US3417814A - Air cooled multiliquid heat transfer unit - Google Patents

Description

Dec. 24, 1968 s. OKTAY AIR COOLED MULTILIQUID HEAT TRANSFER UNIT Filed June 26, 1967 2 Sheets-Sheet l SEVGIN OKTAY ATTORNEY Dec. 24, 1968 s. OKTAY AIR COOLED MULTILIQUID HEAT TRANSFER UNIT Filed June 26. 1967 FIG.3

2 Sheets-Sheet 2 United States Patent 3,417,814 AIR COOLED MULTILIQUID HEAT TRANSFER UNIT Sevgin Oktay, Beacon, N.Y., assignor to International Business Machines Corporation, Armonk, N.Y., a corporation of New York Filed June 26, 1967, Ser. No. 648,719 3 Claims. (Cl. 165105) ABSTRACT OF THE DISCLOSURE A sealed container is provided in which first and second fluids of different boiling points which are immiscible with one another are contained. The first lower boiling point liquid is located at the bottom of the container and has immersed therein, a heat generating assembly. An interface is formed between the two liquids which condenses some of the vapor bubbles arriving thereat, from the heat generating assembly. The top of the container is formed by a heat exchange means having fins for conducting the heat from the second liquid to the ambient air.

This invention relates to cooling of heat generating equipment such as electronic apparatus, and more particularly to an air cooled multiliquid heat transfer unit for cooling heat generating equipment.

Cooling of electronic equipment such as a memory core array by the use of a multiliquid heat transfer technique is set forth in pending US. application Ser. No. 555,730, filed June 7, 1966. The memory core array to be cooled is submerged in a primary coolant liquid. An interface is formed between the primary coolant liquid and a superimposed secondary liquid. As the temperature of the core array rises, the primary liquid rises in temperature until the so called subdued boiling takes place. This consists of the formation at the memory core array of vapor bubbles which rise through the primary liquid and are, under certain conditions, dissipated at the interface by condensation. However, some of the vapor bubbles pass through the interface and enter the secondary or condensation liquid. The vapor bubbles, if sufliciently hot, will rise to the surface of the secondary liquid. If the secondary liquid is maintained below the temperature of the primary liquid in which subdued boiling takes place, the secondary liquid provides the necessary condensation and accordingly, cooling. Several means of maintaining the secondary liquid below the subdued boiling temperature of the primary liquid are suggested. The secondary liquid can be cooled by continually adding more secondary liquid to cause spillage over the top of the container such that heat is conducted from the container wall to the spilling liq-uid. This spilled liquid can be recirculated to the input of the secondary liquid either directly or through some external cooling means. Another means of cooling the secondary liquid is to perform the cooling at some external location on a continuously flowing stream of the secondary liquid. The main disadvantage of these arrangements is the possibility of contamination of the liquids. Another disadvantage in the continual flow arrangements of the secondary liquid is that considerable added equipment is needed such as catching containers and flow controllers.

Accordingly, it is the main object of the present invention to overcome the above noted disadvantages of the prior art by providing a self-contained air cooled multiliquid heat transfer unit.

It is another object of the present invention to provide an air cooled multifluid heat transfer unit in which there is no external flow of liquid coolants.

Patented Dec. 24, 1968 It is a further object of the present invention to provide air cooling of a multiliquid heat transfer unit which is simple and less costly per unit of heat removed in comparison with the conventional single liquid boiling arrangements presently in use.

Briefly, the invention is an improvement in a multiliquid heat transfer unit containing a first and second liquid having an interface therebetween for condensing vapor bubbles originating at an assembly to be cooled which is immersed in the first liquid. The improvement comprises a sealed chamber which contains the first and second liquids with the first liquid located at the bottom of the chamber and having a low boiling point at atmospheric pressure. The second liquid is lighter and immiscible with the first liquid and forms an interface between the top surface of the first liquid and the bottom surface of the second liquid. Heat conducting means are provided located in heat transferring contact with the second liquid for transferring the heat accumulated in the second liquid to the ambient air.

The foregoing and other objects, features and advantages of the invention will be apparent from the following and more particular description of a preferred embodiment of the invention as illustrated in the accompanying drawings.

FIG. 1 is a schematic representation of a multiliquid heat transfer unit having a broken away section showing the heat exchange means.

FIG. 2 is a vertical cross section taken along the line 2-2 of FIG. 1.

FIG. 3 is a schematic diagram of a further embodiment of the multiliquid heat transfer unit having a broken away section showing the heat exchange means thereof.

FIG. 4 is a vertical cross section taken along the line 4-4 of FIG. 3.

The cooling process that takes place in the present invention is known as subdued boiling. The assembly 12 to be cooled, such as a memory core array, is immersed in a first or primary liquid 14, which has a low boiling point. Preferably the first liquid 14, boils at amtospheric pressure and only somewhat above ambient room temperature. A second or condensing liquid 16, is superimposed on the free surface of the first liquid 14. When the first liquid 14 is sufiiciently heated by the assembly 12 immersed therein, vapor bubbles 18, are formed and condense principally at least at the interface 20 of the two liquids, 14 and 16. This phenomenon is achieved only by proper correlation in the selection of liquids, their volumes, their interface surfaces, and the rate of heat generation.

The present invention includes additional apparatus used in conjunction with the above cooling process to keep the second or condensing liquid 16 cooler than the primary liquid, thereby maintaining the above cooling phenomenon.

Referring to FIGS. 1 and 2 there is shown a multiliquid heat transfer unit having a sealed container 22, in which is located the assembly 12, to be cooled, the first or primary liquid 14, and the superimposed or secondary liquid 16. A connecting plate 24 is shown having connecting pins 26 thereon for making various connections to external equipment in conjunction with which the assembly 12 operates. The first liquid 14 is preferably a dielectric liquid, such as perflourodimethyl cyclobutane, which boils at about 113 F. i-S" F. under atmospheric pressures (for example, 12 to 16 p.s.i.a.). The second liquid 16, which has a relatively higher boiling point temperature is superimposed on the free surface of the first liquid 14 so that an interface 20 is formed. As the temperature of the first liquid 14 reaches its boiling point, vapor bubbles 18 form at the assembly 12 and rise in the liquid to the interface 20, where the majority are condensed due to the correlation of liquid selection, the interface area, the boiling point temperatures, the heat absorption rates, the ambient temperature and pressure, the volumes of the liquids, and the maximum rate of heat generation from the directly contacted portions of the assembly 12, giving rise to the vapor bubbles 18. Actually, in a situation where the heat generated by the electronic assembly 12 is increased, all of the vapor bubbles 18 are not condensed at the interface 20. In some situations the vapor bubbles 18 break up into smaller bubbles at the interface which sometimes combine depending upon the heat generated to again form larger bubbles 28 which break away from the interface 20 when sufficiently buoyant and rise into the second or condensation liquid 16. Depending upon the heat generated and, of course, other factors previously mentioned, the larger bubbles 28 will either be condensed in the secondary liquid 16 or might even rise to the surface thereof, where they are condensed. Thus, there is a mode of operation in which the heat generated is sufiicient to produce vapor bubbles 18, which do not condense at the interface 20 between the two liquids 14 and 16, but pass into the secondary liquid 16 and sometimes to the surface thereof. It will be appreciated that the condensation of the vapor bubbles 18 and 28 provides heat to the secondary liquid 16. Accordingly, to maintain operation, some form of cooling of the secondary liquid 16 is necessary. In this connection, the top of the sealed container 22 is shown closed by a fin unit 30. The fins 32, which extend into the secondary liquid 16, are solid throughout and are made of a conducting substance such as copper, cast iron, etc. The conducing substance is utilized for its improved heat conducting qualities over, for example, air. Also, the fins 32 provide a large surface area to the secondary liquid 16 for better heat transfer. The fins 32 are backed by a metal plate 34 of good heat conducting qualities. On the other side of the plate are attached further or upper fins 36, likewise, having the fins 36 solid throughout and made of a material which is a good heat conductor. Mounted above the upper fins 36 is a cooling fan 38 which causes the air to flow over the upper fins 36, thus, improving the heat transfer therefrom. It can be seen that the fan 38, as well as the fin unit 30, fit directly into the top of the container 22. Accordingly, air inlets 40 are provided in the container 22 such that the outside air is directed therethrough and over the upper fins 36 by the force provided by the fan 38.

It was not realized that a simple inexpensive means of cooling the secondary liquid 16 could be used until it was discovered that the bubble condensation within the secondary liquid 16 will even take place at temperatures near the.boiling point of the primary liquid 14, and that the heat transfer characteristics of the primary liquid 14 are unaffected by the changes in the temperature of the secondary liquid 16. Thus, an air cooled multiliquid heat transfer unit is provided which is self-contained, that is, there is no possibility of contamination from the outside or for that matter, escape of vapor, etc.

Referring to FIGS. 3 and 4 of the invention, there is shown a second embodiment of the multiliquid heat transfer unit. In this arrangement, we again have a sealed container 22 within which is located the assembly 12 to be cooled, as well as the first and second liquids 14 and 16, with the interface 20 formed therebetween. As in the previous case, the vapor bubbles 18 are formed at the assembly 12 as the temperature thereof rises. These bubbles 18, rise and in one mode of operation, condensation takes place at the interface 20 while in another mode, the bubbles 28 escape the interface 20 and proceed into the secondary liquid 16 where condensation takes place. In any event, the secondary liquid 16 rises in temperature and, accordingly, cooling is introduced. The top of the container in this embodiment is also closed by a heat exchange unit 44 having fins 46 extending into the secondary liquid, but the fins 46 are arranged at right angles to the fin configuration 32 of the previous embodiment. That is, the heat exchange unit 44 contains a number of fin units 48, which extend vertically into the container 22 with the fins 46 extending horizontally therefrom. The advantage of this arrangement is that increased fin surface area is introduced and thus, the heat transfer from the secondary liquid 16 to the fins 46 is increased, thereby making it possible to remove heat from the container by natural convection. These fin units 48 are arranged in parallel and are separated by short metal rods 50, which not only maintain the fin units 48 in their parallel disposition but also provide heat conduction therebetween to equalize the temperature among the fin units 48.

Each fin unit 48 consists of the fins 46 which are mounted between parallel side plates 52. The side plates 52 are made of a good heat conducting metal for transferring the heat from the secondary liquid 16 to the enclosed fins 46. The fins- 46 themselves form a corrugated configuration between the tWo side plates 52 consisting of alternate ridges or fins 46 and valleys 54. The ridges or fins 46 are completely filled with a solid heat conducting material while the valleys 54 are left hollow. The solid heat conducting ridges or fins 46 provide a large surface area for heat transfer to the hollow valleys 54 through which air circulates. An air channel 56 runs lengthwise of each fin unit 48 along the bottom thereof. Each one of the hollow valleys 54 of the corrugated fin arrangement 46 is connected at its bottom to the respective air channel 56. These air channels 56 connect through the wall of the container 22 to the ambient air. The air channels 56 and vertical hollow valleys 54 of the corrugated fin 46 arrangement each form a chimney and give rise to a natural convection flow of air therethrough to remove the heat from the contacting surfaces thereby providing cooling for the secondary liquid 16.

Thus, two embodiments for maintaining the cooling operation of a multiliquid heat transfer unit confined in a sealed container have been provided wherein the cooling is maintained by exchanging excess heat accumulated in the secondary liquid of the unit with the ambient air.

While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and detail may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. In a multiliquid heat transfer unit containing a first and second liquid having an interface therebetween for condensing vapor bubbles originating at an assembly to be cooled immersed in said first liquid;

a sealed container containing said first and second liquid, said first liquid being located at the bottom of said container and having a low boiling point at atmospheric pressure, said second liquid being superimposed on said first liquid forming an interface therebetween and having a higher boiling point than said first liquid and being immiscible therewith;

a heat exchanger comprising a plurality of fin units extending into the second liquid from the top of the container and extending parallel to one another across the container between opposite sides;

each fin unit including a narrow chamber having fins projecting from one side wall to the other across the narrow dimension of the narrow chamber, said fins extending vertically from the top of the container to a predetermined point above the bottom of the chamher;

a channel along the bottom of the chamber defined by the bottom of the chamber, the side walls thereof and the bottom of the fins;

one end wall of said narrow chamber having an opening therein adjacent said channel, said container having openings therein indexed with said channel open- 3,417 ,814 5 6 ings, the area between said fins forming vertical paths References Cited from said channel to the top of the container; and the UNITED STATES PATENTS top of said container having openings adjacent said vertical paths, thereby completing the air passages 2,214,865 9/1940 Troy 165105 X thru s'aid fin units to provide air flow and heat ex- 5 2,886,746 5/1959 Saby 165-105 X h ge b t l ti 3,024,298 3/1962 Goltsos 165-105 X 2. Apparatus according to claim 1, wherein spacer 3,270,250 8/1966 Davls members extend between said fin units to maintain them 3306-350 2/1967 Beul'theret 165105 substantially spaced and parallel so that said second ROBERT A 01E ARY Primary Examiner liquid can rise therebetween for good heat exchange. 10

3. Apparatus according to claim 2, wherein said spacer A. W. DAVIS, JR., Assistant Examiner.

members comprise pins made of a good heat conducting U S Cl X R material to thereby provide equalization of temperature among the fin units. 165-122; 174-15; 317-234, 100

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