Theoretical model of temperatures in a HotPot
This report describes transient heating experiments with the 5-liter size “HotPot” solar cooker, using 1 liter of cooking oil as the load. The methodology here is “semi-empirical”, meaning that basic physical equations, such as Newton’s Law of Heating and Cooling, will provide a solid physical foundation for the development of a model. However, some parameters in the model are difficult to calculate from first principles, because of complexity in shapes, materials properties and other factors. In these cases, estimated values were used based on experimental measurements.
Temperature measurements of the “HotPot”: a solar cooker
Measurements of heat gain in a HotPot were collected in Tucson, AZ. The measurements showed significant lack of repeatability, which was attributed to variations in the gap between the lid and the vessel. This work led to further efforts to improve repeatability of measurement procedures and the HotPot itself.
Repeatability of HotPot solar cooker heating experiments
Temperature measurements were recorded using a Lascar data logger and thermocouple probe. These devices have a thin (2 mm) wire with high-temperature insulation connected to a small battery-powered data logger. In any case these experiments established that under matched solar input conditions, the measurements of two HotPot solar cookers with a water load can be repeatable within about +/- 3.5 degrees C. With an oil load, the repeatability is generally +/- 2 degrees C. or better.
Lid gaps are the major cause of heat loss and variability in the HotPot
Dry ice was placed in a HotPot. Photographs of escaping vapor showed uneven and significant quantities of vapor leakage from the lid gap in the HotPot. Such leakage is not exclusive to the HotPot; it is likely to be similar for any kind of cooking vessel that has a loose-fitting lid.