Performance simulation of a natural circulation solar air heater with phase change material energy storage

Abstract

The one-dimensional radial heat conduction in a phase change material (PCM) heat storage system that is encapsulated in cylindrical pipes in a single glazed flat plate natural circulation solar air heater is presented. The PCM is prepared in modules, with the modules equispaced across the absorber plate. Enthalpy method is applied to convert the relevant energy balance equations into dimensionless forms for easy tracking of the moving phase boundaries. Crank-Nicolson implicit finite difference scheme which has the features of being stable, accurate and fast in its solution is used in the solution of the governing equations subject to suitable initial and boundary conditions. The scheme is applied at each node and the resulting simultaneous equations are solved using the Gauss-Seidel iterative method. An existing computer programme in BASIC known as the EGGINC which was developed for the rectangular channel containing the PCM is modified to cylindrical coordinate for the pipes containing the PCM to predict the temperature distributions in the solar air heater. The predicted temperatures of the system are compared with the experimental data under daytime no-load condition over the ambient temperature range of 18.5-36.0OC and daily global irradiation of 4.9-20.1MJ/m²-day. The predicted temperatures were found to agree closely with experimental data.

Keywords: Phase change material, Natural circulation; Solar air heater; implicit finite difference, Predicted temperatures