International Scholarly Research Network ISRN Renewable Energy Volume 2012, Article ID 282538, 5 pages doi:10.5402/2012/282538 Research Article Designing and Evaluating an Innovative Solar Air Collector with Transpired Absorber and Cover Ali Zomorodian and Maryam Zamanian Department of Agricultural Engineering, Shiraz University, Iran Correspondence should be addressed to Ali Zomorodian, zomorod@shirazu.ac.ir Received 29 April 2012; Accepted 8 July 2012 Academic Editors: E. R. Bandala and S. Rehman Copyright © 2012 A. Zomorodian and M. Zamanian. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Applying solar collectors is a popular tool for harnessing solar energy. In this work, a ﬂat plate solar air collector was investigated under direct solar radiation in an endeavor to enhance the thermal eﬃciency of solar air collector with a slatted glass cover, perforated absorber aluminum sheets (porosity 0.0177, 0.0314 and absorber thickness of 1.25, 2.5 mm) which is the most suitable for a solar dryer. The eﬀects of porosity and thickness on absorber performance of collector were evaluated. Six levels of air mass ﬂow rates (0.0056 to 0.0385 kg m −2 s −1 ) were adopted. The tests were conducted in three replications on very clear sky days in September and October. The experimental results showed that thermal eﬃciency of collector was increased by an increase in the porosity of the absorber. The absorber with lower porosity showed a better thermal eﬃciency at lower air mass ﬂux. In the minimum air ﬂow rate, absorber eﬃciency with porosity 0.0177 and 0.0314 was 0.31 and 0.29, respectively, whereas at the maximum ﬂow, eﬃciency showed an enormous change of 0.83 and 0.88, respectively. This solar air heater can be used for drying agricultural products, heating the space of greenhouse, and so forth. 1. Introduction Solar air heaters are inherently low in thermal eﬃciency due to low heat capacity and low thermal conductivity of the air in comparison to the liquid-type solar collectors [1]. Many researchers have tried to enhance the eﬃciency of the solar air heaters through providing an intimate heat transfer between air and absorbing media. The main problem is low heat transfer coeﬃcient between the absorber and air which reduces the thermal eﬃciency [2]. Design improvement of solar collectors would lead to better performance of system. Various absorber plates and glazing systems have been used in solar collectors and reported in the literature, porous (transpired) absorber and nonporous one and diﬀerent types of glazing. The main disadvantage of nonporous absorber is depletion of complete heat transfer between absorber and ﬂuid that leads to low thermal eﬃciency because the coeﬃcient of convective heat transfer between air and the absorber plate is quite low, therefore, the temperature of the absorber plate would be high and radiation loss is quite large. In porous type, absorbing the solar radiant heat and the heat convection between air and the absorber can eﬀectively strengthen the air that passes through the collector absorber which improve the quality of heat transfer coeﬃcient and thermal eﬃciency, therefore it would be better in thermal characteristics in comparison with nonporous absorber collector [3]. Porous absorber plates have been studied in diﬀerent studies such as absorber made of aluminum foil cutted [4], wire nets [5, 6], retail glass [7], pieces of coal [8], hollow spheres [9], pages made of black synthetic ﬁber [10], and thick black cotton fabric [11]. The advantage of porous absorber is attributed to the lower thermal energy dissipation to environment due to absorption and penetration depth of solar radiation [1]. In a study conducted by Whilier, 1964 [12], on solar air collector it was found that the use of a transparent coating layer is necessary to increase the economic eﬃciency of the collector. Zomorodian et al., 2001 [11], studied a collector with thick black cotton fabric absorber and slatted glass cover with vertical distance between the slatted glass sheets (tran- spired cover) 3, 5, 7 and 9mm to reduce heat loss from the upper part of collector and to increase the thermal eﬃciency.