Building and Environment 43 (2008) 1046–1054 Experimental energy and exergy analysis of a double-flow solar air heater having different obstacles on absorber plates Hikmet Esen à Department of Mechanical Education, Faculty of Technical Education, Fırat University, 23119 Elazıg˘, Turkey Received 27 June 2006; received in revised form 22 January 2007; accepted 23 February 2007 Abstract This paper presents an experimental energy and exergy analysis for a novel flat plate solar air heater (SAH) with several obstacles and without obstacles. For increasing the available heat-transfer area may be achieved if air is flowing simultaneously and separately over and under the different obstacle absorbing plates, instead of only flowing either over or under the different obstacle absorbing plates, leading to improved collector efficiency. The measured parameters were the inlet and outlet temperatures, the absorbing plate temperatures, the ambient temperature, and the solar radiation. Further, the measurements were performed at different values of mass flow rate of air and different levels of absorbing plates in flow channel duct. After the analysis of the results, the optimal value of efficiency is middle level of absorbing plate in flow channel duct for all operating conditions and the double-flow collector supplied with obstacles appears significantly better than that without obstacles. At the end of this study, the exergy relations are delivered for different SAHs. The results show that the largest irreversibility is occurring at the flat plate (without obstacles) collector in which collector efficiency is smallest. r 2007 Elsevier Ltd. All rights reserved. Keywords: Solar air heater; Experimental; Exergy analysis; Double-flow; Obstacles; Thermal efficiency 1. Introduction The main applications of solar air heaters (SAHs) are space heating and drying. The SAHs occupy an important place among solar heating systems because of minimal use materials. Low heat transfer coefficients result from the unfavourable thermophysical properties of air, which are widely used in different thermal systems. The efficiency of SAH has been found to be low because of low convective heat transfer coefficient between absorber plate and the flowing air which increases the absorber plate temperature, leading to higher heat losses to the environment resulting in low thermal efficiency of such collectors. The remedy is to improve the heat transfer, which can be achieved by creating a fully turbulent flow in these systems. There are different factors affecting the SAH efficiency, e.g. collector length, collector depth, type of absorber plate, glass cover plate, wind speed, etc. The absorber plate shape factor is the most important parameter in the design for any type of SAH. Increasing the absorber plate shape area will increase the heat transfer to the flowing air, but on the other hand, will increase the pressure drop in the collector; this increases the required power consumption to pump the air flow crossing the collector [1]. Several configurations of SAHs have been developed in literature. Various designs, with different shapes and dimensions of the air flow passage in plate type solar air collectors were tested [2–7]. The double-flow type SAHs have been introduced for increasing the heat-transfer area, leading to improved thermal performance [5]. This increases the thermal energy between the absorber plate and the air, which clearly improves the thermal perfor- mances of the solar collectors with obstacles arranged into the air channel duct. These obstacles allow a good distribution of the fluid flow [8,9]. In history, there has been a noticeable increase of interest in the applications of second law analysis to the design of thermal systems [10]. A typical thermal design based on the first law of thermodynamics allows us to address issues ARTICLE IN PRESS www.elsevier.com/locate/buildenv 0360-1323/$ - see front matter r 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.buildenv.2007.02.016 à Tel.: +90 424 237 0000/4228; fax: +90 424 236 7064. E-mail address: hikmetesen@firat.edu.tr.