Thawing of foods in a microwave oven: II. Effect of load geometry and dielectric properties

Non-uniformity of temperatures in thawing of food and biological materials inside a microwave oven is affected by size, shape, and dielectric properti es of the load (food). The objective of this study was to relate the time t o thaw and the non-uniformity of heating to the shape, size, and the dielec tric properties of the load The details of the heat transfer analysis, expe rimental measurement of thermal and dielectric properties, and temperature measurements are described in a companion paper. Results show that both the aspect ratio and the volume have a significant e ffect on the heating rates, time to thaw and the non-uniformity of temperat ures during thawing. A "shield" develops from surface thawing and leads to reduced microwave penetration. This "shield" develops more readily at highe r dielectric loss, thereby effectively increasing the thawing time even mor e for a lossy material at higher power levels. Thawing time increases linea rly with volume. As the load aspect ratio decreases (it is made flatter), i t thaws faster since the energy decays relatively less in a thinner materia l. These new results could provide a more rational and quantitative approac h to development of frozen food products to be heated in a microwave oven.