And the /-chart dimensionless parameter X (plotted on the abscissa of the /-chart) is replaced by a modified dimensionless variable, X', given by
In fact, the change in the X dimensionless variable is that the parameter (100 - Ta) is replaced with an empirical constant 100.
The /-charts can be obtained from actual charts or from the following analytical equation (Klein and Beckman, 1979):
/ = $maxY - 0.015[exp(3.85/) - 1][1 - exp(-0.15X')]Rs0'76 (11.48)
where Rs = ratio of standard storage heat capacity per unit of collector area of 350 kJ/m2-°C to actual storage capacity, given by (Klein and Beckman, 1979):
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