The invention relates to heat packs, and more particularly to heat packs providing heat by exothermic chemical reactions.
Compact, self-heating devices that produce heat through exothermic chemical reactions are known in the art. For example, U.S. Pat. No. 4,397,315, Patel discloses a device having an outer envelope and an inner envelope, with the outer envelope containing sodium thiosulfate and the inner envelope containing ethylene glycol. The walls of the inner envelope are rupturable, allowing the contents of each envelope to mix.
U.S. Pat. No. 5,035,230, Steidl et al. discloses a heat pack having two compartments separated by a frangible seal. Potassium permanganate oxidizing agent coated with sodium silicate is provided in one zone of the heat pack, and aqueous ethylene glycol fuel is provided in the other zone. In operation of the device, the seal is compromised to allow the reactants to come in contact with each other.
U.S. Pat. No. 5,984,953, Sabin et al. discloses a disposable heat pack utilizing an exothermic chemical reaction. Moderation of the reaction is provided through the use of a preformed reversibly stiffenable gel that can be used to alter the rate of the exothermic chemical reaction.
U.S. Pat. No. 6,116,231, Sabin et al. discloses a liquid heat pack utilizing an exothermic chemical reaction to produce heat. Moderation of the reaction is provided by the use of a gelling agent, which can also give structural rigidity to the heat pack.
Heat packs of the types disclosed by Steidl et al. and Sabin et al., for example, have the potential to generate steam, if heat transfer to the heated subject is insufficiently rapid to prevent excessive temperature increase. Inasmuch as steam generation causes swelling and potentially could lead to rupture, such heaters are designed and sized to avoid excessive temperature. That, however, places limits on the range of conditions and applications under which the heater can operate.
An aspect of this invention is a disposable heater that is at once useful over a broader range of conditions yet is compact.
Another aspect of this invention is a disposable heater with improved robustness that provides the needed amounts of heat and temperature rise for a demanding application without xe2x80x9crunning awayxe2x80x9d, that is, generating excessive pressure and temperature, when used in considerably less demanding application or situation. Thus, for example, the same disposable heater can be used for objects requiring a substantially different amount of heat or for heating under widely varying conditions, such as in the tropics and in winter conditions. In one broad aspect, a disposable heating device is disclosed that includes a container having a first zone, a second zone and a third zone. As used herein, xe2x80x9czonexe2x80x9d means at least one chamber or compartment, and will be understood to include a plurality thereof. A fuel is contained within the first zone and an oxidizing agent is contained within the second zone. A first frangible separator is disposed between the first zone and the second zone. The first frangible separator is manually operable to provide communication between the first zone and the second zone thereby defining a reaction chamber or zone. A second frangible separator is responsive to an exothermic chemical reaction within the reaction chamber. The second frangible separator is operable to provide communication between the reaction chamber and the third zone. Communication between the first zone and the second zone allows mixing of the fuel and the oxidizing agent to initiate an exothermic chemical reaction. An environmental parameter associated with the exothermic chemical reaction operates the second frangible separator. The environmental parameter associated with the exothermic chemical reaction can be, for example, an elevated temperature or an elevated pressure or a combination of the two of them. The heater is designed such that, under most conditions of intended use, the second frangible separator will not be compromised. However, when there is a relatively very low rate of heat transfer out of the device, the second frangible separator will be compromised, thereby permitting steam to escape from the reaction chamber into the third zone. This removes water from the reaction chamber, slows dissolution of at least one reactant, and moderates the exothermic reaction. Simultaneously there is created another heat-transmitting zone to increase heat transfer and thereby moderate temperature rise. In some embodiments the additional heat transfer may be to the object being heated. In other embodiments the additional heat transfer may be to the surrounding environment, as persons skilled in the art can readily design. For embodiments of either type, the heating device may include a heat sink thermally coupled to the third zone. A preferred heat sink is a phase change material. If desired, the phase change material can be thermally coupled to the object being heated so as to prolong the time of heating. Preferably the third zone is an expandable zone that balloons when the second frangible seal is compromised so that prior to use and under most conditions of use the third zone occupies minimal space. The control provided by the third zone can be used in conjunction with other controls. Preferably the latter are sufficient to prevent compromise of the second frangible seal under almost all conditions. For example, the disposable heating device may also include a non-fuel gelling agent solution in at least one of the zones, wherein communication between the gelling agent and the reaction chamber initiates gelation of the gelling agent to produce a non-fuel gel that moderates the rate of the reaction independently of dissolution of the gelling agent. A sufficient amount of gelling agent may be provided to produce gel rapidly enough to prevent a temperature associated with the exothermic chemical reaction from exceeding a predetermined maximum value under expected conditions. Embodiments of the disposable heating device of this invention include a preformed stiffenable gel and a vaporizable solvent in the first zone. Oxidizing agent may be embedded and dispersed throughout the second zone in a dissolvable binding agent that dissolves during the exothermic chemical reaction to controllably expose the oxidizing agent at a predetermined rate. The vaporizable solvent may be selected to vaporize when a temperature associated with the exothermic chemical reaction reaches a predetermined maximum value, thereby causing stiffening of the gel to moderate the exothermic chemical reaction. A sufficient amount of preformed stiffenable gel may be included so as to prevent the temperature associated with the exothermic chemical reaction from exceeding the predetermined maximum value in most cases.
As stated earlier, the disposable heating device may include a plurality of compartments as the first zone and/or a plurality of compartments as the second zone. The disposable heating device can be conformable to a shape defined by its surroundings. In preferred embodiments, the material from which the device is constructed is resistant to the exothermic chemical reaction. The material can be, for example, a polymeric material. The exothermic chemical reaction can be a reduction-oxidation type of reaction. The oxidizing agent can be potassium permanganate and the fuel can be an oxidizable organic compound. The disposable heating device can include a valve coupled to the container and operable to provide communication between either the first zone, the second zone, or the third zone and atmosphere. The valve can be responsive to at least one of either temperature or pressure. The disposable heating device can be of modular construction, including two or more complete heating-device modules physically connected as a single unit, wherein each module is isolated from an adjacent module by a separator disposed there between. The second frangible separator can include frangible portions and securely sealed (non-frangible) portions, which may be aligned in an alternating pattern. Where multiple first frangible separators are used, each can be independently operable. The first zone and the second zone can be in thermal contact with a product to be heated, such as food, drink, with a body part of a surgical patient or of a patient undergoing therapy, or with an article of clothing or footwear.
In another broad aspect, a disposable heating device is disclosed that includes a flexible upper sheet, a flexible lower sheet attached to the upper sheet at edges thereby defining a compartment. A manually operable first frangible separator is disposed within the compartment to define a first zone containing a fuel and a second zone containing an oxidizing agent. A second frangible separator, responsive to an exothermic chemical reaction, is disposed within the compartment to provide an interface between at least one of either the first zone or the second zone and a third zone. Manual operation of the first frangible separator allows communication between the first zone and the second zone to create a reaction zone and to initiate an exothermic chemical reaction. The exothermic chemical reaction operates the second frangible separator to provide communication between the reaction zone (at least one of either the first zone or the second zone) and the third zone. Operation of the second frangible separator can be in response to, for example, an elevated pressure or an elevated temperature associated with the exothermic chemical reaction. The upper sheet and the lower sheet can each be conformable to a shape defined by their surroundings. The upper sheet and the lower sheet can be fabricated using a material that is resistant to the exothermic chemical reaction, for example, a polymeric material. The first zone and the second zone can be in thermal contact with a product to be heated. Gelling agents, preformed gels, or heat sink material can be included, as discussed above. The second frangible separator can include a plurality of frangible portions and a plurality of non-frangible portions. The frangible portions and non-frangible portions can be linearly aligned in an alternating manner across the second frangible separator.
In yet another broad aspect, a disposable heating device is disclosed that includes a reaction chamber defining an initial internal volume for initiating an exothermic chemical reaction therein, an expansion chamber adjacent to the reaction chamber and a frangible seal disposed between the reaction chamber and the expansion chamber, the frangible seal being operable in response to the exothermic chemical reaction. Operation of the frangible seal establishes communication between the reaction chamber (in preferred embodiments, the reaction chamber is created through combining a first zone and a second zone) and the expansion chamber thereby defining an increased internal volume for containing the exothermic chemical reaction. Operation of the frangible seal causes a reduction of pressure associated with the exothermic chemical reaction. The increased internal volume through the addition of the third zone can be 101% to approximately 200% greater than the initial internal volume or, preferably, approximately 110% to 150% and even more preferably 125% to 150% greater than the initial internal volume. The frangible seal can be operable in response to an elevated temperature associated with the exothermic chemical reaction. The frangible seal can be operable in response to an elevated pressure associated with the exothermic chemical reaction. A heat sink can be provided within, or, in thermal contact with, the expansion chamber (i.e., the third zone). A valve can be coupled to the reaction chamber, the valve being responsive to at least one of either pressure or temperature, and being operable to provide communication between the reaction chamber and atmosphere.
In still another broad aspect, a method of heating a product is disclosed that includes providing a heating device in thermal contact with the product and compromising a first frangible separator to establish communication between a first zone and a second zone, thereby initiating an exothermic chemical reaction therein and subsequent heating of the product. The heating device comprises a container having a first zone, a second zone and a third zone. A fuel is contained within the first zone, and an oxidizing agent is contained within the second zone. A first frangible separator is disposed between the first zone and the second zone, the first frangible separator being manually operable to provide communication between the first zone and the second zone. A second frangible separator, responsive to temperature and/or pressure, is operable to provide communication either between the third zone and the first zone, the second zone, or both. Communication between the first zone and the second zone allows mixing of the fuel and the oxidizing agent to create an exothermic chemical reaction generating vapor in the first zone and the second zone. A pressure and a temperature associated with generating the vapor operates the second frangible separator to allow the vapor to move into the third zone. The product to be heated can be, for example, food, drink, a body part of a surgical patient, clothing or footwear. The heating device also can include a plurality of containers, as described above, and the method can further include compromising at least one additional first frangible separator to initiate a second exothermic chemical reaction.
Depending on the embodiment selected, one or more of the following advantages may be realized. In all cases, rupture of the heat pack is avoided, and volumetric expansion is controlled both by moderation of the exothermic chemical reaction and increased transfer of heat out of the device. In cases in which the area available for transfer of heat to the object to be heated is limited, heating efficiency is improved by providing a third zone that discharges heat to the environment but does not contain reactants. Less reactant is needed. Heat packs can be designed to generate heat faster under maximum intended load without risking rupture under a much lower load. Heat packs can be made smaller by providing the third zone in a collapsed state. In some implementations, the third zone can be thermally coupled to the product to be heated. In other implementations, the third zone can be thermally isolated from the product to be heated.
The invention is in similar fields as inventions described in and claimed by, for example, U.S. Pat. No. 5,035,230, Steidl et al., U.S. Pat. No. 5,984,953, Sabin et al., and U.S. Pat. No. 6,116,231, Sabin et al., each of which is incorporated by reference in their entirety.
As used herein, the following definitions should be understood in such a manner so as not to limit the scope of the application. The term xe2x80x9cexpansionxe2x80x9d used with reference to heat packs should be understood to include swelling of heat packs and increases in internal volume associated with particular compartments of heat packs. The term xe2x80x9crun awayxe2x80x9d is used to describe any uncontrolled event or any event that might result in an unexpected or undesirable outcome. The term xe2x80x9cenvironmental parameterxe2x80x9d should be understood to include temperature, pressure, a combination of temperature and pressure, or volumetric expansion. The phrase xe2x80x9cstaticxe2x80x9d is used to describe a heat pack that has not been activated (i.e., its first frangible separator has not been compromised).
All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification will control. In addition, the apparatus, methods, and techniques described herein are illustrative only and are not intended to be limiting. The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.