Investigation on heat transfer of in-tube supercritical water cooling accompanying out-tube pool boiling

Abstract

Heat transfer of in-tube supercritical fluid cooling accompanying out-tube pool boiling was investigated. A smooth horizontal circular tube with an inside-diameter of 20 mm was submerged in a water pool at atmospheric pressure. Test parameters of in-tube were as follows: Pressure: 23–28 MPa, mass flux: 600–1000 kg·m−2·s−1, fluid temperature: 400–725 K, and the temperature difference between bulk and wall: 300–374 K. A thermal amplification system based on out-tube pool boiling was used to improve the measurement accuracy of local heat duty near pseudocritical region. According to the experiment, the transition from nucleate boiling to film boiling in the pool occurred near the pseudo-critical fluid region. Sharp variation on thermo-physical properties led to the peak value of heat transfer coefficient in the pseudo-critical region. The pool boiling heat flux increased gradually to 1.19 MW·m−2 near the pseudocritical point. Based on the experimental data, a modified Gnielinski equation was adopted to predict the heat transfer coefficient of in-tube supercritical fluid cooling with out-tube pool boiling. The thermophysical property ratio of the wall to the bulk as well as the effect of buoyancy were taken into consideration in the new correlation. The predicted correlation has an error of less than 20% to the experimental data.