DRYING RATE AND MOISTURE DIFFUSIVITY ANALYSIS OF FREEZE-DRIED PRODUCTS UNDER MICROWAVE HEATING POWER APPLICATION

摘要

The necessary criteria for the design of a freeze-drying operation, where radiant andrnmicrowave heating are combined, are analyzed in this paper. Microwave heating presentsrnindubitable advantages for enhancing drying kinetics. Modifications of different valuerncharacteristics must be also considered. Different freeze-drying strategies using MW heatingrnare analyzed taking into account kinetics and diffusivity characteristics during dehydration ofrnproducts.rnA microwave on-off cycled strategy with simultaneous up-down modification of pressurernwas found to be an acceptable power regulation system when magnetrons, whose fieldrnstrength exceeds the breakdown voltage of gas, are used. In this case chamber pressurernbecomes a convenient control parameter to avoid plasma discharge and subsequent melting ofrnproduct. Different evolutions of specific power inputs per gram were encountered dependingrnon the size and disposition of the product.