Hydraulic Jump due to Jet Impingement on Micro-Patterned Surfaces Exhibiting Ribs and Cavities

2012 ◽  
Author(s):  
M. Johnson ◽  
D. Maynes ◽  
J. C. Vanderhoff ◽  
B. W. Webb
Keyword(s):  
Reynolds Number ◽  
Water Depth ◽  
Hydraulic Jump ◽  
Smooth Surface ◽  
Frictional Resistance ◽  
Jet Impingement ◽  
Liquid Jet ◽  
Patterned Surfaces ◽  
Number Range ◽  
Patterned Surface

This paper reports experimental results characterizing the hydraulic jumps that form due to liquid jet impingement on micro-patterned surfaces with alternating micro-ribs and cavities. The surfaces are characterized by the cavity fraction, which is defined as the width of a cavity divided by the combined width of a cavity and an adjoining rib. The surfaces are all hydrophilic and thus the cavity regions are wetted during the impingement process. Four different surface designs were studied, with respective cavity fractions of 0 (smooth surface), 0.5, 0.8, and 0.93. The experimental data spans a Weber number range (based on the jet velocity and diameter) of 600 to 2100 and a corresponding Reynolds number range of 11500 to 21400. As with jet impingement on a smooth surface, when a liquid jet strikes a ribbed surface it then moves radially outward in a thin film and eventually experiences a hydraulic jump, where the thickness of the film increases by an order of magnitude, and the velocity decreases accordingly. However, the anisotropy of the patterned surface causes a disparity in frictional resistance dependent upon the direction of the flow relative to the orientation of the ribs. This results in a hydraulic jump which is elliptical rather than circular in shape, where the major axis of the ellipse is aligned parallel to the ribs, concomitant with the frictional resistance being smallest parallel to the ribs and greatest perpendicular to the ribs. When the water depth downstream of the jump was imposed at a predetermined value, the major and minor axis of the jump decreased with increasing water depth, following classical hydraulic jump behavior. The experimental results indicate that for a given cavity fraction and downstream depth, the radius of the jump increases with increasing Reynolds number. At a specified Reynolds number and downstream depth, the hydraulic jump radius in the direction parallel to the ribs of a patterned surface is nominally equal to the jump radius for a smooth surface, regardless of cavity fraction. The jump radius perpendicular to the ribs is notably less than that for a smooth surface, and this radius decreases with increasing cavity fraction.

Wall Roughness Effects on Stagnation-Point Heat Transfer Beneath an Impinging Liquid Jet

1994 ◽  
Vol 116 (1) ◽  
pp. 81-87 ◽  
Author(s):  
L. A. Gabour ◽  
J. H. Lienhard
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Stagnation Point ◽  
Rough Surfaces ◽  
Roughness Parameter ◽  
Jet Impingement ◽  
Liquid Jet ◽  
Wall Roughness ◽  
Smooth Wall ◽  
Number Range

Jet impingement cooling applications often involve rough surfaces, yet few studies have examined the role of wall roughness. Surface protrusions can pierce the thermal sublayer in the stagnation region and increase the heat transfer. In this paper, the effect of surface roughness on the stagnation-point heat transfer of an impinging unsubmerged liquid jet is investigated. Experiments were performed in which a fully developed turbulent water jet struck a uniformly heated rough surface. Heat transfer measurements were made for jets of diameters 4.4–9.0 mm over a Reynolds number range of 20,000–84,000. The Prandtl number was held nearly constant at 8.2–9.1. Results are presented for nine well-characterized rough surfaces with root-mean-square average roughness heights ranging from 4.7 to 28.2 μm. Measured values of the local Nusselt number for the rough plates are compared with those for a smooth wall, and increases of as much as 50 percent are observed. Heat transfer in the stagnation zone is scaled with Reynolds number and a roughness parameter. For a given roughness height and jet diameter, the minimum Reynolds number required to increase heat transfer above that of a smooth plate is established. A correlation for smooth wall heat transfer is also given.

Liquid Jet Impingement Cooling of a Rotating Disk

1986 ◽  
Vol 108 (3) ◽  
pp. 540-546 ◽  
Author(s):  
H. J. Carper ◽  
J. J. Saavedra ◽  
T. Suwanprateep
Keyword(s):  
Reynolds Number ◽  
Average Nusselt Number ◽  
Convective Heat Transfer Coefficient ◽  
Jet Impingement ◽  
Rotating Disk ◽  
Liquid Jet ◽  
Flow Rates ◽  
Impingement Cooling ◽  
Angular Velocities ◽  
Jet Nozzle

Results are presented from an experimental study conducted to determine the average convective heat transfer coefficient for the side of a rotating disk, with an approximately uniform surface temperature, cooled by a single liquid jet of oil impinging normal to the surface. Tests were conducted over a range of jet flow rates, jet temperatures, jet radial positions, and disk angular velocities with various combinations of three jet nozzle and disk diameters. Correlations are presented that relate the average Nusselt number to rotational Reynolds number, jet Reynolds number, jet Prandtl number, and dimensionless jet radial position.

The Relationship Between Frictional Resistance and Roughness for Surfaces Smoothed by Sanding

2002 ◽  
Vol 124 (2) ◽  
pp. 492-499 ◽  
Author(s):  
Michael P. Schultz
Keyword(s):  
Reynolds Number ◽  
Frictional Resistance ◽  
Resistance Coefficient ◽  
Polished Surface ◽  
Average Height ◽  
Freestream Velocity ◽  
Number Range ◽  
Test Fixture ◽  
Plate Length ◽  
The Relationship

An experimental investigation has been carried out to document and relate the frictional resistance and roughness texture of painted surfaces smoothed by sanding. Hydrodynamic tests were carried out in a towing tank using a flat plate test fixture towed at a Reynolds number ReL range of 2.8×106−5.5×106 based on the plate length and freestream velocity. Results indicate an increase in frictional resistance coefficient CF of up to 7.3% for an unsanded, as-sprayed paint surface compared to a sanded, polished surface. Significant increases in CF were also noted on surfaces sanded with sandpaper as fine as 600-grit as compared to the polished surface. The results show that, for the present surfaces, the centerline average height Ra is sufficient to explain a large majority of the variance in the roughness function ΔU+ in this Reynolds number range.

Liquid Jet Impingement Without and With Heat Transfer

2009 ◽  
Author(s):  
F. A. Jafar ◽  
G. R. Thorpe ◽  
O¨. F. Turan
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Jet Impingement ◽  
Target Surface ◽  
Reynolds Numbers ◽  
Liquid Jet ◽  
Substantial Impact ◽  
Plate Spacing ◽  
Numerical Predictions ◽  
Surface Configuration

Equipment used to cool horticultural produce often involves three-phase porous media. The flow field and heat transfer processes that occur in such equipment are generally quantified by means of empirical relationships amongst dimensionless groups. This work represents a first step towards the goal of harnessing the power of computational fluid dynamics (CFD) to better understand the heat transfer process that occur in beds of irrigated horticultural produce. The primary objective of the present study is to use numerical predictions towards reducing energy and cooling water requirement in cooling horticultural produce. In this paper, flow and heat transfer predictions are presented of a single slot liquid jet on flat and curved surfaces using a CFD code (FLUENT) for 2-D configurations. The effects of Reynolds number, nozzle to plate spacing, nozzle width and target surface configuration have been studied. Reynolds numbers of 250, 500, 700, 1800 and 1900 are studied where the liquid medium is water. Here, the Reynolds number is defined in terms of the hydraulic nozzle diameter, inlet jet velocity and fluid kinematic viscosity. The results show that Reynolds numbers, nozzle to plate spacing and nozzle width have a significant effect on the flow filed and heat transfer characteristics; whereas the target surface configuration at stagnation area has no substantial impact. The use of a numerical tool has enabled detailed investigation of these characteristics, which have not been available in the literature previously.

A Numerical Study on Flow Characteristics of 2D Vertical Liquid Jet Striking a Horizontal Surface

2010 ◽  
Author(s):  
M. Kimiaghalam ◽  
M. Passandideh-Fard
Keyword(s):  
Reynolds Number ◽  
Hydraulic Jump ◽  
Numerical Study ◽  
Flow Characteristics ◽  
Newtonian Liquid ◽  
Liquid Jets ◽  
Liquid Jet ◽  
Moderate Reynolds Number ◽  
Different Types ◽  
Newtonian Liquids

We studied numerically impingement of vertical liquid jets of moderate Reynolds number for both Newtonian and non-Newtonian liquids to clarify the structure formation of circular hydraulic jump and the phenomenon of jet buckling. First, we have studied the hydraulic jump characteristics and governing parameters for a laminar water jet. Moreover, different types of hydraulic jump have been investigated by varying the height of a circular wall around the bed in flow downstream. The results show that a circular hydraulic jump has two kinds of steady states which can be reached by changing wall height. Next, we studied the impingement of a non-Newtonian liquid jet on a solid surface. In this case, we observe that instead of having a significant hydraulic jump, jet buckling phenomenon happens. The results were used in order to achieve a better understanding of the jet buckling phenomenon and the conditions in which this phenomenon happens.

Laser Velocity and Surface Measurements Toward the Prediction of Turbulent Frictional Resistance on Irregular Rough Surface in Higher Reynolds Number Range

2019 ◽  
Author(s):  
Kyohei Okubo ◽  
Shunpei Suzuki ◽  
Yusuke Kuwata ◽  
Yasuo Kawaguchi
Keyword(s):  
Reynolds Number ◽  
Flow Field ◽  
Rough Surface ◽  
Empirical Formula ◽  
Rough Surfaces ◽  
Frictional Resistance ◽  
Frictional Stress ◽  
Mean Velocity ◽  
Number Range ◽  
High Reynolds

Abstract In this research, we consider the relationship between roughness of the wall and frictional resistance in the range of high-Reynolds number regime which is important for practical use, and its goal is to build a more accurate and highly versatile formula for predicting the frictional resistance acting on the complex surface with irregular roughness. In addition to the parameter corresponding to the distribution of the roughness used in a conventional and empirical formula, we aim to construct an empirical formula including the parameter representing the wavelength of the rough surface. In this study, we conduct laboratory experiments of Taylor-Couette flow, using the cylindrical test specimens roughly sprayed with an actual ship paint, and investigate the influence of irregular roughness on flow field and the surface frictional stress based PIV (Particle Image Velocimetry) measurements and torque measurements in high Reynolds numbers. The azimuthal mean velocity for rough surfaces increased in the entire flow field in comparing to the flow for a smooth surface, and this tendency is remarkable in a bulk region. Also, we measure the rough surfaces of the specimens using a laser type one-shot three-dimensional measurement device. Based on the results of above measurements, we propose the direct relationship between the parameter of a rough surface and frictional resistance.

Thermal Transport From a Rotating Disk During Partially Confined Liquid Jet Impingement

2007 ◽  
Author(s):  
Jorge Lallave ◽  
Muhammad M. Rahman
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Jet Impingement ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Liquid Jet ◽  
Interface Temperature

This paper presents a numerical study that characterizes the conjugate heat transfer results of a semi–confined liquid jet impingement on a uniformly heated spinning solid disk of finite thickness and radius. The model covers the entire fluid region including the impinging jet on a flat circular disk and flow spreading out downstream under the confined insulated wall that ultimately gets exposed to a free surface boundary condition. The solution is made under steady state and laminar conditions. The model examines how the heat transfer is affected by adding a secondary rotational flow under semi-confined jet impingement. The study considered various standard materials, namely aluminum, copper, silver, Constantan and silicon; covering a range of flow Reynolds number (220–900), under a broad rotational rate range from 0 to 750 rpm, or Ekman number (7.08×10−5 – ∞), nozzle to target spacing (β = 0.25 – 1.0), disk thicknesses to nozzle diameter ratio (b/dn = 0.25 – 1.67), Prandtl number (1.29 – 124.44) using ammonia (NH3), water (H2O), flouroinert (FC-77) and oil (MIL-7808) as working fluids and solid to fluid thermal conductivity ratio (36.91 – 2222). High thermal conductivity plate materials maintained more uniform and lower interface temperature distributions. Higher Reynolds number increased local heat transfer coefficient reducing the interface temperature difference over the entire wall. Rotational rate increases local heat transfer coefficient under most conditions. These findings are important for the design improvement and control of semi-confined liquid jet impingement under a secondary rotation induced motion.

scholarly journals Numerical simulation of double jet impinging a flat and fixed wall with WALE model

2020 ◽  
Vol 330 ◽  
pp. 01036
Author(s):  
Rachid Sahnoun ◽  
Aissa Abderrahmane ◽  
Drai Ismail ◽  
Mohmmed El Ganaoui
Keyword(s):  
Numerical Simulation ◽  
Reynolds Number ◽  
Smooth Surface ◽  
Jet Impingement ◽  
Turbulent Intensity ◽  
Experimental Measurements ◽  
Eddy Structure ◽  
Opening Ratio

This work focuses on the study of the averaged velocity and the turbulent intensity of the double jet impingement is used to separate two adjacent cellule. Numerical LES investigations are carried out in this study. A jet impingement against a flat and smooth surface without recirculation was used for this. The WALE (Wall Adapting Local Eddy) structure models the sub grid-scale tensor. The jet opening ratio is H/e = 10 and the Reynolds Number Re= 2000. Result comparisons to available experimental measurements are performed and good agreements are noticed.

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