Solar air heaters: Design configurations, improvement methods and applications - A detailed review

This article aims to present a review of the literature dealing with improvement methods, design configurations and applications of different types of solar air heaters (SAHs). Different investigations have been made on SAHs either experimental or theoretical in order to improve their performance. Different modifications on absorber plate have been made. One of the important improving theories is using fins to increase the heat transfer area. Various types of fins achieved enhancement in the performance such as longitudinal fins, corrugated fins and fins attached with baffles. The recycling process also enhanced the performance of SAHs. Also it is found that to improve both the heat transfer and thermo-hydraulic performance of SAH, artificially roughened absorbers are used. Using artificial roughness, the results showed good enhancement of both Nusselt number and friction coefficient for a wide range of Reynolds number. Also in the view of using heat storage materials, especially phase change materials (PCMs), various types of packing bed and selective coated absorbers give good improvement of the efficiency of SAHs. As a result of these improvements, SAHs became more popular in more applications, with a good reduction in fuel consumption and costs of installation and operation.