Experimental results on boiling heat transfer coefficient, frictional pressure drop and flow patterns for R134a at a saturation temperature of 34 °C

•New available boiling heat transfer and pressure drop data for R134a @ 34 °C.•Increasing mass flux enhances heat transfer mainly at high vapor fractions.•Increasing heat flux enhances heat transfer mainly at low vapor fractions.•Widely used 2-phase correlations accuracy does not change considerably.•Flow patterns have been well predicted by K–T–F flow pattern map.

The current study presents heat transfer and pressure drop data for R134a at a saturation temperature of approx. 34 °C. Study cases have been set for two different mass fluxes and heat fluxes. The flow patterns have also been characterized by means of a fast speed camera and a visualization section between the heat transfer and pressure drop measurements. Comparing with the available results in the open literature for lower saturation temperatures it can be seen that the heat transfer coefficient has a more planar profile as the mass flux decreases and the saturation temperature and the heat flux increase. For the frictional pressure drop the studied cases show a maximum around a quality of 0.85, which seems not to be influenced by the mass flux. Finally, the flow patterns observed show a good agreement with the K–T–F flow pattern map (N. Kattan, D. Favrat, J. R. Thome, Flow boiling in horizontal tubes. Part 1: Development of a diabatic two-phase flow pattern map, Journal of Heat Transfer 120(1):140–147, 1998a).