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Muhammet Balcılar,Ahmet Selim Dalkılıç,Berna Bolat,Somchai Wongwises 대한기계학회 2011 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.25 No.10
The heat transfer characteristics of R134a during downward condensation are investigated experimentally and numerically. While the convective heat transfer coefficient, two-phase multiplier and frictional pressure drop are considered to be the significant variables as output for the analysis, inputs of the computational numerical techniques include the important two-phase flow parameters such as equivalent Reynolds number, Prandtl number, Bond number, Froude number, Lockhart and Martinelli number. Genetic algorithm technique (GA), unconstrained nonlinear minimization algorithm-Nelder-Mead method (NM) and non-linear least squares error method (NLS) are applied for the optimization of these significant variables in this study. Regression analysis gave convincing correlations on the prediction of condensation heat transfer characteristics using ±30% deviation band for practical applications. The most suitable coefficients of the proposed correlations are depicted to be compatible with the large number of experimental data by means of the computational numerical methods. Validation process of the proposed correlations is accomplished by means of the comparison between the various correlations reported in the literature.
Zehra Hasılcı,Muharrem Erdem Boğoçlu,Ahmet Selim Dalkılıç,Altan Kayran 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.2
Bird strike is one of the most hazardous issues facing global aviation. In the present study, a hybrid methodology is developed utilizing, automated data generation and fully connected neural networks to practically and reliably obtain the global deformation of composite structures subject to bird strike. The validation of the proposed numerical bird strike model is accomplished by making comparisons with the available experimental data from three different resources in the literature on the chicken and gelatine strike tests to a rigid plate, and strike test against an aircraft composite vertical leading edge. For three different bird velocities, 9402 input files are created by an automatic data generator considering all possible stacking sequence combinations in accordance with the composite design guidelines. The global deformation of composite laminates caused by bird strike is estimated via the fully connected neural networks established. Results of the present study show that with the use of fully connected neural networks, global deformation of the composite laminate can be estimated reliably and preliminary design of the composite laminate can be performed very fast compared to performing nonlinear finite element analysis involving bird strike. In conclusion, the fully connected neural network model is found to be an alternative for additional LS-Dyna simulations in the optimization process.
Investigation of the effects of geometrical parameters on heat transfer from buried finned pipes
Hakan Demir,Ahmet Koyun,S. Özgür Atayılmaz,Özden Ağra,Ahmet Selim Dalkılıç 대한기계학회 2013 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.27 No.8
Heat transfer from finned pipes buried in the soil has been investigated using experimental, analytical and numerical techniques. The experimental setup consists of a ground source heat pump system and two separate ground heat exchangers. Constant surface temperature approach based on Carslaw and Jaeger’s theory study was used for calculating the heat transfer from the pipes analytically. The problem was modeled and solved using a CFD program numerically. Effects of the fin number, fin length and simulation time on the heat transfer rate have been investigated and compared with bare tube. A modified analytical formula was also proposed for finned pipes in this study.
Nares Chimres,Thunyawat Chittiphalungsri,Lazarus Godson Asirvatham,Ahmet Selim Dalkılıç,Omid Mahian,Somchai Wongwises 대한기계학회 2020 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.34 No.10
The air side thermal performance of wavy fins with rectangular winglets are studied using experimental and numerical methods. The following parameters are selected for investigation: the attack angle, placed location, span and length of the rectangular winglet. The results show that all parameters affect the thermal performance of the air side. The best configurations of the winglet that provide the maximum j/f (1/3) for both winglet lengths are the 3.5 mm horizontal distance, 7 mm vertical distance, 60 o attack angle and 1.25 mm winglet span. Moreover, the thermal performance comparisons between the optimal design of the wavy fin with winglet and normal wavy fin are reported. Wavy fins with winglets provide a larger heat transfer coefficient, pressure drop and j/f (1/3) than those of normal wavy fins. For the j/f (1/3)comparison, wavy fins with winglets provide a j/f (1/3) greater than that of normal wavy fins by 5.4-14.6 %, with the Reynolds number ranging from 1650 to 4423.