Prediction of turbulent heat transfer through straight channels with sudden contraction at inlet

This paper presents comparisons between heat transfer predictions and measurements for developing turbulent flow through straight channels with sudden contraction at inlet. The numerical results presented in this paper were obtained using a finite-volume code which solves the governing equations in Cartesian coordinate system. The pressure field is obtained with the well-known SIMPLE algorithm. The Hybrid scheme was employed for the discretisation of convection in all transport equations. For modeling of the turbulence, a zonal low--Re k-ε model and the linear and non-linear low-Re k-ε models with the 'Yap' and 'NYP' length-scale correction terms have been employed. The main objective of present study is to examine the ability of the above turbulence models in prediction of convective heat transfer in channels with sudden contraction. The results of this study show that the sudden contraction creates a relatively small recirculation bubble immediately downstream of the channel contraction. This separation bubble influences the distribution of local heat transfer coefficient and increases the heat transfer levels to a factor of three. Computational results indicate that all turbulence models employed produce almost similar flow fields. The zonal k-ε model produces wrong Nusselt number distribution by under-predicting the heat transfer levels in the recirculation bubble and over-predicting them in the developing region. The linear low-Re k-ε model, on the other hand, returns correct Nusselt distribution along the channel wall, though somewhat over-predicts the heat transfer levels in the developing region. The application of the non-linear k-ε model significantly improves the thermal predictions. Moreover, the replacement of the 'Yap' term with the 'NYP' term in linear low-Re k-ε model results in a more realistic local Nusselt number distribution. In general, among the three turbulence models examined, the non-linear low-Re k-ε model with the 'NYP' length-scale correction term produces the best heat transfer predictions. (author)