Exergo-economic analysis of micro pin fin heat sinks

Abstract

A parametric study of thermo-economic performance over four micro pin fin heat sinks of different spacing and shapes was conducted. Unit cost per product exergy, relative cost difference, and exergo-economic factor were utilized to evaluate the thermodynamic performance. The effect of working fluid on thermo-economic performance was also investigated using R-123 and water as working fluids. Unit costs per product exergy were obtained to evaluate the product costs (total exergy change between exit and inlet streams) in micro pin fin heat sinks at fixed mass flow rate and fixed pressure drop. The results of the thermo-economic analysis were compared to the results of a past exergy performance study by the author. In the light of raw experimental data acquired from the past studies of the author important differences between the results of exergy and exergo-economic performances were observed. It was found that the unit cost of exergy change decreased as electrical power increased and the relative cost difference approached to unity at high electrical powers (greater than 20 W). Moreover, high exergo-economic factor values (more than 0.5) were obtained at low electrical powers while exergo-economic factors had a small value at high electrical powers. When looking at the effect of the working fluid, higher cost per Watts of the products (up to the double of R-123) was obtained with water compared to R-123 at both fixed mass flow rate and pressure drop. No significant effect of pin fin spacing on the unit cost of exergy change was observed at fixed mass flow rate, while higher unit costs (up to 102%) were recorded at fixed pressure drop for scarcely packaged pin fin heat sinks. Finally, the unit cost of exergy change was found to be independent of pin fin shape at fixed mass flow rate, whereas at fixed pressure drop, the hydrofoil based pin fin heat sink had higher unit costs (up to 1.8 times as much) when compared to the unit costs of pin fin heat sinks having flow separation promoting pin fins.