Chamchong M, Datta A K
Cornell University, Dept. of Agricultural and Biol. Engineering, Riley-Robb Hall, Ithaca, NY 14853, USA.
J Microw Power Electromagn Energy. 1999;34(1):22-32. doi: 10.1080/08327823.1999.11688385.
Non-uniformity of temperatures in thawing of food and biological materials inside a microwave oven is affected by size, shape, and dielectric properties of the load (food). The objective of this study was to relate the time to thaw and the non-uniformity of heating to the shape, size, and the dielectric properties of the load. The details of the heat transfer analysis, experimental 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 effect on the heating rates, time to thaw and the non-uniformity of temperatures during thawing. A "shield" develops from surface thawing and leads to reduced microwave penetration. This "shield" develops more readily at higher dielectric loss, thereby effectively increasing the thawing time even more for a lossy material at higher power levels. Thawing time increases linearly with volume. As the load aspect ratio decreases (it is made flatter), it thaws faster since the energy decays relatively less in a thinner material. These new results could provide a more rational and quantitative approach to development of frozen food products to be heated in a microwave oven.
微波炉内食品和生物材料解冻过程中的温度不均匀性受负载（食品）的尺寸、形状和介电特性影响。本研究的目的是将解冻时间和加热不均匀性与负载的形状、尺寸及介电特性联系起来。传热分析、热学和介电特性的实验测量以及温度测量的详细内容在一篇配套论文中进行了描述。结果表明，长宽比和体积对加热速率、解冻时间以及解冻过程中的温度不均匀性均有显著影响。表面解冻会形成一个“屏蔽层”，导致微波穿透减少。这种“屏蔽层”在较高介电损耗下更容易形成，从而在更高功率水平下，对于有损耗的材料，有效地进一步增加了解冻时间。解冻时间随体积呈线性增加。随着负载长宽比减小（变得更扁平），解冻速度加快，因为在较薄的材料中能量衰减相对较小。这些新结果可为开发在微波炉中加热的冷冻食品提供一种更合理、定量的方法。
