2024-03-29T10:48:43Z
https://www.ije.ir/?_action=export&rf=summon&issue=11397
International Journal of Engineering
IJE
1025-2495
1025-2495
2003
16
3
Full Analysis of Low Finned Tube Heat Exchangers
M. R.
Jafari Nasr
A. T.
Zoghi
In this paper, first the governing parameters characterizing low-finned tubes are reviewed. Second, the more important of the available performance correlations are compared with the available experimental data. The most reliable one can be employed to develop a pressure drop relationship, which has already been used in an algorithm for exchanger sizing. Also a means for the identification of advantages of low-finned tube heat exchangers over plain tube units has been developed. It has been recognized that for low-finned tube units there are some potential benefits to place certain liquids, particularly with high viscosities, in the shell side of heat exchangers rather than the tube side. These benefits can be obtained in both reduction of surface area and the number of shells required for a given duty. They result in heat exchangers, which are more compact and are also easier to construct. The performance evaluation of low-finned units, in terms of area benefits is notdiscussed in this paper. However, the results of this study will complete the author’s investigation for low-finned tubes heat exchangers.
heat exchanger
Low
Finned
Performance Correlations
heat transfer
Shell and Tube
Heat Transfer Coefficient
friction factor
2003
09
01
217
232
https://www.ije.ir/article_71451_2049deff984406ef34ecababa6ad48b9.pdf
International Journal of Engineering
IJE
1025-2495
1025-2495
2003
16
3
A Novel Fuzzy and Artificial Neural Network Representation of Overcurrent Relay Characteristics
M.
Al-Dabbagh Hossein
G.
Heidari
H.
Askarian Abyaneh
H.
K. Karegar
Accurate models of Overcurrent (OC) with inverse time relay characteristics play an important role for coordination of power system protection schemes. This paper proposes a new method for modeling OC relays curves. The model is based on fuzzy logic and artificial neural networks. The feed forward multilayer perceptron neural network is used to calculate operating times of OC relays for various Time Dial Settings (TDS) or Time Multiplier Settings (TMS). The new model is more accurate than traditional models. The model is validated by comparing the results obtained from the new method with linear and nonlinear Sachdev models as applied for various types of overcurrent relays.
Power system
Protection Systems
Overcurrent Relay
2003
09
01
233
246
https://www.ije.ir/article_71452_b6bb29760dceba8e4471984e21e2245c.pdf
International Journal of Engineering
IJE
1025-2495
1025-2495
2003
16
3
Quasi-Static Theory for Uniaxial Chiral Omega Media
Jalil
Rashed-Mohassel
R.
Saraei
The problem of unbounded uniaxial chiral omega media in the presence of both static electric and magnetic point charges is investigated. For this purpose scalar electric and magnetic potentials in these media are introduced. Using these potentials, the corresponding electric and magnetic fields are determined. The similar problem of static electric and magnetic current sources with the goal of finding the electromagnetic fields is carried out. It is observed that either static electric or magnetic point charges produce both electric and magnetic fields.
Anisotropy
Uniaxial
Chiral Omega
Vector Potentials
Chiral Media
2003
09
01
233
246
https://www.ije.ir/article_71453_b5b6e3df680af94ccbeeefa1130656af.pdf
International Journal of Engineering
IJE
1025-2495
1025-2495
2003
16
3
A Novel Stand-Alone Single-Phase Induction Generator Using a Three-Phase Machine and a Single-Phase PWM Inverter
J.
Soltani
N. R.
Abjadi
A new type of single-phase stand-alone induction generator using a three-phase induction machine and a single-phase voltage-source PWM inverter is introduced. The generator scheme is capable of producing constant load frequency with a very well regulated output voltage. A small lead acid battery and a single-phase full diode-bridge rectifier are used to feed the inverter. The inverter feeds one of the stator phases. During the generator voltage build up, the inverter supplies the battery first and after a while a diode-bridge rectifier, which is fed by the generator, replaces it. The system steady state and dynamic equations are derived and are solved to obtain the performance characteristics of the generator scheme. A digital simulation study is carried out for a 2.2 KW threephase induction machine. The simulated results obtained confirm that this generator can achieve an output power of about 0.6 pu.
Generation of Electrical Energy
Induction motors
Modeling
Converter Control
2003
09
01
259
268
https://www.ije.ir/article_71458_1a6b06b52e0c3cc233e3df9e9079e242.pdf
International Journal of Engineering
IJE
1025-2495
1025-2495
2003
16
3
Calculation of Complicated Flows, Using First and Second-Order Schemes (RESEARCH NOTE)
A. R.
Azimian
M.
Goodarzi
The first-order schemes used for discretisation of the convective terms are straightforward and easy to use, with the drawback of introducing numerical diffusion. Application of the secondorder schemes, such as QUICK scheme, is a treatment to reduce the numerical diffusion, but increasing convergence oscillation is unavoidable. The technique used in this study is a compromise between the above-mentioned problem, i.e. reducing the numerical diffusion and increasing the stability of the solution. This double folded task is achieved by introducing a modified second-order hybrid scheme. In addition to that by means of this formulation it is possible to show that the coefficients of the discretised equation at all neighboring points are positive and the value of a coefficient at a pole point is equal to the sum of its neighboring points, which means the two basic conditions defined by Patankar are satisfied. Therefore, this scheme has the benefits of the both first and second order schemes together. Results obtained by this scheme to predict the complicated flow regimes were promising and agreed well with experimental data.
Second
order Hybrid Scheme
Stability
boundedness
Numerical Diffusion
Laminar Flows
2003
09
01
269
278
https://www.ije.ir/article_71460_1fb3088bb425ac41c7d59bfff473c3dd.pdf
International Journal of Engineering
IJE
1025-2495
1025-2495
2003
16
3
Maximum Allowable Load On Wheeled Mobile Manipulators (RESEARCH NOTE)
M. H.
Korayem
H.
Ghariblu
This paper develops a computational technique for finding the maximum allowable load of mobile manipulators for a given trajectory. The maximum allowable loads which can be achieved by a mobile manipulator during a given trajectory are limited by the number of factors; probably the dynamic properties of mobile base and mounted manipulator, their actuator limitations and additional constraints applied to resolving the redundancy are the most important factors. To resolve extra D.O.F introduced by the base mobility, additional constraint functions are proposed directly in the task space of mobile manipulator. Finally, in two numerical examples involving a two-link planar manipulator mounted on a differentially driven mobile base, application of the method to determining maximum allowable load is verified. The simulation results demonstrates the maximum allowable load on a desired trajectory has not a unique value and directly depends on the additional constraint functions which applies to resolve the motion redundancy.
Given Trajectory
Load Carrying Capacity
Base Replacement
Manipulator
2003
09
01
279
292
https://www.ije.ir/article_71462_74db67c4269f8caad3e3a79deec229a5.pdf
International Journal of Engineering
IJE
1025-2495
1025-2495
2003
16
3
Modeling of the Combustion Oscillations and Soot Formation in Aerovalved Pulse Combustors
M.
Moghiman
B.
Rezapoor
This paper describes the modifications and evolution of a thermal pulse combustionmodel for predicting the combustion oscillations of an aerovalved 250 kW pulse combustorincorporating a soot formation-combustion model. Validation of the model is carried out from theexperimental data of an aerovalved Helmholtz type pulse combustor, where a sinusoidal air inlet massflow coupled with pressure oscillations within the combustor is needed to model the instabilities ofcombustion oscillations correctly. The model is used to investigate the influence of different boundaryconditions on combustion oscillations and soot production in the pulse combustor. The results identifythe operating conditions for which continuous oscillations, steady flames and flame extinction occur.The results also show that for ambient temperatures of inlet air (lower than 325 K) with walltemperatures lower than 1100 K soot emission from propane firing pulse combustors is negligible.
Pulse Combustion
Aerovalved Pulse Combustor
Soot Formation
2003
09
01
293
306
https://www.ije.ir/article_71464_bdf07f3f48d24212e787795b1ce5cb22.pdf
International Journal of Engineering
IJE
1025-2495
1025-2495
2003
16
3
Aerodynamic Design Optimization Using Genetic Algorithm (RESEARCH NOTE)
A. R.
Pishevar
S.
Ziaei-Rad
An efficient formulation for the robust shape optimization of aerodynamic objects is introduced in this paper. The formulation has three essential features. First, an Euler solver based on a second-order Godunov scheme is used for the flow calculations. Second, a genetic algorithm with binary number encoding is implemented for the optimization procedure. The third ingredient of the procedure is the use of previous flow that is closest in terms of geometric parameters to the new shape as an initial condition for the new function evaluation. This makes the solution towards the final value progressively faster and reduces the computer time for the convergence of the algorithm. The algorithm is used to optimize two different problems, a simple bump problem, and a two-dimensional transonic airfoil problem using an Euler solver equation. The results indicate that the GA/flow algorithm is robust and can optimize a wide range of problems with a minimum implementation effort.
Aerodynamic Design Optimization
Genetic Algorithm
Euler Solver
Godunov Scheme
2003
09
01
307
318
https://www.ije.ir/article_71465_b2eb53652f7e2649b33f021531d91f00.pdf