Microwave drying of various shape particles suspended in an air stream

Abstract

Fluidization is an efficient way to dry granular materials. Incorporating microwave heating into the fluidization makes the overall drying process shorter, and the quality of the final products can be improved. However, in order to understand the mechanisms of water removal, an exact knowledge of changes inside the dried material is necessary. The temperature and moisture distribution pattern within the heated material should be identified and analyzed. Unfortunately, the microwave environment makes the measurements very difficult. This paper gives new information on the temperature distribution inside small particles of various shapes dried with microwaves. The tests were carried out in a laboratory-scale, fluid-bed dryer equipped with a microwave source. Five different shapes were examined: sphere, cylinder, halfcylinder, rectangular prism, and prism with triangle base. All particles tested were suspended in an air stream and heated with microwaves. The internal temperature distribution has been analyzed in each case. The rate of drying is also presented and discussed for every case tested.

Physico-chemical changes during different stages of MFD/FD banana chips

“…During convective heating, the heat flux reaches the surface of the dried solid and is transferred via the solid matrix to the deeper parts of the material. The source of heat in microwave drying is within the drying body (Araszkiewicz et al, 2007). The wet material contains the heat source as long as water is present within the solid matrix.…”

Heat and mass transfer during microwave‐convective drying

“…The local balance of energy (4) constitutes the basis for developing the differential equation for heat transfer. Substituting Gibbs' Equation (10) and the rate equations (15)- (17) into balance (4), we get the following:…”

“…The paper by Zhang et al 1 presents a review of microwave-related drying methods for fruit and vegetables. Combined drying methods like convective-microwave, [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] convective-microwave-infrared, 19 microwave-vacuum, 20,21 microwave-infrared, 22,23 solar, 24 and other methods [25][26][27][28][29] have been proposed to improve the effectiveness of drying, i.e., to minimize the drying time and the consumption of energy as well as to improve the quality of the dried products. The variety of these drying methods is wide, but, however, they do not embrace the drying kinetics for the process as a whole, which is treated in this article.…”