Influences of nozzle-plate spacing on boiling heat transfer of confined planar dielectric liquid impinging jet

Shin, Chang Hwan; Kim, Kyung Min; Lim, Sung Hwan; Cho, Hyung Hee

doi:10.1016/j.ijheatmasstransfer.2009.08.002

Cited by 28 publications

(13 citation statements)

References 17 publications

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“…Based on the local hydrodynamics, they concluded that the magnitude of single-phase and partial boiling heat transfer coefficient depends heavily on position relative to the impinging jet; however, fully developed boiling heat transfer was largely insensitive to both the position and convective bulk flow. In a study that used thermocouples to make seven discrete local temperature measurements, Shin et al [23] showed that the local heat transfer depended heavily on the orifice-to-target spacing for a confined, planar jet of dielectric liquid, even in fully developed nucleate boiling.…”

Section: Introductionmentioning

confidence: 99%

Local two-phase heat transfer from arrays of confined and submerged impinging jets

Rau

Garimella

2013

International Journal of Heat and Mass Transfer

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a b s t r a c tLocal heat transfer distributions at high spatial resolution are obtained under two-phase transport conditions in confined and submerged impingement from arrays of miniature jets. The dielectric liquid HFE-7100 is investigated to enable direct cooling of electronic components. Three round orifice geometries with the same total orifice open area are investigated, including a single orifice of 3.75 mm diameter, a 3 Â 3 array of 1.25 mm diameter orifices, and a 5 Â 5 array of 0.75 mm diameter orifices. A thin-foil heat source backed by a magnesium-fluoride window is fabricated to allow detailed mapping of the heated surface temperature via infrared (IR) thermography. The rigorous experimental calibration procedures employed, and correction for heat spreading within the thermally conductive IR-transparent window, yield low-uncertainty local heat transfer coefficient distributions. Each of the three orifice geometries is characterized at volumetric flow rates of 450 ml/min, 900 ml/min, and 1800 ml/min, resulting in a Reynolds number range of 1920-39400. Pressure drop across the confined jets is measured for all experimental cases. The test facility and measurement techniques employed are validated against heat transfer and pressure drop correlations in the literature for single-phase jet impingement from a single round orifice. Spatially resolved temperature contour maps, along with local heat transfer coefficient and boiling curves, are presented as a function of applied heat flux. Boiling is shown to coexist with single-phase convection under the impinging liquid jets. Two-phase enhancement is exhibited at large radial distances from the single jet axis, and in regions between neighboring jets within the arrays. The arrays of jets result in higher area-averaged heat transfer than a single jet at a fixed flow rate; however, the arrays display larger relative nonuniformity in local two-phase heat transfer coefficient and surface temperature. While the 5 Â 5 array resulted in a higher (and the 3 Â 3 a lower) pressure drop than the single jet, all orifices displayed pressure drop that is independent of the applied heat flux and vapor generation.

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Section: Introductionmentioning

confidence: 99%

Local two-phase heat transfer from arrays of confined and submerged impinging jets

Rau

Garimella

2013

International Journal of Heat and Mass Transfer

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“…For characterization of the flow morphology, synchronized highspeed visualizations are performed from the top and the side of the confinement gap. During confined and submerged jet impingement, two-phase flow morphology characterization has been mainly limited to optical visualizations from the side of the confinement gap [11,[20][21][22], but the formation of large vapor structures prevents examination of flow phenomena close to the surface in the side view. Visualization from the top of the confinement gap, as performed in this work, enables direct observation of boiling behavior on the heated surface, which is critical to unraveling the connection between flow morphology and the occurrence of critical heat flux.…”

Section: Introductionmentioning

confidence: 99%

Visualizing near-wall two-phase flow morphology during confined and submerged jet impingement boiling to the point of critical heat flux

Mira-Hernández

Weibel

Garimella

2019

International Journal of Heat and Mass Transfer

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Confined and submerged two-phase jet impingement is a compact, low-pressure-drop solution for high heat flux dissipation from electronic components. Nucleate boiling can be sustained up to significantly higher heat fluxes during two-phase jet impingement as compared to pool boiling. The increases in critical heat flux are explained via hydrodynamic mechanisms that have been debated in the literature. In this study, the two-phase flow morphology of a single subcooled jet of water that impinges on a circular heat source is visualized at high speed with synchronized top and side views of the confinement gap. The impinging jet issues from a 3.75-mm-diameter orifice that is held at a height of 2 orifice diameters above a 25.4-mm-diameter heat source. The experiments are conducted at a jet Reynolds number of 15,000 and a jet inlet subcooling of 10 °C across a range of heat fluxes up to the critical heat flux. When boiling occurs under subcooled exit flow conditions and at moderate heat fluxes, a regular cycle is observed of formation and collapse of vapor structures that bridge the heated surface and the orifice plate, which causes significant oscillations in the pressure drop. Under saturated exit flow conditions, the vapor agglomerates in the confinement gap into a bowl-like vapor structure that recurrently shrinks, due to vapor break-off at the edge of the orifice plate, and is again replenished due to vapor generation at the heater surface. The optical visualizations from the top of the confinement gap provide a unique perspective and indicate that the liquid jet flows downwards through the vapor structure, impinges on the heated surface, and then flows underneath the vapor structure as a fluid wall jet that wets the heated surface upon which discrete bubbles are generated due to boiling. At high heat fluxes, intense vapor generation causes the fluid wall jet to transition from a bubbly to a churn-like regime, shearing off some liquid droplets into the vapor structure. The origin of critical heat flux appears to result from a significant portion of the liquid in the wall jet being deflected off the surface, and the remaining liquid film on the surface drying out before reaching the edge of the heater.

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“…Boiling heat transfer has been considered as a powerful method for high-thermal load dissipations accompanying vigorous phase-change of liquid coolant on a hot spot surface [1,2]. The technique with much higher heat transfer coefficients compared to typical single-phase convective cooling methods like natural and forced convection via gasor liquid-phase coolant, has contributed to the appearance of modern electronic devices with astonishing performances [3,4].…”

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confidence: 99%

Nanotechnology on Boiling Heat Transfer for a Next-generation Cooling Technology

Cho

Kim²

2012

J Material Sci Eng

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Cooling technology, which makes possible to dissipate generated or transmissive heat from hot spots to atmosphere, based on heat transfer is an essential ingredients for practical modern industry fields. For instance, lot of industrial products embodying Central Process Unit (CPU) should be designed to maintain the suitable operating temperature not to exceed critical limits which cause performance degradation or even the component's failure. As the quantity of heat generation rapidly increases according to the increase of the integration density of electric circuits, advanced cooling technologies are required as pre-requisite criteria for thermal designing of devices.We have looked for sufficient and feasible methods in the aspect of cooling capacity and effectiveness based on heat transfer dynamics. Boiling heat transfer has been considered as a powerful method for high-thermal load dissipations accompanying vigorous phase-change of liquid coolant on a hot spot surface [1,2]. The technique with much higher heat transfer coefficients compared to typical single-phase convective cooling methods like natural and forced convection via gasor liquid-phase coolant, has contributed to the appearance of modern electronic devices with astonishing performances [3,4].Since the middle of 2000s, nanotechnologies have been magnified as a novel innovative approach to improve the cooling performance of boiling heat transfer [5][6][7]. Based on thermo-physical fundamentals on boiling heat transfer, we can present two principal factors which dominantly determine the cooling performance; one is surface roughness and the other is wettability characteristics. Herein, the manipulated surface morphology via nanoscale structures, like vertically aligned nanowires [6][7][8][9][10], is able to increase the roughness extremely and intensify the hydrophilicity towards super-wetting regime which is clearly favorable to wetting of the target surface by liquid-phase coolant. At first, higher heat dissipation capacity can be attributed to the increase of surface roughness, which means the extended interfacial contact area between the solid surface and the liquid coolant. Even though silicon nanowires have relatively low thermal conductivity of about 8 W/m·K compared to bulk silicon substrate of about 140 W/m·K [11], the heat dissipation capability under boiling conditions was considerably improved. This can be demonstrated by other aspects on the morphological change via the structures. Surface morphology in company with nano/microscale vacant area formed by the coalescence of distributed nano-structures can play a role as a structural catalyst for the vaporizing of the coolant. The other factor, surface wettability, has also been verified that hydrophilic characteristics of the surfaces result in the enhancement of surface re-wetting properties and then it helps to increase Critical Heat Flux (CHF) to extend maximum heat dissipation capacity. The effects of the surface roughness and the wettability on boiling performances are schematically de...

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Influences of nozzle-plate spacing on boiling heat transfer of confined planar dielectric liquid impinging jet

Cited by 28 publications

References 17 publications

Local two-phase heat transfer from arrays of confined and submerged impinging jets

Local two-phase heat transfer from arrays of confined and submerged impinging jets

Visualizing near-wall two-phase flow morphology during confined and submerged jet impingement boiling to the point of critical heat flux

Nanotechnology on Boiling Heat Transfer for a Next-generation Cooling Technology

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