A portable heat generating device in which fuel vapor (e.g. methanol) and an oxygen supply (e.g. air) are uniformly released through porous tubes woven with catalyst-impregnated glass filaments into a sheet-shaped, fabric-like structure enclosed in a mylar envelope. The catalyst promotes flameless combustion of the fuel vapor and oxygen, with consequent heat release occurring uniformly over the fabric-like structure. The heat generation process is started by pumping liquid fuel and air into the porous tubes using a peristaltic pump, thereby building up hydraulic pressure within the liquid fuel portion of the microbore-tubes. The level of pressure sustained within the liquid fuel portion of the microbore-tubes is limited by a manually set variable pressure release valve. The pressure in the microbore-tubes forces the liquid fuel within the porous microbore-tubing through the pores where it is converted into a vapor state before reacting with the oxygen and catalyst to produce flameless combustion. An exhaust tube expels the by-products of flameless combustion (i.e., mainly CO2 and H2O) from the enclosing envelope directly to the ambient atmosphere. As these gases escape from the envelope, a one-way check valve opens to refresh the air supply delivered to the air-carrying microbore-tubes to sustain the heat generating reaction without requiring continuous operation of the pump.

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