R134a flow boiling inside a 2.4 mm ID microfin tube

The refrigerant charge reduction is one of the most challenging issues that the scientific community has to cope with to reduce the anthropic global warming. Since their invention in the ‘70s, microfin tubes have been found to be a smart alternative to smooth tubes, because they can achieve higher heat transfer coefficients with a relatively small increase in pressure drops. Higher heat transfer coefficients imply lower refrigerant charge needed for the refrigeration or air conditioning systems, or for electronics cooling applications. Recently, mini microfin tubes have been matter of research, since they can reach better thermal performance in small domains, thus leading to a further refrigerant charge reduction. Up today, really few researchers investigated the two-phase heat transfer of refrigerants inside such mini microfin tubes [1-3]. This paper presents some preliminary results about the R134a flow boiling inside a mini microfin tube having an internal diameter at the fin tip of 2.4 mm. The mass flux was varied between 375 and 940 kg m-2 s-1, the heat flux from 10 to 50 kW m-2, and the vapour quality from 0.10 to 0.99. The saturation temperature at the inlet of the test section was kept constant and equal to 30 °C, which is suitable for high temperature heat pumps or for electronics cooling applications. The results are given in terms of heat transfer coefficients and frictional pressure drops.