Suppression de la couverture de glace par un rejet thermique

1978 ◽  
Vol 5 (1) ◽  
pp. 53-57
Author(s):  
Luc Robillard
Keyword(s):  
Heat Transfer ◽  
Free Surface ◽  
Numerical Models ◽  
Ice Formation ◽  
Nonlinear Relationship ◽  
Surface Jet ◽  
Winter Time

The thermal discharges from various sources that occur during winter may prevent ice formation at the free surface. In order to predict the extent of the free surface without ice, numerical models of thermal discharges should take into account: (1) the particular heat transfer at the free surface that occurs during winter time and (2) the nonlinear relationship between density and temperature for water near 0 °C. This article indicates a method of modifying existing models and presents some results obtained from a modified buoyant surface jet model.

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.

Toward Modular Prediction of Free-Surface Jet Array Cooling: The Hydraulic Jump Location and Non-Monotonous Heat Transfer

2016 ◽  
Author(s):  
Herman D. Haustein
Keyword(s):  
Heat Transfer ◽  
Free Surface ◽  
Hydraulic Jump ◽  
Liquid Extraction ◽  
Jet Interaction ◽  
Free Jet ◽  
Key Issues ◽  
Surface Jet ◽  
Prediction Approach ◽  
Jet Array

The present study develops the ground work for modular prediction of free-surface jet arrays. Jet arrays generate one of the highest single-phase heat transfer rates, while covering reasonably large areas with good thermal uniformity, relevant to electronics cooling. However, due to liquid evacuation problems, free-jet arrays suffer from flooding, cross-flow and jet interaction, together with the large amount of influencing geometrical parameters, this makes them very difficult to predict. For the modular prediction approach to be applied, key issues are here addressed: experiments were conducted employing de-ionized water in both single and basic multiple-jet array (2×2, with local liquid extraction in the jet interaction zones) configurations. Modular conditions, wherein all jets are similar to each other, were created experimentally in a consistent fashion, by use of liquid extraction in the jet-interaction zones. Based on present and previous experimental data the influencing parameters on the pre-jump depth were identified. This description was then used to predict the location of the hydraulic jump (as dependant on the measured post-jump depth). The model combines elements of two previous approaches the shallow-water vs. jump conservation model, and obtains good agreement with available data. In addition conditions were shown for maximizing the distance at which the hydraulic jump occurs — to the point that the supercritical flows of adjacent jets touch (standing fountain type jump). This not only permits prediction of the supercritical flow heat transfer distribution over almost the entire array area, but also reduces the low heat transfer post-jump regions to a minimum. Finally, a more universal single-jet heat transfer model was developed incorporating inherent self-similarities recently identified by the authors and considering all relevant parameters: jet velocity profiles, nozzle-plate spacing, and inclination relative to gravity, to predict stagnation heat transfer as well as its radial decay. It is further identified that the influence of inclination is also of vital importance to free-surface jets (breakage of symmetry) and must be examined in future studies. By addressing these three key issues the foundation for a modular prediction of heat transfer under a free jet array is laid.

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.

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