Combined Buoyancy and Flow Direction Effects on Saturated Boiling Critical Heat Flux in Liquid Nitrogen

Abstract

Data comparisons showed that the critical heat flux for downflow could "be up to 36 percent lower than for upflow. A nonmonotonic relationship between the critical heat flux and velocity was determined for upflow but not for downflow.A limiting inlet velocity of 4.12 m/s was determined to be the minimum velocity required to completely suppress the influence of buoyancy on the critical heat flux for this saturated inlet flow system. A correlation of this limiting fluid velocity is presented that was developed from previously published subcooled liquid nitrogen data and the saturated data of this investigation.

Prediction of Critical Heat Flux during Downflow in Fully Heated Vertical Channels

“…The previous discussions show that most of the experimental studies indicate that there is no or a small effect of flow direction on CHF. The only studies that show that CHF in downflow is much lower are Pappel et al, (1966) [4] and Pappel (1972) [5] for nitrogen. The two were done on the same test section and all parameters were the same except for inlet subcooling.…”