Performance evaluation of solar air heaters with single and double passess

Abstract

Numbers of studies have been carried out on the performance analysis of single and double pass solar air heaters. These studies include the design of solar air heater, heat transfer enhancement , flow phenomenon and pressure drop in duct. In this thesis, mathematical modeling based on energy analysis for three different configurations of solar air heater namely single pass with one and two covers and double pass have been developed. It was shown that for each collector the energy balance equations of the components of the collector , at quasi steady state, providing a 3×3 non linear differential equation. A code was written to solve the equations by means of finite difference approach using MATLAB software. The effect of the most significant ambient and design parameters such as ambient temperature, mass flow rate and channel height on the performance of each model was investigated and compared to each other. It was shown that the thermal performance of the double cover single pass air heater in terms of fluid outlet temperature and thermal efficiency is higher than single cover one and this amount is even higher in case of a double pass air heater. It was observed also that the performance of solar air heater increases as the height of the lower glass cover to the absorber decreases. This fact was illustrated by introducing a factor of efficiency difference referred to the efficiency of the collector of a special channel height ratio to the one with the same height of the two channels. Finally the numerical simulation was successfully validated with the published results. Computed parameters such as efficiency, outlet temperature and Nusselt number was in good agreement with the existing experimental and numerical data