Flow Boiling Heat Transfer of R134a in a Vertical Helically Coiled Tube

The boiling heat transfer characteristics of R134a in a helically coiled tube under high heat flux condition were investigated experimentally in present paper. The inner diameter and the coil diameter of the coil were 8 mm and 205 mm, respectively. Experiments were carried out with the heat flux in the range of 10–60 kW/m2, pressure 0.8–1.1 MPa, mass flux 195–400 kg/(m2 s) and vapor qualities 0.1–0.9. The results show that nucleate boiling plays a significant role even at high vapor quality. Inversely, the convective boiling was weakened in the high quality region under high heat flux conditions. The available boiling heat transfer coefficient correlations were compared with present experimental results. A new boiling heat transfer coefficient correlation for R134a in helically coiled tube was proposed based on the boiling mechanisms analysis. The new correlation was also proved to be applicable for high mass flux and low heat flux conditions.