A thermal analysis of the performance of a solar flat-plate collector operating in nonboiling, boiling, and superheated regimes is presented. The performance of the collector under these single and multiphase conditions is governed by the axial fractional channel lengths of the subcooled (nonboiling) and the superheated regions. The overall thermal loss coefficient, the dimensionless capacitance rate, and collector efficiency factors for various collector operating regions are defined. A new "Generalized Heat Removal Factor," Fs, and a new overall thermal loss coefficient, UL, for flat-plate collectors under any operation mode are developed. The thermal efficiency a flat-plate collector, whether under nonboiling, boiling, or superheated conditions, is evaluated using, Fs and UL. It is shown that the value of Fs decreases and the value of UL increases as the degree of superheat increases. Current applications of flat-plate collectors having multiphase flows are represented by those charged with refrigerants.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/27542/1/0000586.pd
