Hot air circulation ovens have low thermal efficiency, with heat loss from the dryer accounting for over 60% of the total heating output. The overall thermal efficiency of the oven is closely related to the type of oven used, and the efficiency varies significantly between different oven types.
There are several reasons for low oven thermal efficiency:
1. Excessively high exhaust temperature removes a large amount of heat; the dryer design is not fully integrated with the tea drying process.
2. Uneven distribution of temperature and wind speed fields within the tea dryer.
3. Poor insulation of the oven walls short-circuits the airflow within the oven, resulting in significant air leakage losses.
Analysis of the drying and dehydration thermal process in hot air circulation ovens shows that this heat loss accounts for approximately 5% of the oven's heat output, but the exhaust temperature at the top layer can be controlled. Lower exhaust temperatures improve heat utilization. While lower exhaust temperatures improve heat utilization, they significantly impact tea drying quality and reduce the dryer's drying efficiency. Theoretically, since low-temperature, saturated, moist air cannot remove moisture from the tea leaves, the exhaust temperature should be controlled at the unsaturated point. As for the processing of raw materials, the exhaust temperature and humidity should be controlled, which will not affect the drying quality of tea leaves and save energy consumption. This also requires experimental verification.