An experimental investigation of the Evacuated Tube solar collector in conjunction with a latent heat storage tank

Abstract

A latent heat storage tank with a helical coil heat exchanger was developed, built, connected to an evacuated tube solar collector, and tested in this study. 25 kg of paraffin wax was used as phase change material (PCM) in the storage tank. During the charging (melting) process, the storage system was evaluated with varied mass flow rates of hot water as a heat transfer medium (5, 8, 9, 10.5 and 13 L/min). The system was also tested with a constant mass flow rate of domestic water during the discharging cycle (solidification). The results also showed that increasing the flow rate from 5 L/min to 13 L/min reduced the charging time from 218 min to 157 min and increased the system's overall efficiency from 28.4 % to 40.5 %. A solar collector area (m2) m PCM mass of the PCM (kg) C W specific heat of the water (J/kg °C) m w mass of water in domestic reservoir (kg) C PCM specific heat of the PCM (J/kg °C) PW paraffin wax ETSWH Evacuated Tube solar water heater PCM phase change material HTF heat transfer fluid Q in the energy inlet to of the ETSWH (kJ) HP horse power Q w the stored energy in water (kJ) I Global solar radiation intensity (W/m 2) Q PCM the stored energy in PCM (kJ) í µí±™ Litter T am ambient temperature (°C) LH Latent heat of the wax (kJ/kg). T w_h Hot water temperature at the end of discharge cycle (°C) Greek Symbols T w_c Cold water temperature at the start of discharge cycle (°C) η storage Storage efficiency T temperature, (°C) η useful useful efficiency heating domestic water ΔT temperature difference (°C) η overall System overall efficiency T PCM Paraffin wax (temperature , (°C) í µí¼” Uncertainty t Cycle time (s)