CFD study of Marangoni condensation heat transfer of vapor mixture on a horizontal tube
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ORIGINAL
CFD study of Marangoni condensation heat transfer of vapor mixture on a horizontal tube Hoon Chae Park 1 & Hang Seok Choi 1 Received: 3 December 2018 / Accepted: 16 April 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Over the past few decades, experimental studies have been conducted on the condensation heat transfer of vapor mixtures. However, the local heat transfer characteristics of vapor mixture affected by surface tension have not been fully investigated. The present work, for the first time, suggested the CFD simulation method for the Marangoni condensation of ethanol-vapor mixture and analyzed the calculated result with flow structure. A CFD study has been performed for the condensation heat transfer of steam–ethanol mixtures on a horizontal tube to elucidate the Marangoni condensation phenomenon and the consequent heat transfer mechanism, which are difficult to fully obtain experimentally. In the present study, the numerical predictions of condensation heat transfer using a liquid film model agree well with those of the experimental results. The CFD analysis of steam–ethanol mixture compares with pure steam to clearly show the influence of surface tension on the heat transfer. In particular, when a small amount of ethanol is added to pure steam, the condensation heat transfer is enhanced because the local liquid film thickness is changed because of the surface tension gradient on the gas–liquid interface, which is caused by a concentration difference. Keywords Marangoni effect . Condensation . Heat transfer . Steam–ethanol mixture;
1 Introduction The movement of liquid resulting from unbalanced surface tension is an important surface phenomenon, known as the Marangoni effect. The Marangoni effect is triggered by gradients of concentration (solutocapillary) or/and temperature (thermocapillary) on a liquid surface. In fact, these two effects are typically coupled together and the magnitude of solutocapillary is generally much greater than that of thermocapillary. The Marangoni effect can drive film instability and can eventually form a local film area such as droplets on a surface. This may be beneficial in heat transfer enhancement. The Marangoni effect can be shown by adding small amounts of heat transfer additives (ammonia, ethanol, etc.) into water. This results in binary or multicomponent mixtures. In a given thermal field, if the local concentration or the temperature of a liquid surface is not homogeneous, liquid * Hang Seok Choi [email protected] 1
Department of Environmental Engineering, Yonsei University, Wonju 26493, Republic of Korea
droplets may be induced on the surface and finally enhance the condensation heat transfer rate. Over the past few decades, a considerable number of studies have been conducted on the heat transfer characteristics of Marangoni condensation. Morrison et al. [1] performed an experiment for the condensation of a weak binary vapor on a horizontal tube, where the concentration of ammonia vapor in steam ranges from 0.1 to 0.2 (w
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