EXPERIMENTAL ANALYSIS OF A QUADRUPLE-PASS SOLAR AIR HEATER WITH EXTENDED HEAT TRANSFER SURFACES AND NANO-ENHANCED ABSORBER COATING

Abstract

In recent years, selective solar absorber surface coating applications have become quite popular in terms of enhancing the thermal performance of solar-thermal systems. Generally, nano-sized particles with high thermal conductivity values are preferred to be utilized in this type of modifications. In this study, nanoparticle-enhanced absorber coating material was applied to a quadruple-pass solar air heater to improve the thermal performance. In this regard, copper oxide nanoparticles with 38-nm average particle size and 32.9 W/m K thermal conductivity were mixed with industrial matte-black paint (2% wt./wt.). The obtained mixture was then applied to the heater and the developed heater has been experimented at three flow rate values. Embedding nanoparticles to the pure paint improved the average thermal conductivity as 0.033 W/m K (from 0.6392 W/m K to 0.6722 W/m K). According to the experimentally attained outcomes, mean thermal efficiency values were obtained in the range of 71.27-79.63%. Improving the flow rate from 0.007 kg/s to 0.013 kg/s enhanced the sustainability index value from 1.1696 to 1.2123. Moreover, maximum instantaneous thermal efficiency was found to be 4.05% higher in comparison with the system without nano-enhanced modification which was tested in a previous work.