Abstract:
A field-ready oven has reinforced telescoped side walls that extend and hold a base, shelf, tray support and cover spaced apart. A low air intake and a semipermeable membrane deliver air and vapor fuel to catalyst pads on the shelf. Radiant heat from exothermic reaction is diffused over a bottom of a tray. Hot gas circulates around the diffuser and tray with a chimney effect before exhausting. A lid on the cover lifts for access to the tray. A fuel container in the oven forces fuel through a capillary restriction to limit fuel flow. A spring in the container is released to start fuel flow.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a divisional of Ser. No. 13/045,311, filed Mar. 10, 2011, which application is herein incorporated by reference in its entirety for all purposes. 
     
    
     SUMMARY OF THE INVENTION 
       [0002]    One embodiment is a portable, disposable oven consisting of food in a tray supported above one or more flameless catalytic burner(s). Fuel vapor and oxygen from air flow produce a flameless exothermic chemical reaction at a catalyst. Radiant heat may be diffused to uniformity for the food tray by a heat diffuser. Hot exhaust gases pass between the burner and the food tray, around the sides of the food tray, up and over the top of the food tray and out through one or more exhaust vent(s). 
         [0003]    One embodiment of the device has the following elements. Food tray containing food to be heated, a heat diffuser, food tray support, catalytic heating assembly, fuel container, fuel motivator (to move the fuel to the heater assembly) the fueling transfer system (pipes hoses, etc.), initiation system (may consist of one or more items such as a valve to allow the fuel to begin, a means of initiating the fuel motivator, exposing the catalyst to oxygen, etc.), and the container which performs many functions in addition to storing and transporting the device. 
         [0004]    The food tray can be made of any number of materials. Some are made of aluminum, while others are made of plastic. Each material has its own advantages and disadvantages. In one embodiment the food is sealed into the food tray for storage and heating. 
         [0005]    When using a catalytic heating device it is necessary to provide an air gap between the catalytic heater assembly and the food tray to allow oxygen rich air to reach the combustion area. Therefore some means of supporting the food tray above the catalytic heater assembly is required. This can be as simple as providing one or more ledges on which a lip on the food tray can rest. Another embodiment involves a course wire metal mesh formed in such a way as to support the food tray. 
         [0006]    When a support frame is used to support the food tray, it can additionally be used for several other purposes. It can have portions which protrude downward to additionally support and ensure a given gap between the food tray and the heater assembly(s) and other components. It can also be used to hold the heat diffuser in place. Additionally the support frame could be a heat diffuser in and of itself which could either totally eliminate the need for a separate heat diffuser or allow the heat diffuser to be smaller or in some other way modified in design which may be desirable. 
         [0007]    The food tray could be a proprietary design or, more likely, an existing design. Food and plastic are all subject to scorching, burning, and or melting when exposed to excessive heat. In order to ensure that the heat is not too concentrated over the catalytic heater assembly one embodiment includes a heat diffuser. One material which is good for this component is aluminum, especially if painted, anodized, or in some other way darkened. It works as a radiant heat barrier to reduce the direct radiant heat transfer as well as conducts heat well throughout the aluminum body to spread the heat out over a larger surface area allowing more heat energy to be transferred into the food tray at lower temperatures reducing overheating is isolated areas. The dark color aids in its ability to absorb radiant heat. 
         [0008]    Additionally the heat diffuser can have an amount of water or other heat absorbing material held on it. If the material is a phase change material, such as water which will change phase from a liquid to a gas, or a paraffin which will change from a solid to a liquid at these temperatures, it will assist in reducing hot spots and spreading heat more evenly. Each of these materials is inserted between the heat diffuser and the food tray or between the heat diffuser and the heat source. This added material could also be infused with a scent so that the heating process would release a pleasant smell. The use of a binder or pouch to hold the material in place if it is or may be in liquid from before use may be needed. One such embodiment includes the use of a product called dry water which is a relatively dry powder which contains water within it, which is released upon heating. We may want to allow the heating process to release the water or we may want to release the water before, at the same time as, or after, the start of the unit. 
         [0009]    The catalytic heater assembly is comprised of one or more catalysts above a semipermeable or porous membrane above a cavity with one or more openings in which fuel enters. In this way the liquid fuel enters the cavity. The only path for the fuel to exit the assembly is through the catalyst. However, mostly fuel vapor can pass through the membrane. The fuel vapor is conducive to combustion. Once the heater is started some of the heat from the combustion will heat the bottom of the cavity. Once the boiling point of the fuel is reached incoming fuel will be vaporized and only vapor fuel should exit through the membrane and the catalyst. The fuel vapor then meets the air at the surface of the catalyst which encourages an exothermic chemical reaction between the fuel and the oxygen in the air, a flameless catalytic combustion. The heat from this reaction transfers to the food via radiant, convective and conductive means. 
         [0010]    The fuel can be any number of fuels which combust on a catalyst. These can include, but are not limited to, methyl alcohol, ethyl alcohol, hydrogen, etc. 
         [0011]    The fuel container design is specific to the fuel being used. When alcohol is used as the fuel a fuel container made of polypropylene or polyethylene is preferable to many other materials. This container can have a mechanism to pressurize the fuel as an integral part of its design. As one example the fuel container can have a plunger within it which can move inward reducing the internal volume of the container by any number of means including one or more springs. In this way the liquid fuel is pressurized, and then motivated to leave the fuel container through the fuel transfer system to the catalytic heater assembly. 
         [0012]    As discussed in the fuel container section the fuel motivator can be one or more springs or other elastic devices inside or outside the fuel container. However, the fuel motivator can also be any number of pump types either integrated into or around the fuel container or separate of the fuel container all together. 
         [0013]    The fuel transfer system includes hoses, pipes and capillary tubes which are used to conduct the fuel from the fuel container to the catalytic heater assembly. In order to maintain a steady flow of fuel one or more orifice or capillary tubes may be placed within the fuel transfer system. With a given fuel pressure the flow rate through a given orifice or capillary tube can be quite consistent and used to limit the power output of the catalytic heater assembly. 
         [0014]    From the time of manufacture to the time of use the fuel must be kept separate from the catalytic heating assembly. At the time of use some means of triggering the flameless catalytic combustion is required. One possible means is the addition of a manually activated valve within the fueling transfer system. In this way the operator can open a valve which allows the flow of fuel from the fuel container to the catalytic heater assembly. 
         [0015]    When a spring is used as the fuel motivator it can either be compressed at the time of use or pre compressed with the spring held in compression for release at the time of use to initiate the device. As an example a pin can be inserted into a hole in a spring retainer which holds the spring. When the pin is removed the spring then pressurizes the fuel. 
         [0016]    The initiation system components can each be activated individually in individual steps, etc. One or more of the initiation system components can be attached to the container in such a way as to allow the motion of the container opening to activate the device. 
         [0017]    It may also be desirous to enclose the catalyst, or an assembly including the catalyst, in an airtight container to prevent contamination of the catalyst. 
         [0018]    In one embodiment the container is comprised mostly of corrugated cardboard. It is probably best manufactured in three main parts, the bottom, the top and the false bottom. 
         [0019]    In order for the oxidation of the methanol to occur a flowing fresh supply of oxygen, obtained from the air, must be maintained. In order to insure this supply is sufficient to supply enough oxygen, sufficient channels, or voids, must be maintained between the various components. However, this means that in a normally designed container for this application the container would have large volumes of air in the container. This is not efficient for shipping. 
         [0020]    As the air in the device is heated, the chimney effect causes the hot air to rise and exit the upper exhaust openings. As this occurs fresh air is drawn in through the lower intake openings to take its place. By positioning air intake openings as low as possible, and air exhaust openings as high as possible the chimney effect can be maximized. 
         [0021]    One design would involve the various components of the container able to slide one within another in a telescopic manner. This way the box is stored and shipped in a small form with the ability to expand the box before use to allow room for air flow. 
         [0022]    When ready for use the container will have one or more voids in the bottom, possibly created by a false bottom in the container, with one or more openings on the sides to allow for air intake. The false bottom includes one or more openings in the top of the false bottom to allow the air from the void(s) in the bottom to come up to the catalytic heater assembly which would be located above the false bottom. 
         [0023]    The air passes between the one or more catalytic heating assemblies and the food tray. The air then flows up between the food tray and the container&#39;s vertical walls. 
         [0024]    After the air flows vertically it can either exit through exhaust vents near this point either on the sides or the top or it can be channeled across the top of the food tray between the food tray and the top of the box to exit through one or more exhaust vents on the center of the lid. In this way the warm exhaust air can pass more heat into the food as it travels past. 
         [0025]    The above embodiments are to illustrate, not limit the invention. Other embodiments are also envisioned including use of other fuels; the lid, bottom, and false bottom potentially being made of other materials like plastic, wood, metal, etc.; the fuel cartridge being made of other fuel compatible materials such as metal, etc.; the fuel pressurized by other means, such as gravity, by the fuel cartridge being held higher than the system to develop pressure, or the fuel cartridge being flexible and placed beneath some or all of the unit allowing the mass of the unit to pressurize the fuel. Many other embodiments are envisioned. 
         [0026]    In one embodiment of the system, the catalytic burner is supported on a false bottom. Air enters through one or more air inlet(s) in the side below the false bottom on which the burner is supported. Fuel flow is controlled through a fuel transfer system including on or more capillary tube(s) to one or more semipermeable or porous semipermeable membrane(s) which allow fuel vapor to pass through to the catalyst. Flameless combustion occurs at the catalyst, producing radiant and conductive heat and hot gases pass heat to the food tray via convective contact. 
         [0027]    The false bottom is a shelf like part which supports the burner(s) and creates a void beneath the false bottom to allow for incoming air flow to enter from under the burner(s) which has several advantages, including increasing the vertical distance between the air inlet and the exhaust vent, thus increasing the chimney effect, as well as allowing more oxygen rich air to come in contact with more catalyst, thus improving the combustion. 
         [0028]    An optional layer of dry water  36 , a dry powder container water droplets surrounded by silica, placed on top of the heat diffuser releases water on heating, to create steam and enhance heat transfer. 
         [0029]    Two or more substantially vertical side surfaces form an enclosure. Less than four sides are needed if at least one is curved. Two similar sides could form a single elliptical or circular sleeve which would accommodate a squashed envelope and make clear the vent situation. 
         [0030]    The food tray could be, for example, similar to those used in unified group military rations (e.g. UGR-E™), a covered food grade plastic tray with food sealed inside. Multiple food trays can be packed in one oven, or multiple ovens can be placed in one box to provide a multi course meal to a field group such as soldiers. The food trays to be heated are each housed in a disposable telescopic self-contained individual heating oven. 
         [0031]    One embodiment of the oven is of the form of a corrugated box enclosing one or more food trays to be heated. In an example, the disposable telescopic self-contained heating oven is telescoped inward, occupying a height of about 3 inches, thus saving space for shipping. The food tray is about 2½ inches thick. The oven has distinct corrugated parts which, when expanded by telescoping outward, increase the height of the oven to produce spaces between the components to allow for air flow; a bottom, a false bottom spaced about ¾ inch above the bottom, a food tray support spaced about ¾ inch above the one or more burner(s) resting on the false bottom, and a lid spaced about ¾ inch above the top of the food tray, all surrounded by vertical walls. 
         [0032]    The vertical walls of the lid and bottom of the corrugated box oven are configured to hold the separations of the parts and to hold the food tray. The food tray and the oven box can be rectangular in shape. Two opposite support sides of the box are closely positioned to two opposite sides of the food tray. The non-support sides of the oven box are spaced outward from other sides of the food tray to allow for vertical air flow around these sides. 
         [0033]    The support sides of the oven box supporting the food tray have reinforced wall designs and tabs that bend inward to hold the food tray above the burner on the false bottom. Similar tabs on telescoping walls of the bottom and the false bottom hold the false bottom above the bottom. In one embodiment, the bottom and the false bottom are formed or assembled in a rigid connection. 
         [0034]    The cover is held separated from the top of the food tray by similar inward bent tabs. A lid is integrally hinged on the cover to inspect, remove or replace the tray. 
         [0035]    The end walls of the bottom have one or more air inlet(s) to admit air. A hole near the center of the false bottom allows the air to flow upward. The air flows outward from the center hole and contacts the fuel vapor at the burners that are supported on the false bottom. Flameless combustion occurs on surfaces of the catalyst producing heat. 
         [0036]    The false bottom may be left out and the oven appears more as a traditional box. One or more air inlet(s) located near the bottom of the oven allows air flow in and across between the food tray and the burner(s), at the opposite end of the food tray the air flow is forced upward, where it could exit via an exhaust vent at this end of the food tray or the air flow may then be forced across the top of the food tray between the food tray and the lid. 
         [0037]    A heat diffuser is located above the burners and is held between the bottom of the food tray and the burners to diffuse the radiant heat from the burners over the entire food tray bottom. The heat diffuser is in thermal contact with the bottom of the food tray to transfer heat and so as not to interfere with the air flow across top of burner(s). The hot exhaust gases of the fuel and air combustion pass between the burners and the bottom of the food tray, then around the ends of the food tray and over the top of the food tray and out of one or more exhaust vent(s) on the top of the lid or near the top of the vertical walls of the lid. Thus the tray is heated by radiant heat, convection and conduction aided by contact of heat diffuser (in proximity to food tray) with convective flow of hot gases. The heat diffuser can be made of numerous materials, for example aluminum or zinc. The heat diffuser can be manufactured in numerous ways, for example cast, stamped, die cut or simply sheared. It may be desired to darken the color of the heat diffuser on one or both sides to aid in its ability to absorb radiant heat for its diffusion, as well as optimize its heat conduction and/or radiation to the food tray. 
         [0038]    The fuel cartridge is designed to contain a fuel within the oven. An activating pin is removed releasing a pre compressed spring to pressurize the fuel cartridge which is connected to one or more capillary tube(s) that lead to the burners. Fuel vapor diffuses through the molecularly permeable or porous semipermeable membrane and contacts the catalyst in the presence of air, producing flameless combustion. 
         [0039]    The fuel may flow by capillary action or may be forced through the flow-limiting capillary tube or orifice by a spring forced diaphragm in or on the fuel cartridge. The spring may be released by removing the activating pin. 
         [0040]    The fuel supply lasts for any length of time required to produce sufficient continuous heat to heat the contents of the food trays to desired temperatures for consumption. 
         [0041]    The heaters are described in copending U.S. patent application Ser. No. 12/729,702, filed Mar. 23, 2010 and Ser. No. 13/026,848, filed Feb. 14, 2011, which respectively have priority of U.S. provisional applications 61/162,503, filed Mar. 23, 2009 and 61/304,704, filed Feb. 15, 2010, the disclosures of which are incorporated herein in their entirety as if fully set forth herein. 
         [0042]    These and further and other objects and features of the invention are apparent in the disclosure, which includes the above and ongoing written specification, with the claims and the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0043]      FIG. 1  is a top view of the oven box containing a sealed food tray and a heater. 
           [0044]      FIG. 2  is a longitudinal side view of the tray-containing heater box as it is shipped and received in telescoped form. 
           [0045]      FIG. 3  is an end view of the tray-containing heater box as it is shipped and received in telescoped form. 
           [0046]      FIG. 4  is an end view of the heater box after it is expanded for use. 
           [0047]      FIG. 5  is an end view of the food tray-containing heater box after it is expanded and in use. 
           [0048]      FIG. 6  is a vertical cross-section schematic view of the food tray-containing heater box taken along line  6 - 6  in  FIG. 5 . 
           [0049]      FIG. 7  is a cross-sectional quarter view detail of a telescoped tray-containing heater box taken along line  7 - 7  in  FIG. 2 . 
           [0050]      FIG. 8  is a cross-sectional quarter view detail of an expanded tray-containing heater box taken along line  8 - 8  in  FIG. 3 . 
           [0051]      FIG. 9  is a schematic representation of a fuel container with flow-limiting connection to a semipermeable membrane for releasing vapor to a catalyst pad. 
           [0052]      FIG. 10  shows a cross sectional side elevation of an alternate embodiment. 
           [0053]      FIG. 11  is an end cross sectional view showing how parts of the intern walls of the cover are inward extended. 
           [0054]      FIG. 12  shows how tabs  145  on the lower reinforced walls  145  of the box may be extended outward. 
           [0055]      FIG. 13  shows a support frame  147  supported by hooks  159  engaging the lower reinforced walls  145  of the oven box. 
           [0056]      FIG. 14  schematically shows an oven box with an air entrance at one end with air and hot gas flowing across the full length of the shelf and exiting at locations spaced on the lid. 
       
    
    
     DETAILED DESCRIPTION 
       [0057]      FIG. 1  is a top view of the oven box  10  containing a sealed food tray and a heater and having a hinged lid for inspecting, removing and replacing the heat tray. 
         [0058]      FIG. 2  is a longitudinal side view of the tray-containing heater box  10  as it is shipped and received in telescoped form  11 . 
         [0059]      FIG. 3  is an end view of the tray-containing heater box  10  as it is shipped and received in telescoped form  11 . 
         [0060]      FIG. 4  is a side view of the heater box  10  after it is expanded  15  for use. 
         [0061]      FIG. 5  is an end view of the food tray-containing heater box  10  after it is expanded  15  for use. 
         [0062]      FIG. 6  is a vertical cross-section schematic view of the food tray-containing heater oven  10  in expanded form  15  taken along line  6 - 6  in  FIG. 5 . 
         [0063]    Food in a food tray  20  is supported above a catalyst  31  of a burner  30 . Fuel vapor and air produce flameless heat at the catalyst  31 . Radiant heat is diffused by heat diffuser  35  from direct contact with the food tray  20 . Hot exhaust gases  33  flow below the food tray  20  and heat diffuser  35 , around the food tray sides  21  and over the top 23 of the food tray  20 , heating the food tray  20  and its contents before the hot gases  33  exhaust through a central opening. In one embodiment of the system, burners  30  are supported on a shelf or false bottom  40 . Air enters through air inlets  17  below the false bottom  40  on which the burners  30  are supported. Fuel flow is controlled through a capillary tube to a semipermeable membrane which allows fuel vapor to pass through to the catalyst  31 . Flameless combustion occurs when fuel vapor and oxygen in the air reacts at the catalyst surfaces, producing radiant conductive and convective heat and hot gases which carry heat to the food tray. 
         [0064]    The food tray could be, for example, similar to those used in unified group military rations (e.g. UGR-E™), a covered food grade plastic tray with food sealed inside. Multiple food trays can be packed in one oven, or multiple ovens can be placed in one box to provide a multi course meal to a field group such as soldiers. The food trays to be heated are each housed in a disposable telescopic self-contained individual heating oven  10 . 
         [0065]    The heating oven  10  is in the form of a corrugated box  50  enclosing one or more food trays  20  to be heated. In an example, the disposable telescoped self-contained heating oven  10  is telescoped inward  11 , occupying a height of about 3 inches. The food tray is about 2½ inches in height. The oven has distinct corrugated parts which, when expanded by telescoping outward, provide a bottom  51 , a false bottom  40  spaced about ¾ inch above the bottom  51 , a food tray support frame  149  for spacing, the bottom of the food tray  20  about ¾ inch above the burners  31  on the false bottom  40 , and a lid  53  spaced about ¾ inch above the top of the food tray  20 . 
         [0066]    The walls  55  of the lid  53  and bottom  51  of the corrugated box  50  are configured to hold the separations of the parts and to hold the food tray  20 . The food tray  20  and the oven  10  are rectangular. 
         [0067]    Elongated sides  57  of the box  50  are spaced outward from elongated sides  27  of the food tray  20 . Shorter ends  59  of the oven  10  are closely positioned to shorter ends  29  of the food tray  20 . 
         [0068]    As shown in  FIGS. 7 and 8 , the elongated sides  57  of the oven  10  have reinforced walls  60  and tabs  61  that bend inward to engage outward extended rims or edges of the top of the food tray  20  and top edges of the bottom  51  to hold the food tray  20  spaced above the burners  30  on the false bottom  40 . Similar tabs on telescoping walls of the bottom  51  and the false bottom  40  hold the false bottom  40  above the bottom  51 . In one embodiment, the bottom  51  and the false bottom  40  are formed in a rigid connection which does not move with the telescoping motion. 
         [0069]    The lid  53  is held separated from the top of the food tray  20  by similar inward bent tabs  61  or by friction between the telescoping walls  70 . 
         [0070]    The end walls  71  of the bottom  51  have air inlets  17  to admit air. A hole  47  near the center of the false bottom  40  allows the air to flow inward between the bottom  51  and the false bottom  40 , then flows upward through the center hole  47  in the false bottom  40 . The air flows outward over the burners  30  and meets the fuel vapor at the catalyst  31 . Flameless combustion occurs on surfaces of the catalyst  31 , producing heat. 
         [0071]    A heat diffuser  80  is located above the burners  30  and is held between the bottom of the food tray  20  and the burners  30  to diffuse the radiant heat from the burners  30  over the entire food tray  20  bottom. The heat diffuser  80  is in thermal contact with the bottom of the food tray  20  to transfer heat and so as not to interfere with the air flow across top of burners  30 . The hot exhaust gases  33  of the fuel and air combustion pass between the burners  30  and the bottom of the food tray  20 , then around the ends  29  of the food tray and over the top of the food tray and out of one or more exhaust vent(s)  58  on the top of the lid  53  or near the top of the vertical walls of the lid  53 . Thus the food tray  20  is heated by radiant heat, convection and conduction aided by contact of heat diffuser  80  (in proximity to food tray) with convective flow of hot gases. The heat diffuser  80  can be made of numerous materials, for example aluminum or zinc. The heat diffuser  80  can be manufactured in numerous ways, for example cast, stamped, die cut or simply sheared. It may be desired to darken the color of the heat diffuser  80  on one or both sides to aid in its ability to absorb radiant heat for its diffusion, as well as optimize its heat conduction and/or radiation to the food tray  20 . 
         [0072]      FIG. 7  is a cross-sectional quarter view detail of the telescoped heater oven  10  taken along line  7 - 7  in  FIG. 2  and showing the reinforced wall structures  60  of the elongated side walls  57  of the box. 
         [0073]      FIG. 8  is a cross-sectional quarter view detail of an expanded oven  10  taken along line  8 - 8  in  FIG. 3 . Reinforced wall portions  65 , to which the tabs  61  and tray support tops  67  are attached, slide in the recesses  63  to extend the oven  10  and hold it in expanded form  15 . The slidable wall portions  63 , tabs  61  and support tops  67  are positioned in at least one place along each longitudinal side wall so that the tray is supported. 
         [0074]      FIG. 9  is a schematic representation of a fuel cartridge  100  with a flow-limiting connection  101  to a semipermeable membrane  110  for releasing fuel vapor to a catalyst  31 . 
         [0075]    The fuel cartridge  100  is designed to contain a fuel  103  within the oven. An activating pin  113  is removed releasing a pre compressed spring  107  to pressurize the fuel cartridge  100  which is connected to one or more capillary tube(s)  119  that lead to the burner  30 . Fuel vapor  131  diffuses through the molecularly semipermeable or porous membrane  110  and contacts the catalyst  31  in the presence of air, producing flameless combustion. 
         [0076]    The fuel may flow by capillary action or may be forced through the flow-limiting capillary tube  119  or orifice by a spring forced diaphragm or plunger  105  in or on the fuel cartridge  100 . The spring  107  may be released by removing the activating pin  113 . 
         [0077]    Fuel container  100  contains fuel  103  and a plunger  105  having a seal  106  which is urged inward by spring  107  compressed between a cap  109  and the plunger  105 . 
         [0078]    The spring  107  is held compressed by a piston rod  111  that extends through the cap and by a pin  113  that extends through an opening in the piston rod. 
         [0079]    Activating pin  113  is removed from the piston rod  111  to release the spring  107  and pressurize the fuel  103  in the container  100 . Valve  115  is opened to allow the fuel to flow through tube  117  to capillary tube  119 . Capillary tube  119  has a fine lumen  121  that restricts the flow rate of the fuel  103  from the container. A tube  123  is connected between the capillary tube  119  and a pipe  125  which supplies fuel to a reservoir  127 . The reservoir may be a sealed sponge. In the reservoir  127  fuel vapor  131  is released from the liquid fuel  103 . 
         [0080]    A semipermeable or porous membrane  110  on the reservoir  127  allows the fuel vapor  131  to flow into the catalyst  31  where the fuel vapor  131  and oxygen in the air unite in a flameless exothermic reaction. The heated air and hot gas flow under the heat diffuser  35  and around sides and ends of the food tray and over its top and finally exhaust through vent openings in the lid  53 . Food in the tray is heated within a short time. 
         [0081]    The oven  10  in expanded form  15  is heated by flameless catalytic burning of hydrogen bearing fuels. The oven  10  has a housing having top and bottom surfaces and two or more side and end surfaces. Three or more side surfaces are used, if none is curved to form an enclosure. At least one air intake opening and at least one exhaust gas vent opening enable the convective flow of heated air and exhaust gases. A catalytic heater is in contact with air and fuel vapor, such that upon activation the heat produced motivates the heated air and exhaust gases to rise causing a convective single pass flow of air by chimney effect. Air enters from the intake opening and hot air and combustion product gases exit through the exhaust gas vent. 
         [0082]    A container, the contents of which are to be heated, is suspended over the burner such that air entering through the intake opening, located lower than the container, passes between the container and the burner. Then heated air and hot combustion gases, having traversed the bottom of the container, are directed by air gaps between the container and a side surfaces of the oven such that heated air and hot combustion gases flow upward motivated by chimney effect, to cross over the top of the container before that heated air and hot combustion gases exit the oven&#39;s one or more exhaust vents. 
         [0083]    A thermally conductive sheet or panel is suspended below the container such that it does not divert or interrupt the convection of gases, but absorbs radiant heat from the burner, and heat from the heated gases, to make random and, hence, uniform spatial distribution of temperatures experienced by the bottom of the container, and to re-radiate heat from the conductive sheet to the container. 
         [0084]    The burner has a fuel inlet and distribution system below a molecularly semipermeable membrane, through which fuel vapor is capable of diffusion. The semipermeable membrane is positioned below a porous layer comprised of or coated or impregnated with catalyst(s) such that fuel vapor and air approaching it from opposite sides meet at the catalyst layer. 
         [0085]    The semipermeable membrane is constructed as an envelope to contain the fuel, and the fuel boils in the envelope. 
         [0086]    The oven surfaces have one or more hinged parts or panels allowing for opening or closing the oven to access internal components and a container, the contents of which are to be or have been heated by the oven. The oven enclosure is a fireplace with a flue. The container is a shelf-stable military ration in a sealed polymeric or laminated container or pouch. 
         [0087]    In the oven a container, the contents of which are to be heated, is suspended over multiple burners with one or more slots between burners such that air entering through the one or more intake openings, located lower than the burner, passes between the burners upwards toward the container, and is directed by one or more air gaps between the container and one or more side surfaces of the oven such that heated and not exhaust gases flow upward, motivated by chimney effect, around the container and out of a central exhaust vent in the top surface of the oven. 
         [0088]      FIG. 10  shows a cross sectional side elevation of an alternate embodiment  140  in telescoped condition  11  in which the fuel container  100  is held within an internal compartment  151  in the oven  10  and connections such as shown in  FIG. 9  are used. When the oven  10  is expanded to the ready condition  15  as shown in  FIG. 12 , the valve and/or pin are exposed to provide access. The walls  54  of the lid  53  are configured to hold the lid  53  above the top of the food tray  20 . 
         [0089]      FIG. 11  is an end cross sectional view showing how parts of the intern walls of the cover are inward extended  143  such as by bent tabs or internal reinforcements of the type shown in  FIGS. 7 and 8  to support the extended rim of the food tray  20 . 
         [0090]    One inner side of the cover wall shows the inward supporting extensions which like tabs  61  shown in  FIG. 8  are spaced along opposite side walls. 
         [0091]      FIG. 12  shows how tabs  145  on the lower reinforced walls  145  of the box may be extended outward to support the reinforced cover walls  154  to lift and support the elements of the oven box. 
         [0092]      FIG. 13  shows a support frame  147  supported by hooks  159  engaging the lower reinforced walls  145  of the oven box. 
         [0093]      FIG. 14  shows one embodiment in which the air comes in the air inlet  17 , flows between the heat diffuser  80  and the burner  31  around the food tray sides  21 . The hot exhaust gasses  33  flow up due to chimney effect. The hot exhaust gasses  33  can then escape through exhaust vent  58   a , exhaust vent  58   b , or exhaust vent  58   c , or any combination thereof. There are advantages and disadvantages to each and the specifics of the application will indicate which to use and in what combination. Exhaust vent  58   a  provides for the greatest air flow since the hot exhaust gasses  33  will travel the shortest distance in the oven  10 ; however, the hot exhaust gasses  33  will also have the shortest distance and time in contact with the food tray  20 , thereby imparting the least amount of heat into the food tray  20 . Exhaust vent  58   b  and exhaust vent  58   c  provide for the greatest amount of distance and time for the hot exhaust gases  33  to remain in thermal contact with the food tray  20 , thereby imparting more heat to the food tray  20 ; however, the reduced air flow due to the longer distance as well as the increased horizontal travel of the hot exhaust gasses  33  may cause the total air flow to be insufficient to provide ample oxygen for the combustion process. It may be desirable to use a combination. If exhaust vent  58   a  in placed in the oven  10 , but it is not of sufficient area to allow all of the hot exhaust gasses  33  to leave the oven  10  unencumbered, exhaust vent  58   b  can then be placed in the oven  10  to allow for additional exhausting. In this way some of the hot exhaust gasses  33  travel across the top of the food tray  20  imparting more heat to the food tray  20 , while some of the hot exhaust gasses  33  escape through exhaust vent  58   a  thereby increasing the total volume of air flow entering air inlet  17  increasing the amount of oxygen available for the combustion reaction. 
         [0094]    While the invention has been described with reference to specific embodiments, modifications and variations of the invention may be constructed without departing from the scope of the invention, which is defined in the following claims.