Second-Law Analysis of a Two-Phase Self-Pumping Solar Water Heater

Entropy generated by operation of a two-phase self-pumping solar water heater under Solar Rating and Certification Corporation rating conditions is computed numerically in a methodology based on an exergy cascade. An order of magnitude analysis shows that entropy generation is dominated by heat transfer across temperature differences. Conversion of radiant solar energy incident on the collector to thermal energy within the collector accounts for 87.1 percent of total entropy generation. Thermal losses are responsible for 9.9 percent of total entropy generation, and heat transfer across the condenser accounts for 2.4 percent of the total entropy generation. Mixing in the tempering valve is responsible for 0.7 percent of the total entropy generation. Approximately one half of the entropy generated by thermal losses is attributable to the self-pumping process. The procedure to determine total entropy generation can be used in a parametric study to evaluate the performance of two-phase hot water heating systems relative to other solar water heating options.