Heat and Moisture Transfer in a Stationary Dispersed Layer of Vegetable Materials with Combined Power Input
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Journal of Engineering Physics and Thermophysics, Vol. 93, No. 4, July, 2020
HEAT AND MOISTURE TRANSFER IN A STATIONARY DISPERSED LAYER OF VEGETABLE MATERIALS WITH COMBINED POWER INPUT P. V. Akulich and D. S. Slizhuk
UDC 532.5:66.047
The results of modeling and investigating heat and moisture transfer in a stationary dispersed layer of vegetable materials with convective and cyclic SHF-convective power input are presented. The mathematical model is made up of equations for conservation of gas-phase mass, filtration, and heat and moisture transfer in phases accounting for internal resistance to transfer of heat and moisture in particles in calculating the processes of heat and mass transfer and on the basis of deepening the evaporation zone. The conformity of the calculated results with the experimental data using the example of drying sliced potato particles and the possibility of stepping up the process of dehydration is shown. Keywords: heat and moisture transfer in a stationary layer, drying of vegetable materials, SHF-convective drying. Introduction. The processes of drying vegetable materials relating to colloid capillary-porous bodies, as a rule, require significant energy costs. This is due to the heat consumption for the moisture phase transition, the high initial moisture content of the materials, their thermolabile properties preventing the use of high temperatures for treatment, and also, in many cases, due to an inefficient power input resulting in energy losses. More recently, due to the aggravation of the problem of energy saving and the intention to reduce the cost of production, the efforts of many investigators are focused on looking for ways to raise the efficiency of the existing technologies and developing radically new ones. Note that in this area of science and technology, the researchers′ attention is attracted by the use of combined pulse and oscillating electromagnetic-convective methods of heat and moisture treatment of materials, and also regimes of vacuum or freeze-drying impacts in combination with SHF (superhigh-frequency) and IR radiation [1–4]. This is due to the fact that such methods of power input make it possible to create soft regimes of thermal action and to raise the process efficiency. For example, in [2], it is shown that the use of IR radiation in heat treatment as an initial pulse of external action on a wet product significantly intensifies the dehydration of fruits, reduces energy expenditures by 25–35%, improves the quality of the final product, and results in a decreased loss of vitamins. Investigations into the oscillating SHF convective method of drying some vegetable materials in stationary [3] and fluidized beds [4] are indicative of a reduction in the time of dehydration and energy expenditures. For drying and heat treatment of vegetable origin materials, wide use is made of devices with dense stationary or quasi-stationary disperse layer (bed) systems with convective heat input, for example, belt-type, conveyor, and chamber rack installations. However, in most
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