Development of a mathematical procedure for controlling air flow rate in tea withering

A control system was developed for optimizing the electrical energy consumption while preserving the required quality of withered tea leaves. The electrical energy saving was achieved by controlling the speed of the fan through a variable speed drive (VSD) and controlling the hot and ambient air delivering into the trough. The fan speed was determined based on the theoretical mass flow rate requirement of air calculated by the mathematical model developed for withering, while calculating the thermodynamic properties of withering air and the moisture content of tea leaves in real time. A single board computer, Raspberry pi 3 model B, was used as the controller to run the mathematical model and the software programme to control the VSD for controlling the mass flow rate of air delivered, the air temperature and the relative humidity. Finally, the electrical energy consumption of the fan and the quality parameters of tea were measured through experiments and compared in the withering process with or without control system. The specific energy consumption of withering was in the range of 0.17 to 0.18 kWh/kg of made tea with the control system and it was 0.27 to 0.35 kWh/kg of made tea without control system. The electrical energy consumption was 36 kWh to 39 kWh with the control system and it was in the range of 55 kWh to 67 kWh in without control system. Therefore, 39% of electrical energy was saved by introducing the control system compared to the withering process without control system