Exergy analysis of second generation micro heat sinks under flow boiling conditions
Koşar, Ali and Özseçen, Yalgın Muzaffer (2009) Exergy analysis of second generation micro heat sinks under flow boiling conditions. In: 3rd International Conference on Energy Sustainability (ES2009), San Francisco, California, USA
An exergy analysis was performed for flow boiling of R-123 in a hydrofoil-based micro pin fin heat sink. It was found that exergy efficiencies decreased with mass velocity at fixed heat input, pressure drop and pumping power under flow boiling conditions, and exergy efficiency could be better represented using the exit mass quality. The outcome of this study also proved noteworthy in view that exergy efficiency could be utilized to assess thermodynamic performance. ************ Heat and fluid flow in micro heat sinks has been a major research area during the last decade in many applications such as aerospace, mechanical, biological, chemical, and optical applications. Forced convective flow in plain microchannel heat sinks was extensively studied in the literature. Thermal hydraulic performances of microchannel heat sinks were evaluated starting from the early 80s. Recently, second generation micro heat sinks with extended surface areas were employed to promote convective heat transfer in micro scale. Significant enhancement in heat transfer was reported for such novel designs in the literature. However, second generation micro heat sinks also introduce additional pressure losses, which should be considered seriously. Thermal and hydrodynamic performances were combined to perform thermal hydraulic performance analysis of second generation micro heat sinks, and important design guidelines have been provided. Despite the heavy focus on the design of second generation micro heat sinks, the scope on this emerging research area is restricted to the thermalhydraulic performance. A thermodynamic approach including their environmental impact would be imperative to add new dimensions to micro heat sink design so that the effect of such heat sinks on the environment could be taken into consideration. In this study, the author intended to address to the lack of information about the thermodynamic performance and the environmental impact of second generation micro heat sinks. To address to this lack of information, an exergy analysis was performed for flow boiling with R-123 in a hydrofoil based micro pin fin heat sink. It was observed that exergy efficiencies decrease with mass velocity at fixed heat input, pressure drop and pumping power under flow boiling conditions and could be better represented using the exit mass quality. The main findings from this boiling study are as follows: • Exergy efficiencies are greater for low mass velocities at fixed heat input, pressure drop and pumping power. • The trends in thermal and exergy performances with mass velocity contradict with each other.
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