TRANSIENT MIXED CONVECTION HEAT-TRANSFER IN VERTICAL PIPE FLOWS

The characteristics of transient mixed convection heat transfer has been investigated numerically. The effects of buoyancy ratio Gr/Re and wall-to-fluid heat capacity on the temporal distributions of velocity, temperature and dimensionless wall hat flux are studied id detail. The important role of the wall-to-fluid heat capacity ratio under the situations of buoyancy-aiding and opposing flows is clearly demonstrated. The results show that the dominant factor to determine the time for the flow to approach the steady state is wall-to-fluid heat capacity ratio.