An evaporative refrigerator or cooler comprising a bundle of spaced, porous walled tubes closed at one of their ends and vented to a vacuum at the other end is disclosed. The tube bundle is surrounded by a water jacket having a hot water inlet distribution manifold and a cooled water outlet through a plenum chamber. Hot water is pumped into the jacket to circulate around the tubes, and when this water meets the vacuum existing inside the tubes, it evaporates thereby cooling the water in the jacket. If cooling proceeds to the point where water penetrating or surrounding all or part of the tubes freezes, operation continues with local sublimation of the ice on the tubes while the circulating water attempts to melt the ice. Both sublimation and evaporation may take place simultaneously in different regions of the device

Webbon, B. W.

English

NASA Technical Reports Server

United States Patent [19] [I11 4,007,601 
Webbon [451 Feb. 15, 1977 
[ 541 TUBULAR SUBLIMATOR/EVAPORATOR 
[75] Inventor: Bruce W. Webbon, San Jose, Calif. 
[ 731 Assignee: The United States of America as 
represented by the Administrator of 
the National Aeronautics aQd Space 
Administration, Washington, D.C. 
HEAT SINK 
[22] Filed: Oct. 16, 1975 
[21] Appl. No.: 623,187 
[52] U.S. CI. ................................... 62/100; 62/121; 
62/269; 6213 15 
[ 5 11 Int. C1.* ...................... F25B 19/00; F28C 1/00 
[58] Field of Search ............ 62/100, 268, 269, 315, 
62/ 12 1, 404, 467 
[561 References Cited 
UNITED STATES PATENTS 
1,285,415 1 111918 Schou .................................. 621269 
2.1 82,788 12/1939 Cornell, Jr. .......................... 62/3 15 
2,461,636 211949 Gaylor ................................. 6213 15 
3,079,765 3/1963 Vantine ............................... 621259 
3,170,303 211965 Rannenb 
3,196,634 7/1965 Rich ...... 
3,197,973 811965 Rannenb 
3,362,186 111968 Patterson 
3,403,531 10/1968 Oesterheld .......................... 62/121 
3,543,41 1 11/1968 Bardsley et al. ..................... 621268 
Primary Examiner-Lloyd L. King 
Attorney, Agent, or Firm-Darrell G. Brekke; Gary F. 
Grafel; John R. Manning 
[571 ABSTRACT 
An evaporative refrigerator or cooler comprising a 
bundle of spaced, porous walled tubes closed at one of 
their ends and vented to a vacuum at the other end is 
disclosed. The tube bundle is surrounded by a water 
jacket having a hot water inlet distribution manifold 
and a cooled water outlet through a plenum chamber. 
In operation, hot water is pumped into the jacket to 
circulate around the tubes, and when this water meets 
the vacuum existing inside the tubes, it evaporates 
thereby cooling the water in the jacket. If cooling pro- 
ceeds to the point where water penetrating or sur- 
rounding all or part of the tubes freezes, operation 
continues with local sublimation of the ice on the tubes 
while the circulating water attempts to melt the ice. 
Under some conditions, both sublimation and evapora- 
tion may take place simultaneously in different regions 
of the device. 
8 Claims, 2 Drawing Figures 
https://ntrs.nasa.gov/search.jsp?R=19770012409 2020-03-20T07:30:32+00:00Z
US. Patent Feb. 15,1977 Sheet 1 of 2 4,007,601 
FIG.1 
42 
14’ 

4,007,60 1 
1 
stainless steel. A series of helices are placed in the 
chamber to agitate the refrigerant for increased surface 
The mode of operation in the Rannenberg et a1 de- 
5 vices is with the initial operation starting with a solid 
plug of ice in the passage 52. Sublimation occurs with 
the application of heat, and, as a result, the ice layer is 
reduced. A flow of water, once it encounters the sub- 
cooled passage wall 50, freezes thereby forming a new 
TUBULAR SUBLIMATOR/EVAPORATOR HEAT 
STATEMENT OF ORIGIN 
The invention described herein was made by an em- 
ployee of the United States Government and may be 
manufactured and used by or for the Government for 
Governmental purposes without t payment Of any 
royalties thereby or therefor. 
SINK effect. 
10 plug of ice to renew the cycle. 
U.S. Pat. No. 3,403,53 1 to Oesterheld discloses an 
evaporation device where liquid to be cooled flows 
over the outside of a stack of porous tubes and the 
liquid is absorbed by the tubes. A chimney device, 
suitable for Operation in high altitude environment 15 adjacent to the tubes, draws air through the tubes to 
situations such as outer space. evaporate small amounts of liquid. The cooling effect, 
as a function of evaporation, then cools the liquid pass- 
in conjunction with a variety of environments are Pat. N ~ .  3,079,765 to Levantine discloses a space unit 
known. These devices find utilization in many diverse 20 utilizing the evaporation principle to cool liquid ab- 
areas: cooling towers, air conditioning, space suits, and sorbed by a network of tubes made from a sponge-like 
the like. In general, the use of a cooling fluid or source substance when the liquid is in commun~cat~on with a 
of low pressure is utilized to stimulate heat transfer. A 
most basic technique merely uses the passage of air to 
create a surface where evaporation may occur to facili- 25 SUMMARY OF THE INVENTION 
tate cooling of a liquid. Other basic techniques rely on The tubular sublimator~evaporator system of this 
sublimation as the thermodynamic effect cooling the invention departs from the prior art in several critical 
liquid. In practical application, heat sinks for cooling concepts. First, the relative position of the circulating 
fluids may take the form Of many different ‘Onfigura- liquid evaporant and the low pressure vapor passages 
tions. These devices can generally be categorized as 30 are reversed. In the present invention, the liquid flows 
membrane evaporator/sublimators. The metal plate no active control of the vapor pressure under any cir- and foam sublimators both use flat plate sublimation 
cumstances. In the basic configuration, the device com- surfaces, and in terms of size are relatively large for a 35 prises a core having a bundle of tubes, each tube being given heat rejection rate. Also, both systems require a sealed at one end with the other end vented to a vac- finite time from the start of the operation until the 
uum through a plenum chamber. The evaporant circu- system reaches a full capacity operation. In contrast, 
the spraying flash evaporator has an extremely short lates through a container that encloses the tube bun- 
start-up time, but it requires a large volume and control 40 dles, and a part Of the water is evaporated through the 
system with moving parts rather than being self-regulat- tube 
The tubes themselves must be considerably larger ing as are the metal plate and foam sublimators. 
The wick-fed water boiler technique requires active than those used in prior art membrane evaporatodsub- 
difficult to achieve with a compact reliable system. The 45 pressure rather than liquid. The tubes can be ‘On- 
the prior art approaches to this invention and a material, a metal or glass with controlled porosity, Or a 
number of small tubes made of a water-permeable foam with a supporting s c ~ e n .  
membrane material. The water is pumped through the The operation of the invention is such that under 
inside ofthe tubes while the tube exterior is exposed to 50 most conditions it functions‘as an evaporator since the 
a pressure below the water’s saturation pressure. Water Pressure drops and the sonic, choked flow effect in the 
then migrates through the tube wall to the outer surface vapor flowing out through the tubes is sufficient to 
where it evaporates, cooling the water remaining inside maintain the satwation pressure at the tube walls above 
the tube. The major disadvantage of this approach is the triple point of water (0.088 psia). As the heat load 
that excess cooling, such as occurring during operation 55 is decreased, the Pressure in the tubes drops until ice 
at low heat rejection rates or in case of failure of the forms on the tube wall. The device then functions as a 
backpressure control system, may cause freezing of the subha to r .  However, the tube spacing and flow ar- 
water remaining in the tubes. This situation can result rangement is such that this ice will not prevent the flow 
in stoppage of water circulation and breaking of the of liquid under any combination of heat load and liquid 
tubes. 60 temperature within the design parameters of the sys- 
Within the patent literature, many of these concepts tem. The resulting volume change as a result of the 
are described. U.S. Pat. No. 3,170,303, Rannenberg et  formation of ice is accommodated by a liquid accumu- 
al, shows a porous plate sublimator, and an improve- lator. The liquid flowing around the tubes is effectively 
ment, U.S. Pat. No. 3,197,973, shows sublimation COOL cooled to account for any increase in liquid tempera- 
ing through a porous walled tube with a vacuum ap- 65 ture or flow rate caused by a heat load transient. 
plied to the outside surface of the tube. As shown in Hence, it is an object of this invention to provide a 
FIG. 2 of this patent, the sublimator has an outer wall cooling device that is self-regulating, more compact 
made from a porous material such as sintered nickel or and more reliable than prior art systems. 
BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to heat sinks for Cooling fluids 
2. Prior Art 
Many attempts for providing heatsink devicesfor use ing Over the outer surfaces of the tube. Similarly, U.S. 
of low pressure. 
porous plate foam sublimators, 
and around the outside of the tubes while the tube interior is vented directly to a vacuum. This approach requires ’praying flash wick-fed water 
control of the evaporation chamber pressure which is 
membrane evaporator/sublimator is the most similar of 
h a t o r s  since they are required to flow vapor at a low 
strutted of a hydrophobic or hydrophilic membrane 
4,007,60 1 
3 4 
Another object of this invention is to provide a cool- FIG. 2, and may number in the order of 150, depending 
ing system which eliminates flow stoppage and tube on the particular design heat load. 
breakage caused as a result of freezing inside a tube A baffle can 76, whose function is to be described 
containing liquid. later, is disposed in the casing having its bottom end 
Yet another object of this invention is to provide a 5 bedded in lower support plate 66. Means are also pro- 
device not requiring a vapor pressure controller to vided for the discharge of fluid from the system by 
prevent freezing. discharge passages 78 emptying into outlet 80. 
A further object of this invention is to provide a In operation, fluid, typically water, enters the unit 
system having a large heat transfer rate to function as a through inlet 54 and is dispersed outward from ports 56 
heat sink in high altitude environments such as outer 10 in the manner shown in the arrows 82. The outlet port 
space. 84 in cap 32 is coupled to a vacuum environment or 
The specific nature of the invention, as well as other source of low pressure, and therefore the interior of 
objects, aspects, uses and advantages thereof, will tubes 68 with an open end in chamber 72 are also 
clearly appear from the following description and from coupled to the vacuum. Part of the liquid is evaporated 
the accompanying drawings, in which: 15 through the porous tubes 68 as it circulates around. 
The vapor flow conditions in the tubes are such that a 
sonic, choked flow condition is maintained at the tube BRIEF DESCRIPTION OF THE DRAWINGS 
FIG. 1 is a cut away side view of the evaporator/sub- outlet. The device functions solely as an evaporator as 
long as the choked vapor outflow, shown by arrows 86, 
FIG. 2 is a top sectional view of the device of FIG. 1, 2o is sufficient to maintain the saturation pressure as the 
tube walls, upstream of the outlet, above the triple 
limator heat sink. 
cut along section line 2-2. 
point of water (0.088 psia). Evaporation has a cooling 
effect on the circulating liquid discharged through out- 
let 80. and as the heat load is decreased. the vapor 
DESCRIPTION OF THE PREFERRED 
EMBODIMENT 
Referring now to FIGS. 1 and 2, the preferred em- 25 pressuie drops and ice may form on all or a part of the 
bodiment to the evaporator/sublimator is shown. The tube walls. The presence of ice -causes the device to 
device, generally indicated at 10, has an outer cylindri- function as a sublimator with the gas escape through 
cal casing 12 which is welded at 14 and 16 to a flange discharge 84. During the sublimation phase, the tem- 
20. Flange 20 is coupled to base 18 by a series of bolts perature of the porous tube wall may drop to the point 
22 suitably tightened by nuts 24. The bolts are disposed 30 that ice forms on the liquid side of the tube. However, 
about the perimeter of the base, typically about twelve the configuration of the tube placement, coupled with 
in number. Additionally, disposed in a notch 26 in the the flow arrangement, is such that ice formation will 
flange 20, is an O-ring seal 28 to prevent leakage from not prevent continued circulation of the fluid. The 
the casing 12. If desired, a suitable fillet weld 30 may be 35 resulting volume change in the device is accommo- 
utilized, typically by Heliarc techniques to further seal dated by an accumulator in the liquid circulation loop. 
the casing 12. The baffle can 76 guarantees that fluid to be circulated 
The top section of the unit 10 has a cap 32 placed in will be dispensed throughout the casing 12. 
a locking relationship with flange 34 by a series of bolts The liquid flowing around the ice on the tubes is 
36 tightened by nuts 38. As in the case of the base, the 4o effectively cooled, and as the heat load is increased, the 
bolts 36 are disposed about the perimeter of the cap to ice will melt. The device then functions as an evapora- 
uniformly couple the cap 32 to the casing 12. A fillet tor. A simple shut off valve, not shown, at the vapor 
weld 40 joins flange 34 to the casing 12, and top plate dutlet port 84 is used to start and stop the operation. 
44 is joined to the casing and the flange by weld 42. A Typically, a unit containing a bundle of 150 tubes, 
notch 46 in the top portion of the top plate 44 has an 45 four inches long with YS inch inside diameters, arbitrar- 
O-ring 48 to provide a seal between plate 44 and cap ily located on 0.200 inch centers, can reject from 
32. Also, a lower notch 50 is provided with O-ring 52 to 400-2000 Btu/hr with liquid temperatures from 32" to 
seal the top plate 44 and flange 34. 50" F. In this configuration, the required water perme- 
A fluid inlet tube 54 is positioned in the center of the ation rate to reject the maximum heat load is approxi- 
device and has a number of flow passages 56 to effectu- 50 mately 1.7 Ibm/hr-ft2. A variety of tube wall materials 
ate the discharge of fluid to be cooled within the casing such as sintered nickel, various membrane materials or 
12. A number of discrete levels of flow passages are plastic foams with supporting screens can be employed. 
provided, as shown. The tube 54 is sealed by means of The inside diameter of these tubes must be considera- 
O-ring 58 in notch 60 at  the point where it passes bly larger than those used in prior art membrane 
through the flange plate 20 and has a sealed end 62 5 5  evaporatorlsublimator systems since they are required 
embedded in top plate 44. A weld 64 may also be em- to flow vapor at a low pressure, rather than liquid. 
ployed to hold the tube 54 in position. The prime advantages provided by the invention thus 
Disposed within casing 12, at the lower end, is a described over prior art systems lie in the elimination of 
lower support plate 66 having a number of holes drilled flow stoppage and breakage of tubes caused by freezing 
to support a plurality of porous sublimator tubes 68. 60 inside the tube of the liquid contained therein, and the 
The sublimator tubes 68 can be fashioned from a num- elimination of a requirement for a vapor pressure con- 
ber of porous or sintered materials well-known in the troller previously needed to prevent this freezing. 
art. These tubes have their lower ends closed off and It is to be understood that the invention is not limited 
bedded with a layer of epoxy 70, and the upper ends to the specific embodiment herein illustrated and de- 
protruding through top supporting plate 44 and ex- 65 scribed, but may be used in other ways without depart- 
posed to the chamber 72 in the cap 32. An epoxy layer ing from its spirit. 
74 bonds the tubes 68 to the plate 44. Typically, these 
tubes are disposed in a regular pattern, as shown in 
What is claimed is: 
1. A self-regulating cooling system comprising: 
5 
4,007,60 1 
6 
a. a chamber having inlet means for the circulation of 
fluid to be cooled and outlet means for effectuating 
a discharge of cooled fluid; 
b. a plurality of porous hollow heat exchangers dis- 
posed in said chamber, said porous hollow heat 5 
exchangers having one end thereof open and pro- 
truding through a wall of said chamber and another 
end sealed in said chamber; 
c. means for coupling the open ends of said heat 
exchangers to a source of low pressure, thereby I O  
exposing the inner portions of said heat exchangers 
to said source of low pressure; and 
d. means within said chamber for channeling fluid to 
be cooled past said heat exchangers, whereby as 
fluid circulates in said chamber, a portion evapo- 15 
rates through said porous hollow heat exchangers, 
said system then functioning as a sublimator until 
the heat load due to circulation of fluid to be 
cooled increases, melting the ice such that evapo- 
ration then resumes. 20 
2. The device of claim 1, wherein said chamber is 
circular and said inlet means is disposed in the center of 
the chamber to evenly distribute fluid to be cooled. 
3. The device of claim 2, wherein said channeling 
means is a circular baffle disposed in said chamber 25 
around said inlet means. 
4. The device of claim 3 wherein said porous hollow 
heat exchangers comprise a bundle of tubes disposed in 
a regular pattern in said chamber, and said outlet 
means is located around said bundle. 
5. The device of claim 4, wherein said source of low 
pressure is the vacuum of outer space, and said means 
coupling the open ends of said heat exchangers is a 
plenum chamber vented to said source of low pressure. 
6. The device of claim 5, wherein said fluid to be 
cooled is water. 
7. The device of claim 5, wherein said fluid to be 
cooled is Freon. 
8. A method of cooling fluid comprising the steps of: 
a. circulating the fluid to be cooled in a chamber, said 
chamber having a plurality of hollow porous heat 
exchangers such that fluid, liquid or vapor is ab- 
sorbed by said heat exchangers; 
b. coupling the inside of said hollow porous heat 
exchangers to a source of low pressure; 
c. evaporating fluid absorbed and venting the result- 
ing vapor; 
d. allowing ice to form on said heat exchanger as a 
result of evaporation such that sublimation occurs 
across said heat exchanger; 
e. maintaining the volume of fluid in said chamber to 
melt said ice while cooling fluid to the point where 
the ice melts; and, 
f. repeating steps c through e repeatedly to cycle said 
cooling through evaporation and sublimation. * * * * *  
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Tubular sublimatory evaporator heat sink

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