Numerical Analysis of Three-Dimensional Turbulent Heat Transfer in a 180.DEG.-Bent Tube by Two-Equation Heat Transfer Models.

Abstract

A numerical analysis of convective heat transfer has been performed for a three-dimensional turbulent flow developing in a 180°-bent tube with straight inlet and outlet sections using several two equation heat transfer models. The calculated results for three types of turbulent model for temperature field are compared with the available experimental data. Althouth the calculated results using the three models predict well the experimental data of time-averaged temperature, one of these models shows a tendency to overpredict the experimental result. Near the bend inlet the decrease of local Nusselt number, which is caused by laminarization, is observed experimentally at the inner wall. By comparing this decrease of local Nusselt number with the calculated results, we find some discrepancies among the heat transfer models. As regards the difference among the models, the eddy diffusivity for heat is examined quantitatively. As a result of this examination, it is clarified that a reasonable prediction is dependent on the model of the eddy diffusivity for heat and that the mixed time scale, which is a parameter of the eddy diffusivity for heat, plays an important role in predicting the temperature distributions. Therefore, it is necessary to propose on elaborated mixed time scale in order to predict precisely the convective heat transfer in both the near-wall region and a region remote from the wall,