Individual droplet heat-transfer rates for splattering on hot surfaces

Mcginnis, F. K.; Holman, J.P.

doi:10.1016/0017-9310(69)90081-7

Cited by 54 publications

(20 citation statements)

References 3 publications

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“…Thus, to determine the condition that best approached the physical situation, the measured impact-pressure distribution of air was compared against calculated values obtained by solving Eqs. [3], [4], [6], [7], and [11] through [13], imposing different air-velocity profiles at the nozzle tip. [28] The best agreement between both profiles was obtained by specifying an air-velocity distribution with the shape shown in Figure 2(b); i.e., along the x-direction, the profile was uniform over the flat empty portion of the flanged orifice, and in the rest, it decreased to zero varying in angle from 0 to 45 deg at the edge; this distribution was held uniform over the whole orifice thickness.…”

Section: Continuous Phase-airmentioning

confidence: 99%

“…It has been reported that there is a direct dependency of the heat transfer on the droplet diameter and its initial collision velocity [4,5] and that this is an indication of the important relationship between the heat-transfer process and the droplet-deformation behavior during impact. [6] The Weber number (We zs = q d u zs 2 d d /r) associated with the normal-collision velocity, u zs , has in general been agreed to characterize the impact or deformation mode of the drops.…”

Section: Introductionmentioning

confidence: 98%

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The Fluid Dynamics of Secondary Cooling Air-Mist Jets

C.¹,

G.²,

E.³

et al. 2008

Metall Mater Trans B

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For the conditions of thin-slab continuous casting, air-mist secondary cooling occurs in the transition-boiling regime, possibly as a result of an enhanced intermittent contact of highmomentum water drops with the hot metallic surface. The dynamics of the intermittent contact or wetting/dewetting process should be primarily dependent on the drop size, drop impactvelocity and -angle and water-impact flux, which results from the nozzle design and the interaction of the drops with the conveying and entrained air stream. The aim of this article was to develop a model for predicting the last three parameters based on the design and operating characteristics of air-mist nozzles and on experimentally determined drop-size distributions. To do this, the Eulerian fluid-flow field of the air in three dimensions and steady state and the Lagrangian velocities and trajectories of water drops were computed by solving the turbulent Navier-Stokes equation for the air coupled to the motion equation for the water drops. In setting this model, it was particularly important to specify appropriately the air-velocity profile at the nozzle orifice, as well as, the water-flux distribution, and the velocities (magnitude and angle) and exit positions of drops with the different sizes generated, hence special attention was given to these aspects. The computed drop velocities, water-impact flux distributions, and airmist impact-pressure fields compared well with detailed laboratory measurements carried out at ambient temperature. The results indicate that under practical nozzle-operating conditions, the impinging-droplet Weber numbers are high, over most of the water footprint, suggesting that the droplets should establish an intimate contact with the solid surface. However, the associated high mean-droplet fluxes hint that this contact may be obstructed by drop interference at the surface, which would undermine the heat-extraction effectiveness of the impinging mist. The model also points out that a large proportion of fine drops would be prevented by the air-flow pattern from reaching the surface. The numerical analysis of air-mist jets under conditions relevant to secondary cooling had not been addressed before, and it constitutes a first step in an effort to develop a model to describe the dynamic and thermal interaction of dense-drop media with hot metallic surfaces.

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Section: Continuous Phase-airmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 98%

The Fluid Dynamics of Secondary Cooling Air-Mist Jets

C.¹,

G.²,

E.³

et al. 2008

Metall Mater Trans B

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“…Kato et al [4] suggested that thermal interactions between spray droplets and vapor during pre-impact have a significant influence on heat transfer in spray cooling. The effects that the mass flow rate [5][6][7], the impact angle [8], the surface roughness [9,10], and reduced gravity [4,11] may have on heat removal capacity in spray cooling have been investigated under transient conditions. Ortiz and Gonzalez [12] carried out spray cooling under steady-state conditions.…”

Section: Introductionmentioning

confidence: 99%

Hybrid turbulence simulation of spray impingement cooling: The effect of vortex motion on turbulent heat flux

Kondaraju

Lee

2008

Numerical Methods in Fluids

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SUMMARYSpray impingement has been a major interest of researchers in the areas of spray cooling, internal combustion, fire suppression and spray cooling, etc. for a long time. Numerous studies have been done in the area of spray cooling. Spray cooling with phase change takes advantage of relatively large amounts of latent heat and is capable of removing high heat fluxes from the surface, which has generated the interest of many researchers. In this paper, the turbulent characteristics of vapor formed during the spray impingement are studied. Water and gasoline are used in the numerical analysis of the two-phase spray impingement on a heated wall. Hybrid turbulence modeling was used for the analysis where the subgrid scale model was employed away from the wall and k-model was used near the wall. Gasoline, at 298 K, was sprayed on the heated wall, kept constant at 650 K. The surrounding temperature was maintained at 400 K at the start of the simulation. In case of water and gasoline at Reynolds number 2750, the heated wall was kept constant at 400 K and the surrounding temperature was maintained at 298 K at the start of the simulations. The nozzle diameter of 100 m was used for this study, with the nozzle plate spacing ratio at 10. The spray was impinged on the flat plate at angles of 0, 15, and 30 • . Root mean-squared velocities and turbulent heat flux were plotted in the water spray impingement for the different angles of impingement. The effect of turbulence on the heat transfer was observed. The effect of vortex motion on the turbulent heat flux values was analyzed using different Reynolds numbers of impingement and at different angles in case of gasoline. The turbulent heat flux attained the maximum values with high vortex formation. Upwash of fluid transported heat away from the wall, producing higher heat flux values in the region.

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“…Wachters and Westerling (1966a) and Wachters et al (1966b) examined the kinematic motion of a single droplet impacting a hot surface using high-speed photographs above the Leidenfrost temperature. McGinnis and Holman (1969) investigated the effect of droplet velocity and impact frequency on the heat transfer rate, but also at temperatures above Leidenfrost. Toda (1972Toda ( , 1974 reported extensive measurements of an evaporating water droplet and proposed a heat transfer model based on three regions (low temperature, transitional, and high temperature), according to the thermal behavior of the thin liquid film formed on the heated surface.…”

Section: Introductionmentioning

confidence: 99%

Time and Space Resolved Heat Transfer - Boiling and Droplet Cooling Studies Using Microheaters. Droplet and Spray Cooling Heat Transfer

Kim¹

2003

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Individual droplet heat-transfer rates for splattering on hot surfaces

Cited by 54 publications

References 3 publications

The Fluid Dynamics of Secondary Cooling Air-Mist Jets

The Fluid Dynamics of Secondary Cooling Air-Mist Jets

Hybrid turbulence simulation of spray impingement cooling: The effect of vortex motion on turbulent heat flux

Time and Space Resolved Heat Transfer - Boiling and Droplet Cooling Studies Using Microheaters. Droplet and Spray Cooling Heat Transfer

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