Investigation of Flow Boiling in Micro-Channels: Heat Transfer, Pressure Drop and Evaluation of Existing Correlations

In this study, the flow boiling heat transfer and pressure drop characteristics of refrigerant R۱۳۴a in micro-channels were experimentally investigated. The tests were performed in circular horizontal micro-channels with inner diameters of ۰.۵ mm and ۱ mm and a heating length of ۳۰۰ mm. The mass velocities varied from ۵۰۰ kg/m۲s to ۲۵۰۰ kg/m۲s, and the heat fluxes varied from ۱۵ kW/m۲ to ۱۴۷ kW/m۲. The heat transfer coefficient (HTC) and frictional pressure drop (FPD) were measured and discussed in detail. According to the results, HTC was significantly affected by heat flux, whereas it was independent of mass velocity. Nucleate boiling was the dominant heat transfer mechanism for R۱۳۴a flow boiling in the micro-channels. In comparison to the ۱ mm channel, the ۰.۵ mm channel shows better performance in heat transfer, with a maximum increase of approximately ۲۲ %. In addition, FPD increased with increasing mass velocity and decreasing channel diameter. Finally, several existing correlations for HTC and FPD were evaluated by comparing them with the experimental values. Tran’s correlation (۱۹۹۶) presented a better agreement in terms of the average HTC, while for the FPD, the model of Kim and Mudawar (۲۰۱۳b) showed good prediction accuracy.

Keywords:

Micro-channel , Flow Boiling , Heat transfer , Frictional pressure drop , Predictive correlations