An experimental study on micro-scale flow boiling heat transfer

This paper was presented at the 2nd Micro and Nano Flows Conference (MNF2009), which was held at Brunel University, West London, UK. The conference was organised by Brunel University and supported by the Institution of Mechanical Engineers, IPEM, the Italian Union of Thermofluid dynamics, the Process Intensification Network, HEXAG - the Heat Exchange Action Group and the Institute of Mathematics and its Applications.New experimental flow boiling heat transfer results in micro-scale tubes are presented in this paper. The experimental data were obtained in a horizontal 2.32 mm I.D. stainless steel tube with heating length of 464 mm, R245fa as working fluid, mass velocities ranging from 50 to 500 kg/m2s, heat flux from 5 to 55 kW/m2, exit saturation temperatures of 22, 31 and 41 oC, and vapor qualities from 0.05 to 0.99. Flow pattern characterization was also performed from images obtained by high speed filming. Heat transfer coefficient results from 2 to 6 kW/m2K were measured. It was found that the heat transfer coefficient is a strong function of the heat flux, mass velocity and vapor quality. The experimental data were compared against the following micro-scale flow boiling predictive methods from the literature: Bertsch et al. (2008), Saitoh et al. (2007), Kandlikar and Balasubramanian (2004), Zhang et al. (2004), Thome et al. (2004) and Liu and Winterton (1991). Although not satisfactory, Thome et al. (2004) worked the best when predicting the present database.This study is funded under contract numbers 05/60031-0, 06/52089-1 and 07/53950-5 by FAPESP (The State of São Paulo Research Foundation, Brazil)