Stoves and furnaces – Heaters – Chemical
Reexamination Certificate
2001-08-29
2003-11-04
Bennett, Henry (Department: 3743)
Stoves and furnaces
Heaters
Chemical
C126S204000
Reexamination Certificate
active
06640801
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to heat packs, and more particularly to heat packs providing heat by exothermic chemical reactions.
BACKGROUND
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.
SUMMARY OF THE INVENTION
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 “running away”, 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, “zone” 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-f
Pitz Kevin J.
Sabin Cullen M.
Sabin Martin W.
Xiong Yan
Barrow James
Bennett Henry
Tempra Technology Inc.
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