ABSTRACT
The most convenient model of flat-plate collector performance, a model which neglects thermal capacitance effects, is that proposed by H. C. Hottel and A. Whillier, Whillier and R. W. Bliss. As pointed out by H. Tabor, the values of the convection coefficients between parallel flat plates and the glass emittance used by Hottel and B. B. Woertz in formulating their relation have been modified based on more recent measurements. The changes were compensating for the case of collectors with non-selective absorber plates so that the empirical relationship derived from their analysis yields acceptable results. Hottel and Woertz recognized that their relation was not suitable for collectors with selective surfaces. The collector geometry efficiency factor can be determined in the manner presented by Whillier or Bliss. However, the overall energy loss coefficient is more difficult to evaluate because it is a function of the operating conditions of the collector.
