NUMERICAL SIMULATION OF TURBULENT HEAT TRANSFER IN INDUSTRIAL DRYING PROCESSES

Aiming to model drying processes in automotive industry, numerical investigations of turbulent heat transfer in a laboratory dryer and an industrial dryer have been carried out using CFD. Flat sheets, a 3-D driver’s cab model, as well as more complicated geometries of substrates, for instance, a real car body were used in the simulations. The suitable turbulence model and appropriate grid resolutions were applied for the present industrial computations. The calculated heating-up behaviour on substrates was compared with experimental results. The distribution of local temperature gradients obtained in CFD calculations can be used to develop models for predicting paint film defects in drying processes. 1. INTRODUTION In order to meet the increasing demands on the reproducibility and reliability of drying processes in car industry, a joint research project funded by the German BMBF has been launched in cooperation with different research institutes, four car manufacturers, four plant and paint manufacturers and two software houses. The aim of this project is to develop an experimentally verified simulation tool to predict the convective unsteady drying of paint films on complex, three-dimensional work pieces, e.g., car bodies. Within this project different stages of experimental and numerical studies have been identified. In general, there are two parts of the investigation. One is the modelling of unsteady turbulent heat transfer on complex 3D objects; another is the modelling of the evaporating process of water born base coats on objects. The current paper only deals with the investigation on the prediction of turbulent heat transfer without paint film. It was decided to apply CFD (Computational Fluid Dynamics) based methods to predict the drying process. In our previous stage of the research [1-2], assessments of available turbulence models used in CFD codes for turbulent heat transfer were carried out by means of suitable data sources, for instance, DNS (Direct Numerical Simulation) data, single jet impingement, as well as experimental data obtained in a laboratory dryer, in order to find out models with low sensitivity of heat transfer prediction to the grid spacing for flow calculations in drying processes of car industry. In this stage of the research the selected turbulence model and the suitable mesh resolution in the vicinity of the substrate were applied to the unsteady simulation of convective heat transfer of realistic turbulent flow in a laboratory dryer (Hygrex dryer) and Eisenmann dryer for car industry. A commercial CFD code (FLUENT 6.3) was used in the numerical studies. A 3D model of a driver’s cab and a more complicated