Drying of agricultural crops by solar energy

The main application for solar energy in southern Mediterranean countries in agriculture is the drying of agricultural crops. The optimisation of dryers necessitates complete knowledge of the whole drying process, thus leading to energy savings and avoiding environmental pollution by using renewable sources of energy. We present a study concerning thermal behaviour of a solar air heater as a source of energy for drying agricultural products. In order to simulate the functioning of our solar collector, we chose a simple model based on the evaluation of different heat transfer coefficients in the collector and within the external environment, which allows determining the overall collector heat loss coefficient. Our purpose was to calculate the fluid outlet temperature, the output energy used and thermal efficiency as a function of ambient temperature, incident solar radiation, wind speed and air mass flow rate. The present suggested model’s results demonstrated that the air heater has paid off since we can attain the temperature on the order of 80°C at the fluid outlet and 60% in thermal performance.

The use of solar collectors for the heating of air is very profitable since some important outlet temperatures are obtained at the exit (on the order of 80°C in free outflow and 60°C in forced outflow). We perceived that the efficiency of the collector is weak in free outflow (brings in 10% and 15%); to benefit more from the available energy, we can increase the air mass flow which increases the efficiency in a remarkable way (on the order of 50–60%). This study will be useful in a later stage to examine the thermal behaviour of the whole dryer and to develop solar drying of agricultural crops.