Isothermal cooking or heating device

Claim 1

A cooking utensil comprising a heat-conducting wall for supporting and heating on the upper surface thereof a substance to be cooked, means for retaining cooking fluids on said surface, a sealed reservoir evacuated of all air and noncondensible gases disposed beneath said wall in heat exchange relation therewith, said reservoir being defined by said wall and also by a second wall spaced beneath the first wall, said second wall having a size and shape coextensive with that of the first wall, capillary means in said reservoir in contact with the underside of said first wall and extending toward the second wall, said capillary means comprising a porous structure, a working agent in the reservoir which in liquid form is flowable throughout the entire reservoir and is able to pass through and to saturate the porous capillary means, said agent being heatable to form vapors which condense on said underside of the first wall and which isothermally transfer latent heat of condensation thereto, thereby to maintain said first wall at a substantially uniform elevated temperature, said porous capillary means being permeable to said vapors so that the vapors are flowable throughout the entire reservoir and are condensable on the entire underside of the first wall, said agent at said elevated temperature having a vapor pressure in the vicinity of atmospheric pressure, thereby avoiding pressures which exceed the breaking strength of the utensil, said capillary means acting to drain said condensed vapors from said underside to avoid any buildup thereon of thick liquid films and also acting to facilitate transfer of the condensed vapors toward the bottom of said reservoir, an electrical heat source for heating said agent disposed on said utensil beneath said reservoir and out of contact with said agent, heat control means for said heat source to permit selection of the operating temperature of the utensil, and said utensil being capable of cooking a food in the substantial absence of local overheating or local hot spots and with reduced sticking and splattering in the case of a food conventionally subject to sticking and splattering.