A tomographic-PIV investigation of vapor-induced flow structures in confined jet impingement boiling

Rau, Matthew J.; Vlachos, Pavlos P.; Garimella, Suresh V.

doi:10.1016/j.ijmultiphaseflow.2016.03.024

Cited by 9 publications

(4 citation statements)

References 40 publications

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“…The boiling curve obtained during the jet impingement experiments is presented in Figure 2 [20], is a heat flux non-dimensionalization that is used to characterize the thermodynamic state of the fluid at the exit as either subcooled, Bl * < 1, or saturated, Bl * ≥ 1. Relative to use of a vapor quality, the modified boiling number is more useful in describing the phenomena of interest that span across subcooled and saturated exit flow conditions.…”

Section: Resultsmentioning

confidence: 99%

“…During confined, submerged two-phase jet impingement of water at low orifice-to-target spacings, the formation of large vapor structures in the confinement gap has been observed for a wide range of surface heat fluxes [20]. The vapor structures remain in the confinement gap for long periods as compared with the characteristic times for formation and departure of large vapor bubbles during nucleate pool boiling.…”

Section: Introductionmentioning

confidence: 99%

“…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%

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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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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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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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“…A 25.4 mm-diameter (6.7d) circular copper surface was flush-mounted on the bottom wall of the confinement gap with its center aligned with the jet axis. This experimental arrangement allowed for heat transfer experiments in prior studies; 15,16 however, no heat input was used in the current study. Due to a tiny gap around the perimeter of the copper surface (on the order of 100 µm), a small flow disruption was introduced in the wall layer of the wall jet at this location.…”

Section: A Test Sectionmentioning

confidence: 99%

Axisymmetric wall jet development in confined jet impingement

et al. 2017

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The flow field surrounding an axisymmetric, confined, impinging jet was investigated with a focus on the early development of the triple-layered wall jet structure. Experiments were conducted using stereo particle image velocimetry at three different confinement gap heights (2, 4, and 8 jet diameters) across Reynolds numbers ranging from 1000 to 9000. The rotating flow structures within the confinement region and their interaction with the surrounding flow were dependent on the confinement gap height and Reynolds number. The recirculation core shifted downstream as the Reynolds number increased. For the smallest confinement gap height investigated, the strong recirculation caused a disruption of the wall jet development. The radial position of the recirculation core observed at this small gap height was found to coincide with the location where the maximum wall jet velocity had decayed to 15% of the impinging jet exit velocity. After this point, the self-similarity hypothesis failed to predict the evolution of the wall jet further downstream. A reduction in confinement gap height increased the growth rates of the wall jet thickness but did not affect the decay rate of the wall jet maximum velocity. For jet Reynolds numbers above 2500, the decay rate of the maximum velocity in the developing region of the wall jet was approximately −1.1, which is close to previous results reported for the fully developed region of radial wall jets. A much higher decay rate of −1.5 was found for the wall jet formed by a laminar impinging jet at Re = 1000.

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Simultaneous measurements of bubble deformation and breakup with surrounding liquid-phase flow

et al. 2022

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A tomographic-PIV investigation of vapor-induced flow structures in confined jet impingement boiling

Cited by 9 publications

References 40 publications

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

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

Axisymmetric wall jet development in confined jet impingement

Simultaneous measurements of bubble deformation and breakup with surrounding liquid-phase flow

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