Flow boiling heat transfer of refrigerant R-134a in copper microchannel heat sink

This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.In this paper we present experimental data on heat transfer and pressure drop characteristics at flow boiling of refrigerant R-134a in a horizontal microchannel heat sink. The primary objective of this study is to establish experimentally how the local heat transfer coefficient and pressure drop correlate with the heat flux, mass flux and vapor quality. The copper plate of microchannel heat sink contains 21 microchannels with 335x930 m2 cross-section. The microchannel plate and heating block were divided by the partition wall for the local heat flux measurements. Distribution of local heat transfer coefficients along the length and width of the microchannel plate were measured in the range of external heat fluxes from 50 to 500 kW/m2; the mass flux was varied within 200-600 kg/m2s, and pressure was varied within 6-16 bar. The obvious impact of heat flux on the magnitude of heat transfer coefficient was observed. It shows that nucleate boiling is the dominant mechanism for heat transfer. The new model of flow boiling heat transfer, which accounts nucleate boiling suppression and liquid film evaporation, was proposed and verified experimentally in this paper