On the performance and entropy generation of the double-pass solar air heater with longitudinal fins Paisarn Naphon * Center for Alternative and Renewable Energy (CARE), Department of Mechanical Engineering, Faculty of Engineering, Srinakharinwirot University, 63 Rangsit-Nakhonnayok Road, Ongkarak, Nakhon-Nayok 26120, Thailand Received 9 July 2004; accepted 22 October 2004 Available online 28 December 2004 Abstract The performance and entropy generation of the double-pass flat plate solar air heater with longitudinal fins are studied numerically. The mathematical models described the heat transfer characteristics of the double-pass flat plate solar air heater derived from the conservation equations of energy. The predictions are done at air mass flow rate ranging between 0.02 and 0.1 kg/s. The effects of the inlet condition of working fluid and dimension of the solar air heater on the heat transfer characteristics, performance, and entropy generation are considered. q 2004 Elsevier Ltd. All rights reserved. Keywords: Double-pass solar air heater; Entropy generation; Performance; Fin 1. Introduction The improvement of the heat transfer rates has been continuously performed to obtain smaller and more effective thermal systems. Many researchers have been conducted regarding flow and heat transfer characteristics in the solar air heater. Hegazy [1] analyzed a criterion for determining the optimum flow-channel depth of conventional flat-plate solar air heaters. Toure [2] studied the characteristic temperatures in a natural convection solar 0960-1481/$ - see front matter q 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.renene.2004.10.014 Renewable Energy 30 (2005) 1345–1357 www.elsevier.com/locate/renene * Tel.: C6637 322 625x2064; fax: C6637 322 609. E-mail address: paisarnn@swu.ac.th.