Browsing by Author "Akkus, Y."

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Open Access
Capillary boosting for enhanced heat pipe performance through bifurcation of grooves: Numerical assessment and experimental validation
(2022-10) Saygan, S.; Akkus, Y.; Dursunkaya, Z.; Cetin, Barbaros
In this study, an enhanced heat pipe performance for grooved heat pipes has been demonstrated through capillary boosting with the introduction of the bifurcation of grooves. Wider grooves regularly branch to narrower grooves such that the total cross-sectional liquid flow area remains approximately the same. Following the computational framework drawn by a recently developed heat pipe analysis toolbox (H-PAT), we develop a numerical model for the heat pipes with tree-like groove architecture. Then we utilize the model to design a flat-grooved heat pipe with one step groove bifurcation at the evaporator. To verify our numerical findings, two heat pipes with and without groove bifurcation are manufactured and experimented under the same conditions. Experimental results show that the numerical model can predict the thermal performance quite accurately. The results reveal that groove bifurcation can be a viable option for a better thermal performance than that of heat pipes with standard grooved heat pipes with straight grooves which leads to at least 25% higher maximum heat transport capacity. The effect of number of branching on the temperature flattening across the heat pipe is also demonstrated for different evaporator lengths.
Open Access
Interplay of transport mechanisms during the evaporation of a pinned sessile water droplet
(American Physical Society, 2021-07-27) Akdag, O.; Akkus, Y.; Çetin, Barbaros; Dursunkaya, Z.
Droplet evaporation has been intensively investigated in past decades owing to its emerging applications in diverse fields of science and technology. Yet the role of transport mechanisms has been the subject of a heated debate, especially the presence of Marangoni flow in water droplets. This work aims to draw a clear picture of the switching transport mechanisms inside a drying pinned sessile water droplet in both the presence and absence of thermocapillarity by developing a comprehensive model that accounts for all pertinent physics in both phases as well as interfacial phenomena at the interface. The model reveals a hitherto unexplored mixed radial and buoyant flow by shedding light on the transition from buoyancy induced Rayleigh flow to the radial flow causing the coffee ring effect. Predictions of the model excellently match previous experimental results across varying substrate temperatures only in the absence of Marangoni flow. When thermocapillarity is accounted for, strong surface flows shape the liquid velocity field during most of the droplet lifetime and the model starts to overestimate evaporation rates with increasing substrate temperature.