Performance optimization of solar collector equipped with different arrangements of square-celled honeycomb

Honeycomb materials are inserted between the glass cover and the absorber of flat plate solar collector to suppress natural convection. This paper presents the results of an experimental investigation of the thermal performance of solar collector equipped with different arrangements of square-celled honeycomb material. The collector test facility installed at the College of Technological Studies, Kuwait is used to carry out this study. The adapted honeycomb unit is structured from polycarbonate sheet of 10 mm cell size. The effect of air gap thickness above and below the honeycomb material is examined using different arrangements of honeycomb panels with different lenghs. The bottom and top air gap thicknesses are varied from 0 to 12 mm. Experimentally obtained Nusselt number-Rayleigh number plots are presented for free convective heat transfer across honeycomb panels for a wide range of Rayleigh number. Linear regression analysis is implemented to determine the thermal and optical parameters of the solar collector with different honeycomb configurations. A solar collector with air gaps below and above the honeycomb is found to be superior in convection suppression. It is found that the bottom gap thickness is crucial with respect to the heat loss coefficient. The arrangement of honeycomb material with bottom gap thickness of 3 mm is the optimum as it offers the highest efficiency between all arrangements and the lowest heat loss coefficient among other honeycomb configurations. Generally, the results of the present study reveals that compound honeycomb solar collector with proper air gap thickness above and below the honeycomb material attains substantial suppression of free convection.