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Volume 16, Issue 4, 2009
Transaction on Mechanical Engineering


Similarity Solution in the Study of Flow and Heat Transfer Between Two Rotating Spheres with Constant Angular Velocities
 
        A. Baradaran Rahimi (Professor)
  • A. Jabari Moghadam [MSc.]

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Abstract:
The similarity solution of the steady-state motion and heat transfer of a viscous incompressible uid contained between two concentric spheres, maintained at di erent temperatures and rotating about a common axis with di erent constant angular velocities, is considered. The resulting ow pattern, temperature distribution and heat transfer characteristics are presented for various cases. Aside from the energy equation, the same results as previous works are obtained for Navier-Stokes equations, but with less computational complexities.

Keywords:
Similarity solution

    Steady-state ow and heat transfer
      Concentric rotating spheres; Constant angular velocities.


Effect of Di erent Geometries in Simulation of 3D Viscous Flow in Francis Turbine Runners
 
        B. Firoozabadi (PhD.)
  • R. Dadfar [MSc.]
  • A.R.P. Pirali [MSc.]
  • G. Ahmadi [Professor]

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Abstract:
Overall turbine analysis requires large CPU time and computer memory, even in the present days. As a result, choosing an appropriate computational domain accompanied by a suitable boundary condition can dramatically reduce the time cost of computations. This work compares di erent geometries for numerical investigation of the 3D ow in the runner of a Francis turbine, and presents an optimum geometry with least computational e ort and desirable numerical accuracy. The numerical results are validated with a GAMM Francis Turbine runner, which was used as a test case (GAMM workshop on 3D computation of incompressible internal ows, 1989) in which the geometry and detailed best eciency measurements were publically accessible. In this simulation, the ow is assumed to be steady and the inlet boundary condition is prescribed using experimental data. The e ect of turbulence is considered by the k 􀀀" model. The present investigation demonstrates that consideration of 2-blade geometry with periodic boundary conditions is the best choice of computational domain. By 1-blade geometry, convergence of the numerical simulation is not appropriate, whereas 13-blade geometry leads to a coarse grid that can increase inaccuracy and computational cost. Finally, this paper presents a qualitative survey to forecast cavitation region inception which correlates satisfactorily with experimental observations.

Keywords:
Numerical simulation

    Francis turbine runner
      GAMM
        Viscous ow analysis.


Modeling of Twin-Entry Radial Turbine Performance Characteristics Based on Experimental Investigation Under Full and Partial Admission Conditions
 
        A. Hajilouy-Benisi (PhD.)
  • M. Rad [Professor]
  • M. R. Shahhosseini [MSc.]

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Abstract:
In this paper, the performance of a turbocharger twin-entry radial in ow turbine is investigated analytically and experimentally under steady state, full and partial admission conditions. In this modeling, the mass ow rate, pressure ratio and eciency of the turbine are assumed unknown. The turbine geometry and the inlet total pressure and temperature are known, hence, the turbine performance characteristics can be obtained. In the turbocharger laboratory, performance characteristics of the turbine are determined, measuring the main parameters for various operating conditions. Comparing the model and experimental results shows good agreement. Also, considering the e ect of test parameters on performance uncertainty, it shows that the pressure ratio has more in uence. Finally, the uncertainty of eciency decreases as the pressure ratio increases.

Keywords:
Radial in ow turbine

    Full and partial admission conditions
      Modeling
        Turbocharger.


Experimental Analysis of Cavitaion E ects on Drag Force and Back Pressure of Circular Cylinder with Free Turbulence
 
        I. Jafari Gavzan (MSc.)

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Abstract:
The characteristics of a cavitation water tunnel test setup and the experiments of cavitation around a circular cylinder with free stream turbulence are presented in this paper. The Reynolds number of ow is limited in the range of 1:26105 to 3105 and the far upstream ow has free turbulence. Drag force, back pressure, location of cavitation inception, length of cavity and appearance of cavitation are measured or observed and their results are presented here. It was found that the cavitation e ects on the boundary layer and separation of ow over the cylinder and drag force become minimum at the cavitation number of 1.94. The cavitation inception occurs in the sub-layer and at an angle of about 105, with respect to ow direction (inception location depends on Reynolds number). The back pressure coecient becomes maximum at the cavitation number of 1.94.

Keywords:
Drag force

    Cavitation tunnel
      Free turbulence.


Some Experimental Studies on the Performance of a Rigid Wing Land Yacht Model in Comparison with VPP
 
        M. Khayyat (PhD.)
  • M. Rad [Professor]

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Abstract:
It is important to understand the ow characteristics and performance of wings for designers who want to have an ecient thrust in a land yacht. In this paper, a comparison of aerodynamic forces obtained by testing the land yacht model in a wind tunnel and by the Velocity Prediction Program (VPP) is presented. The wind tunnel testing of a land yacht is an e ective design tool, but at present it is mainly used for VPP validation, which allows for a faster and more ecient design process. The rigid wing land yacht model, which is a radio controlled model, is tested in the national open jet wind tunnel of the Malek Ashtar University of Technology in Iran. The wing data, which is obtained from the wind tunnel, is used in the VPP as input data and then the parasitic drag and aerodynamic forces that are measured in the wind tunnel are compared to those in the VPP. Comparison of the results shows a reasonably good agreement between experimental data and VPP data. So the latter can be used as an e ective tool in the design of a land yacht.

Keywords:
Land yacht

    Wind tunnel
      Aerodynamic
        Wing.


E ect of Payload Variation on the Residual Vibration of Flexible Manipulators at the End of a Given Path
 
        M. H. Korayem (Professor)
  • A. Heidari [MSc.]
  • A. Nikoobin [PhD.]

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Abstract:
In rest-to-rest motion, the gripper of the exible manipulators vibrates not only in the duration of the tracking but also after reaching the goal point. This vibration, which is called residual vibration, continues with a speci c amplitude and frequency after reaching the goal point. In this paper, the e ect of a carried payload on the residual vibration magnitude is investigated. The nite element method is employed for modeling and deriving the dynamic equations of the manipulator with exible links and joints. Compared with previous works, the assumptions of low frequency and small amplitude of vibration about the nal con guration are released and all terms in the dynamic equations are taken into account. Some simulations for a two-link exible manipulator along two given paths are then performed for di erent payloads at the end-e ector. In the rst state, a polynomial-Fourier function is considered for joint motion and then a linear path for gripper motion. Finally, a straightforward approach for predicting the residual vibration amplitude, in terms of the payload, is proposed.

Keywords:
Manipulator

    Flexible link and joint
      Residual vibration
        Finite element method.


Coordination of Process Integration and Exergoeconomic Methodology for Analysis and Optimization of a Pulp and Paper Mill
 
        A. A. Mozafari (PhD.)
  • M. Fani [MSc.]
  • B. Farhanieh [Professor]

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Abstract:
By simultaneously applying pinch technology and the exergoeconomic method to a complex process system, bene cial and energy-ecient measures are identi ed. The \three-link-model" exergoeconomic methodology optimizes the design and operability of a system. In this work, contrary to traditional exergoeconomic methods, a reversed method is used. The approach proposed for the optimization of such a complex system is to iteratively optimize subsystems. Since the reversed exergoeconomic method is used, assumptions considered by Tsatsaronis (based on four assumptions for calculating the costoptimal exergetic eciency and relative cost di erence) are not applicable and new assumptions are to be considered. Unlike traditional exergoeconomic methods, the product exergetic speci c cost is considered to be known and the objective will be to maximize the exergetic cost of the fuel. Heat ows costs are calculated with the assistance of a Pinch analysis. The strength of the combination of a Pinch analysis and the exergoeconomic method is elucidated in a case study applied to the Mazandaran wood and paper industry. Replacement of the pressure valve and Direct Cyclone Contact Evaporation (DCCE) is proposed, while by selection of the optimum decision variable and applying Pinch technology simultaneously, the recoverable black liquor could be increased by 7% and energy consumption decreased by 12%.

Keywords:
Pinch technology

    Exergoeconomic methodology
      Process system
        Optimization
          Pulp and paper.


Numerical Investigation of Fluid Flow and Heat Transfer Characteristics in Parallel Flow Single Layer Microchannels
 
        M.H. Saidi (PhD.)
  • O. Asgari [PhD.]

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Abstract:
Heat generation from Very Large-Scale Integrated (VLSI) circuits increases with the development of high-density integrated circuit technology. One of the ecient techniques is liquid cooling by using a microchannel heat sink. Numerical simulations on the microchannel heat sink in the literature are mainly two dimensional. The purpose of the present study is to develop a three-dimensional procedure to investigate ow and conjugate heat transfer in the microchannel heat sink for electronic packaging applications. A nite volume numerical code with a multigrid technique, based on an additive correction multigrid (AC-MG) scheme, which is a high-performance solver, is developed to solve the steady incompressible laminar Navier-Stokes (N-S) equations over a colocated Cartesian grid arrangement. The results show that the thermophysical properties of the liquid can essentially in uence both the ow and heat transfer in the microchannel heat sink. Comparison of the numerical results with other published numerical results and experimental data, available in the literature for Reynolds numbers less than 200, indicates that the assumption of hydrodynamically fully developed laminar ow is valid. The accuracy of the prediction has been veri ed by comparing the results obtained here with the numerical and analytical results from the open literature which showed a good agreement. The detailed temperature and heat ux distributions, as well as the average and bulk heat transfer characteristics, are reported and discussed. The analysis provides a unique fundamental insight into the complex heat ow pattern established in the channel due to combined convection-conduction e ects in the three-dimensional setting.

Keywords:
Microchannel

    Finite volume numerical simulation
      Multigrid technique
        Colocated grid arrangement
          Heat transfer and uid ow
            Electronic cooling.