Visualization of Electrohydrodynamic Effects and Time Scale Analysis for Impinging Spray Droplets of HFE-7000

Kreitzer, Paul J.; Kuhlman, John M.

doi:10.1063/1.2845053

Cited by 6 publications

(5 citation statements)

References 21 publications

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“…The liquid film has been assumed to have a uniform thickness of 50 microns. This value falls within the published values of Selvam et al (2006), Pautsch et al (2004), and Kreitzer and Kuhlman (2008).…”

Section: Section 42: Parameters Testedsupporting

confidence: 90%

“…Work by Sivakumar and Tropea (2002) identified a film thickness ranging from 55 − 192 µm. Work by Kreitzer and Kuhlman (2008) used high speed imagery to determine an estimated liquid film thickness ranging from 50 -300 µm for their apparatus. Therefore a combination of the two ranges will be used herein to establish the film thickness and impingement classification.…”

Section: Section 231: Estimated Film Thicknessmentioning

confidence: 99%

“…Initial conditions include the heater size, spray characteristics (flow rate, operating pressure, droplet diameter, and impingement radial flux distribution), preexisting film thickness, and fluid temperature. Table 3.2 displays typical values for these parameters that are predefined in the simulation, based on the work of Kreitzer and Kuhlman (2008). The initial size constraints were dictated by the experimental design, and the droplet diameter range was a function of the spray nozzle used.…”

Section: Section 32: Description Of Parameter Input Program Blockmentioning

confidence: 99%

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Spray cooling simulation implementing time scale analysis and the Monte Carlo method

Kreitzer¹

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Spray Cooling Simulation Implementing TimeScale Analysis and the Monte Carlo Method PAUL JOSEPH KREITZER Spray cooling research is advancing the field of heat transfer and heat rejection in high power electronics. Smaller and more capable electronics packages are producing higher amounts of waste heat, along with smaller external surface areas, and the use of active cooling is becoming a necessity. Spray cooling has shown extremely high levels of heat rejection, of up to 1000 W/cm 2 using water. Simulations of spray cooling are becoming more realistic, but this comes at a price. A previous researcher has used CFD to successfully model a single 3D droplet impact into a liquid film using the level set method. However, the complicated multiphysics occurring during spray impingement and surface interactions increases computation time to more than 30 days. Parallel processing on a 32 processor system has reduced this time tremendously, but still requires more than a day. The present work uses experimental and computational results in addition to numerical correlations representing the physics occurring on a heated impingement surface. The current model represents the spray behavior of a Spraying Systems FullJet 1/8-g spray nozzle. Typical spray characteristics are indicated as follows: flow rate of 1.05x10-5 m 3 /s, normal droplet velocity of 12 m/s, droplet Sauter mean diameter of 48 µm, and heat flux values ranging from approximately 50-100 W/cm 2. This produces non-dimensional numbers of: We 300-1350, Re 750-3500, Oh 0.01-0.025. Numerical and experimental correlations have been identified representing crater formation, splashing, film thickness, droplet size, and spatial flux distributions. A combination of these methods has resulted in a Monte Carlo spray impingement simulation model capable of simulating hundreds of thousands of droplet impingements or approximately one millisecond. A random sequence of droplet impingement locations and diameters is generated, with the proper radial spatial distribution and diameter distribution. Hence the impingement, lifetime and interactions of the droplet impact craters are tracked versus time within the limitations of the current model. A comparison of results from this code to experimental results shows similar trends in surface behavior and heat transfer values. Three methods have been used to directly compare the simulation results with published experimental data, including: contact line length estimates, empirical heat transfer equation calculations, and nondimensional Nusselt numbers. A Nusselt number of 55.5 was calculated for experimental values, while a Nu of 16.0 was calculated from the simulation.

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Section: Section 42: Parameters Testedsupporting

confidence: 90%

Section: Section 231: Estimated Film Thicknessmentioning

confidence: 99%

Section: Section 32: Description Of Parameter Input Program Blockmentioning

confidence: 99%

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Spray cooling simulation implementing time scale analysis and the Monte Carlo method

Kreitzer¹

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“…The results of Puterbaugh et al [14,15] suggested that the amount of dissolved air in FC-72 has an insignificant effect on CHF. Kreitzer et al [16][17][18] investigated body force effects on spray cooling by applying a high voltage coulombic, electrostatic, force to the spray cone, demonstrating small changes in heat transfer performance under specific conditions. Additionally, Glaspell [19] applied a Kelvin force, a magnetic field, to the spray, achieving results that provided a maximum heat transfer improvement of 5.2% at a 6 [kV] electrode voltage.…”

Section: List Of Tablesmentioning

confidence: 99%

Effect of Variable Gravity on the Cooling Performance of a 16-Nozzle Spray Array

Elston

Yerkes

Thomas

et al. 2009

47th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition

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It was found that the cooling performance was enhanced in micro-gravity over terrestrial and elevated gravity. In addition, a sudden degradation in performance was found at high mass flow rates in micro-gravity, possibly due to liquid buildup on the surface between the nozzle impact zones. A high degree of subcooling was found to be beneficial, but the dissolved air content had little effect on the heat transfer performance either in micro-gravity or elevated gravity. Also, an improved liquid-vapor separator concept was implemented to enable flow stability during the micro-gravity portions of the flight. Multiple liquid-vapor separator concepts were tested during micro-gravity flights until a final design was settled on. The final separator design went through more rigorous evaluation to compare performance at multiple fill levels, each with a higher percentage of vapor space within the reservoir. It was found that, using the final reservoir design, stable flow operation was achieved in micro-gravity for mass flow ratesṁ = 14, 17.5 and 21 [g/s].iv

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“…The results of Puterbaugh et al [14] and Puterbaugh [15] suggested that the amount of dissolved air in FC-72 has an insignificant effect on CHF. Kreitzer and Kuhlman [16], Kreitzer [17] and Kreitzer et al [16][17][18] investigated body force effects on spray cooling by applying an electrostatic force to the spray cone, demonstrating small changes in heat transfer performance under specific conditions. Additionally, Glaspell [19] applied a magnetic field to the spray, achieving results that provided a maximum heat transfer improvement of 5.2% at a 6 kV electrode voltage.…”

Section: Introductionmentioning

confidence: 99%

Cooling Performance of a 16-Nozzle Array in Variable Gravity

Elston

Yerkes

Thomas

et al. 2009

Journal of Thermophysics and Heat Transfer

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The objective of this paper was to investigate the cooling performance of a 16-nozzle spray array using FC-72 as the working fluid in variable-gravity conditions. A flight-test experiment was modified to accommodate a 16-nozzle spray array, which was then tested in the parabolic flight trajectory environment of NASA's C-9 reduced-gravity aircraft. The 16-nozzle array was designed to cool a 25:4 25:4 mm 2 area on a thick-film resistive heater used to simulate an electronic component. Flight tests were conducted over the course of two flight weeks (each week consisting of four flights and each flight consisting of 40 to 60 parabolas). The mass flow rate through the 16-nozzle spray array ranged from 13:1 _ m 21:3 g=s. The heat flux at the thick-film resistor ranged from 2:9 q 00 25 W=cm 2 , the subcooling of the working fluid ranged from 1:6 T sc 18:4 C, the saturation temperature ranged from 37:4 T sat 47:2 C, and the absorbed air content in the working fluid was C 10:1, 14.3 and 16.8% by volume. The spray chamber pressure ranged from 42 P 78 kPa and the acceleration ranged from 0:02 a 2:02 g. Two-phase cooling was emphasized, but some single-phase data were also collected. A one-dimensional model was used to predict the heater surface temperature from the heat input and mean heater base temperature. It was found that the cooling performance was enhanced in microgravity over terrestrial and elevated gravity. In addition, a sudden degradation in performance was found at high mass flow rates in microgravity, possibly due to liquid buildup on the surface between the nozzle impact zones. A high degree of subcooling was found to be beneficial, but the dissolved air content had little effect on the heat transfer performance in either microgravity or elevated gravity. Nomenclature A = area, m 2 a = acceleration, m=s 2 C = percent of dissolved air content by volume, V air =V FC-72 V air 100 D = mean droplet diameter, m Fr = Froude number, v 2 =aD f = fraction of heat lost down the pedestal Ga = Galileo number, aD 3 2 = 2 G = nondimensional heat input, Q=2k r WT sat T 1 k = thermal conductivity, W=m K L = heater layer thickness, m _ m = mass flow rate, kg=s P = chamber pressure, kPa Q = heat rate, W q 00 = heat flux, W=m 2 T = temperature, K T = average temperature, K V = volume, m 3 v = droplet velocity, m=s W = heater width, m We = Weber number, v 2 D= T = temperature difference, K = viscosity, Pa s = density, kg=m 3 = surface tension, N=m, or standard deviation = nondimensional temperature, T T 1;surf =T sat T 1;surf Subscripts c = heater ceramic layer (substrate) g = heater glass layer (cover plate) in = nozzle inlet int = interface between phenolic base and bottom of heater r = heater resistive layer sat = saturated condition sc = subcooling surf = heater surface exposed to spray 1 = freestream condition

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Visualization of Electrohydrodynamic Effects and Time Scale Analysis for Impinging Spray Droplets of HFE-7000

Cited by 6 publications

References 21 publications

Spray cooling simulation implementing time scale analysis and the Monte Carlo method

Spray cooling simulation implementing time scale analysis and the Monte Carlo method

Effect of Variable Gravity on the Cooling Performance of a 16-Nozzle Spray Array

Cooling Performance of a 16-Nozzle Array in Variable Gravity

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