Thermal performance of a solar water tank with variable inlet/outlet under various charging strategies

The plummet of the inflow temperature could cause dramatic temperature mixing during the charging process in a solar water storage tank, resulting in severe destruction of thermal stratification. To address this issue, two new charging strategies are proposed in this paper for the water tank with variable inlet and outlet ports. We study the charging process of the tank under various strategies using Computational Fluid Dynamics (CFD) simulation and assess the thermal performance improvement according to the numerical comparisons and theoretical analysis. A laminar numerical model considering gravity effect is built based on the experimental platform and is well validated against the experimental data. Energy and exergy analysis are conducted to evaluate the impact of the strategies on the thermal performance of the solar charging. The findings show that both the proposed charging strategies substantially mitigate the temperature mixing caused by the port switch and achieve a better thermal stratification with the reduction in exergy destruction by over 30%. Strategy A maintains better thermal stratification during the charging process, while strategy B prevails in inhibiting the temperature mixing after port switches. Nevertheless, the improvement in the overall thermal performance is relatively modest with the increment of less than 1% in energy efficiency and 0.02 in exergy efficiency.