Effect of Dissimilar Impingement Velocities on Local Heat Transfer for Adjacent Rows of Circular Free-Surface Jets

1995 ◽  
Vol 117 (4) ◽  
pp. 1061-1064 ◽  
Author(s):  
S. J. Slayzak ◽  
R. Viskanta ◽  
F. P. Incropera
Keyword(s):  
Heat Transfer ◽  
Free Surface ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Surface Jets

Effects of Interactions Between Adjoining Rows of Circular, Free-Surface Jets on Local Heat Transfer From the Impingement Surface

1994 ◽  
Vol 116 (1) ◽  
pp. 88-95 ◽  
Author(s):  
S. J. Slayzak ◽  
R. Viskanta ◽  
F. P. Incropera
Keyword(s):  
Heat Transfer ◽  
Free Surface ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Constant Heat Flux ◽  
Separation Distance ◽  
Interaction Zone ◽  
Wall Jets ◽  
Local Coefficients ◽  
Surface Jets

Experiments have been conducted to obtain single-phase local heat transfer coefficient distributions associated with impingement of one or two rows of circular, free-surface water jets on a constant heat flux surface. The nozzle diameter, the centerline-to-centerline distance between nozzles in a row, and the nozzle-to-heater separation distance were fixed at 4.9, 6.3, and 89.7 mm, respectively. Two row-to-row separations (81 and 51 mm) were considered, and nozzle discharge Reynolds numbers were varied over the range from 16,800 to 30,400. The interaction zone created by opposing wall jets from adjacent rows is characterized by an upwelling of spent flow (an interaction fountain) for which local coefficients can approach those of the impingement zones. Interactions between wall jets associated with nozzles in one row can create sprays that impact the adjoining row with sufficient momentum to induce a dominant/subordinate row behavior. In this case the interaction zone is juxtaposed with the subordinate row, and local coefficients in the impingement and wall jet regions of the affected row may be significantly enhanced. This result contrasts with the deleterious effects of crossflow reported for submerged jets throughout the literature. Spray-induced enhancements, as well as interaction zone maxima, increase with decreasing row-to-row pitch and with increasing Reynolds number.

Effect of Nozzle Configuration on Transport in the Stagnation Zone of Axisymmetric, Impinging Free-Surface Liquid Jets: Part 2—Local Heat Transfer

1992 ◽  
Vol 114 (4) ◽  
pp. 880-886 ◽  
Author(s):  
Y. Pan ◽  
J. Stevens ◽  
B. W. Webb
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Free Surface ◽  
Radial Velocity ◽  
Velocity Gradient ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Liquid Jets ◽  
Stagnation Zone ◽  
Surface Liquid

This is the second of a two-part study on the flow structure and heat transfer characteristics of turbulent, free-surface liquid jets. Part 2 deals with the effect of selected nozzle configurations on the local heat transfer in the stagnation zone. Infrared techniques have been used to characterize the local heat transfer for the four nozzle configurations whose mean and turbulent flow structure was detailed in Part 1. The results show that for identical jet Reynolds numbers, significant differences exist in the magnitudes of the local Nusselt number for the nozzle types studied. Differences of approximately 40 percent were observed. Local heat transfer results reveal that for already turbulent jets, the mean radial velocity gradient appears to be more influential in determining the heat transfer than incremental changes in the level of turbulence (as measured by the radial component of the fluctuations). An empirical correlation of the experimental data supports this conclusion, and reveals that the stagnation Nusselt number is affected independently by the jet Reynolds number and the dimensionless mean radial velocity gradient.

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.

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.

The Effect of Drainage Configuration on Heat Transfer Under an Impinging Liquid Jet Array

1999 ◽  
Vol 121 (4) ◽  
pp. 803-810 ◽  
Author(s):  
K. Garrett ◽  
B. W. Webb
Keyword(s):  
Heat Transfer ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Liquid Jets ◽  
Heated Plate ◽  
Transfer Coefficients ◽  
Plate Spacing ◽  
Single Jet ◽  
Local Temperature Distribution ◽  
Surface Jets

The heat transfer characteristics of single and dual-exit drainage configurations for arrays of liquid jets impinging normal to a heated isoflux plate has been studied experimentally. The interaction of drainage channel crossflow from upstream jets and the stagnation jets and its impact on heat transfer was the focus of the investigation. Infrared thermography was used to measure the local temperature distribution on the heated plate, from which local heat transfer coefficients were determined. A single jet diameter was used, and jet arrays with jet-to-jet spacings of 4.8, 6, 8, and 12 jet diameters were studied. Average jet Reynolds numbers in the range 400–5000 were investigated for jet nozzle-to-impingement plate spacings of 1, 2, and 4 jet diameters for fully flooded (submerged) drainage flow. A single jet-to-plate spacing large enough to yield free-surface jets was also studied. The data reveal a complex dependence of local and average Nusselt numbers on the geometric parameters which describe the problem configuration.

Heat Transfer Characteristics of Arrays of Free-Surface Liquid Jets

1995 ◽  
Vol 117 (4) ◽  
pp. 878-883 ◽  
Author(s):  
Y. Pan ◽  
B. W. Webb
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Free Surface ◽  
Local Heat Transfer ◽  
Jet Flow ◽  
Local Heat ◽  
Liquid Jets ◽  
Heat Transfer Characteristics ◽  
Array Configuration ◽  
Surface Liquid

In this study, local heat transfer data under arrays of free-surface liquid jets are measured with a two-dimensional infrared radiometer. Experimental measurements were made for three nozzle diameters using a seven-jet staggered and a nine-jet inline geometric array configuration. Nozzle-to-plate spacings of two and five nozzle diameters were investigated for four jet center-to-center spacings ranging from two to eight diameters in the jet Reynolds number range of 5000 to 20,000. Results show that the stagnation Nusselt number under the central jet is independent of array configuration and jet-to-jet spacing. The different inter jet flow interaction, as represented by different jet array configurations (the in-line array and the staggered array with different nozzle-to-nozzle spacings), shows negligible influence on local heat transfer under the central jet. Differences in the heat transfer characteristics for the two nozzle-to-plate spacings investigated were the result of an observed transition from confined submerged central jet flow to free-surface jet flow as the nozzle-to-plate spacing was increased. Secondary maxima in the Nusselt number were observed between the adjacent jets, being a direct consequence of the radial flow interaction between jets. A correlation for average heat transfer is presented.

Sign in / Sign up

Export Citation Format

Share Document