Genç, Ayten

Article | 2009 | Turkish Journal of Engineering and Environmental Sciences33 ( 1 ) , pp.73 - 81

The membrane potentials for asymmetric membranes where fixed charges varied linearly with position were evaluated from the numerical solutions of Nernst-Planck flux and Donnan potential equations. The evaluated membrane potentials were compared with the results obtained from the conventional TMS theory where the fixed charge concentration in the membrane was assumed to be uniform. In the comparison, the number of fixed charges was kept constant by defining an average for the fixed charge concentration. The numerical results showed that the membrane potential increased in magnitude when the distributions of fixed charges at the membr . . .ane-solution interfaces were unequal. In addition, the deviation from TMS theory increased more as the charge difference at the interfaces increased. © TÜBİTAK Daha fazlası Daha az

Salamci E.

Article | 2002 | Turkish Journal of Engineering and Environmental Sciences26 ( 4 ) , pp.345 - 352

Mechanical properties of spray deposited and extruded 7xxx series aluminum alloys were investigated in peak aged condition. To study the influence of Zn additions on the mechanical behaviour of spray deposited materials, three alloy compositions were selected, namely: SS70 (11.5% Zn), N707 (10.9% Zn) and 7075 (5.6% Zn). After ageing treatment, notched and unnotched specimens of spray deposited alloys were subjected to tensile tests at room temperature. Experimental results showed that the SS70 alloy exhibited the highest strength. Spray deposited Al alloys showed a very high strength as compared to conventionally processed 7xxx seri . . .es Al alloys. Compared with the PM processed 7xxx series A1 alloys, fracture toughness values of these alloys were higher Daha fazlası Daha az

Genç, Ayten

Other | 2009 | Turkish Journal of Engineering and Environmental Sciences33 ( 1 ) , pp.73 - 81

The membrane potentials for asymmetric membranes where fixed charges varied linearly with position were evaluated from the numerical solutions of Nernst-Planck flux and Donnan potential equations. The evaluated membrane potentials were compared with the results obtained from the conventional TMS theory where the fixed charge concentration in the membrane was assumed to be uniform. In the comparison, the number of fixed charges was kept constant by defining an average for the fixed charge concentration. The numerical results showed that the membrane potential increased in magnitude when the distributions of fixed charges at the membr . . .ane-solution interfaces were unequal. In addition, the deviation from TMS theory increased more as the charge difference at the interfaces increased. The membrane potentials for asymmetric membranes where fixed charges varied linearly with position were evaluated from the numerical solutions of Nernst-Planck flux and Donnan potential equations. The evaluated membrane potentials were compared with the results obtained from the conventional TMS theory where the fixed charge concentration in the membrane was assumed to be uniform. In the comparison, the number of fixed charges was kept constant by defining an average for the fixed charge concentration. The numerical results showed that the membrane potential increased in magnitude when the distributions of fixed charges at the membrane-solution interfaces were unequal. In addition, the deviation from TMS theory increased more as the charge difference at the interfaces increased Daha fazlası Daha az

Karabulut H. | Yücesu H.S. | Koca A.

Article | 2000 | Turkish Journal of Engineering and Environmental Sciences24 ( 2 ) , pp.71 - 80

An air charged V-type Stirling engine, having 260 cm3 swept volume, was manufactured and tested. Speed-torque characteristics of the engine were obtained for different temperature and charge pressure values in the range of 600°C to 1100°C and 1 to 4 bars. The experiments intended to determine the performance characteristics of the engine at different set up values of pressure and hot source temperature. Maximum output power was obtained at 1100°C and 2.5 bars charge pressure as 65 W. The results are presented in diagrams.

Yücesu H.S. | Altin R. | Çentinkaya S.

Article | 2001 | Turkish Journal of Engineering and Environmental Sciences25 ( 1 ) , pp.39 - 49

In this experimental study, the effect of the usage of vegetable oils, as alternative fuels, on engine performance and exhaust emissions in a single cylinder diesel engine were investigated. No 2-D diesel fuel and nine different oils (raw sunflower oil, raw cottonseed oil, raw soybean oil, and sunflower methyl ester, cottonseed methyl ester, soybean methyl ester, obtained from the raw oils respectively and refined opium poppy oil, rapeseed and corn oil) were used. In order to determine emission and performance characteristics, the engine was tested with full load-varied speed and constant speed-varied load tests. Chemical and physic . . .al properties of the raw oils were improved by transesterification. Test results showed that, when using vegetable oils, the engine performance and NO? are lower, and smoke density is higher than the engine performance in which No 2-D diesel fuel is used. The engine performance with the methyl ester fuels is higher than that with the raw oils and are close to diesel fuel performance Daha fazlası Daha az

Kopaç M. | Arikol M.

Article | 1997 | Turkish Journal of Engineering and Environmental Sciences21 ( 3 ) , pp.149 - 154

In this study using some constitutive equations present in the literature, a rate-type constitutive equation is developed which is successful with the experimental results. The method being used is a nonlinear regression method that is known as Marquardt Method. Studies were done considering flow along the centerline of the flow channel. In this study the general form of the proposed constitutive equation was reduced on the centerline by using the flow kinematics and derivative operator for cartesian coordinates. Developing the difference of the normal stress components in the 1 - and 2- directions a nonlinear ordinary differential . . .equation was obtained for the normal stress difference. When this differential equation that was reduced on the centerline was solved by this nonlinear regression method, model parameters, normal stress difference values along the centerline and sum of squares were determined simultaneously. When the proposed constitutive equation was compared with the existing equations, the proposed equation was found to be more successful in the flow along the centerline Daha fazlası Daha az

Kaçar R.

Article | 2001 | Turkish Journal of Engineering and Environmental Sciences25 ( 5 ) , pp.459 - 469

The risk of hydrogen cracking in steel welds depends on a number of interrelated factors, the most important of which is the hydrogen content that originates from the welding consumable. In designing a welding procedure to avoid cracking, it is necessary to define the hydrogen level associated with a given welding consumable, using standard methods. In this study, the Oerlikon/Yanaco hydrogen gas analysis method, which is widely used to determine the hydrogen content of ordinary ferritic steel welds, was modified, and thus the time-temperature relationship of hydrogen evolution from duplex stainless steel weld metal at 200, 400, 600 . . . and 950°C was investigated experimentally and determined theoretically on the basis of BS 6693 samples. It was found that diffusible hydrogen evolution from weld metal heated at 400°C for 24 hours was completed experimentally and theoretically. In conclusion, the diffusible hydrogen amount which is potentially hazardous in the long term in duplex stainless steel weld metal can be easily determined by modification of the Oerlikon/Yanaco methods Daha fazlası Daha az

Candan E.

Article | 2002 | Turkish Journal of Engineering and Environmental Sciences26 ( 1 ) , pp.1 - 5

The wettability at a liquid Al-alloy/SiC interface was evaluated by the sessile drop method at 750°C. The wetting angle, ?, of a sessile drop on SiC substrate decreased with the addition of Pb, Mg and Ca to pure aluminium. The reduction in ? of the Al-Pb alloy was proportional to the reduction in surface tension, ?lv of aluminium, whereas in Al-Mg and Al-Ca alloys the reduction in ? was greater than the reduction in ?lv of Al. This was attributed to reactions that took place at the Al-alloy/SiC interface. Scanning electron microcopy (SEM) analysis showed that severe interactions had taken place at the interfaces of Al-Mg alloy/SiC a . . .nd Al-Ca alloy/SiC Daha fazlası Daha az

Büyüksalih G. | Oruç M. | Koçak G.

Article | 2003 | Turkish Journal of Engineering and Environmental Sciences27 ( 5 ) , pp.347 - 360

This paper addresses the metric accurracy potential of Ikonos Geo imagery for 2D geopositioning. For this, alternative sensor orientation models including rational functions, satellite orbital modelling and terrain relief-corrected affine transformation were used since the Ikonos camera model and the information for external parameters are not provided to the users. Test results arising from the application of these alternative models in a Zonguldak testfield confirm that Ikonos Geo-scenes can yield 2D geopositioning to pixel and in some cases even sub-pixel, accuracy. The paper describes the Zonguldak testfield, discusses geopositi . . .oning approaches in the 2D adopted and reports on the geometric accuracy obtained with different sensor orientation models Daha fazlası Daha az

Aydemir A. | Günay D.

Article | 2004 | Turkish Journal of Engineering and Environmental Sciences28 ( 2 ) , pp.121 - 127

An adhesive-bonded single lap joint is analyzed using a new fuzzy finite element model. In the model, Young's moduli and Poisson's ratios of the joint materials are taken as fuzzy numbers in order to take the uncertainty of the material properties into account. The fuzzy numbers are modeled using linear triangular membership functions. At a selected material point, in the adhesive layer, the possibility distributions for the displacements and shear stresses are depicted by graphics. © TÜBITAK.

Yakar Elbeyli I. | Pişkin S. | Sütcü H.

Article | 2004 | Turkish Journal of Engineering and Environmental Sciences28 ( 4 ) , pp.233 - 239

Simultaneous thermogravimetry-differential thermal analysis (TG-DTA) was used to study the pyrolysis kinetics of Turkish bituminous coals. Thermogravimetry (TG) and derivative thermogravimetry (DTG) were employed to measure the weight changes and rates of weight loss, which were used for comparison of the thermal behaviour of several coals and calculation of their kinetic parameters. Coal samples were heated in TG-DTA apparatus in an inert atmosphere (100 ml min-1 nitrogen) at a temperature range of 25-1000 °C. The activation energy (Ea) and pre-exponential factor (A) were calculated from the experimental results by using an Arrheni . . .us-type kinetic model. The data indicate that the pyrolysis of coals is a 1-stage process. The decomposition stage (350-700 °C) has a best fit with first-order kinetics with Ea = 65-97 kJ mol-1 Daha fazlası Daha az

Aytekin H. | Baldik R.

Article | 2008 | Turkish Journal of Engineering and Environmental Sciences32 ( 2 ) , pp.101 - 105

This paper presents a study performed on the radiological character of the Çatalagz? Thermal Power Plant, (ÇTPP/ ÇATES), on the west Black Sea coast of Turkey. Natural radioactivity distribution of the terrestrial radionuclides 238U, 232Th, and 40K of surface soil samples around the ÇTPP was analyzed. The average radioactivity concentrations for 232Th, 238U, and 40K for soil samples were 39.7, 30.5, and 378.7 Bq kg-1, respectively. 238U and 40K concentrations are lower than the world average values, 35 Bq kg-1 and 400 Bq kg-1, respectively, and the 232Th concentration is higher than the world average value, 30 Bq kg-1. © TÜBİTAK.