Application of Electrohydrodynamic Atomization to Two-Phase Impingement Heat Transfer

2008 ◽  
Vol 130 (7) ◽  
Author(s):  
Xin Feng ◽  
James E. Bryan
Keyword(s):  
Heat Transfer ◽  
Capillary Tube ◽  
Heated Surface ◽  
Heat Fluxes ◽  
Operating Conditions ◽  
Working Fluid ◽  
Heater Surface ◽  
Two Phase ◽  
Impingement Heat Transfer ◽  
Repulsive Forces

The effect of electric fields applied to two-phase impingement heat transfer is explored for the first time. The electric field applied between a capillary tube and heated surface enhances the heat transfer by controlling the free boundary flow modes from discreet drops to jets, to sprays. Through an experimental study, the impingement heat transfer was evaluated over a range of operating conditions and geometrical parameters with subcooled ethanol used as the working fluid. The ability to change the mode of impinging mass did change the surface heat transfer. The characteristics of the impinging mass on heat transfer were dependent on flow rate, applied voltage, capillary tube to heated surface spacing, capillary tube geometry, heat flux, heater surface geometry, and capillary tube array configuration. Enhancement occurred primarily at low heat fluxes (below 30W∕cm2) under ramified spray conditions where the droplet momentum promoted thin films on the heated surface resulting in 1.7 times enhancement under certain conditions. Higher heat fluxes resulted in greater vapor momentum from the surface, minimizing the effect of different impingement modes. The use of capillary tube array allowed for electrohydrodynamics atomization enhancement and higher liquid flow rates, but electrostatic repulsive forces diverted the spray from the heater surface. This reduced the mass flux to the surface, leading to premature dryout under certain conditions.

Effect of Electric Fields on Two-Phase Impingement Heat Transfer

2007 ◽  
Author(s):  
Xin Feng ◽  
James E. Bryan
Keyword(s):  
Heat Transfer ◽  
Electric Fields ◽  
Capillary Flow ◽  
Heated Surface ◽  
Heat Fluxes ◽  
Working Fluid ◽  
Geometrical Parameters ◽  
Two Phase ◽  
Transfer Rates ◽  
Impingement Heat Transfer

The effect of electric fields applied to two-phase impingement heat transfer is explored for the first time. The application of an electric field between a capillary and heated surface results in the ability to control the free boundary flow from discreet drops to jets to sprays. Through an experimental study, the impingement heat transfer was evaluated over a range of operating and geometrical parameters using subcooled ethanol as the working fluid. The ability to change the mode of impinging mass did change the surface heat transfer. The characteristics of the impinging mass on heat transfer was dependent on capillary flow rate, applied voltage, capillary to heated surface spacing, capillary geometry, and heat flux. Enhancement occurred primarily at low heat fluxes (below 30 W/cm2) under ramified spray conditions where the droplet momentum promoted thin films on the heated surface. Higher heat fluxes resulted in greater vapor momentum from the surface minimizing the effect of different modes. However, under ramified spray conditions less mass was impacting the heated surface showing that heat transfer rates at higher heat fluxes were achievable with less mass, resulting in greater evaporation efficiency.

scholarly journals Experimental Investigation of Embedded Micropin-Fins for Single-Phase Heat Transfer and Pressure Drop

2018 ◽  
Vol 140 (2) ◽  
Author(s):  
Chirag R. Kharangate ◽  
Ki Wook Jung ◽  
Sangwoo Jung ◽  
Daeyoung Kong ◽  
Joseph Schaadt ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Friction Factor ◽  
Integrated Circuit ◽  
Single Phase ◽  
Absolute Error ◽  
Heat Fluxes ◽  
Operating Conditions ◽  
Working Fluid ◽  
Pin Fin

Three-dimensional (3D) stacked integrated circuit (IC) chips offer significant performance improvement, but offer important challenges for thermal management including, for the case of microfluidic cooling, constraints on channel dimensions, and pressure drop. Here, we investigate heat transfer and pressure drop characteristics of a microfluidic cooling device with staggered pin-fin array arrangement with dimensions as follows: diameter D = 46.5 μm; spacing, S ∼ 100 μm; and height, H ∼ 110 μm. Deionized single-phase water with mass flow rates of m˙ = 15.1–64.1 g/min was used as the working fluid, corresponding to values of Re (based on pin fin diameter) from 23 to 135, where heat fluxes up to 141 W/cm2 are removed. The measurements yield local Nusselt numbers that vary little along the heated channel length and values for both the Nu and the friction factor do not agree well with most data for pin fin geometries in the literature. Two new correlations for the average Nusselt number (∼Re1.04) and Fanning friction factor (∼Re−0.52) are proposed that capture the heat transfer and pressure drop behavior for the geometric and operating conditions tested in this study with mean absolute error (MAE) of 4.9% and 1.7%, respectively. The work shows that a more comprehensive investigation is required on thermofluidic characterization of pin fin arrays with channel heights Hf < 150 μm and fin spacing S = 50–500 μm, respectively, with the Reynolds number, Re < 300.

Spatial and Temporal Wall Temperature Fluctuations in Two-Phase Flow in Microgap Coolers

2010 ◽  
Author(s):  
Jessica Sheehan ◽  
Avram Bar-Cohen
Keyword(s):  
Heat Transfer ◽  
High Heat ◽  
Heat Fluxes ◽  
Operating Conditions ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Heat Transfer Coefficients ◽  
High Heat Transfer ◽  
Volumetric Cooling ◽  
Very High

Heat transfer to an evaporating refrigerant and/or dielectric liquid in a microgap channel can provide very high heat transfer coefficients and volumetric cooling rates. Recent studies at Maryland have established the dominance of the annular flow regime in such microgap channels and related the observed high-quality peak of an M-shaped heat transfer coefficient curve to the onset of local dryout. The present study utilizes infrared thermography to locate such nascent dryout regions and operating conditions. Data obtained with a 210 micron microgap channel, operated with a mass flux of 195.2 kg/m2-s and heat fluxes of 10.3 to 26 W/cm2 are presented and discussed.

Heat Transfer Correlations for Liquid Film in the Evaporator of Enclosed, Gravity-Assisted Thermosyphons

1998 ◽  
Vol 120 (2) ◽  
pp. 477-484 ◽  
Author(s):  
M. S. El-Genk ◽  
H. H. Saber
Keyword(s):  
Heat Transfer ◽  
Liquid Film ◽  
Nucleate Boiling ◽  
Heat Fluxes ◽  
Smooth Transition ◽  
Working Fluid ◽  
Two Phase ◽  
Data Set ◽  
Evaporator Section ◽  
Heat Transfer Correlations

Heat transfer correlations were developed for the liquid film region, in the evaporator section of closed, two-phase, gravity-assisted thermosyphons in the following regimes: (a) laminar convection, at low heat fluxes, (b) combined convection, at intermediate heat fluxes, and (c) nucleate boiling, at high heat fluxes. These correlations were based on a data set consisting of a total of 305 points for ethanol, acetone, R-11, and R-113 working fluids, wall heat fluxes of 0.99–52.62 kW/m2, working fluid filling ratios of 0.01–0.62, inner diameters of 6–37 mm, evaporator section lengths of 50–609.6 mm, and vapor temperatures of 261–352 K. The combined convention data were correlated by superimposing the correlations of laminar convention and nucleate boiling using a power law approach, to ensure smooth transition among the three heat transfer regimes. The three heat transfer correlations developed in this work are within ±15 percent of experimental data.

Effect of Jet Arrays and Structured Surfaces on Two-Phase Impingement Heat Transfer

2007 ◽  
Author(s):  
Xin Feng ◽  
James E. Bryan
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Performance ◽  
Jet Impingement ◽  
Heat Fluxes ◽  
Transfer Efficiency ◽  
Surface Wetting ◽  
Two Phase ◽  
Structured Surfaces ◽  
Heat Transfer Efficiency ◽  
Impingement Heat Transfer

When heat fluxes and heat transport exceed 100 W/cm2, heat transfer efficiencies decrease rapidly. Experimental work will be presented exploring how micro jet arrays and structured surfaces can be used to increase heat transfer efficiency. Using water, ethanol, and HFE-7000 as working fluids, the effect of jet momentum, subcooling temperature and surface wetting are experimentally investigated on 1cm2 smooth and structured surfaces. From results obtained so far, heat transfer efficiency increases with increasing surface tension (decreasing surface wetting) with micro-jet arrays. Further, existing correlations for two-phase jet impingement cannot predict the heat transfer performance with acceptable accuracy as they do not account for surface wetting characteristics.

Liquid Crystal Imaging of Flow Boiling in Minichannels

2004 ◽  
Author(s):  
D. Keith Hollingsworth
Keyword(s):  
Heat Transfer ◽  
Liquid Crystal ◽  
Flow Boiling ◽  
Heated Surface ◽  
Working Fluid ◽  
Hysteresis Phenomenon ◽  
Two Phase ◽  
Channel Effects ◽  
Mini Channels ◽  
Boiling Incipience

Quantitative liquid crystal thermography was used to investigate boiling incipience and nucleate flow boiling in rectangular mini-channels with channel heights of 2 mm to 500 μm. Distributions of surface temperature along the heated surface were measured from the liquid crystal images, and streamwise profiles of heat transfer coefficient on the heated surface were calculated. The working fluid was the refrigerant R-11. Observations of the boiling incipience superheat excursion, the hysteresis phenomenon, and saturated flow boiling are presented. Comparisons to established two-phase heat transfer correlations are performed to investigate the existence of “thin channel” effects.

Correlation of Heat Transfer Data to Film Thickness Data of the Thin Film Found in Spray Cooling

2004 ◽  
Author(s):  
Adam G. Pautsch ◽  
Timothy A. Shedd
Keyword(s):  
Thin Film ◽  
Heat Transfer ◽  
Film Thickness ◽  
Heated Surface ◽  
Spray Cooling ◽  
Heat Fluxes ◽  
Experimental Measurements ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Heat Transfer Coefficients

As electronic circuit design and packaging technology progresses, the density and power levels of electronic components is increasing at a nearly exponential rate. The higher heat loads dissipated by these devices are nearing the limits of traditional cooling techniques. One method capable of removing heat fluxes as high as 100 W/cm2 is spray cooling. This process involves the impingement of liquid droplets onto a heated surface, forming a thin two-phase film. In order to create reliable models of the heat transfer during spray cooling, the behavior of the film must be understood. This paper presents an investigation into the behavior of the thin film found in spray cooling. A study was performed to relate experimental measurements of the heat transfer coefficients to experimental measurements of film thickness as they vary spatially over a die surface. Both a single nozzle and a multi-nozzle array were investigated. Measured heat transfer coefficients ranged from 0.2 to 1.2 W/m2K and film thicknesses ranged from 90 to 300 μm.

Choosing Working Fluid for Two-Phase Thermosyphon Systems for Cooling of Electronics

2003 ◽  
Vol 125 (2) ◽  
pp. 276-281 ◽  
Author(s):  
Bjo¨rn Palm ◽  
Rahmatollah Khodabandeh
Keyword(s):  
Heat Transfer ◽  
High Pressure ◽  
Heat Fluxes ◽  
Working Fluid ◽  
Air Cooling ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Heat Transfer Coefficients ◽  
And Performance ◽  
Cooling Of Electronics

The heat fluxes from electronic components are steadily increasing and have now, in some applications, reached levels where air-cooling is no longer sufficient. One alternative solution, which has received much attention during the last decade, is to use heat pipes or thermosyphons for transferring or spreading the dissipated heat. In this paper two-phase thermosyphon loops are discussed. Especially, the choice of fluid and its influence on the design and performance is treated. The discussion is supported by results from simulations concerning heat transfer and pressure drop. In general it is found that high-pressure fluids will give better performance and more compact designs as high-pressure results in higher boiling heat transfer coefficients and smaller necessary tube diameter.

Loop Thermosyphon Design for Cooling of Large Area, High Heat Flux Sources

2007 ◽  
Author(s):  
John R. Hartenstine ◽  
Richard W. Bonner ◽  
Jared R. Montgomery ◽  
Tadej Semenic
Keyword(s):  
Saturation Temperature ◽  
High Heat ◽  
Heat Fluxes ◽  
Operating Conditions ◽  
Working Fluid ◽  
High Heat Flux ◽  
Flow Loop ◽  
Large Area ◽  
Two Phase ◽  
Porous Wick

Two-phase flow loop technologies capable of acquiring high heat fluxes (&gt;1kW/cm2) from large area heat sources (10cm2) are being considered for the next generation naval thermal requirements. A loop thermosyphon device (∼1 meter tall) was fabricated and tested that included several copper porous wick structures in cylindrical evaporators. The first two were standard annular monoporous and biporous wick designs. The third wick consists of an annular evaporator wick and an integral secondary slab wick for improved liquid transport. In this configuration a circular array of cylindrical vapor vents are formed integral to the primary and secondary transport wick composite. Critical heat fluxes using these wick structures were measured between 240W/cm2 and 465W/cm2 over a 10cm2 area with water as the working fluid at 70°C saturation temperature. A thermosyphon model capable of predicting flow rate at various operating conditions based on a separated flow model is presented.

Two-Phase Flow and Heat Transfer in Pin-Fin Enhanced Micro-Gaps With Non-Uniform Heating

2013 ◽  
Author(s):  
Steven A. Isaacs ◽  
Yogendra Joshi ◽  
Yue Zhang ◽  
Muhannad S. Bakir ◽  
Yoon Jo Kim
Keyword(s):  
Heat Transfer ◽  
Two Phase Flow ◽  
Flow Boiling ◽  
Heat Fluxes ◽  
Working Fluid ◽  
Phase Flow ◽  
Two Phase ◽  
Pin Fin ◽  
Flow And Heat Transfer ◽  
Imaging Results

In modern microprocessors, thermal management has become one of the main hurdles in continued performance enhancement. Cooling schemes utilizing single phase microfluidics have been investigated extensively for enhanced heat dissipation from microprocessors. However, two-phase fluidic cooling devices are becoming a promising approach, and are less understood. This study aims to examine two-phase flow and heat transfer within a pin-fin enhanced micro-gap. The pin-fin array covered an area of 1cm × 1cm and had a pin diameter, height and pitch of 150μm, 200μm and 225μm, respectively, (aspect ratio of 1.33). Heating from two upstream heaters was considered. The working fluid used was R245fa. The average heat transfer coefficient was evaluated for a range of heat fluxes and flow rates. Flow regime visualization was performed using high-speed imaging. Results indicate a sharp transition to convective flow boiling mechanism. Unique, conically-shaped two-phase wakes are recorded, demonstrating 2D spreading capability of the device. Surface roughness features are also discussed.

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