Thickness measurements of the thin film in spray evaporative cooling

Pautsch, Adam G.; Shedd, Timothy A.; Nellis, Gregory

doi:10.1109/itherm.2004.1319156

Cited by 23 publications

(13 citation statements)

References 8 publications

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“…Another complication to understanding the spray-cooling heat transfer mechanism is the small scales at which these phenomena occur. For example, the thin liquid film in which the nucleation takes place and heat is transferred had been measured to be anywhere from 1 to 350 m (Pautsch et al [9]). Measurement of temperature and visualization of liquid-vapor-interface dynamics in such small thicknesses in which heat transfer and phase change occur during spray experimentation are very difficult.…”

Section: Doi: 102514/134982mentioning

confidence: 99%

“…When a droplet (i.e., the cold liquid) impacts and mixes with the liquid over the hot surface for each thermal layer, due to the impact, some amount of cold liquid starts moving upward and some moves toward the hot surface (as shown in Figs. [7][8][9]. Because the density of the vapor is lower, the vapor bubble also tries to move upward.…”

Section: A Effect Of Thermal-boundary-layer Thicknessmentioning

confidence: 99%

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Modeling Thermal-Boundary-Layer Effect on Liquid-Vapor Interface Dynamics in Spray Cooling

Selvam¹,

Sarkar²,

Sarkar³

et al. 2009

Journal of Thermophysics and Heat Transfer

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Spray cooling is a way of efficiently removing the heat from a hot surface and is considered for high-power systems such as advanced lasers. The heat transfer phenomenon in spray cooling is complex in nature because it occurs due to conduction, convection, and phase change. A brief review of the modeling of spray cooling is presented here. In the present work, the effect of thermal-boundary-layer thickness on liquid-vapor-interface dynamics and its influence on heat transfer in spray cooling is investigated through multiphase-flow modeling. The multiphase-flow modeling is done using the level-set method to identify the liquid-vapor interface. Some modifications to the incompressible Navier-Stokes equations to consider surface tension, viscosity, gravity, and phase change are discussed. The governing equations are solved using the finite difference method. Here, the droplet impact on a growing vapor bubble in a 44-m-thick liquid film is taken as a benchmark problem to represent the spray cooling. The computed liquid-vapor-interface and temperature distributions are also visualized for better understanding of heat removal. In this study, the high-heat-transfer mechanism in spray cooling is explained with systematic illustrations. Nomenclature c p = specific heat at constant pressure, J=kg K Fr = Froude number (u r = p gl r ) g = gravity vector, m=s 2 H = step function h = grid spacing, m h fg = latent heat of evaporation, J=kg Ja = Jacob number (cplT=h fg ) k = thermal conductivity, W=m K l r = characteristic length [ p =g l v ], m m = mass flux vector, g=m 3 =m 2 s m = mass flux Nu = Nusselt number [ql r =Tk l ] n = surface normal Pe = Peclet number ( l u r l r c pl =k l ) Pr = Prandtl number (c pl l =k l ) p = pressure, Pa q = heat flux, W=m 2 Re = Reynolds number ( l u r l r = l )time, s t r = characteristic time (l r =u r ), s u = velocity vector u; v, m=s u = x-direction velocity, m=s u int = interface velocity, m=s u r = characteristic velocity ( p gl r ), m=s v = y-direction velocity, m=s We = Weber number ( l u 2 r l r =) = thermal diffusivity, m 2 =s T = temperature difference (T w T sat ) = interfacial curvature = dynamic viscosity, N s=m 2 = density, g=m 3 = surface tension, N=m ' = level-set function Subscripts int = interface l, v = liquid, vapor r = reference sat = saturation w = wall Superscript * = nondimensional quantity

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Section: Doi: 102514/134982mentioning

confidence: 99%

Section: A Effect Of Thermal-boundary-layer Thicknessmentioning

confidence: 99%

Modeling Thermal-Boundary-Layer Effect on Liquid-Vapor Interface Dynamics in Spray Cooling

Selvam¹,

Sarkar²,

Sarkar³

et al. 2009

Journal of Thermophysics and Heat Transfer

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“…The film thickness may be the most important but one of the least studied parameters. The film thickness must be known in order to calculate the fluid velocity, the conduction rate, the nucleation size, as well as other important parameters [13].…”

Section: Review Of Film Thickness and Temperaturementioning

confidence: 99%

“…However, the variations in the film thickness and the film temperature are sometimes contradicted to each other. For example, Yang et al [14,15] concluded that the variation in the film thickness was less than 1µm in the spray impact area under their study, and Tilton et al [14,16] also assumed that the film had a uniform thickness under the spray, while Pautsch [13,14] measured the film thickness using an optical method involving total internal reflection, the film thickness measurements were compared with a numerical model of the film, the results indicated that the thinnest film is in the region under the orifice and the thickest is at the corner. Some discussions about the temperature variation observed in the liquid film on a spray cooled surface are as follows: Gu et al [17,18] found that spray cooling resulted in a relatively uniform temperature distribution over the heater surface, while Shedd and Pautsch [17,19] found quite significant temperature variation over their test heater reaching as high as 17°C.…”

Section: Review Of Film Thickness and Temperaturementioning

confidence: 99%

Modeling and Experimental Research on Spray Cooling

Jia

Guo²,

Wang

et al. 2008

2008 Twenty-Fourth Annual IEEE Semionductor Thermal Measurement and Management Symposium

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As a promising solution for high heat flux applications, spray cooling has been widely studied in recent years. A little theoretical knowledge for the heat transfer mechanism of spray cooling is applied to practical design. In order to obtain a better understanding of spray cooling, models of the thickness and the temperature distribution within the range of the impact area were established considering the micro-scale phenomena, such as velocity slip and temperature jump. The heat transfer coefficient (HTC) was calculated. An experimental apparatus was set up to validate the HTC in the models. Experiments were performed for a commercial pressurized full cone nozzle using distilled water as the working fluid. The maximum error between the experimental HTC and the simulated HTC is within 16%.

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“…Pautsch et al (2004) have reported spray impingement cooling liquid film thicknesses ranging between 80 jim and 300 jim. The assumed liquid film thickness in the region of droplet impact (1.5 jim) has then been computed based on the assumed value of the crater diameter (250 gim), and assuming no splashing.…”

mentioning

confidence: 99%

Electromagnetic Control of High Heat-Flux Spray Impingement Boiling Under Microgravity Conditions

Gray¹,

Kuhlman²,

Glaspell³

et al. 2007

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Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources. gathering and maintaining the data needed, and completing and reviewing this collection of information. Send comments regarding this burden estimate or any other aspect of this cOllectioni of information, including suggestions for reducing this burden to Departnient of Defense. Washington Headquarters Services, Directorate for Information Operations and . 1215 Jefferson Davis Highway, Suite 1204, Arlington. VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information i it does not display a currently valid OMB control number. PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. REPORT DATE (DD-MM-YYYY)2. REPORT TYPE 14. ABSTRACT The primary goal of this project was to discover how to most effectively use electromagnetic forces to enhance spray impingement boiling heat transfer in microgravity (jg). This project was closely coordinated with the non-electromagnetic spray impingement boiling experiments conducted by Dr. Kirk L. Yerkes of the Air Force Research Laboratory (AFRL) . The West Virginia University (WVU) investigation of electrical body forces to enhance and control spray impingement boiling extended the AFRL research. The computational phase of the WVU project was based on the commercial multiphysics code CFD-ACE+, which was successfully modified to incorporate the Coulomb and electric Kelvin forces. DATES COVERED (From -ToWVU's ground-based experiments demonstrated for the first time that modest increases in heat transfer coefficient and Nusselt number can be achieved in spray impingement boiling by using electrical forces, thus confirming the fundamental hypothesis of this research.Further increases in heat transfer performance are likely to result from a better understanding of the relevant microphysics and better electrode designs. Experimental results have been used to estimate the time scales for various phenomena that occur in spray impingement boiling, which could lead to improved electrode designs. SUBJECT ABSTRACTThe primary goal of this project was to discover how to most effectively use electromagnetic forces to enhance spray impingement boiling in microgravity (ýLg). This project was closely coordinated with the non-electromagnetic spray impingement boiling heat transfer experiments conducted by Dr. Kirk L. Yerkes of the Air Force Research Laboratory (AFRL). The West Virginia University (WVU) investigation of electrical body forces to enhance and control spray impingement boiling extended the AFRL research. The computational phase of the WVU project was based on the commercial multiphysics code CFD-ACE+, which was successfully modified to incorporate the Coulomb and electric Kelvin forces. WVU's ground-based experiments demonstrated for the first time that modest increases in heat tra...

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Thickness measurements of the thin film in spray evaporative cooling

Cited by 23 publications

References 8 publications

Modeling Thermal-Boundary-Layer Effect on Liquid-Vapor Interface Dynamics in Spray Cooling

Modeling Thermal-Boundary-Layer Effect on Liquid-Vapor Interface Dynamics in Spray Cooling

Modeling and Experimental Research on Spray Cooling

Electromagnetic Control of High Heat-Flux Spray Impingement Boiling Under Microgravity Conditions

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