The influence of the stagnation zone on the fluid dynamics at the nozzle exit of a confined and submerged impinging jet

Abstract

Low profile impinging jets provide a means to achieve high heat transfer coefficients while occupying a small quantity of space. Consequently, they are found in many engineering applications such as electronics cooling, annealing of metals, food processing, and others. This paper investigates the influence of the stagnation zone fluid dynamics on the nozzle exit flow condition of a low profile, submerged and confined impinging water jet. The jet was geometrically constrained to a round, 16mm diameter, square-edged nozzle at a jet exit to target surface spacing (H/D) that varied between 0.25 < H/D < 8.75. The influence of turbulent flow regimes is the main focus of this paper, however laminar flow data is also presented between 1350 < Re < 17300. A custom measurement facility was designed and commissioned to utilise Particle-Image Velocimetry (PIV) in order to quantitatively measure the fluid dynamics both before and after the jet exits its nozzle. The velocity profiles are normalised with the mean velocity across the nozzle exit. The primary objective of this paper is to present accurate flow profiles across the nozzle exit of an impinging jet confined to a low H/D, with a view to guide the boundary conditions chosen for numerical simulations confined to similar constraints.The results revealed in this paper suggest that the fluid dynamics in the stagnation zone strongly influences the nozzle exit velocity profile at confinement heights between 0 < H/D < 1. This is of particular relevance with regards to the choice of inlet boundary conditions in numerical models, and it was found that it is necessary to model a jet tube length L/D > 0.5

Challenges surrounding nanosheets and their application to solar-driven photocatalytic water treatment

“…181,182 Microfluidisation Microfluidisation for LPE is a relatively recent method, and was first demonstrated in 2017. 167,183 The process involves pumping a precursor/liquid mixture through a series of microfluidic channels, where the extreme shear forces within the channels (which include bends, tight turns, localised flow impingement and wall jets 184 that induce high shear stresses) exfoliates the precursor (Fig. 12).…”

Opportunities in Jet-Impingement Cooling for Gas-Turbine Engines

“…As discussed in this paper, the study of free jets is perhaps not the most useful as the recirculation caused in the presence of a backplate is very important and can alter the heat transfer pattern significantly. Katti et al [41] provided experimental measurement of single free jet heat transfer, and Jeffers et al [42] studied the stagnation zone with a single confined and submerged jet. They used a long tube to develop flow at the jet exit.…”

Investigation on Circular Array of Turbulent Impinging Round Jets at Confined Case: A CFD Study

“…C. Wang et al [33] experimentally investigated the air jet with uniform constant heat flux boundary condition and found that air velocity near the impact area was an important factor in improving heat transfer. Katti et al [34] conducted experimental measurements of single free jet heat transfer and Jeffers et al [35] examined the stagnation zone with a single confined and submerged impinging jet. Both of them noticed that stagnant pressure could migrate to the exit of the nozzle and change the nozzle outlet velocity profile in the proximity of the nozzle exit.…”

“…Although unconfined impinging jets are widely available in the literature, possibly due to their huge applicability to industrial applications and uncomplicated correlation with experimentations, in numerous functional applications heat transfer operations are applied in a confined atmosphere. Nevertheless, a few number of research has been conducted on confined impinging jets, which are often limited to non-swirl flow [35], [40]- [42]. The results show significantly different behavior of flow and heat transfer compared to their unconfined complements.…”