Development and performance evaluation of a combined infrared and hot air dryer

Abstract

In this study, a laboratory scale infrared and hot air dryer was developed in which some parameters such as the temperature of drying chamber, input air temperature, air flow rate and distance from the infrared source was adjustable by operator. Drying of tomato thin layers was performed under various combinations of these parameters. Experimental results showed that drying time for temperatures of 60, 70 and 80 °C was 60, 75 and 116 minutes, respectively. Drying is directly related to the amount of operational infrared power. Moreover, drying time for two air velocities of 0.6 and 1.1 m s-1 was 109 and 95 minutes, respectively. Increasing the drying air velocity leaded to reduction of drying time because of an increasing in evaporation rate of moisture from the surface of the product at low speeds. Results showed that by increasing the distance of drying chamber from the infrared source, drying time will increase due to reduction of heat that transferred to the product. Minimum and maximum drying times were belonging to the temperatures of 80 and 60 °C, respectively. Also, the drying rate was directly related to the velocity and temperature of input air.