JP2020200993A - Heat transfer pipe, evaporator, and manufacturing method of heat transfer pipe - Google Patents

Abstract

To achieve improvement of heat transfer performance in a heat transfer pipe for an evaporator for evaporating a refrigerant on an outer surface.SOLUTION: In a heat transfer pipe for an evaporator, a cooled fluid flows at the inner side and a refrigerant flows at the outer side. The heat transfer pipe includes: a pipy pipe body 51 in which fins 53 protruding outward are formed; and a porous layer 61 covering an entire outer surface of the pipe body 51. The porous layer 61 covers an entire outer surface of the pipe body 51. The porous layer 61 including fine cavities enables improvement of heat transfer performance when the refrigerant is evaporated at the outer side of the heat transfer pipe 50.SELECTED DRAWING: Figure 4

Description

The present disclosure relates to heat transfer tubes, evaporators, and methods for manufacturing heat transfer tubes.

Patent Document 1 discloses a heat transfer tube for an evaporator that evaporates a refrigerant on the outer surface. Fins extending spirally in the longitudinal direction of the heat transfer tube are formed on the outer surface of the heat transfer tube. In this heat transfer tube, a build-up is provided at the tip of the fin, and the gap between the tips of adjacent fins is narrowed by the build-up. Then, in this heat transfer tube, by forming a cavity surrounded by fins and a build-up, the heat transfer performance when the refrigerant evaporates outside the heat transfer tube can be improved.

Japanese Unexamined Patent Publication No. 60-2400993

In the heat transfer tube of Patent Document 1, since the cavity is formed by partially covering the gap between the tip ends of the adjacent fins by overlaying, the size of the formed cavity becomes relatively large. Therefore, there is a possibility that the heat transfer promoting effect by forming the cavity cannot be sufficiently obtained.

An object of the present disclosure is to improve the heat transfer performance of a heat transfer tube for an evaporator in which a refrigerant flows on the outside.

The first aspect of the present disclosure is for a heat transfer tube (50) for an evaporator in which a fluid to be cooled flows inside and a refrigerant flows outside, and a tubular tube having fins (53) protruding outward is formed. It is characterized by including a main body (51) and a porous layer (61) that covers the entire outer surface of the tube main body (51).

In the first aspect, a porous layer (61) containing fine cavities can be formed over the entire outer surface of the tube body (51) on which the fins (53) are formed. Therefore, according to this aspect, it is possible to improve the heat transfer performance when the refrigerant evaporates outside the heat transfer tube (50).

The second aspect of the present disclosure is characterized in that, in the first aspect, the porosity of the porous layer (61) is 30% or more.

In the second aspect, since the porosity of the porous layer (61) is 30% or more, the heat transfer performance can be improved by forming the cavity.

A third aspect of the present disclosure is characterized in that, in the first or second aspect, the fin (53) is formed in a spiral shape extending in the axial direction of the pipe body (51).

In the third aspect, a spiral fin (53) is formed on the tube body (51). The fin (53) extends in the axial direction of the pipe body (51) while turning in the circumferential direction of the pipe body (51).

In the fourth aspect of the present disclosure, in the third aspect, the value obtained by dividing the pitch of the fins (53) in the axial direction of the pipe body (51) by the height of the fins (53) is 0. It is characterized by being .6 or more.

In the heat transfer tube (50) of the fourth aspect, the value (FP / FH) obtained by dividing the pitch FP of the fin (53) by the height FH of the fin (53) is 0.6 or more.

In a fifth aspect of the present disclosure, in the third or fourth aspect, the pipe body (51) has a notch (54) that divides the fin (53) in the axial direction of the pipe body (51). It is characterized in that it is formed side by side.

In a fifth aspect, the fins (53) are separated by a notch (54). In the pipe body (51), cuts (54) are formed side by side in the axial direction of the pipe body (51). The refrigerant flowing along the outer surface of the heat transfer tube (50) flows along the spiral fin (53) in the circumferential direction of the heat transfer tube (50) and passes through the notch (54) that divides the fin (53). It flows in the axial direction of the heat transfer tube (50).

The sixth aspect of the present disclosure is intended for the evaporator (10), and the heat transfer tube (50) of any one of the first to fifth aspects and the shell (20) accommodating the heat transfer tube (50). ) Is provided.

In the evaporator of the sixth aspect, the heat transfer tube (50) of any one of the first to fifth aspects is housed in the shell (20).

A seventh aspect of the present disclosure is characterized in that, in the sixth aspect, a refrigerant having a density ratio of 0.02 or less, which is a value obtained by dividing the density of saturated vapor at a predetermined temperature by the density of a saturated liquid, is evaporated. To do.

The evaporator (10) of the seventh aspect is used to evaporate a refrigerant having a density ratio (ρ_V / ρ_L) of 0.02 or less. ρ_V is the “density of saturated vapor at a predetermined temperature”, and ρ_L is the “density of saturated liquid at a predetermined temperature”. In a saturated refrigerant in which a saturated vapor and a saturated liquid coexist, the smaller the density ratio of the refrigerant, the greater the buoyancy acting on the bubble-like saturated vapor existing in the saturated liquid. Therefore, the smaller the density ratio of the refrigerant, the easier it is for saturated vapor to escape from the fine cavities formed in the porous layer (61) of the heat transfer tube (50). When the saturated vapor escapes from the cavity of the porous layer (61), the saturated liquid flows into the cavity and evaporates. Therefore, the smaller the density ratio of the refrigerant evaporated in the evaporator (10), the higher the effect of improving the heat transfer performance by forming the porous layer (61) in the heat transfer tube (50).

The eighth aspect of the present disclosure is intended for the method for manufacturing a heat transfer tube (50) according to any one of the first to fifth aspects, by spraying a metal onto the outer surface of the tube body (51) by arc spraying. It is characterized by forming the porous layer (61).

In the eighth aspect, the porous layer (61) is formed by arc spraying a metal onto the outer surface of the tube body (51).

FIG. 1 is a schematic cross-sectional view of the evaporator of the embodiment. FIG. 2 is a cross-sectional view showing a section II-II of FIG. FIG. 3 is a front view and a side view of the heat transfer tube of the embodiment. FIG. 4 is a cross-sectional view showing an IV-IV cross section of FIG. FIG. 5 is a photograph of a cross section of the heat transfer tube of the embodiment corresponding to FIG. FIG. 6 is a photograph of a cross section of a heat transfer tube showing a sample region used for calculating porosity. FIG. 7 is a graph showing the heat transfer performance of the heat transfer tube of the present embodiment and the low fin tube to be compared. FIG. 8 is a front view and a side view of the heat transfer tube of the first modification of the embodiment. FIG. 9 is a front view and a side view of the heat transfer tube of the first modification of the embodiment. FIG. 10 is a front view and a side view of the heat transfer tube of the first modification of the embodiment. FIG. 11 is a front view and a side view of the heat transfer tube of the second modification of the embodiment. FIG. 12 is a schematic cross-sectional view of the evaporator of the third modification of the embodiment. FIG. 13 is a cross-sectional view showing a cross section of XIII-XIII of FIG. FIG. 14 is a schematic cross-sectional view of the evaporator of the modified example 4 of the embodiment. FIG. 15 is a cross-sectional view showing the XV-XV cross section of FIG.

An embodiment will be described. The evaporator (10) of the present embodiment is provided in the refrigerant circuit of the refrigerating apparatus that performs the refrigerating cycle, and cools the heat medium such as brine by exchanging heat with the refrigerant in the refrigerant circuit.

-Evaporator-
As shown in FIGS. 1 and 2, the evaporator (10) of this embodiment is a shell-and-tube heat exchanger.

<Evaporator configuration>
The evaporator (10) of the present embodiment is a flow-down liquid film type evaporator, and includes a shell (20), a heat transfer tube (50), and a spreader (41).

The shell (20) includes one body portion (21), two end plate portions (22a, 22b), and two tube plates (23a, 23b). The body portion (21) is a cylindrical member. The axial direction of the body (21) is generally horizontal. Each end plate portion (22a, 22b) is a bowl-shaped member. One end plate portion (22a, 22b) is provided at one end and one end plate portion (21) of the body portion (21). The end plate portions (22a, 22b) are provided so as to cover each end of the body portion (21). The tube plate (23a, 23b) is a disk-shaped member. One tube plate (23a, 23b) is provided at one end of the body portion (21) and one at the other tube. Each tube plate (23a, 23b) traverses the interior space of the shell (20).

The internal space of the shell (20) is divided into a portion on the body portion (21) side and a portion on the end plate portion (22a, 22b) by the tube plate (23a, 23b). Further, the portion of the internal space of the shell (20) surrounded by one end plate portion (22a) and the pipe plate (23a) is vertically partitioned by a partition plate (24). Specifically, the space surrounded by the body (21) and the pair of tube plates (23a, 23b) becomes the evaporation chamber (31). In the space surrounded by one end plate (22a) and the pipe plate (23a), the lower part of the partition plate (24) becomes the entrance chamber (32), and the upper part of the partition plate (24) becomes the exit. It becomes a room (33). The space surrounded by the other end plate (22b) and the pipe plate (23b) becomes the confluence chamber (34).

The body portion (21) is provided with a refrigerant inlet pipe (26) and a refrigerant outlet pipe (27). The refrigerant inlet pipe (26) penetrates the upper part of the body (21) and connects to the spreader (41). The refrigerant outlet pipe (27) is provided in the upper part of the body portion (21) and communicates with the evaporation chamber (31).

A heat medium inlet pipe (28) and a heat medium outlet pipe (29) are provided on one end plate portion (22a). The heat medium inlet pipe (28) is located below the end plate portion (22a) and communicates with the inlet chamber (32). The heat medium outlet pipe (29) is arranged above the end plate portion (22a) and communicates with the outlet chamber (33).

The evaporator (10) is provided with a large number of heat transfer tubes (50). Each heat transfer tube (50) is provided from one tube plate (23a) to the other tube plate (23b). The axial direction of each heat transfer tube (50) is substantially horizontal. As shown in FIG. 2, in the evaporator (10), a large number of heat transfer tubes (50) are arranged so as to be aligned vertically and horizontally.

One end of each heat transfer tube (50) penetrates one tube plate (23a). One end of the heat transfer tube (50) located below the partition plate (24) communicates with the inlet chamber (32). One end of the heat transfer tube (50) located above the partition plate (24) communicates with the outlet chamber (33). The other end of each heat transfer tube (50) penetrates the other tube plate (23b) and communicates with the confluence chamber (34).

The spreader (41) is housed in the evaporation chamber (31). The spreader (41) is located above all heat transfer tubes (50). The spreader (41) sprays the liquid refrigerant supplied through the refrigerant inlet pipe (26) toward the heat transfer pipe (50) arranged below.

<Operation of evaporator>
In the evaporator (10), the heat medium, which is a liquid, flows into the inlet chamber (32) through the heat medium inlet pipe (28) and is separated into a plurality of heat transfer tubes (50) communicating with the inlet chamber (32). Inflow. The heat medium flowing through these heat transfer tubes (50) flows into the confluence chamber (34), merges once, and then separates and flows into a plurality of heat transfer tubes (50) communicating with the outlet chamber (33). The heat medium flowing through these heat transfer tubes (50) flows into the outlet chamber (33), merges, and then flows out from the evaporator (10) through the heat medium outlet tube (29).

In the evaporator (10), the liquid refrigerant supplied from the refrigerant inlet pipe (26) to the spreader (41) is sprayed on the heat transfer pipe (50). The liquid refrigerant sprayed on the heat transfer tube (50) flows down along the outer surface of the heat transfer tube (50), absorbs heat from the heat medium, and evaporates. As a result, the heat medium flowing inside the heat transfer tube (50) is cooled. The evaporated refrigerant flows out of the evaporator (10) through the refrigerant outlet pipe (27).

<Refrigerant>
The evaporator (10) of the present embodiment is provided in a refrigerating apparatus using a specific refrigerant. In the evaporator (10), this specific refrigerant evaporates.

The specific refrigerant has a density ratio (ρ_V / ρ_L) of 0.02 or less (ρ_V / ρ_L ≦ 0. 02) is a refrigerant. The predetermined temperature is an arbitrary temperature included in the range of 0 ° C. or higher and 10 ° C. or lower. Examples of the specific refrigerant include R513A, R134a, R1234ze, R1233zd and the like.

-Heat transfer tube-
The heat transfer tube (50) provided in the evaporator (10) of the present embodiment is a so-called low fin tube.

<Structure of heat transfer tube>
As shown in FIGS. 3 and 4, the tube body (51) and the porous layer (61) are provided.

The tube body (51) includes a circular tube portion (52) and fins (53). The material of the tube body (51) is a copper alloy. The circular tube portion (52) is formed in a straight circular tubular shape. The fin (53) is a strip-shaped portion protruding from the outer surface of the circular tube portion (52). The fin (53) is formed in a spiral shape extending in the axial direction of the circular tube portion (52) while rotating in the circumferential direction of the circular tube portion (52).

As shown in FIG. 5, the porous layer (61) is a layer in which a large number of fine voids (cavities) are formed. The porous layer (61) is formed by spraying a copper alloy on the surface of the tube body (51) by arc spraying. As shown in FIG. 4, the porous layer (61) covers the entire outer surface of the tube body (51). In the heat transfer tube (50) of the present embodiment, the porous layer (61) is formed over the entire portion that can come into contact with the refrigerant.

<fin>
In the tube body (51), the value (FP / FH) obtained by dividing the pitch FP of the fin (53) by the height FH of the fin (53) is 0.6 or more. The value of FP / FH in the tube body (51) is preferably 1.5 or less.

If the FP / FH is smaller than 0.6, the distance between the fins (53) in the axial direction of the tube body (51) becomes too narrow, and it becomes difficult for the sprayed metal to enter between the fins (53). There is a risk that the porous layer (61) cannot be formed near the root of (53). On the other hand, if the FP / FH is larger than 1.5, the amount of expansion of the outer surface area of the tube body (51) due to the formation of the fins (53) becomes small, and sufficient heat transfer performance may not be obtained. .. Therefore, in the heat transfer tube (50) of the present embodiment, it is desirable that the tube body (51) satisfies the relationship of 0.6 ≦ FP / FH ≦ 1.5.

<Porous layer>
In the heat transfer tube (50) of the present embodiment, the porosity of the porous layer (61) is 30% or more and 50% or less. Porosity is the percentage of voids in the porous layer (61).

When the porosity of the porous layer (61) is smaller than 30%, the number of voids in which bubble nuclei are formed decreases, and the effect of promoting heat transfer by forming voids on the surface of the heat transfer tube (50) becomes small. On the other hand, when the porosity of the porous layer (61) is larger than 50%, the voids contained in the porous layer (61) become too large, and the shape of the porous layer (61) is maintained to maintain the shape of the porous layer (61). ) May be difficult to hold on the surface of the tube body (51). Therefore, in the heat transfer tube (50) of the present embodiment, it is desirable that the porosity of the porous layer (61) is 30% or more and 50% or less.

The method of calculating the porosity of the porous layer (61) will be described with reference to FIG.

First, the heat transfer tube (50) is cut at an arbitrary cross section including the central axis of the tube body (51), and a sample cross section that is a part of the cross section is photographed. Next, the average height H of the porous layer (61) included in the image of the cross section of the sample is calculated. Next, a rectangular sample region (62) is set, in which the length L of the sample cross section is the long side and the calculated average height H of the porous layer (61) is the short side. The sample area (62) is an area surrounded by a horizontally long rectangle in FIG. Next, the area A_c of the voids included in the sample region (62) is calculated by image processing or the like. Then, the value obtained by expressing the ratio of the calculated void area A_c to the area A_s (= L × H) of the sample region as a percentage is defined as the porosity R_c (R_c = A_c / A_s × 100).

<Manufacturing method of heat transfer tube>
The manufacturing method of the heat transfer tube (50) will be described.

First, a preparatory step for preparing the pipe body is performed. The tube body is a straight tubular copper tube with fins formed by rolling or other processing.

Next, a thermal spraying step of spraying metal on the outer surface of the tube body (51) is performed. In this thermal spraying step, the copper alloy is sprayed onto the outer surface of the tube body (51) by thermal spraying. As a result, a porous layer (61) is formed on the outer surface of the tube body (51), and the entire outer surface of the tube body (51) is covered with the porous layer (61).

-Features of the embodiment (1)-
The heat transfer tube (50) provided in the evaporator (10) of the present embodiment is a heat transfer tube for an evaporator in which a heat medium as a fluid to be cooled flows inside and a refrigerant flows outside. The heat transfer tube (50) includes a tubular tube body (51) on which fins (53) projecting outward are formed, and a porous layer (61) that covers the entire outer surface of the tube body (51). ..

In the heat transfer tube (50) of the present embodiment, the entire outer surface of the tube body (51) on which the fins (53) are formed is covered with the porous layer (61). In this heat transfer tube (50), a porous layer (61) containing fine cavities (voids) is formed over the entire outer surface of the tube body (51) including fins (53). Therefore, according to the present embodiment, the heat transfer area of the heat transfer tube (50) can be expanded by providing the fins (53) in the tube body (51), and at the same time, the entire outer surface of the tube body (51) (that is, that is). A porous layer (61) containing fine cavities can be formed over the enlarged heat transfer surface). Therefore, according to the present embodiment, the refrigerant evaporates outside the heat transfer tube (50) due to both the expansion of the heat transfer area by the fins (53) and the formation of fine cavities by the porous layer (61). The heat transfer performance can be improved.

FIG. 7 is a graph showing the heat transfer performance of the heat transfer tube (50) of the present embodiment in which the porous layer (61) is formed and the general low fin tube in which the porous layer (61) is not formed. In the figure, the square points indicate the heat transfer coefficient of the heat transfer tube (50) of the present embodiment, and the diamond-shaped points indicate the heat transfer coefficient of the general low fin tube to be compared. As described above, the heat transfer tube (50) of the present embodiment has a significantly higher heat transfer coefficient than the general low fin tube to be compared, particularly in a region where the heat flux is low.

The shape of the low fin tube to be compared whose heat transfer performance is shown in FIG. 7 is the same as the shape of the tube body (51) of the heat transfer tube (50) of the present embodiment whose heat transfer performance is shown in FIG. .. Further, in the heat transfer tube (50) of the present embodiment showing the heat transfer performance in FIG. 7, the porosity of the porous layer (61) is 50%.

-Characteristics of the embodiment (2)-
In the heat transfer tube (50) of the present embodiment, the porosity of the porous layer (61) is 30% or more. According to the heat transfer tube (50) of the present embodiment, since the porous layer (61) has a porosity of 30% or more, the heat transfer performance can be improved by forming the cavity.

-Features of the embodiment (3)-
In the heat transfer tube (50) of the present embodiment, the fins (53) are formed in a spiral shape extending in the axial direction of the tube body (51). The fin (53) extends in the axial direction of the pipe body (51) while turning in the circumferential direction of the pipe body (51).

-Features of the embodiment (4)-
The heat transfer tube (50) of the present embodiment is a value (FP / FH) obtained by dividing "the pitch FP of the fins (53) in the axial direction of the tube body (51)" by "the height FH of the fins (53)". Is 0.6 or more. Therefore, in the thermal spraying step of spraying the metal on the outer surface of the pipe body (51), the sprayed metal can reach the vicinity of the root of the fin (53). Therefore, according to the present embodiment, the entire outer surface of the tube body (51) can be reliably covered by the porous layer (61), and the heat transfer performance of the heat transfer tube (50) can be improved. ..

-Features of the embodiment (5)-
The evaporator (10) of the present embodiment includes a heat transfer tube (50) of the present embodiment and a shell (20) for accommodating the heat transfer tube (50). Then, the evaporator (10) of the present embodiment evaporates a refrigerant having a density ratio (ρ_V / ρ_L) of 0.02 or less, which is a value obtained by dividing the density ρ_V of the saturated vapor at a predetermined temperature by the density ρ_L of the saturated liquid. ..

In a saturated refrigerant in which a saturated vapor and a saturated liquid coexist, the smaller the density ratio of the refrigerant, the greater the buoyancy acting on the bubble-like saturated vapor existing in the saturated liquid. Therefore, the smaller the density ratio of the refrigerant, the easier it is for saturated vapor to escape from the fine cavities formed in the porous layer (61) of the heat transfer tube (50). When the saturated vapor escapes from the cavity of the porous layer (61), the saturated liquid flows into the cavity and evaporates. Therefore, the smaller the density ratio of the refrigerant evaporated in the evaporator (10), the higher the effect of improving the heat transfer performance by forming the porous layer (61) in the heat transfer tube (50).

-Characteristics of the embodiment (6)-
In the method for manufacturing the heat transfer tube (50) of the present embodiment, the porous layer (61) is formed on the outer surface of the tube body (51) by spraying a metal with an arc. Therefore, the porous layer (61) can be formed on the outer surface of the pipe body (51) at a relatively low cost.

− Modifications of the embodiment 1-
In the heat transfer tube (50) of the present embodiment, a plurality of notches (54) may be formed in the fins (53) of the tube body (51). Each notch (54) is formed to divide the fin (53). Further, the plurality of cuts (54) are arranged in the axial direction of the pipe body (51). A plurality of cuts (54) arranged in a row in the axial direction of the pipe body (51) form a cut row (55).

In the heat transfer tube (50) of the present modification shown in FIG. 8, one notch row (55) is formed at the top of the tube body (51). That is, in the heat transfer tube (50) shown in FIG. 8, one notch (54) is formed in each of the portions of the fins (53) that go around the circular tube portion (52).

In the heat transfer tube (50) of the present modification shown in FIG. 9, four cut rows (55) are formed at intervals of 90 ° in the circumferential direction of the tube body (51). That is, in the heat transfer tube (50) shown in FIG. 9, four notches (54) are formed at intervals of 90 ° in each of the portions of the fins (53) that go around the circular tube portion (52).

In the heat transfer tube (50) of this modified example shown in FIG. 10, twenty-four notch rows (55) are formed at intervals of 15 ° in the circumferential direction of the tube body (51). That is, in the heat transfer tube (50) shown in FIG. 10, 24 notches (54) are formed at intervals of 15 ° in each of the portions of the fins (53) that go around the circular tube portion (52). ..

<Characteristics of Modification 1>
In the tube body (51) of the heat transfer tube (50) of this modification, notches (54) that divide the fins (53) are formed so as to be arranged in the axial direction of the tube body (51).

The refrigerant flowing along the outer surface of the heat transfer tube (50) flows along the spiral fin (53) in the circumferential direction of the heat transfer tube (50) and passes through the notch (54) that divides the fin (53). It flows in the axial direction of the heat transfer tube (50). Therefore, the liquid refrigerant supplied from the spreader (41) to the heat transfer tube (50) can be distributed over the entire length of the heat transfer tube (50). Therefore, the refrigerant can be evaporated on almost the entire outer surface of the heat transfer tube (50), and the cooling capacity of the evaporator (10) can be fully exhibited.

− Modified example of the embodiment 2-
As shown in FIG. 11, in the heat transfer tube (50) of the present embodiment, an inner surface groove (56) for promoting heat transfer may be formed on the inner surface of the tube body (51). The inner surface groove (56) is a spiral groove formed on the inner peripheral surface of the circular pipe portion (52) of the pipe body (51). In the heat transfer tube (50) of this modification, the flow of the heat medium flowing inside the tube body (51) is disturbed by the inner groove (56), and as a result, heat transfer between the heat medium and the tube body (51). Is promoted.

− Modified example of the embodiment 3-
As shown in FIGS. 12 and 13, the evaporator (10) of the present embodiment may be a full-liquid evaporator. Here, the difference between the evaporator (10) of this modification and the evaporator (10) shown in FIGS. 1 and 2 will be described.

In the evaporator (10) of this modification, the spreader (41) is omitted, and the refrigerant inlet pipe (26) is arranged at the bottom of the body (21) of the shell (20). The refrigerant inlet pipe (26) of this modification penetrates the body portion (21) and communicates with the evaporation chamber (31). Further, in the evaporator (10) of this modified example, a baffle member (42) is provided so as to cover above the outlet of the refrigerant inlet pipe (26). In the evaporator (10) of this modification, substantially all the heat transfer tubes (50) are immersed in the liquid refrigerant.

− Modified example of the embodiment 4-
As shown in FIGS. 14 and 15, the evaporator (10) of the present embodiment may be a hybrid type of a flowing liquid film type and a full liquid type. In the evaporator (10) of this modification, a part of the heat transfer tube (50) located below is immersed in the liquid refrigerant, and the remaining heat transfer tube (50) located above is above the liquid level of the liquid refrigerant. Is also located above.

Although the embodiments and modifications have been described above, it will be understood that various modifications of the forms and details are possible without departing from the purpose and scope of the claims. In addition, the above embodiments and modifications may be appropriately combined or replaced as long as they do not impair the functions of the present disclosure.

As described above, the present disclosure is useful for heat transfer tubes, evaporators, and methods for manufacturing heat transfer tubes.

10 evaporator
20 shell
50 heat transfer tube
51 Tube body
53 fins
54 notch
61 Porous layer

Claims (8)

A heat transfer tube for an evaporator in which a fluid to be cooled flows inside and a refrigerant flows outside.
A heat transfer tube including a tubular tube body (51) on which fins (53) projecting outward are formed, and a porous layer (61) that covers the entire outer surface of the tube body (51). .. In claim 1,
A heat transfer tube characterized in that the porosity of the porous layer (61) is 30% or more. In claim 1 or 2,
The fin (53) is a heat transfer tube characterized in that the fin (53) is formed in a spiral shape extending in the axial direction of the tube body (51). In claim 3,
A heat transfer tube characterized in that the value obtained by dividing the pitch of the fins (53) in the axial direction of the tube body (51) by the height of the fins (53) is 0.6 or more. In claim 3 or 4,
A heat transfer tube characterized in that cuts (54) for dividing the fins (53) are formed in the tube body (51) so as to be arranged in the axial direction of the tube body (51). The heat transfer tube (50) according to any one of claims 1 to 5.
An evaporator characterized by including a shell (20) for accommodating the heat transfer tube (50). In claim 6,
An evaporator characterized by evaporating a refrigerant having a density ratio of 0.02 or less, which is a value obtained by dividing the density of saturated vapor at a predetermined temperature by the density of a saturated liquid. The method for manufacturing a heat transfer tube according to any one of claims 1 to 5.
A method for manufacturing a heat transfer tube, which comprises forming the porous layer (61) on the outer surface of the tube body (51) by spraying metal with an arc.