End-clearance effects on rectangular-honeycomb solar collectors

Abstract

Results are reported of an experimental program to measure the effects of gaps between a honeycomb core and its coverglass and absorber plate. Nusselt numbers up to values of 2 vs Rayleigh number are reported for gaps of 0, 1.5, 2.3, 3.0 and 4.6 mm above and 0 and 1.5 mm below a 19 mm thick honeycomb core with 4.69 × 40.3 mm rectangular cells. The nontranspired honeycomb system was heated from below and oriented at 0°, 15° and 30° from the horizontal with the long dimension of the cells running horizontally. The results indicate that a well-designed honeycomb core will give good performance in a solar collector even with clearance gaps of 1.5 mm above and/or below the core.