Shiraz UniversityIranian Journal of Science and Technology Transactions of Mechanical Engineering2228-618739M220151001DYNAMICAL BEHAVIOR OF AN AXIALLY MOVING STRING CONSTITUTED BY A FRACTIONAL DIFFERENTIATION LAW283290324010.22099/ijstm.2015.3240END. DÖNMEZDEMİRDept. of Math., Faculty of Art & Sciences, Celal Bayar University, 45047, Manisa, TurkeyB. G. SİNİRDept. of Civil Eng., Faculty of Engineering, Celal Bayar University, 45140 Manisa, TurkeyN. BİLDİKDept. of Math., Faculty of Art & Sciences, Celal Bayar University, 45047, Manisa, TurkeyJournal Article20140401In this paper, the dynamical behavior of an axially moving string modeled by fractional derivative is investigated. The governing equation represented motion is solved by the method of multiple scales. Considering principal parametric resonance, the stability boundaries for string with simple supports are obtained. Numerical results indicate the effects of fractional damping on stability.Shiraz UniversityIranian Journal of Science and Technology Transactions of Mechanical Engineering2228-618739M220151001FINITE ELEMENT MODELING AND EXPERIMENTAL STUDY OF RESIDUAL STRESSES IN REPAIR BUTT WELD OF ST-37 PLATES291307324110.22099/ijstm.2015.3241ENA. FadaeiDept. Mechanical Engineering, Engineering Faculty, Bu-Ali Sina University, Hamedan, I. R. IranH. MokhtariDept. Mechanical Engineering, Engineering Faculty, Bu-Ali Sina University, Hamedan, I. R. IranJournal Article20140405Welding is one of the most important assembling methods which are widely applied in different applications. In service conditions, some of the weld joints which meet defects must be repaired. The residual stresses impress the operation and efficiency of the repair weldment. In this study, the temperature and the residual stress fields were investigated by both the finite element simulation and the experimental measurement due to repair butt weld of the two thin St 37 plates. The welding process was simulated using the three-dimensional finite element and the Goldak double-ellipsoid heat source models. The temperature distribution and the residual stresses were computed both in the initial and repair welds. The element birth and death technique was used to simulate the filler metal deposition into the weld pool. The experimental measurements were performed to verify the numerical results in the both initial and repair welds. The residual stresses were measured using the hole drilling method. The experimental results revealed that the finite element simulations obtained in the present work were capable of predicting the residual stresses in the initial and repair welds. Also, the effect of the repair length variation on both magnitudes and distribution of the transverse and longitudinal residual stresses were shown.Shiraz UniversityIranian Journal of Science and Technology Transactions of Mechanical Engineering2228-618739M220151001A NUMERICAL STUDY OF A THREE-DIMENSIONAL PROTON EXCHANGE MEMBRANE FUEL CELL (PEMFC) WITH PARALLEL AND COUNTER FLOW GAS CHANNELS309323324210.22099/ijstm.2015.3242ENN. AhmadiDept. of Mechanical Engineering, Urmia University of Technology, Urmia, I. R. of IranH. TaraghiDept. of Mechanical Engineering, Urmia University of Technology, Urmia, I. R. of IranM. SadeghiazadDept. of Mechanical Engineering, Urmia University of Technology, Urmia, I. R. of IranJournal Article20140202Modeling the heat and mass transport in micro channel is being used extensively in researches and industrial applications. The aim is optimizing fuel cell designs before building a prototype for engineering application. In this study, numerical, three-dimensional, single phase computational fluid dynamics model of a proton exchange membrane fuel cell with both the gas distribution flow channels and the Membrane Electrode Assembly (MEA) has been developed. A single set of conservation equations which are valid for the flow channels, gas-diffusion electrodes, catalyst layers, and the membrane region, are solved by finite volume technique. The present simulated straight channels PEMFC model, accounts for major transport phenomena and the performance. Additionally, the effect of reversing the flow direction at cathode side has been investigated to study the fuel cell performance and species distribution. The results showed that, in the PEMFC with the counter flow channels, the output current density has been decreased and also the kind of species distributions has been influenced by this phenomenon. It is very important to model the back diffusion and electro-osmotic mass flux for determination of ionic conductivity of membrane which affects the performance of fuel cell. Finally, the numerical results are validated by available experimental data.Shiraz UniversityIranian Journal of Science and Technology Transactions of Mechanical Engineering2228-618739M220151001USING MULTI-WALL CARBON NANOTUBE (MWCNT) BASED NANOFLUID IN THE HEAT PIPE TO GET BETTER THERMAL PERFORMANCE325335324310.22099/ijstm.2015.3243ENY. BakhshanDept. of Mechanical Engineering, University of Hormozgan, P.O.Box 3995, I. R. of IranA. HajhosseiniDept. of Mechanical Engineering, University of Hormozgan, P.O.Box 3995, I. R. of IranJournal Article20131229In this study, thermal performance of a cylindrical heat pipe is investigated numerically. Three different types of water based nanofluids, namely (Al2O3+Water), (Diamond+Water) and (Multi-Wall Carbon Nano tube (MWCNT) +Water) have been used. The influence of using the simple nanofluids and MWCNT nanofluid on the heat pipe characteristics such as liquid velocity, pressure profile, temperature profile, thermal resistance and heat transfer coefficient of heat pipe have been studied. A new correlation developed by Bakhshan and Saljooghi, for viscosity of nanofluids has been implemented. The results show good agreement with the available analytical and experimental data. Also, the MWCNT based nanofluid has lower thermal resistance, higher heat transfer coefficient and lower temperature difference between evaporator and condenser sections, so it has good thermal specifications as a working fluid for use in heat pipes. The prepared code has capability for parametric studies also.Shiraz UniversityIranian Journal of Science and Technology Transactions of Mechanical Engineering2228-618739M220151001EXPERIMENTAL INVESTIGATION OF TRANSIENT TEMPERATURE DISTRIBUTION AND HEAT TRANSFER BY JET IMPINGEMENT IN GLASS TEMPERING PROCESSING337349324410.22099/ijstm.2015.3244ENH. YaziciDept. of Automotive Engineering, Technology Faculty, Pamukkale University, Denizli, TurkeyM. Akcay2Dept. of Mechanical Education, Technical Education Faculty, Pamukkale University, Denizli, TurkeyM. GolcuDept. of Automotive Engineering, Technology Faculty, Pamukkale University, Denizli, TurkeyM.F. KoseogluDept. of Mechanical Engineering, Engineering Faculty, Pamukkale University, Denizli, TurkeyY. SekmenDept. of Automotive Engineering, Engineering Faculty, Karabuk University, Karabuk, TurkeyJournal Article20141015Heating and sudden cooling are among the most important processes affecting temper quality in the production period of tempered auto glass. In this study, heat transfer characteristics and cooling times during the sudden cooling process of tempered glass production have been experimentally investigated. Flat glass with dimensions of 50x50x4 mm has been heated up to 680 ºC in the furnace and was then exposed to sudden cooling process until its surface temperature dropped to 70 ºC. In the cooling process two mutually placed 8 cm long air jet nozzles with an internal diameter of 8 mm have been used. Experiments have been conducted for Reynolds numbers in the range of (20000≤Re≤40000) and for dimensionless jet to plate distances in the range of (1≤H/D≤10). Based on the above parameters cooling periods, local (Nux), average (Nuaver) and stagnation point (Nustag) Nusselt numbers have been experimentally determined.Shiraz UniversityIranian Journal of Science and Technology Transactions of Mechanical Engineering2228-618739M220151001MODELLING THE IMPACT OF RADIATIVE HEAT LOSS ON CO2 EMISSION, O2 DEPLETION AND THERMAL STABILITY IN A REACTIVE SLAB351363324510.22099/ijstm.2015.3245ENR.S. LebeloDept. of Mathematics, Vaal University of Technology, Private Bag X021, Vanderbijlpark, 1911, South AfricaO.D. MakindeFaculty of Military Science, Stellenbosch University, Private Bag X2, Saldanha 7395, South AfricaJournal Article20141105In this paper, we examine the effects of thermal radiation on CO2 emission and O2 depletion in an exothermic reactive slab of combustible materials with uniform surface temperature. The governing equations for the nonlinear heat and mass transfer problem are derived and solved numerically using Runge-Kutta-Fehlberg method with shooting technique. Numerical expressions for temperature field, CO2 emitted and O2 depleted are derived and utilised to obtain expressions for Nusselt number and Sherwood number at the material surface. The effects of various thermo-physical parameters on the temperature field, CO2 emission and O2 depletion are depicted graphically and discussed quantitatively. Thermo-physical parameters that help to reduce CO2 emission and hence O2 preservation, are identified, including those which help to monitor measures to avoid explosions in spontaneous combustion processes.Shiraz UniversityIranian Journal of Science and Technology Transactions of Mechanical Engineering2228-618739M220151001OPTIMAL SHAPE DESIGN FOR HEAT CONDUCTION USING SMOOTHED FIXED GRID FINITE ELEMENT METHOD AND MODIFIED FIREFLY ALGORITHM367387324610.22099/ijstm.2015.3246ENM.J. Kazemzadeh-ParsiDept. of Mechanical Engineering, Shiraz Branch, Islamic Azad University, Shiraz, I. R. of IranJournal Article20140505The present study is concerned with optimal shape determination of inhomogeneous and temperature dependent domains under steady state heat conduction. Such situations are important in many thermal design problems, especially in shape design of electronic components and chips. In the present paper, we formulate the shape optimization problem based on volume minimization of heat conductive material while limiting maximum temperature. The smoothed fixed grid finite element method which is a new approach based on the non-boundary-fitted meshes is used to obtain temperature field. The boundary parameterization technique using splines is also adopted to manipulate the shape variations. A modified version of the firefly algorithm which is a recently developed metaheuristic optimization technique is proposed as the optimizer. These modifications consist of adding memory, adding newborn fireflies and proposing a new updating formula. To evaluate the applicability of the proposed method five numerical examples are solved and the results are presented.Shiraz UniversityIranian Journal of Science and Technology Transactions of Mechanical Engineering2228-618739M220151001STUDY OF SPRAY CHARACTERISTICS OF BIODIESEL USING DIMENSIONLESS ANALYSIS UNDER NON EVAPORATING CONDITIONS389398324710.22099/ijstm.2015.3247ENP. RaghuSri Venkateswara College of Engineering, Post Bag No. 1, Irrungattukottai, Pennalur - 602 117, Tamil Nadu, IndiaN. NallusamySSN College of Engineering, OMR, Kalavakkam - 603 110, Tamil Nadu, IndiaJournal Article20140511The spray characteristics of the fuel greatly influence emissions from diesel engines. Spray development plays a vital role in improving the combustion and emission characteristics of fuel because it directly affects the air- fuel mixture formation. The spray characteristics of fuel mainly depend on fuel injection process, fuel density, fuel viscosity, ambient pressure and temperature. Among these, the effect of fuel injection pressure is a very important parameter directly affecting spray structure. This study investigates the effects of fuel injection pressure on the spray characteristics such as spray angle and spray tip penetration in a constant volume chamber under non evaporating conditions by image processing techniques. The macroscopic spray characteristics were quantified using dimensionless analysis by examining the role of the dominating forces associated with liquid jet breakup. The Weber number, Reynolds number and air- to- fluid density ratio were used to capture the primary forces including the inertia, surface tension and aerodynamics drag forces. The Weber number has a more profound effect on the spray penetration and spray cone angle compared to the Reynolds number contribution. This analysis yielded dimensionless correlations for spray cone angle and spray tip penetration that provided important insight into the spray breakup and atomization process.Shiraz UniversityIranian Journal of Science and Technology Transactions of Mechanical Engineering2228-618739M220151001EXPERIMENTAL AND NUMERICAL INVESTIGATION OF THE EFFECT OF DIMPLE AND PERFORATIONS ON NUSSELT NUMBER AND FLOW EFFICIENCY IN MULTI-LOUVERED HEAT EXCHANGER399412324810.22099/ijstm.2015.3248ENH. ShokuhmandDept. of Mechanical Engineering, University of Tehran, Tehran, I. R. of IranF. SangtarashDept. of Mechanical Engineering, University of Tehran, Tehran, I. R. of IranJournal Article20141203Numerical and experimental analyses are performed on multilouvered fin banks in low and medium Reynolds regimes to investigate the effects of dimples and perforations on flow structure and heat transfer capacity. In different Reynolds numbers the flow efficiency has been calculated numerically and experimentally by flow visualization method and the results showed that dimples and perforations can increase flow efficiency more than 5% in fin banks. Additionally, a set of numerical and experimental analysis has been done to evaluate temperature contours and total heat transfer in simple, dimple and dimple-perforation fin banks in different Reynolds Numbers. The simulations revealed that the heat transfer and temperature augmentations occur due to the existence of a circulation region that is created by the dimple. The results showed that adding dimples with perforations increased the heat transfer capacity of the fin banks up to 9% compared with the simple louver fin banks.Shiraz UniversityIranian Journal of Science and Technology Transactions of Mechanical Engineering2228-618739M220151001NUMERICAL INVESTIGATION OF THE UNSTART SUPPRESSION IN A SUPERSONIC AIR INTAKE413426324910.22099/ijstm.2015.3249ENM.R. SoltaniDept. of Aerospace Engineering, Sharif University of Technology, Tehran, I. R. of IranJ. Sepahi YoinsiDept. of Aerospace Engineering, Sharif University of Technology, Tehran, I. R. of Iran
and
Mesbah Research Institute, Tehran, I. R. of IranV. Farajpoor KhanaposhtaniMesbah Research Institute, Tehran, I. R. of IranJournal Article20140608The starting behavior of a supersonic axisymmetric mixed compression air intake was numerically investigated. The code solves Reynolds-averaged Navier–Stokes equations using an explicit finite volume method in a structured grid by the Roe flux difference splitting scheme. Further, it uses the Baldwin–Lomax algebraic model to compute the turbulent viscosity coefficient. The correct method of surveying the intake starting problem and effects of several geometrical parameters such as: intake throat area, cowl lip roundness and spike surface curvature upstream of the throat on the starting and performance of the intake were studied. Results showed that correct combinations of the mentioned parameters can suppress the intake unstart problem and in addition can prevent the reduction of the intake efficiency.Shiraz UniversityIranian Journal of Science and Technology Transactions of Mechanical Engineering2228-618739M220151001PARAMETRIC STUDY FOR RESIDUAL STRESSES AND DEFORMATIONS IN WELDED PIPE-FLANGE JOINTS427436325010.22099/ijstm.2015.3250ENM. AbidInterdisciplinary Research Center, COMSATS Institute of Information Technology, Wah Cantt, PakistanH. Abdul WajidDepartment of Mathematics, COMSATS Institute of Information Technology, Lahore, Pakistan
and
Department of Electrical Engineering, Faculty of Engineering, Islamic University Medina, KSAS UllahFaculty of Mechanical Engineering, GIK Institute of Engineering Sciences and Technology, Topi, PakistanJournal Article20141027Welding produces residual stresses and distortion, having detrimental effect on structure integrity and service performance of the welded pipe joints. This paper investigates residual stresses and distortion during Gas Metal Arc Welding (GMAW) of pipes of schedule 40 and 60, nominal diameter 100mm and 200mm and thickness 8mm and 10mm with ANSI flanges of class 300#. Welding parameters including voltage, current and heat input are varied to find the optimized set to control stresses and deformations. Stress variation on the flange side is observed prominent compared to the pipe side due to its dimensional variation. Axial flange displacement along 360 degrees is also concluded obvious, hence effecting sealing performance of the gasketed flanged pipe joints.Shiraz UniversityIranian Journal of Science and Technology Transactions of Mechanical Engineering2228-618739M220151001FUZZY RULE BASED PREDICTION OF IAQ CHARACTERISTICS IN AIR CONDITIONED CAR437450325110.22099/ijstm.2015.3251ENP. ThirumalDept. of Mechanical Engineering, Government College of Engineering, Bargur, IndiaK.S. AmirthagadeswaranDept. of Mechanical Engineering, Government College of Technology, Coimbatore, IndiaS. JayabalDept. of Mechanical Engineering, A.C. College of Engineering Technology, Karaikudi, IndiaJournal Article20131202Air conditioning is widely applied for the improvement of standard of living in human life. This present investigation focused on the prediction of indoor air quality characteristics of air conditioned car using fuzzy logic algorithm. The conditioned space was selected and the experiments were planned as per design of experiments to study the effect of human load, fresh air supply and air velocity on the human comfort conditions. The mathematical models were developed to predict the comfort conditions, namely temperature, CO2 level and relative humidity over a specified range of input conditions. Carbon dioxide exhalation rate differs person to person based on their body weight and burning rate of calories, etc. Fuzzy logic predicted the intermediate response of IAQ parameters for varying input conditions in this present investigation. The proposed multi response fuzzy model predicted better results comparing with nonlinear regression models. The absolute error percentage of fuzzy model for carbon dioxide level, temperature and relative humidity is 2.05%, 3.81 % & 2.24 % respectively.