Improving the performance of solar air heater using high thermal storage materials

Abstract

The solar air heater is a widely used thermal application of renewable energy. Various thermal storage materials, either sensible or latent, could be adopted for solar air heater, so that the thermal energy can be saved at sunny hours for use after the sunset. Considering its latent heat of fusion, paraffin wax, a phase change materials (PCM) was selected to store latent thermal energy, applied on a forced convection solar air heater (airflow: 4.47 kg/s), and compared with a sensible thermal storage material under the meteorological conditions of Baghdad city. Three tests were conducted on February 24, 25 and 27, 2019, respectively. In the first test, no thermal storage material was used; in the second test, pure cement was adopted as the sensible thermal storage material (specific heat: 1.55 kJ/kg·K; thermal conductivity: 0.29 W/m·K); in the third test, paraffin wax was selected as the latent thermal storage material (solid phase: specific heat: 2.0kJ/kg·K; thermal conductivity: 0.24 W/m·K; liquid phase: specific heat: 2.15kJ/kg·K; thermal conductivity: 0.22 W/m·K). The results show that the latent thermal storage material of paraffin wax achieved better thermal performance than the sensible thermal storage material of pure cement; the solar air heater with paraffin wax had a 50% higher thermal storage efficiency and realized twice the heating period after 6:30pm than that with pure cement.