JPH1089804A - Out-tube boiling type heat exchanger and absorption refrigerator with this heat exchanger - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a high heat-exchanging performance by providing a heat exchanger in such a manner that a plurality of heat transfer tubes disposed at a lower portion of a container effect out-tube boiling at a temperature lower than those of a plurality of heat transfer tubes disposed at an upper portion of the container. SOLUTION: This heat exchanger is so constituted that plural stages of a plurality of heat transfer tubes 6, 7 extending in a lateral direction are provided vertically inside a container 1 and that a boiling region of a low- temperature fluid is formed outside the heat transfer tubes by carrying out heat-exchanging between the low-temperature fluid A flowing inside the container 1 and a high-temperature fluid S flowing through the heat transfer tubes. In this case, one or plural heat transfer tubes 6, which are disposed at a lower portion of the container among the plurality of heat transfer tubes 6, 7, are composed of boiling accelerating tubes which effect out-tube boiling at a temperature lower than those of the plurality of heat transfer tubes 7 disposed at an upper portion of the container 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat exchanger for exchanging heat between a high-temperature fluid and a low-temperature fluid flowing through a pipe wall, and more particularly to a heat exchanger in which a high-temperature fluid flows inside a vessel through which a low-temperature fluid flows. TECHNICAL FIELD The present invention relates to an extra-boiling heat exchanger in which a heat transfer tube is arranged and a low-temperature fluid is boiled outside the heat transfer tube, and an absorption refrigerator equipped with the heat exchanger as a low-temperature regenerator.

[0002]

2. Description of the Related Art Generally, a partition type heat exchanger is provided with two partition plates (2) and (3) inside a container (1) as shown in FIG. An inlet chamber (12) and an outlet chamber (13) are formed, and a low-temperature fluid inlet pipe (42) and a low-temperature fluid outlet pipe (43) are connected to the heat exchange chamber (11), and the inlet chamber (12) is connected to the inlet chamber (12). A high-temperature fluid outlet pipe (41) is connected to the high-temperature fluid inlet pipe (4) and the outlet chamber (13), and the heat exchange chamber (11) has an inlet chamber between the two partition plates (2) and (3). (12) and a plurality of heat transfer tubes (5) communicating with the outlet chamber (13). High temperature fluid inlet pipe (4) to container
The high-temperature fluid S flowing into the inlet chamber (12) of (1) flows into the heat exchange chamber (1).
After passing through the plurality of heat transfer tubes (5) of (1), it flows out of the outlet chamber (13) to the high temperature fluid outlet tube (41). On the other hand, the cryogenic fluid inlet pipe
Cryogenic fluid A flowing from (42) into the heat exchange chamber (11) of the container (1)
After passing through the heat exchange chamber (11),
Outflow from (43) to the outside. In this process, multiple heat transfer tubes
The outer peripheral surface of (5) serves as a heat transfer surface, and heat exchange is performed between the high-temperature fluid and the low-temperature fluid.

A double-effect absorption refrigerator is equipped with a high-temperature regenerator and a low-temperature regenerator in order to concentrate an aqueous solution of lithium bromide as an absorbing solution. The refrigerant vapor (water vapor) generated from the liquid (aqueous lithium bromide) is sent to the low-temperature regenerator,
Reused as a heating source for the absorbing solution. The low-temperature regenerator has basically the same configuration as the partition type heat exchanger shown in FIG. 10, and steam is supplied from the high-temperature regenerator to the high-temperature fluid inlet pipe (4) as a high-temperature fluid. In (42), an aqueous solution of lithium bromide is supplied from a high-temperature regenerator as a low-temperature fluid.

Thus, in the heat exchange chamber (11) of the container (1), the lithium bromide aqueous solution is heated by the heat of the steam flowing through the heat transfer tube (5), and the water contained therein evaporates. The aqueous lithium bromide solution is concentrated. In the low-temperature regenerator, the surface temperature of the heat transfer tube is high in the upstream portion of the heat transfer tube into which high-temperature steam flows, and at least a part of the lithium bromide aqueous solution boils due to heat received from the high-temperature region. Become.

[0005]

The refrigeration efficiency of a double-effect absorption refrigerator is higher than that of a single-effect absorption refrigerator, but the effect largely depends on the heat exchange performance of the low-temperature regenerator. ing. Like a low-temperature regenerator, an extra-boiling heat exchanger that boils on the surface of the heat transfer tube is governed by a heat transfer mechanism that is essentially different from a heat exchanger that does not boil on the surface of the heat transfer tube . However, conventionally, no sufficient research has been made on the improvement of the performance of the extra-boiling heat exchanger, and there is room for improvement in the heat exchange performance. An object of the present invention is to provide an extra-tube heat-boiling heat exchanger having higher heat exchange performance than conventional heat exchangers.

[0006]

According to the present invention, there is provided an extra-boiling boiling heat exchanger comprising one or a plurality of heat transfer tubes disposed at a lower portion of a container among a plurality of heat transfer tubes disposed inside the container. The heat pipe is characterized in that the heat pipe is a boiling accelerating pipe that causes external boiling at a lower temperature than a plurality of heat transfer pipes arranged in the upper part of the container. The above-mentioned extra-boiling heat exchanger is equipped as a low-temperature regenerator of a double-effect absorption refrigerator, for example.

In the above-mentioned outside-tube boiling heat exchanger of the present invention, heat is exchanged between a high-temperature fluid flowing inside the heat transfer tube and a low-temperature fluid flowing outside the heat transfer tube. Here, the temperature of the high-temperature fluid and the temperature of the low-temperature fluid vary depending on the position in the heat exchange chamber, but in a region where the temperature of the high-temperature fluid is relatively high, the low-temperature fluid receives sufficient heat and boils, In regions where the temperature of the hot fluid is relatively low, the cold fluid does not boil. Thus, in a relatively low temperature outside-boiling boiling heat exchanger, a region where boiling occurs and a region where boiling does not occur are mixed. In such a case, even if the heat transfer tube arranged at the top of the container does not cause boiling, the heat transfer tube arranged at the bottom of the container may cause boiling even in a relatively low temperature region due to its boiling promoting action. become.
A large number of air bubbles are continuously generated from the periphery of the heat transfer tube due to the boiling, and these air bubbles are stitched between the heat transfer tubes at the upper portion of the container to float. In this process, these bubbles disturb the low-temperature fluid surrounding the heat transfer tube at the top of the container, and promote heat exchange by convective heat transfer on the surface of the heat transfer tube.

In the heat transfer tube at the lower part of the vessel, due to the occurrence of boiling outside the tube, the heat transfer characteristic inherent to boiling is exhibited, and the heat exchange is more efficient than in the non-boiling state where convective heat transfer is dominant. Is promoted. On the other hand, in the heat transfer tube in the upper part of the container, heat exchange by convective heat transfer is promoted by bubbles generated from the lower heat transfer tube as described above. As a result,
The heat exchange performance of the heat exchanger as a whole is improved.

In a specific configuration, the plurality of heat transfer tubes disposed inside the container are disposed at a lower portion of the container and one or more first heat transfer tubes into which a high-temperature fluid is to flow first, and a heat transfer tube of the container. A plurality of second heat transfer tubes, which are disposed at the top and through which the high-temperature fluid passing through the first heat transfer tubes is to flow next. Here, the first heat transfer tube can be constituted by a normal heat transfer tube having a smooth surface.

In this specific configuration, the high-temperature fluid flows into the first heat transfer tube first, so that the low-temperature fluid surrounding the first heat transfer tube is heated through the surface of the first heat transfer tube.
Then, the high-temperature fluid having a lowered temperature after passing through the first heat transfer tube flows into the second heat transfer tube, whereby the low-temperature fluid surrounding the second heat transfer tube is heated through the surface of the second heat transfer tube. At this time, since the surface of the first heat transfer tube is heated to a higher temperature than the surface of the second heat transfer tube by the high-temperature fluid in which the temperature does not decrease, it functions as a boiling promoting tube,
The surrounding cold fluid will cause boiling.

In another specific configuration, one or a plurality of heat transfer tubes disposed at the lower part of the vessel are subjected to a surface treatment for promoting boiling, and the heat transfer tubes are provided with a boiling promoting tube. Make up. In this specific configuration, the boiling accelerating tube has a structure in which boiling is easily caused by surface treatment. For example, countless fine recesses are formed on the surface of the boiling promoting tube, and even at a relatively low temperature, bubble nuclei are generated in these recesses, and the bubble nuclei grow into bubbles, and the surface of the tube increases. Break away from Nucleate boiling is continued by repeating generation, growth, and detachment of the bubbles.

More specifically, the plurality of heat transfer tubes arranged at the top of the vessel are constituted by convection promotion tubes having better convection heat transfer characteristics than the boiling promotion tubes arranged at the bottom of the vessel. . The convection promoting tube is configured by, for example, protruding a fin for promoting convective heat transfer from an outer peripheral surface thereof. In this specific configuration, air bubbles floating between the convection promoting tubes at the top of the container promote the convection promoting function of the convection promoting tubes, thereby further promoting heat exchange by convective heat transfer.

[0013]

According to the extra-boiling heat exchanger of the present invention, the heat exchange performance is improved as compared with the conventional extra-boiling heat exchanger.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the present invention applied to a low-temperature regenerator of a double-effect absorption refrigerator will be specifically described below with reference to the drawings. The low-temperature regenerator shown in FIG. 3 has two partition plates (2) and (3) installed inside a container (1) serving as a body thereof, and a heat exchange chamber (11), an inlet chamber (12), and An outlet chamber (13) is formed, and the inlet chamber (12) has a hot fluid inlet pipe (4) and an outlet chamber (1).
A high temperature fluid outlet pipe (41) is connected to 3), and a low temperature fluid inlet pipe and a low temperature fluid outlet pipe (both not shown) are connected to the heat exchange chamber (11). In the heat exchange chamber (11),
A plurality of heat transfer tubes (6) (7) communicating with the inlet chamber (12) and the outlet chamber (13) are provided between the two partition plates (2) and (3). Here, a plurality of heat transfer tubes installed in the lower part of the heat exchange chamber (11)
(6) is constituted by a boiling accelerating tube subjected to a surface treatment described later, and a plurality of heat transfer tubes (7) installed at the upper part of the heat exchange chamber (11) are constituted by bare tubes having a smooth surface. ing.

[0015] From the hot fluid inlet pipe (4) to the inlet chamber of the vessel (1)
The steam S flowing into (12) passes through the plurality of heat transfer tubes (6) and (7) of the heat exchange chamber (11), and then flows out of the outlet chamber (13) to the high-temperature fluid outlet pipe (41). The aqueous solution of lithium bromide A that has flowed into the heat exchange chamber (11) of the container (1) flows in the heat exchange chamber (11) in a direction opposite to the flow of steam, and then flows out.
In this process, the outer peripheral surfaces of the plurality of heat transfer tubes (6) and (7) become heat transfer surfaces, and heat exchange is performed between steam and the aqueous solution of lithium bromide.

As shown in FIG. 5, for example, as shown in FIG. 5, the plurality of heat transfer tubes (6) installed at the lower part of the heat exchange chamber (11) are provided with fine grooves (61) having an enlarged depth in the tube surface. This promotes boiling on the tube surface (for example, trade name “Everfin for boiling Δ” (US Pat. No. 4,216,826)).
Further, by forming the heat transfer tube (6) from a sintered metal, it is also possible to form a fine uneven surface on the surface of the tube, thereby forming a similar boiling promoting tube.

In the above low-temperature regenerator, as shown in FIG. 1, high-temperature steam S flows into the plurality of heat transfer tubes 6 and 7, so that the heat is generated around the heat transfer tube 6 serving as a boiling promoting tube. The aqueous solution A of lithium bromide causes nucleate boiling, and the bubbles B continuously generated by the nucleation float between the heat transfer tubes 7 above the heat exchange chamber 11. Due to the boiling of the lithium bromide aqueous solution, heat exchange is promoted in the lower part of the heat exchange chamber (11) by the heat transfer characteristic inherent in nucleate boiling.

On the other hand, there is a region where boiling does not occur around the heat transfer tube (7) above the heat exchange chamber (11). In this region, the floating of the bubble B causes the aqueous solution of lithium bromide to be scratched. Disturbed and promotes heat exchange by convective heat transfer. As a result, the heat exchange performance of the entire low-temperature regenerator is improved as compared with the conventional low-temperature regenerator.

The low-temperature regenerator shown in FIG. 2 is the same as the low-temperature regenerator in that a heat transfer tube (6) serving as a boiling accelerating tube is arranged below the heat exchange chamber (11). A heat transfer tube (71) having a convection promoting effect is installed at the upper part. The heat transfer tube (71) having a convection promoting effect can be constituted by a so-called middle fin tube or high fin tube having a plurality of fins (72) projecting from the outer peripheral surface as shown in FIG. 6, for example.
Here, the heat transfer tube (71) is made of, for example, phosphorous deoxidized copper, and the height of the fin (72) is formed in a range of 2 to several mm for a tube main body having an inner diameter of about 15 mm. This further promotes heat exchange by convective heat transfer in the upper part of the heat exchange chamber (11).

In the low-temperature regenerator shown in FIG. 3, the heat transfer tubes 6 and 7 to be installed in the heat exchange chamber 11 of the container 1 are all constituted by bare tubes having a smooth surface. The room formed by the left partition plate (2) in the container (1) is further divided vertically by a horizontal partition plate (8), and the inlet chamber (12) and the outlet chamber (1) are separated.
3) are formed adjacent to each other, a relay chamber (14) is formed by the right partition plate (3) in the container (1), and the inlet chamber (12) has a high-temperature fluid inlet pipe (4) and an outlet chamber. (13) has a high temperature fluid outlet pipe (41)
Are connected. The partition plate (3) is provided with a baffle plate (81) projecting into the relay room (14). The steam from the high-temperature regenerator flows into the inlet chamber (12) from the high-temperature fluid inlet pipe (4), and further flows into the heat transfer pipe (6) below the heat exchange chamber (11).
After passing through (6), it flows out to the relay room (14). This water vapor is guided by the baffle plate (81), rises in the relay chamber (14), flows into the heat transfer pipe (7) above the heat exchange chamber (11), passes through the heat transfer pipe (7), and then exits. It flows out of the chamber (13) to the hot fluid outlet pipe (41).

Accordingly, high-temperature steam flows from the inlet to the outlet of the heat transfer tube (6) at the lower part of the heat exchange chamber (11), and the surrounding lithium bromide aqueous solution flows through the heat transfer tube (6).
Will receive enough heat to boil. Thus, the heat transfer tube (6) below the heat exchange chamber (11) functions as a boiling promoting tube. In contrast, the heat exchange chamber
(11) The upper heat transfer tube (7) passes through the lower heat transfer tube (6), and the steam whose temperature has decreased flows through the lower heat transfer tube (6). In the region, bubbles generated from the heat transfer tube (6) below the heat exchange chamber (11) promote heat exchange by convective heat transfer. In the structure shown in FIG. 4, it is needless to say that a higher boiling promoting effect can be obtained by disposing a boiling promoting tube as shown in FIG. 5 as the heat transfer tube (6) below the heat exchange chamber (11).

FIGS. 7 to 9 are graphs showing the results of experiments conducted to verify the heat exchange performance of the low-temperature regenerator as boiling curves. In the experiment, as shown in these figures, heat transfer tubes S4, S2, and S3 each containing a heater were arranged in upper and lower three stages in an aqueous solution of lithium bromide, and the heat flux q (W / W / m ² ) while measuring the temperature difference ΔTsat (K) between the temperature (saturation temperature) of the aqueous solution of lithium bromide and the surface of the heat transfer tube, and simulates the apparatus of the present invention having a boiling promoting tube. In order to do this, one of the three heat transfer tubes is given a heat quantity of 40 kW / m ² sufficient to forcibly cause boiling, and this is used as a boiling accelerating tube, and the other two tubes An experimental system for changing the heat flux of the heat transfer tubes (hereinafter referred to as tube group system) was constructed. In addition, in order to simulate a conventional apparatus without a boiling accelerating tube, heat was not applied to the upper and lower heat transfer tubes, and an experimental system in which the heat flux was changed only for the middle heat transfer tube (hereinafter referred to as a single tube system) ).

FIG. 7 compares the boiling curves of the middle and upper heat transfer tubes S2 and S4 in the tube bundle system in which the lower heat transfer tube S3 is a boiling accelerating tube with the boiling curves of the single tube system. In any of the heat transfer tubes of the tube group system and the single tube system, the slope of the boiling curve becomes large on the way, and it is understood that boiling occurs at this point. In addition, in both the middle and upper heat transfer tubes in the tube bank system, a higher heat flux was obtained than in the single tube system, and it can be seen that the heat exchange performance was significantly improved. This is because, as described above, air bubbles are continuously generated around the lower boiling accelerating tube, and these air bubbles promote heat exchange by convective heat transfer of the middle and upper heat transfer tubes. Also, even after boiling occurs outside the middle and upper heat transfer tubes in the tube bundle system, these heat transfer tubes have a larger heat flux than the single tube system, and heat exchange by boiling heat transfer is also difficult. You can see that it is promoted.

FIG. 8 shows a comparison between the boiling curves of the lower and upper heat transfer tubes S3 and S4 in the tube bank system in which the middle heat transfer tube S2 is a boiling accelerating tube, and the boiling curve in the single tube system. In both the lower and upper heat transfer tubes of the tube bank system, a higher heat flux is obtained than in the single tube system, and the heat exchange performance is improved. From this result, it is understood that the air bubbles generated from the periphery of the boiling promotion tube promote heat exchange by convective heat transfer not only in the upper stage heat transfer tube but also in the lower stage heat transfer tube. However, the effect of the boiling accelerating tube is more conspicuous in the upper heat transfer tube than in the lower heat transfer tube. This is because the influence of bubbles generated from around the boiling accelerating tube is relatively weak for the lower heat transfer tube.

FIG. 9 shows middle and lower heat transfer tubes S2, S in a tube bank system in which the upper heat transfer tube S4 is a boiling accelerating tube.
3 compares the boiling curve for 3 with the boiling curve in a single tube system. Regarding any of the middle and lower heat transfer tubes in the tube bank system, a higher heat flux is obtained than in the single tube system, and the heat exchange performance is improved. From this result, it is understood that the bubbles generated from the periphery of the boiling promoting tube promote heat exchange by convective heat transfer also in the two middle and lower heat transfer tubes disposed below the boiling promoting tube. However, the effect of the upper boiling tube is not so large in the lower heat transfer tube.

As is clear from the comparison of the boiling curves in FIGS. 7 to 9, the highest heat exchange performance was obtained also in the tube bank shown in FIG. 7 in which the boiling accelerating tube was arranged in the lower stage. As shown in FIGS. 1 to 4, the effect of the low-temperature regenerator of the present invention in which a boiling accelerating tube is arranged below the heat exchange chamber (11) is demonstrated.

The description of the above embodiment is for the purpose of describing the present invention, and should not be construed as limiting the invention described in the claims or reducing the scope thereof.
Further, the configuration of each part of the present invention is not limited to the above embodiment, and various modifications can be made within the technical scope described in the claims. For example, the present invention is not limited to the low-temperature regenerator of the double effect absorption refrigerator, but can be of course applied to any extra-boiling heat exchanger.

[Brief description of the drawings]

FIG. 1 is a sectional view of an embodiment of an extra-boiling boiling heat exchanger according to the present invention.

FIG. 2 is a sectional view showing another embodiment.

FIG. 3 is a cross-sectional view in a direction orthogonal to FIG.

FIG. 4 is a sectional view showing still another embodiment.

FIG. 5 is an enlarged perspective view showing a part of the surface of the boiling promoting tube.

FIG. 6 is a cross-sectional view of a heat transfer tube on which fins are protruded.

FIG. 7 is a graph showing a boiling curve when a boiling accelerating tube is arranged in a lower stage.

FIG. 8 is a graph showing a boiling curve when a boiling accelerating tube is arranged in a middle stage.

FIG. 9 is a graph showing a boiling curve when a boiling accelerating tube is arranged in an upper stage.

FIG. 10 is a partially cutaway perspective view of a partition type heat exchanger.

[Explanation of symbols]

 (1) Vessel (11) Heat exchange chamber (6) Heat transfer tube (boiling accelerating tube) (7) Heat transfer tube (71) Heat transfer tube A Low temperature fluid (lithium bromide aqueous solution) S High temperature fluid (steam) B

Claims (6)

[Claims] A plurality of heat transfer tubes extending in a lateral direction are arranged in a plurality of upper and lower stages inside a container, and heat exchange between a low-temperature fluid flowing inside the container and a high-temperature fluid flowing through the heat transfer tubes is performed.
In an extra-boiling boiling heat exchanger in which a boiling region of a low-temperature fluid is formed outside a heat transfer tube, one or more of the plurality of heat transfer tubes disposed at a lower portion of the container are a container, An extra-boiling heat exchanger characterized in that it is a boiling accelerating tube that causes extra-boiling at a lower temperature than a plurality of heat transfer tubes arranged above the heat transfer tube. 2. A plurality of heat transfer tubes disposed inside the container, one or more first heat transfer tubes which are disposed at a lower portion of the container and into which a high-temperature fluid is to flow first, and are disposed at an upper portion of the container. 2. The outside-tube boiling heat according to claim 1, further comprising a plurality of second heat transfer tubes into which the high-temperature fluid that has passed through the first heat transfer tubes flows into next, wherein the first heat transfer tubes constitute a boiling promoting tube. 3. Exchanger. 3. The method according to claim 1, wherein one or a plurality of heat transfer tubes disposed at a lower portion of the container are subjected to a surface treatment for promoting boiling, and the heat transfer tubes constitute a boiling promotion tube. An extra-tube boiling heat exchanger as described. 4. The plurality of heat transfer tubes arranged at the upper part of the container are constituted by convection enhancer tubes having better convection heat transfer characteristics than the boiling enhancer tubes arranged at the lower part of the container. The outside-tube boiling heat exchanger according to claim 3. 5. The outside-tube boiling heat exchanger according to claim 4, wherein the convection promoting tube has fins on its outer peripheral surface for promoting convective heat transfer. 6. A double-effect absorption refrigerator comprising the extra-boiling boiling heat exchanger according to claim 1 as a low-temperature regenerator.