Heat and Mass Transfer in Infrared Assisted Heat Pump Drying of Purple Yam

This study focused on an engineering problem of heat and mass transfer in infrared (IR) assisted heat pump (HP) drying of purple yam including both a drying experiment and theory of heat and mass transfer mathematical equations. The experimental drying of yam by the IR assisted HP drying method was performed to evaluate the effect of IR power on drying rate and heating rate. The input drying parameters included the drying air temperature of 50 degrees C, drying air velocity of 2.5 m<middle dot>s-1 and IR power of 0, 300 and 350 W, in which, at the IR power of 0 W, the HP-only drying mode was performed. The experimental drying results showed that the IR assisted HP drying method could improve the drying rate and heating rate as compared to HP-only drying. At the IR power of 350 W, the drying time was the shortest (150 minutes), followed by the IR power of 300 W (210 minutes) and HP-only drying (300 minutes). The IR assisted HP drying obtained the high heating rate as the time required for the drying material to reach the drying temperature was about 35 and 25 minutes corresponding to the IR power of 300 and 350 W. While in HP-only drying, it took about 270 minutes for the drying material's temperature to reach nearly the drying air temperature value. Besides, the comparison between the predicted data by numerically solving the heat and mass transfer equations and experimental drying data was also conducted. The analysis results indicated that the predicted data could be used to predict the experimental data accurately. The theoretical results of heat and mass transfer in the IR assisted HP drying process as well as experimental drying results would be the basis for improving the IR assisted HP drying equipment to achieve the drying efficiency including the drying rate, quality of dried products, and energy consumption.