Critical Heat Fluxes of Subcooled Water Flow Boiling against Inlet Subcooling in Short Vertical Tube(<Special Issue>International Conferences on Power and Energy System)

The critical heat fluxes (CHFs) of subcooled water flow boiling for the test tube inner diameters (d=3 and 6mm) and the heated lengths (L=67, 120 and 150mm) are systematically measured for the flow velocities (u=4.0 to 13.3m/s), the inlet subcoolings (⊿T_<sub,in>=48 to 148K), the outlet subcoolings (⊿T_<sub,out>=10.5 to 95.1K), the inlet pressure (P_<in>=753 to 995kPa) and the outlet pressure (P_<out>=720 to 887kPa). The SUS304 tubes of L=67, 120 and 150mm for d=3mm and L=150mm for d=6mm are used. The values of L/d are 22, 40 and 50 for d=3mm, and 25 for d=6mm, respectively. The CHFs, q_<cr,sub>, for a fixed ⊿T<sub,out> become gradually lower with an increase in the L/d in the whole experimental range. The CHF correlation against outlet subcooling, which has been previously derived for L/d lower than 16, was modified to new one containing the L/d effect based on these experimental data. Furthermore, the relation between q_<cr,sub> and L/d for a fixed ⊿T_<sub,in> was checked. The values of q_<cr,sub> for a fixed ⊿T_<sub,in> became exponentially lower with the increase in L/d. CHF correlation against inlet subcooling has been given based on the experimental data for L/d ranging from 4.08 to 50. The correlations against outlet and inlet subcoolings can describe not only the CHFs obtained in this work for the inner diameter of 3 and 6mm at the outlet pressure of around 800kPa but also the authors' published CHFs data (1611 points) for the wide ranges of P_<in>=159kPa to 1MPa, d=3 to 12mm, L=33 to 150mm and u=4.0 to 13.3m/s within 15% difference for 30K〓⊿T_<sub,out>〓140K and 40K〓⊿T_<sub,in>〓151K.