LEIDENFROST TEMPERATURE AND HEAT-TRANSFER COEFFICIENTS FOR WATER SPRAYS IMPINGING ON A HOT SURFACE

1974 ◽  
Author(s):  
Charles J. Hoogendoorn ◽  
R. den Hond
Keyword(s):  
Heat Transfer ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Water Sprays ◽  
Leidenfrost Temperature ◽  
Hot Surface

Heat Transfer Coefficients and Lifetimes of Micro-Droplet Evaporation in the Transition Regime

2012 ◽  
Author(s):  
Michael S. Hanchak ◽  
Alejandro M. Briones ◽  
Jamie S. Ervin ◽  
Larry W. Byrd
Keyword(s):  
Heat Transfer ◽  
Droplet Radius ◽  
Transition Regime ◽  
Volume Data ◽  
Transfer Coefficients ◽  
Vapor Interface ◽  
One Dimensional ◽  
Heat Transfer Coefficients ◽  
Hot Surface ◽  
Liquid Vapor

The goal of the present work is to determine the heat transfer characteristics of evaporating micro-droplets of water from a hot surface. To accomplish this, a one-dimensional, finite-difference model is used to simulate the transport of water vapor and energy from the droplet’s liquid-vapor interface toward and inside the hemispherical, gaseous region surrounding the droplet. The model incorporates a transition regime correction to the kinetic theory evaporative mass flux. The transition regime correction, a multiplier applied to the kinetic flux, is a function of the Knudsen number, the ratio of molecular mean free path to the droplet radius. The transition regime encompasses droplet sizes for which neither the kinetic model of evaporation nor the hydrodynamic continuum theory is entirely appropriate. The model simulates the liquid phase as one-dimensional conduction between the hot surface and the liquid-vapor interface. Previously, we validated our model against measured volume data as a function of time for several evaporating droplets. Using the model, overall heat transfer coefficients and total evaporation times are determined. Linear fits of both are provided against dimensional groupings of initial droplet volume and surface temperature superheat.

Numerical Analysis of Heat Conduction in Cooling of Aluminum Extrusion

2002 ◽  
Author(s):  
Nicola Bianco ◽  
Oronzio Manca
Keyword(s):  
Heat Transfer ◽  
Heat Conduction ◽  
Cooling System ◽  
Heat Conduction Problem ◽  
Aluminum Extrusion ◽  
Transfer Coefficients ◽  
Lower Velocity ◽  
Heat Transfer Coefficients ◽  
Water Sprays ◽  
Volume Method

A thermal analysis of the cooling of an extruded aluminum alloy by means of water sprays is carried out. The heat conduction problem has been solved numerically by means of a finite volume method. The heat transfer coefficients used in the boundary conditions has been evaluated by means of spray heat transfer correlations, which relate these coefficients to the spray hydrodynamic parameters. The influence of the number of sprays and of the solid velocity has been investigated. Results show that the efficiency of the cooling system decreases as the number of jets increases. The efficiency of each spray increases with the velocity for the same number of sprays. As the workpiece velocity increases it needs to increase the number of sprays to obtain the same temperature difference between the entry and the exit of the cooling system. The greater the number of sprays related to the case with lower velocity, the smaller the increase of the number of sprays.

Spray Cooling of an Inverted Heated Surface

2006 ◽  
Author(s):  
Frank Pyrtle ◽  
Alberto D. Sato
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Cooling System ◽  
Heated Surface ◽  
Spray Cooling ◽  
Open Loop ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Water Sprays ◽  
Compressed Gas

Experiments were performed to determine heat transfer characteristics of water sprays impacting a flat, inverted surface. Using a compressed gas tank to provide motive force in an open loop spray cooling system, droplet sprays were produced without the assistance of an atomizing gas stream. A range of droplet volumetric fluxes was produced for cooling the inverted heated surface using a full-cone spray nozzle. Heat transfer curves were plotted in the form of heat flux as a function of wall temperature difference, for volumetric flow rates up to 627 mL/min, dissipating up to 451 W/cm2. Heat transfer coefficients were also determined as functions of heat flux. The results were compared to prior data for standard, downward spraying onto heated surfaces.

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