CA1105922A

CA1105922A - Heat transfer apparatus

Info

Publication number: CA1105922A
Application number: CA314,625A
Authority: CA
Inventors: Peter Rohner; Klausdieter Schippl
Original assignee: KM Kabelmetal AG
Current assignee: KM Kabelmetal AG
Priority date: 1977-10-28
Filing date: 1978-10-27
Publication date: 1981-07-28
Also published as: IT1106149B; SE7811178L; GB2006950B; AT358081B; AU4090878A; FR2407445A1; BR7807051A; IT7851371A0; CH632084A5; ATA662578A; GB2006950A; DD139757A5; JPS5472557A

Abstract

P/3089,04 HEAT TRANSFER APPARATUS
Abstract of the Disclosure Heat transfer apparatus of the type wherein a heat transfer fluid flows through a sealed evacuated tube between hot and cold zones with the fluid being evaporated in the hot zone and condensed in the cold zone wherein the tube is wound to provide a plurality of windings, each of which has one portion in the hot zone and a second portion in the cold zone.

Description

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This invention i9 directed to an apparatus for transferring heat between two locations at a different temperature. More particularly, the invention is directed to heat transfer apparatus comprised of a closed tube filled with a suitable heat transfer fluid which evaporates at the location with a higher temperature (hot zone) and condenses at the location with a lower temperature (cold æone).
The condensate can continuously be returned to the hot zone through the tube, The interior space of such a vacuum-tight closed system has a heat transfer fluid which is partly present in liquid form and partly as saturated vapor, with the heat transfer fluid evaporating in the hot zone and flowing to the cold zone, where it condenses and thereby releases its heat of evaporation, If the cold zone lies above the hot zone, the condensate will flow back into the hot zone on account of gravity and such devices for returning are called heat siphon~. If the condensate is returned by the use of capillary forces, the devic pv/Oe~ J~
is called a heat ~ube. The heat transfer fluid is circulated by means of the temperature difference between the hot zone and the cold zone, which is frequently very small. The higher vapor pressure which prevails in the hot zone provides a pressure gradient which drives the vapor to the cold zone. An essential advantage of these heat transfer devices is that their effective heat conductivity is o~,ders of magnitude higher than that of the best metallic conductors. In addition, such devices are easy to handle, easy to assemble, and ...... .. . . . . . .................................. . .
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``` 11~5922 maintenance-free, and heat can be transferred counter to gravity. Such heat transfer devices, however, must first be evacuated, subsequently filled with a predetermined quantity of heat transfer fluid, and then closed vacuum tight.
The present invention is based on the task of providing a heat transfer apparatus of the heat siphon or heat pipe type which for a given transfer ability is much more easily fabricated. This task is solved with a device of the type mentioned in the introduction, by providing a sealed, evacuated pipe, which includes a heat transfer fluid, which is shaped along its length such that it traverses the hot and cold zones several times. By using the evacuated and filled pipes of great length, and by giving them the claimed form, several mutually connected heat siphons or heat pipes are created. It has been unexpectedly found that neighboring heat pipes or heat siphons do not dry out as a result of the condensation zone of the neighboring tube or siphon, which is still carrying liquid, expanding into the region that is in danger of drying out. As a consequ_nce, this region is also filled with liquid and a stable state is thus reached.
It is to be understood that the term "hot zone"
as used herein refers to the zone in which the heat transfer fluid in the pipe is heated and the term "cold zone" as used herein refers to the zone in which the heat transfer fluid is cooled.
It is especially advantageous to wind the tube in a spiraling or serpentine shape in that such an arrangement results in a device which transfers large quantities of heat in a very narrow space. This effect is still further enhanced if several tubular sections, designed with a 1~59Z2 serpentine shape, are arranged above one another, According to a urther aspect of the invention, the ~be is designed as a drawn, /~
seamless, soft-annealed, thin-walled copper tube, In accordance with another aspect, the tube is a corrugated metal tube with a welded seam along its length. The soft-annealed, thin-walled copper tube as well as the corrugated metal tube with a welding seam along its length are flexible, so that they can be wound in nearly any desired shape. Because of its good thermal conductivity, copper provides good heat transfer in both the hot and cold zones. The tube could also be formed of aluminum or stainless steel. The design with the corrugated tube has the further advantage that the surface is enlarged in the area of the hot zone and cooling zone, respectively. A particularly good effect is achieved if the portions of the tube which form the hot zone lie at a lower level than the IS portions of the tube which form the cold zone, In this case, no further special steps need to be taken to return the condensate, since the condensate flows back to the hot zone by gravity, Nevertheless, for some applications it may be advantageous to arrange capillaries in the interior of the tube in order to transport the condensate to the hot zone, whereby it is possible to transport the condensate against gravity, Another advantage results from the fact that the capillaries distribute the condensate uniformly over the entire region of the hot zone, and consequently the effectiveness of the system can be increased, ..

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In accordance with one embodiment, the device is capable of being used to exchange heat between the transfer fluid and massive components, for example, electronic components, such as thyristors and the like. In accordance with such embodiment, in the area of the hot zone and/or the cold zone of the apparatus, there is provided a connector member formed of a material having good heat conductivity, such as copper, which is in contact with the individual windings of the tube which are in the area of the hot or cold zone. One or more units or devices which are to be heated or cooled by the apparatus are in heat conducting contact with the connectirg member. The heat exchange device of this embodiment significantly improves the ability to heat or cool such massive components. ~or example, in the case where the components are to be cooled, the connecting member interconnects the windings of the tube in the area of the hot zone and the heat released from the components is uniformly distributed over the windings of the tube in the hot zone.
The heat transfer ability of the device can be increased, particularly in the case of a wound corrugated tube, by providing the connecting member with a recess for each winding of the tube which is matched to and in heat transfer contact with the corrugation.
For example, it is possible to produce recesses in the connecting member by means of machine-tooling, or by casting the connecting member with such recesses. The windings can be connected to the connecting member through a layer of solder with good heat conductivity; e.g., a solder with a copper-silver base.

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In accordance with another aspect of the invention, the tube iB
a wound tube having individual windings thereof, in either the hot or cold zone, interconnected through a vertically disposed connecting member. In accordance with this aspect, each of the individual windings includes a portion which is inclined with respect to horizontal so that heat transfer fluid condensate flows back into the hot zone by gravity. The direction of inclination is dependent upon whether the individual windings are connected by the connecting member in the area of the hot or cold zone, The vertical arrangemer~t is particularly advantageous wherein the heat transfer fluid in the tube at the cold zone is cooled by a gas ~connecting member at hot zone) in that convection is increased by the upward flow of the heated gas. The individual windings are spaced from each other to permit gas to flow all around such windings.
In accordance with another embodiment, the windings or bends of the tube in the area of the hot and/or cold zone are surrounded by a liquid tight vessel, with the medium which is to be heated or cooled by the heat exchange apparatus flowing through such vessel, In accordance with another aspect, a heat exchanger unit can be provided by providing as a unit the heat transfer tube with the individual windings or bends thereof extending into a vessel through openings therein, with such windings or bends being connected to the walls at the openings; e.g., by soldering. In this manner, the vessel can be connected in fluid flow communication with a circulating

2 5 system having a medium which is to be heated or cooled, with such medium being heated or cooled by flow through the veEsel in heat transfer contact with the individual windings of the tube within the .. . . .... .
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vessel. Such a unit can be used, for example, with particular advantage as a cooling system for motor vehicles in that there is a weight saving of up to 5 kg, and reliability is increased since the cooling loop itself can remain tight even if the heat tube is destroyed. Such a unit in accordance with the invention can be employed with every type of cooling system which employs a liquid coolant, including, for example, in addition to motor vehicles, rail-bound vehicles, stationary cooling systems, such as engines, dry cooling towers at power plants, etc.
Another preferred application is to obtain heat from the ground or from the air. In contrast to cooling systems, the medium to be heated, for example the working medium of a heat pump system, is conducted through the vessel and in heat transfer contact with the windings of the tube. The portion of the windings outside the vessel can be in the ground, in ground water-or in the open air. It is particularly advantageous to use a corrugated tube in that its increased sur-face per unit length improves the heat exchange, and for many cases, the flexi-bility resulting from the corrugations can also be advantageous.
Thus, in accordance with the present teachings, a heat transfer apparatus is provided for use in exchanging heat from a hot zone to a cold zone, the apparatus comprising a plurality of pipe sections each having a first end portion extending into the hot zone and a second end portion extending into the cold zone, each of the pipe sections being at least partially filled with a heat transfer media which is readily vaporized while in the hot end portion and condensed while in the second end portion whereby the heat transfer media constantly moves as a vapor from the hot zone to the cold zone and as the condensate from the cold zone to the hot zone between the first and second portions of the plurality of pipe sections. The improvement which is provided in such apparatus comprises the plurality of pipe sections being formed from a single, transversely corrugated, thin wall metal tube length wound in a spiral or serpentine shape and having a its opposite ends closed pressure-tight, and the first end portion of each of the plurality of pipe sections being positioned at a lower level than the second end portion of the pipe section.

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The invention will be further described with respect to the accompanying drawings wherein:
Figure 1 is a simplified isometric view of an embodiment of the heat transfer device of the present invention;
Figure 2 is a simplified eleyational view of another embodiment of the heat transfer device of the present invention;
Figure 3 is a simplified isometric view of a further embodiment of the heat transfer device of the present invention; and -6a-~S92Z

Figure 4 is a simplified isometric view of still another embodiment of the heat transfer device of the present invention, The figures show heat transfer devices which include a metal tubelO wound in the shape of a helix ~Figure 1) or wound in a serpentine fashion ~Figure 2), The tube 10 is advantageously fabricated from a copper band, whose walls are e. g., O. 3 mm thick. In a continuous operating process, this band is formed into an open seam tube, welded along its length, and subsequently corrugated. But the possibility also exists of using a seamless drawn copper tube for the tube 10. AMer being finally drawn, this tube is soft-annealed and is consequently quite flexible.
A certain length is separated from the finished tube length and ;~ is closed pressure-tight at both ends by means of the caps 12. One of the caps 12 has a tube stud (not shown), to which a vacuum pump can be connected for evacuation of the tube. After evacuation, the heat transfer fluid is introduced and the tube stud is closed pressure-tight. The tube 10 can be wound either before evacuation and filling or else it can also be wound afterwards.
In the embodiments shown in Figures I and 2, the hot zone 13 is in the lower region, while the cold zone 14 is located in the upper region, so that the condensate is returned to the hot zone 13 by gravity .
When the wound tube 10 is filled, no special provision must be made for filling each individual winding with heat transfer fluid in that after start-up, the fluid distributes itself uniformly among the individual windings. With the embodiments shown, all the lower regions form the hot zone 13, while all the upper regions form the cold zone 14. By means of the invention, a tube 10, prepared 11(~)5922 as a heat siphon or heat tube, has successully been made into a large number of neighboring heat siphons or heat tubes, which considerably reduces costs and greatly multiplies the efficiency of the heat tube or heat siphon. It has been unexpectedly found that a tube S winding cannot dry out since, in this case, the condensation zone of neighboring windings extends into the region of the winding that is threatening to dry out, whereby the condensate again flows into this winding .
Obviously the invention is not limited to the heat siphons shown in the embodiments, but is just as well applicable to heat transfer systems which work according to the principle of the heat tube, i.e., in which the condensate is returned by capillary forces. For this application, however, it is necessary to insert a capillary system into the interior of the tube, for example in the form of a plastic network.
Figure 3 shows a heat transfer device comprised of a corrugated copper tube 10 wound in the form of a spiral or helix. The corrugated copper tube 10 as previously described is evacuated, filled with a heat transfer fluid according to a precise dosage, and closed vacuum-tight. A connecting member 15, made of copper, is soldered to the outside of the tube parallel to the axis of the helix, with the member 15 including recesses 16 for each winding. So that condensate can return to the hot zone 13 by gravity, the individual windings of the corrugated copper tube 10 are aligned at an angle oC to the long axis of the connecting member 15, where ~ is less than 9oo. Heat generators 17, for example electronic components like thyristors, can be affixed in heat transfer contact with member 15 whereby the heat released therefrom is transferred through the connecting member 15 .. ~ . .. .
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~1~5922 and attached tube windings to the heat transfer fluid within the windings.
The heat transfer fluid, in liquid form situated in the area of the hot zone 13 is evaporated by the heat energy that is transferred through the connecting member 15 and windings. As a result of the pressure differential, the evaporated fluid flows into the cold zone 14, where it condenses, and flows back to the hot zone 13 through the inclined portion of the windings. Cooling in the region of the cold zone 14 which is effected by a gas, such as air. can be increased by forced convection, for example by a ventilator ~not shown).
It is to be understood that the connecting member 15 could be connected to the windings in the area of cold zone 14, in which case the inclined portion of the windings would extend in the opposite direction .
The heat transfer device in accordance with the embodiment of Figure 3 could also be employed in a manner such that two heat transfer devices are connected together through their respective connecting members 15 in heat transfer contact with each other. In such case, the heat connecting member 15 of one device is in the area of the cold zone thereof, and the heat connecting member 15 of the second device is in the area of the hot zone thereof.
The heat transfer device of Figure 3 can also be employed by connecting two or more of such devices through connecting member 15 to an element which is to be heated or cooled. For example, two or more of such devices can be connected in heat transfer contact with the outside wall of a vessel or tube through which a medium to be heated or cooled flows.
A further embodiment is shown in Figure 4, wherein the metal _g _ ., . . . . . . . . .. ~

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tube 10 is formed into a serpentine structure, as shown. The windings 18 of the tube 10, are introduced through openings into a container l9, for example, a tube shaped container, and the windings 18 are tightly soldered to the wall of the container 19. For example, the medium to be cooled, possibly water in an automobile engine, can be introduced into and withdrawn from the container 19, through connecting openings 21 and 22. The heat transferred from the medium being cooled to the heat transfer fluid in the windings 18 of tube 10 within container l9 evaporates the fluid which flows into the cold zone 14, outside of vessel l9 wherein the fluid is cooled and condensed by a gas, such as air, which is caused to flow in heat transfer contact with the portion of the windings in cold zone 14.
A similar device may be used with stationary installations, where the required air circulation is taken care of either by ventilators or by a cooling tower. Depending on the design, the windings can be arranged approximately horizontally to or on both sides of container .; 19 Alternatively, the device can be used to heat a fluid in container 19, in which case the container 19 will be connected to the top portion of the windings in cold zone 14.
Numerous modifications and variations of the present invention are possible in light of the above teachings and, therefore, within the scope of the appended claims the invention may be practiced otherwise than as particularLy described.

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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A heat transfer apparatus for use in exchanging heat from a hot zone to a cold zone, comprising a plurality of pipe sections each having a first end portion extending into said hot zone and a second end portion extending into said cold zone, and each of said pipe sections being at least partially filled with a heat transfer media which is readily vaporized while in said first end portion and condensed while in said second end portion; whereby, said heat transfer media constantly moves as a vapor from said hot zone to said cold zone, and as a condensate from said cold zone to said hot zone, between said first and second end portions of said plurality of pipe sections; the improvement comprising said plurality of pipe sections being formed of a single, transversely corrugated, thin walled metal tube length wound in a spiral or serpentine shape and having its opposite ends closed pressure-tight; and said first end portion of each of said plurality of pipe sections being positioned at a lower level than the second end portion of said pipe section.

2. The apparatus of Claim 1 wherein a heat conducting connecting member is connected in heat transfer contact to a plurality of first end portions of said pipe sections within said hot zone to thermally interconnect longitudinally displaced sections of said single metal tube length.

3. The apparatus of Claim 2 wherein a heat generating device is connected in heat transfer contact to said heat conducting connecting member for providing a transfer of heat through said connecting member into said plurality of first end portions of said pipe sections within said hot zone.

4. The apparatus of Claim 2 wherein said connecting member includes recessed portions for receiving said plurality of first end portions of said pipe sections within said hot zone, said recessed portions having contact surfaces which are matched to the outer surface corrugations of said plurality of sections.

5. The apparatus of Claim 2 wherein the connecting member is formed of copper.

6. The apparatus of Claim 2 wherein the connecting member is vertically disposed and each of such pipe sections includes an inclined portion whereby condensed fluid flows from the cold zone to the hot zone, by gravity, through the inclined portion.

7. The apparatus of Claim 1 wherein the portion of the pipe sections in at least one of the hot and cold zones are disposed within a vessel, with a medium in said vessel being in heat transfer contact with the portion of the windings in said vessel to effect heating or cooling of the medium.

8. The apparatus of Claim 7 wherein the portion of said pipe sections in the vessel pass through openings in the wall of the vessel and are connected to the vessel wall.

9. The apparatus of Claim 7 wherein the portion of said pipe sections in the hot zone are in the vessel and a medium to be cooled is circulated through the vessel.