Sh. Delfani - Department of Installations, Building and Housing Research Center (BHRC), Tehran, PO Box ۱۳۱۴۵-۱۶۹۶, Iran.
M. Karami - School of Mechanical Engineering, College of Engineering, University of Tehran, Tehran, PO Box ۱۴۳۹۵-۵۱۵, Iran.
M. A. Akhavan Bahabadi - School of Mechanical Engineering, College of Engineering, University of Tehran, Tehran, PO Box ۱۴۳۹۵-۵۱۵, Iran.

In the present work, a prototype of a new type of solar collectors, which called Direct Absorption Solar Collector, was built and its thermal performance is experimentally compared with conventional flat plate solar collector under transient and steady state conditions. Different volume fractions of multi wall carbon nanotubes in water and ethylene glycol mixture (۷۰%:۳۰% in volume) were used as working fluid of direct absorption solar collector.The transient comparison show that the efficiency of the direct absorption solar collector becomes about ۷% (in average) more than that of flat plate solar collector at ۷۲l/hr flowrate. Thesteady state performance tests were performed in different flowrates from ۵۴to ۹۰l/hr,based on the procedure of EN ۱۲۹۷۵-۲ standard.Under similar operating conditions, adirect absorption solar collector using ۱۰۰ppm carbon nanotube nanofluid has the zero-loss efficiency of ۲۳% higher than that of a flat plate collector;whereas, the zero-loss efficiency of a direct absorption solar collector using the base fluid is ۴.۴% lower than that of a flat plate collector. Based onthe results, the performance of a direct absorption solar collector using carbon nanotube nanofluidsis better than a flat-plate solar collector.

Carbon nanotubes, Direct absorption solar collector, Flat plate solar collector, nanofluid, Solar Energy