Experimental Study on the Boiling Heat Transfer Characteristics of R134a in a Helically Coiled Tube

The characteristics of R134a boiling heat transfer in a vertically helically coiled tube are studied. The experimental parameters are as follows: the heat flux is 10∼60 kW•m^-2, the mass flux is 195∼400 kg•m^-2 •s^-1, the pressure is 0.8∼1.1 MPa, and the outlet vapor quality is 0.1∼0.9. The experimental data are compared with the existing correlations of boiling heat transfer coefficient. Based on the analysis of boiling heat transfer mechanism, a new correlation for boiling heat transfer in coiled tube is proposed. The circumferential distribution characteristics of wall temperature and heat transfer coefficient are analyzed. The wall temperatures at inner and top side are relatively higher, and the heat transfer coefficients at the bottom and the outer side are relatively higher. The local heat transfer coefficients are compared with the new correlation proposed in this paper. The results show that the heat transfer coefficients at top and bottom sides can be predicted by the new correlation. However, the new correlation underestimates the heat transfer coefficient at the outer side and overestimates that at the inner side, the deviations are 16.6% and -11.9% respectively.