Laminar film condensation on the underside of an inclined flat plate

Howarth, John; Poots, G.; Wynne, D.

doi:10.1016/0093-6413(78)90013-7

Cited by 6 publications

(4 citation statements)

References 4 publications

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“…Subtle differences between the purely free-surface and the limiting shear-driven flows are discussed by Miesen & Boersma (1995). As a separate, but potentially related and extremely interesting application, we should also mention problems involving the film formation due to condensation, for example on inclined cold walls placed in a saturated vapour stream; see Beckett & Poots (1972), Howarth, Poots & Wynne (1978), Shu & Wilks (1995).…”

Section: Introductionmentioning

confidence: 99%

Instabilities in a high-Reynolds-number boundary layer on a film-coated surface

Timoshin

1997

J. Fluid Mech.

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A high-Reynolds-number asymptotic theory is developed for linear instability waves in a two-dimensional incompressible boundary layer on a flat surface coated with a thin film of a different fluid. The focus in this study is on the influence of the film flow on the lower-branch Tollmien-Schlighting waves, and also on the effect of boundary-layer/potential flow interaction on interfacial instabilities. Accordingly, the film thickness is assumed to be comparable to the thickness of a viscous sublayer in a three-tier asymptotic structure of lower-branch Tollmien-Schlichting disturbances. A fully nonlinear viscous/inviscid interaction formulation is derived, and computational and analytical solutions for small disturbances are obtained for both TollmienSchlichting and interfacial instabilities for a range of density and viscosity ratios of the fluids, and for various values of the surface tension coefficient and the Froude number. It is shown that the interfacial instability contains the fastest growing modes and an upper-branch neutral point within the chosen flow regime if the film viscosity is greater than the viscosity of the ambient fluid. For a less viscous film the theory predicts a lower neutral branch of shorter-scale interfacial waves. The film flow is found to have a strong effect on the Tollmien-Schlichting instability, the most dramatic outcome being a powerful destabilization of the flow due to a linear resonance between growing Tollmien-Schlichting and decaying capillary modes. Increased film viscosity also destabilizes Tollmien-Schlichting disturbances, with the maximum growth rate shifted towards shorter waves. Qualitative and quantitative comparisons are made with experimental observations by Ludwieg & Hornung (1989).

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Section: Introductionmentioning

confidence: 99%

Instabilities in a high-Reynolds-number boundary layer on a film-coated surface

Timoshin

1997

J. Fluid Mech.

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“…An analytical solution for the laminar film in the case of simplified steady-state equations for pure water vapor was conducted by [25][26]. Thy interested in film respectively in an inclined and horizontal tube.…”

Section: Cpmentioning

confidence: 99%

Heat and mass transfer modeling during laminar condensation of non-cryogenic downward fluids flow in a small vertical tube

Belkassmi

Elmaimouni

Rafiki

et al. 2020

International Journal of Thermofluid Science and Technology

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The purpose of this paper is to investigate mass and heat transfer in the process of film condensation of vapor-air mixture for non-cryogenic fluids flow in a small vertical tube. A two-phase mathematical model is developed to model the mixture and liquid film. The governing equations for mixture and liquid-film have been resolved using a numerical method. Furthermore, this phenomenon analyzed is linked to a steady-state. Therefore, the development of numerical codes allows us to investigate the effect of implicated parameters on this phenomenon. Ethanol and methanol as non-cryogenic typical working fluids are realized for a good understanding of the heat and mass transfer mechanism during condensation. In this way, several effects of influencing parameters were examined. The predicted results showed a good agreement with experimental data.

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“…On the other hand, MD membranes are hydrophobic. Thin films of water can stay on the underside of inclined hydrophilic surfaces up to very high tilt angles [69][70][71]. Additionally, in small air gaps where droplets can exceed the size of the gap, droplets on the hydrophobic surface may touch and be reabsorbed into the liquid film on the hydrophilic condensing plate.…”

Section: Thermal Bridgingmentioning

confidence: 99%

Comprehensive condensation flow regimes in air gap membrane distillation: Visualization and energy efficiency

Warsinger

Swaminathan

Morales

et al. 2018

Journal of Membrane Science

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The thermal performance of air gap membrane distillation (AGMD) desalination is dominated by heat and mass transfer across the air gap between the membrane and the condensing surface. However, little is known about the impact of condensate flow patterns in some design variations of the air gap. In this study, air gap membrane distillation experiments were performed at various inlet temperatures, varying module inclination angle, condensing surface hydrophobicity, and gap spacer design to identify the effect of each on the permeate production rate and thermal efficiency of the system. Energy efficiency modeling was performed as well. Additionally, this study is one of the first with enhanced visualization of flow patterns within the air gap itself, by using a transparent, high thermal conductivity sapphire plate as the condenser surface. System-level numerical modeling is used to further understand the impact of these flow regimes on overall energy efficiency, including flux and GOR. A brief review of membrane distillation condensation regimes is provided as well. For tilting the AGMD flat-plate module, permeate flux was barely influenced except at extreme positive angles (>80ᵒ), and moderate negative angles (<-30ᵒ), where condensate fell onto the membrane surface. The surface with the hydrophobic coating (for dropwise condensation) was shown to have better droplet shedding (with very small nearly spherical droplets) and fewer droplets bridging the gap. Superhydrophobic surfaces (for jumping droplet condensation) were similar, with much smaller droplet sizes. Meanwhile, the hydrophilic surface for small gap sizes (< 3 mm) often had pinned regions of water around the hydrophilic surface and plastic spacer. Overall, the various results imply that the common assumption of a laminar condensate film poorly describes the flow patterns in real systems for all tilt angles and most spacer designs. Real system performance is likely to be between that of pure AGMD and permeate gap membrane distillation (PGMD) variants, and modeling shows that better condensing in air gaps may improve system energy efficiency significantly, with strong relative advantages at high salinity.

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Laminar film condensation on the underside of an inclined flat plate

Cited by 6 publications

References 4 publications

Instabilities in a high-Reynolds-number boundary layer on a film-coated surface

Instabilities in a high-Reynolds-number boundary layer on a film-coated surface

Heat and mass transfer modeling during laminar condensation of non-cryogenic downward fluids flow in a small vertical tube

Comprehensive condensation flow regimes in air gap membrane distillation: Visualization and energy efficiency

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