Critical Heat Flux of Subcooled Water Flow Boiling for High L/d Region

Influence of Test Tube Material on Subcooled Flow Boiling Critical Heat Flux in Short Vertical Tube

“…The CHFs become higher with an increase in flow velocity at a fixed ∆T sub,out . These trends have been already reported by Hata et al (12)- (19) on steady state CHF data for the inner diameters of 2, 3, 6, 9 and 12 mm with the heated lengths of 22 to 150 mm.…”

“…Hata et al (12)-(16), (19) have clarified that the steady state CHFs, q cr,sub,st , against ∆T sub,out for ∆T sub,out ≥30 K are almost proportional to d -0.4 and u 0.4 for fixed ∆T sub,out and L/d, to (∆T sub,out ) 0.7 for a fixed L/d and to (L/d) -0.1 for a fixed ∆T sub,out based on the experimental data by using the thin SUS304 test tube. And, the steady state CHF correlations against outlet and inlet subcoolings, Eqs.…”

“…On the other hand, many researchers have experimentally studied the CHFs on the uniformly heated stainless steel test tube by a steadily increasing current for the most part (5)- (11) . We have already measured the steady state CHFs, q cr,sub,st , (2229 points) on the uniformly heated SUS304 test tubes by a steadily increasing current for wide ranges of experimental conditions to establish the database for designing the divertor of a helical type fusion experimental device, which is a Large Helical Device (LHD) located in the National Institute for Fusion Science, Japan (12)- (19) . It has been clarified that the q cr,sub,st against ∆T sub,out for ∆T sub,out ≥30 K are almost proportional to d -0.4 and u 0.4 for fixed ∆T sub,out and L/d, to (∆T sub,out ) 0.7 for a fixed L/d, and to (L/d) -0.1 for a fixed ∆T sub,out based on the experimental data (12)- (19) .…”

“…We have already measured the steady state CHFs, q cr,sub,st , (2229 points) on the uniformly heated SUS304 test tubes by a steadily increasing current for wide ranges of experimental conditions to establish the database for designing the divertor of a helical type fusion experimental device, which is a Large Helical Device (LHD) located in the National Institute for Fusion Science, Japan (12)- (19) . It has been clarified that the q cr,sub,st against ∆T sub,out for ∆T sub,out ≥30 K are almost proportional to d -0.4 and u 0.4 for fixed ∆T sub,out and L/d, to (∆T sub,out ) 0.7 for a fixed L/d, and to (L/d) -0.1 for a fixed ∆T sub,out based on the experimental data (12)- (19) . We have given the following steady state CHF correlations against outlet and inlet subcoolings based on the effects of test tube inner diameter (d), flow velocity (u), outlet and inlet subcoolings (∆T sub,out and ∆T sub,in ) and ratio of heated length to inner diameter (L/d) on CHF.…”

Influence of Heating Rate on Subcooled Flow Boiling Critical Heat Flux in a Short Vertical Tube

“…Incipient boiling superheat may shift to a high value at a high heating rate, and direct transition to film boiling already observed in liquid nitrogen and water by Sakurai et al (22) may occur in such a case. That may be the cause of very low published data (3), (6), (7) that were about a half or lower of those given by our CHF equation (14) - (16) . However, the q cr, sub at a fixed flow velocity is almost constant for the exponential period lager than 800 ms and it becomes monotonously higher with the decrease in period from around 800 ms. And no direct transition to film boiling and no trend of a decrease in CHF with a decrease in the exponential period in smaller exponential period range was observed on the rough finished surface (R a = 3.18 µm) used here even at the highest heating rate (Q 0 exp(t/τ), τ = 38.1 ms) and the lowest dissolved oxygen concentration (O 2 = 5.88 ppm).…”