Performance characterisation of front-pass thermosyphoning air panels

Abstract

SYNOPSIS Characterising the performance of thermosyphoning air panels (TAPS) is particularly difficult because the mass flow-rate, and therefore the collector efficiency factor and heat loss coefficient, is dependant on the incident solar radiation. An expression is derived, which allows mass flow to be deduced, as a function of collector characteristics which may be functions of mass flow themselves (dynamic fluid friction coefficients, efficiency factor, heat loss coefficients, etc.), operating conditions and ambient weather parameters. Dynamic friction losses are determined from experimental data for the entrance and exit regions of a TAP, and for flow through a TAP with finned absorber plates. For the laminar flows in the TAP, loss coefficients were determined to be functions of Reynolds number of the form f = CRer, with C being of the order 107 and r typically about −1.6, the exact values of the constants depending on the arrangement of the TAP.