A correlation for critical pressure with subcooled upstream conditions

A simple correlation for critical pressure has been developed by examining 283 critical flow data for subcooled inlet conditions. Present correlation predicts critical pressure at the critical location in the channel with the geometry of converging rounded inlet followed by sufficiently long constant diameter pipe and then gradually diverging diffuser. The flow directions are horizontal and vertical upflow. Major assumptions used are (1) the critical pressure resembles the nucleation pressure and (2) the main parameters that affect the critical pressure are the inlet temperature and the degree of subcooling. Present work is an extension of the static flashing undershoot correlation to broader upstream ranges of data from the previous critical flow experiments. The ranges of variables covered for stagnation pressure is from 94 to 12000 KPa, inlet temperatures from 69 to 324 .deg. C, and inlet subcooling from 0.1 to 115.1 .deg. C (or stagnation quality from -0.0002 to -0.15). The present correlation predicts total 283 critical pressure data with mean relative error of 0.3 %, RMS relative error of 3.94 % and standard deviation of 3.93 %. The present correlation can be applied directly to simple homogeneous nonequilibrium critical flow models for subcooled upstream conditions where the critical pressure should be known a priori