Thermophysical properties of fruit—a review with reference to postharvest handling

Thermal properties of municipal solid waste components and their relative significance for heat retention, conduction, and thermal diffusion in landfills

Significant amounts of heat can be generated during the initial stages after wastes are deposited in landfills, primarily due to decomposition of food waste. Objectives of this study are to compile, examine and compare thermal properties of municipal solid waste (MSW) components, and liquid and gas phases in MSW landfills and their thermal responses that effect temperature increases in gas and leachate. Specific thermal properties examined include thermal conductivity, thermal diffusivity, and specific heat of waste materials deposited in landfills, liquids (water), and gases present. Compilation of these properties will allow in depth thermal analyses to evaluate heat transfer dynamics in landfills with different waste compositions. Examination of thermal characteristics of MSW components indicate that heat generated during decomposition of waste components would primarily be transferred to liquid (leachate) due to formation of water and gaseous components and their high specific heats. As a result, both the leachate and gases released from a landfill during the initial stages after wastes are deposited and when some oxygen is present as an electron acceptor will be warmer. Except for the metals and construction waste, it is likely that most waste components will have a significant temperature gradient during warming up and cooling off stages due to their low thermal conductivities and low thermal diffusivities. Even when the gas phase is at higher temperatures, it will take long time for waste materials (other than food waste and metals) to come to a uniform temperature during the heat generation (primarily due to decomposition of food waste) in a landfill.

Temperature and Moisture Dependent Dielectric and Thermal Properties of Walnut Components Associated with Radio Frequency and Microwave Pasteurization

To provide necessary information for further pasteurization experiments and computer simulations based on radio frequency (RF) and microwave (MW) energy, dielectric and thermal properties of walnut components were measured at frequencies between 10 and 3000 MHz, temperatures between 20 and 80 °C, and moisture contents of whole walnuts between 8.04% and 20.01% on a dry basis (d.b.). Results demonstrated that dielectric constants and loss factors of walnut kernels and shells decreased dramatically with raised frequency within the RF range from 10 to 300 MHz, but then reduced slightly within the MW range from 300 to 3000 MHz. Dielectric constant, loss factor, specific heat capacity, and thermal conductivity increased with raised temperature and moisture content. Dielectric loss factors of kernels were greater than those of shells, leading to a higher RF or MW heating rate. Penetration depth of electromagnetic waves in walnut components was found to be greater at lower frequencies, temperatures, and moisture contents. The established regression models with experimental results could predict both dielectric and thermal properties with large coefficients of determination (R2 > 0.966). Therefore, this study offered essential data and effective guidance in developing and optimizing RF and MW pasteurization techniques for walnuts using both experiments and mathematical simulations.