Thermal test procedure for mixed mode solar dryer

In present study, the simple test procedure is proposed for thermal performance evaluation of solar dryers in general and mixed mode dryer in particular. Steady state heat balance concept has been applied to the absorber surface of collector- dryer assembly for identification of a dimensionless parameter called Dryer Performance Ratio (DPR) representing the effectiveness of a dryer. No-load experiments on mixed mode dryer have been performed for natural and forced air circulation under indoor controlled conditions. The dryer is tested for a wide range of operating conditions of absorbed thermal energy (300- 800W/m²) and air mass flow rate (0.009-0.026 kg/s). Comparison of DPR values obtained for natural and forced air circulations indicates a significant performance improvement of 94% at the minimum air flow rate of 0.009 kg/s. It is also found that there is sharp rise in DPR by 31% is observed when airflow is increased from 0.009 to 0.017 kg/s and thereafter a marginal increase of 4% can be noticed for air flow enhancement of ~ 53%. Another important finding of present study relates to invariable DPR values obtained for a wide range of absorbed energy and ambient air temperature data irrespective of air circulation mode adopted for a dryer.