Influence of the shape of the orifice on the local heat transfer distribution between smooth flat surface and impinging incompressible air jet

An experimental investigation is performed to study the influence of the shape of the orifice (circular, square, triangular and elliptical), jet to plate distances and Reynolds number on the local heat transfer distribution to normally impinging submerged air jet on smooth and flat surface. The Reynolds numbers were varied from 5000 to 30,000 in the steps of 5000 and the jet to plate distances used were 0.5, 1, 2, 4, 6 and 8. The equivalent diameter (ratio of area to the perimeter) of all the orifices were maintained nearly constant (5.7 mm). The local heat transfer characteristics are estimated using thermal images obtained by infrared thermal imaging technique. For all the shapes, the area averaged Nusselt number increases with increase in Reynolds number. The area averaged Nusselt number at all Reynolds number is observed to be highest at a z/d of 4. Axis switching is observed for all the shapes except circular orifice. The square, triangular and elliptical orifice respectively undergoes a 45 degrees, 180 degrees and 90 degrees axis switch. Pressure loss coefficients of various orifices are reported. (C) 2015 Elsevier Inc. All rights reserved

Influence of the orifice shape on the local heat transfer distribution and axis switching by compressible jets impinging on flat surface

An experimental investigation is performed to study the effects of the orifice shape and Mach number (M) on the local heat transfer distribution by normally impinging compressible jets. Four different orifice cross-sections namely circular, elliptical, square and triangular are used and jets Mach number is maintained from 0.4 to 1in present study. The heat transfer is measured by thin foil IR technique for different nozzle to plate distances. To calculated Nusselt number, adiabatic wall temperature is used as a reference temperature. The stagnation point Nusselt number is significantly higher for circular orifice as compared to other three shapes while that for the elliptical orifice is minimum. Recovery factor distribution is independent of the Reynolds number and the Mach number. The square, triangular and elliptical orifice respectively undergoes a 45 degrees, 180 degrees and 90 degrees axis switching. (C) 2016 Elsevier Masson SAS. All rights reserved

Application of DOE for the study of a multiple jet impingement system

Jet impingement is widely implemented in a variety of engineering applications and industrial processes where high average heat transfer coefficients and the uniformity of the heat transfer over the impinging surface are required to enhance the process and to avoid local hot (or cold) spots. Multiple jet impingement involves several parameters that interfere with the performance of the process, and there are no universal optimal solutions. To ensure the optimization of the process, it is important to understand the influence of these parameters in the heat transfer over the target surface. To perform this study an experimental research will be performed on a purpose-built test facility which has been commissioned, using a Particle Image Velocimetry system. However, to reduce time and costs associated to the experimental tests, it is important to perform a Design of Experiments, that allows to reduce the number of trials, focusing on the parameters that have a greater influence on the process performance. Taguchi’s method allows the optimization of the process through the selection of the most suitable parameters values. This work presents the method that must be followed before the development of experiments related to the multiple jet impingement over a complex surface, from the design of the experimental setup to the design of the matrix of experiments.The first author would like to express her gratitude for the support given by the Portuguese Foundation for Science and Technology (FCT) and the MIT Portugal Program. This work has been supported by FCT within the Project Scope UID/CEC/00319/2019 (ALGORITMI Center) and Project Scope UID/EMS/04077/2019 (METRICS Center)