Convective drying of agricultural products. Effect of continuous and stepwise change in drying air temperature

Samples of banana were dried in a two-stage heat pump dryer capable of prod ucing stepwise control of the inlet drying air temperature while keeping ab solute humidity constant. Two stepwise air temperature profiles were tested . The incremental temperature step change in temperature of the drying air about the mean air temperature of 30 degreesC was 5 degreesC. The total dry ing time for each temperature-time profile was about 300 minutes. The dryin g kinetics and color change of the products dried under these stepwise vari ation of the inlet air temperature were measured and compared with constant air temperature drying. The stepwise air temperature variation was found t o yield better quality product in terms of color of the dried product. Furt her, it was found that by employing a step-down temperature profile, it was possible to reduce the drying time to reach the desired moisture content.