Body heating system

[57] ABSTRACT

A lightweight, compact, portable, personal body heating system utilizes an inner casing containing a material having a high heat of fusion. A heater is operatively associated with the inner casing for charging the material. A closed recirculating conduit means lies about the inner casing to permit recirculating liquid flow about the casing so that a heat transfer liquid is heated by the heat of fusion of the material. The conduit comprises an inlet tube and an outlet tube permitting passage of the fluid to a body protective device through the outlet tube and recirculation through the inlet tube.

Claims, 2 Drawing Figures

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SUIT

PATENTED JUN 51973

3.737,620

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THERMOELECTRIC ¹⁰ P---------POWER SOURCE BODY

PROTECTIVE SUIT

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INVENTOR.

DOUGLAS G. HARVEY

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ATTORNEY

3,737,620

BODY HEATING SYSTEM

BACKGROUND OF THE INVENTION

There are many human endeavors in the pursuit of both employment and pleasure which expose the body to a cold ambient environment. The endurance of the body in such an environment is limited by the loss of body heat to the environment and the inability of human body metabolism to produce sufficient heat to maintain sufficient body temperature for efficient and/or comfortable operation. The problem often arises in connection with underwater divers, cold weather workers, sportsmen and high altitude fliers. Under such conditions, it is necessary to either limit heat loss from the body and/or provide supplemental heat.

There have been many past attempts to solve this problem, various heat retention protective garments have been designed. While such garments are completely self-contained, they are limited by their effective thermal conductivity, cost and bulkiness.

Heat supplementing devices such as electrically heated suits have also been used but are limited due to cost, hazards of open circuits and shorts as well as size and weight of the power source. Various chemical reactive systems have been used which often create hazardous toxic conditions as a result of the chemical reactions involved which reactions are difficult to control and establish. Use of various hot water suits has been suggested but is limited because of difficulties in temperature control, high capital investments and undesirable features such as umbilical cords and the like.

The use Of high heat of fusion materials to heat air used by an individual has been suggested. However, this suggestion has not met with widespread use probably because of inherent difficulties in controlling heat in gas systems while maintaining low cost, safety and other necessities of heating systems.

It is an object of this invention to provide a personal body heating system for use in cold ambient environments. Another object of this invention is to provide a personal body heating system in accordance with the preceding object which is preferably lightweight, compact and portable and which can be made and used inexpensively in a wide variety of applications.

SUMMARY OF THE INVENTION

According to the invention, a lightweight, compact, portable, personal body heating system is formed. The system comprises an inner casing containing a material having a high heat of fusion and heating means are operatively associated with the inner casing for charging the material. A closed recirculating conduit means surrounds the inner casing permitting recirculation of liquid about the casing to cause the liquid to be heated by the heat of fusion of the material. The conduit means has an inlet tube and an outlet tube so that the liquid can be passed to a body protective device through the outlet tube and recirculated over the material having a high heat of fusion after passing through the inlet tube. Preferably an outer casing surrounds the inner casing, heating means and conduit means.

In a preferred embodiment, the heating means comprises an electrical heater which is actuated by periodic connection with an electric power source to charge the material having a high heat of fusion. The system can be used for long periods of time, without attachment to the heater, as a self-contained portable unit. Preferably the conduit means comprises inlet and outlet plenums with interconnecting tubes surrounding the inner casing to maximize heat transfer from the material to a heat transfer liquid which is recirculated. Recirculation of the liquid lowers the requirement for heat output from the material permitting use of small amounts of material maintained at constant temperatures due to heat fusion.

In an alternate embodiment of the invention, the heating means is a radioisotope charge preferably located at the center of the material having a high heat of fusion.

BRIEF DESCRIPTION OF THE DRAWINGS

The above objects, features and advantages of the present invention will be better understood from the following specification when read in conjunction with the accompanying drawings, in which:

FIG. 1 is a semidiagrammatic cross sectional view of a preferred embodiment of this invention; and

FIG. 2 is a semidiagrammatic cross-sectional view thereof taken through line 2—2 of FIG. 1.

BRIEF DESCRIPTION OF PREFERRED EMBODIMENTS

With reference now to the drawings and more particularly FIG. 1, a preferred embodiment of the personal body heating system of this invention is illustrated generally at 10 comprising a heat source enclosed within an outer container 11. An inlet tube 12 and an outlet tube 13 form part of a conduit system for passing a recirculated heat transfer liquid over the heat source. The inlet and outlet tubes are connected with a body protective suit 14.

The heat source within the outer casing 11 comprises a material 15 having a high heat of fusion, which material is preferably hermetically sealed within a cylindrical container 16. The material 15 is selected for its high heat of fusion. As is known, during the melting or freezing of a pure compound or element, a precise defined amount of thermal energy is required to effect the change of state. This amount of thermal energy is termed the heat of fusion of the material. During the input (melting) or release (freezing) of the material, it remains at a constant temperature referred to as the melting point. These properties are used in this invention to provide constant thermal energy in a fluid recirculating personal heating system.

The material 15 is preferably a material which has a high heat of fusion. For example, lithium hydride can be used to obtain minimum weight or lithium fluoride can be used when minimum volume is desired. The container or inner casing 16 is preferably metallic and is compatible with the material 15 which preferably fills the space within the casing 16. The material of the casing 16 has a melting temperature well in excess of the melting temperature of material 15 and preferably by a margin of at least 10 percent. Suitable metals for casing 16 include pure iron (for LiH) and stainless steel (for LiF).

A normally expanded cylindrical metallic bellows 17 is preferably enclosed within the container 16 preferably attached to one end thereof. The bellows provides room for expansion and contraction while maintaining the material 15 in a confined state during melting or solidification. This feature advantageously prevents unwanted internal forces created by expansion or con

3,737,620 traction during the change of state and also prevents inertial movement of the material 15 as during movement of the body with which the system is used.

An electrical heating coil 18 preferably surrounds the inner casing 16. The heating coil 18 is attached through suitable leads 19 and 20 to a recharge plug outlet 21 mounted on the outer casing 11. Thus, an electric power supply can be attached to leads 19 and 20 to heat the material 15 within the inner casing 16 to its melting point and beyond whereby the material 15 is charged with heat of fusion to. be released at a constant temperature over a substantial time period. In some cases, the heater coil can bepositioned in an indentation or well incorporated in the cylinder 16.

The inlet tube 12 is connected with an inlet plenum 22. The plenum 22 preferably lies above the cylindrical casing 16 and is coaxial therewith as is an outlet plenum 23 located below the inner casing 16 as shown in FIG. 1. A plurality of preferably parallel tubes 24 interconnect plenum 22 and plenum 23. This arrangement of tubes provides for recirculating liquid flow in the closed conduit system provided by inlet tube 12, inlet plenum 22, tubes 24, outlet plenum 23, outlet tube 13 and liquid passage tubes (not shown) within the body protective suit 14. The heat transfer liquid flows about the inner casing 16 and thus picks up heat from the material 15 for use during circulation through the system.

Suitable insulating material 25 such as Min-K (a fibrous insulating material) fills the space within the outer casing 11 and aids in maintaining the components in position. The spacing of the tubes 24 and plenums from the inner casing 16 plays a part in determining the amount of heat of fusion picked up by the heat transfer liquid.

A liquid pump is diagrammatically illustrated at 30. The pump is preferably an electrical pump actuated by a series of thermoelectric modules 32. The use of the thermocouples in a thermopile arrangement is preferred since the cold junctions of the thermocouples can be positioned adjacent the working liquid within the plenum 23 while the hot junction thereof is positioned against the inner casing 16 thereby creating the necessary electric current to operate the fluid pump 30. Known silicon germanium thermoelectric modules are suitable for use in this invention. In some embodiments of this invention, the pump 30 is located outside of the casing 11 and/or operated by portable batteries or other power sources such as radioisotope sources in conjunction with power converters.

The protective device 14 is preferably in the form of a human body protective suit containing a plurality of tubes insulated from the wearer to provide the desired thermal effect to the body when a heated liquid is passed through the suit. Such body protective suits are known in the art for use with hot water systems and their design may vary considerably depending upon the liquid flow rate in the recirculating system of this invention as well as the particular material 15 used.

Suitable fittings not shown can be employed at the liquid inlet and outlets from the casing 11 and at the body protective suit to allow disconnect when desired.

The outer casing 11 is preferably a cylinder coaxial with the inner casing 16. The casing 11 preferably carries suitable straps, hooks or the like to attach the system directly to the body protective suit of the user.

The specific material 15 used can vary widely depending upon the particular application and the following table illustrates illustrative examples of materials suitable for use as the high heat of fusion material in this invention:

Formula

Latent

Melting heat point (Kcal./ (T_m,mole) ° C.)L„

Density Formula (gm./ wt. (g./ cc.) P mole) F

Figure of merit

Cal./gm. Cal/cc.

L„/F L_m/F

Te_____450

B2O2....450

LiCl...614

Sb------630

Mg_____651

SbiOfl__656

Al......660

VaOs...670

FeCh..677

LiH....680

MoOa...795

L1F_...870

2.7

3.36

2.98

0.78

4.7

2.6

128 33216

75140

42.4 76160

122 39260

24.3 86140

583 45230

93250

182 86290

127 81240

7.94 610480

144 87410

25.9 248655

The particular heat transfer liquid can vary depending on the material 15 and other factors. Ethylene glycol, Dowtherm A and other known heat transfer liquids ²⁵ can be used.

In operation, the heat of fusion material is charged by connecting the outlet 21 to a suitable electrical supply thereby heating the material 15 and changing it from a solid to a liquid. The heat within the inner casing 16 ³⁰ thereby causes pump 30 to recirculate the heat transfer liquid in the direction of arrows 40 whereby the liquid flows about the closed system. The electrical energy source is then disconnected and the unit can be attached to the body protective suit 14 and worn by a ³⁵ user with constantly recirculating liquid maintained at a substantially constant temperature which temperature is determined by the heat of fusion of the specific material 15 employed and design features of the system. Since the fluid is recirculated from the body of the ⁴⁰ user, heat is conserved in the system and the amount of material 15 needed to produce a comfortable can be temperature canbe minimized.

In a specific example of this invention, an underwater system suitable for operating as a self-contained unit ⁴³ for 4 hours at a 28° F outside temperature with a well insulated diving suit (conductivity = 0.025 B/ft-°F-hr) is devised. The supplemental thermal power requirements are 500 thermal watts over the 4 hour mission life. Using lithium hydride as the heat of fusion material ³⁰ 15, the following properties are used in determining the amount of lithium hydride necessary and thus the size and weight of the system:

Melting point Heat of fusion

Density = 680’C = 608 calories/gram = 2.41BTU/gm = 0.705 watt hours/gm = 0.78 grn/cc = 48.6 lb./ff ,θ In this example, 2,000 watt hours are required. Thus 2000 watt hrs./0.705 watt hrs./gm (pound/454 gms) = 6.25 pounds LiH required

The 6.25 pounds of lithium hydride can be contained in a central inner container 16 in the form of a cylinder ₆₅ having a volume of 222 in³ with a radius of 3.31 inches and a length of 6.62 inches. The entire device is contained within a cylindrical casing 11, 7 inches long and having a 7 inch outside diameter. The amount of heat

3,737,620 delivered to the diving suit is adjusted by predetermining the velocity of’the liquid flow by a predetermined pumping power. Alternately, a flow valve can be used on the conduit in the heat transfer liquid circuit to regulate liquid flow.

In a second example where a personal heating system is employed for sportsmen and the like and where heat input is determined by 0° F ambient temperature approximately 200 thermal watts are required. In designing a heating system for 4 hours of exposure, the following calculations are employed:

200 X 4 = 800 watt hours required

Using a lithium fluoride system 248cal/gmX3.968X10^-3xBTU/calX2.928X10^-1 (watt hrs./BTU) = 0.288watt hrs./gm = 128watt hrs./lb

Thus for this system

800 watt hrs.

_1QO watt hrs. = 6.25 pounds LiF ¹²⁸ —IbT^-

This quantity of lithium fluoride can be contained in a volume of 45.5 in³ or a spherical central container whose inside diameter is 4.42 in.

In an alternate embodiment of this invention, the electric heater 18 along with plug connection 21 and lines 19 and 20 are eliminated and in place thereof a radioisotope capsule 41 is centrally positioned within the inner casing 16 as shown in dotted outline in FIG. 1. The radioisotope containing capsule can contain any of the standard heat producing radioisotope materials such as isotopes of strontium or plutonium. A sufficient quantity of the radioisotopic material is used to charge the high heat of fusion material 15 by melting the material over a period of time. The use of the high heat of fusion materials allows storing of large amounts of energy at temperatures near their respective heat of fusion temperatures, radioisotopic shielding When a radioisotope capsule charging source is used for the ma. terial 15, it is desirable to employ suitable redioisotopio shielding about the inner container 16 as is well-known in the art.

While specific embodiments of the present invention have been shown and described, it should be understood that many modifications thereof are possible. The use of the recirculating heat transfer liquid about a high heat of fusion material is a basic feature of the invention. This feature is incorporated in an uncomplicated system which is easy to operate and build at low cost with negligible safety problems. The systems are portable and have unlimited range with accurately controlled predictable endurance. No electrical hazards occur since the material 15 can be charged while the casing 11 is disconnected from the body protective suit if desired. The systems are completely self-contained, lightweight and portable.

It should be understood that the size, shape and dimensions of the various components recited can very greatly depending upon specific applications. Thus, in some cases the conduit arrangement about the container 16 can vary with coiled continuous tubing used or other configurations employed. Similarly, the containers 11 and 16 can be cylindrical, spherical, rectangular, octagonal and the like. While the tubing used for the conduit means in the recirculating closed fluid system is preferably metal within the container 11, por tions of the tubing leading to the body protective suit can be conventional flexible tubing of plastics, rubber and the like.