A Retained-Heat Cooker Sized from Its Own Cooling Curve: Insulation Thickness, Holding Hours, and the Fuel It Displaces

A retained-heat cooker - a pot taken off the fire at a simmer and sealed into an insulated box - is sized here from its own cooling curve. The stated pot holds 4.0 kg of food and water with a total thermal capacitance of 15700 J/K, starts at 95 C in a room at 20 C, and loses heat by conduction through insulation of conductivity 0.040 W/m/K over a box area of 0.40 m2. The insulation thickness that keeps the contents at or above 60 C is 23.3 mm for 4 hours, 35.0 mm for 6 hours, and 46.7 mm for 8 hours. During those hours the retained heat does further cooking equivalent, under a stated rate rule, to 80.3, 120.5, and 160.6 minutes at a constant 95 C respectively. Each use that replaces 6 hours of continued simmering displaces 1.08 kg of firewood at a stated stove efficiency of 20 percent, worth USD 0.22 at stated prices, or 0.141 kg of liquefied petroleum gas worth USD 0.21. The device cannot fry, cannot keep a rolling boil, and cannot cook any dish that requires sustained boiling; those limits are stated in the paper. SIMULATED, NOT MEASURED.