evaluation and optimization drying raspberries and energy consumption in the combined fluidized bed- microwaves drying system via response surface methodology

the present research surveyed the effect of five factors including: microwaves power, air temperatures and its flow rates, microwaving time onset and amount of substances on the requested time and energy for combined fluidized bed- microwaves drying of black raspberry into 50% dry base wet content. response surface methodology and central composite was used as experimental design. multiple linear regression was used for obtaining second polynomials models for each analyses followed by anova analysis in order to confirming the adequacy and accuracy of resulted models. using the empirical resulted model the relationship between variables and responses were determined via response surface method. correlation coefficients of the regression models were 0.964 and 0.970 respectively for the drying time and energy consumption. the optimized drying condition were including; 600 watts for microwaves power and microwaving onset from that time as the moisture content was 344% decreased,73 g for amount of substances, and 85˚c and 15 m.s-1 for air temperatures and its flow rates respectively. under mentioned conditions, the fitted model was predicted 52.66 min and 65.2 kj respectively for the requested drying time and energy consumption at combined drier. as a conclusion, the results showed that requested drying time and energy consumption were decreased with increasing of temperatures, microwaving time and its power, and decreasing of air flow rates. in this regard, the drying kinetics curve samples were drawn under the conditions listed that showed drying time is reduced to 76% with increasing temperature from 55 to 85 and use the microwave reduced drying time until 30 to 80%.