Fig 1 - uploaded by Chandra Shekhar
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Schematic diagrams of the flow geometry. The spatial dimensions are normalized by the inlet diameter. The vector g represents the gravity.
Source publication
Upward, laminar, axisymmetric, submerged impinging jets, with water as the working fluid, are numerically investigated in detail, with the impingement surface subjected to high heating rates. The heating greatly changes the density, viscosity, and thermal conductivity of the fluid, which causes the post-impingement wall-jet to prematurely separate...
Contexts in source publication
Context 1
... schematic diagrams of the flow geometry are shown in Fig 1, with the normalized spatial dimensions. The impingement chamber is a confined, vertical, three-dimensional, cylindrical domain, with top, bottom, and side walls. ...
Context 2
... the flow domain is axisymmetric, the computations are carried out only in an angular slice of the physical domain, which is shown in the Fig 1. The three-dimensionality of the computation domain is retained in order to observe any peripheral fluid motion that may get induces as a result of the heating. ...
Context 3
... 5 o z> = 0.010~0.153. At the side boundaries of the computational domain (marked as B1 and B2 in Fig 1), the periodic boundary condition is used; whereas, the no-slip boundary condition is used on the solid surfaces. Moreover, the solid boundaries, except at the heater, are also considered thermally insulated. ...
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Citations
... The sub-atmospheric region disappeared when h/d > 1 (Colucci and Viskanta, 1996;Baydar, 1999;Baydar and Ozmen, 2005). When the base plate was absent, such a region never appeared, irrespective of whether h/d ≤ 1 (Gao and Ewing, 2006;Katti and Prabhu, 2008) or h/d > 1 (Gardon and Akfirat, 1965;Donaldson and Snedeker, 1971;Giralt et al., 1977;Shekhar and Nishino, 2013). Effect of the presence of the base plate on heat transfer characteristics are also reported in the literature. ...
... For 0.25 ≤ h/d ≤ 4, Gao and Ewing (2006) observed 5-50% reduction in the heat transfer rate in the wall jet region when the base plate was introduced. The reduction became negligible when h/d was increased to 6. Due to their extensive usage, many confined laminar impinging jet flows have also been studied, such as, a study by Miranda and Campos (1999) who used a conical base plate, study of 0.25 ≤ h/d ≤ 1 flows by Ichimiya and Yamada (2003) who considered effects of buoyancy on heat transfer rate and on flow characteristics, studies by Shekhar and Nishino (2011) and Shekhar and Nishino (2014) who investigated flow oscillations and heat-induced flow separations for h/d = 5.95 and h/d = 1.89 flows, and a study by Shekhar and Nishino (2013) who examined heat transfer rate and skin-friction coefficient for various h/d flows. Lupton et al. (2008) studied miniature impinging jet flows in which degree of the base-plate confinement was explicitly varied by shifting it to different upstream positions, successively, while keeping d and h/d constant at 0.95 mm and 1.00, respectively. ...
Radially confined, axisymmetric impinging jet flows are investigated by using the standard particle image velocimetry experimental technique. The confinement is achieved by placing a confinement block around a jet, co-axially. The inner diameter of the block is successively varied to nine different values. The inlet-based Reynolds number of the jet is kept constant at 5000. The nine diametric values yielded nine different flows of widely different characteristics. Among other usage, an insight into the flow characteristics can be helpful in designing compact impinging jet applications, as such a radially confined flow is equivalent to passing the pre-impingement jet through a hole perforated in a solid wall (i.e. the jet source can be placed behind a wall). The study has revealed that the flows, in general, form two circulation zones, three mixing layers, and two boundary layers. Based on turbulence characteristics of the five shear layers, overall characteristics of the flows are understood systematically. Mean velocity and various turbulence statistics are also presented, and mechanisms underlying behind their variations are explained. Finally, scaling laws are obtained for the mean velocity and for the turbulence statistics, both in the impingement and in the wall jet regions.
... Shekhar and Nishino (2011) indicated that the separated flow oscillates due to a periodic ejection of heated fluid from the dead zone. In a later study, Shekhar and Nishino (2013) found that the heat transfer rate in the dead zone decreases when either the surface heating rate is increased or the Reynolds number is decreased. Lin and Armfield (2008) also numerically studied similar upward impinging jet flows, but did not observe the flow separation, because they analyzed the flow only for a short time. ...
Upward, laminar, axisymmetric, pipe-issued, submerged impinging jets, with the water as the working fluid, are numerically investigated. The impingement surface is subjected to heating, which causes the wall jet to prematurely separate from the impingement surface and turns the following region into a dead zone where the heat transfer rate deteriorates. Effects of (I) the inlet-based Reynolds number, (2) the heating-rate dependent Grashof number, and (3) the impingement-surface height to the inlet-diameter ratio are examined in detail. It is found that the separated jet oscillates when the Richardson number of the flow is moderate, but it separates without any oscillation when the Richardson number is large. The flow oscillation also induces cyclic fluctuations in on-surface quantities, such as, the Nusselt number, the surface temperature, and the skin-friction coefficient. The flows slowly approach to statistically steady states where oscillation parameters and heat transfer properties tend to stabilize about fixed values. (C) 2014 The Authors. Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license
Method for investigation, modelling and optimisation of cleaning processes with coherent liquid jet
