Near-surface turbulence for evaporative convection at an air/water interface

Flack, Karen A.; Saylor, J. R.; Smith, Geoffrey B.

doi:10.1063/1.1410126

Cited by 33 publications

(34 citation statements)

References 22 publications

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“…Instead, they only observed regions with vortical structures, which could be explained by their relatively high Rayleigh number and/or the presence of surface contamination. Flack, Saylor & Smith (2001), for instance, observed that surface contamination can significantly affect the surface temperature pattern. A detailed investigation on how the surface pattern in buoyancy-driven flow is affected by surface contamination, Rayleigh number or Schmidt number is still lacking.…”

Section: J G Wissink and H Herlinamentioning

confidence: 99%

Direct numerical simulation of gas transfer across the air–water interface driven by buoyant convection

Wissink

Herlina

2015

J. Fluid Mech.

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A series of direct numerical simulations of mass transfer across the air-water interface driven by buoyancy-induced convection have been carried out to elucidate the physical mechanisms that play a role in the transfer of heat and atmospheric gases. The buoyant instability is caused by the presence of a thin layer of cold water situated on top of a body of warm water. In time, heat and atmospheric gases diffuse into the uppermost part of the thermal boundary layer and are subsequently transported down into the bulk by falling sheets and plumes of cold water. Using a specifically designed numerical code for the discretization of scalar convection and diffusion, it was possible to accurately resolve this buoyant-instability-induced transport of atmospheric gases into the bulk at a realistic Prandtl number (Pr = 6) and Schmidt numbers ranging from Sc = 20 to Sc = 500. The simulations presented here provided a detailed insight into instantaneous gas transfer processes. The falling plumes with highly gas-saturated fluid in their core were found to penetrate deep inside the bulk. With an initial temperature difference between the water surface and the bulk of slightly above 2 K, peaks in the instantaneous heat flux in excess of 1600 W m −2 were observed, proving the potential effectiveness of buoyant-convective heat and gas transfer. Furthermore, the validity of the scaling law for the ratio of gas andfor the entire range of Schmidt numbers considered was confirmed. A good time-accurate approximation of K L was found using surface information such as velocity fluctuations and convection cell size or surface divergence. A reasonable time accuracy for the K L estimation was obtained using the horizontal integral length scale and the root mean square of the horizontal velocity fluctuations in the upper part of the bulk.

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Section: J G Wissink and H Herlinamentioning

confidence: 99%

Direct numerical simulation of gas transfer across the air–water interface driven by buoyant convection

Wissink

Herlina

2015

J. Fluid Mech.

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“…Thus, the surface layer presents a thin film of practically motionless liquid ("cool skin"), covering thermogravitational convection vortices. In [20] this behavior was attributed to possible contamination of water surface layer with various surfactants. In fact, small cells typical for Marangoni convection were observed only after special cleaning procedure, applied both to water and tank.…”

Section: Fig 2 Surface Temperature (mentioning

confidence: 99%

Combined study of evaporation from liquid surface by background oriented schlieren, infrared thermal imaging and numerical simulation

Vinnichenko

Uvarov

Plaksina

2013

EPJ Web of Conferences

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Abstract. Temperature fields in evaporating liquids are measured by simultaneous use of Background Oriented Schlieren (BOS) technique for the side view and IR thermal imaging for the surface distribution. Good agreement between the two methods is obtained with typical measurement error less than 0.1 K. Two configurations of surface layer are observed: thermocapillary convection state with moving liquid surface and small thermal cells, associated with Marangoni convection, and "cool skin" with negligible velocity at the surface, larger cells and dramatic increase of velocity within 0.1 mm layer beneath the surface. These configurations are shown to be formed in various liquids (water with various degrees of purification, ethanol, butanol, decane, kerosene, glycerine) depending rather on initial conditions and ambient parameters than on the liquid. Water, which has been considered as the liquid without observable Marangoni convection, actually can exhibit both kinds of behavior during the same experimental run. Evaporation is also studied by means of numerical simulations. Separate problems in air and liquid are considered, with thermal imaging data of surface temperature making the separation possible. It is shown that evaporation rate can be predicted by numerical simulation of the air side with appropriate boundary conditions. Comparison is made with known empirical correlations for Sherwood-Rayleigh relationship. Numerical simulations of water-side problem reveal the issue of velocity boundary conditions at the free surface, determining the structure of surface layer. Flow field similar to observed in the experiments is obtained with special boundary conditions of third kind, presenting a combination of no-slip and surface tension boundary conditions.

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“…There are only few studies reported in the literature that investigated the flow and thermal behavior beneath the air water interface during natural convection. Volino and Smith [1], Flack et al [2] and Saylor et al [3] measured water surface temperature using infrared imagery. All these studies observed that the temperature field at the water surface is complex and comprised of different scales of thermal structures that appear to be randomly located on the water surface.…”

Section: Introductionmentioning

confidence: 99%

“…Volino and Smith [1], Flack et al [2] and Bukhari and Siddiqui [5] have reported velocity measurements beneath the water surface during natural convection. Flack et al [2] found that the surfactant influences the subsurface flow field and reduces the magnitude of turbulent fluctuations.…”

Section: Introductionmentioning

confidence: 99%