Tehran, Iran
Tehran, Iran

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Heidary H.,Mapna Group | Kermani M.J.,Amirkabir University of Technology
International Communications in Heat and Mass Transfer | Year: 2012

In this paper heat transfer and flow field analysis in a wavy channel linked to a porous Gas Diffusion Layer (GDL) is numerically studied. The domain is very similar to our earlier computations of proton exchange membrane fuel cells (see Khakbaz-Baboli and Kermani (2008)). The fluid temperature at the channel inlet (T in) is taken less than that of the walls (T w). The governing equations are numerically solved in the domain by the control volume approach based on the SIMPLE technique (1972). A wide spectrum of numerical studies is performed over a range of Reynolds number Re H: 100≤Re H≤1000, wave number β: 0≤β≤10, the wave amplitude α: 0≤α≤0.3 and Darcy number Da: 0.1≤Da≤0.001. Simulations show that heat transfer in channels can enhance up to 100%, depending on the duct α, β and flow Re H. Computations show excellent agreement with the literature. The present work can provide helpful guidelines to the manufactures of the compact heat exchangers. © 2011 Elsevier Ltd.


Heidary H.,Mapna Group | Kermani M.J.,Amirkabir University of Technology
International Journal of Thermal Sciences | Year: 2012

In this study heat transfer and fluid flow analysis in a channel with blocks attached to bottom wall and utilizing Nano-fluid is numerically studied. The fluid temperature at the channel inlet (T in) is taken less than that of the walls (T w). The governing equations are numerically solved in the domain by the control volume approach based on the SIMPLE technique. A wide spectrum of numerical simulations has been done over a range of Reynolds number, Nano-fluid volume fraction and the block number. The influence of these parameters is investigated on the local and average Nusselt numbers. From this study, it is concluded that heat transfer in channels can enhance by addition of Nano-particles, and usage of block on hot walls. Simulations show that heat transfer in channels can enhance up to 60% due to the presence of nano-particles and the blocks in channels, but there exist a saturated number of blocks, beyond which, the average Nu do not increase. The present work can provide helpful guidelines to the manufactures of the compact heat exchangers. © 2012 Elsevier Ltd. All rights reserved.


Heidary H.,Mapna Group | Kermani M.J.,Amirkabir University of Technology
International Journal of Hydrogen Energy | Year: 2013

In this paper, a method called "bipolar plate duct indentation" is introduced, in which some partial blocks (indents) are recommended to be placed along the fluid delivery channels being machined in bipolar plates (BPPs) of fuel cells (FCs). The indents are to enhance the over-rib convections and the kinetics of reactions in catalyst layers to improve the cell performance. As an initial step to numerically model this problem, a partially porous channel of BPP of a Direct Methanol FC (DMFC) is taken as the model geometry, and the level of heat exchange enhancement due to channel indentation is examined in this geometry. The performed parametric studies show that channel indentation enhances the heat exchange by 40%; with some minor increases in fluid delivery pumping power. From the analogy between the heat and mass transfer problems in dynamically similar problems, it is believed that the mass exchanges between the core channel and the catalyst layer in FC will enhance the same order as that in the pure heat transfer problem. The present work provides helpful guidelines to the bipolar plate manufactures of low-temperature FCs to considerably alleviate the losses on the side(s) of slow reaction electrodes. Crown Copyright © 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.


Heidary H.,Mapna Group | Kermani M.J.,Amirkabir University of Technology | Kermani M.J.,Head of Energy Conversion Research Laboratory
International Communications in Heat and Mass Transfer | Year: 2010

In this paper heat transfer and flow field in a wavy channel with nano-fluid is numerically studied. The temperature of input fluid (T c) is taken less than that of the wavy horizontal walls (T w). The governing equations are numerically solved in the domain by the control volume approach based on the SIMPLE technique. Copper-water nano-fluid is considered for simulation. A wide spectrum of numerical simulations has been done over a range of Reynolds number, Re H, 5≤Re H≤1500, nano-fluid volume fraction, Φ, 0≤φ≤20% and the wave amplitude, α, 0≤α≤0.3. The effects of these parameters are investigated on the local and average Nusselt numbers and the skin friction coefficient. Simulations show excellent agreement with the literature. From this study, it is concluded that heat transfer in channels can enhance by addition of nano-particles, and usage of wavy horizontal walls. These can enhance the heat transfer by 50%. The present work can provide helpful guidelines to the manufacturers of the compact heat exchangers. © 2010 Elsevier Ltd.


This paper investigates the Granger causality between Electricity consumption per capita (ECC) and real GDP per capita, GDP based on Purchasing Power Parity (PPP) per capita, government spending, and total national savings. The data period is from 1980 to 2010. The results of the Stationary test show that all variables are integrated to an order of one. ECC and real GDP per capita, GDP based on PPP per capita, and government spending are not cointegrated and there is no long run relationship between them and for examining the causality nexus the Vector Auto Regression model (VAR) is applied. On the other hand, ECC and total national savings are cointegrated so the Vector Error Correction Model (VECM) is used for causality analysis. The results of the Granger causality test indicate that GDP based on PPP per capita granger causes the ECC. Since GDP based on PPP is a comparative measure of standard of living, it can be concluded that when the relative standard of living in Iran improves, ECC increases as well. However, PPP figures are estimates rather than hard facts, and should be used with caution. © 2014 IEEE.


Yazdani H.,Mapna Group
2014 5th Conference on Thermal Power Plants, CTPP 2014 | Year: 2015

Pipe equipment widely are used in power plants. Many studies have been devoted to lifetime assessmentof pipeusing different approaches. In the present paper pipe under internal pressure and cyclic bending is studied (bending may be induced by heat). Chaboche's kinematic hardening model is used to simulate tube response in plastic zone. At the plastic zone microscopic defects in the material are developed into macroscopic defects and tube this leads to pipe fracture. This phenomenais simulated with continuum damage mechanics. Evolution of whole-life ratcheting behavior and fatigue damage of pipe are discussed. © 2014 IEEE.


Fazeli Nahrekhalaji A.R.,Mapna Group
Proceedings of the 10th WSEAS International Conference on Robotics, Control and ManufProceedings of the 10th WSEAS International Conference on Robotics, Control and Manufacturing Technology, ROCOM '10 | Year: 2010

Creep feed grinding is widely used in manufacturing suppe-ralloy materials. The main objectives of this research deal with the influences of major process parameters and their interactions of creep feed grinding process such as wheel speed, workpiece speed, grinding depth and dresser speed on the root geometrical dimensions of gas turbine blade by design of experiments using design of experiments (DOE). Experimental results are analyzed by analysis of variance (ANOVA) and empirical model of root geometrical dimensions is developed. It is found that higher wheel speed with slower workpiece speed, lower grinding depth and higher dresser speed, have advantages for obtaining smaller root geometrical dimensions of blade.


Mazhary D.,Mapna Group
International Review on Modelling and Simulations | Year: 2012

Common mode voltage produced by fast switching IGBT inverter may cause problems like bearing damage and resultant current flow through these bearing after break-down of lubrication films. In this paper three level back to back converter is applied in doubly fed induction generator and new space vector modulation (SVM) switching method is proposed which select appropriate voltage vectors among 27 voltage vector of three-level NPC_VSI to achieve three main goals: 1. Decreasing common mode voltage of DFIG. 2. Balancing the neutral point voltage of Dc link. 3. Controlling the active and reactive powers delivered by the wind generator to the electrical network. Mathematical analyses besides simulation using Matlab/Simulink have been carried out to validate the proposed method. © 2012 Praise Worthy Prize S.r.l. - All rights reserved.


Najafi H.R.,Birjand University | Dastyar F.,Mapna Group
International Journal of Electrical Power and Energy Systems | Year: 2013

Increasing of wind power penetration at power systems requires the development of adequate wind turbine models and consequently useful indexes. Among different models, dynamic model has an important role as a fundamental part of wind farms for representing the dynamic behavior of wind farms at different operating conditions. In this paper, a suitable dynamic model is introduced for wind farms with fixed speed wind turbines. This model is proposed by aggregating the individual wind turbines into an equivalent wind turbine model that operates on an equivalent wind farm electric network. Thus, the system under study is modeled by a set of dynamic and algebraic equations. Based on proposed dynamic model a useful novel index is introduced for calculation of the injection power ability of the wind farm that is an urgent issue in the planning and operating of wind farms. This index is named Dynamic Maximum Available Power (DMAP). In addition, sensitivity analysis of DMAP with respect to effective parameters is carried out and the results are shown. © 2012 Elsevier Ltd. All rights reserved.


Patent
Mapna Group | Date: 2012-08-17

A new, more economical design for intentionally frequency mistuned turbine blades for more efficient turbine engines is disclosed. A rotating disk of a turbine engine includes first turbine blades that alternate between second turbine blades. The second turbine blades are thicker than the first turbine blades, within manufacturing tolerances, in sections from about their mean line to their airfoil tip. The first and second turbine blades can be cast using two different molds, resulting in an economical manufacturing method. As such, the natural frequency of the second turbine blades is about 3% less than the natural frequency of the first turbine blades. As a result of the intentional difference in natural frequencies of the two different turbine blades, the rotating disk does not experience flutter instability.

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