Characterising micro-channel absorber plates for building integrated solar thermal collectors

Abstract

This paper discusses the characterisation of micro-channel absorber plates for compact flat plate solar thermal collectors, which are suitable for building integration. Experimental and computational studies were carried out at typical operating conditions for flat plate solar collectors. Three-dimensional numerical analysis using commercial CFD package, ANSYS CFX, showed that heat transfer occurred on only three surfaces of the channel and there was a peripheral variation of the heat flux density. It was also observed that axial thermal conduction could modify the surface boundary at the inlet and outlet; however, the middle section of the channel could be approximated as a rectangular channel with three walls transferring heat under an H1 boundary condition. Experimental studies were used to estimate the standard parameters for predicting performance of the flat plate collectors, which indicated promising performance results. The collector flow factor F″ and the heat removal factor could be improved by increasing the collector capacitance rate; this can be achieved by increasing the mass flow rate per collector area $\stackrel{·}{m}/A_c$ as well as reducing the overall heat loss, U_L. This analysis is important for optimising design and operating parameters, especially to minimise temperature gradient in the transverse and longitudinal directions.

Practical application : The proposed compact micro-channel absorber plate has the potential to make flat plate collectors more efficient, cheaper and aesthetically attractive in building integration. It could therefore promote the uptake of solar thermal collectors in buildings. The analysis presented in this study would be beneficial for optimising the design and operating parameters of building integrated solar thermal collectors with micro-channels.