Evaporators and heat pumps

Abstract

To provide an evaporator which can prevent dry out and enables reduction of the amount of refrigerant.SOLUTION: An evaporator includes: a supply part which supplies a refrigerant flowing from the outside to an internal space; and a heat transfer pipe which is disposed in the internal space and in which heat exchange between a heat medium circulating from the outside and the supplied refrigerant is conducted and a retaining layer which retains a liquid film of the refrigerant and evaporates the refrigerant is formed on its surface. The retaining layer is formed by a porous material and formed having a predetermined layer thickness which inhibits dry out on the heat transfer pipe and improves the heat transfer coefficient.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a refrigerant reducing evaporator and heat pump. [Background technology]

[0002] Heat pumps used in air conditioners, freezers, and the like include an evaporator that exchanges heat with a refrigerant. The evaporator is a key component of a heat pump and affects its overall performance. A so-called immersion type evaporator has traditionally been the mainstream. An immersion type evaporator is configured, for example, by immersing a heat transfer tube through which a heat transfer medium flows in a refrigerant liquid. Heat transfer tubes used in immersion types include, for example, finned tubes with multiple fins and 3D tubes (see, for example, Patent Document 1). It has also been pointed out that the refrigerants used in evaporators contribute to global warming. Therefore, efforts are being made to reduce the impact on global warming, such as by introducing new refrigerants with low global warming potential. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-036035 [Non-patent literature]

[0004] [Non-Patent Document 1] Tsutomu Ubara, Hitoshi Asano and Katsumi Sugimoto” Heat Transfer Enhancement of Falling Film Evaporation on a Horizontal Tube by Thermal Spray Coating” Applied Sciences Volume 10 Issue 5 1632, February 29, 2020. [Non-patent document 2] Maria E. Mondejar, Mark O. McLinden, and Eric W. Lemmon “Thermodynamic Properties of trans-1-Chloro-3,3,3-trifluoropropene (R1233zd(E)): Vapor Pressure, (p, ρ, T) Behavior, and Speed ​​of Sound Measurements, and Equation of State” Journal of Chemical & Engineering Data, 2477-2489, July 8, 2015. Summary of the Invention [Problem to be solved by the invention]

[0005] New refrigerants with low global warming potential are expensive, hindering their introduction. Liquid film evaporation evaporators are known as a way to reduce the amount of refrigerant used. Liquid film evaporation evaporators are configured to drip refrigerant onto the surface of a heat transfer tube, causing the refrigerant to evaporate on the surface of the heat transfer tube. However, with liquid film evaporation evaporators, the dripped refrigerant may evaporate completely from the surface of the heat transfer tube, potentially causing dryout (the phenomenon in which the tube surface dries up). Therefore, liquid film evaporation evaporators have the problem of reduced performance when dryout occurs on the tube surface.

[0006] Conventional heat transfer tubes for immersed evaporators are primarily finned or 3D tubes, and do not specifically consider measures to prevent dryout, such as retaining the refrigerant. When these tubes are applied to liquid film evaporators, they are prone to dryout, resulting in reduced performance and increased costs. While there is a method for forming a thermally sprayed copper coating on the surface of a heat transfer tube in a liquid film evaporation evaporator to retain the liquid film on the tube and prevent dryout (see, for example, Non-Patent Document 1), the thickness of the retention layer formed by thermal spraying is thin, and it is not possible to form a retention layer thick enough to sufficiently suppress dryout. Another issue is that the overall system (liquid film flow rate, heat transfer tube type, and heat transfer tube spacing) when using a liquid film evaporation evaporator is not optimized.

[0007] An object of the present invention is to provide an evaporator that can reduce the amount of refrigerant and prevent dryout. [Means for solving the problem]

[0008] The present invention provides a supply unit that supplies a refrigerant flowing in from the outside to an internal space, and a heat transfer unit that is disposed in the internal space and exchanges heat between a heat transfer medium circulating from the outside and the supplied refrigerant, thereby maintaining a liquid film of the refrigerant and The refrigerant and a heat transfer tube having a retention layer formed on the surface thereof, the retention layer being made of a porous material, which prevents the supplied refrigerant from drying out on the heat transfer tube and improves the heat transfer coefficient. To achieve this, copper powder is sintered on the surface of the heat transfer tube to form three-dimensional porous voids throughout the retention layer so that the refrigerant can flow into the retention layer, and the porosity of the retention layer is 60% or more and 70% or less, The aforementioned Retention layer The layer thickness is 1 mm or more and 2 mm or less. R , an evaporator.

[0009] According to the present invention, a retention layer is formed on the surface of the heat transfer tube, so that the supplied refrigerant is retained as a liquid film and evaporates due to the heat of the heat medium circulating through the heat transfer tube, thereby reducing the amount of refrigerant. Furthermore, according to the present invention, the retention layer has a predetermined thickness that suppresses dryout of the supplied refrigerant on the heat transfer tube and improves the heat transfer coefficient, thereby stabilizing performance. Furthermore, according to the present invention, the retention layer is formed of a porous material, so that the refrigerant penetrates and retains a liquid film, and the refrigerant evaporates from the surface, thereby preventing dryout while maintaining performance.

[0010] The heat transfer tube of the present invention may include a pipe line formed of a copper pipe, and the retaining layer formed by sintering copper powder onto the surface of the pipe line.

[0011] According to the present invention, the support layer is formed on the surface of the copper tube by sintering copper powder, thereby improving thermal conductivity and enabling efficient heat exchange.

[0012] The support layer of the present invention may be formed to a thickness of 2 mm or less.

[0013] According to the present invention, the retention layer is formed to a predetermined thickness, thereby making it possible to improve the efficiency of heat transfer.

[0014] The support layer of the present invention may be made of a fibrous material.

[0015] According to the present invention, the support layer is formed by wrapping a fibrous material around the surface of the pipe, so that the evaporator can be constructed easily.

[0016] Furthermore, the present invention may also provide a heat pump including the evaporator having the above-described configuration.

[0017] According to the present invention, a heat pump can be realized that maintains performance while reducing the amount of refrigerant. [Effects of the Invention]

[0018] According to the present invention, the amount of refrigerant can be reduced and dry-out can be prevented. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a diagram showing the configuration of a heat pump to which an evaporator according to the present invention is applied; [Figure 2] FIG. 2 is a diagram showing the configuration of an evaporator. [Figure 3] FIG. 2 is a cross-sectional view of a heat transfer tube of the evaporator. [Figure 4] FIG. 2 is a diagram showing the configuration of a test device for testing the performance of an evaporator. [Figure 5] FIG. 10 is a diagram showing an example of test results. [Figure 6] FIG. 10 is a diagram showing the test state. [Figure 7] FIG. 10 is a diagram showing an example of test results. [Figure 8] FIG. 10 is a diagram showing the test state. [Figure 9] FIG. 10 is a diagram showing an example of test results. DETAILED DESCRIPTION OF THE INVENTION

[0020] Hereinafter, an evaporator and a heat pump according to the present invention will be described with reference to the drawings.

[0021] As shown in Fig. 1, the heat pump 1 is, for example, an air conditioning system configured with a refrigeration circuit. The heat pump 1 may be applied to, for example, an air conditioning / refrigeration system, a heating system such as a hot water supply system, an industrial high-temperature heat pump, etc. The heat pump 1 includes, for example, a compressor 10 that compresses a refrigerant, a condenser 20 that condenses the compressed refrigerant through heat exchange, an expansion valve 30 that decompresses the refrigerant, an evaporator 40 that evaporates the refrigerant, and piping Q that connects the various devices. A refrigerant flows through the piping Q.

[0022] The evaporator 40 is connected to, for example, a pipe C1 of an air conditioner C, and performs heat exchange of cold. The air conditioner C is, for example, a cooling device that cools indoor air. The condenser 20 is connected to, for example, a pipe H1 of a heat exchanger H, and performs heat exchange of hot, which is then released into the atmosphere. The pipe C1 of the air conditioner C and the pipe H1 of the heat exchanger H may be switched to make the air conditioner C function as a heating device, and cause the heat exchanger H to release cold into the atmosphere.

[0023] The refrigeration cycle of the heat pump 1 is as follows: A gaseous refrigerant is compressed by the compressor 10. The refrigerant compressed to a high pressure exchanges heat with a heat medium circulating in a pipe H1 connected to the condenser 20, condensing and becoming a liquid. The condensed refrigerant is reduced in pressure by an expansion valve 30 to a state where it is easy to evaporate, and then flows into the evaporator 40. The refrigerant that flows into the evaporator 40 exchanges heat with a heat medium circulating in a pipe C1 connected to the evaporator 40, evaporates, and then returns to the compressor 10 to be compressed again.

[0024] 2, the evaporator 40 is a liquid film heat exchanger. The evaporator 40 includes a housing 45 formed in the shape of a sealed container, a supply unit 41 connected to a pipe Q through which refrigerant F flowing in from the outside flows, and a heat transfer tube 42 connected to a pipe C1 through which a heat medium from an air conditioner or the like flows. The heat transfer tube 42 may be one or more heat transfer tubes 42 branching from the pipe C1 and arranged in parallel. The housing 45 has the supply unit 41 and the heat transfer tube 42 arranged therein. The housing 45 is connected to the upstream side of the pipe Q through which refrigerant F flows to the supply unit 41 and the downstream side of the pipe Q through which evaporated refrigerant F flows out.

[0025] Liquid refrigerant F flows in from the upstream side of pipe Q. Gas refrigerant F flows out from the downstream side of pipe Q. Liquid refrigerant F is stored in the lower part of the interior of casing 45. To casing 45, the upstream side of pipe C1 that circulates the heat medium through heat transfer pipe 42 and the downstream side of pipe C1 that discharges the heat medium that has circulated through heat transfer pipe 42 are connected.

[0026] The supply unit 41 supplies the refrigerant F by causing it to flow downward into, for example, an internal space formed within the housing 45. The internal space is the space above the liquid level of the refrigerant F stored at the bottom of the housing 45. The supply unit 41 is disposed above the heat transfer tubes 42. The supply unit 41 is formed, for example, in the shape of a tube having one end connected to the upstream side of the pipe Q and the other end closed. The supply unit 41 has, for example, a large number of fine discharge holes (not shown) formed downward along the axial direction of the tube through which the refrigerant F leaks out.

[0027] The supply unit 41 drips the refrigerant F leaking from the discharge port, and supplies the refrigerant F to the surfaces of the heat transfer tubes 42. The configuration of the supply unit 41 is an example, and the refrigerant F may be sprayed to supply the refrigerant F to the surfaces of the heat transfer tubes 42. In other words, the supply unit 41 may have any configuration as long as it can supply the refrigerant F to the surfaces of the heat transfer tubes 42 inside the housing 45.

[0028] As shown in FIG. 3 , the heat transfer tube 42 is formed, for example, as a liquid film type pipe. The heat transfer tube 42 is disposed in the internal space of the housing 45. That is, the heat transfer tube 42 is not immersed in the refrigerant F stored at the bottom of the housing 45. The heat transfer tube 42 is formed of a metal such as copper. The heat transfer tube 42 includes, for example, a conduit 43 in which a flow path for a heat medium is formed, and a retaining layer 44 formed on the surface of the conduit 43. A high-temperature heat medium from, for example, an air conditioning device C flows through the conduit 43. The conduit 43 is formed in the shape of a conduit with a circular cross section. The heat transfer tube 42 may be formed in another cross-sectional shape, such as an elliptical cross section. The conduit 43 is formed, for example, of a copper pipe.

[0029] The retention layer 44 is formed to form and temporarily retain a liquid film of the refrigerant supplied from the supply unit 41, and to evaporate the refrigerant using heat supplied from the pipe 43. The retention layer 44 is formed to retain the dropped refrigerant F without drying out due to the latent heat of the heat medium circulating through the pipe 43, while also allowing evaporation. In other words, the retention layer 44 is formed to a predetermined layer thickness that retains the refrigerant F so as to prevent the supplied refrigerant F from drying out on the heat transfer tubes 42 and improve the heat transfer coefficient. When the latent heat of the heat medium circulating through the pipe 43 fluctuates, the supply amount of the refrigerant supplied from the supply unit 41 is adjusted to maintain the liquid film in the retention layer 44.

[0030] The retaining layer 44 is formed, for example, from a porous material. The retaining layer 44 is formed, for example, by sintering copper powder. The retaining layer 44 is formed, for example, by sintering dendritic electrolytic copper powder having a size of about 10 to 100 μm. The retaining layer 44 is formed, for example, to have a bulk density of 30 to 40% (porosity of 60 to 70%).

[0031] The material and composition of retaining layer 44 are merely examples, and other configurations may be used as long as a liquid film of refrigerant F can be maintained on the surface of pipe 43. Retaining layer 44 may be formed by sintering copper powder onto the surface of pipe 43, or may be formed by sintering pre-divided shapes. This divided retaining layer 44 may be adhered to the surface of pipe 43 using an adhesive or the like with high thermal conductivity, or may be fixed to the surface of pipe 43 by wrapping wire or the like around it. Retaining layer 44 may also be formed from other materials with good thermal conductivity, such as aluminum, silver, diamond, etc., in addition to copper.

[0032] Furthermore, the retaining layer 44 may be formed not only from a porous material but also from a fibrous material. For example, the retaining layer 44 may be formed by wrapping a sheet-like fibrous material around the surface of the pipe 43. The fibrous material may be formed by weaving, for example, metal wires with high thermal conductivity, or by woven carbon fibers. Alternatively, the fibrous material may be a nonwoven material.

[0033] Next, a performance test of the evaporator 40 will be described.

[0034] As shown in FIG. 4, a test apparatus 100 is constructed for testing the performance of the heat transfer tube 42. The test apparatus 100 is configured to reproduce the internal conditions of the evaporator 40. The test apparatus 100 includes, for example, a housing 101 formed in the shape of a sealed container, and a condenser tube 102 and a heat transfer tube 103 arranged in the housing 101. A first constant temperature bath 104, which circulates a low-temperature heat medium therein, is connected to the condenser tube 102 via a pipe 105. A second constant temperature bath 106, which circulates a high-temperature heat medium therein, is connected to the heat transfer tube 103 via a pipe 107.

[0035] Within the housing 101, the refrigerant is cooled and condensed on the outer surface of the condenser tube 102, to which cooling water is supplied from the first constant temperature bath 104, and drips onto the heat transfer tube 103 located directly below the condenser tube 102. Heated water is supplied to the heat transfer tube 103 from the second constant temperature bath 106. The refrigerant dripped onto the surface of the heat transfer tube 103 evaporates as it flows down the outer surface of the heat transfer tube 103. The amount of refrigerant evaporating on the surface of the heat transfer tube 103 is the same as or less than the amount of refrigerant condensing on the surface of the condenser tube 102. In the latter case, an auxiliary electric heater 110 installed at the bottom within the housing 101 evaporates the refrigerant so that the pressure within the housing 101 remains constant.

[0036] The average mixed temperature of the heat source water (cooling water and heating water) is measured by a platinum resistance thermometer pt in mixing chambers 102A, 103A installed at the inlet and outlet of condenser tube 102 and heat transfer tube 103, respectively. The volumetric flow rate of the heat source water is measured by volumetric flow meters 102B, 103B installed on the outlet side of each tube. The refrigerant pressure inside the housing 101 is measured by an absolute pressure gauge P installed near and at the same height as the heat transfer tube 103, and the tube wall temperature of the heat transfer tube 103 is measured by the electrical resistance method. In addition, the evaporation pattern is photographed by a high-speed camera through a glass window G installed on the side of the housing 101.

[0037] In the tests, R1233zd(E) was used as the test refrigerant, and the pressure was adjusted so that the saturation temperature of the refrigerant in the housing 101 was 60°C. Two types of heat transfer tubes 103 were used in the tests: a smooth tube with an outer diameter of 19.05 mm, and a tube with an outer diameter of 19.05 mm and a smooth tube with a 2 mm thick porous support layer formed on the surface. The tube with the support layer has the same structure as the heat transfer tube 42. The base material of the porous support layer is electrolytic copper powder, with a porosity of about 70%, and is formed in the same structure as the support layer 44 of the heat transfer tube 42. The evaporation heat flux was calculated based on the outer surface area of ​​the 19.05 mm smooth tube for both tubes, and was 5 to 40 kWm -2 The experiment was carried out by changing the temperature in the range of

[0038] The amount of liquid refrigerant dropped from the condenser tube 102 is 0.058 to 0.350 kgm per unit reference area of ​​the heat transfer tube 103 under test.-2 s -1 This liquid refrigerant amount was multiplied by the latent heat of vaporization of the refrigerant, resulting in a value of 10 to 60 kWm -2 This corresponds to the maximum heat flux that can be removed from the heat transfer tube surface by evaporation. Hereinafter, the amount of liquid refrigerant dripping onto the heat transfer tube 103 will be referred to as the "liquid refrigerant supply heat flux" in terms of this heat flux. Evaporation heat flux q wall is the heat exchange rate Q of the heat source water flowing through the test heat transfer tube H2O can be calculated as follows:

[0039]

number

[0040]

number

[0041]

number

[0042] Figure 5 shows the performance test results of the heat transfer tube 103 formed as a smooth tube. The test results show the change in heat transfer coefficient with respect to the evaporation heat flux in the heat transfer tube 103. The symbols represent the liquid refrigerant supply heat fluxes of 60, 40, and 25 kW m -2 The vertical bars attached to the symbols indicate the error in the heat transfer coefficient measurement. In addition, the measurement results of the pool boiling heat transfer coefficient using the same heat transfer tube 103 are shown.

[0043] The evaporation heat transfer coefficient of the falling film, like the pool boiling heat transfer coefficient, generally increases with increasing evaporation heat flux. When the evaporation heat flux is relatively close to the liquid refrigerant supply heat flux (qc = 25 kWm in the figure), -2 q wall =20kWm -2 and qc=40kWm -2 q wall =30kWm -2 Except for the case of ( ), there is little difference between the heat transfer coefficients for falling film and pool boiling.

[0044] Figure 6 shows the liquid refrigerant supply heat flux of 25 kW m -2 The evaporation heat flux in Fig. 6(a) is 10 kW m -2 The evaporation heat flux in Fig. 6(b) is 20 kW m -2 The evaporation heat transfer coefficient decreases as the evaporation heat flux approaches the liquid refrigerant supply heat flux. This is because the liquid supply rate is low relative to the evaporation rate, causing most of the heat transfer surface to dry out (see Figure 6(b)). Also, an evaporation heat flux of 10 kW m, which shows a heat transfer coefficient equivalent to pool boiling, -2 However, as shown in Figure 6(a), unwetted areas are observed on the heat transfer surface. This suggests that the local heat transfer coefficient of the wetted area in falling film evaporation is higher than the average heat transfer coefficient of the heat transfer surface in pool boiling.

[0045] Figure 7 shows the change in heat transfer coefficient with respect to the evaporation heat flux in the heat transfer tube 103 with a porous layer. The symbols represent liquid refrigerant supply heat fluxes of 60, 40, 25, and 10 kW m -2 The vertical bars on the symbols indicate the error involved in the heat transfer coefficient measurements. In addition, pool boiling results using the same tube are shown.

[0046] Figure 8 shows the heat flux of the liquid refrigerant supply at 40 kW m -2 The results of the evaporation behavior are shown in Fig. 8(a). -2 and the evaporation heat flux in Fig. 8(b) is 32 kW m -2 When comparing the heat transfer coefficients of the smooth tube and the heat transfer tube 103 with a porous layer, they are qualitatively the same, but the heat transfer coefficient of the heat transfer tube 103 with a porous layer is up to about nine times higher than that of the smooth tube.

[0047] In addition, as shown in Fig. 7, the liquid refrigerant supply heat flux is large, at 60 kW m -2In the case of falling film boiling, as the evaporation heat flux increases, the heat transfer coefficient becomes about 1.5 times higher than pool boiling, and the improvement rate is higher than that of a smooth tube. This is thought to be due to the effect of increasing the surface area due to the porous layer, as well as the fact that the entire tube is more likely to be wet than a smooth tube due to capillary action.

[0048] On the other hand, the evaporation heat transfer coefficient increased with the evaporation heat flux, as in the case of the smooth tube, but decreased as the evaporation heat flux approached the liquid refrigerant supply heat flux. For example, when the liquid refrigerant supply heat flux was 40 kW m -2 The maximum heat transfer rate is 25-30kW m -2 The degree of distortion is almost the same as that of a smooth tube.

[0049] Figure 9 shows the heat flux of the liquid refrigerant supply at 60 kW m -2 The graph shows a comparison of the performance of a smooth tube, a heat transfer tube 103 with a porous layer 103 having a thickness of 1 mm, and a heat transfer tube 103 with a porous layer 103 having a thickness of 2 mm. As shown in the figure, the heat transfer tube 103 with a porous layer 103 having a thickness of 1 mm has a higher heat transfer coefficient than the heat transfer tube 103 with a porous layer 103 having a thickness of 2 mm. When the porous layer is 1 mm thick, the refrigerant is maintained in a wet state, and the supply of liquid refrigerant and the discharge of evaporated refrigerant proceed more smoothly compared to when the porous layer is 2 mm thick, which is thought to improve the heat transfer coefficient. Considering the above experimental results, the porous layer thickness is preferably greater than 0 mm and equal to or less than 2 mm, and is preferably formed to a thickness of approximately 1 mm, at which point heat transfer efficiency is significantly improved.

[0050] A falling film evaporation heat transfer experiment was carried out using a tube with a porous material, and the following conclusions were obtained. (1) The heat transfer coefficients of the porous tubes were generally larger than those of the smooth tubes in both falling film evaporation and pool boiling, and were up to about nine times larger. (2) For both smooth tubes and tubes with a porous layer, the falling film evaporation heat transfer coefficient generally increased as the evaporation heat flux increased, but decreased as the liquid refrigerant supply heat flux approached. There was almost no difference in the heat flux conditions at which the maximum heat transfer coefficient was obtained between smooth tubes and tubes with a porous layer. (3) For both the smooth tube and the tube with a porous layer, the falling film heat transfer coefficient was equivalent to that of pool boiling at low heat fluxes, and higher than that of pool boiling at high heat fluxes, provided that the liquid refrigerant supply heat flux was sufficiently large relative to the evaporation heat flux. In the latter case, the tube with a porous layer showed a higher improvement over pool boiling. (4) When the thickness of the porous layer (retaining layer) of the heat transfer tube was formed to a specified thickness greater than 0 mm and less than 2 mm, the heat transfer coefficient improved, and a particularly significant improvement in the heat transfer coefficient was observed when the layer thickness was approximately 1 mm.

[0051] As described above, the evaporator 40 can reduce the amount of refrigerant and prevent dryout. In the evaporator 40, the retention layer 44 is formed on the surface of the heat transfer tubes 42, so that the refrigerant that flows down is retained as a liquid film and evaporates due to the heat of the heat medium circulating through the heat transfer tubes 42, thereby reducing the amount of refrigerant. In the evaporator 40, the retention layer 44 has a predetermined layer thickness that prevents the supplied refrigerant from drying out on the heat transfer tubes and improves the heat transfer coefficient, so performance can be stabilized even when the amount of refrigerant is reduced.

[0052] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are within the scope and spirit of the invention, as well as the scope of the invention described in the claims and their equivalents. For example, the material forming the retention layer 44 may be not only metal or carbon, but also resin, ceramic, or a composite material thereof. [Explanation of symbols]

[0053] 1...heat pump, 10...compressor, 20...condenser, 30...expansion valve, 40...evaporator, 41...supply section, 42...heat transfer tube, 43...pipe line, 44...retaining layer, 45...casing, 100...test equipment, 101...casing, 102...condenser tube, 102A...mixing chamber, 102B...volumetric flow meter, 103...heat transfer tube, 103A...mixing chamber, 103B...volumetric flow meter, 104...first constant temperature bath, 105...piping, 106...second constant temperature bath, 107...piping, 110...auxiliary electric heater, C...air conditioning unit, C1...piping, F...refrigerant, G...glass window, H...heat exchanger, H1...piping, P...absolute pressure gauge, pt...platinum resistance thermometer, Q...piping

Claims

1. a supply unit that supplies the refrigerant flowing in from the outside to the internal space; a heat transfer tube that is disposed in the internal space and exchanges heat between a heat medium circulating from the outside and the supplied refrigerant, and that has a retention layer formed on its surface that maintains a liquid film of the refrigerant and evaporates the refrigerant; The retaining layer is formed of a porous material, and copper powder is sintered onto the surface of the heat transfer tube to form three-dimensional porous voids throughout the retaining layer so that the refrigerant flows into the retaining layer, thereby suppressing drying out of the supplied refrigerant on the heat transfer tube and improving the heat transfer coefficient. An evaporator, wherein the porosity of the retaining layer is 60% or more and 70% or less, and the thickness of the retaining layer is 1 mm or more and 2 mm or less.

2. The heat transfer tube includes a pipe formed of a copper pipe and the support layer formed on a surface of the pipe. The evaporator of claim 1 .

3. The evaporator according to claim 1 or 2 is provided. heat pump.

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