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Elektro - eğirme yöntemiyle nanofiber tabakalı hava filtresi üretimi ve karakterizasyonu
(2016) Dincer, Kevser; Önal, Gürol; Ahmet, Akdemir; Selbes, Mehmet
Bu çalışmada, makro boyuttaki gözeneklere sahip farklı malzemelerin, yüzeylerinin filtreleme performansını arttırmak amacıyla, elektro-eğirme yöntemiyle nanofiber tabaka ile kaplanması amaçlanmıştır. Çalışma sonunda sadece mikrofiberfiltrelerin yüzeyine kaplanan nanofiber tabakaların filtre olarak kullanılabileceği görülmüştür. Mikro partiküllerin filtrasyonunda kullanılan 25-85g/m2gramaj arasındaki mikrofiber filtrelerin yüzeyi, polimer solüsyonu besleme debisi 21-30ml/h, uygulanan gerilim 28-32kV ve elektrotlar arası mesafe 19-23cm aralığında elektro-eğirme deney parametreleri ile kaplanmıştır. Nanofiber tabaka ağırlığı 2-4g/m2, nanofiber çapı 77-200nm arasında değişen beş farklı hava filtresi numuneleri elde edilmiştir. Elektro-eğirme deney parametrelerindeki değişim ile nanofiber tabaka ağırlığı, nanofiber çapı ve yüzey morfolojisindeki değişimler gözlenmiş ve üretilen numunelere etkisi incelenmiştir. Sonuçta, makro gözenekli malzemelerin nanofiber tabakalı filtre olarak kullanılamayacağı görülmüştür.
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.
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.
Investigation of electrical conductivity of PAN nanofibers containing silica nanoparticles produced by electrospinning method
(Elsevier, 2019) Mpukuta, Olivier Mukongo; Dincer, Kevser; Erdal, Mehmet Okan
This paper sheds new light on how an amount of silica nanoparticles (1, 3 and 5 wt. %) acts on the morphology, the hydrophobicity and on the electrical conductivity of polyacrylonitrile (PAN) nanofibers. In this study, electrospinning technique was used to fabricate nanofibers composites consisting of PAN, dimethylformamide (DMF) and silica at two different applied voltages (15 kV and 20 kV). The scanning electron microscopy (SEM), X-ray diffraction technique (XRD), contact angle technique and the four-point probe technique were respectively used to investigate the morphology and diameter range, the crystalline structure, the hydrophobicity and the electrical conductivity of the obtained nanofibers. At the end, different results of the investigation were compared each other and discussed. (C) 2019 Elsevier Ltd. All rights reserved.
Investigation of Electrical Conductivity of Polyacrylonitrile (PAN) Nanofibers/Nano Particul (Ag, Cu, CNT and GNR)
(Trans Tech Publications Ltd, 2017) Onal, Gurol; Erdal, Mehmet Okan; Dincer, Kevser
In this study 1% Ag (silver), Cu (copper), CNT (carbon nanotube) and graphene nanoribbon (GNR) nanoparticle reinforced PAN fibers were prepared and the effects of nanoparticle reinforcements upon electrical conductivity were investigated. In experimental study, graphene nanoribbon powders were produced from multiwalled carbon nanotube (MWCNT) through using the chemical approach of Hummers method. Fiber layer was dissolved at room temperature in magnetic mixer with Polyacrylonitrile(PAN) and Dimethil Formamide (DMF) which was at the rate of 10 % by mass. Thus, a viscou gel solution was obtained then nanoparticles were added to the PAN/DMF solution and the solution was vigorously stirred for one hour at room temperature. After stirring that solution was continued for 15 m in ultrasonic bath. The polymeric solution was first transferred to a 5 mL syringe, which was connected to a capillary needle with an inside diameter of 0,8 mm. A copper electrode was attached to the needle, a DC power supply produces 25 kV against a grounded collector screen distant 15cm. With the syringe pump set at 2 mL/h, the electric force overcomes the surface tension of the solution at the capillary tip, and a jet emerges. Produced fibers were collected on the rotary collector which spins at 250 rpm. Nanofiber was dried at 60 degrees C for 12 h in vacuum oven. Eventually, nanofiber of polyacrylonitrile (PAN) reinforced by metallic nanoparticles and graphene nanoribbon (GNR) were prepared by electro spinning process. Electrical conductivity of the obtained nanofiber were studied by measuring the electrical resistance thanks to home-made plate electrodes.
Investigation of Performance of Heating and Cooling of Counter Flow Ranque-Hilsch Tubes with L/D=15, 16, 17, 18 for Brass
(Trans Tech Publications Ltd, 2013) Dincer, Kevser; Berber, Adnan; Ozen, Dilek Nur
In this study, heating and cooling performances of counter flow Ranque-Hilsch vortex tubes (RHVTs) were experimentally investigated for brass. The vortex tubes were made of brass. Diameter of vortex tube (D) was 10 mm. Length of vortex tube (L) was 15D, 16D, 17D and18D. The number of nozzles (Nn) was 5. The conical edges of the plugs have a slope of 30 degrees angle. Working pressure of Ranque-Hilsch was 460 kPa (absolute). According to the experimental results, the maximum heating performance of the RHVT system was found to be 39,5 degrees C at P-17 and the maximum cooling performance of the RHVT in this study was found to be -28,6 degrees C at P-18. An increase in fraction of cold flow (xi) led to a increase in the heating performance.
Rule-Based Mamdani-Type Fuzzy Modeling of Heating and Cooling Performances of Counter Flow Ranque-Hilsch Vortex Tubes with Different Geometric Construction for Brass
(Trans Tech Publications Ltd, 2013) Ozen, Dilek Nur; Berber, Adnan; Dincer, Kevser
In this study, thermal performances of counter flow Ranque-Hilsch vortex tubes were experimentally investigated and modeled with a Rule Based Mamdani-Type Fuzzy (RBMTF) modeling technique. The vortex tubes were made of brass. Diameter of vortex tube (D) was 10 mm. Length of vortex tube (L) was 10D, 11D, 12D, 13D, 14D. Input parameters (xi, L/D) and output parameters (Delta T-h, Delta T-c) were described by RBMTF if-then rules. 45 experimental data sets were used in the training step. R-2 for the Delta T-h was found to be 99.42 % and R-2 for the Delta T-c was 99.66 %. The actual values and RBMTF results demonstrated that RBMTF can be successfully used for the determination of heating and cooling performances of counter flow RHVT with different geometric constructions for brass.
Rule-based Mamdani-type fuzzy modeling of heating and cooling performances of counter-flow Ranque-Hilsch vortex tubes with different geometric construction for steel
(Pergamon-Elsevier Science Ltd, 2013) Berber, Adnan; Dincer, Kevser; Yilmaz, Yusuf; Ozen, Dilek Nur
In this study, heating and cooling performances of counter-flow Ranque-Hilsch vortex tubes (RHVT) were experimentally investigated and modeled with a RBMTF (Rule-Based Mamdani-Type Fuzzy) modeling technique. Input parameters (xi, L/D) and output parameters Delta T-h, Delta T-c were described by RBMTF if-then rules. 81 experimental data sets were used in the training step. Numerical parameters of input and output variables were fuzzificated as linguistic variables: Very Very Low (L1), Very Low (L2), Low (L3), Negative Medium (L4), Medium (L5), Positive Medium (L6), High (L7), Very High (L8) and Very Very High (L9) linguistic classes. R-2 for the Delta T-h was found to be 99.60% and R-2 for the Delta T-c was 99.80%. The actual values and RBMTF results indicated that RBMTF can be successfully used for the determination of heating and cooling performances of counter-flow RHVT with different geometric constructions for steel. (C) 2013 Elsevier Ltd. All rights reserved.
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.

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