Study on Dry-out CHF Characteristics of R134a Flow Boiling in Horizontal Helically-coiled Tubes

An experimental study of critical heat flux（CHF） using R134a as work fluid in horizontal helically-coiled tubes was performed to investigate the CHF characteristics.The stainless steel test section was directly heated uniformly by high-power source.The experiment parameters were: a.outlet pressures of 0.40～1.05 MPa,b.mass fluxes of 51～257 kg/m²s,and c.inlet qualities of-0.18～0.43.And the structure parameters of the test section were: inner diameter of 7.6mm,helix diameter of 300 mm,helix pitch of 40 mm and heated length of 7.07 m.The characteristics of wall temperature and the effects of pressure,mass flux and vapor qualities on CHF were investigated and discussed in this paper.Experiment data were compared with the calculated results by Bowring correlation and Shah correlation,respectively.It was found that the two correlations were not suitable for predicting CHF under the present experiment conditions.