The double-pass solar dryer for drying palm oil fronds

Problem statement: The solar collector is one of the vital components of the solar drying system. Conventional solar air collectors mainly consist of an absorber plate with a parallel plate forming a passage of air flow. The heat transfer for this type of solar collector is low which results in lower thermal efficiency. Hence, different modifications are suggested and applied to improve the heat transfer coefficient between the absorber plate and the air. These modifications include the used an extended heat transfer area, such as finned absorber. Approach: A solar dryer system suitable for agricultural products have been designed, constructed and evaluated under the Malaysia climate conditions. The main components of the system are double-pass solar collector with finned absorber, the blower, the auxiliary heater and the drying chamber. Results: The solar drying system has been evaluated for drying the oil palm fronds. The initial and final moisture content of the fronds are 60% (wet basis) and 10% (product basis) respectively. The drying time is about of 22 hours at average solar radiation of about 557 W/m2 and air flow rate 0.1278 kg/s. Conclusion: The collector, drying system and pick-up efficiencies were found to be 31, 19 and 67% respectively.