Transport Processes for a Row of Confined Jets Impinging on a Moving Surface

The common architecture of the fluid delivery devices employed in the horizontal processing of printed wiring boards, makes use of high velocity jets directed normally or at some angle towards the board which moves above rollers. Usually, a single slot jet or a linear arrays of jets are employed in order to increase the transport properties of the flow in the vicinity of the printed wiring board. In the present study, a geometry resembling a fluid delivery device used in printed wiring board manufacturing was investigated both experimentally and numerically. The printed wiring board is represented by an endless belt, which is transported horizontally by a system of rollers. The working fluid is delivered by an array of 13 square jets with a hydraulic diameter of 5.02 mm and a separation distance between jets of 4 hydraulic diameters. Two confinement plates located on each side of the jet array are used to confine the flow region and adjust the flow resistance at the two openings — between the rollers and the confinement plates — symmetrically located with respect to the centerline of the row of jets. The experimental setup and the numerical model both allowed the investigation of the effect of complex confinement (due to the board, confinement plates and rollers) and of the moving boundaries (impingement surface and rollers) on the characteristics of impinging flow. The flow field and the heat transfer characteristics were investigated for the jet Reynolds number ranging from 500 to 2000, non-dimensional impingement surface velocity ranging from 0 to 1 and non-dimensional impingement distance of 3 and 5. The CFD simulations were performed using the commercial CFD code PHOENICS. Flow visualization and particle image velocimetry were employed in order to experimentally investigate the flow field and validate the CFD simulations. The predicted results compare well with the observed jet behavior. A detailed description of the flow physics is presented. The numerical simulations show that for the same mass flow rate, the row of jets has a higher transport effectiveness when compared to a slot jet.