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 R-407C 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/m2 s, pressure from 15 to 45.6 bar and heat flux from 5 to 80 kW/m2. 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.