Ultra-high critical heat flux (CHF) for subcooled water flow boiling—II: high-CHF database and design equations

Abstract

A high-CHF (critical heat flux) database for subcooled flow boiling of water in tubes was compiled from the world literature. The bulk of the database is for high mass velocity flow ( G ⩾5000 kg m −2 s −1) in small diameter tubes ( D ⩽ 3 mm) . Over half of the 1596 valid data points in the database had CHF values in excess of 25 MW m −2. The database included the highest CHF for uniform heating ever reported in the literature, 276 MW m −2, which was obtained in Part I of the present study. A pressure drop model applicable to subcooled flow boiling in tubes with inlet and outlet plenums was developed in order to determine the pressure at the end of the heated length where burnout (CHF) was observed. The pressure at this location is often significantly different from that measured downstream in the outlet plenum. A subcooled high-CHF correlation superior to previously published correlations was systematically developed using data only from the authors institution and Kiev Polytechnic Institute, Kiev, Ukraine. The correlation was validated with data covering a broad range of pressures (from atmospheric to near the critical point) and mass velocities (1500–134 000 kg m −2 s −1) which are required in the cooling of high-heat-flux components, such as those in fusion reactors. Although it was developed by examining the parametric trends exhibited by a small fraction of the database, the correlation had a root-mean-square error of 19.5% for the entire database, lowest among the correlations tested. In sharp contrast to other correlations, this new, dimensionless CHF correlation consisted of a single equation having only five adjustable constants.