collector efficiency in downward-type double-pass solar air heaters with attached fins and operated by external recycle收集器效率downward-type双向太阳能空气加热器与附加鳍和由外部回收.pdf

Energies 2012, 5, 2692-2707; doi:10.3390/en5082692 OPEN ACCESS energies ISSN 1996-1073 /journal/energies Article Collector Efficiency in Downward-Type Double-Pass Solar Air Heaters with Attached Fins and Operated by External Recycle Ho-Ming Yeh and Chii-Dong Ho * Energy and Opto-Electronic Materials Research Center, Department of Chemical and Materials Engineering, Tamkang University, Tamsui, New Taipei 251, Taiwan; E-Mail: hmyeh@.tw * Author to whom correspondence should be addressed; E-Mail: cdho@.tw; Tel.: +886-2(ext. 2724); Fax: +886-2 Received: 30 April 2012; in revised form: 4 June 2012 / Accepted: 19 July 2012 / Published: 26 July 2012 Abstract: The collector efficiency in a downward-type double-pass external-recycle solar air heater with fins attached on the absorbing plate has been investigated theoretically. Considerable improvement in collector efficiency is obtainable if the collector is equipped with fins and the operation is carried out with an external recycle. Due to the recycling, the desirable effect of increasing the heat transfer coefficient compensates for the undesirable effect of decreasing the driving force (temperature difference) of heat transfer, while the attached fins provide an enlarged heat transfer area. The order of performances in the devices of same size is: double pass with recycle and fins double pass with recycle but without fins single pass without recycle and fins. Keywords: solar air