STEFAN AKIŞININ DAMLACIK BUHARLAŞMA MODELLERİ ÜZERİNDEKİ ETKİSİ

Year 2020, Volume: 40 Issue: 2, 309 - 318, 31.10.2020

Yigit Akkus

https://doi.org/10.47480/isibted.817053

Cited By: 6

Abstract

Bilim ve endüstrideki çeşitli uygulamalarda kilit rolü olması nedeniyle damlacık buharlaşması literatürde yaygın olarak incelenmektedir. Damlacık buharlaşması problemi, sıvı ve buhar fazları ile bu fazları ayıran ara yüzeyde meydana gelen çeşitli mekanizmaları içerir. Modellenmesi kolay olmayan bu çok-fazlı problem birçok araştırmacı tarafından çalışılmıştır, ancak içerdiği mekanizmalardan sadece birkaçı ön plana çıkarılabilmiştir. Bir sıvının o sıvı içerisinde çözünmeyen gaz ortamına buharlaşması sırasında her zaman ortaya çıkan Stefan akışı, bulmacanın parçalarından biridir. Ancak Stefan akışının buharlaşmaya olan katkısını araştıran çalışmaların sayısı oldukça sınırlıdır. Bu çalışmada, Stefan akışının etkisi, tüm ilgili fiziksel mekanizmaları içeren yenilikçi bir model kullanılarak ölçülmüştür. Damlacık yüksek sıcaklıkta bir katı yüzey üzerine yerleştirildiğinde Stefan akışının toplam buharlaşmanın %17'sinden sorumlu olabileceği bu çalışmada gösterilmiştir. Ayrıca, Stefan akışının ara yüzey kütle akısı denklemine dâhil edilmesiyle difüzyon temelli modellerin (gaz fazındaki) düşük performansının büyük ölçüde arttırılabileceği gösterilmiştir. Ayrıca bu çalışmada, sadece difüzyon ile difüzyon ve Stefan akışına dayalı mevcut ilgileşimlerin buharlaşma oranlarını bulma performansları tartışılmıştır. Son olarak, gaz ortamının değişen nem oranları altında, gaz fazındaki münferit taşıma mekanizmalarının toplam buharlaşma hızına olan katkılarında bir değişiklik olmadığı bulunmuştur. Bu sonuca dayanarak, Stefan akışı ve doğal konveksiyonun katkılarının, sadece difüzyonun katkısına doğrusal bir bağımlılığı olduğu düşünülmüştür. Bu çalışma, Stefan akışının, bilhassa ısıtılmış katı yüzeyler üzerinde duran damlacıkların buharlaşma hızlarını kayda değer şekilde arttırdığını göstermiştir. Bu yüzden, bundan sonra yapılacak ilgili damlacık buharlaşması modelleme çalışmaları Stefan akışını da içermelidir.

Keywords

Damlacık buharlaşması, Stefan akışı, doğal taşınım, gaz difüzyonu, sıcaklığa bağlı değişen kılcallık, kaldırma

THE EFFECT OF STEFAN FLOW ON THE MODELS OF DROPLET EVAPORATION

Abstract

Droplet evaporation has been widely studied in the literature due to its key role in various applications in science and industry. The problem of droplet evaporation involves various mechanisms in both liquid and vapor phases together with the interface separating them. Modeling of this multiphase problem is not straightforward thereof studied by many researchers but in every time a few different contributing mechanisms could be highlighted. One of the pieces of this puzzle is undoubtedly the Stefan flow, which is always present during the evaporation of a liquid to an insoluble surrounding gas, yet the number of studies exploring its individual contribution to the evaporation remain very restricted. In the current study, the effect of Stefan flow is assessed by employing a recent state-of-the-art model that accounts for all pertinent physics of droplet evaporation. Results reveal that Stefan flow can be responsible for 17% of total evaporation when the droplet is placed on a high temperature substrate. Moreover, it is shown that lower performance of diffusion based models (in gas phase) can be greatly enhanced by incorporating the effect of Stefan flow into the interfacial mass flux equation. In addition, performances of existing purely diffusion and diffusion and Stefan flow based correlations in the prediction of evaporation rates are elucidated. Last but not least, under varying humidity of the surrounding gas, contribution of individual transport mechanisms in gas phase to the total evaporation rate is found to be unaffected. Based on this result, it is hypothesized that contributions of Stefan flow and natural convection have a linear dependence on the contribution of sole diffusion. The current study clearly demonstrated that Stefan flow considerably enhances the evaporation rate of droplets, especially in the case of high substrate heating. Therefore, future studies on the topic should account for the Stefan flow during the modeling of droplet evaporation.

Keywords

Droplet evaporation, Stefan flow, natural convection, gas diffusion, thermocapillarity, buoyancy

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