Mechanical Engineering / Makina Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/4129
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Article Citation - WoS: 31Citation - Scopus: 31Snowflake Shaped High-Conductivity Inserts for Heat Transfer Enhancement(Elsevier Ltd., 2018) Konan, Hasel Çiçek; Çetkin, Erdal; Çetkin, Erdal; 03.10. Department of Mechanical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of TechnologyHere, we show numerically how thermal resistance in a two-dimensional domain with a point heat source can be reduced with embedded high-conductivity snowflake shaped pathways. The external shape of the domain is square, and its boundaries are heat sink. The geometry of the inserted pathways which corresponds to the minimum Tmax was uncovered with the consideration of Constructal Theory, i.e. the constructal design. In the first assembly, number of mother (big) fins was uncovered as the area fraction increases. The results of the first assembly indicate that the increase in number of mother fins does not increase heat transfer after a limit number for the fins. After uncovering the mother pathway geometry corresponding to the minimum Tmax, the daughter (small) fins inserted at the tip of them, i.e. second assembly. In the second assembly, the fin ratios, small fin location and angle were discovered when the area fraction is fixed. In addition, in the third assembly, larger daughter fins were attached to mother fins. The results of the second and third assemblies document what should be the geometric length scales and the number of daughter fins in order to minimize Tmax. The constructal design uncovered is similar to the shape of snowflakes. Therefore, the results also uncover snowflakes correspond to the designs with minimum thermal conductivity, i.e., not mimicking the nature but understanding it with physics.Article Citation - WoS: 6Citation - Scopus: 6The Effect of Cavities and T-Shaped Assembly of Fins on Overall Thermal Resistances(International Information and Engineering Technology Association, 2017) Çetin, Eylem; Çetkin, Erdal; Çetkin, Erdal; 03.10. Department of Mechanical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of TechnologyIn this study, authors show that maximum excess temperature on a heat generating cylindrical solid domain can be minimized with numerically optimized rectangular cavities and T-shaped fins. The effect of the cavities and the fins on overall thermal resistances were compared while their volume fraction in a unit volume element is fixed. Furthermore, the designs correspond to the minimum thermal resistance were uncovered for two types of flows; parallel and cross-flow. The governing equations of the heat transfer and the fluid flow were solved simultaneously in order to show the effects of design on the flow characteristics and the thermal performance. Two-dimensional solution domain was used to uncover the thermal performance in cross-flow case because the flow direction is perpendicular to the heat transfer surface area of the heat generating domain. However, three-dimensional domain was used in parallel flow case because the fluid flows along the outer surface of the heat generating domain. For the cross-flow case, the results show that T-shaped assembly of fins with longer stem and shorter tributaries correspond to the lower peak temperature. In addition, the results also show that there is an optimal cavity shape that minimizes the peak temperature. This optimal shape becomes thinner when the number of the cavities increase. In parallel flow case, fins with thicker and shorter stem and longer tributaries correspond to the minimum excess temperature. In addition, the longer and thinner cavities increase the thermal performance in parallel flow case.Article Citation - WoS: 13Citation - Scopus: 15Constructal Vascular Structures With High-Conductivity Inserts for Self-Cooling(The American Society of Mechanical Engineers(ASME), 2015) Çetkin, Erdal; Çetkin, Erdal; 03.10. Department of Mechanical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of TechnologyIn this paper, we show how a heat-generating domain can be cooled with embedded cooling channels and high-conductivity inserts. The volume of cooling channels and high-conductivity inserts is fixed, so is the volume of the heat-generating domain. The maximum temperature in the domain decreases with high-conductivity inserts even though the coolant volume decreases. The locations and the shapes of high-conductivity inserts corresponding to the smallest peak temperatures for different number of inserts are documented,Article Citation - WoS: 32Citation - Scopus: 38Fully Developed Forced Convection in a Parallel Plate Channel With a Centered Porous Layer(Springer Verlag, 2012) Çekmer, Özgür; Mobedi, Moghtada; Özerdem, Barış; Özerdem, Barış; 03.10. Department of Mechanical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of TechnologyIn this study, fully developed heat and fluid flow in a parallel plate channel partially filled with porous layer is analyzed both analytically and numerically. The porous layer is located at the center of the channel and uniform heat flux is applied at the walls. The heat and fluid flow equations for clear fluid and porous regions are separately solved. Continues shear stress and heat flux conditions at the interface are used to determine the interface velocity and temperature. The velocity and temperature profiles in the channel for different values of Darcy number, thermal conductivity ratio, and porous layer thickness are plotted and discussed. The values of Nusselt number and friction factor of a fully clear fluid channel (Nu cl = 4. 12 and fRe cl = 24) are used to define heat transfer increment ratio (ε th = Nu p/Nu cl)and pressure drop increment ratio (ε p = f Re p/f Re cl) and observe the effects of an inserted porous layer on the increase of heat transfer and pressure drop. The heat transfer and pressure drop increment ratios are used to define an overall performance (ε = ε th/ε p) to evaluate overall benefits of an inserted porous layer in a parallel plate channel. The obtained results showed that for a partially porous filled channel, the value of ε is highly influenced from Darcy number, but it is not affected from thermal conductivity ratio (k r) when k r > 2. For a fully porous material filled channel, the value of ε is considerably affected from thermal conductivity ratio as the porous medium is in contact with the channel walls.Article Citation - WoS: 12Citation - Scopus: 16Numerical Optimization of a Fin-Tube Gas To Liquid Heat Exchanger(Elsevier Ltd., 2012) Bilir, Levent; İlken, Zafer; Erek, Aytunç; 03.10. Department of Mechanical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of TechnologyThe influence of plate fin, fin tube and protrusion parameters on heat transfer and pressure drop characteristics of a finned tube gas to liquid heat exchanger is examined in this study. The optimization of plate fin, fin tube and protrusion dimensions as well as protrusion locations on plate fin surface is performed numerically using a computational fluid dynamics (CFD) program named "Fluent". The dimensions of the plate fin of a commercially available combi boiler apparatus heat exchanger are taken as basic dimensions. As the first step, the best plate fin and fin tube geometry is determined. Secondly, the best dimensions for three different protrusions (balcony, winglet and imprint) and their most suitable locations on the plate fin surface are found. Finally, the cumulative effects of several combinations of these three protrusions on the plate fin surface are analyzed. The placement combinations of protrusions are decided according to the results obtained for the individual effect of each protrusion. The fin named as I5B2W3 is found to be the most efficient fin among the investigated cases. A comparison with a numerical and computational study is also performed to validate the numerical results of the present study. © 2011 Elsevier Masson SAS. All rights reserved.