Makine Mühendisliği Bölümü

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Citation - WoS: 2
Citation - Scopus: 2
Analysis of Heat Transfer Enhancement in Tubes With Capsule Dimpled Surfaces and Al2o3-Water Nanofluid
(Turkish Soc thermal Sciences Technology, 2022) Ibrahim, Mahmoud Awni A. Haj; Turkoglu, Hasmet; Yapici, Ekin Ozgirgin
This study aims to numerically investigate and evaluate the enhancement of heat transfer by new capsule dimples on tube surfaces for flow of water and Al2O3-water nanofluid with different concentrations, under uniform surface heat flux. The originality of this work lies in combining two passive heat transfer enhancement methods such as geometrical improvements and nanofluids together. Capsule dimples with different depths were considered. Al2O3- water nanofluid was modeled as a single-phase flow based on the mixture properties. The effects of dimple depth and nanoparticle concentrations on Nusselt number, friction factor and performance evaluation criteria (PEC) were studied. Numerical computations were performed using ANSYS Fluent commercial software for 2000-14000 Reynolds number range. It was found that when laminar, transient and fully developed turbulent flow cases are considered, increase in the dimple depth increases the Nusselt number and friction factor for both pure water and Al2O3-water nanofluids cases. Also, the friction factor increases as dimple depth increases. Results show that increase in PEC is more pronounced in the laminar region than in the transition region, it starts to decrease for turbulent flows. For nanofluid, PEC values are considerably higher than pure water cases. The variation of PEC for capsule dimpled tubes are dependent on flow regimes and dimple depths. Increasing the nano particle volume concentration and dimple depth in laminar flows increase the PEC significantly.
Citation - WoS: 5
Citation - Scopus: 5
Ann and Anfis Performance Prediction Models for Francis Type Turbines
(Turkish Soc thermal Sciences Technology, 2020) Aylı, Ülkü Ece; Ayli, Ece; Ulucak, Oguzhan; Makine Mühendisliği
Turbines can be operated under partial loading conditions due to the seasonal precipitation fluctuations and due to the needed electrical demand over time. According to this partial working need, designers generate hill chart diagrams to observe the system behavior under different flow rates and head values. In order to generate a hill chart, several numerical or experimental studies have been performed at different guide vane openings and head values which are very time consuming and expensive. In this study, the efficiency prediction of Francis turbines has been performed with ANN and ANFIS methods under different operating conditions and compared with simulation results. The obtained results indicate that it is possible to obtain a hill chart using ANFIS method instead of a costly experimental or numerical tests. ANN and ANFIS parameters which effect the output, have been optimized with trying 100 different cases. 75% of the numerical data set is used for training and 25 % is used for validation as testing data. To asses and compare the performance of multiple ANN and ANFIS models several statistical indicators have been used. Insight to the performance evaluation, it is seen that ANFIS can predict the efficiency distribution with higher accuracy than the ANN model. The developed ANFIS model predicts the efficiency with 1.41% mean average percentage error and 0.999 R-2 value. To the best of the author's knowledge, this is the first study in the literature that ANN and ANFIS are used in order to predict the efficiency distribution of the turbines at different loading conditions.
Citation - WoS: 14
Citation - Scopus: 20
Cavitation in Hydraulic Turbines
(Edizioni Ets, 2019) Ayli, Ece
Hydroenergy is one of the richest and most useful renewable energy sources in the world. Hydropower is a vital source as it is the clean energy source, sustainable and last but not least it is also cost-effective. One of the most important parameters that affect the performance of the hydraulic machines is the cavitation phenomenon, which is defined as the formation of the vapor bubbles in the liquid through any hydraulic turbine. In this paper, hydraulic machines, cavitation, types of cavitation are briefly described. After theoretical studies, analytical and numerical researches about cavitation in hydraulic machinery are discussed extensively. With those studies which are summarized in this paper covers a lot of ground about cavitation on the other hand further studies are needed about cavitation in hydro turbines. Numerical methods provide sufficient predictions for cavitation. However, numerical results should be verified by experimental measurements and detection methods to decide what intensity and which shape of cavitation is hazardous and vital, where the local pressure is lower than the vapor pressure and at which static pressure cavities start to grow and collapse.
Citation - WoS: 1
Citation - Scopus: 2
Dynamic Analysis and Design Optimisation of a Heavy Military Vehicle
(inderscience Enterprises Ltd, 2021) Acar, Bulent; Ider, S. Kemal; Cicek, Burak Can
This paper investigates the dynamic response of a heavy military vehicle which is subjected to a dynamic firing load while it is settled on its outriggers. Dynamic behaviour of a settled heavy military vehicle under a dynamic firing load is one of the major design factors of a launching vehicle. Two different finite element (FE) models are created in ANSYS software to obtain the dynamic behaviour of the launching vehicle. The first model is a detailed finite element model (DFEM) and the second model is a simple and less degree of freedom (DOF) parametric FE model which is created with the ANSYS Parametric Design Language (APDL) in order to perform the design optimisation by swiftly varying the parameters such as clamp attachment positions on the chassis, outrigger deployment and outrigger case cross section.
Citation - WoS: 3
Citation - Scopus: 2
Energy Recovery Using Pumps as Turbines in Water Supply Systems: a Case Study
(Emerald Group Publishing Ltd, 2022) Kocak, Eyup; Karaaslan, Salih; Andrade-Campos, A. Gil; Yucel, Nuri
An investigation was undertaken into energy recovery from water supply systems (WSSs) using pumps that can work in reverse as turbines. Napoli Est network in Italy was selected as a case study. To find the optimal locations for the installation of reversible pumps in the network, a methodology was developed and implemented using computer programming and hydraulic simulation software. A technical feasibility analysis was conducted to create different scenarios for implementation and a suitable pump was designed using computational fluid dynamics. Pump mode and reverse mode operation were simulated numerically and the performance was improved. Financial analysis showed that energy production in WSSs using pumps as turbines is a profitable alternative to traditional turbines and a renewable solution for the world's growing energy needs.
Experimental Study and Theoretical Investigation of High Temperature Proton Exchange Membrane Fuel Cell Micro-Cogeneration Application
(Turkish Soc thermal Sciences Technology, 2018) Yapıcı, Ekin; Devrim, Yilser; Ozgirgin Yapici, Ekin; Makine Mühendisliği
In this study, a house hold micro-cogeneration system is designed using high temperature proton exchange membrane (HTPEM) fuel cell. HTPEM type fuel cells gain the highest interest lately, due to their advantages in terms of increasing efficiency and power quality, reducing harmful emissions and flexibility of operation with respect to the other fuels. The micro-cogeneration system involves producing both electrical energy and hot water and/or vapor together in an economical way, utilizing single fuel (HTPEM fuel cells) for household applications. During the operation of the fuel cell, for high efficiency and stable power production, the access heat of the stack should be removed constantly and the temperature of the stack should be held stable. Heat recovered from the designed innovative cooling system is used for acquiring energy for heating water. This way, thermal efficiency is almost doubled compared to simple cycle. In the scope of this study, 225 W HTPEM fuel cell stack is designed and tested at 160 degrees C operation temperature with hydrogen gas and air. During operation, for homogenous distribution of temperature among the cells, for a short start up period leading to a fast required steady state temperature and for constantly removing the access heat produced in the cell, the cell stack is cooled by using a cooling fluid (Heat Transfer Oil 32- Petrol Ofisi). Selection of insulation material type and thickness for the cell stack is done using natural convection and radiation loss calculations. For the most efficient operating conditions, micro-cogeneration system water inlet and exit temperatures, water and cooling fluid flow rates, convenient pipe diameter and pump power calculations are done to finalize the design. With the cogeneration system designed during the studies, by recovering the access heat of the insulated HTPEM cell stack, district water with initial temperature of 15-20 degrees C is heated around 50 degrees C. Data gathered during studies indicate that fuel cell micro-cogeneration application is highly viable.
Finite Element Method Application for Nonlinear Mechanical Response of Three-Dimensonal Beams Using Mathematica
(Gazi Univ, 2019) Tanriover, Hakan
Mechanical behavior of beams under large rotations and displacements was investigated. Using co-rotational approach given by Crisfield, three dimensional beam finite elements was modeled in Mathematica environment. The symbolic process of Mathematica provides keeping the parameters in the model as variables and beams having different geometries can be modelled easily. The yielding non-linear equation system was solved by utilizing Newton-Raphson technique. Dynamic balance equations and numerical time integration method were introduced, the solution process was left as a future work, however. Comparisons with the results of ANSYS and those of the works from the literature are accomplished.
Citation - WoS: 36
Citation - Scopus: 41
Improvement of Electric Discharge Machining (Edm) Performance of Ti-6al Alloy With Added Graphite Powder To Dielectric
(Assoc Mechanical Engineers Technicians Slovenia, 2015) Cogun, Can; Unses, Emre
Ti-6Al-4V is a well-known Ti alloy widely used in the aerospace industry and belongs to the group of difficult-to-machine materials. It is less suitable for both conventional chip removal (machining) techniques and electric discharge machining (EDM). The very low material removal rate (MRR) of the Ti alloys during the EDM process causes prohibitively long machining durations. The goal of this study was to improve the EDM performance of the Ti-6Al-4V alloy by the addition of graphite powder into the kerosene dielectric liquid. The EDM performance was quantified by MRR, tool electrode wear rate (EWR), relative wear (RW), surface roughness and texture properties. The experiments conducted have shown that the use of graphite powder mixed with the kerosene dielectric (GPMKD) during machining considerably increases the MRR, improves the R-a and R-z(DIN) surface roughness and decreases the RW. 3D topographic views of the machined workpiece surfaces attained with GPMKD revealed uniformly distributed surface valleys and peaks over the surface and peaks with short arid round tops since the discharge energy of a spark is distributed over a large area at the machining gap. The experimental results strongly indicate the adaptability of the proposed technique to EDM die sinking and EDM drilling applications of the Ti-6Al-4V alloy in the aerospace industry. The ED machining performance of Ti-6Al-4V alloy using GPMKD is also compared to that of AISI 1040 steel, which is commonly used in EDM applications.
Citation - WoS: 23
Citation - Scopus: 33
A New Algorithm for U-Shaped Two-Sided Assembly Line Balancing
(Canadian Science Publishing, 2010) Agpak, Kursad; Yavuz, Mustafa; Yegul, Mustafa Fatih
This study introduces a new hybrid design for a specific case-of assembly lines, and proposes a multi-pass random assignment algorithm to find the minimum number of stations required. The algorithm also finds the sequence and the schedule of the tasks assigned. The new design is a combination of two-sided lines and U-shaped lines, which benefits from the advantages of both designs at the same time. One side of the line is arranged in U-shape allowing stations with crossovers, and the other side of the line is balanced like a traditional straight flow. Depending on product direction, either Left or Right side of the line can be designed in U-shape. Small and large-sized two-sided assembly line test-bed problems were solved using the algorithm. Optimal results are achieved for all small-sized problems. Due to the novelty Of the design, results of large-sized problems are compared to findings of studies on simple two-sided balancing. Algorithm produced better results in most of the cases.
Citation - WoS: 1
Numerical Analysis of Pulsating Circular Impinging Laminar Jet on a Planar Disc
(Turkish Soc thermal Sciences Technology, 2017) Kahroba, Mitra; Türkoğlu, Haşmet; Turkoglu, Hasmet; Makine Mühendisliği
In this study, the flow and heat transfer characteristics of pulsating circular air jets impinging on a flat surface were numerically analyzed. The jet velocity pulsated in time. The objective of the work is to investigate the influence of the jet Reynolds number, pulsation amplitude and pulsation frequency on the rate of heat transfer from the target hot surface. For the analysis, a computer program, based on the control volume method and SIMPLE algorithm, was developed. Laminar flow with the time averaged jet Reynolds numbers between 300 and 700 were analyzed. The pulsation amplitude is ranged between 0.0V(0) (steady jet) and 0.8V(0) (m/s) (V-0 is period averaged jet velocity), and the frequency is ranged between 1 and 6 Hz. The nozzle-to-plate distance was kept constant at H/d=3. From the simulation results, it was observed that at any instant of the pulsation period, the local Nusselt number is maximum at the stagnation point, and it decreases along the plate. This decrease in the local Nusselt number is not monatomic as in the steady jet cases. It has local maximum and minimum values (fluctuations) due to the moving recirculating flow regions along the bottom plate. At low frequencies, the time (period) averaged stagnation point Nusselt numbers are lower than the corresponding steady jet Nusselt numbers. However, with the increasing frequency, the stagnation point Nusselt number increases and become higher than the steady jet Nusselt number.
YÜKSEK SICAKLIK PROTON DEĞİŞİM MEMBRAN YAKIT HÜCRESİ MİKROKOJENERASYON UYGULAMASININ DENEYSEL VE TEORİK İNCELENMESİ
(2018) Devrim, Yılser; Özgirgin Yapıcı, Ekin
Bu çalışmada, yüksek verimlilikleri ve çevre dostu teknolojiler olmaları sebebiyle tercih edilen, güvenilir güç üretim tekniklerinden biri olan yüksek sıcaklık proton değişim membran (YSPEM) yakıt hücreleri kullanılarak bir evsel mikro-kojenerasyon (birlikte ısı-güç) sistemi tasarlanmıştır. Tasarlanan sistem, YSPEM yakıt hücresi tarafından üretilen elektrik gücü ve faydalı ısının kombine bir şekilde, kullanılmasını içermektedir. Hücrenin çalışması sırasında, yüksek performans ve kararlı güç üretimi sağlanabilmesi için hücre içerisinde üretilen ısının uzaklaştırılması ve hücre içi sıcaklığın sabit kalması gerekmektedir. Bu sebeple tasarlanan yenilikçi soğutma sisteminin atık ısısı, sıcak su ısıtmasında kullanılacak olan ısıl enerjinin teminini sağlamaktadır. Böylelikle toplam verim basit çevrimlere göre yaklaşık iki katına çıkabilmektedir. Çalışma kapsamında tasarlanan 225 W gücünde YSPEM yığını 160°C çalışma sıcaklığında hidrojen ve hava gazları ile test edilmiştir. Çalışması sırasında sıcaklığın hücre içerisinde homojen olarak dağılımı, hücrenin kısa sürede gerekli çalışma sıcaklığına ulaşabilmesi, yakıt hücresinde oluşan ısının hücreden sürekli olarak uzaklaştırılabilmesi için yakıt hücresi yığını soğutucu akışkan (Isı Transfer Yağı 32-Petrol Ofisi) kullanılarak soğutulmuştur. Hücre izolasyon malzemesi seçimi ve kalınlığı, doğal taşınım ve radyasyon yolu ile ısı kaybı hesabıyla belirlenmiştir. Maksimum verim çalışma koşulları için mikro-kojenerasyon sisteminin su giriş çıkış sıcaklıkları, su ve soğutucu akışkan debileri, uygun boru çapı hesabı ve pompa güç hesabı yapılarak nihai sistem tasarlanmıştır. Çalışmada tasarlanan kojenerasyon sisteminde, YSPEM yığınının soğutulması ile açığa çıkan atık ısı, 15-20C’lik şebeke suyunun ısıtılması için kullanılmıştır. Şebeke suyu sıcaklığı yalıtımlı hücre kullanılması durumunda ortalama 50C’ye kadar ısıtılmıştır. Elde edilen veriler yakıt hücresi mikro-kojenerasyon uygulamasının kullanılabilirliğini göstermektedir. Anahtar Kelimler: YSPEM, Yakıt hücresi, Polibenzimidazol membran, Mikro-kojenerasyon

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