A glazed flat-plate collector is tested at

PHYSICS · Multi-part · Fermi University Physics · Thermal, Statistical & Complex Systems · Earth, Climate & Energy Physics · The laws of thermodynamics

Energy from Physics, Ch The solar resource resolved: geometry, spectrum and the limits of concentration

Problem

F_{\rm c}=1000\,\mathrm{W\,m^{-2}}

. With the inlet

20\,\mathrm K

above the air its efficiency is

0.68

, and with the inlet

70\,\mathrm K

above the air it is

0.48

. ((a)) Fit the collector efficiency equation to these two points and find

F_R(\tau\alpha)

and

F_RU_L

. ((b)) Predict the efficiency and the useful heat per unit area on a winter day with

F_{\rm c}=500\,\mathrm{W\,m^{-2}}

, air at

280\,\mathrm K

and the inlet at

320\,\mathrm K

. ((c)) Treating that heat as delivered at the single temperature

T_i

, with the air as the dead state, find its exergy per unit area and as a fraction of

F_{\rm c}

. State which way this approximation errs.

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