An Experimental Study on Optimum Honeycomb Sizes of a Flat-Plate Solar Collector

평판형(平板形) 태양열집열기(太陽熱集熱器)의 최적(最適)하니콤 크기에 관(關)한 연구(硏究)

To suppress the natural convection within enclosure spacing it has been shown theoretically and experimentally that the introduction of cell walls will effectively raise the critical Rayleigh number by providing more shear surfaces within the fluid. For a solar collector, a useful solar thermal converter requires effective control of heat losses. It has been reported that the natural convection can be suppressed and the heat performances of the solar collector increased by placing thin, poorly conducting material honeycomb between the absorber plate and the coverglass. The heat performances were measured and compared directly throughout the simultaneous installation of two solar collectors, one with honeycomb structures fabricated from thin poly carbonate sheet and the other without honeycomb structures. Various tilt angles of 30, 45 and 60 deg. from the horizontal and the honeycomb sizes ($W{\times}H$) of $10{\times}10,\;10{\times}20$ and $10{\times}40mm$ were utilized in the present investigation. It is found that the larger the tilt angle are, the greater the heat losses are, and that the smaller the honeycomb size is, the larger suppression effect of heat losses are. Especially, at tilt angles of 30 degree, the heat use ratio of solar collector with the honeycomb sizes of $10{\times}10mm$ improved approximately 29.5% more than that without honeycomb structures.