CHF for uniformly heated vertical tube under low pressure and low flow conditions [nuclear power plants]

The description of critical heat flux (CHF) phenomena under low pressure (P⩽10 bar) and low flow (G⩽300 kg/m²s) condition is further complicated by the large specific volume of vapor and the effect of buoyancy that are inherent in the condition. In this study, a total of 834 data points of CHF in uniformly heated round vertical tube for water were collected from 5 different published sources. A comparative analysis is made on available correlations and a new correlation is presented. The new CHF correlation comprise of local variables, namely, “true” mass quality, mass flux, tube diameter, and two parameters as a function of pressure only. This study reveals that by incorporating “true” mass quality in the local condition hypothesis, the prediction of CHF under these conditions can be obtained accurately, overcoming the difficulties of now instability and buoyancy effects. The new correlation predicts the CHF data significantly better than those currently available correlations, within the root mean square errors of 7.16, by the heat balance method