US 3677337 A
An apparatus for transferring thermal energy from a heat source to a heat sink having a closed space containing a saline solution and an evaporator wherein the heat input evaporates the liquid so that a water vapor moves toward a condenser where heat is rejected to return the water vapor to the liquid phase. The closed space containing the saline solution extends to the region of the condenser and has a water permeable membrane positioned adjacent the condenser. The water is returned to the evaporator by osmotic pumping.
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Description (OCR text may contain errors)
United States Patent I [451v July 18, 1972 Midolo  HEAT TRANSFER APPARATUS WITH OSMOTIC PUMPING  inventor: Lawrence L. Midolo, Centerville, Ohio  Assignee: The United States of America as represented by the Secretary of the Air Force  Filed: Sept. 10, 1970  Appl.No.: 70,977
 U.S. Cl... ..l65/l05 [5 1] Int. Cl. ..F28d 15/00  Field of Search 165/105  References Cited UNITED STATES PATENTS 3,561,525 2/1971 Baer ..l65/l05 Primary Examiner-Albert W. Davis, Jr. AttomeyHarry A. Herbert, Jr. and Richard J. Killoren ABSTRACT An apparatus for transferring thermal energy from a heat source to a heat sink having a closed space containing, a saline solution and an evaporator wherein the heat input evaporates the liquid so that a water vapor moves toward a condenser where heat is rejected to return the water vapor to the liquid phase. The closed space containing the saline solution extends to the region of the condenser and has a water permeable membrane positioned adjacent the condenser. The water is returned to the evaporator by osmotic pumping.
9 l0 Clalns, 7 Drawing Figures Patented July 18, 1972 3,677,337
2 Sheets-Sheet 2 Fig-E INVENTOR. zflwenvca 4. 31/0 0 BY flrrol? y HEAT TRANSFER APPARATUS WITH OSMOTIC PUMPING BACKGROUND OF THE INVENTION Various techniques have been used for transferring thermal energy from a heat source to a heat sink. These include systems that rely on thermal conduction, forced convection, and systems which depend upon evaporation and condensation of a heat exchange fluid. The systems which depend upon evaporation and condensation of a heat exchange fluid overcome some of the shortcomings of other heat exchange systems. However, the systems which depend upon evaporation and condensation of a heat exchange fluid depend upon gravity or capillary pumping to return the cooling liquid to the heat source. These systems suffer from orientational problems and are not suitable in a high gravitational field or in an aircraft flight dynamic environment wherein the pumping force of such systems is exceeded by the gravitational force or the flight dynamic forces.
BRIEF SUMMARY OF THE INVENTION According to this invention use is made of osmotic pressure to transport the working fluid from the heat sink to the heat source in a system that depends upon the evaporation and condensation of a heat transfer fluid as the heat transfer medium. A heat transfer system using osmotic pumping with zero gravity, equal diameter heat pipes and the same basic configuration as used in a capillary pumping system will provide approximately 10 times the heat transfer capacity. Also the osmotic pumping will operate at higher gravity levels where the capillary pumping will cease to operate.
IN THE DRAWING FIG. 1 is a schematic illustration of a heat transfer system according to the invention.
FIG. 2 is an enlarged partially cut away sectional view of the condenser and permeable membrane for the device of FIG. 1.
FIG. 3 is an enlarged partially cut away sectional view of a modified condenser section for the device of FIG. 1
FIG. 4 is an enlarged partially cut away sectional view of a further embodiment of the invention.
FIG. 5 is an enlarged partially cut away sectional view of another embodiment of the invention.
FIG. 6 is a schematic illustration of a heat transfer system of another embodiment of the invention.
FIG. 7 is an enlarged partially cut away sectional view of the heat input section of the device of FIG. 6.
DETAILED DESCRIPTION OF THE INVENTION With reference to FIG. 1 of the drawing reference 10 shows a heat transfer system having a heat input section 12 and a condenser section 14. A double wall container 16 has a space 17 between the inner wall 18 and the outer wall 19 to hold a saline solution which is preferably a saturated solution. The double wall container may be made of a material such as stainless steel. A water permeable membrane 20 of a material such a cellulose acetate, polyvinyl chloride or polyvinyl alcohol, covers an opening at the lower end of walls 18 and 19. The membrane may be secured to walls 18 and 19 in conventional manner, for example with an adhesive. A metal screen, a support of sintered bronze or other known type of support, not shown, may be used to provide support for membrane 20, if needed. The saline solution empties into an evaporation chamber 22. The heat input to chamber 22 causes water to evaporate from the saline solution and leave chamber 22 through aperture 24. Very little salt leaves with the water vapor so that the device can operate for a considerable time before cleaning is needed.
The vapor passing through aperture 24 is condensed at condenser surface 25 of condenser plate 26. The condenser plate 26 may be made of a material such as aluminum or copper. The condensed water vapor collects in space 27 between condenser surface 25 and the membrane 20 where it is returned to space 17 by osmotic diffusion pumping. When the ambient temperature near condenser plate 26 is sufficiently low, no special heat sink is required. However, when needed cooling coils or other cooling means, not shown, may be provided adjacent condenser plater 26.
A metal mesh wick 30, of a material such as aluminum or copper may be provided adjacent condenser surface 25 and membrane 20, as shown in FIG. 3. Other configurations for the condenser section and permeable membrane than thus far described may also be used, if desired. For example, the condenser and permeable section may be as shown in FIG. 4. In this device the wall 19' extends across a portion of the bottom of channel section 32. The membrane 20' is then positioned as a parallel extension of wall I8 and is secured to wall 18' and the extension of wall 19.
Since the water flux through the membrane is a function of the area of the membrane, the water flux can be increased by increasing the area of the membrane as shown in FIG. 5. In this device walls 18" and 19" have curved extensions 33 perpendicular to the walls. The membrane 20" has a sinuous configuration and is secured to projections 33 on walls 18" and 19". Other configurations can also be used to increase the surface area of the water permeable membrane.
With the device thus far described, as can be seen from FIG. 1, tilting or inverting the apparatus would tend to cause saline solution to pass through aperture 24. Thus, this device is suitable only when the apparatus is substantially stationary 'or where an artificial gravity would keep the saline solution in place. In some flight dynamic environments some means must be provided to keep the saline solution from entering the chamber adjacent surface 25. The device of FIGS. 6 and 7 can be used to overcome these problems. In this device a wick 35 is positioned adjacent end wall 37 and extends into the space 38 between walls 40 and 41. The wall 40 extends over to contact the wick 35 adjacent wall 41. Other apparatus than that shown may be used for containing the saline solution within chamber 37.
While metal mesh wicks have been described as the wick material, other wick materials can be used, for example, glass beads, avril rayon cloth or felt material.
The solutes used may be any water soluble material which will not pass through or attack the particular membrane used. Examples of solute materials that can be used are the water soluble clorides such as NaCl, I(Cl and Cacl the water soluble chlorates such as K,co,, cs,co, CsH CO Na CO and the water soluble borates, such as Na,B,O -l0H,O. Also some sugars can be usedwith certain membranes.
While saline solution andwater have been described as the working agents, other materials may also be used, for example sugar could be substituted for salt in some applications.
There is thus provided an improved apparatus for transporting thermal energy from a heat source to a heat sink.
1. Apparatus for transferring thermal energy from a heat source to a heat sink, comprising: a closed container having a first portion adapted to be positioned adjacent the heat source and a second portion adapted to be positioned adjacent the heat sink; means for dividing said closed container into a first compartment and a second compartment, a liquid solution of predetermined concentration in said first compartment, means, within said container adjacent the first portion, for permitting the flow of solvent vapor evaporated by said heat source to flow into the second compartment; means extending into the second compartment adjacent the second portion of said container for providing a condensing surface for the solvent vapor; and a membrane, permeable only to the solvent, of the solution, positioned adjacent said condensing means and located between the first compartment and the second compartment whereby the condensed solvent is pumped toward the first portion of said closed container by osmotic diffusion pumping.
2. The device as recited in claim 1 wherein the solvent is water and the solute in the solution is a water soluable salt selected from the group Na Cl, K Cl, CaCl,, K,CO Cs,CO,,-
Csl-l C0,, Na,CO;,, Na B H 0.
3. The device as recited in claim 2 wherein said first and second compartments are concentrically positioned compartments separated by a cylindrical wall member extending to a position adjacent the condensing means; said permeable membrane being annular in shape and closing the space between the wall of the closed container and said wall member positioned adjacent the condensing means.
4. The device as recited in-claim 3 including a wicking material positioned in said second compartment at the first portion of said container'and having a portion extending into the second compartment; said cylindrical wall having means for closing the end of said first compartment adjacent the heat source except for the portion where the wicking material extends into the first compartment.
5. The device as recited in claim 3 wherein wick material is positioned over the condensing means and contacts the permeable membrane.
6. The device as recited in claim 3 including an annular channel surrounding the condensing means with the condensing means and said channel forming one endwall of the container; the side wall of said container and said cylindrical wall member extending into said annular channel and forming an opening adjacent the condensing means; said permeable membrane forming a closure for said opening to thereby provide an osmotic barrier permeable only to said solvent.
7. The device as recited in claim 6 including means for providing a greater length of permeable membrane than the circumferential length of said cylinder wall member.
8. The device as recited in claim 7 wherein the means for providing a greater length of permeable membrane includes means projecting from the side wall and the cylindrical wall member toward said condensing means. for forming substantially sinusoidal shaped edges; said permeable membrane having a substantially sinusoidal shape conforming to the substantially sinusoidal shaped edges.
9. The device as recited in claim 7 wherein wick material is positioned over the condensing means and connects the permeable membrane.
10. The device as recited in claim 2 wherein the solute is Na Cl.