Turbulence Dissipation in a Free-Surface Jet of Water and Its Effect on Local Impingement Heat Transfer From a Heated Surface: Part 1—Flow Structure

1995 ◽  
Vol 117 (1) ◽  
pp. 85-94 ◽  
Author(s):  
D. H. Wolf ◽  
R. Viskanta ◽  
F. P. Incropera
Keyword(s):  
Heat Transfer ◽  
Free Surface ◽  
Flow Structure ◽  
Heated Surface ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Mean Velocity ◽  
Planar Jet ◽  
Impingement Heat Transfer ◽  
Surface Jet

This study investigates the relationship between jet turbulence and local impingement heat transfer for a free-surface, planar jet of water. Employing a thermal anemometer system, measurements of the mean velocity and turbulence intensity are reported at different streamwise and spanwise locations throughout the jet. The flow conditions at the nozzle discharge were controlled by using different nozzle designs (parallel-plate and converging) and flow manipulators (wire grid and screens). Measurements of the velocity gradient along the impingement surface, known to influence heat transfer from analytical considerations of a laminar impinging jet, were also made for the same sets of nozzle conditions. The test matrix also included variations in the Reynolds number (23,000 and 46,000) and distance from the nozzle discharge to the surface (0 to 30 nozzle widths). The local heat transfer results corresponding to the flow structure measurements are reported in Part 2 of this paper.

Turbulence Dissipation in a Free-Surface Jet of Water and Its Effect on Local Impingement Heat Transfer From a Heated Surface: Part 2—Local Heat Transfer

1995 ◽  
Vol 117 (1) ◽  
pp. 95-103 ◽  
Author(s):  
D. H. Wolf ◽  
R. Viskanta ◽  
F. P. Incropera
Keyword(s):  
Heat Transfer ◽  
Free Surface ◽  
Stagnation Point ◽  
Heated Surface ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transition To Turbulence ◽  
Convection Coefficient ◽  
Impingement Heat Transfer ◽  
Surface Jet

This paper presents local heat transfer data for a planar, free-surface jet of water impinging normal on a uniformly heated surface. The hydrodynamic conditions of the jet were altered through the use of different nozzle types (parallel-plate and converging) and flow manipulators (wire grid and screens) to investigate the relationship between jet turbulence and local impingement heat transfer. The flow structures for each of the various nozzle conditions are reported in a companion paper (Wolf et al., 1995), and results are used in this paper to interpret their effect on local heat transfer. In addition to qualitative interpretations, correlations are developed for both the onset of transition to turbulence and the dimensionless convection coefficient at the stagnation point. Higher levels of jet turbulence are shown to induce transition to a turbulent boundary layer at smaller streamwise distances from the stagnation point. The effect of stream-wise turbulence intensity on the convection coefficient is shown to scale approximately as the one-quarter power.

Modeling of Continuous and Intermittent Gas Jet Impingement and Heat Transfer on a Solid Surface

2001 ◽  
Author(s):  
A. K. Chaniotis ◽  
D. Poulikakos
Keyword(s):  
Heat Transfer ◽  
Stokes Equations ◽  
Heated Surface ◽  
Quantitative Description ◽  
Jet Impingement ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Navier Stokes ◽  
Planar Jet ◽  
Particle Hydrodynamics

Abstract The present work focuses on the effect of flow pulsation on the characteristics of the planar jet impingement normally on a heated surface. Specifically, the influence of frequency, amplitude and Reynolds number of the jet is examined, concerning the instantaneous and time average convective heat transfer. The simulations are conducted using a novel, improved Smooth Particle Hydrodynamics (SPH) methodology that is based on particle discretization of the governing compressible Navier-Stokes equations. The simulation of jet impingement focuses on the quantitative description of the flow field and the energy exchange between jet and surface. The strong aerodynamic and thermal interaction that exists between the gaseous jet and the impingement surface greatly enhances the local heat transfer in the stagnation and wall jet regions as well as the average heat transfer over the surface. This study is the first step toward modeling the same process but in the presence of chemical reactions and ablation between the gaseous jet and the plate.

Convective Thermal Transfer From a Heated Surface to an Impinging Multiphase Incompressible Turbulent Liquid Jet

2010 ◽  
Author(s):  
Ludovic Osmar ◽  
Ste´phane Vincent ◽  
Jean-Paul Caltagirone ◽  
Gabriel Cavallaro
Keyword(s):  
Heat Transfer ◽  
Turbulent Flow ◽  
Heated Surface ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Liquid Jet ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Planar Jet ◽  
Jet Cooling

The cooling process controlled by an impinging unsubmerged jet on a heated surface is tackled. Numerical studies about cooling by a two-phase incompressible turbulent flow have not been significantly treated in the literature and are considered here. The liquid jet cooling method is modelled by associating the energy equation with a multiphase incompressible turbulent flow model, the final objective being to be able to predict the heat transfer coefficient between the cooling liquid jet and the impinged surface. Turbulence is modelled by Large Eddy Simulation (LES). It is coupled with an Eulerian Volume of Fluid (VOF) method to follow the evolution of the interface between two fluids. In a first part, a work of validation is led and the model is compared to experimental results available in the literature [1]. Convective heat transfer induced by a planar jet of water impinging normally onto a flat heated surface is simulated. Knowing the imposed heat flux, local heat transfer coefficients are deduced from predicted surface temperatures. The next step will be to study cooling due to a cylindrical jet of water impinging onto a heated semi-hemispherical concave surface.

Effect of Nozzle Configuration on Transport in the Stagnation Zone of Axisymmetric, Impinging Free-Surface Liquid Jets: Part 1—Turbulent Flow Structure

1992 ◽  
Vol 114 (4) ◽  
pp. 874-879 ◽  
Author(s):  
J. Stevens ◽  
Y. Pan ◽  
B. W. Webb
Keyword(s):  
Heat Transfer ◽  
Free Surface ◽  
Flow Structure ◽  
Nozzle Exit ◽  
Local Heat Transfer ◽  
Liquid Jet ◽  
Mean Velocity ◽  
Stagnation Region ◽  
Surface Liquid ◽  
Nozzle Type

This study characterized the mean and fluctuating parts of the radial component of the local velocity in the stagnation region of an impinging, free-surface liquid jet striking a smooth flat plate. Four different nozzle exit conditions were studied, including fully developed pipe flow, a contoured nozzle, and turbulence-damped and -undamped sharp-edged orifices. Liquid jet Reynolds numbers in the range 30,000 to 55,000 were investigated. Velocities were measured using laser-Doppler velocimetry. Mean velocities were found to vary nearly linearly with radial location, with the slope of the line being a function of distance from the impingement plate. Dimensionless mean velocity gradients, of relevance to the heat transfer, were found to be a strong function of nozzle type, but roughly independent of jet Reynolds number for a given nozzle type. Turbulence levels were also found to be strongly influenced by the nozzle exit condition. Local heat transfer data corresponding to the flow structure measurements presented here are reported in Part 2 of this study.

An Experimental Study of High Rayleigh Number Mixed Convection in a Rectangular Enclosure With Restricted Inlet and Outlet Openings

1987 ◽  
Vol 109 (2) ◽  
pp. 446-453 ◽  
Author(s):  
L. Neiswanger ◽  
G. A. Johnson ◽  
V. P. Carey
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Rayleigh Number ◽  
Mixed Convection ◽  
Transfer Coefficient ◽  
Heated Surface ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Test Fluid ◽  
Rectangular Enclosure

Measured local heat transfer data and the results of flow visualization studies are reported for cross-flow mixed convection in a rectangular enclosure with restricted inlet and outlet openings at high Rayleigh number. In this study, experiments using water as the test fluid were conducted in a small-scale test section with uniformly heated vertical side walls and an adiabatic top and bottom. As the flow rate through the enclosure increased, the enhancement of heat transfer, above that for natural convection alone, also increased. The variation of the local heat transfer coefficient over the heated surface was found to be strongly affected by the recirculation of portions of the forced flow within the enclosure. Mean heat transfer coefficients are also presented which were calculated by averaging the measured local values over the heated surface. A correlation for the mean heat transfer coefficient is also proposed which agrees very well with the experimentally determined values. A method of predicting the flow regime in this geometry for specified heating and flow conditions is also discussed.

The Effect of Entrainment Temperature on Jet Impingement Heat Transfer

1984 ◽  
Vol 106 (1) ◽  
pp. 27-33 ◽  
Author(s):  
S. A. Striegl ◽  
T. E. Diller
Keyword(s):  
Heat Transfer ◽  
Jet Impingement ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Recirculation Region ◽  
Measured Temperature ◽  
Air Jets ◽  
Impingement Heat Transfer ◽  
Single Jet ◽  
Multiple Plane

An experimental study was done to determine the effect of entrainment temperature on the local heat transfer rates to single and multiple, plane, turbulent impinging air jets. To determine the effect of entrainment of the surrounding fluid, the single jet issued into an environment at a temperature which was varied between the initial temperature of the jet and the temperature of the heated impingement plate. An analytical model was used to correlate the measured heat transfer rate to a single jet. The effect of the entrainment temperature in a single jet was then used to analyze the effect of entrainment from the recirculation region between the jets of a jet array. Using the measured temperature in the recirculation region to include the effect of entrainment, the single jet correlations were successfully applied to multiple jets.

Numerical Investigation of Heat Transfer Enhancement on a Small Scale Vortex Generator

2009 ◽  
Author(s):  
Jiansheng Wang ◽  
Zhiqin Yang
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Flow Structure ◽  
Rectangular Channel ◽  
Vortex Generator ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Vortex Generators ◽  
Small Scale ◽  
Transfer Enhancement

The heat transfer characteristic and flow structure of fluid in the rectangular channel with different height vortex generators in small scale are investigated with numerical simulation. Meantime, the properties of heat transfer and flow of fluid in the rectangular channel are compared with the channel which located small scale vortex generator. The variation law of local heat transfer and flow structure in channel is obtained. The mechanism of heat transfer enhancement of small scale vortex generators is discussed in detail. It is found that the influence of vortex generator on heat transfer is not in proportion to the size of vortex generator. What is more, turbulent flow structure near the wall, which influences the temperature distribution near the wall, induces the variety of local heat transfer. The fluid movement towards to the wall causes the heat transfer enhanced. On the contrary, the fluid movement away from the wall decreases the local heat transfer.

Heat Transfer Enhancement Caused by Sliding Bubbles

2003 ◽  
Vol 125 (3) ◽  
pp. 503-509 ◽  
Author(s):  
Baris B. Bayazit ◽  
D. Keith Hollingsworth ◽  
Larry C. Witte
Keyword(s):  
Heat Transfer ◽  
Liquid Crystal ◽  
Heated Surface ◽  
Local Heat Transfer ◽  
Thin Foil ◽  
Local Heat ◽  
Superheated Liquid ◽  
Enhancement Of Heat Transfer ◽  
Inclined Plates ◽  
Inclined Surface

Measurements that illustrate the enhancement of heat transfer caused by a bubble sliding under an inclined surface are reported. The data were obtained on an electrically heated thin-foil surface that was exposed on its lower side to FC-87 and displayed the output of a liquid crystal coating on the upper (dry) side. A sequence of digital images was obtained from two cameras: one that recorded the response of the liquid crystal and one that recorded images of the bubble as it moved along the heated surface. With this information, the thermal imprint of the bubble was correlated to its motion and position. A bubble generator that produced FC-87 bubbles of repeatable and controllable size was also developed for this study. The results show that both the microlayer under a sliding bubble and the wake behind the bubble contribute substantially to the local heat transfer rate from the surface. The dynamic behavior of the bubbles corresponded well with studies of the motion of adiabatic bubbles under inclined plates, even though the bubbles in the present study grew rapidly because of heat transfer from the wall and the surrounding superheated liquid. Three regimes of bubble motion were observed: spherical, ellipsoidal and bubble-cap. The regimes depend upon bubble size and velocity. A model of the heat transfer within the microlayer was used to infer the microlayer thickness. Preliminary results indicate a microlayer thickness of 40–50 μm for bubbles in FC-87 and a plate inclination of 12 deg.

Internal Heat Transfer Enhancement by Two Perforated Baffles in a Rectangular Channel

1998 ◽  
Author(s):  
Prashanta Dutta ◽  
Sandip Dutta ◽  
Jamil A. Khan
Keyword(s):  
Heat Transfer ◽  
Heated Surface ◽  
Rectangular Channel ◽  
Internal Heat ◽  
Internal Flow ◽  
Jet Impingement ◽  
Local Heat Transfer ◽  
Boundary Layer Separation ◽  
Local Heat ◽  
Augmentation Techniques

The effect of two in-line inclined baffles on the local heat transfer distributions and the associated frictional losses for a turbulent flow with uniform heating from the top surface of a rectangular channel is presented for different Reynolds numbers. A combination of two baffles of same overall size is used in this experiment. The upstream baffle remains attached to the top heated surface and the position, orientation, and geometry of the other is varied. These inclined perforated baffles combine the three major heat transfer augmentation techniques, i.e., jet impingement, internal flow swirls, and boundary layer separation. The results indicate that placement of two inclined baffles augment the overall heat transfer coefficient significantly along with the local heat transfer distribution. The pattern of local Nusselt number ratio strongly depends on the position, orientation, and geometry of the second plate. Like single inclined baffles and rib mounted channels, two baffles offer more pressure drop at higher flow Reynolds number.

Local Heat-Transfer Measurements during Forced-Convection Boiling in a Helically Coiled Tube

1969 ◽  
Vol 184 (3) ◽  
pp. 52-58 ◽  
Author(s):  
K. J. Bell ◽  
A. Owhadi
Keyword(s):  
Heat Transfer ◽  
Forced Convection ◽  
Flow Structure ◽  
High Pressures ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Two Phase ◽  
Radial Acceleration ◽  
Local Coefficients ◽  
Small Density

Forced-convection boiling heat transfer to water at atmospheric pressure was studied in two helically coiled tubes. Temperature measurements were made at four positions round the tube at each of nine stations along the tube, permitting calculation of the local heat-transfer coefficient at each point. The local coefficients are correlated by the Lockhart-Martinelli parameters for two-phase flow, using the Seban-McLaughlin correlation for liquid phase heat transfer in coiled tubes. The curves for each of the four peripheral positions, compared to that previously obtained for the peripheral mean coefficient, are consistent with a flow structure having a vapour core with a strong secondary flow serving to distribute the liquid over the entire surface of the tube. The correlation and its interpretation in terms of flow structure may fail at high pressures as a result of the much smaller change in the radial acceleration in systems with small density difference between liquid and vapour.

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