Mechanical Engineering / Makina MühendisliğiColleciton of Mechanical Engineering / Makina Mühendisliği Bölümü koleksiyonuhttps://hdl.handle.net/11147/41292020-02-12T11:24:34Z2020-02-12T11:24:34ZConstructal structures with and without high-conductivity inserts for self-coolingÇetkin, Erdalhttps://hdl.handle.net/11147/76912020-02-12T09:00:07Z2016-01-01T00:00:00ZConstructal structures with and without high-conductivity inserts for self-cooling
Çetkin, Erdal
Here we show how a heat generating domain can be gained self-cooling capability with embedded cooling channels and with and without high-conductivity fins. The volume of the heat generating domain is fixed, so is the overall volume of the cooling channels and high-conductivity inserts. Even though the coolant volume decreases with embedded high-conductivity fins, the peak temperature also decreases with high-conductivity inserts. The peak temperature is affected by the location, shape and complexity of the fins and the volume fraction. This paper documents how these degrees of freedoms should be changed in order to minimize peak temperature. This paper also discusses how the volume fraction affects each fin shape in order to minimize the peak temperature. This paper uncovers that the fins should be distributed non-equidistantly, and that high-conductivity material should be inserted as fins (bulks of high-conductivity materials) rather than uniform distribution in the domain. This paper concludes that the overall thermal conductance of a heat generating domain can be maximized by freely morphing the shape of the high-conductivity material. The optimal design exists for given conditions and assumptions, and this design should be morphed when conditions and assumptions change. This conclusion is in accord with the constructal law. Each optimal design for given conditions and assumptions is the constructal design
2016-01-01T00:00:00ZSurface charge-dependent transport of water in graphene nano-channelsÇelebi, Alper TungaBarışık, MuratBeşkök, Alihttps://hdl.handle.net/11147/76622020-02-05T13:00:14Z2018-01-01T00:00:00ZSurface charge-dependent transport of water in graphene nano-channels
Çelebi, Alper Tunga; Barışık, Murat; Beşkök, Ali
Deionized water flow through positively charged graphene nano-channels is investigated using molecular dynamics simulations as a function of the surface charge density. Due to the net electric charge, Ewald summation algorithm cannot be used for modeling long-range Coulomb interactions. Instead, the cutoff distance used for Coulomb forces is systematically increased until the density distribution and orientation of water atoms converged to a unified profile. Liquid density near the walls increases with increased surface charge density, and the water molecules reorient their dipoles with oxygen atoms facing the positively charged surfaces. This effect weakens away from the charged surfaces. Force-driven water flows in graphene nano-channels exhibit slip lengths over 60 nm, which result in plug-like velocity profiles in sufficiently small nano-channels. With increased surface charge density, the slip length decreases and the apparent viscosity of water increases, leading to parabolic velocity profiles and decreased flow rates. Results of this study are relevant for water desalination applications, where optimization of the surface charge for ion removal with maximum flow rate is desired.
2018-01-01T00:00:00ZSnowflake shaped high-conductivity inserts for heat transfer enhancementKonan, Hasel ÇiçekÇetkin, Erdalhttps://hdl.handle.net/11147/76592020-02-05T07:14:29Z2018-12-01T00:00:00ZSnowflake shaped high-conductivity inserts for heat transfer enhancement
Konan, Hasel Çiçek; Çetkin, Erdal
Here, 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.
2018-12-01T00:00:00ZDynamic crushing behavior of a multilayer thin-walled aluminum corrugated core: The effect of velocity and imperfectionSarıyaka, MustafaTaşdemirci, AlperGüden, Mustafahttps://hdl.handle.net/11147/76502020-02-03T13:00:15Z2018-11-01T00:00:00ZDynamic crushing behavior of a multilayer thin-walled aluminum corrugated core: The effect of velocity and imperfection
Sarıyaka, Mustafa; Taşdemirci, Alper; Güden, Mustafa
The crushing behavior of a multilayer 1050 H14 aluminum corrugated core was investigated both experimentally and numerically (LS-Dyna) using the perfect and imperfect models between 0.0048 and 90 m s−1. The dynamic compression and direct impact tests were performed in a compression type and a modified Split Hopkinson Pressure Bar set-up, respectively. The investigated fully imperfect model of the corrugated core sample represented the homogenous distribution of imperfection, while the two-layer imperfect model the localized imperfection. The corrugated core experimentally deformed by a quasi-static homogenous mode between 0.0048 and 22 m s−1, a transition mode between 22 and 60 m s−1 and a shock mode at 90 m s−1. Numerical results have shown that the stress-time profile and the layer crushing mode of the homogeneous and transition mode were well predicted by the two-layer imperfect model, while the stress-time profile and the layer crushing mode were well approximated by the fully imperfect model. The fully imperfect model resulted in complete sequential layer crushing at 75 and 90 m s−1, respectively. The imperfect layers in the shock mode only affected the distal end stresses, while all models implemented resulted in similar impact end stresses. The distal end initial crushing stress increased with increasing velocity until about 22 m s−1; thereafter, it saturated at ~2 MPa, which was ascribed to the micro inertial effect. Both the stress-time and velocity-time history of the rigid-perfectly-plastic-locking model and the critical velocity for the shock deformation were well predicted when a dynamic plateau stress determined from the distal end stresses in the shock mode was used in the calculations.
2018-11-01T00:00:00Z