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Öğe An exergy analysis of a concentric tube heat exchanger using hBN-water nanofluids(Inder Science Publishers, 2021) Budak Ziyadanoğulları, Neşe; Perçin, SüleymanThis study investigated the effects of using nanofluids prepared with hexagonal boron nitride (hBN) nanoparticles on the thermal performance and pressure drop of a concentric tube heat exchanger. Experiments were carried out with water-hBN nanofluids for stable, dispersed, 0.01%, 0.1% and 1% volume concentrations, at different flow rates and Reynolds numbers under parallel and counter-flow conditions. When the experimental results were examined, the exergy loss was higher in the parallel-flow heat exchanger compared to the counter-flow heat exchanger. The highest exergy loss value was obtained for distilled water at the highest Reynolds number (Re = 8,700) for parallel flow operation at 170 W. The exergy loss of water at the highest Reynolds number (Re = 8,700) for parallel flow operation increased by 15.7%, 24.8% and 49.8% for hBN-water concentrations of 0.01%, 0.1% and 1%, respectively. Exergy loss of water at the highest Reynold number (Re = 8,700) for counter flow operation increased by 11.3%, 17.3% and 29.2% for hBN-water concentrations of 0.01%, 0.1% and 1%, respectively. When evaluating the exergy analysis of the system, exergy losses due to pressure drops were negligible for both flows (parallel and counter).Öğe Numerical and experimental investigation of solar chimney power plant system performance(Taylor & Francis, 2020-03-15) Karakaya, Hakan; Durmuş, Aydın; Avcı, Ali SerkanA prototype of a solar chimney power plant was performed by modeling in this study. The performed prototype was experimentally confirmed. Temperature, velocity, and radiation values were measured to actualize the confirmation. Experimental data that were obtained to determine the performance of solar chimney whose prototype was actualized by the help of measured values were computationally analyzed. The geometry of a solar chimney in the analysis was bidimensionally (2D) drawn on an axis of symmetry. The numerical simulation was analyzed with computational fluid dynamics (CFD) method. Since analysis results show that there is turbulent flow in system (RNG), k-ɛ turbulence model was used. Continuity, momentum, and energy equations were applied to the solar chimney system via the finite volume method. Moreover, DO (discrete ordinates) model was inserted in analysis to evaluate the radiation effect in the collector area. In addition to all these, correlation results between SPSS 17 statistics program and data obtained were evaluated. Finally, with reference to the comparison between numerical and experimental results, data obtained and numerical data are close to each other; the prototype is applicable to the real systems.Öğe Effects of ethanol addition to biodiesel fuels derived from cottonseed oil and its cooking waste as fuel in a generator diesel engine(Taylor & Francis, 2020-03) Karakaya, HakanExploration of energy sources such as renewable and non-edible vegetable oils has been continued during the recent two decades of 2000s. Cottonseed oil is a non-edible, abundant oil and is generally used as cooking oil. In the present study, the usability of biodiesel derived from both cottonseed oil and its cooking wastes was investigated by blending them with ULSD or ethanol in 50 percentages. B50, WB50, B50E50 and WB50E50, biodiesel and ethanol-contained fuels and ULSD were prepared for experiments. Combustion, performance, and emissions tests were conducted on a diesel engine used for power-producing electrical generator. In the combustion tests, cylinder pressure, HRR, CHR, MGT, and MFB were analyzed while MFC, BSFC, exhaust manifold temperature, and thermal efficiency were obtained in the performance tests. In the emissions tests, CO, HC, and NOx emissions were measured and compared with the results of ULSD. Combustion and performance findings of ULSD contained biodiesel blends were found more similar to those of ULSD. The duration of combustion stage can clearly be seen to be narrowed for ethanol-contained blend because of the rabid combustion characteristics of ethanol. Besides, the peak of HRR was found 10% higher for B50E50 while it was found averagely 8% for WB50E50 blends. NOx emissions were found 48% lower averagely for ethanol contained biodiesel blends that it is the most important finding of ethanol using with biodiesel. Besides, HC emissions were also found about 75% for biodiesel contained diesel fuel blends.Öğe An experimental investigation of the effect of thermophysical properties on time lag and decrement factor for building elements(Gazi University, 2020-06-01) Oktay, Hasan; Yumrutaş, Recep; Argunhan, ZekiThe time lag (TL) and decrement factor (DF) are essential for the heat storage capabilities of building elements, which strictly depend on the thermophysical properties of the elements. Many investigations are presented in literature arguing to find the influence of each thermophysical property on TL and DF by keeping the other properties constant. This study aims to investigate the effect of each property on TL and DF, utilizing relationships between the measurement values of the thermophysical properties of wall materials. Therefore, first, 132 new concrete wall samples were produced, and their thermophysical properties were tested. Secondly, TL and DF values for each building element are computed from the solution of the problem by Complex Finite Fourier Transform (CFFT) technique. Finally, a multivariate regression analysis has been performed, and the variations of each thermophysical property versus TL and DF are presented, and also the findings are compared with literature. The results show that each property alone (keeping the other properties constant) is not adequate to identify the thermal inertia and thermal performance of a wall element. Besides, 87.3 % decrease in thermal diffusivity corresponds to 6.03 h increase in the value of TL and 88.8 % decrease in value of DF; respectively, for W1 wall assembly.Öğe Milling Inconel 718 workpiece with cryogenically treated and untreated cutting tools(SpringerLink, 2021-07-17) Gürbüz, Hüseyin; Baday, ŞehmusAlthough Inconel 718 is an important material for modern aircraft and aerospace, it is a kind material, which is known to have low machinability. Especially, while these types of materials are machined, high cutting temperatures, BUE on cutting tool, high cutting forces, and work hardening occur. Therefore, in recent years, instead of producing new cutting tools that can withstand these difficult conditions, cryogenic process, which is a heat treatment method to increase the wear resistance and hardness of the cutting tool, has been applied. In this experimental study, feed force, surface roughness, vibration, cutting tool wear, hardness, and abrasive wear values that occurred as a result of milling of Inconel 718 material by means of cryogenically treated and untreated cutting tools were investigated. Three different cutting speeds (35-45-55 m/min) and three different feed rates (0.02- 0.03-0.04 mm/tooth) at constant depth of cut (0.2 mm) were used as cutting parameters in the experiments. As a result of the experiments, lower feed forces, surface roughness, vibration, and cutting tool wear were obtained with cryogenically treated cutting tools. As the feed rate and cutting speed were increased, it was seen that surface roughness, vibration, and feed force values increased. At the end of the experiments, it was established that there was a significant relation between vibration and surface roughness. However, there appeared an inverse proportion between abrasive wear and hardness values. While BUE did not occur during cryogenically treated cutting tools, it was observed that BUE occurred in cutting tools which were not cryogenically treated. Also, in this study, the statistical validity of the experimental values was tested with the help of secondorder equations and analyses of variance (ANOVA). R2 values obtained as 99.14%, 99.76%, and 97.98% for vibration, surface roughness, and feed force values were modeled statistically with the help of second-order equations, respectively.Öğe Silica gel-immobilized 5-aminoisophthalohydrazide: A novel sorbent for solid phase extraction of Cu, Zn and Pb from natural water samples(Wiley Online Library, 2020-03-11) Aydın, Funda; Çakmak, Reşit; Levent, Abdulkadir; Soylak, MustafaA novel silica sorbent, silica gel‐immobilized 5‐aminoisophthalohydrazide (SiO2‐APH), was prepared by the condensation of 3‐chloropropyl‐functionalized silica gel with 5‐aminoisophthalohydrazide (APH) derived from dimethyl 5‐aminoisophthalate as a starting material and used for separation and preconcentration of Cu, Zn, and Pb metals in water samples using Flame Atomic Absorption Spectrometry (FAAS). The characterization of the new sorbent was carried out by Elemental Analysis, Thermogravimetric Analysis (TGA) and Fourier Transform Infrared Spectroscopy (FTIR). Important analytical parameters including as pH, amount of sorbent, type and amount of eluting solvent, sample volume, vortex and ultrasonic bath time, matrix ions that effect the developed SiO2‐APH‐solid phase extraction (SPE) method were investigated and optimum parameters were detected. Recoveries of examined metals were obtained as 98% for Cu and Pb and 101% for Zn. The relative standard deviation (RSD, n = 8) of Cu, Zn and Pb metals were 3.2, 2.8 and 1.6%, respectively. Limit of detections (LODs) (n = 10) were found as 2.7 μg L−1 for Cu, 7.4 μg L−1 for Zn and 3.5 μg L−1 for Pb μg L−1. The accuracy of the new method was assessed by analyzing of TMDA‐51.4 and TMDA‐70.2 certified reference materials. The results obtained for metals were in a good agreement with certified values. Addition/recovery test was applied to the real well, river, dam and stream water samples to check the accuracy of the method. The results showed that the developed SiO2‐APH‐SPE method can be effectively used as an alternative method for determination of Cu, Zn, and Pb metals in water samples.Öğe Synthesis, characterization and antioxidant activity of heterocyclic Schiff bases(Journal of the Chinese Chemical Society, 2020-08-04) Aral, Tarık; Dağ, Beşir; Kızılkaya, Hakan; Genç, Nusret; Erenler, RamazanSchiff base derivatives have gained great importance due to revealing a great number of biological properties. Schiff bases were synthesized by treatment of 4-amino-1,5-dimethyl-2-phenyl-1H-pyrazol-3(2H)-one (1) with various aldehydes in methanol at reflux. In addition, diamine was reacted with an aldehyde to yield the corresponding Schiff bases. The structures of synthesized Schiff bases were elucidated by spectroscopic methods such as microanalysis, 1 H-NMR, 13C-NMR, and FTIR. Antioxidant activities of synthesized Schiff bases were carried out using different antioxidant assays such as 1,1-diphenyl-2-picryl-hydrazyl free radical (DPPH• ) scavenging, 2,20 -azino-bis (3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) radical scavenging, and reducing power activity. (E)-4-((1H-indol-3-yl)methyleneamino)-1,5-dimethyl-2-phenyl-1H-pyrazol-3(2H)-one (3), (E)-1,5-dimethyl-4-((2-methyl-1H-indol-3-yl) methyleneamino)-2-phenyl-1H-pyrazol-3(2H)-one (5), (E)-1,5-dimethyl-2-phenyl-4-(thiophen-2-ylmethyleneamino)-1H-pyrazol-3(2H)-one (7), (E)-1,5-dimethyl2-phenyl-4-(quinolin-2-ylmethyleneamino)-1H-pyrazol-3(2H)-one (9), (1S,2S, N1,N2)-N1,N2-bis((1H-indol-3-yl)methylene)cyclohexane-1,2-diamine (11), and (1S,2S,N1,N2)-N1,N2-bis((2-methyl-1H-indol-3-yl)methylene)cyclohexane-1,2-diamine (12) were synthesized in high yields. Compound 5 displayed a good ABTS•+ activity. Compound 3 revealed the outstanding activity in all assays. Compound 7 has the best-reducing power ability in comparison to other synthesized compounds. Although compounds 5, 11, 12 are new, compounds 3, 7, 9 are known. Due to revealing a good antioxidant activity, the synthesized compounds (3, 5, 7) have the potential to be used as synthetic antioxidant agents.Öğe Effect of welding parameters on microstructure and mechanical properties of AA7075/AA5182 alloys joined by TIG and MIG welding methods(SpringerLink, 2020) Çelik, Yahya Hışman; Temiz, Şemsettin; Çetkin, EdipIn this study, V and X welding grooves were opened to the forehead positions of the AA5182 and AA7075 aluminum alloy pairs and these alloy pairs were joined with tungsten inert gas (TIG) and metal inert gas (MIG) methods. Three diferent welding currents were used in joints. Gas fow rates of 12 and 17 l/min at the TIG welding and wire feed rates of 38 and 45 cm/min at MIG welding were selected. The efect of the welding grooves, welding current, gas fow rate and wire feed rate on microstructure and mechanical properties were investigated. Microstructures of welding zones were analyzed by an optical microscope and a scanning electron microscope (SEM). Vickers hardness of these zones was also measured. In addition, tensile and fatigue tests were carried out. Fracture mechanisms of failed specimens were conducted after the tensile tests were examined by using SEM. The highest hardness, tensile and fatigue strengths were obtained from the alloy pairs joined by opening X welding groove with TIG welding method. These values were 89 HV, 262.87 MPa, and 131.5 MPa, respectively. Similarly, the lowest tensile and fatigue strengths were obtained from the alloy pairs joined by opening V welding groove in the TIG welding method. These values were, respectively, 94.48 MPa and 19.1 MPa. However, the minimum hardness value was measured as 58 HV from the alloy pairs joined by opening V welding groove with MIG welding methods. In addition, it was observed on the fracture surfaces that the grain distributions and mechanisms difered depending on the welding methods, welding groove, and welding parameters.Öğe Assessment of heavy metal pollution of urban soils of Batman by multiple pollution indices(Taylor & Francis, 2021-03-28) Baran, Hacı Alim; Gümüş Kıral, NurcanHeavy metal accumulation is observed in urban soils, sometimes due to anthropological effects and sometimes due to natural geological units. In order to determine the heavy metal content of the Upper MioceneLower Pliocene Selmo Formation, which is observed in the whole study area and consists of conglomerate, sandstone and silt stone, soil and river sediment samples were taken. Within the scope of pollution assessment, geo-accumulation index (Igeo), enrichment factor (EF) and pollution index (PI) calculations of Batman urban soil samples were made and different degrees of pollution values were determined. High pollution values were obtained for As, Mo and Sb elements in all pollution indices calculated. The pollution levels of the three elements were determined as strongly to extremely contaminated according to Igeo values, the others except As (very severe enrichment) according to EF values were determined as severe enrichment, and according to PI, all three were determined as strong polluted. Pollution and element distribution maps were created with a geographical information system software. According to the results of correlation analysis and cluster analysis, the elements found to be contaminated are divided into two groups, whose locations and sources of contamination are different. The first group (Sn, Zn and Pb) is observed in the approximate centre of the study area and developed due to traffic emissions. The elements belonging to the second group (especially As, Mo and Sb) show high pollution values in the south-southeast of the study area. These pollutions are thought to be caused by the inadequate storage of mineral oils and batteries that are changed in the industrial site and from leaks in the oil production, storage, refining and transmission phase in TPAO, TÜPRAŞ and BOTAŞ. The analysed samples were compared with the Soil Pollution Control Regulation and WHO standards, and Co, Ni and As element values were found to exceed the permissible values for healthÖğe Mechanical properties of fiber/graphene epoxy hybrid composites(SpringerLink, 2020-11-18) Çelik, Yahya Hışman; Topkaya, Tolga; Kılıçkap, ErolThe aim of this study is to determine the effect of graphene nanoparticle (GNP) reinforcement on the mechanical properties of glass fiber reinforced polymer (GFRP), carbon fiber reinforced polymer (CFRP) and aramid fiber reinforced polymer (AFRP) composites commonly used in the space and defense industry. Accordingly, GFRP, CFRP and AFRP composites were produced by using hot pressing method. In addition, hybrid fiber composites were produced by adding 0.1 %, 0.2 % and 0.3 % GNP to these fiber reinforced composites. The tensile strength and modulus of elasticity of the composites were determined. The tensile damage fracture regions were analyzed by scanning electron microscopy (SEM) and energy distribution spectrum (EDS). It was observed that the addition of 0.2 wt. % GNP to GFRP and CFRP composites increased tensile strength and modulus of elasticity. However, the addition of 0.2 wt. % GNP to AFRP composites had no effect on the tensile strength; on the contrary, it partially reduced the tensile strength but increased the modulus of elasticity. On the fracture damage surfaces of the GFRP and CFRP composites and the GNP/GFRP and GNP/CFRP hybrid composites, the fibers were completely separated. On the damage surfaces of AFRP composite and GNP/AFRP hybrid composites, the fibers were deformed but these fibers were not separated from each other. From the EDS analysis, it was observed that the element C increased in the composites with the addition of GNP to the fiber reinforced composites
