Several engineering applications use multiple jets to increase the heat transfer over the target surface and to ensure the uniformization of the cooling process. Even if very effective, multiple jet impingement is governed by several process variables, from jets interactions (jet-to-plate distance, jet-to-jet spacing, etc.) to fluid flow parameters (Reynolds number, jet temperature) and geometry of the target surface. Due to the complexity of the interactions between jets, it is crucial to perform an in-depth study to understand the influence of these parameters on the heat transfer over the impinging plate. Furthermore, several applications require the motion of the target plate, such as reflow soldering process, food processing, drying, and heat treatments. In these processes, the motion of the target plate increases, even more, the complexity of the flow over the surface. In that sense, the development of accurate numerical models to predict the multiple jet's flow structure and the heat transfer over a moving plate is important to optimize the process before the product manufacturing, avoiding several issues in the initial phase of the project. These models ensure the best efficiency, minimizing product defects, energy consumption, and wastes, leading to a decrease in time and costs. Therefore, this work analyses numerically the effect of the target plate motion in multiple jet impingement performance and compares the results with a static plate case. To conduct this research, a widespread commercial software, the ANSYS FLUENT, is used. Between the different turbulence models available to conduct the numerical simulations, the SST k-ω model is implemented since it provides accurate predictions of impinging flows at reduced computational costs. From the numerical modeling, a detailed characterization of the flow is performed, and the heat transfer is analyzed at the vicinity of the target plate. Since a low nozzle-to-plate distance (H/D = 2) and jet-to-jet spacing (S/D = 3) are implemented, strong interactions between jets are identified. These interactions are well predicted in both static and moving plates. Jet’s shear layers interactions are observed prior to the impingement as well as wall jets collisions over the surface. Moreover, the increased flow turbulence induced by the plate motion is clearly identified by the numerical model, being observed strong shear layer regions in direction to the motion, which lead to a modification of the boundary layer compared with the static plate. This effect increases the local heat transfer rate over the moving plate. The results obtained are then compared with experimental data to validate the numerical models.

Numerical Analysis of Multiple Jets Impinging on a Moving Surface

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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