be measured from the movement of the fine aluminum powder 6 by cutting a part of the upper surface of the tube a between BC and dropping the inside.

In the kerosene-based magnetic fluid of Example 2 described above,
A velocity of 1.2 cm / s was obtained at the center of the tube, and a velocity of 0.6 mm / s was obtained with the water-based magnetic fluid of Example 3.

Accordingly, it was confirmed that the kerosene-based magnetic fluid and the water-based magnetic fluid of the present invention obtained in Examples 2 and 3 had a large magnetization change rate near room temperature.

FIG. 11 shows an embodiment of a method for preventing snow accumulation on the ground surface. A heat siphon 11 is formed by forming a tube a, which is filled with a magnetic fluid of the present invention in a filled shape, into a quadrilateral shape. The heat siphon 11 is buried in the vertical direction, the upper part of the heat siphon 11 approaches the ground surface GL, the lower part is located deep in the ground, and the permanent magnets 12, 12 face upward.

Therefore, when the ground surface is at a low temperature and there is a temperature change between the ground and the ground, thermal energy in the ground acts on the ground surface in combination with the change in the magnetization of the magnetic fluid and the action of the magnetic field of the permanent magnet 12. In addition, it is possible to prevent snow and freeze.

FIG. 12 shows another embodiment of the method for preventing snow accumulation on the ground surface. A heat pipe 21 is formed by bending a tube a in which a magnetic fluid of the present invention is sealed in a part of the inside thereof into an inverted L-shape. ,
This heat pipe 21 is buried vertically in the ground and the upper part approaches the ground surface GL, and the corporation is located deep underground,
The configuration is such that the permanent magnets 22, 22 face downward.

Therefore, when the ground surface is at a low temperature and there is a temperature change between the ground and the ground, the change in the magnetization of the magnetic fluid and the magnetic field of the permanent magnet 22 cause the heat energy in the ground to act on the ground surface to prevent snow accumulation, Freezing can be prevented.

[Brief description of the drawings]

FIG. 1 is a thermomagnetic curve of a conventional kerosene-based magnetic fluid in which magnetite is dispersed as a magnetic material, and FIG. 2 is a thermomagnetic curve obtained by separating only the magnetic material from the kerosene-based magnetic fluid described above. 3 is a thermomagnetic curve of the mixed zinc-based ferrite of the present invention and the conventional zinc-based ferrite, and FIG. 4 is a diagram showing the magnitude of magnetization and the change in magnetization per temperature of the Ni-Ca-Zn ferrite of the present invention. FIG. 5 is a diagram showing the magnitude of magnetization and the change in magnetization per temperature of other wet ferrites of the present invention, and FIG.
7 is a thermomagnetic curve of the sample obtained in Example 1, FIG. 8 is a magnetization curve of the kerosene-based magnetic fluid obtained in Example 2, and FIG. FIG. 10 is a schematic plan view of a heat pipe using a magnetic fluid, and FIG.
FIG. 11 is a schematic diagram showing one embodiment of a method for preventing snow accumulation using a heat siphon, and FIG. 12 is a schematic diagram showing another embodiment of a method for preventing snow accumulation using a heat pipe. .

Claims (3)

(57) [Claims] 1. A magnetic fluid obtained by coating the surface of fine particles of ferromagnetic metal oxide with a surfactant and then dispersing the fine particle in an organic solvent or water, wherein the magnetic metal oxide is obtained by a wet method. And the composition formula (MeO) _X • (CaO) _Y • (ZnO) _Z • Fe ₂ O ₃ A magnetic fluid characterized by being represented by: 2. A magnetic fluid comprising the surface of fine particles of ferromagnetic metal oxide coated with a surfactant and then dispersed in an organic solvent or water, wherein the magnetic metal oxide is obtained by a wet method. And the composition formula (MeO) _X • (CaO) _Y • (ZnO) _Z • Fe ₂ O ₃ A tube sealed with a magnetic fluid represented by 3. A magnetic fluid obtained by coating the surfaces of fine particles of ferromagnetic metal oxide with a surfactant and then dispersing the particles in an organic solvent or water, wherein the magnetic metal oxide is obtained by a wet method. And the composition formula (MeO) _X • (CaO) _Y • (ZnO) _Z • Fe ₂ O ₃ A heat pipe or heat siphon composed of a tube sealed with a magnetic fluid represented by
A method for preventing snow accumulation, which comprises using geothermal heat to prevent snow falling on the ground surface or melting the accumulated snow.