Thermal-hydraulic characteristics of supercritical pressure CO2 in vertical tubes under cooling and heating conditions

Abstract

The thermal-hydraulic properties of supercritical pressure CO2 (SCO2) in vertical tubes under cooling and heating conditions were numerically investigated by using SST turbulent model with variable turbulent Prandtl number model. Under cooling condition, the peak of heat transfer coefficient appears near the pseudo-critical point, the buoyancy effect enhances local heat transfer for upward flow while deteriorates that for downward flow, and the criterion Gr¯/Re27 is more accurate than Bo∗ in the evaluation of buoyancy effect. Under heating condition, the buoyancy effect improves local heat transfer for downward flow while deteriorates that for upward flow. The local heat transfer deterioration only occurs in the case of Tb,in<Tpc for upward flow, and the increasing Tb,in may alleviate the local heat transfer deterioration. The decreasing heat flux and tube diameter could reduce or even eliminate the local heat transfer deterioration for upward flow. The present work may provide a practical guidance on mechanism acknowledge of thermal-hydraulic properties of SCO2 and optimization design of heat exchanger.