Numerical investigation of air–steam condensation in a vertically enhanced tube with dimples and protrusions

Abstract

The thermo-hydraulic performance of air–steam condensation in a vertically enhanced tube with dimples and protrusions is investigated numerically. A forming experiment is conducted to test the validity of the physical model establishment. The heat transfer enhancement mechanism is investigated. In addition, the effects of inlet air mole fraction, the depth and pitch of the dimples on thermo-hydraulic performance are presented and discussed. The results showed that the error between the actual manufacture and mechanical simulation geometric model is less than 15 %. The structure of interlaced dimples and protrusions can disrupt the air concentration layer, promote fluid mixing, and eventually enhance the heat transfer between steam and condensing walls. The lower inlet air mole fraction, greater dimple depth, and longer dimple pitch of the enhanced tube, the better thermo-hydraulic performance is obtained. Among all the cases, the best design of geometric parameters occurs when the inlet air mole fraction, the dimple depth, and the pitch are 10 %, 4 mm, and 25 mm respectively. In addition, the comprehensive heat transfer performance is compared among different enhanced tubes and the results show that the enhanced tube with dimples and protrusions has better comprehensive heat transfer performance.