Development and validation of a coupled Navier–Stokes/DSMC simulation for rarefied gas flow in the production process for OLEDs

In this paper we present a coupled Navier–Stokes/direct simulation Monte Carlo (NS/DSMC) solver for simulating the production of organic light-emitting diodes. In this production process layers of organic molecules are deposited from gas phase on a substrate. Guided in a pipe system at low pressure the precipitating material flows through nozzles into a high-vacuum chamber where the deposition takes place. Typical for this system is a strong decrease of pressure along the flow path with an equivalent increase in Knudsen number. Therefore only a coupled NS/DSMC simulation is possible. The commercial simulation software ANSYS Fluent was used for the whole domain while for the domain with high Knudsen numbers DSMCFoam was applied, which is part of the open source CFD toolbox OpenFOAM. Starting with an NS solution of the whole domain the breakdown parameter was computed defining the beginning of the DSMC subdomain. Data is exchanged using a state based coupling and compared in an overlapping region, where both are valid. An analysis in the number of lattice cells in the NS simulation and in the number of DSMC particles per cell in the DSMC simulation was performed. Furthermore the effect of different numbers of degrees of freedom of the fluid was examined. For the validation of the full simulation, results were compared with the results from two experiments, and very good agreement was achieved.