Heat Exchange System

Abstract

Heat transfer is accomplished by having two adjacent chambers with an oute partition of a first chamber made of heat conductive material for conducting heat inwardly into the first chamber which has a coolant liquid flowing through it. A second chamber has a gas at a pressure higher than the water in the first chamber. A partition between both chambers is made of a gas porous material so that the gas in the second chamber penetrates the connecting wall and flows through the coolant liquid breaking up the formation of liquid coolant film on the heat conductive material.

Description

STATEMENT OF GOVERNMENT INTEREST

The invention described herein may be manufactured and used by or for The Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION

The present invention generally relates to heat transfer systems and more particularly to systems suitable for cooling of avionics equipment by the enhancement of enthalpy and heat of vaporization of suitable coolants.

Many prior known systems for cooling avionic equipment use variations of the well-known heat pipe. The heat pipe is a sealed thermodynamic system relying on internal evaporation and condensation cycles. It comprises an enclosure, a wicking material lining the internal walls of the enclosure, and a working fluid for saturating the wick. One end of the heat pipe is called the evaporator and serves to absorb heat energy. Vapor formed in the evaporator is then transported to the other end of the heat pipe called the condenser. Here the heat is released from the heat pipe by means of internal condensation of the working fluid to the internal walls of the heat pipe. The working fluid is then recirculated to the evaporator end by the capillary action of the wick where the cycle is repeated.

Certain performance characteristics of the heat pipe including heat flux handling capacity vary depending on the vertical orientation of the evaporator end with respect to the condenser. During aircraft maneuvers this is apt to continually change. Other limitations of the device include heat extraction dependence on operating temperature level, sonic vapor flow velocities and fluid entrainment flow, wick dryout, internal generation of noncondensable gases and shock and vibration problems. In addition a high heat dissipating component must be mounted to the heat pipe by suitable means. This introduces thermal impedances that are detrimental to any heat transfer system.

SUMMARY OF THE INVENTION

It is therefore a general object of the present invention to provide an improved system for the cooling of avionics equipment. It is a further object to provide a system that is independent of attitude or gravity so as to eliminate variation in operational characteristics during aircraft maneuvers. Another object is to provide a system whereby the enthalpy and heat of varporization are more effectively utilized and controlled. A further object is to provide a system in which liquid evaporating film ajacent the surface to be cooled may be more uniformly controlled and reduced than heretofore known. Additional objects are to improve the operating temperature level and to obviate other known limitations on effectiveness of prior systems.

This is accomplished in accordance with the present invention by providing a heat transfer system in which a liquid coolant is directly applied to a surface to be cooled and a pressurized gas is uniformly applied to the surface through a gas porous material forming a part of an enclosure for the liquid coolant. The porous material is separated from the surface to be cooled by a finite distance. The physical characteristics of the porous material are such that the material will readily permit the passage of gas or vapor molecules but will restrict the liquid coolant from passing quickly through the porous material by its surface tension properties. In addition the gas is at higher pressure and will restrict the flow of liquid through the porous material. Also, the gas passes through the porous material in a direction opposite to that of the liquid coolant and quickly dries any liquid that starts to seep through the material. The gas on striking the surface to be cooled reduces the thickness of a liquid evaporating film that forms on the surface thus improving the heat transfer capability of the device.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is an embodiment according to the present invention partially shown in cross section;

FIG. 2 is a view along the line 2--2 of FIG. 1;

FIG. 3 is an alternate embodiment of the present invention partially shown in cross section; and

FIG. 4 is a view of the alternate embodiment along the lines 4--4 of FIG. 3 .

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIGS. 1 and 2 there is shown a first embodiment 10 having liquid coolant lines 11 which may be identical and comprised of hoses or piping for supplying a liquid coolant such as water through openings 12 of a plate 14. Plate 14 is secured to heat transfer panels 15 by means of screws 16. The panels 15 are secured to sidewalls 17 by any conventional means such as screws (not shown). The plate 14 can be metallic and has four shoulders 18 holding one end of porous membrane panels 19 in place. The porous membrane panels 19 can be a material such as brass or copper and can be matched to the gas and coolant used to permit flow of the gas and restrict flow of the coolant therethrough. Such items are readily available commercially.

The other end of porous membranes 19 is held in place by the shoulders 25 of plate 26. Openings 27 in plate 26 are used for discharging through lines 28 which may be comprised of hoses or piping. Enclosures 29 are formed by surrounding plates 14 and 26, porous membrane 19, heat conductor 15 and sidewalls 17.

An inlet 25 receives a gas line 36 which may be comprised of a hose or piping. Gas such as air flows into an opening 36 where it is blocked at the far end by the plate 26. The plate 26 can be metallic and differs noticeably from plate 14 in that there is no aperture similar to 35 for the flow of gas. The gas is regulated to a higher pressure than that of the liquid coolant and the porous membranes 19 permit passage of the gas therethrough into enclosures or chambers 29. High heat flux components 37 are connected to conducting plate 15 by means of brazing or screws or any other well-known method. The high heat flux component 37 may comprise a transistor or integrated circuit chip and has electrical leads connected thereto (not shown).

The operation of the device will now be explained with reference to FIGS. 1 and 2. High heat flux generators 37 conduct heat through conductor surface 15 into enclosures 29. The liquid coolant such as water is supplied to enclosure 29 for removing heat from the inner surface of conducting plate 15. A gas such as air is supplied to enclosure 36 through opening 35 and being regulated to a higher pressure than that of the liquid coolant flows through gas porous plates 19 and the liquid coolant. The gas then impinges against the inner surface of conducting plate 15 to dissipate liquid film formed on the inner surface of plate 15 thereby enhancing the heat removal by the liquid coolant. Much of the liquid coolant becomes vapor and the liquid coolant, vapor and gas are removed through outlets 27 over lines 28. The lines 28 may discharge either overboard in an open loop system or to a condenser for liquifying the vapor and then to a vent for removing gases before recycling. Neither the condenser nor the venting is shown as neither comprise a part of this invention and are not required for operation of the device in an open loop cycle operation.

FIGS. 3 and 4 show an alternate embodiment of the present invention. Like components are given the same numerals as those described in FIGS. 1 and 2 and these components will not be further described. A plate 51 which may be solid metal such as copper or brass is bonded to porous material 52 which has a circular cross-sectional area as shown in FIG. 4. The porous material 52 may be made out of copper or brass or any suitable compatible material for bonding with plate 51. The porous material 52 has the same physical characteristics as membrane 19 of FIG. 1. A pair of plates 53 have high heat flux components 37 mounted to them. These plates differ from plate 15 in that they have a circular cutout 54 with a similar cross section as porous component 52.

The operation of the device shown in FIGS. 3 and 4 is somewhat similar to that of FIGS. 1 and 2, differing in that the gas entering inlet 35 is blocked by plate 51 and only enters enclosure 29 through porous material 52. This directs the gas directly to the bottom plate of heat flux generator 37 for dissipation of the liquid film. The size of cutout 54 is chosen so that the plate 53 does not contact the portion of generator 37 where the majority of thermal cooling takes place.

There has therefore been shown a highly effective heat extraction, heat transfer and cooling technique that is applicable to cooling high heat flux surfaces such as mounting boards, printed circuit boards, chassis, etc., which are used for mounting high flux density devices, parts, components, etc., in a limited space. It provides a method whereby the enthalpy and heat evaporization of coolants are more effectively utilized, enhanced and controlled for extracting waste heat from hot high heat flux surfaces. It increases the rate of evaporation and consequently the rate of heat extraction by incorporating a porous material passing a gas under pressure to the surface from which the heat is to be extracted. The coolant is kept in the chamber in which the heat is to be extracted by a material porous to gas and highly resistant to liquids. Additional features are the utilization of the suitable open pore porous structures which are separated from the surface from which heat is to be extracted and used to control and more effectively utilize the heat evaporization of coolants. The porous structure separates the gas flow into high velocity air jets for impaction with the surface to be cooled. This breaks up the coolant film at the hot surface, exposes more particle or coolant surface for heat absorption and evaporation. The gas also acts as a vehicle for removing coolant vapors. The porous material acting as gas jet impactors reduces the coolant film resistant to heat transfer with the resultant increase in the overall effective film coefficient of heat transfer.

It will be understood that various changes in the details, materials, steps and arrangements of parts, which have been herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims.

Claims

What is claimed is:

1. A heat exchanger for dissipating heat from avionic equipment, comprising:

a first pair of parallel plates;

a continuous sidewall sealingly connected between the peripheries of said plates to form an enclosure;

a second pair of parallel plates parallelly spaced between said first pair of plates and sealingly connected at their peripheries to said sidewall forming thereby one inner and two outer laminated chambers in said enclosure;

each one of said plates having an opening coextensive with and aligned with each other opening for communication between opposite sides of their respective plates;

a pair of gas-porous, liquid-restriction elements contiguously supported within respective openings of said second pair of plates;

a pair of heat generative avionic members sealingly supported at respective openings of said first pair of plates; and

said sidewall further including a pair of inlet openings to respective ones of said outer chambers for receiving a liquid coolant, a pair of outlet openings from said respective ones of said outer chambers for said liquid coolant, and a single inlet opening to said inner chamber for receiving a gas;

whereby said gas is emitted from said inner chamber through said pair of elements and said coolant to impinge on the confronting surfaces of said members.