Yazar "Altinisik, Kemal" seçeneğine göre listele

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    Effects of operation temperature and reactant gas humidity levels on performance of PEM fuel cells
    (Pergamon-Elsevier Science Ltd, 2016) Ozen, Dilek Nur; Timurkutluk, Bora; Altinisik, Kemal
    In this study, the effects of operation conditions on the performance of a polymer electrolyte membrane fuel cell are investigated and the results are presented together with a comprehensive literature review on the related topics. The cells with 25 cm(2) active area are tested for different inlet gas humidification levels and inlet temperatures, operating temperatures and oxidant type. The cells are characterized by the performance curves together with the cell resistance measurements. The results indicate that the humidification of the inlet gases positively affect the cell performance. However, the improvement in the cell performance is higher when the cathode gas is humidified. In addition, the operating temperature and the inlet gas temperatures are found to be the most significant parameters. The cell performance tends to increase significantly with increasing the operating and inlet gas temperatures. The effect of the oxidant type is also considered and the cell tested with pure oxygen shows slightly higher performance. (C) 2016 Elsevier Ltd. All rights reserved.
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    Experimental and Numerical Analysis of one Dimensional Heat Transfer on Open Cell Aluminum Foams
    (Gazi Univ, 2015) Sertkaya, Ahmet Ali; Ates, Ali; Altinisik, Kemal; Dincer, Kevser
    In this study, one dimensional heat transfer of open cell aluminum metal foams is investigated both experimentally and by using numerical methods as well. Open cell aluminum foams with pore densities of 10, 20 and 30 (Number of Pores Per Inch) PPI were shaped into heat exchangers. The foams having sizes of 200 x 100 x 20 mm were insulated on their three faces. Steady heat flux was maintained on the base section of the foam by heating a plate shaped coil electrically. Temperature distributions on the vertical sections and mostly on locations near heaters were measured with the thermocouples located on the aluminum foams. With the help of the recorded temperatures from the tests the graphs of open cell aluminum foams with pore densities of 10, 20 and 30 were plotted. First of all, one dimensional heat transfer equations were derived for the numerical solution of the system. The governing equations obtained were then discretized by using the Central Difference Method and finally solved with the Finite Difference Method. The results obtained were converted into graphs and compared with the empirical results obtained beforehand. The fastest drop in temperature close to the heater was observed at the foam with 10 PPI while the lowest falling rate took place at the foam with 30 PPI pore density. At an interval of three aluminum foams, the temperature difference was found to be higher near the heater and lower away from the heater. It was found that both experimental and numerical results are closely related.
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    EXPERIMENTAL INVESTIGATION AND NUMERICAL MODELING OF THERMAL PERFORMANCE OF FIN-TUBE EVAPORATOR UNDER FROSTING CONDITIONS
    (Turkish Soc Thermal Sciences Technology, 2014) Ozen, Dilek Nur; Altinisik, Kemal; Dincer, Kevser; Ates, Ali
    Formation of frost in a heat exchanger reduces air passage area and lowers the performance of the heat exchanger due to the insulation effects it possesses. In this study, the performance of finned tube evaporator at transient regime was investigated both experimentally and numerically. When the experimentally obtained values of the evaporator's the total conductivity (UA) are compared with those obtained from the numerical model, it is found that they are very close to one another. On the numerical model, the effects of inlet air temperature, relative humidity and air velocity on evaporator's total conductivity (UA), air side pressure drop (Delta P-a) and frost thickness (delta(fst)), were respectively, studied. The results obtained from the numerical model show that Delta P-a and delta(fst) values increase with increasing air temperature and relative humidity while decreasing UA values.
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    Rule-based Mamdani-type fuzzy modelling of thermal performance of fintube evaporator under frost conditions
    (E D P Sciences, 2016) Ozen, Dilek Nur; Altinisik, Kemal; Dincer, Kevser; Ates, Ali; Sertkaya, Ahmet Ali; Tolu, Muhammed Emin
    Frost formation brings about insulating effects over the surface of a heat exchanger and thereby deteriorating total heat transfer of the heat exchanger. In this study, a fin-tube evaporator is modeled by making use of Rule-based Mamdani-Type Fuzzy (RBMTF) logic where total heat transfer, air inlet temperature of 2 degrees C to 7 degrees C and four different fluid speed groups (ual=1; 1.44; 1.88 m s-1, ua2=2.32; 2.76 m s-1, ua3=3.2; 3.64 m s-1, ua4=4.08; 4.52; 4.96 m s-1) for the evaporator were taken into consideration. In the developed RBMTF system, outlet parameter UA was determined using inlet parameters Ta and ua. The RBMTF was trained and tested by using MATLAB (R) fuzzy logic toolbox. R-2 (%) for the training data and test data were found to be 99.91%. With this study, it has been shown that RBMTF model can be reliably used in determination of a total heat transfer of a fm-tube evaporator.