JPH05340656A - Natural circulation type thermosiphon - Google Patents

Abstract

PURPOSE:To improve heat transfer characteristics at a boiling portion in a thermosiphon to be used for a heat radiator and the like of an electronically cooling refrigerator by providing a heat radiating block contacting with a heating source on the periphery of the boiling portion so as to be in contact with the boiling portion and providing the boiling portion in the heat radiating block in such a manner as to be inclined. CONSTITUTION:An electronically cooling refrigerator has an electronically cooling element 53 provided in a through-hole 51 for setting up communication between a cooling chamber 47 and a heat radiating chamber 49 disposed on the outside thereof, and a cooling block 55 and a heat radiating block 57 are provided so as to hold the element 53 therebetween. Further, a thermosiphon type heat radiator 61 is provided on the side of the heat radiating block 57 wherein a pipe insertion hole 57a is formed which is inclined at about 30 degrees with respect to a vertical line, and a loop-like refrigerant pipe 63 with a refrigerant packed therein is inserted into the insertion hole 57a. A part of the refrigerant pipe 63, which is inserted into the pipe insertion hole 57a to be in contact with the heat radiating block, is formed into a boiling portion where the refrigerant receives heat from the heat radiating block 57 to boil, and a heat exchanger 65 for condensation is mounted at an other part of the refrigerant pipe 63.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a natural circulation type thermosiphon, in which a boiling part in which a refrigerant absorbs heat and boils, and a condensing part in which the refrigerant radiates heat and condenses are connected by a closed pipe line. Regarding

[0002]

2. Description of the Related Art Natural circulation thermosiphons are used, for example, as radiators in electronic cooling refrigerators. The electronic cooling refrigerator uses an electronic cooling element in which a low temperature region is formed at one end and a high temperature region is formed at the other end when power is supplied. The heat equivalent to the cooling capacity generated in the low temperature area of the electronic cooling element exerts a cooling effect by moving from the room to be cooled through the cooling heat exchanger, and the heat generated in the high temperature area is the heat dissipation heat. It is discharged to the outside through the exchanger.

An example of characteristics of such an electronic cooling element is shown in FIG. Assuming that the temperature difference between the high temperature region and the low temperature region of the device is 50 deg and the heat absorption amount Q _C on the low temperature region side is about 20 W, the heat radiation amount Q _H on the high temperature region side is about 90 W. Therefore, the heat radiating heat exchanger provided on the high temperature region side needs to have a heat exchange capacity about 5 times that of the cooling heat exchanger on the low temperature region side. For this reason, when the capacity of a 30-liter class is large for an electronic cooling refrigerator, the cooling heat exchanger in the room to be cooled may be a fin type by extrusion molding, but the heat radiating heat exchanger is not a fin type. Since a sufficient amount of heat cannot be obtained, a natural circulation type thermosiphon radiator is often used.

A conventional example of an electronic cooling refrigerator using a radiator of a natural circulation type thermosiphon is shown in FIGS. 10 and 11. This electronic cooling refrigerator has a heat insulating wall 3 of a cabinet 1.
A through hole 7 that communicates the cooled chamber 5 inside the cabinet 1 and the heat radiation chamber 6 outside the cabinet 1 is formed in the back surface of the cooling block 9 inside the cooled chamber 5 and the through hole 7. The electronic cooling element 13 is provided so as to be sandwiched between the heat radiation block 11 and the external heat radiation block 11.

A fin type cooling heat exchanger 15 formed by extrusion molding is mounted on the cooling block 9 to absorb the heat load from the inside of the cooled chamber 5. On the other hand, a radiator 16 including a natural circulation type thermosiphon is provided on the heat radiation block 11 side. In the heat dissipation block 11,
In the drawing, a pipe insertion hole 11a penetrating in the vertical direction is formed, and a loop-shaped refrigerant pipe line 17 in which a refrigerant is enclosed is inserted into the pipe insertion hole 11a. Refrigerant pipeline 1
7, a portion to be inserted into the pipe insertion hole 11a serves as a boiling portion for absorbing heat from the heat dissipation block 11 to boil the refrigerant, and serves as a condensing portion for the boiling refrigerant to release heat and condense. The heat exchanger 19 is attached to another part of the refrigerant line 17. A blower 21 is installed below the condensing heat exchanger 19 in order to promote condensation in the condensing heat exchanger 19. A power supply 23 that supplies a direct current to the electronic cooling element 13 is provided below the heat dissipation chamber 6.

The operation of the radiator 16 composed of a natural circulation type thermosiphon will be described with reference to FIG. A refrigerant, which is a medium that carries heat, is enclosed in the refrigerant conduit 17. Generally, it is called a siphon effect to carry the liquid refrigerant in a high place to a low place.
7 is located at a higher portion, and the liquid (refrigerant _RL ) condensed in the condensing part 27 is continuously connected to the boiling part 25. Therefore, the head difference H between the liquids in the condensing part 27 and the boiling part 25 is H. As a result, the liquid refrigerant R _L flows from the condensing section 27 to the boiling section 25, and thereby the siphon effect is obtained.
In order to maintain this head difference H, the pipe line is a closed loop circulation type.

The liquid refrigerant R _L absorbs heat from the high temperature region of the electronic cooling element 13 serving as a heating source in the boiling section 25 and boils.
The gas refrigerant R _G rises in the refrigerant pipeline 17 and reaches the condenser 27. Here, the gas refrigerant R _G is cooled from the condensing heat exchanger 19 serving as a heat absorption source and is condensed by discarding heat. When the gas refrigerant R _G moves from the boiling section 25 to the condensing section 27, the refrigerant moves so that the pressure loss received from the refrigerant conduit 17 is balanced with the liquid head difference H.

By selecting the positions of the boiling part 25 and the condensing part 27, the inner diameter of the refrigerant conduit 17, and the kind and amount of the refrigerant,
While maintaining the head difference H, the refrigerant can circulate naturally, and as a result, the heat of the heating source of the boiling section 25 is condensed into the condensing section 2.
It can be transported to the unit 7 and radiated by an endothermic source. This is the basis of the natural circulation type thermosiphon.

By the way, regarding the boiling heat transfer characteristics of the heat exchanger using the natural circulation type thermosiphon, the theoretical elucidation has been hardly conducted in the past, and it is common to use the empirical formula of pool boiling which handles boiling of a stationary liquid. Consider the characteristic of boiling heat transfer of thermosiphon based on this relational expression. The pool boiling heat transfer equation for a chlorofluorocarbon refrigerant is given by the following equation. Here, the refrigerant pipe line is a so-called smooth pipe whose inner surface is smooth.

Α _P = C ₁ · q ^0.745 (1) where α _P is the heat transfer coefficient of pool boiling (W / m ² h
C) and C ₁ are constants determined by the type and pressure of the refrigerant. q
Is a heat flow rate (W / m ² ), and is calculated by the heat radiation amount of the electronic cooling element and the pipeline area of the boiling portion.

In equation (1), the heat flow rate q and the heat transfer coefficient α
The relationship with _P is shown by the broken line in FIG. According to this, it is understood that the heat transfer coefficient α _P increases as the heat flow rate q increases.

Next, a plan for improving boiling heat transfer will be considered. Considering the heat transfer coefficient α _P A _P by multiplying both sides of the equation (1) by the heat transfer area A _{P with} which the boiling portion of the refrigerant pipe comes into contact, if the heat transfer area A _P is doubled, When the heat quantity Q is constant,
It can be seen from the following equation that the increase is only about 20%.

Α _P · A _P = C ₁ · Q ^0.745 · A _P ^0.255 (2) (α _P2 · A _P2 ) / (α _P1 · A _P1 ) = (A _P2 / A _P1 ) ^0.255 (3) where , A _P2 / A _P1 = 2, (α _P2 · A _P2 ) / (α _P1 · A _P1 ) = 1.19 (4) That is, even if the heat transfer area is doubled, the boiling heat transfer amount increases. Is only about 20%, and increasing the area is not an effective method for improving the heat exchanger on the heat radiation side.

It is also conceivable to increase the air volume of the blower 21 in order to accelerate the condensation in the condensing heat exchanger 19, but in this case, the problem of increased noise occurs. For this reason, conventionally, in order to improve the boiling heat transfer characteristics in the heat exchanger on the heat radiation side, it has been considered that the refrigerant pipe line has a structure in which boiling nuclei are easily formed and nuclei are easily grown.

Here, paying attention to the promotion of boiling, it is said that a tunnel structure as shown in FIG. 13A is preferable as a conventional technique. This is a structure in which fins 31 are provided on the flat plate heat transfer surface 29, and the liquid refrigerant R _L is the fins 31.
By being heated in the portion surrounded by, boiling is promoted as compared with a flat plate, and a large number of boiling nuclei 33 are generated. But,
The portion surrounded by the fins 31 is easily affected by the liquid refrigerant R _L moving convectively around the fins 31, so that the light-gas phase boiling nuclei 33 are convected before they grow into sufficiently large bubbles. As a result, the liquid refrigerant R _L is moved from the fins 31 so as to be replaced with the liquid refrigerant R _L, and new liquid refrigerant R _L is moved to the fins 31. Then, the boiling nuclei 33 are generated again due to the heat received from the fins 31. Boiling with the fins 31 having such a shape does not take advantage of the feature of the boiling phenomenon that a large heat transfer is obtained during the growth process of bubbles because the growth from the boiling nuclei 33 to bubbles is not sufficient, and heat transfer is promoted. Is limited.

A possible solution is a structure in which the tops of the fins 35 are flattened as shown in FIG. 13 (b).
With this structure, the boiling nuclei 33 generated in the portion surrounded by the fins 35 are prevented from moving affected by the surrounding liquid refrigerant R _L, and even into large bubbles 37 that obtain an internal pressure capable of resisting the liquid refrigerant R _L. It is possible to grow, with which an improved boiling heat transfer is achieved.

Although the tunnel structure as described above is relatively easily provided on the outside of the flat plate or the pipe, the refrigerant pipe line 1
As described in No. 7, the pipe is almost never used because it may be crushed and completely closed, which makes the manufacturing difficult and the cost is high.

As a conventional example for promoting boiling in the tube,
As shown in FIGS. 14 (a) and (5), there is a grooved pipe in which a plurality of grooves 39 are formed on the inner wall of the pipe. FIG. 14A shows
FIG. 13 shows a boiling state on the upstream side of the boiling portion, and like the fins 31 of FIG. 13, the liquid refrigerant R _L is sufficiently heated in the groove 39, the boiling nuclei 33 are likely to be generated, and a tube having a smooth inner surface is shown. Boiling heat transfer is promoted compared to.

However, even with such a grooved tube, as shown in FIG.
In the same manner as described above, the boiling nuclei 33 are easily moved by the convection of the liquid refrigerant R _L and easily move from the grooves 39.
There is a problem that sufficient heat transfer cannot be obtained due to the bubble growth. FIG. 14B shows the boiling state on the downstream side of the boiling portion, but the bubbles 37 grown by boiling are
The liquid refrigerant R _L merges in the flow direction to gradually increase in size to cover the groove 39. In such a case, since the pressure of the bubble 37 is received in the groove 39, a sufficient amount of the liquid refrigerant _RL does not exist, and a non-boiling region in which the generation of the boiling nuclei 33 is also prevented is formed, resulting in deterioration of heat transfer characteristics. There is also a problem.

[0020]

As described above, in the conventional natural circulation type thermosiphon, even if the heat transfer area of the boiling part is expanded by using the empirical formula of pool boiling, the boiling heat transfer amount is not increased. It is believed that there are few and not many. Further, in the structure example of the inner wall of the pipe in the conventional boiling part, the growth of bubbles during boiling is not sufficient due to the influence of convection of the liquid refrigerant, and the non-boiling region of the heat transfer surface is easily formed. There is a problem that there is a limit to the promotion of thermal characteristics.

Therefore, the object of the present invention is to improve the heat transfer characteristics in the boiling portion.

[0022]

In order to achieve the above object, the present invention is directed to a boiling portion in which a refrigerant enclosed therein boils by absorbing heat from a heating source, and a condenser in which the refrigerant radiates heat to the surroundings and condenses. In the natural circulation type thermosiphon, which is configured to be connected by a closed pipe, a heat dissipation block in contact with the heating source is provided in contact with the periphery of the boiling part,
The boiling portion in the heat dissipation block is provided so as to be inclined with respect to the vertical line.

Further, according to the present invention, the boiling portion in which the refrigerant enclosed therein boils by absorbing heat from the heating source and the boiling portion and the condenser portion in which the refrigerant radiates heat to the surroundings and condenses are connected by a closed pipe line. In the constituted natural circulation type thermosiphon, a cylindrical member having a plurality of openings in the periphery may be provided in the conduit in the boiling section.

[0024]

In the natural circulation type thermosiphon having such a structure, since the boiling portion is inclined with respect to the heat radiating block, the heat transfer area where the boiling portion and the heat radiating block contact each other is increased. Conventionally, by using the empirical formula of pool boiling, it was thought that the expansion of the heat transfer area of the boiling part could not effectively improve the heat transfer characteristics, but by actually measuring the heat transfer characteristics of the boiling part, It turned out that it can be greatly improved.

Further, in the natural circulation type thermosiphon according to claim 2, since the cylindrical member is provided inside the pipe line in the boiling portion, the boiling nuclei generated on the inner wall of the pipe are not affected by the liquid refrigerant. As it grows, the boiling heat transfer efficiency is improved. Even if the grown bubbles enter the cylindrical member from the inner wall of the pipe through the plurality of openings of the cylindrical member and move to the downstream side, most of the gas pressure of the large bubbles is generated by the cylindrical member having the plurality of openings. As a result, the bubbles do not come into direct contact with the inner wall of the tube, the generation of non-boiling portions on the inner wall of the tube on the downstream side is suppressed, and the heat transfer efficiency of the boiling section is improved.

[0026]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a side sectional view of an electronic cooling refrigerator showing an embodiment of the present invention, and FIG. 2 is a sectional view taken along line BB of FIG. In this electronic cooling refrigerator, the room to be cooled 4 is housed in a cabinet 45 constituted by a door 41 and a heat insulating wall 43.
7 are formed. A through hole 51 that communicates the cooling chamber 47 with a heat radiation chamber 49 outside the cooling chamber 47 is formed in substantially the center of the back surface of the heat insulating wall 43, and an electronic cooling element 53 is provided in the through hole 51 at substantially the center. There is. The left and right sides of the through hole 51 in the figure are expanded to a greater extent than the central portion where the electronic cooling element 53 is provided, and the cooling block 55 on the cooled chamber 47 side and the external heat radiation block 57 are provided at the respective enlarged portions. And the electronic cooling element 53 is sandwiched between the blocks 55 and 57.

A fin-type cooling heat exchanger 59 formed by extrusion molding is mounted on the cooling block 55 to absorb the heat load from the inside of the cooled chamber 47. On the other hand, a thermosiphon type radiator 61 is provided on the side of the heat radiation block 57. In the heat dissipation block 57, a pipe insertion hole 57a is formed so as to connect to the upper left end and the lower right end in a state inclined at 30 degrees with respect to the vertical line in FIG. 2, and the inclined pipe insertion hole 57a is formed. A refrigerant pipe 63 in which the refrigerant is sealed is inserted inside the loop.

The portion of the refrigerant pipe 63 that is inserted into and in contact with the pipe insertion hole 57a serves as a boiling portion for absorbing heat from the heat dissipation block 57 to boil the refrigerant, and the boiling refrigerant releases heat. Condensing heat exchanger 65 that serves as a condensing unit for condensing
Is attached to the other part of the refrigerant pipe line 63. A blower 67 is installed below the condensing heat exchanger 65 in order to improve the heat transfer efficiency of the condensing heat exchanger 65. Further, in the lower part of the heat dissipation chamber 49, a direct current is supplied to the electronic cooling element 53 to generate a low temperature region at one end of the electronic cooling element 53 on the cooling block 55 side, and at the same time, on the heat dissipation block 57 side. Power supply 69 for generating a high temperature region at the other end
Is provided.

As shown in the schematic view of FIG. 4, the refrigerant pipe 63 has a boiling portion 63a at a lower portion in the height direction of the pipe.
However, the condensing part 63b is provided in each of the high parts, and the liquid refrigerant R _L condensed in the condensing part 63b does not flow backward and continuously exists in the downstream boiling part 63a, and the condensing part 63b and the boiling part 63a In order to balance the difference in height of the liquid refrigerant, that is, the head difference H, with the pressure loss when the boiled vapor moves to the condensing section 63b, the refrigerant is boiled in the boil section 63.
It moves depending on the heating amount of the heating source of a, that is, the heat radiation block 57, and the heat radiation amount of the heat absorption source of the condensing unit 63b, that is, the condensation heat exchanger 65.

A wire mesh 75 as a cylindrical member as shown in a perspective view in FIG. 5 is inserted into the refrigerant pipe 63 in the boiling portion 63a in a state of being in contact with or close to the inner wall. FIG. 6 shows the refrigerant pipe 6 with the wire net 75 inserted.
3 is a vertical sectional view, and FIG. 7 is a horizontal sectional view thereof. In this example, the refrigerant pipe 63 is a so-called grooved pipe in which a large number of grooves 77 are formed on the inner wall.

In the electronic cooling refrigerator thus constructed, the pipe insertion hole 57a is inclined 30 degrees from the vertical line with respect to the heat radiation block 57, so that the refrigerant pipe 63 and the heat radiation block 57 inserted therein are inserted. Contact area with
That is, the heat transfer area between the two can be about twice as large as that of the conventional case by using the same heat dissipation block.

Conventionally, it was considered that the expansion of the heat transfer area had little effect on the improvement of heat transfer characteristics as an estimate of pool boiling, but the pool boiling test result of the natural circulation type thermosiphon was used as the smooth tube and groove. FIG. 3 showing the attached tube and
From the formulas (2) to (4), it was found that the expansion of the heat transfer area was sufficiently effective in improving the heat transfer characteristics.

In FIG. 3, the solid line is that of a smooth tube and is represented by α _P = C ₁ · q ^0.43 , and its slope is 0.43.
Is. The alternate long and short dash line is for a grooved tube, and α _P = C ₁
- represented by q ^{0. 26,} the slope is 0.26. From this relationship, when the effect of improving the heat transfer coefficient α _P · A _P when the heat transfer area in the above equations (2) to (4) is doubled is seen, in the smooth tube, (α _P2 · A _P2 ) / (Α _P1・ A _P1 ) = (A _P2 / A _P1 ) ^(1-0.43) (α _P2・ A _P2 ) / (α _P1・ A _P1 ) = 2 ^0.57 = 1.48 On the other hand, Similarly, (α _P2 · A _P2 ) / (α _P1 · A _P1 ) = 2 ^0.74 = 1.67, which shows that the smooth tube improves by 48% and the grooved tube by 67%.

Such improvement of the heat transfer characteristics does not increase the cost due to the complicated structure of the inner wall of the boiling section pipe line, does not cause difficulty in the manufacturability, and increases the amount of air blown by the blower 67. This can be achieved without any difficulty and can easily contribute to the improvement of the cooling performance of the electronic cooling refrigerator.

Further, since the boiling portion 63a is provided so as to be inclined, the angle at the inlet portion and the outlet portion of the conduit of the boiling portion 63a with respect to the heat radiation block 57 becomes an obtuse angle, and the resistance of the refrigerant flow becomes small. Performance improvement and refrigerant line 63
The cost can be reduced by shortening the length of the.

In the operation of the natural circulation type thermosiphon in which the wire net 75 is inserted in the boiling portion 63a of the refrigerant pipe 63, the liquid refrigerant existing in the groove 77 is first heated from the heat radiation block 57 as shown in FIG. Then, the boiling nucleus 79 is generated. The boiling nuclei 79 prevent the influence of the convection of the liquid refrigerant existing in the center of the tube with the wire net 75, so that they grow as bubbles and promote the boiling heat transfer. The gas pressure of the grown bubbles rises, overcomes the resistance of the wire net 75, passes through the wire net 75 and moves to the center of the tube, and becomes large air bubbles 81 to lower the gas pressure.

The bubble 81 that has grown greatly grows further as it moves upward and the bubbles 81 coalesce with each other. Even if the large bubble 81 moves upward, since the gas pressure of the bubble 81 is small, the bubble 81 does not pass through the wire net 75 and does not come into contact with the inner wall of the pipe. For this reason, the liquid refrigerant is always present in the groove 77 on the upper downstream side, and the generation of the boiling nuclei 79 and the growth of the bubbles 81 are recognized as in the lower upstream side, and the promotion of heat transfer is hindered. The heat transfer efficiency is improved.

FIG. 8 shows the relationship of the heat transfer coefficient with respect to the heater (heating source) input in the boiling portion having the groove on the inner wall, and the broken line shows the case where the wire net 75 according to the above embodiment is inserted. The solid line is the one when the wire net 75 is not inserted. According to this, it can be seen that the average heat transfer coefficient in the boiling portion is improved in the example of this embodiment as compared with the case without the wire mesh, and it is considered to be about 10%.

[0040]

As described above, according to the present invention, since the refrigerant pipeline is inclined with respect to the heat dissipation block, the heat transfer area where the refrigerant pipeline and the heat dissipation block come into contact with each other is large. This area expansion can achieve sufficient heat transfer effect by the boiling experiment result of the natural circulation type thermosiphon without the cost increase and the difficulty of manufacturability due to the complicated inner wall of the refrigerant pipe. it can.

Further, since the cylindrical member provided with a plurality of openings in the periphery is provided inside the pipe in the boiling portion, the generation of boiling nuclei and the growth of bubbles are promoted without being affected by the liquid refrigerant, and the boiling occurs. It is possible to improve the heat transfer efficiency in the section without increasing the cost and making the manufacturability difficult by complicating the inner wall of the refrigerant pipe.

[Brief description of drawings]

FIG. 1 is a side sectional view of an electronic cooling refrigerator showing an embodiment of the present invention.

FIG. 2 is a sectional view taken along line BB of FIG.

FIG. 3 is a characteristic diagram showing conventional pool boiling heat transfer characteristics and experimental data of thermosiphon boiling performed in the present invention.

FIG. 4 is a schematic overall configuration diagram of a refrigerant pipe line.

5 is a perspective view of a wire mesh inserted into a boiling portion of the refrigerant pipe line of FIG. 4. FIG.

6 is a vertical cross-sectional view of a boiling portion of the refrigerant pipe line of FIG.

7 is a cross-sectional view of the boiling portion of the refrigerant pipe line of FIG.

FIG. 8 is a heat transfer coefficient characteristic diagram showing a relationship between a heat source input and a heat transfer coefficient in a boiling portion of a grooved refrigerant pipe, comparing the case where a wire net is inserted and the case where the wire net is not inserted. ..

FIG. 9 is a characteristic diagram of an electronic cooling element.

FIG. 10 is a side sectional view of an electronic cooling refrigerator showing a conventional example.

11 is a cross-sectional view taken along the line AA of FIG.

FIG. 12 is a schematic overall configuration diagram of a conventional refrigerant pipe.

FIG. 13 is an explanatory diagram of a boiling heat transfer surface having a conventional tunnel structure.

FIG. 14 is an explanatory diagram showing a boiling phenomenon in a conventional grooved tube.

[Explanation of symbols]

 53 Electronic Cooling Element (Heating Source) 57 Heat Dissipation Block 63 Refrigerant Pipeline 63a Boiling Section 63b Condensing Section 75 Wire Mesh (Cylindrical Member)

Claims (2)

[Claims] 1. A natural structure constructed by connecting a boiling portion in which a refrigerant enclosed therein boils by absorbing heat from a heat source and a condensing portion in which the refrigerant radiates heat to the surroundings and condenses in a closed pipeline. In the circulation type thermosiphon, a heat radiation block in contact with the heating source is provided in contact with the periphery of the boiling portion, and the boiling portion in the heat radiation block is inclined with respect to a vertical line. Natural circulation type thermosiphon. 2. A natural structure constituted by connecting a boiling portion in which a refrigerant enclosed therein boils by absorbing heat from a heat source and a condensing portion in which the refrigerant radiates heat to the surroundings and condenses in a closed pipeline. In the circulation type thermosiphon, a natural circulation type thermosiphon is characterized in that a cylindrical member having a plurality of openings in the periphery is provided in the pipe line in the boiling portion.