Flow dynamics and heat transfer characteristics analysis for floatation nozzle using large eddy simulation and proper orthogonal decomposition method

Floatation nozzle is a key component for manufacturing high performance substrates in the roll to roll processes because it can support the substrate without contact. The heat transfer and pressure distribution of the floatation nozzle, which is highly associated with the flow dynamics, greatly affect drying/heating/cooling efficiency and operating costs of the nozzle. However, the flow dynamics and heat transfer of the floatation nozzle have not well been understood. In this study, a large eddy simulation model validated against experimental result and proper orthogonal decomposition were employed to study the flow dynamics and heat transfer of floatation nozzle. In addition, the large eddy simulation results of confined slot jet and unconfined slot jet impinging on a vertical surface were provided to get an in-depth understanding of the floatation nozzle. We found that a secondary stagnation region was existed in the floatation nozzle which did not appear in a single slot jet and was quietly different than that of multiple jets. Moreover, the primary and secondary vortices of the floatation nozzle and slot jets were identified by proper orthogonal decomposition method and instantaneous flow field. Furthermore, heat transfer mechanisms in different regions were illustrated, and the reasons of primary and secondary Nusselt number peaks were explained. Finally, it was found that an air cushion is generated for floatation nozzle, which leaded to the floatation ability of the floatation nozzle is about 20 times as much as that of the unconfined slot jet.