PREDICTION OF CONVECTIVE HEAT TRANSFER COEFFICIENTS AND EXAMINATION OF THEIR EFFECTS ON DISTORTION OF CYLINDRICAL TUBES QUENCHED BY GAS COOLING

摘要

The primary objectives of this study are to model the nature of the high-turbulence complex quenching cooling-gas flow, with flow separations, and to examine its effects on the resulting distortions, here of bearing steel tubes. A k-∈ turbulent flow and heat tran- sfer model we have adopted was found to predict the convective heat transfer coefficient distribution reasonably well for Reynolds number up to about (0.3) 10~6. At higher Reynolds number (here examined up to 10~6) it predicts them reasonably well in most of the cylinder windward and leeward zones, and predicts well the angles at which transition to turbulent starts and at which the flow separates, as well as the existence of two maxima and two mininia in the heat transfer coefficient. It, however predicts values about 100 higher than those available from the available experimental data in the laminar-to-turbulent boundary layer transition zone. This model, as well as available experimental and representative data, were used to define the distributions of the convective heat transfer coefficient around the body surface as the boundary condition of a finite-element program developed at the Swedish institute for Metals Research for Predicting the temperature distribution history, phase transformations, distortions and mechanical properties of quenched steel bodies. The dependence of the distortions on the extent of convective heat transfer coefficient nonunifornity was analyzed.