Critical heat flux of R-407C in upflow boiling in a vertical pipe

The critical heat flux (CHF) in forced convective upflow has been investigated in a uniformly heated vertical tube of 12.7 mm internal diameter and 3 m length for different reduced pressures ranging from 0.32 to 0.98, with non-azeotropic ternary refrigerant mixture R407C as the working fluid. The onset of CHF was determined by the sudden rise in the wall temperature of the electrically heated tube. Experiments were performed over a wide range of parameters: mass flux values from 200 to 2000 kg/m s, pressure from 15 to 45.6 bar and heat flux from 5 to 80 kW/m. The results show considerably lower critical heat flux at higher pressures as in the case of pure fluids. Finally, a comparison of the experimental data with the available pure fluid correlations has been performed. 2007 Elsevier Ltd. All rights reserved.