Critical heat fluxes of subcooled water flow boiling against inlet subcooling in short vertical tube

Abstract

The critical heat fluxes (CHFs) of subcooled water flow boiling for the test tube inner diameters (d = 3 and 6 mm) and the heated lengths (L = 67, 120 and 150 mm) are systematically measured for the flow velocities (u = 4.0 to 13.3 m/s), the inlet subcoolings (ΔTsub,in = 48 to 148 K), the outlet subcoolings (ΔTsub,out = 10.5 to 95.1 K), the inlet pressure (Pin = 753 to 995 kPa) and the outlet pressure (Pout = 720 to 887 kPa). The SUS304 tubes of L = 67, 120 and 150 mm for d = 3 mm and L = 150 mm for d = 6 mm are used. The values of L/d are 22, 40 and 50 for d = 3 mm, and 25 for d = 6 mm, respectively. The CHFs, qcr,sub, for a fixed ΔTsub,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 qcr,sub and L/d for a fixed ΔT sub,in was checked. The values of qcr,sub for a fixed ΔTsub,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 6 mm at the outlet pressure of around 800 kPa but also the authors' published CHFs data (1611 points) for the wide ranges of Pin = 159 kPa to 1 MPa, d = 3 to 12 mm, L = 33 to 150 mm and u = 4.0 to 13.3 m/s within 15% difference for 30 K≤ΔTsub,out≤ 140 K and 40 K≤ΔTsub,in≤ 151 K.