NUMERICAL SIMULATION OF TURBULENT CONVECTIVE HEAT TRANSFER IN SQUARE RIBBED DUCTS

Abstract

This article reports on an investigation on numerical prediction of thermal characteristics of a certain type of duct. The ducts considered have rib turbulators to enhance the heat transfer rate. The calculation method consists of a low Re number turbulence model and two methods for determining the turbulent Reynolds stresses, namely, a simple eddy viscosity model (EVM) [1] and an explicit algebraic stress model (EASM) [2]. The model development is carried out to make the original EASM consistent with the low Re number k- epsilon turbulence model applied. A certain method is developed to deal with the decoupling of the velocity and Reynolds stress fields inthe collocated grid arrangement that is chosen in this study. The SIMPLEC algorithm handles the pressure-velocity coupling. The computations are performed with the assumption of fully developed periodic conditions. These models are used to predict the convective turbulent forced convection in different test cases and the results are compared with experiments. A ribbed duct with two ribs on opposite walls is chosen and the obtained results including the mean thermal characteristics of the considered duct are compared with an experimental correlation. Two further duct configurations, identical to an experimental setup, are then computed. These experimental cases are chosen because detailed thermal-hydraulic information is available and then local comparisons between the two prediction models and experimental results are possible. The calculated mean and local thermal-hydraulic values are compared with corresponding experimental data and the prediction capabilities of the two turbulence models (EVM and EASM) are discussed. Theresults show that the EASM has some superiority over the EVM in the prediction of the velocity field structure, but the mean thermal predictions are not very different. There are also some important features of the flow field, whichare not revealed by theEVM calculations. However, the required CPU times are considerably higher for the EASM case.