Browsing by Author "Çorumlu, V"

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    Gamma ray irradiation dose dependent methanol sensing with ZnO nanoparticles
    Urfa, Y; Çorumlu, V; Altindal, A
    This study reports the influence of gamma ray irradiation of various doses in the range of 1?150 kGy on methanol sensing performance and adsorption kinetics of ZnO nanoparticles based sensors. ZnO nanoparticles were synthesized via sol-gel method and characterized with X-ray diffraction (XRD), transmission electron microscope (SEM), and Fourier transform infrared spectroscopy (FTIR) techniques. The results revealed that the methanol sensing performance of ZnO nanoparticles based sensor including sensitivity, response and recovery times improved by the gamma ray irradiation. Additionally, Elovich equation, Ritchie?s equation and pseudo first order model were selected to follow the methanol adsorption process. The preliminary result of the methanol adsorption kinetic studies revealed that the adsorption kinetics strongly depends on the gamma irradiation dose. Among other kinetic models investigated, the pseudo first-order equation was the best to describe the adsorption kinetics of methanol on ZnO nanoparticles up to 50 kG dose of gamma ray, as evidenced by the highest correlation coefficients. On the other hand, for higher doses than of 50 kGy of gamma irradiation, our analysis showed that Elovich equation generates a straight line that best fit to methanol adsorption data on ZnO nanoparticles.
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    Optimizing Optical and Structural Properties of Nanocomposites by ZnO and BP-3
    Türemis, M; Keskin, IÇ; Kati, MI; Kibar, R; Sirin, K; Çanli, M; Çorumlu, V; Çetin, A
    This study aims to find out usage of zinc oxide (ZnO) and 2-hydroxy-4-methoxybenzophenone (BP-3) for getting better optical and structural properties of nanocomposites. Polymer nanocomposites were prepared by adding zinc oxide for minimizing UV rays effects of the sun with the particle size of nanometer in different ratios to a low density polyethylene (LDPE). The polymer mixtures were synthesized by mixing nanocomposite samples with BP-3 featuring UV stabilizer. Besides making tensile testing measurements, in order to find out the optical, structural, mechanical and thermal changes, the new polymer nanocomposites were characterized by XRD, TG-DTA spectra, and SEM images. The samples with zinc oxide which show luminescent properties were examined in terms of radioluminescence features. Radioluminescence spectrum showed characteristic peaks of zinc oxide dispersed nanocomposites prepared with LDPE. The intensity of the characteristic peaks at 530 and 390 nm (exciton) increased by increasing rates of nanopowder zinc oxide while adding BP-3 to the composites caused a decrease in intensity of radioluminescence.
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    The effects of input power and ambient temperature on the thermal performance of conical pin fin heat sink in natural convection
    Çorumlu, V
    In the present study, thermal performance tests of horizontally oriented HSconical, HScross-cut, and HSflat with a base plate dimensions of 80*80*5 mm3 were performed in natural convection. The effects of ambient temper-ature (30 and 40 degrees C), input power (16.5 and 33 W), and conical pin fin geometry on the thermal performance of the HSs were investigated. The thermal resistance of the heat sinks decreases while the convective heat transfer coefficient, average surface temperature, and average junction temperature increase with increasing ambient temperature and input power. However, the Nusselt number increases with increasing ambient temperature for all HSs at 16.5 W, while the Nusselt number decreases with increasing ambient temperature at 33 W. The highest convective heat transfer coefficients are 32.17, 30.68, and 19.61 W/m2K for HSconical, HSflat, and HScross-cut at 33 W and 40 degrees C, respectively. The lowest thermal resistances are 2.75, 2.80, and 3.81 K/W for HSconical, HScross-cut, and HSflat at 33 W and 40 degrees C, respectively. Thermal resistances of HSconical and HScross-cut decreased by 27.78 % and 26.44 % at maximum and 27.06 % and 24.58 at minimum, respectively, compared to HSflat. The results show that the conical fins have better thermal performance in natural convection.
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    Evaluation of prediction and modeling performance using machine learning methods for thermal parameters of heat sinks under forced convection: The case of external validation
    Çorumlu, V; Altintas, V; Abuska, M
    The capability of ML models in thermal systems is generally determined by internal validation, while this study investigates the prediction performance of ML models with external validation. ANN, XGBoost, and RF models were created with the training-test data set obtained from the results of flat, conical, and cross-cut pin fin heat sinks. Data of 33, 66, and 99 W for the training-test data set were used for training and internal validation, while data of 49.5 W for conic Model-I and 82.5 W for conic Model-II were used for external validation. The RF showed the highest performance on the test data-internal validation and the ANN on the external validation. According to the test data not used in training, the lowest MSE is 0.0270-(RF), 1.7437-(ANN), and 14.7140-(XGBoost). In RF and XGBoost, the external validation performance decreased significantly compared to the internal validation. The MSE of the models are 8.0683-ANN, 214.4047-XGBoost, and 300.6012-RF for external validation. The thermal resistance provides more realistic results than the Nusselt number for the thermal performance evaluation of heat sinks with ML methods. The ANN based on external validation may be used to predict heat sinks' thermal performance and save money, labor, and time compared to CFD simulations.
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    Microstructure and Electrical Conductivity of ZnO Addition on the Properties of (Bi0.92Ho0.03Er0.05)2O3
    Ermis, I; Çorumlu, V; Sertkol, M; Öztürk, M; Kaleli, M; Çetin, A; Turemis, M; Ari, M
    The solid electrolyte is one of the most important components for a solid oxide fuel cell (SOFC). The various divalent or trivalent metal ion-doped bismuth-based materials exhibit good ionic conductivity. Therefore, these materials are used as electrolytes in the SOFC. In this paper, the samples of (Bi0.92-x Ho0.03Er0.05)(2)O-3 + (ZnO) (x) solutions with a 0 aecurrency sign x aecurrency sign 0.2 molar ratio are synthesized by the solid state reaction method. The detailed structural and electrical characterizations are investigated by using x-ray diffraction (XRD), alternating current electrochemical impedance spectroscopy, and scanning electron microscopy (SEM). The XRD patterns of all samples are indexed on a monoclinic symmetry with a P2(1)/c space group. In addition, the rietveld parameters are determined by using the FullProf software program. The impedance measurements of the samples are obtained at the 1 Hz to 20 MHz frequency range. The impedance value of the pellets increases with temperature. Based on the impedance results, it is found that the contribution of grain (bulk) is more than a grain boundary in terms of conductivity, which permits the attribution of a grain boundary. The ionic conductivity decreases with an increasing amount of Zn contribution. The value of highest electrical conductivity among all samples is calculated as 0.358 S cm(-1) at 800A degrees C for undoped (Bi0.92Ho0.03Er0.05)(2)O-3.