JPH0827100B2 - Heat transfer tube for absorber - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a heat transfer tube used in an absorber such as an absorption refrigerator and an absorption heat pump, and in particular, absorption efficiency can be improved by providing fins and grooves on the wall surface. The heat transfer tube for the absorber which improved.

[Conventional technology]

An absorber in an absorption refrigerator, an absorption heat pump, or the like is configured by arranging a large number of heat transfer tubes horizontally or vertically in a closed container. In this case, an absorbing liquid, for example, a LiBr aqueous solution (concentration of about 60% by mass) is dropped and sprinkled on the outside of the heat transfer tube to condense the steam generated in the evaporator, and at the same time,
The absorbed heat is transferred to the cooling water flowing in the pipe. Commercially, a surfactant such as diethylhexanol is added to the absorbing solution. The addition of a surfactant is empirically known as a method of improving the absorption capacity.

Absorption in the absorber is caused by a pressure difference between the water vapor pressure in the evaporator and the saturated vapor pressure of the absorbing liquid dropped on the surface of the heat transfer tube. A large pressure difference indicates high performance. The saturated vapor pressure decreases as the temperature or concentration of the absorbing liquid decreases. For this reason, it is desired to improve the heat conduction to lower the temperature of the absorbing liquid and to diffuse the condensed water into the absorbing liquid to reduce the concentration. Therefore, the heat transfer tube is required to improve the efficiency of both heat conduction and mass transfer such as diffusion of condensed water. However, there are many unclear points regarding this absorption mechanism, and smooth tubes have been the mainstream as heat transfer tubes.

On the other hand, the mainstream method of the absorber is to arrange the heat transfer tubes horizontally and drop the absorbing liquid from above. At this time, the absorbing liquid flowing on the surface of the tube is in the form of a thin film, and in order to further improve the heat transfer resistance and the efficiency of the entire device, the absorbing liquid is being further thinned.

[Problems to be solved by the invention]

However, mass transfer is considered to be more important than heat transfer in absorber heat transfer tubes. In order to significantly improve the absorption performance, the conventional thin film method can reduce the thermal resistance but cannot promote the mass transfer. Recently, it has been attempted to use a processing tube such as a low fin tube for the purpose of increasing the heat transfer area and at the same time making the heat absorbing liquid into a thin film. The ability has not been improved.

Since the absorber is an important component that affects the performance of the refrigerator and the like, it is important to improve the performance of the absorber in order to reduce the size and performance of the device in the future.

[Means for solving problems]

The present invention has been made in view of the above, and in order to obtain a compact and high-performance heat transfer tube for an absorber, a plurality of high fins different from the conventional concept are provided on the outer wall of the heat transfer tube, and Provided is a heat transfer tube for a heat absorber in which minute fins or grooves are formed.

That is, the heat transfer tube for a heat absorber of the present invention has the following configuration.

(1) Fins that form an absorbing liquid layer having a predetermined thickness (fins for forming a liquid film) A plurality of fins are provided on the outer wall of the heat transfer tube in parallel to the longitudinal direction of the tube and at a predetermined height, for example, 0.5 to 5 mm. To be

The absorbing liquid on the surface of the heat transfer tube absorbs the water vapor sent from the evaporator and becomes a low concentration, but the movement in the depth direction does not progress much only by diffusion. Therefore, if convection occurs, agitation occurs in the liquid film, and only the surface of the absorbing liquid becomes low in concentration, and mass transfer is not suppressed. Moreover, when a surfactant is added, the liquid film becomes thick due to the surface tension, and convection easily occurs. Therefore, a thick liquid film is formed on the surface of the heat transfer tube, and at the same time, agitation is actively performed when the circumferential liquid flow moves over the fins.

(2) A plurality of minute fins or grooves formed between the liquid film forming fins A plurality of fins or grooves are formed in parallel with the tube axis or at a predetermined angle. The grooves may intersect at different predetermined angles. Increase the amount of heat transfer by increasing the outer surface area.

〔Example〕

 Hereinafter, examples of the present invention will be described in detail.

1 and 2 show an embodiment of the present invention.
The figure shows a cross section perpendicular to the longitudinal direction of the tube, and FIG. 2 shows the plane in the longitudinal direction of the tube. On the surface of the copper tube 1 for heat transfer tubes with an outer diameter of 19 mm, fins 3 with a height of 2 mm extending in the axial direction of the tube are evenly distributed on the circumference.
30 mm in the axial direction with a depth of 0.5 mm between each fin 3.
The spiral groove 2 of ° is provided at a pitch of 1.2 mm in the circumferential direction.

This heat transfer tube was set to 1, and the measurement was carried out by incorporating it into the measuring device shown in FIG. The measuring device 4 comprises an absorber part 5 and an evaporator part 10.
Divided into 24 heat transfer tubes 1 in absorber 5, effective length 300m
Assemble in 3 rows and 8 stages at m, and let cooling water 8 flow inside. The thick absorbing liquid 6 is dripped from the nozzle 7a of the dropping pipe 7, and the absorbing liquid 9 diluted by the absorption of water vapor described later is discharged from below the absorber section 5. The evaporator section 10 also has the same configuration, and cold water 13 is flown inside the heat transfer tube 11 and a refrigerant (water) 12 is added to the dropping tube.
It is dropped from the nozzle 15a of 15 and moves to the absorber section 5 as water vapor 14, and the rest is discharged from below the evaporator section 10.
In this example, the absorption liquid 6 was a 58 wt% concentration LiBr aqueous solution, and 250 ppm by weight of n-octyl alcohol was added,
The liquid temperature was 40 ° C. The temperature of the cooling water 8 is 28 ° C, and the cold water 13
The amount of water is controlled so that the evaporation temperature of the refrigerant 12 is constant at 10 ° C. In the absorber section 5, heat transfer and mass transfer on the surface of the heat transfer tube 1 are rapidly performed, so that water vapor
The amount of 14 absorbed by the absorbing liquid 6 increases, and the cooling capacity of the cold water 13 in the evaporator unit 10 improves.

FIG. 4 compares the measurement results in the example of the present invention with the cooling capacity of the conventional smooth tube. The liquid film flow rate (Γ) on the horizontal axis indicates the flow rate per unit length flowing on one side of the pipe,
The vertical axis shows the cooling capacity Q _c in the evaporator section 10. According to this embodiment, at the liquid film flow rate Γ = 0.015 kg / m · s, the cooling capacity Q _c is about 1.5 times that of the conventional smooth tube, which shows that the cooling capacity is improved. When observing the flow state of the absorbing liquid 6 on the surface of the heat transfer tube 1, the liquid stays between the fins 3 at a predetermined liquid film thickness, so that stirring based on convection becomes active, and the surfactant causes The expected lateral running of the liquid was observed, and it was further confirmed that the liquid was disturbed at each stage of the fin 3. Therefore, it is considered that in the examples of the present invention, the heat transfer and the mass transfer were significantly promoted by the stirring of the absorbing liquid and the increase of the heat transfer area.

FIG. 5 is a second embodiment of the present invention and shows a heat transfer tube 1 in which a groove 20a having a predetermined angle with respect to the tube axis and a groove 20b parallel to the tube axis intersect.

Although the inner surface of the heat transfer tube is smooth in the above embodiments, it may be a machined surface having grooves or protrusions on the inner surface.

〔The invention's effect〕

As described above, according to the heat transfer tube for a heat absorber of the present invention, since a plurality of fins are provided on the outer wall of the heat transfer tube and minute fins, grooves, etc. are formed between the fins, the inside of the absorbing liquid film on the surface of the heat transfer tube is formed. It is possible to activate the stirring based on the convection that is generated in the above step and increase the heat transfer area. As a result, both heat conduction and mass transfer can be promoted, and a compact and high-performance absorber heat transfer tube can be obtained.

[Brief description of drawings]

1 and 2 show an embodiment of the present invention, and FIG. 1 is an explanatory view showing a cross section perpendicular to the pipe longitudinal direction. FIG. 2 is an explanatory view showing a plane. FIG. 3 is an explanatory view of an apparatus for measuring the capacity of the heat transfer tube of the embodiment. FIG. 4 is a diagram comparing the cooling capacities of the heat transfer tubes for heat absorbers of the example and the related art. FIG. 5 is a diagram showing a second embodiment of the present invention. Explanation of symbols 1 ... Absorber heat transfer tube 2 ... Groove 3 ... High fin 4 ... Measuring device 5 ... Absorber section 6 ... High-concentration absorbing liquid 7, 15 ... Drip pipe 7a, 15a ...... Nozzle 8 …… Cooling water, 9 …… Low concentration absorption liquid 12 …… Refrigerant (water), 13 …… Cold water 14 …… Steam

Claims (2)

[Claims] 1. A heat transfer tube of an absorber which is disposed in a closed container, in which an absorbing liquid is dripped on the outside and cooling water is flowed on the inside, and a plurality of fins extending in the longitudinal direction of the tube are provided on an outer wall of the heat transfer tube. A heat transfer tube for an absorber, characterized in that it has a plurality of fine fins or a plurality of grooves formed between the fins and lower than the fins. 2. A heat transfer tube for an absorber according to claim 1, wherein a plurality of grooves are formed so as to intersect with each other.