Influence of the Coulomb Force on Spray Cooling

Kuhlman, John M.; Kreitzer, Paul J.; Mehra, Deepak; Gray, Donald D.; Yerkes, Kirk L.

doi:10.1063/1.2437446

Cited by 10 publications

(8 citation statements)

References 13 publications

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“…It is believed that existence of these large ligaments or sheets of liquid may result in inaccuracies in the PDA droplet diameter measurements of Yerkes et al (2006). As a result, the time scale analysis by Kuhlman et al (2007) should be revised in light of the presence of the large features in the spray. Similar video files recorded at 9,600 frames per second with better spatial resolution that also show the heater surface indicate significant splashing of these larger droplets, ligaments, and sheets when they impact the heater.…”

Section: Resultsmentioning

confidence: 99%

“…An initial study of the use of the electric Kelvin force has been summarized in the thesis by Glaspell (2006) and by Kreitzer et al (2006). The use of the Coulomb force via inductive charging electrode designs (Law, 1978) is described in the thesis by Kreitzer (2006) and by Kuhlman et al (2007). Both the Kelvin force studies by Glaspell (2006) and the inductive charging Coulomb force work by Kreitzer (2006) used FC-72 and a second 3M dielectric coolant, HFE-7000.…”

Section: Previous Workmentioning

confidence: 99%

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Effects of Contact Charging on Spray Impingement Heat Transfer Performance and Spray Behavior

Kreitzer

Kuhlman

Mehra

et al. 2007

39th AIAA Thermophysics Conference

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The effects of contact charging on the heat transfer performance of a full-cone spray of the dielectric coolant, HFE-7000, has been studied using a Thick Film Resistor (TFR) heater with an active surface area of 1.46 cm 2 at a nozzle-to-heater spacing of 13 mm. Tests have been conducted at coolant flow rates between 1.3 and 6.8 GPH (1.4 x 10 -6 to 7.1 x 10 -6 m 3 /s), for heater power ranging from 0 to 60 Watts, yielding heat fluxes between 0 and 400 kW/m 2 . Voltage levels applied to the brass spray nozzle to charge the spray range from 0 to 30 kV, using both negative and positive polarity.A dramatic change in the visual spray flow pattern is observed as the charging voltage exceeds approximately 15 kV in magnitude. Above this voltage, the spray changes from droplets and collections of clearly observable discrete sheets to what appears to primarily be a finer mist of smaller droplets between the spray nozzle and the heater surface. This is due to exceeding the Rayleigh limit for the maximum charge on the liquid droplets, resulting in electrostatic atomization to a smaller average droplet size. However, no significant change in the measured heat transfer performance is seen between the no voltage and the high voltage cases up to a maximum charging voltage of 30 kV.

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Section: Resultsmentioning

confidence: 99%

Section: Previous Workmentioning

confidence: 99%

Effects of Contact Charging on Spray Impingement Heat Transfer Performance and Spray Behavior

Kreitzer

Kuhlman

Mehra

et al. 2007

39th AIAA Thermophysics Conference

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“…The Coulomb force electrodes were designed by attempting to follow the recommendations of Law (1978) The complete results using the Coulomb force electrode geometries shown in Figures 4.211B and 4.30 for a vertical downward spray have been presented in detail by Kreitzer (2006), and summarized by Kuhlman et al (2007). The present data for the Coulomb force electrodes have been obtained for applied voltage levels of up to 5 kV.…”

Section: Coulomb Force Experimentsmentioning

confidence: 99%

“…It is believed that the actual levels of charge achieved on the electrodes may have been less than listed in Table 1, due to non-optimal axial spacing of the electrodes, and/or inadequate charging time. Kuhlman et al (2007) of the time scales for FC-72 for physical phenomena that are expected to be relevant in spray impingement cooling, in an effort to develop some understanding of how a body force might be able to influence spray cooling performance. First, a kinematic time scale has been computed as the time between droplet impacts onto a region of the heater surface equal to the estimated area of the thin liquid film "crater" that forms due to the previous droplet impact.…”

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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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“…When it reaches the surface, a thin liquid layer is formed, termed the "subcavity liquid layer" in the current work. The thickness of this thin liquid layer is of interest, as a region of high transient heat flux in spray cooling applications (Kuhlman et al, 2007). After reaching the impact surface, the cavity starts to spread, thus increasing the cavity radius.…”

Section: Overviewmentioning

confidence: 99%

Comparisons of Single Drop Impact Simulations with Experiments

Medam¹

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Comparisons of Single Drop Impact Simulations with Experiments Krishna Teja Medam As the size of electronic equipment is reduced, the ability to reject waste heat is also reduced due to smaller component surface areas, thereby affecting the component performance and finally leading to the damage of the component. Spray cooling offers a means to achieve high rates of heat transfer from microelectronic components and other high energy density devices. As a first step in investigating spray cooling, a single liquid drop impacting onto a thin liquid film was studied at isothermal conditions. 2D axisymmetric cases were simulated with ANSYS Fluent and 3D cases with OpenFOAM using the Volume of Fluid (VOF) model. The post processing of the results was performed in Surfer (Version 9) software in order to determine the liquid film thickness and then calculate the volume of the liquid under the cavity (sub-cavity liquid volume) as functions of time. These simulations agreed with the experimental data during the cavity formation phase, but did not closely match with the experiments during the refilling of the cavity in the majority of the cases. It was speculated that the discrepancies could be due to the three dimensional instabilities leading to droplet ejection from the crown during the retraction phase. These instabilities are omitted from the 2D simulations, and were not adequately resolved in the 3D simulations. For this reason, identical cases were simulated in 3D in OpenFOAM using the VOF model. The improved agreement with experiments obtained with the three dimensional simulations is discussed.

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Influence of the Coulomb Force on Spray Cooling

Cited by 10 publications

References 13 publications

Effects of Contact Charging on Spray Impingement Heat Transfer Performance and Spray Behavior

Effects of Contact Charging on Spray Impingement Heat Transfer Performance and Spray Behavior

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

Comparisons of Single Drop Impact Simulations with Experiments

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