Investigation on solar drying system with double pass solar air heater coupled with paraffin wax based latent heat storage: Experimental and numerical study

Abstract

Since solar energy uses the sun's free energy and is environmentally friendly, it is generally accepted for various applications like drying products. However, the drawback of this system is the inconsistent and unpredictable nature of solar radiation. The best solution for the above said problem is using thermal energy storage. In this study forced convection indirect solar drying system that has a double pass solar air heater (DPSAH), shell and tube type latent heat storage (LHS) with paraffin wax as phase change material (PCM), blower and drying chamber is developed and tested. Numerical study is conducted on the DPSAH to determine the effect of mass flow rate on its performance and appropriate flow rate is selected for the drying experiment. It was found that outlet temperatures of the DPSAH is higher at lower mass flow rates and lower at higher mass flow rates and mass flow rate of 0.01 kg/s gives the required outlet temperature. Whereas numerical simulation is done on the LHS to predict the charging and discharging behavior of the PCM and found that the storage can reach a fully charged state within 133 min, which can be achieved around the peak hours during the experiment. The performance of the components of the dryer and the overall performance of the dryer is investigated with experiment. From the experimental result, a maximum temperature of 69 °C is obtained at the outlet of the DPSAH and the energy and exergy efficiencies are 25 % and 1.5 %, respectively. The LHS reduces the fluctuations in the outlet temperature of the SAH and extends the drying process for extra 3 h a day. The drying experiment is conducted by drying 5 kg fish and took 21 h to reduce the moisture content of the fish from an initial value of 75 %–12.5 %. The efficiency of the drying chamber was 35 % and the overall efficiency of the dryer was 9.4 %.