Influence of viscous flow relaxation time on self-similarity in free-surface jet impingement

Rohlfs, Wilko; Ehrenpreis, Claas; Haustein, Herman D.; Kneer, Reinhold

doi:10.1016/j.ijheatmasstransfer.2014.06.086

Cited by 22 publications

(15 citation statements)

References 29 publications

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“…Being able to describe the flow field in the jump region, the introduced AT (Bohr et al 1997) can be used to study heat transfer in CHJs of type Ia. So far, jet impingement heat transfer has been thoroughly studied from the stagnation point (Liu, Gabour & Lienhard 1993;Rohlfs et al 2014) up to the jump position (Liu & Lienhard 1989;Liu, Lienhard & Lombara 1991) and corresponding correlations for determining the heat transfer coefficient have been proposed. However, theoretical analysis of the heat transfer problem in the jump region has not yet been reported.…”

Section: Introductionmentioning

confidence: 99%

Averaging theory for heat transfer in circular hydraulic jumps with a separation bubble

Solana Gómez,

Bohr,

Nielsen

et al. 2024

J. Fluid Mech.

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Analytical investigations of heat transfer during the vertical impingement of an unsubmerged axisymmetric liquid jet on a horizontal plate have been limited to the regions ahead of the jump. This limitation is due to the complex flow physics in the jump region arising from sudden changes in the flow field. This is addressed in here by extending the averaging theory (AT) introduced by Bohr et al. (Phys. Rev. Lett., vol. 79, issue 6, 1997, pp. 1038–1041) which was further developed by Watanabe et al. (J. Fluid Mech., vol. 480, 2003, pp. 233–265), to describe the heat transfer problem in circular hydraulic jumps including separation. The applicability of the resulting theory to determine the temperature field in the jump region is evaluated using the data available in the literature and also by means of fully resolved numerical solutions. Good agreement is observed for moderate Prandtl numbers. However, for sufficiently high Prandtl numbers, deviations become notable. The reasons for the deviations according to their relevance are (i) monotonically decreasing temperature profile inherent to the AT, whereas the fully resolved numerical solutions exhibit a local maximum in the temperature profile away from the plate; and (ii) inapplicability of the concept of dividing the flow field into a region affected and a region unaffected by heat transfer according to the thermal boundary layer thickness. This concept leads to the overestimation of the temperature close to the wall and to the existence of a threshold Prandtl number, for which the thermal boundary layer thickness does not meet the free surface anymore. Around this threshold Prandtl number, the temperature field shows a discontinuous behaviour.

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Section: Introductionmentioning

confidence: 99%

Averaging theory for heat transfer in circular hydraulic jumps with a separation bubble

Solana Gómez,

Bohr,

Nielsen

et al. 2024

J. Fluid Mech.

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“…The present study deals with the stagnation zone heat transfer and focuses on this flow-wall interaction. For predictive purposes, a previous submerged jet study by the authors showed the heat transfer's dependence on centerline velocity [5], more recently the authors showed an additional dependence on arrival profile shape [6], which may be found [7]. Here it is shown that for the free-surface jet impingement, only a few key characteristics of the arrival profile, located at zw -the height of the stagnation zone and onset of static pressure [8], are needed in order to describe the entire stagnation zone heat transfer.…”

Section: Introductionmentioning

confidence: 99%

Stagnation point heat transfer under a free-surface jet

Harnik,

Haustein

2024

J. Phys.: Conf. Ser.

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Laminar free-surface jet impingement is a crucial configuration for heat transfer processes. Focusing on the link between stagnation-point heat transfer and near-axis radial acceleration, its dependence on jet width and profile is studied. Thus, heat transfer depends on: fluid properties, flow rate, nozzle length, nozzle-to-plate spacing, surface tension and gravity (Pr, Re, L/d, H/d, We & Fr, accordingly). As existing theory is limited to specific cases, a new general description is developed from analogy to submerged jets. Validated by two-phase flow simulations, this description captures key jet dynamics evolution (centerline velocity, profile curvature). It reveals significant property changes during jet flight due to relaxation (L dependence) and contraction (Re/Fr dependence). Unlike submerged jets, contraction raises arrival Reynolds number, leading to additional dependencies Nu ∝ L and Nu ∝ H/Fr, and further deviations at low-We and -Re. The theory successfully predicts heat transfer across diverse conditions and converges to negligible gravity (horizontal jet) as expected.

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“…This flow acceleration depends significantly on the impinging velocity profile and thus on the nozzle velocity profile and its evolution. Beyond the stagnation zone, a configuration-specific wall jet is formed: For the submerged jet, the heat transfer in the wall jet region can be substantially influenced by large scale vortices impinging and traveling along the wall [1]. In the jet-to-jet interaction zone, two or more wall jets approach each other, leading to a strong deflection of the flow.…”

Section: Introductionmentioning

confidence: 99%

“…However, a profound basis for such correlations sometimes can be derived on an analytical basis, as for instance shown by Liu & Lienhard [3] for a free-surface jet. In recent studies by the author, the velocity profile developing in the free jet region (while traveling from the nozzle exit to the wall) has been found to have a substantial effect on the local heat transfer coefficient [1]. With a more detailed understanding of the underlying physical processes, a new mathematical form for scaling laws in laminar free-surface [1] and submerged [2] jet impingement has been developed.…”

Section: Introductionmentioning

confidence: 99%

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Flow structures and heat transfer characteristics in arrays of submerged laminar impinging jets

Rohlfs

Bieber

Ehrenpreis

et al. 2016

Proc Appl Math and Mech

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This study summarizes the scaling behavior of single laminar submerged jets with circular and planar cross sections. Unified correlations for the stagnation zone heat transfer of both configurations, based on the dominant dimensionless numbers, are presented. In technical applications, impinging jets are often applied in jet array configurations. Compared to single jet impingement, jet-to-jet interaction can have a substantial influence on local heat transfer. A distinct pattern of the heat transfer coefficient was observed experimentally. Numerical simulations revealed two counter-rotating vortices in the interaction zone between two jets to be the causing mechanism of this pattern.

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Influence of viscous flow relaxation time on self-similarity in free-surface jet impingement

Cited by 22 publications

References 29 publications

Averaging theory for heat transfer in circular hydraulic jumps with a separation bubble

Averaging theory for heat transfer in circular hydraulic jumps with a separation bubble

Stagnation point heat transfer under a free-surface jet

Flow structures and heat transfer characteristics in arrays of submerged laminar impinging jets

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