JPH04335969A - Dry evaporator - Google Patents

Abstract

PURPOSE:To provide a dry evaporator with good efficiency in heat-exchanging performance available at a low cost by using cooling tubes which function at an optimal heat-transfer rate in dealing with the changes in state of the refrigerant flowing through a refrigerant circuit. CONSTITUTION:A channel for refrigerant passed through a shell 1 is formed of a ripple-finned tube 5, which has spiral groove 52 cut inside, on the side of the inlet and of an inner-finned tube 6, which is provided with inner fins 62 inside, on the side of the outlet. In the region where the refrigerant becomes a slag flow and a vapor flow in the form of rings, the groove 52 accelerates the boiling of the refrigerant and collects the atomized particles that the boiling produces in the vapor flow so that the overall heat-transmission coefficient is improved. In the region where the refrigerant dries out and turns from a vapor flow to a single-phase vapor flow, that is, on the side of the outlet of the refrigerant channel, the refrigerant undergoes exchange of heat with liquid to be cooled through the inner-finned tube 6 whose area effective for the exchange of heat per unit length is large. Thus by putting a ripple- finned tube 5 and an inner-finned tube 6 to effective use in heat-transfer rate on the side of refrigerant a dry evaporator can be made available at a low cost relative to improvement in the heat-exchange efficiency.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a dry evaporator, in particular, a refrigerant that exchanges heat with the liquid to be cooled is passed through a shell having an inlet and an outlet for the liquid to be cooled, and the refrigerant is evaporated. This invention relates to a dry evaporator equipped with a refrigerant flow system consisting of cooling pipes.

0002

[Prior Art] Conventionally, this type of dry evaporator has been used, for example.
As shown in Japanese Utility Model Application Publication No. 59-67776 and as shown in FIG. A refrigerant inlet F and a refrigerant outlet G are formed at one end of the shell C, and a refrigerant reversal section H is formed at the other end of the shell C. , a refrigerant is passed through the cooling pipe E from the refrigerant inlet F through the refrigerant reversing part H to the refrigerant outlet G, and the refrigerant and the refrigerant are connected to each other from the inlet A to the outlet B.
A refrigerant flow system is formed in which the liquid to be cooled flowing through the refrigerant evaporates through heat exchange with the liquid to be cooled through the cooling pipes E and E. The cooling tube E used in this manner may be, for example, a smooth tube with a smooth inner surface, a ripple fin tube with a spiral groove on the inner surface (Japanese Utility Model Publication No. 55-14956), or a tube. Inner fin tube with fins inside (
One type is selected and used from Japanese Utility Model Application Publication No. 126780/1983).

0003

[Problems to be Solved by the Invention] By the way, the inner fin tube can have a higher heat transfer coefficient on the refrigerant side than a ripple fin tube or a smooth tube, and can improve the heat exchange performance of the evaporator. , the state of liquid single-phase flow,
In a liquid-gas mixed state where liquid refrigerant is attached to the inner wall of the tube, even if an expensive inner fin tube is used, there is little difference in performance compared to when a ripple fin tube is used. The problem with using a tube was that the performance of the evaporator was not improved despite the high cost of the evaporator.

That is, generally when a refrigerant is passed through the cooling pipe E to exchange heat with the liquid to be cooled, the state of the refrigerant changes as shown in FIG. In other words, as heat exchange progresses from a liquid single-phase flow state, bubbles are generated in the liquid single-phase flow, resulting in a slug flow, and as the bubble generation progresses further, a part of the liquid adheres to the inner wall of the cooling pipe E, forming an annular shape. A part of the liquid adhering to the inner wall of the pipe disappears and dries out, leaving only a spray stream.The number of droplets in the spray stream decreases and a superheated state occurs in the middle of the spray stream. It becomes overheated.

On the other hand, the ripple fin tube can promote boiling by the spiral groove provided on the inner surface of the tube, and
Since it can capture mist particles in the spray stream, it can improve the heat transfer coefficient on the refrigerant side compared to smooth pipes, and
Since the inner fin tube has an inner fin inside, it is of course not suitable for the smooth tube.
Compared to the ripple fin tube, the heat exchange area per unit length can be increased, and the heat transfer coefficient on the refrigerant side can be further improved.

However, when the refrigerant is in a dry-out to overheated state, the amount of heat exchanged is small, and the difference in heat transfer coefficient due to the difference in the heat transfer coefficient on the refrigerant side of the cooling pipe is large, whereas in the case of an annular spray flow, In the liquid-gas mixing zone where the liquid adheres to the inner wall of the tube, the amount of heat exchanged is large, and the difference in heat transfer coefficient due to the difference in the heat transfer coefficient on the refrigerant side of the cooling tube is small, so in the liquid-gas mixing zone, Even if an inner fin tube with good heat transfer coefficient is used, there is little difference in performance compared to using a ripple fin tube.Therefore, even if an expensive inner fin tube is used over the entire length of the cooling tube, the performance will be lower than the cost. It will not lead to improvement.

Furthermore, in the case of using a ripple fin tube over the entire length of the cooling tube, even if it can be made cheaper than in the case of using the inner fin tube, especially -10
In the case of a low evaporation temperature below .degree. C., it is not possible to sufficiently improve the heat exchange efficiency from dryout to superheated state, and therefore there is a limit to the improvement of heat exchange performance.

[0008]The present invention was invented in order to solve the above problems, and its purpose is to provide an optimal heat transfer coefficient in response to changes in the state of the refrigerant flowing through the refrigerant distribution system. The object of the present invention is to provide a dry evaporator that has good heat exchange performance by using a cooling pipe, is inexpensive, and is particularly suitable for an evaporator used at a low evaporation temperature.

[0009]

[Means for Solving the Problems] In order to achieve the above object, in the present invention, a refrigerant that exchanges heat with the liquid to be cooled is caused to flow into a shell 1 having an inlet portion 11 and an outlet portion 12 for the liquid to be cooled. , in a dry evaporator equipped with a refrigerant flow system consisting of cooling pipes for evaporating the refrigerant, the inlet side of the refrigerant flow system to the shell 1 is connected to a ripple fin tube 5 having a spiral groove 52 on the inner wall of the pipe. The outlet side of the refrigerant flow system to the shell 1 is formed by an inner fin tube 6 having inner fins 62 installed inside the tube.

[0010] Furthermore, the refrigerant flowing through the refrigerant circulation system adheres to the inner surface of the pipe of the refrigerant circulation system, and a spiral groove is formed on the inner wall of the pipe to extend beyond the end region of the annular flow and reach the saturated gas in the region before the saturated gas. 52, and an inner fin tube 6 with inner fins 62 inside the tube from the region in front of the saturated gas to the outlet of the refrigerant flow system.
It is preferable to form it by.

Furthermore, it is more preferable to form a smooth pipe 7 with a smooth inner surface from the inlet of the refrigerant flow system to the area just before the end of the annular flow.

0012

[Operation] The refrigerant flowing through the refrigerant distribution system exchanges heat with the liquid to be cooled via the ripple fin tube 5 on the inlet side of the refrigerant distribution system, that is, in the slag flow and annular spray flow regions. Therefore, boiling is promoted by the spiral groove 52, and the spray particles generated by the boiling are transferred to the groove 5.
2, the heat transmission coefficient is improved and heat exchange with the liquid to be cooled is performed efficiently. On the other hand, on the outlet side of the refrigerant flow system, that is, after dryout, in the spray flow and steam single-phase flow regions, the inner tube has a larger heat exchange area per unit length than the ripple fin tube 5. Heat can be exchanged with the liquid to be cooled through the fin tube 6, and heat exchange between the spray flow and the single-phase steam flow and the liquid to be cooled can be performed more effectively than in the ripple fin tube 5. Therefore, the heat exchange efficiency in the overheated state from dryout, where the difference in heat transfer coefficient due to the difference in heat transfer coefficient on the refrigerant side of the cooling pipe is large, can be improved by using the inner fin pipe 6 and the ripple fin pipe 5 over the entire length of the refrigerant flow system. This can be improved compared to the case where it is used.

Furthermore, when the ripple fin tube 5 is used up to the region before the saturated gas, the groove 52 of the ripple fin tube 5 captures the spray droplets in the spray stream, so the annular spray droplet region with good heat transfer coefficient is used. In other words, the dryout point can be shifted, and the heat exchange efficiency can be further improved.

Furthermore, when a smooth pipe 7 with a smooth inner surface is used from the inlet of the refrigerant flow system to the region just before the end of the annular flow, the difference in heat transfer coefficient due to the difference in heat transfer coefficient on the refrigerant side of the cooling pipe Since heat can be exchanged through the smooth tube 7, which is cheaper than the ripple fin tube 5, even in the region of the annular spray flow with a small amount, the evaporator can be provided at a low cost without any performance deterioration.

[0015]

[Embodiment] The dry evaporator shown in FIG. The shell 1 is constituted by a pair of tube sheets 14, 14 that close the openings on both sides, and lids 15, 15 fixed to each tube sheet 14, and the shell 1
On one side thereof, a refrigerant inlet 2 having a refrigerant inlet pipe 21 and a refrigerant outlet 3 partitioned by the refrigerant inlet 2 and the partition wall 22 and having a refrigerant outlet pipe 31 are formed. On the other side inside the shell 1, a refrigerant reversal section 4 surrounded by one tube plate 14 and a lid 15 is formed. Reference numeral 23 denotes an expansion valve installed in the refrigerant pipe 24, and the liquid refrigerant reduced in pressure by the expansion valve 23 is made to flow into the refrigerant inlet pipe 21.

[0016] Therefore, between the pair of tube sheets 14, 14,
As shown in FIGS. 2 and 3, there is a ripple fin tube 5 with a spiral groove 52 on the tube inner wall 51, and an inner fin tube 6 with inner fins 62 inside the tube body 61 as shown in FIG. Both ends of the ripple fin tube 5 are opened to the refrigerant inflow section 2 and the refrigerant reversal section 4 to form a first path, and the inner fin tube 6
is opened to the refrigerant inversion section 4 and the refrigerant outflow section 3 to form a second path. A refrigerant distribution system consisting of a first and a second path is formed, and the refrigerant flowing from the first path to the second path is transferred to the inlet portion 11.
The liquid is evaporated by exchanging heat with the liquid to be cooled flowing from the liquid to the outlet section 12. That is, in the first pass, the refrigerant, which has been depressurized by the expansion valve 23 and is about to become a slag flow, changes from a slag flow to an annular spray flow and then dries out to become a saturated gas state. Furthermore, in the second pass, the dried-out refrigerant is passed through as a vapor single-phase flow so as to be brought into a superheated state. Note that although one ripple fin tube 5 and one inner fin tube 6 are each shown in FIG. 1, one tube represents a plurality of tubes.

That is, the refrigerant flowing from the refrigerant inlet pipe 21 into the refrigerant inlet 2 passes through the ripple fin pipe 5 and the inner fin pipe 6 while exchanging heat with the liquid to be cooled. The refrigerant that flows into the refrigerant outflow section 3 and flows into the ripple fin tube 5 from the refrigerant inflow section 2 in a state of becoming a slag flow as shown in FIG. Said groove 52
As the liquid refrigerant exchanges heat with the liquid to be cooled while being swirled by the slag, bubbles are generated in the liquid refrigerant, and a spray flow is generated from the slag flow at the center of the cross section of the ripple fin tube 5, and a part of the liquid refrigerant is The state becomes an annular spray flow adhering to the groove 52 of the ripple fin tube 5, and then the state becomes a spray flow in which a part of the liquid refrigerant does not adhere to the groove 52 of the ripple fin tube 5, that is, a dry-out state. The refrigerant is reversed in the refrigerant reversing section 4 before the refrigerant reaches a saturated gas state. Then, the reversed refrigerant exchanges heat with the liquid to be cooled in the inner fin tube 6, and the number of mist particles in the spray flow decreases to become a saturated gas state, and at the same time becomes a superheated state from the middle of the spray flow, and then , the vapor single-phase flow becomes superheated and the refrigerant outflow portion 3
The refrigerant flows out from the shell 1 through the refrigerant outlet pipe 31.

That is, the refrigerant flowing through the refrigerant flow system exchanges heat with the liquid to be cooled via the ripple fin tube 5 on the inlet side of the refrigerant flow system, that is, in the area until it reaches a saturated gas state. Since boiling is promoted by the spiral groove 52 and spray particles generated by boiling are captured by the groove 52, an annular spray flow state with good heat exchange efficiency can be maintained for a long time, that is, dryout is prevented. Since the points can be shifted, the heat transmission coefficient is improved accordingly, and heat exchange with the liquid to be cooled is performed efficiently. On the other hand, on the outlet side of the refrigerant flow system, that is, after the region before the saturated gas, the inner fin tube 6 has a larger heat exchange area with the refrigerant per unit length than the ripple fin tube 5.
The heat exchange between the saturated gas and the liquid to be cooled can be carried out more effectively than with the ripple fin tube 5, and in particular, for example, a low evaporation temperature of -10°C or less can be performed. In the case of temperature, the larger the temperature difference between the liquid to be cooled and the evaporation temperature, the higher the refrigerant side heat transfer coefficient of the inner fin tube 6 can be effectively exhibited. Therefore, while the refrigerant-side heat transfer coefficient of the ripple fin tubes 5 and the inner fin tubes 6 can be effectively exhibited, the number of expensive inner fin tubes 6 used can be reduced, so that the total length of the refrigerant flow system can be reduced. Compared to the case where the ripple fin tube 5 or the inner fin tube 6 is used, the heat exchange performance can be improved, and the cost can be reduced considering the improved heat exchange performance, especially at a low evaporation temperature. This makes it suitable for use.

Furthermore, in the above embodiment, a two-pass type dry evaporator has been described, but a four-pass type dry evaporator as shown in FIG. 5 may be used. A refrigerant inlet 2 having a refrigerant inlet pipe 21, a refrigerant outlet 3 having the refrigerant outlet pipe 31, and a refrigerant outlet 3 sandwiched between the refrigerant inlet 2 and the refrigerant outlet 3 on one side of the shell 1. A second refrigerant inversion part 4b is formed, and first and third refrigerant inversion parts 4 adjacent to each other are formed on the other side of the shell 1.
a and 4c are formed. In addition, a pair of tube plates 14, 14
In between, the ripple fin tube 5 is inserted as shown in FIG.
In addition to supporting a plurality of the inner fin tubes 6, a plurality of smooth tubes 7 having a smooth inner surface 71 are also supported as shown in FIG. A first path is formed by the smooth pipe 7, which is opened to the first refrigerant reversal section 4a. Further, both ends of half of the plurality of ripple fin tubes 5 are opened to the first refrigerant reversing section 4a and the second refrigerant reversing section 4b, and the remaining half of the ripple fin tubes 5 Both ends thereof are opened to the second and third refrigerant reversing sections 4b and 4c, and the ripple fin tube 5 forms second and third paths. Furthermore, both ends of the inner fin tube 6 are opened to the third refrigerant inversion section 4c and the refrigerant outflow section 3, and a fourth path is formed by the inner fin tube 6, and a fourth path is formed in the shell 1. A refrigerant flow system consisting of the first to fourth passes is formed. Note that in FIG. 5, explanations of the same symbols as in FIG. 1 will be omitted.

With this configuration, when the refrigerant flows from the smooth pipe 7 forming the first path to the first refrigerant reversal section 4a, the refrigerant is in a state just before the end of the annular flow, and the refrigerant enters the first refrigerant reversal section 4a. The water is reversed and flows into the ripple fin tube 5 forming a second path. Then, the refrigerant flows through the ripple fin tube 5 which is reversed at the second refrigerant reversing part 4b and forms a third path,
The refrigerant is reversed in the third refrigerant reversing section 4c, and in the second and third passes, the refrigerant dries out while shifting the dry point from the annular flow state, and the refrigerant reaches the third refrigerant in a state before saturated gas.
The refrigerant is reversed in the refrigerant reversing section 4c. Furthermore, the third refrigerant reversing section 4c
The reversed refrigerant flows into the inner fin tube 6 forming the fourth path, becomes a saturated gas, and then flows out to the refrigerant outlet 3 as a superheated vapor single-phase flow.

That is, the refrigerant flowing through the refrigerant distribution system in this manner changes from a liquid single-phase flow state to the annular flow front region using the smooth pipe 7 which is cheaper than the ripple fin pipe 5 or the inner fin pipe 6. Heat can be exchanged with the liquid to be cooled through the evaporator, and by using the smooth tube 7, the cost of the evaporator can be reduced. In addition, in the region before the saturated gas beyond the end region of the annular flow and reaching the saturated gas, heat is exchanged via the ripple fin tube 5, so the dryout point can be shifted to the exit side as described above. From the saturated gas region to the refrigerant outlet 3, heat is exchanged with the liquid to be cooled via the inner fin tube 6, which has a larger heat exchange area per unit length than the smooth tube 7 or the ripple fin tube 5. be able to. Therefore, in the region from the refrigerant inflow section 2 to the end of the annular flow, where the difference in heat exchange efficiency due to the difference in heat transfer coefficient on the refrigerant side between the smooth pipe 7, the ripple fin pipe 5, and the inner fin pipe 6 is small, an inexpensive smooth pipe is used. Even if the tube 7 is used, the replacement performance of the entire evaporator will not deteriorate much. As a result, the cost of the evaporator can be further reduced without deteriorating the performance while effectively utilizing the good refrigerant-side heat transfer coefficient of the ripple fin tube 5 and the inner fin tube 6.

[0022] In this embodiment, the first
The path was formed by the smooth tube 7, the second and third passes by the ripple fin tube 5, and the fourth path by the inner fin tube 6, but the two-pass format was used, and the first path was formed by the smooth tube and the ripple fin tube. You may. Further, in each of the above embodiments, two-pass and four-pass type dry evaporators have been described, but the number of passes may be three, or five or more passes. Further, although the ripple fin tube 5 having the spiral groove 52 on the inner wall of the tube is used, for example, a corrugated tube having a groove on the inner wall and being cheaper than the ripple fin tube 5 may be used.

[0023]

As explained above, the present invention allows a refrigerant to exchange heat with the liquid to be cooled to flow into the shell 1 having an inlet section 11 and an outlet section 12 for the liquid to be cooled, and evaporates the refrigerant. A dry evaporator equipped with a refrigerant flow system consisting of cooling tubes, the inlet side of the refrigerant flow system to the shell 1 being formed by a ripple fin tube 5 having a spiral groove 52 on the inner wall of the tube. Since the outlet side of the refrigerant flow system to the shell 1 is formed by the inner fin tube 6 having inner fins 62 inside the tube, the refrigerant flowing through the refrigerant flow system is connected to the inlet side of the refrigerant flow system, That is,
In the region of the slag flow and the annular spray flow, heat can be exchanged with the liquid to be cooled through the ripple fin tube 5, boiling is promoted by the spiral grooves 52, and the spray particles generated by boiling are Since the heat is trapped in the grooves 52, the heat transmission coefficient is high and heat exchange with the liquid to be cooled is performed efficiently. On the other hand, on the outlet side of the refrigerant flow system, that is, after dryout, in the spray flow and steam single-phase flow regions, the inner tube has a larger heat exchange area per unit length than the ripple fin tube 5. Heat can be exchanged with the liquid to be cooled through the fin tube 6, and heat exchange between the spray flow and the single-phase steam flow and the liquid to be cooled can be performed more effectively than in the ripple fin tube 5. Therefore, it is possible to improve the heat exchange efficiency in the dryout to superheated state, where the difference in heat transfer coefficient due to the difference in the heat transfer coefficient on the refrigerant side of the cooling pipe is large, compared to the case where the ripple fin tube 5 is used.
In particular, in the case of a low evaporation temperature of, for example, −10° C. or lower, the temperature difference between the liquid to be cooled and the evaporation temperature is large, and the inner fin tube 6 can effectively exhibit a high refrigerant-side heat transfer coefficient. As a result, the heat transfer coefficient on the refrigerant side of the ripple fin tubes 5 and the inner fin tubes 6 can be effectively exhibited, and the number of expensive inner fin tubes 6 used can be reduced, so that the refrigerant flow system can be improved. Compared to the case where the inner fin tube 6 or the ripple fin tube 5 is used over the entire length, the heat exchange performance can be improved, and the cost can be reduced even though the heat exchange performance has been improved, and the evaporation temperature is particularly low. This makes it suitable for use in.

Furthermore, a spiral groove is formed on the inner wall of the pipe so that the refrigerant flowing through the refrigerant flow system adheres to the inner surface of the pipe of the refrigerant flow system and extends beyond the end region of the annular flow and reaches the saturated gas region before reaching the saturated gas. 52, and an inner fin tube 6 with inner fins 62 inside the tube from the region in front of the saturated gas to the outlet of the refrigerant flow system.
In the case where the spray particles are formed by the groove 52 in the spray flow state, the dryout point can be extended to the outlet side of the refrigerant flow system, and the heat exchange performance of the evaporator can be further improved. can be improved.

Furthermore, if the area from the inlet of the refrigerant flow system to the region just before the end of the annular flow is formed by a smooth pipe 7 with a smooth inner surface, the difference in heat exchange efficiency due to the difference in heat transfer coefficient on the refrigerant side of the cooling pipe will be reduced. Even if the smooth tube 7 is used in a region with a small annular spray flow, there is little deterioration in the heat exchange performance of the entire evaporator.
It is less expensive than the ripple fin tube 5 and the inner fin tube 6, and while the high heat exchange efficiency of the ripple fin tube 5 and the inner fin tube 6 can be effectively exhibited, the evaporator can be made even cheaper without deteriorating the performance. It can be done.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a dry evaporator showing one embodiment of the present invention.

FIG. 2 is a cross-sectional view of a ripple fin tube used in the dry evaporator of FIG. 1;

FIG. 3 is a sectional view taken along line AA in FIG. 2;

4 is a sectional view of an inner fin tube used in the dry evaporator of FIG. 1. FIG.

FIG. 5 is a sectional view showing another embodiment.

6 is a sectional view of the smooth tube used in FIG. 5. FIG.

FIG. 7 is an explanatory diagram showing changes in the state of the refrigerant due to heat exchange with the liquid to be cooled.

FIG. 8 is a sectional view showing a conventional example.

[Explanation of symbols]

1 Shell 5 Ripple fin tube 6 Inner fin tube 7 Smooth tube 11 Entrance 12　　　　　　　Exit part 52 Spiral groove 62 Inner fin

Claims (3)

[Claims] Claim 1: A refrigerant flow system consisting of a cooling pipe for flowing a refrigerant that exchanges heat with the liquid to be cooled and evaporating the refrigerant is provided in a shell 1 having an inlet portion 11 and an outlet portion 12 for the liquid to be cooled. In this dry type evaporator, the inlet side of the refrigerant flow system to the shell 1 is formed by a ripple fin tube 5 having a spiral groove 52 on the inner wall of the pipe, and the inlet side of the refrigerant flow system to the shell 1 A dry evaporator characterized in that the outlet side is formed by an inner fin tube 6 having inner fins 62 installed inside the tube. 2. The refrigerant flowing through the refrigerant flow system adheres to the inner surface of the pipe of the refrigerant flow system, exceeding the end region of the annular flow and reaching the saturated gas in the region before the saturated gas. formed by a ripple fin tube 5 with 52,
2. The dry evaporator according to claim 1, wherein the region from the front region of the saturated gas to the outlet of the refrigerant flow system is formed by an inner fin tube (6) having inner fins (62) inside the tube. 3. The dry evaporator according to claim 2, wherein the region from the inlet of the refrigerant flow system to the region just before the end of the annular flow is formed by a smooth pipe 7 having a smooth inner surface.