US2960847A

US2960847A - Heat exchanger

Info

Publication number: US2960847A
Application number: US681915A
Authority: US
Inventors: Donald A Potter
Original assignee: Stewart Warner Corp
Current assignee: Stewart Warner Corp
Priority date: 1957-09-04
Filing date: 1957-09-04
Publication date: 1960-11-22
Anticipated expiration: 1977-11-22
Also published as: GB897130A

Description

D. A. POTTER HEAT EXCHANGER Nov. 22, 1960 3 Sheets-Sheet l Filed Sept. 4, 1957 D. A. POTTER HEAT EXCHANGER Nov. 22, 1960 i ll /NVE NroR .Daad/ Pdf/ez' Nov. .22, 1960 D. A. PoTTER 2,960,847

HEAT EXCHANGER Filed Sept. 4, 1957 3 Sheets-Sheet 5 [Ns/ENIGE @afm/a Paz/fer 7- rafa/way United States Patent() HEAT EXCHANGER Donald A. Potter, Indianapolis, Ind., assignor to Stewart- Warner Corporation, Chicago, Ill., a corporation of Virginia Filed Sept. 4, 1957, Ser. No. 681,915

5 Claims. (Cl. 62-314) This invention relates to heat exchangers of the submerged or pool boiling type in which a boiling or evaporating liquid on one side of a heat exchange wall cools a uid on the other side of this wall. The invention relates in particular to improved exchangers of the foregoing type in which the cooling liquid is retained within the exchanger casing without regard to the attitude of the exchanger.

In the heat exchangers of the prior art in which a liquid is used for cooling, it is necessary to tix the heat exchanger in -a stationary position in order to keep the liquid in its proper plate; or in the alternative, complicated means must be provided to contain the liquid and at the same time enable the resulting vapor formed from any boiling coolant to escape to the atmosphere.

Some exchangers employ complex vent valves which permit one side or the top of the unit to be opened to the atmosphere, while the other sides and bottom remain closed to prevent loss of the liquid coolant. This type of exchanger requires means for closing one or more of the valves should the exchanger be turned on the one side or top, and means for opening one or more of the other valves to permit escape of vapor to the atmosphere.

Other exchangers employ a reservoir suliciently large so that a vent pipe extending approximately into the middle of this reservoir is always above the level of liquid regardless of the attitude of the exchanger. Obviously, if the exchanger is inverted, the liquid coolant at best is in contact with only a portion of the heat exchange surfaces. This mode of operation reduces the cooling capacity of the heat exchanger during those periods in which all or part of the liquid is not in contact with the heat exchange surfaces.

Additionally, the usual submerged or pool boiling exchangers of the prior art are characterized by a heat flux density which increases as the temperature difference between the hot heat exchange surface and the boiling liquid increases. This relationship prevails until a point is reached at which a vapor layer or lm is formed covering the hot surface. At this point, because of the insulating action of the vapor film, the heat flux begins to diminish resulting in a substantially decreased etliciency.

A principal object of this invention is to retain the coolant liquid for a heat exchanger in contact with the heat exchange surface for all attitudes ofthe exchanger through the use of a simple construction employing a wick and not necessarily requiring valves.

Another object is to increase heat exchange efficiency in submerged or pool boiling type heat exchangers by providing means for breaking up or eliminating the vapor lm which is usually formed on the heat exchange surfaces. This object is attained by placing a wick in contact with the hot exchange surfaces. The wick prevents the formation of the layer and permits the further increase of heat flux which the film would otherwise prevent. The wick contributes further to the attainment of a high eciency, because the capillary attraction of the wick ICC material evenly distributes the liquid coolant throughout the wick.

Another object is to provide in a heat exchanger simple and reliable wick means for distributing to a heat exchange surface a liquid coolant from a storage reservoir. The liquid is carried from this storage reservoir to the heat exchange surface by wick action.

Another object is to regulate the flow of liquid to heat exchange surfaces by using the rate at which a given liquid will ow through a given Wick material as lthe means of regulation.

Another object is to reduce the weight and size of a heat exchanger, and at the same time maintain a high heat exchange etliciency, by using a wick to bring the least amount of liquid in contact with the heat exchange surface required to establish a uniform wetting thereof.

Another object is to prevent damage that would be normally caused by the freezing within a heat exchanger of a liquid coolant, such as water.

A preferred embodiment of the heat exchanger of this invention employs an outer casing which encloses a multipass heat exchanger core of the plate and iin type having a plurality of passes all of which are embodied within a mass of wick material. The wick material communicates with a source of liquid coolant in such a manner that the liquid is carried to the hot heat exchange surfaces of the exchanger by wick action. The liquid coolant isV elevated to a boiling temperature upon contact with the exchange surfaces, and the resulting vapor escapes to the atmosphere through a vent outlet in the casing. The wick material retains the liquid coolant within the casing independently of the attitude of the heat exchanger and without the use of valve arrangements.

In order that all of the structural features for attaining the objects of this invention may be readily understood, detailed reference is herein made to the drawings wherein:

Figure 1 is a side elevation view of a heat exchanger constructed in accordance with the principles of this invention and having portions of the casing thereof broken away so as to show the internal construction;

Figure 2 is a sectional View taken along line 2 2 of Figure 1;

Figure 3 is a side elevation view of a second heat exchanger embodiment employing the principles of this invention and having portions of the casing thereof broken away so as to show the internal construction;

Figure 4 is a sectional View taken along line `4 4 of Figure 3;

Figure 5 is an elevation View of a third heat exchanger embodiment employing the principles of this invention and having portions of the casing thereof broken away so as to show the internal construction; and

Figure 6 is a sectional view taken along line 6-6 of Figure 5 and including also a simplified representation of a liquid storage tank connected to the exchanger.

Referring now to heat exchanger l@ shown in Figures l and 2 0f the drawings, outer shell 1l forms part of a casing which encloses the internal structure of the exchanger hereinafter described in detail. The circular end openings (not shown) of outer shell 11 are closed in part by adapters or

collectors

12 and 13. Adapter l2 is formed with an end 14 that defines inlet opening 15, and adapter 13 is formed with an end 16 that denes outlet opening 17. The fluid to be cooled enters the inlet opening 15, passes through the adapter 12, and enters into the hot fluid passages 18. The passages 18 shown in the drawings are formed by conventional plate and n core construction. These passages may have other kinds of extended surfaces, or they may be plain or smooth depending upon the heat exchange requirements.

The plates and fins forming passages 18 are sandwiched` between layers of Wick material 20. Spaces 21 are employed as storage spaces for the liquid coolant 22'. The spaces in which the layers of wick 1S are contained are defined Vby `smooth sides 23 Which form hot heat exchange surfaces from which the liquid coolant 22 is boiled or evaporated. These surfaces are shown as smooth surfaces in Figures 1 and 2, but they may have or other means for extending the heat exchange surfaces. l K Heat exchanger is advantageously suited for use in a system in which all of the liquid necessary for coolingA can be contained within the outer casing of the unit, for

example, aircraft applications requiring only a few minutes of cooling. y Y v Y 4 l A Maximum cooling time is attainedV by filling theV spaces occupied by the many layers of Wick ,2G and the spaces 21 at the bottomV of the exchanger shelll 171 with liquid coolant 22. As boiling or evaporatingi takes place, the amount of liquid diminishes, with the' resulting Vapor being released through vent 24, until only the liquid remaining in spaces 21 and lower portions of, the Wick is left. With this occurrence, the Wick material will continue to draw the liquid by capillary attraction throughA its length thereby keeping the hot surfaces 23 supplied with liquid. At the same time, because the Wick material 18 is porous, it permits the vapor to escape from all parts of the Wick and travel to the vapor space 25 at the top of the exchanger Where it is discharged through the vapor outlet 24. If exchanger 10 is turned'on its side or inverted, liquid 22 Will be retained by the Wick material 18 and vaporwill still travel to the space- 25 and through the outlet vapor vent 24.

The inclusion of porous Wick material between the passages and in contact with all of the submerged or boiling surfaces prevents the formation of a vapor lm which Would otherwise be formed if these spaces had no Wick and Were filled with liquid.

Referring now tothe second embodiment shown in Figs. 3 and 4, heat exchanger 28 and the liquid storage .tank 29 are formed with an outer shell portion 30` which en` closes the heat exchanger 28 and an outer shellportion 31 lwhich encloses the liquid storage tank 29. The end openings of Vheat exchanger 28 are partially closed by

adapters

32 and 33. Inlet adapter 32 is formed with an end 34 that defines inlet opening 35, and' outlet adapter 33 is formed with an end 36 that defines outlet opening 37.

The vapor vent 38 permits the escape of vapor to the atmosphere. Tank 29 contains a reserve supply of liquid 40 in the space 41. This reserve gives the heat exchanger' an added cooling capacity. Liquid 40 is supplied to the tank through a ller connection 42 which is closed by an appropriate ricket type cap 43. The fluid to be cooled enters the inlet opening 35, passes through theV adapter 32 and enters into the hot fluid passages 44. The passages shown in Figures 3 `and 4 are plate and iin construction; however, these passages may have other forms of extended surfaces or may be plain.

The hot fluid passages are embedded in Wick material 45, which fills the bottom of the heat exchanger shell 31B. Wick material 45 is in contact with the outer surfaces of the hot uid passages 44 Where the heat exchange takes place. Y

Liquid 40 is carried from the space 41' in the tank 29 through additional Wick material 45a which lines the sides and bottom of space 41. Wick material" 45a is a continuation of the previously described wick 45, and therefore the liquid is carried by capillary attraction from tank 29 to the hot heat exchange surfaces 46.

The vapor formed by the evaporation or boiling of liquid 4i) which is adjacent the hot surfaces 46 passes,V lthrough Wick material 45 to top space 47 within the heat .exchanger 36 and then out through the vapor outlet vent 38 to the atmosphere.

Inasmuch as the tank is closedvvith a 'ricket'V type cap .43, and because the wick material 45 Vand 45ajretains the liquid 40, this complete unit will hold liquid 40 without spilling if it is placed on its side or upside down and will continue to boil orvaporize steam which can escape through the outlet vent 38.

As the level of Water diminishes in the tank 29, wick material 45a in the tank is in a saturated condition.- Wick material 45 that contacts the hot heat exchange surfaces 46 loses part of its liquid because of the boiling or evaporation that takes place due to the heat exchange. This material then has less moisture than saturated material 45a. This action causes moisture to travel by capillary attraction from the more highly saturated Wick 45a to the less saturated wick 45 until all of the liquid has been boiled or vaporized. Y

Referring now to the heat exchanger 49 and tank 50 shown in Figs. 5 and 6, shell 5l encloses the internal structure of the heat exchanger as hereinafter described in detail, and shell 52 encloses the structure of the liquid storage tank. The end openings of the outer shell are partially closed by adapters or ,collectors 53 and 54. Adapter 53 is formed with an end 55 4that definesV inlet opening 56, and adapter 54 is formed with an end53 that defines inlet opening 59.Y The vapor vent 60 permits the escape of vapor to the atmosphere. The liuid to be cooled enters the inlet opening 56, passes through the adapter 53 and enters into the hot uid passages 61. The passages 61' shown are of a conventional plate and fin construction.

The Wick material 62, as shown in Figure 6, Vextends from the top of the hot fluid passages 61 ,down to the bottom of these same passages, and also completely fills the lower part of the enclosure formed by shell 51. The wick is Vin contact with the hot heat exchange surfaces 57 of the fluid passages 61. The hot heat exchange surfaces 57 shown in Figure 6 are plain surfaces. However, they may be any form of extended surface that is required for a particular heat exchange purpose. Liquid 64 is stored in tank 50. This tank is filled through a ill connection 65 which is closed by ricket type cap 66.

When a control pressure. is appliedto tube 67, it causes the liquid in tank to be forced into the supply tube 68 up to control valve 69 and into the wick material 62.Y

Thus, liquid 64 is supplied to Wick 62 in anyl desired'or controlled quantity and is evenly distributed by the'wick to the hot surfaces 63 Where it is boiled or evaporated. The vapor thus formed trave-ls to space 7); and then out of the exchanger through the vapor outlet6f'.

The Wick material for the heat exchangers herein-be-V fore described is preferably fabricated from an inert and ireproof substance such as fiber glass. For example, the fibrous silicaV insulation material: manufactured and sold by the H. I. Thompson Fiber Glass Company ofvLos v Angeles, California, under the tradename Refrasil is highly satisfacto-ry as Wick material for the novel heat exchangers described herein.

It is to be understood that the above-described arrangements are illustrative of the application o-f the'piinciples of this invention. Numerous other arrangements may be devised by those skilled in the -art without departing from the scope o-f the invention.

What is claimed is:

l. ln a heat exchanger, a tubular container having a liquid inlet and a vapor outletspaced from the inlet, a plurality of heat exchange members having passages therein and spaced from one' another, a mass ofV wick material embedding the heat exchange members therein and filling the spaces between the members,v the heat exchange membersV and the mass of vvick material so completely filling a portionrof the containerbetvveen the liquid inlet and the vapor outlet as to prevent direct liow of liquid from the inlet to the outlet, inlet meansV for supplying fluid to be cooled tothe passages inthe members, and outlet means for exhausting'flu'idfroni the passages.

2. In a heat exchanger,` a container havinga lower reservoir portion and also provided with an upper vent, a plurality of heat exchange members in the portion of the container above the lower reservoir portion and spaced from one another, and wick material embedding the heat exchange members and substantially completely covering the reservoir portion of the container to restrict flow of liquid from the reservoir portion to the vent, the wick material also extending to the reservoir portion to absorb liquid therefrom.

3. In a heat exchanger, a container, a generally vertical partition in the container dividing the container into a reservoir compartment and a cooling compartment, the partition having an opening at the bottom thereof permitting passage of a coolant liquid from the reservoir compartment to the cooling compartment, the cooling compartment having a vent therein, a plurality of heat exchange members in the cooling compartment and spaced from one another, and wick material positioned between the heat exchange members and covering the opening in the partition to prevent free ow of coolant liquid from the reservoir compartment.

4. In a heat exchanger, a container and a heat exchanger core defining two independent passages leading into and out of said container, a mass of wick material disposed within said container and completely enveloping said core, a uid inlet and a uid outlet communicating with said heat exchanger core to dene a rst of said independent passages, and a liquid inlet and a vapor vent communicating with the mass of wick material to form the second of said independent passages with the wick material interposed between said liquid inlet and the vapor vent to isolate completely the liquid inlet from the vapor vent except through the wick material.

5. In a heat exchanger, a container including a heat exchanger core defining two independent passages leading into and out of said container, a mass of wick material disposed within said container and completely enveloping said core, a fluid inlet and a uid outlet communicating with said heat exchanger core to dene a rst of said independent passages, and only a liquid inlet and a vapor vent communicating with the mass of wick material to form the second of said independent passages with the wick material interposed between said liquid inlet and the vapor vent to isolate completely the liquid from the vapor vent except through the wick material.

References Cited in the le of this patent UNITED STATES PATENTS 1,428,661 Richardson Sept. 12, 1922 1,808,982 Harris June 9, 1931 2,209,999 Patch Aug. 6, 1940 2,218,407 Meyerhoefer Oct. 15, 1940 FOREIGN PATENTS 147,993 Australia Sept. 1, 1952