CHF of forced convection boiling in uniformly heated vertical tubes: Experimental study of HP-regime by the use of refrigerant 12

For the critical heat flux in HP-regime, that is high-pressure regime, almost no data having been published for fluids other than water, an experimental study is attempted on R-12 boiling in 5- and 3-mm dia. and 1000-mm long tubes. Critical heat flux q_c is measured in the range of pressure p = 19.6?34.3 bar (vapor-to-liquid density ratio $\text{ρ}{}_{\mathrm{G}}\text{ρ}{}_{\mathrm{L}}\text{= 0.109?0.306}$), mass velocity G = 1100?9000 kg/m²s, and inlet subcooling enthalpy ΔH_i= 0?65 kJ/kg. Depending on the condition of G and ΔH_i, CHF takes place with natures which can be divided into two categories, regular and anomalous. For regular CHF, critical condition is detected first at the exit end of heated tube and a linear q_c ? ΔH_i relationship holds, whereas anomalous CHF initiates its critical condition upstream of the tube exit and exhibits involved relationship between q_c and ΔH_i. Experimental data of regular CHF are found to agree fairly well with the predictions of two different generalized correlations proposed recently by Katto and by Shah respectively although some systematic differences proper to each correlation exist.