Correlations for surface temperatures of the glass cover for estimation ofheat-transfer coefficients in upward heat-flow in solar collectors with single glazing

A set of correlations for predicting the temperatures of inner and outer su rfaces of the glass-cover of flat-plate solar collectors with single glazin g is developed, enabling estimation of the heat-transfer coefficients. The temperatures of the inner surface of the glass-cover (T-gi) and outer surfa ce of glass-cover (T-go) are computed using the proposed relations and the results are compared with those obtained by numerical solution of heat bala nce equations. Using the proposed relations maximum computational errors in T-gi and T-go are within 1.5 degrees and 3.0 degrees respectively: for the range of glass-cover thicknesses 3 mm to 5 mm. (Using the previously avail able relation in the literature computational error in glass-cover temperat ure is 9 to 11 degrees). As a result the maximum errors in calculation of c onvective and radiative heat-transfer coefficients between the absorber-pla te and the glass-cover are reduced from about 8.8 percent to 1.1 percent an d from 3.7 percent to 0.5 percent respectively. With such low errors in com putation of the heat-transfer coefficients, numerical solution of heat bala nce equations is not required. The proposed method can also take into accou nt absorption in the glass-cover.