Slow Cooking Heating Formula

Abstract

Chemical heating using a first reactant, a second reactant and a complexing agent adapted to complex reversibly with the first reactant and, thereby moderate the reaction between the first and second reactants. The heating formula is particularly well suited for heaters that are used to heat materials having relatively high viscosities.

Description

CROSS-REFERENCE TO RELATED APPLICATION(S)

[0001] This application claims the benefit of U.S. Provisional Application No. 60/685,134, filed May 27, 2005.

TECHNICAL FIELD

[0002] This disclosure relates to a heating formula and, more particularly to a slow cooking heating formula.

BACKGROUND

[0003] Single-use chemical heaters for heating objects, for example food and beverage items, and body parts are well known. One type of heater utilizes the exothermic reaction of a metal oxide, typically calcium oxide, and water to generate heat. U.S. Pat. No. 5,035,230 ("the '230 patent"), incorporated by reference herein in its entirety, discloses heaters utilizing the oxidation of primary or secondary alcohols by appropriate oxidizers to provide exothermic chemical reactions. Compounds of manganese and chromium are the most common oxidizing agents utilized. For primary alcohol fuels, such as glycerol or ethylene glycol, alkali metal permanganates are useful as oxidizing agents, generally in aqueous reactions. Water dilutes the fuel component and lowers the chemical reaction rate by reducing fuel-oxidizer contact. The '230 patent discloses embedding solid oxidizer particles, particularly particles of potassium permanganate, in a dissolvable binder, for example sodium silicate, to further reduce fuel-oxidizer contact for control of the rate of reaction.

[0004] PCT Publication No. WO 2005/108878 ("the '878 publication"), published Nov. 17, 2005, incorporated by reference, discloses a method of providing a releasable reaction suppressant composition, and in response to a selected temperature occurring at a product compartment, automatically releasing the suppressant composition into the reaction chamber, thereby suppressing the exothermic reaction.

[0005] U.S. Pat. No. 6,640,801 ("the '801 patent"), also incorporated by reference, discloses a flexible disposable heating device conformable to a shape defined by its surroundings. The heating device includes a first zone containing a fuel, a second zone containing an oxidizer and a collapsed third zone capable of serving as an expansion chamber. A first frangible separator is disposed between the first zone and the second zone, the first frangible separator being manually operable to provide communication there between, defining a reaction chamber comprising at least one of said first and second chambers. A second frangible separator is provided that is responsive to an exothermic chemical reaction within the reaction chamber. The second frangible separator is operable to provide vapor 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 capable of generating a vapor and an environmental parameter associated with the exothermic chemical reaction operates the second frangible separator, permitting said vapor to flow into said third zone, thereby reducing pressure in the reaction chamber.

SUMMARY OF THE INVENTION

[0006] This invention includes a heating formula, a portable, single-use chemical heater comprising the heating formula and heating methods utilizing the heating formula to modify reaction rate.

[0007] The heating formula provides for extended duration heating that may be useful, for example, for portable heating of food, beverage, and other items. The heating formula includes a fuel, an oxidizing agent and a complexing agent. The complexing agent reversibly complexes with the fuel. Portions of the complexed fuel are released over time in response to the decline in concentration of uncomplexed fuel as it is used up by the reaction. Controlled slow release is achieved by the type of complexing agent and amount (relative to fuel) of complexing agent. The duration of the reaction for a particular heater may be increased by adding more complexing agent. Such an arrangement may be helpful to provide a slower reaction of longer duration reaction to heat material with low thermal conductivity, such as pasta, stews, or cements. The longer duration permits more efficient and safe use of the heat energy supplied by a heater.

[0008] The methods disclosed herein include the addition of a fuel-complexing reagent to the reaction mixture of an oxidation/reduction exothermic reaction between a fuel and an oxidizing agent. In some implementations the fuel is an alcohol fuel, preferably a polyol such as glycerol or ethylene glycol. In some implementations the oxidizing agent is a compound of manganese or chromium, preferably an alkali metal permanganate, more preferably a solid oxidizer, and most preferably potassium permanganate particles coated with a dissolvable binder, preferably sodium silicate.

[0009] Preferred heaters include an oxidizer compartment, preferably containing solid, coated potassium permanganate, and a fuel compartment, preferably containing a liquid polyol such as aqueous glycerol, wherein a user initiates the reaction by compromising the separation of the compartments, permitting the reactants to come into contact, thereby initiating an exothermic chemical reaction. In certain implementations, heaters include a fuel-complexing agent in one of the compartments. For polyol fuels the complexing agent is a polyoxygenated ion such as borate, carbonate, nitrate, silicate, or sulfate, preferably boric acid or a borate, most preferably borax (Na.sub.2B.sub.2O.sub.7.10H.sub.2O). It is preferred to include the fuel-complexing agent in the fuel compartment. In certain implementations, heaters include a complexing agent adapted to reversibly complex with the oxidizer. An example of an oxidizer-complexing agent is a chelating agent, such as ethylenediaminetetraacetic acid (EDTA), which is generally adapted to complex with metal compounds.

[0010] In one aspect, a heating formula for a chemical heater is disclosed. The formula includes a first reactant, a second reactant and a complexing agent. The complexing agent is adapted to complex reversibly with at least a portion of the first reactant so as to progressively release the complexed first reactant over time as a concentration of uncomplexed first reactant decreases during an exothermic reaction with the second reactant.

[0011] In some implementations, the first reactant is an oxidizing agent and the second reactant is an alcohol fuel. In those implementations the complexing agent complexes reversibly with at least a portion of the fuel so as to progressively release complexed fuel over time as a concentration of uncomplexed fuel decreases during the exothermic reaction with the oxidizing agent.

[0012] In other implementations, the first reactant is an alcohol fuel and the second reactant is an oxidizing agent. In those implementations the complexing agent complexes reversibly with at least a portion of the oxidizing agent so as to progressively release complexed oxidizing agent over time as a concentration of uncomplexed oxidizing agent decreases during the exothermic reaction with the fuel.

[0013] According to certain implementations, the fuel is a polyol, for example, aqueous glycerol. The complexing agent can be boric acid, a borate or, more preferably, borax. Alternatively, the complexing agent can be carbonate, nitrate, silicate or sulfate.

[0014] Certain implementations include a complexing agent for the oxidizing agent that is a chelating agent, for example, ethylenediaminetetraacetic acid (EDTA).

[0015] In some implementations, a ratio of complexing agent to fuel is between 1:20 and 1:5. In some implementations, the ratio of complexing agent to fuel is between 1:100 and 1:1.

[0016] Some Implementations include an oxidizing agent of an alkali metal permanganate, such as potassium permanganate. The fuel and the complexing agent can form an aqueous solution. The fuel concentration can be between 24 wt. % and 84 wt. %. The fuel concentration can be between 34 wt. % and 44 wt. %.

[0017] In another aspect, a single-use chemical heater includes a disposable container with a first compartment and a second compartment. A first reactant is disposed in the first compartment and a second reactant is disposed in the second compartment. A separator is disposed between the first compartment and the second compartment. The separator is compromisable to provide fluid communication between the first compartment and the second compartment. Fluid communication initiates an exothermic chemical reaction between the first reactant and the second reactant within the container. A complexing agent that reversibly complexes with the first reactant is disposed in at least one of the first compartment and the second compartment.

[0018] In some implementations, the first reactant is an oxidizing agent and the second reactant is an alcohol fuel. In those implementations, the complexing agent complexes reversibly with at least a portion of the fuel so as to progressively release complexed fuel over time as a concentration of uncomplexed fuel decreases during the exothermic reaction with the oxidizing agent.

[0019] In some other implementations, the first reactant is an alcohol fuel and the second reactant is an oxidizing agent. In those implementations, the complexing agent complexes reversibly with at least a portion of the oxidizing agent so as to progressively release complexed oxidizing agent over time as a concentration of uncomplexed oxidizing agent decreases during the exothermic reaction with the fuel.

[0020] Yet another aspect includes a method of moderating a rate of heat generation from a single-use chemical heater operable by exothermic chemical reaction of a first reactant and a second reactant. The method includes including in the exothermic chemical reaction a complexing agent that complexes reversibly with at least a portion of the first reactant so as to release portions of the first reactant to react with the second reactant over time as a concentration of uncomplexed first reactant decreases during the reaction.

[0021] In some implementations, the first reactant is a fuel and the second reactant is an oxidizing agent. In those implementations, the complexing agent complexes reversibly with at least a portion of the fuel so as to release portions of the fuel to react with the oxidizer over time as a concentration of uncomplexed fuel decreases during the reaction.

[0022] According to other implementations, the first reactant is an oxidizing agent and the second reactant is a fuel. In those implementations, the complexing agent complexes reversibly with at least a portion of the oxidizing agent so as to release portions of the oxidizing agent to react with the fuel over time as a concentration of uncomplexed oxidizing agent decreases during the reaction.

[0023] In certain implementations, one or more of the following advantages may be present. A portable heater may be provided that is well suited for heating products having varying viscosities. The heater may be particularly well suited to heat relatively high viscosity fluids such as certain sauces, cement and the like. A heater is able to provide heating over an extended period of time. Additionally, the possibility that dangerous hot spots in such a heater might occur may be reduced.

[0024] Other features and advantages will be apparent from the descriptions, drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] FIG. 1 is a plan view of a heater.

[0026] FIG. 2 is a bowl that was used to conduct Experiments 1, 2 and 3.

[0027] FIG. 3 is a graph showing temperature profiles related to Examples 1, 2 and 3.

[0028] FIG. 4 is a bowl that was used to conduct Experiments 4 and 5.

DETAILED DESCRIPTION

[0029] This invention relates to a slow cooking heating formula and, more particularly one adapted to be used in a chemical heater. By "slow cooking" we mean an exothermic reaction whose rate of heat generation is slowed, in this case by a release mechanism wherein one of the reactants (e.g., fuel) already released into the reaction mechanism inhibits release of additional fuel into the reaction.

[0030] In one implementation, the slow cooking heating formula includes a fuel and an oxidizing agent adapted to react exothermically with the fuel. The slow cooking heating formula further includes a fuel-complexing agent. In some implementations, the complexing agent is adapted to affect the duration of the exothermic reaction. More particularly, the complexing agent may be adapted to extend the duration of the reaction and to regulate its intensity.

[0031] Without being bound by a particular theory, the following explanation for this phenomena is provided. It is believed that by adding to the fuel-oxidizer formula a complexing agent that reversibly complexes with the fuel, the amount of fuel available to react at any given time is effectively reduced. That is because the complexing agent complexes reversibly with the fuel so as to "tie up" a portion of fuel and thereby prevent it from reacting. The complexing agent does not itself react with the oxidizer. At any particular time during the reaction, it is believed that only uncomplexed portions of the fuel react with the oxidizer. Because the complex formation is reversible, as the uncomplexed fuel reacts with the oxidizing agent, the complexing agent releases "tied up" portions of fuel, thereby replenishing the supply of uncomplexed fuel available to react. It will be appreciated that reversible complex formation provides a means to tailor or adapt a single-use chemical heater to the ability of an object being heated to absorb heat so as to avoid excessively high temperature, thereby slowing heat generation as needed and providing slower and longer lasting heating. It is believed that an approximate balance is maintained between the complexed and uncomplexed fuel throughout the course of the reaction. Accordingly, by including a complexing agent in the heating formula, the intensity of heat generated by the reaction may be moderated and the length of time of that the reaction lasts may be extended.

[0032] The preferred complexing agent, borax, complexes with polyol fuel in a 1:1 mole ratio. However, it has been found that a much smaller ratio of complexing agent-to-fuel in the formula is sufficient to moderate and extend the reaction. In a preferred implementation, the complexing agent-to-fuel ratio is between 1:100 and 1:1. In another preferred implementation, the complexing agent to fuel ratio is between 1:20 and 1:5. The complexing agent typically is boric acid or a borate, and is preferably borax (Na.sub.2B.sub.4O.sub.7.10H.sub.2O).

[0033] In some implementations, the oxidizer is a compound of manganese or chromium. More preferably, the oxidizer is an alkali metal permanganate. Most preferably, the oxidizer is potassium permanganate. In a typical implementation, the oxidizer includes solid potassium permanganate particles dispersed throughout a dissolvable binder agent, preferably sodium silicate.

[0034] The fuel typically is an alcohol fuel. More preferably, the fuel is a polyol such as glycerol or ethylene glycol in a liquid state, preferably an aqueous solution. Our most preferred fuel is aqueous glycerol. The fuel concentration in the aqueous solution may be between 24% and 84%, based on weight, but preferably is between 34% and 44%, based on weight. In certain implementations, the fuel and the complexing agent are adapted to combine and form an aqueous solution. It is noted that other oxidizing agents and fuels may be suitable for use with the techniques disclosed herein.

[0035] In some implementations, the moderating ("slow cooking") heating formula is used in a disposable, single-use chemical heater of the type that operates on the principle of evolution of the heat of reaction between complementary pairs of chemical entities. An exemplary chemical heater includes a first compartment containing oxidizing agent, preferably solid, coated potassium permanganate, and a second compartment containing a fuel, preferably a liquid polyol such as aqueous glycerol. The chemical heater typically is configured so that a user can initiate a reaction by compromising the separation of the compartments, for example, turning a valve or compromising a frangible separator, thereby permitting the fuel and the oxidizing agent to come into contact with each other, initiating an exothermic chemical reaction. The complexing agent is initially provided in at least one of the compartments. For polyol fuels, a preferable complexing agent is boric acid or a borate, most preferably borax (Na.sub.2B.sub.4O.sub.7.10H.sub.2O). It is preferred that the complexing agent initially be provided in the fuel compartment. The complexing agent either is a liquid or dissolves in the fuel or aqueous fuel mixture.

[0036] An example of such a heater is shown in FIG. 1. This example is commonly known as a "heat pack." A heat pack typically comprises two plastic sheets. The illustrated heater has a container 1 formed by an upper sheet 2 and a lower sheet (not shown). The sheets are sealed together at the edges by edge seals 3, 4, 5, and 6. Heat or adhesive forms the edge seals, which preferably are made so that they are not readily opened by a user. A separator 7 is disposed from one edge seal of the heater 3 to another edge seal 5, thus dividing the heater 1 into a first compartment 8 and a second compartment 9. The separator 7, in this embodiment a frangible seal, is adapted to be compromised by a user to compromise separation of the components and establish fluid communication between the first compartment 8 and the second compartment 9. The heater's container is designed to include a space for vapor above the reactants when the heat pack is in use.

[0037] In some implementations, the first compartment 8 contains an aqueous solution of fuel and complexing agent and the second compartment 9 includes an oxidizing agent. Fuel in the first compartment 8 is complexed with the complexing agent so that only a portion of the fuel in the first compartment is uncomplexed. When a user compromises the separator 7, the aqueous solution containing fuel and complexing agent is permitted to flow into the second compartment 9 and to mix with the oxidizer. Uncomplexed portions of the fuel react with the oxidizing agent. As the uncomplexed portions of fuel react, complexed fuel is released essentially to replenish a supply of fuel to react with the oxidizing agent.

[0038] Reversible complexing of fuel can be represented by the formula

COMPLEX=FUEL+COMPLEXING AGENT.

[0039] It will be appreciated that as free FUEL on the right side of the formula decreases due to reaction, fuel is released from the COMPLEX to move the reaction toward equilibrium.

[0040] A number of implementations are disclosed herein. Adjustment by simple trial and error can be made to tailor a particular container/system to a product to be heated. Numerous modifications are possible. For example, a heater may be provided with multiple first and second compartments, with each compartment separated from adjacent compartment(s) by a valve or frangible separator. As another example, complexing agent may be provided in either one or both of the first and second compartments. Additionally, it is feasible that other fuels, oxidizing agents, binding agents and/or complexing agents may be utilized.

[0041] Also, complexing agent may be adapted to reversibly complex with the oxidizing agent. An example of such a complexing agent is a chelating agent, such as ethylenediaminetetraacetic acid (EDTA).

[0042] Additionally, the techniques disclosed herein may be implemented in conjunction with any combination of the techniques and devices for controlled single-use chemical heaters. For example, in preferred implementations, a heater formulation may include a solid oxidizer embedded in or coated with dissolvable binding agent as is disclosed in U.S. Pat. No. 5,035,230. The heat packs disclosed in the '230 patent have separate zones of two types. One zone type contains a dry reactant, i.e., short cylinders comprising potassium permanganate crystals within a sodium silicate binding agent. The other zone type contains an glycerol/water solution, which serves as a fuel mixture. In certain implementations, the fuel serves as a solvent, eliminating the need for a separate solvent. The two types of zones are separated, for example, by a frangible seal that is meant for single use. When the frangible seal between the two zones is ruptured, the fuel solution flows to the oxidizing agent pellets and reaction occurs. The rate of reaction, and hence the rate of heat production, is moderated by the rate of dissolution of the binding agent, as dissolution is required to expose the oxidizer to the fuel. The formula and methods disclosed herein could be readily incorporated into the heat packs of the '230 patent.

[0043] In some implementations, a heater may include preformed stiffenable gel as disclosed in the U.S. Pat. No. 5,984,953. The heat packs disclosed in the '953 patent also utilize an exothermic oxidation/reduction chemical reaction. In those heat packs, a dissolvable binding agent was utilized. Additionally, a preformed stiffenable gel was provided to affect the rate of reaction. By adjustment of these two rate-controlling features, persons skilled in the art would have been able to select and achieve rates of temperature rise and operating temperature in heat packs. By implementing stiffenable gel, the modulation of the exothermic chemical reactions takes place through certain reversible physical changes of the reaction medium in order to produce the self-regulating effects desired in the heat packs of the invention. Modulation helps prevent the exothermic chemical reaction from raising the operating temperature of the heat pack above a predetermined maximum temperature. Modulation also acts to increase the rate of an ongoing exothermic reaction when the container temperature falls low enough to reverse the physical changes of the reaction medium. The formula and methods disclosed herein could be readily incorporated into the heat packs of the '953 patent.

[0044] In some implementations, a heater may include a releasable reaction suppressant to guard against high-temperature exotherms as disclosed in the '878 publication. The methods disclosed in the '878 publication include providing a container with a releasable reaction suppressant composition, and in response to a selected temperature occurring at the product compartment, automatically releasing the suppressant composition into the reaction chamber, thereby suppressing the exothermic reaction. In some implementations, the suppressant composition includes water. The formula and methods disclosed herein could be readily adapted to the disclosure of the '878 publication.

[0045] In some implementations a heater may include an expansion chamber as disclosed in the '801 patent. The '801 patent discloses a flexible disposable heating device conformable to a shape defined by its surroundings. The heating device includes a first zone containing a fuel, a second zone containing an oxidizer and a collapsed third zone capable of serving as an expansion chamber. A first frangible separator is disposed between the first zone and the second zone, the first frangible separator being manually operable to provide communication therebetween, defining a reaction chamber comprising at least one of said first and second chambers. A second frangible separator is provided that is responsive to an exothermic chemical reaction within the reaction chamber. The second frangible separator is operable to provide vapor 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 capable of generating a vapor and an environmental parameter associated with the exothermic chemical reaction operates the second frangible separator, permitting said vapor to flow into said third zone, thereby reducing pressure in the reaction chamber. The formula and methods disclosed herein could readily be incorporated into the heating devices of the '801 patent.

EXAMPLES

Example 1

[0046] FIG. 2 illustrates a prototype heater assembly that was used to conduct the experimental work reported in this example.

[0047] The illustrated assembly includes a pair of nested circular bowls, a 14 cm diameter.times.5 cm deep inner (or upper) plastic bowl 21 nested in a 14 cm diameter.times.7 cm deep outer (or bottom) plastic bowl 22, leaving an approximately 2 cm annular clearance gap 24 between the top bowl 21 and the bottom bowl 22. Several vents 11 were provided to allow the escape of vapor/steam from the clearance area.

[0048] Forty-five grams of coated potassium permanganate crystals 23 were placed in the bottom of outer bowl 22, residing in the clearance gap. The potassium permanganate crystals were coated with a water-soluble barrier coating, so that potassium permanganate crystals would not react until the coating was dissolved. The soluble barrier coating was a sodium silicate.

[0049] The coated potassium permanganate 23 was a mixture of crystals having coatings having various thickness. In particular, 25% of the potassium permanganate powder had a coating of 14% by weight, 30% of the potassium permanganate powder had a coating of 17% by weight, and 45% of the potassium permanganate powder had a coating of 20% by weight. Three hundred milliliters of water 24 were placed in the inner bowl 21 to serve as the product to be heated. Thermocouples were placed in the water in the top bowl 21 and in the potassium permanganate powder 23 in the bottom bowl 22.

[0050] To achieve functionally what would happen if liquid fuel were released from a separate compartment by breaking a seal or opening a valve, approximately 70 ml of an aqueous solution of 38.2 wt. % glycerol was added to the bottom bowl 22 specifically to the gap containing oxidizer 23, via the vents 11. The glycerol reacted exothermically with the potassium permanganate powder 23 and produced steam, which heated the water 24 in the top bowl 21.

[0051] FIG. 3 shows temperature profiles for the water (indicated by curve "D") and the reactants (indicated by curve "A") for several minutes following the addition of glycerol to the bottom bowl 23. Curve "D" indicates that the temperature of the water increased from about 21.degree. C. to about 64.degree. C. in approximately 6 minutes. Curve "A" indicates that the temperature of the reactants began decreasing after about 6 minutes.

Example 2

[0052] The test of Example 1 was repeated using a complexed fuel according to this invention. The heater assembly of FIG. 2 was used in this Example.

[0053] Forty-five grams of the same coated potassium permanganate powder 23 as used in Example 1 were placed in the bottom bowl 22. Three hundred milliliters of water 24 were placed in the top bowl 21. Thermocouples were placed in the water 24 and in the coated potassium permanganate 23 in the bottom bowl 22. Seventy milliliters of an aqueous solution of 37.9 wt. % glycerol and 0.9 wt. % borax (Na.sub.2B.sub.4O.sub.7.10H.sub.2O) was added to the bottom bowl 22. The glycerol reacted with the potassium permanganate and produced steam.

[0054] FIG. 3 shows temperature profiles for the water 24 (indicated by curve "E") and the reactants (indicated by curve "B") for several minutes following the addition of glycerol to the bottom bowl 22. Curve "E" indicates that the temperature of the water increased from about 21.degree. C. to about 64.degree. C. in approximately 6 minutes. Curve "B" indicates that the temperature of the reactants 2 began decreasing after about 7 minutes, representing a prolongation of heating at maximum temperature by about one minute or about 17%.

Example 3

[0055] The test of Example 1 was again repeated, this time using a more heavily complexed fuel according to this invention. The assembly of FIG. 2 was used in this Example.

[0056] Forty-five grams of the same coated potassium permanganate powder as used in Examples 1 and 2 were placed in the bottom bowl 22. Three hundred milliliters of water were placed in the top bowl 21. Thermocouples were placed in the water and in the coated potassium permanganate powder 23. Seventy milliliters of an aqueous solution of 37.4 wt. % glycerol and 2.2 wt. % borax was added to the bottom bowl 22. The glycerol reacted with the permanganate and produced steam.

[0057] FIG. 3 shows temperature profiles for the water (indicated by curve "F") and the reactants (indicated by curve "C"). Curve "F" indicates that the temperature of the water increased from about 21.degree. C. to about 64.degree. C. in approximately 8 minutes, some two minutes or one-third slower than Example 1. Curve "C" indicates that the temperature of the reactants began decreasing after about 8 minutes.

[0058] In view of the above examples, it can be appreciated that by adding progressively higher amounts of complexing agent, in this embodiment by progressively increasing the concentration of borax in the heating formulas, the rate of the exothermic reaction can be slowed and the duration of the reaction can be progressively extended. In Example 1 (no borax), the temperature of the reactants began decreasing after about 6 minutes. In Example 2 (0.9% borax), the temperature of the reactants began decreasing after about 7 minutes. Finally, in Example 3 (2.2% borax), the temperature of the reactants began decreasing only after about 8 minutes.

[0059] It also is noted that, Examples 1, 2 and 3 illustrate that the heating rate of the water in Examples 1, 2 and 3 (curves 4, 5 and 6, respectively) varied depending on the amount of borax complexing agent added to the heating formula. For example, in Examples 1 and 2 (no borax and 0.9% borax, respectively), the time required to heat the water from about 21.degree. C. to about 64.degree. C. was about 6 minutes. However, in Example 3 (2.2% borax), the time required to heat the water from about 21.degree. C. to about 64.degree. C. was about 8 minutes.

[0060] The above examples illustrate certain ways in which temperature profiles associated with exothermic chemical reactions and the products being heated by those reactions can be altered by adding borax to the reactants.

[0061] In some implementations it may be desirable to add more or less borax to a heating formula depending on characteristics of the product intended being heated. For example, for higher viscosity products (e.g., stew or oatmeal), it might be desirable to add more borax to the heating formula. That is because higher viscosity products do not enjoy the same benefits associated with convection heating currents as do lower viscosity products. Since fewer connection currents flow in high viscosity products, it may be desirable to extend the duration of a reaction. By extending the duration of the reaction, it might be possible to more fully heat the highly viscous product.

[0062] On the other hand, for lower viscosity products (e.g., coffee or tea), it might be desirable to add less borax to the heating formula. That is because convection aids in distributing heat throughout lower viscosity products. Accordingly, a shorter duration of reaction time may be suitable to heat such products.

[0063] FIG. 4 illustrates a heater assembly that was used to conduct the tests reported in Examples 4 and 5.

[0064] The illustrated assembly includes a pair of rectangularly shaped pans or trays, a 29 cm.times.23 cm.times.5 cm plastic top or inner tray 41 that was nested in a 29 cm.times.23 cm plastic bottom or outer tray 42, leaving an approximately 3 cm clearance gap 45 between the top tray 41 and the bottom tray 42. Clearance gap 45 extended cross the tray bottoms and up their vertical sides. A vent 43 also was provided in outer tray 42 to vent the space 45 between the top tray and the bottom tray.

Example 4

[0065] Five hundred grams of the coated potassium permanganate powder was placed in the bottom tray 42. Twenty-seven hundred milliliters of water was placed in the top tray 41 as the product to be heated. Thermocouples were placed in the water in the top tray 41 and in the potassium permanganate powder in the bottom tray 42.

[0066] Seven hundred milliliters of an aqueous solution including 29.2% glycerol and 0.2% of Dow Corning H-10 silicone antifoam emulsion was added to the bottom tray 42. The aqueous solution included no complexing agent. The glycerol reacted with the potassium permanganate and produced steam. Steam was allowed to vent through the vent 43 throughout the duration of the reaction. The reactants reached a maximum temperature of 119.degree. C. The steam heated the water in the top tray 41 from an initial temperature of about 21.degree. C. to a final temperature of about 66.degree. C. in approximately 21 minutes. Therefore, the average heating rate was:

(66.degree. C.-21.degree. C.)/21 min=2.1.degree. C./min.

Example 5

[0067] Five hundred grams of coated potassium permanganate powder (similar to the coated potassium permanganate powder 44 described with reference to Example 1) were placed in the bottom tray 42. Twenty-seven hundred milliliters of water were placed in the top tray 41 to act as the product to be heated. Thermocouples were placed in the water in the top tray 41 and in the potassium permanganate powder in the bottom tray 42.

[0068] Six hundred milliliters of an aqueous solution of 33.5% glycerol, 3.2% borax, and 0.2% of Dow Corning H-10 silicone antifoam emulsion was added to the bottom tray 42. The glycerol reacted with the potassium permanganate and produced steam. The steam was allowed to escape through the vent 43 throughout the duration of the reaction. The reactants reached a maximum temperature of about 107.degree. C. The steam heated the water in the top tray 41 from an initial temperature of about 21.degree. C. to a final temperature of about 69.degree. C. in approximately 23 minutes. Therefore, the average heating rate for the water was:

(69.degree. C.-21.degree. C.)/23 min=2.1.degree. C./min.

[0069] While the heating rate and final water temperature for Example 4 were similar to that of Example 5, the reactor temperature was hotter, indicating that a more significant amount of steam was lost through the vent 43 in Example 4 than in Example 5. Vented steam, of course, represents wasted heat, which was reduced in Example 5.

[0070] Other implementations are within the scope of the following claims.

Claims

1. A heating formula for a chemical heater, the formula comprising: a first reactant; a second reactant; and a complexing agent that complexes reversibly with at least a portion of the first reactant so as to progressively release the complexed first reactant over time as a concentration of uncomplexed first reactant decreases during an exothermic reaction with the second reactant.

2. The heating formula of claim 1, wherein: the first reactant is an oxidizing agent; the second reactant is an alcohol fuel; and the complexing agent complexes reversibly with at least a portion of the fuel so as to progressively release complexed fuel over time as a concentration of uncomplexed fuel decreases during the exothermic reaction with the oxidizing agent.

3. The heating formula of claim 1, wherein: the first reactant is an alcohol fuel; the second reactant is an oxidizing agent; and the complexing agent complexes reversibly with at least a portion of the oxidizing agent so as to progressively release complexed oxidizing agent over time as a concentration of uncomplexed oxidizing agent decreases during the exothermic reaction with the fuel.

4. The heating formula of claim 2 wherein the fuel comprises a polyol.

5. The heating formula of claim 4 wherein the fuel comprises aqueous glycerol.

6. The heating formula of claim 2 wherein the complexing agent comprises boric acid or a borate.

7. The heating formula of claim 6 wherein the complexing agent comprises borax.

8. The heating formula of claim 2 wherein the complexing agent is selected from the group consisting of carbonate, nitrate, silicate and sulfate.

9. The heating formula of claim 3 wherein the complexing agent comprises a chelating agent.

10. The heating formula of claim 9 wherein the complexing agent comprises ethylenediaminetetraacetic acid (EDTA).

11. The heating formula of claim 2 wherein a ratio of complexing agent to fuel is between 1:20 and 1:5.

12. The heating formula of claim 2 wherein a ratio of complexing agent to fuel is between 1:100 and 1:1.

13. The heating formula of claim 2 wherein the oxidizing agent comprises an alkali metal permanganate.

14. The heating formula of claim 13 wherein the oxidizing agent comprises potassium permanganate.

15. The heating formula of claim 2 wherein the fuel and the complexing agent comprise an aqueous solution.

16. The heating formula of claim 2 wherein the fuel concentration is between 24 wt. % and 84 wt. %.

17. The heating formula of claim 2 wherein the fuel concentration is between 34 wt. % and 44 wt. %.

18. A single-use chemical heater comprising: a disposable container comprising a first compartment and a second compartment; a first reactant disposed in the first compartment; a second reactant disposed in the second compartment; a separator disposed between the first compartment and the second compartment, wherein the separator is compromisable to provide fluid communication between the first compartment and the second compartment, wherein the fluid communication initiates an exothermic chemical reaction between the first reactant and the second reactant within the container; and disposed in at least one of the first compartment and the second compartment, a complexing agent that reversibly complexes with the first reactant.

19. The heater of claim 18, wherein: the first reactant is an oxidizing agent; the second reactant is an alcohol fuel; and the complexing agent complexes reversibly with at least a portion of the fuel so as to progressively release complexed fuel over time as a concentration of uncomplexed fuel decreases during the exothermic reaction with the oxidizing agent.

20. The heater of claim 18, wherein: the first reactant is an alcohol fuel; the second reactant is an oxidizing agent; and the complexing agent complexes reversibly with at least a portion of the oxidizing agent so as to progressively release complexed oxidizing agent over time as a concentration of uncomplexed oxidizing agent decreases during the exothermic reaction with the fuel.

21. The heater of claim 19 wherein the first compartment contains aqueous polyol fuel, a portion of which is complexed with a borax fuel-complexing agent.

22. The heater of claim 21 wherein the aqueous polyol fuel comprises glycerol.

23. The heater of claim 19 wherein a ratio of complexing agent to fuel is between 1:20 and 1:5.

24. The heater of claim 19 wherein a ratio of complexing agent to fuel is between 1:100 and 1:1.

25. The heater of claim 19 wherein the fuel concentration is between 34 wt. % and 44 wt. %.

26. The heater of claim 19 wherein the fuel concentration is between 24 wt. % and 84 wt. %.

27. The heater of claim 19 wherein the fuel-complexing agent comprises boric acid or borate.

28. The heater of claim 27 wherein the fuel-complexing agent comprises borax.

29. The heater of claim 22 wherein the fuel-complexing agent is selected from the group consisting of carbonate, nitrate, silicate and sulfate.

30. The heater of claim 20 wherein the complexing agent comprises a chelating agent.

31. The heater of claim 20 wherein the complexing agent comprises ethylenediaminetetraacetic acid (EDTA).

32. The heater of claim 19 wherein the oxidizing agent comprises sodium silicate-coated potassium permanganate.

33. A method of moderating a rate of heat generation from a single-use chemical heater operable by exothermic chemical reaction of a first reactant and a second reactant, the method comprising: including in the exothermic chemical reaction a complexing agent that complexes reversibly with at least a portion of the first reactant so as to release portions of the first reactant to react with the second reactant over time as a concentration of uncomplexed first reactant decreases during the reaction.

34. The method of claim 33 wherein the first reactant is a fuel and the second reactant is an oxidizing agent, wherein the complexing agent complexes reversibly with at least a portion of the fuel so as to release portions of the fuel to react with the oxidizer over time as a concentration of uncomplexed fuel decreases during the reaction.

35. The method of claim 33 wherein the first reactant is an oxidizing agent and the second reactant is a fuel, wherein the complexing agent complexes reversibly with at least a portion of the oxidizing agent so as to release portions of the oxidizing agent to react with the fuel over time as a concentration of uncomplexed oxidizing agent decreases during the reaction.

36. The method of claim 34 wherein the complexing agent comprises boric acid or a borate.

37. The method of claim 34 wherein the fuel is a polyhydroxol compound and the complexing agent is borax.

38. The method of claim 34 wherein the complexing agent is selected from the group consisting of carbonate, nitrate, silicate and sulfate.

39. The method of claim 34 wherein the fuel is aqueous glycerol.

40. The method of claim 34 wherein the fuel concentration is between 34 wt. % and 44 wt. %.

41. The method of claim 34 wherein the fuel concentration is between 24 wt. % and 84 wt. %.

42. The method of claim 34 wherein the ratio of complexing agent to fuel is between 1:20 and 1:5.

43. The method of claim 34 wherein the oxidizing agent is potassium permanganate.

44. The heating formula of claim 3 wherein the fuel comprises a polyol.

45. The heating formula of claim 3 wherein the oxidizing agent comprises an alkali metal permanganate.

46. The heating formula of claim 3 wherein the fuel and the complexing agent comprise an aqueous solution.