Investigation of thermo-hydraulic performance of concentrated solar air-heater with internal multiple-fin array Jacek Kasperski * , Magdalena Nem  s Wroclaw University of Technology, Institute of Power Engineering and Fluid Mechanics, Wybrzeze Wyspianskiego 27, 50-370 Wroclaw, Poland highlights  An internal multiple-fin array arrangement of solar air heater is proposed.  Simple efficiency test confirms preliminary thermal feature of the arrangement.  A mathematical model of heat transfer processes was build.  Calculation showed optimum of thermo-hydraulic efficiency against the volume flux.  Optimal duct amounts for the receiver were found. article info Article history: Received 15 January 2013 Accepted 11 April 2013 Available online 4 May 2013 Keywords: Solar air heater Thermal efficiency Fin Thermal package abstract This study presents a thermo-hydraulic analysis of a solar air heater with an internal multiple-fin array. A preliminary simple test was carried out to confirm the efficiency enhancement of the proposed arrangement. A mathematical model of heat transfer processes was proposed. A thermo-hydraulic efficiency test was used to find the best fin arrangement of the receiver. For an applied set of ducts, calculations were carried out to find the thermo-hydraulic efficiency of the collector against the volumetric air flux. As a comparison, a smooth pipe arrangement was used. Calculation results of the mathematical model showed an existing optimum of thermo-hydraulic ef- ficiency against the volume flux, fin thickness and duct width. If there is no limitation of the air speed, proposed half-pipe finned technology enables a 14% efficiency improvement in relation to the smooth pipe arrangement of the solar collector with black paint and double glass envelope, and 3.3% for the solar collector with selective layer and single glass envelope. If 5 m/s speed limit of air in piping system is assumed, proposed half-pipe finned technology enables a 13% efficiency improvement in relation to the smooth pipe arrangement of the solar collector with black paint and double glass envelope, and 11% for the solar collector with selective layer and single glass envelope. Proposed multiple fin-array technology enables to decrease the demanded air flux of 7e10 times in comparison to the smooth pipe arrangement of the absorber. Even with the flux decreased, the efficiency of internal multiple-fin array arrangement is higher than the one available for smooth pipe arrangement. The solution could be applied in solar space heating with rock bed storage systems or in solar dryers. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction 1.1. Concentrating solar air collectors Solar concentrators are usually used in solar power plants or industry, mainly to produce high-temperature process heat. As an operation medium in concentration collectors, oil, glycol, water, phase change fluids, or less frequently gases, are used. Concen- trating collectors for liquid are heated up to 400  C. A higher temperature level is very useful for thermal electricity generation, process heat application, desalination, chemical conversion of fuels, detoxification [1]. Concentrating collectors for air heating are rarely used. Main applications are: drying, thermal conversion, solar air space heating. The research on high-thermal solar air space heating is developed by the authors. Concentrating solar air collectors are most commonly used in warm climate countries, where only the direct component of solar radiation is used. Nevertheless, it does not exclude their use in * Corresponding author. Tel.: þ48 71 3203505; fax: þ48 71 3283818. E-mail address: jacek.kasperski@pwr.wroc.pl (J. Kasperski). Contents lists available at SciVerse ScienceDirect Applied Thermal Engineering journal homepage: www.elsevier.com/locate/apthermeng 1359-4311/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.applthermaleng.2013.04.018 Applied Thermal Engineering 58 (2013) 411e419