US3479838A - Cooling material - Google Patents

Description

NOV. 25, H9159 i BlTTERLY 3,479,838

COOLING MATERIAL Filed May 15I 1967 3 Sheets-Sheet 1 M0007 20A/f fawn/v0 a 40mm/0 200 00 0 /ff/z/ma @Are f i. j Q0 M M INVENTOR Nov. 25, i969 J. e. Eni-raaml 3,479,833

COOLING MATERIAL Filed May l5, 1967 3 Sheets-Sheet 2 NOV 25, 3%@ J. c5. BITTERLY '3,479,838

COOLING MATERIAL Q A@ A@ 40 ma $000 /Za @ma 20pm wao' 25000 329m nit-ed States Patent O 3,479,838 COOLING MATERIAL Jack G. Bitterly, Woodland Hills, Calif., assignor to McDonnell Douglas Corporation, a corporation of Maryland Filed May 1S, 1967, Ser. No. 638,227 Int. Cl. F25d 23/12; FZSb 19/00 ILS. Cl. 62-259 4 Claims ABSTRACT F THE DISCLOSURE A material to be used as a blanket, article or garment that provides cooling of a persons body or other objects in contact therewith. It consists of an inner heat conducting and moisture absorbent layer, a water permeable or impermeable inner membrane, a second water absorbent layer, an internal vapor conduit, and an outer impervious layer forming a exible protective pressure barrier having a vapor outlet. A negative pressure between the object and the inner layer assists in the heat and moisture transfer to the second absorbent layer. Supplemental coolant liquids also may be pumped through the evacuation chamber contained within the outer layers. A- negative pressure from without removes the heated moisture through the outer layer at a controlled rate to regulate the cooling rate and thus the surface temperature of the object or person protected by the material.

BACKGROUND OF THE INVENTION The net body temperature and, of vital importance, the intra-cranial temperatures of a person or animal, are maintained within a very few degrees at all times. If the normal brain temperature ranges are exceeded, unconsciousness and eventually death will ensue, as is often the case in prolonged cold exposure and/ or high fever. Man compensates primarily for increased body temperature by producing sweat. Sweat will evaporate to the atmosphere only if the ambient air relative humidity is below 100%. During this evaporation, heat is removed from the skin at about 1000 B.t.u./lb. of sweat, thus cooling the skin and peripheral blood and subsequent cooling of the deep muscle cores of the body. Other temperature control factors relating to the human include radiation to or from the environment, and conduction either to the air or to solid objects. The most eiective and immediate cooling process other than direct emersion in cold fluids (swimming) still remains the evaporation loss of heat to the atmosphere by means of sweating.

Aside from providing a brute force capacity environmental control system, the only techniques thus far in use are the radiation cooled and conduction water cooled blanket, space suit, or heat resistant garment which contains an undergarment attached to a complex network of plastic tubes, within which is circulated cold water from an external pump-reservoir heat exchanger. The accumulation of sweat raises the relative humidity which in turn retards further cooling. Further discussion of such a prior art garment will be made hereinafter.

3,479,838 Patented Nov. 25, 1969 ICC SUMMARY OF PRESENT INVENTION The present invention is based upon the principle that water will boil at a lower temperature under a reduced air pressure. Heat is extracted from an object by boiling or vaporization of water within the multiple layer material whose inner spaces have been evacuated to enable water boiling to take place at a lower temperature. The multiple layers of the cooling material comprising the present invention absorb heat from the object to be cooled through the medium of water, which may be sweat, or supplemental fluids. This fluid is then boiled out to dissipate the absorbed heat.

BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a chart showing heat generated by persons performing various activities;

FIG. 2 is a representation of the performance of a known water-cooled material;

FIGS. 3 and 4 are block diagrams showing a cornparison of a known water-cooled system with that of the present invention;

FIG. 5 is a chart showing low-pressure water boiling heat transfer data;

FIG. 6 is a cross-sectional view showing the multiple layers of the cooling material;

FIG. 7 is a chart showing orice characteristics;

FIG. 8 is a chart showing membrane heat transfer characteristics;

FIG. 9 is an illustration showing the cooling material used as undergarment patches as part of a cooling garment; and

FIG. l() is a chart showing the performance of several types of thermal cooling suits.

DESCRIPTION OF THE PRESENT EMBODIMENT Physical exertion, particularly in a heated environment, produces sweating which tends to compromise work efficiency, raises the immediate air humidity if in a close environment, and tends to lessen further skin cooling by the normal evaporation process. Ideally, an optimum cooling system would have the capability of removing body heat without the production of apocrine sweat. In other words, the skin temperature-core thermal balance should be maintained to keep a person constantly in a comfort zone. As shown in FIG. l, there are numerous exemplary work activities in which is shown a related average and peak heat generation. As can be seen, sustained metabolic rates for an eight-hour period could average about 2000 to 2500 B.t.u./hr. over an eighthour work day, although peak averages for the same activities could exceed this amount by a general factor of 21/2 times. Thus it would appear that any cooling material or garment having a heat dissipation ability of about 6000 B.t.u./hr. would be a reasonable design expectation. Present thermal cooling blankets or garments that are water-cooled are the most efficient available until the present invention, although they have been limited to the removal of heat on the order of 2000 B.t.u./hr. and have a high power requirement in the circulating cooling subsystem. This performance characteristic is shown in FIG. 2 wherein it can be seen that reducing the skin temperature from 85 F. to 40 F. requires an increase in heat removal rate from 200 B.t.u. per hour up to 2000 B.t.u. per hour, with sweating or shivering occurring outside the comfort zone. This circulation of cool water through tubes adjacent the body follows a generalized heat transfer equation as follows:

- (Tin i"Tout)] q-T [Takin 2 In this formula, A is the body contact area of the tubing and t is the tubing thickness. Tskin is the temperature of the body skin, Tin is the temperature of Water in the tube before it crosses over the body and Tout is the temperature of the water in the tube as it leaves contact with the body. k is the thermal conductivity of the tubing which preferably has been polyvinylchloride. To increase the heat removal capacity of the liquid-cooled garment, k values must increase, which appears diicult to accomplish and still maintain flexibility for wearing comfort or, the area of contact must be increased, which requires increased coolant mass flow. Finally, tubing thickness could be decreased, but this decrease is limited by dimensional integrity during operation. Other terms of the equation, such as skin temperature, cannot be increased without exceeding the comfort zone boundaries and the water temperatures cannot be substantially decreased without causing local cool spots on the skin. For these reasons the water-cooled garment has an upper limit of about 2000 B.t.u. heat removal per hour, as shown in FIG. 2.

A block diagram of the previously used water-cooled garment is shown in FIG. 3 and may be compared with the block diagram of the garment comprising the present invention as shown in FIG. 4. The state-of-the-art garment in FIG. 3 has a water sublimator-boiler and coolant pump attached to, but external of, the garment. In the garment utilizing the present invention, the flexible boiler is an integral part of the garment, with the result that no coolant flow heat exchanger subsystem is required. Battery power required to operate the water pump is also eliminated. The system is thus reduced to a sublimator Water tank-accumulator, the gaseous side of which is referenced to a reduced atmospheric pressure. Since the sublimator or boiled is contained within the cooling garment, the only required control is a water valve which will add water directly to the garment. The boil-off steam for the evaporative heat transfer is Vented directly to a space vacuum by the control valve. Of course, if there is no natural space vacuum, an artificial reduced pressure must be provided. For a cooling rate of 2000 B.t.u./hr. the system in FIG. 4 requires water handlng of 1.89 pounds per hour as compared to the water-cooled suit in FIG. 3 which requires 235 pounds per hour.

The temperature at which the water boils depends upon the pressure, which in turn may be determined by using pressure drop restrictors in the vapor exit portion of the system. The pressure-boiling temperature relationships and the boiling temperature-enthalpy values are shown in FIG. 5. For example, if the boiler pressures were set at 0.15 p.s.i.a., the water boiling temperature of 45 F. would result, along with a heat rejection of 1068 B.t.u. per pound of water expended.

Heat transfer from the skin to the garment can be described by the equation:

where qm denotes inner membrane heat transfer, km is inner membrane thermal conductivity, Am is the membrane/ body contact area, im is the inner membrane thickness, and AT is the difference between the skin surface temperature and the garment interior boiling temperature.

The cooling blanket or garment utilizing the concept of boiling water in a reduced pressure atmosphere as a means for cooling, such a material is shown in FIG. `6. Here adjacent the body skin 10 is an inner absorbent layer 12 having a favorable thermal and fluid absorption property. It may be a black material such as cotton netting, for example. An inner membrane 14 is adjacent the netting 12. It may be desirable that a pressure reduction means, not shown, be inserted between the heat conducting membrane 14 and the body 10 for the purpose of enhancing the membrane 14 in proximity with the skin. This will serve to increase the heat transfer to the garment and/or to better film any sweat formed in intimate contact with the inner membrane (if this material were to be selectively permeable to water). The water permeable membrane could be of a material such as cellulose acetate. The water permeable membrane 14 is also gas tight and forms a parallel walled chamber 16 in close contact with the skin. This chamber thus formed may be lightly inflated and/ or suction deflated on a periodic basis. This would, if desired, provide a free air space next to the skin or under suction which would gently press the absorption material layer 12 next to the skin. This undulating frequency, controlled by the subject for optimum comfort, would have the tendency of distributing any sweat formed under extreme activity evenly over the body. This chamber 16 also may be used to contain a circulating wash-water to periodically cleanse the skin if the thermal garment were used as a constantwear clothes. Negative pressure after cleansing would void the chamber of excessive cleansing fluid and the remainder would diffuse through the permeable membrane 14 into the middle chamber exterior of the membrane. The diffusion of sweat through the semi-permeable membrane obeys the laws of osmotic pressure, wherein water will diffuse towards a reduced pressure area and/or towards a higher salinity (which salinity level need only be initiated in the garment manufacture). The reduced pressure difference across the membrane 14 is provided by the atmospheric pressure next to the skin and a reduced pressure in the evacuation chamber. A water absorption layer of material 18 is adjacent the inner membrane 14. It should vbe pointed out that for the inner skin-membrane 14, semi-permeable material may be substituted for an impermeable membrane for cases where the cooling produced may negate sweat formation. In addition to absorbing sweat or carbon dioxide (if the membrane is so constructed) from the body, an external water supply through water inlet 20 may be used to moisten this wicking material, the outlet of which is located between the inner membrane 14 and the water absorbent layer 18. This water boils at a reduced pressure when body heat is transferred to it. An outer impervious or impermeable membrane 22 has a reflective outer surface to reflect heat away from the garment. This may be a metallized Mylar material. This outer membrane has a property of low permeability to liquids and gases and also is tough, resilient, and wear resistant. The inner surface must have the capability of sealing to the inner evacuation chamber support grid to provide a quilting concept for flexibility if desired. Between the outer membrane 22 and the water absorbent material 18 is a boiler void material 24 like small spheres of absorbent Styrofoam which will provide for free passage of the steam boil-off by means of their interstitial spaces, and in addition, will provide structural integrity between the inner and outer membranes .14 and 22. The spheres in this case will provide thickness integrity but not garment bending resistance, which will enhance form fitting for wearing comfort. Alternate boiler void materials may be constructed out of flexible perforated plastic tubing, coarse woven strands of woven fabric, three-dimensional fabrics like Trilock (a material manufactured by Uniroyal, a division of Goodyear Company), woven strands of metal, glass and fabric combinations such that the flexibility is maintained along with compression resistance and which allows free passage of the steam boil-off.

In order to enhance the free steam fiow out of the boiler void material with a minimum pressure drop, branching vacuum arteries within a given patch area have been employed. These arteries can be constructed of fiexible perforated plastic tubing or of Spirap made by AMP, Inc., Harrisburg, Pa., and they are also sewn into the peripheral edge of the patch in direct communication with the boiler void material. This same concept is used to evenly distribute the boiler feed water to the absorbent wicking material.

As a desirable optional feature, a double walled bal- [onet 26 may be used to increase the efficiency of the garment when greater cooling is required. A slight air pressure between the inner wall 28 and outer wall 30 presses all inner materials more closely against the body skin. This provides more efficient heat tranfer and also enhances body comfort. The outer membrane is provided with a sonic limiting orifice 32 and a valve 34 for permitting the escape of vapor into a rarified atmosphere which may be either a natural condition or an artificially provided condition. This valve 34 could be adjustable for the regulation of suit temperatures below the limiting orifice mass fiow for maximum comfort and safety, it being understood that the faster the vapor escapes the quicker wiil ibe the cooling rate. The valve in the closed position will reduce the cooling to zero if desired.

A chart is provided in FIG. 7 showing the relationship of the boiling temperatures to the size of the limiting steam orifice. For example, a steam orifice having a diameter of .4 inch, when the undergarment surface area is 41/2 square feet, results in a boiling temperature of 60 F. and thus cools the skin having a temperature higher than this.

The efficiency of such a cooling garment depends in part upon the heat conductivity of the inner layer heat transfer membrane 14, it being desired to have its heat transfer capability greater than that provided by the limiting steam orifice. As shown in FIG. 8, a membrane thickness relationship is shown with heat removal characteristics for various average skin temperatures. For example, if a skin temperature is 90 F. and a membrane thickness is .0l inch, a heat removal of 22,000 B.t.u./hr. may be achieved for a differential temperature of 50 F.

In FIG. 9 there is shown a garment made in accordance with the present invention. Ten separate cooling patches, two on each leg, two on each arm, and one around the upper torso area, and a head patch comprise coverage for the total area that is to be evaporatively cooled. For a 50 percentile man, the area of the lower arms 40 and the upper arms 42 have an effective area of 2.44 square feet and with a .010 inch skin contact membrane, a 3700 B.t.u./hr. heat removal rate may be achieved. The lower legs 44 and upper legs 46 have an effective area of 5.33 square feet and under the same canditions, 10,800 B.t.u./hr. of heat may be removed. The upper torso 4S has a square footage of 2.03 and a 14,400 B.t.u./hr. heat removal rate is possible. The top of the head S0 has a square footage of .56. The total body, minus the head and feet, has a square footage of 9.80 which permits a 29,100 B.t.u./hr. heat removal rate. The cooling patches are linked together by an absorbent material 52 next to the body to permit capillary wicking of body moisture in the areas not covered by the cooling patches. The total garment consists of a fiexible, close fitting comfortable material in the shoulder, waist, knee, elbow and foot areas that do not bind or restrain the person. Access to the cooling patches are provided by Velcro-secured flaps 54, a device well-known for fastening two materials with interlocking fibers. Alternate acces means are zippers, lacing or stitching. Dual or multiple vacuum and Water lines 56 are attached under the outer garment 58 in such manner as to prevent mobility restrictions. A valve or vacuum limiting orifice 60, which may have a fixed or variable area, is provided in easy reach for manipulation by the occupant and a fiexible plastic water storage tank 62 is provided and carried around his waist. The outer protective material 58 cornpletes the garment.

The performance of various garments is shown in the chart in FIG. 10 wherein the area to the left of I shows the temperature range provided in a prior art water-cooled garment and shows a maximum heat-removal rate of about 2000 B.t.u./hr. The area 66 to the left of the line II applies to a torso garment, only, the area 68 to the left of line III, an arm garment, only, the area 70 to the left of line 1V, a leg garment, only, and area 72 to the left of line V, the garment shown in FIG. 9. As an example, in the garment of line V, by adjustment of the valve to a 60J temperature, a heat-removal rate of above 8000 B.t.u./ hr. is achieved.

The cooling garment just described has many uses and advantages. Thermal protection is virtually instantaneous and may use expendable materials for cooling, such as waste fluids or potable liquids. By the addition of a condenser at the steam-escape outlet 60, potable drinking water can be produced from sweat or waste fluids. The entire highly fiexible suit has been demonstrated to function at a cooling rate in excess of 5000 B.t.u/hr. at less than 1/s of an inch in thickness. The suit may be used as a constant wear garment and bathing could be accomplished without its removal. By constructing the suit with multiple evacuation chambers (each parallel to the skin) with each chamber boiling separate fluids of decreasing temperatures from the outside in, the suit may be used as an intense heat resisting, fire fighting suit having a minimum thickness. The boiling fiuids, other than water, could be selected to boil at ambient pressure such that a portable vacuum unit need not be carried by the wearer. Thus oil may be the outer boiling fiuid which is subjected to high temperatures and alcohol or ether may be in the inner chamber next to the skin. The garment can be made into a cooling bed blanket or bed mattress cover for hot, humid climates where air-conditioning is not available and can provide the opposite function to that of the universally electrically heated blanket. The cooling garment can be used in medical fields where applications of body cooling is required. It may be used in remote combat zone hospital units to enhance recovery of the sick or injured where air-conditioning is not available. The cooling garment may be used to protect equipment and other inanimate objects that are subject to thermal damage. The cooling garment concept may also be used for a compact air-conditioner and/ or a heat exchanger.

Having thus described the present invention, it is to be understood that other modifications and variations will occur to those skilled in the art and it is to be understood that these deviations from the just described embodiment are to be considered part of the present invention as claimed.

I claim:

1. A cooling material comprising in combination:

a heat conducting and liquid absorbent layer for placement against an object to be cooled by absorption of heat and moisture therefrom,

a liquid absorbent layer,

a liquid permeable heat conducting membrane between said layers,

an impervious pressure barrier membrane adjacent to said last mentioned liquid absorbent layer having a vapor outlet, and

an internal vapor passage for conducting vapor from said last mentioned liquid absorbent layer to said vapor outlet.

2. A cooling material as in claim 1 in which said membrane is permeable to carbon dioxide between said layers.

3. A cooling material for cooling an object as in claim 7 8 1 in combination with a means providing a negative pres- References Cited sure between said heat conducting layer and the object to UNITED STATES PATENTS be cooled thereby.

4. A cooling garment including a plurality of cooling 3,079,765 3/1-963 Le Vantme e- 62-259 patches adapted to be positioned on an object to be cooled, 5 3:125865 3/1964 Bemflman 62-259 each of said patches including an inner heat conducting 312121286 10/1965 CUTS 62-29 layer for placement against said object, 312791201 10/ 1966 WOTZ 6229 a absorbent layer, 3,3 Burton an outer pressure barrier having a Vapor outlet,

and a passage for vapor in a path between said liquid 10 WILLIAM J WYE Primary Examiner absorbent layer and said outlet, the outlets of said U S C1 XR pressure barriers being connected to vapor ejecting passage means. 2-2.l, 81; 62-100', 261

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