Control of a solar dryer using a hybrid solar gas collector

Drying is one of the most energy intensive processes in agro product industry using solar energy appears as an attractive free and not polluting alternative to be used in drying processes. However the daily and seasonal fluctuations in the irradiation level requires using a solar-gas collector an auxiliary heating system to have a continuous drying process and allows the use of the solar dryer in unfavorable weather condition. A control system is essential to vary the gas flow in the injector by coordinating the control of a proportional valve, in order to maintain a suitable temperature in the drying cell. In this paper, an experimental study of solar dryer has been established under the solar irradiation of 935W/m2 and 1045W/m2. The maximum temperatures reached on the top of the collector and at drying chamber inlet were 81°C and 61 °C respectively. A polynomial approach is used to generate the solar dryer model, afterward; a PI controller has been implemented to ensure the monitoring of the gas valve for controlling the temperature in dryer cell related to the optimum temperature of each product.