Browsing by Author "Erdem, Ali Kerem"

Now showing 1 - 3 of 3

Embargo
Numerical analysis of the dispersion and deposition of particles in evaporating sessile droplets
(American Chemical Society, 2024-06-20) Erdem, Ali Kerem; Denner, Fabian; Biancofiore, Luca
Evaporating sessile droplets containing dispersed particles are used in different technological applications, such as 3D printing, biomedicine, and micromanufacturing, where an accurate prediction of both the dispersion and deposition of the particles is important. Furthermore, the interaction between the droplet and the substrate must be taken into account: the motion of the contact line, in particular, must be modeled carefully. To this end, studies have typically been limited to either pinned or moving contact lines to simplify the underlying mathematical models and numerical methods, neglecting the fact that both scenarios are observed during the evaporation process. Here, a numerical algorithm considering both contact line regimes is proposed whereby the regimes are distinguished by predefined threshold contact angles. After a detailed validation, this new algorithm is applied to study the influence of both regimes on the dispersion and deposition of particles in an evaporating sessile droplet. In particular, the presented analysis focuses on the influence of (i) the contact line motion characteristics by varying the limiting contact angle and spreading speed, (ii) the Marangoni number, characterizing the importance of thermocapillarity, (iii) the evaporation number, which quantifies the importance of evaporation, (iv) the Damköhler number, a measure of the particle deposition rate, and (v) the Peclet number, which compares the convection and diffusion of the particle concentration. When thermocapillarity becomes dominant or the limiting contact angle is larger, the particle accumulation near the contact line decreases, which, in turn, means that more particles are deposited near the center of the droplet. In contrast, increasing the evaporation number supports particle accumulation near the contact line, while a larger Damköhler number and/or smaller Peclet number yield more uniform final deposition patterns. Finally, a larger characteristic speed of spreading results in fewer particles being deposited at the center of the droplet.
Open Access
Numerical study on the dispersion and deposition of particles in evaporating sessile droplets
(2022-09) Erdem, Ali Kerem
Evaporating sessile droplets including dispersed particles are utilized in the coating, printing, and biomedical applications. Modeling this problem is a challenging process, therefore diﬀerent assumptions are used in the literature. It is important to have a model which covers both pinned and moving contact line regimes for the droplet, thus whole evaporation process and deposition proﬁle can be understood. Therefore, in this work, a numerical and mathematical model is derived to simulate two-dimensional symmetric thin evaporating sessile droplets whose contact line is ﬁrstly pinned and then moving. This model is derived by combining diﬀerent models in literature with the help of lubrication theory and rapid vertical diﬀusion assumption. This model includes a temporal change in the droplet’s surface height, contact line dynamics, particle dispersion, and deposition. The ﬁnite diﬀerence method is used in the numerical solution. Cases including pinned and moving contact lines in the literature are solved separately by diﬀerent numerical algorithms developed in this work and these algorithms were combined. This new algorithm ﬁrst solves a mathematical model in the pinned contact line regime. When the contact angle goes below the deﬁned limit, the second part of the algorithm solves the mathematical model in the moving contact line regime until 95 percent of the total particle mass is deposited. A parametric study has been done with the developed algorithm. A set of parameters is deﬁned and chosen parameters are changed to see their eﬀects. It is observed that increasing the Marangoni number and Capillary number, increased particle accumulation near the center. Decreasing evaporation number and increasing Damkohler number result in more uniform particle deposition.
Restricted
Türk havacılığının gövdesiz uçağı: THK-13 Planörü
(Bilkent University, 2018) Kalaycı, Selin; Birinci, Aleyna; Uysal, Ege Can; Erdem, Ali Kerem; Yanık, Hakan
Türk Hava Kurumu Uçak Fabrikası 1941 yılında faaliyetlerine başladı ve bu dönemde birçok uçak tasarlayıp üretti. Bu uçaklardan biri de THK-13 planörüydü. THK-13 sadece kanat şeklinde ve diğer elemanların kanada birleşik olarak tasarlandığı bir planördü. Planör fabrikada üretildi ve bir çok test aşamasından geçti. Ancak planör deneme uçuşları sırasında iki tane kaza geçirdi. Bu kazalar ve diğer sebeplerden ötürü bu projeye devam edilmedi ve proje iptal edildi. Bu yazıda bu planörün öncesindeki dönem de dahil olmak üzere hikayesi anlatıldı ve o dönemin havacılığına belli bir çerçeveden bakılmış oldu.