Microwave Drymg of Grapes in a Single Mode Cavity at 2450 Mhz - i: Drying Kinetics

ABSTRACT Grapes were dried into raisins using combined microwave and convective drying in a single mode cavity specially designed for the studies. Effect of processing parameters, viz.microwave power density (P) air temperature (T) and velocity (u) on drying kinetics was studied in an effort to optimize the operating conditions. The individual and interactive effects of these variables were srudied using three levels of P, four levels of T and two levels of u. Higher drying rates observed with the higher P and T were atuibuted to the increased product temperature and higher partial vapour pressure difference between the surface of the fruit and the air stream. Increase of air velocity increased the drying times. Low drying rate at higher air velocity was attributed to decreased fruit temperature due to rapid convective heat mnsfer at the surface.

[1]  Ian Turner,et al.  COMBINED MICROWAVE AND CONVECTIVE DRYING OF A POROUS MATERIAL , 1991 .

[2]  Vaios T. Karathanos,et al.  Comparison of Two Methods of Estimation of the Effective Moisture Diffusivity from Drying Data , 1990 .

[3]  C. Peri,et al.  Kinetics of sun and air drying of different varieties of seedless grapes , 1986 .

[4]  P. Schmidt,et al.  AN INTEGRAL MODEL FOR DRYING OF HYGROSCOPIC AND NONHYGROSCOPIC MATERIALS WITH DIELECTRIC HEATING , 1990 .

[5]  R. E. Treybal.  Mass-Transfer Operations , 1955 .

[6]  D. Jayas,et al.  A METHOD OF DETERMINATION OF THE DIFFUSION COEFFICIENT BASED ON KERNEL MOISTURE CONTENT AND ITS TEMPERATURE , 1992 .

[7]  T. Kudra,et al.  SIMULATION OF RF-ASSISTED CONVECTCVE DRYING FOR SEED QUALITY BROAD BEAN , 1990 .

[8]  S. Simal,et al.  Storage Conditions Affect Quality of Raisins , 1993 .

[9]  T. Tulasidas,et al.  Combined Convective and Microwave Drying of Grapes , 1995 .

[10]  G. Saravacos,et al.  Effect of ethyl oleate on the rate of air-drying of foods , 1988 .

[11]  Bushra Al-Duri,et al.  Comparison of drying kinetics of foods using a fan-assisted convection oven, a microwave oven and a combined microwave/convection oven , 1992 .

[12]  F. P. Caldas.  Experimental High Frequency Dryer for Granular Materials , 1992 .

[13]  G. Raghavan,et al.  Modelling the drying kinetics of maize in a microwave environment , 1994 .

[14]  J. Ponting,et al.  Temperature and dipping treatment effects on drying rates and drying times of grapes, prunes and other waxy fruits , 1970 .

[15]  G. Raghavan,et al.  Microwave and Convective Drying of Grapes , 1993 .

[16]  C. Geankoplis.  Transport processes and unit operations , 1978 .

[17]  Zacharias B. Maroulis,et al.  Application of the GAB model to the moisture sorption isotherms for dried fruits , 1988 .

[18]  R. Perkin.  SIMPLIFIED MODELLING FOR THE DRYING OF A NON HYGROSCOPIC CAPILLARY POROUS BODY USING A COMBINATION OF DIELECTRIC AND CONVECTIVE HEATING , 1990 .