Journal of Mechanical Engineering 58 (2012) 1

 

 

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Experiments on a Modular Magnetic Refrigeration Device

Authors - Kurt Engelbrecht ‒ Jesper Buch Jensen ‒ Christian Robert Haffenden Bahl

Abstract

An experimental magnetic refrigeration test device has been built at Risø DTU. The device is designed to be modular, and thus all parts of the device can easily be replaced depending on the experiment. This makes the device highly versatile, with the possibility of performing a wide variety of different experiments. The test device is of the reciprocating type, and the magnetic field source is provided by a permanent Halbach magnet assembly with an average flux density of 1.03 Tesla. This work presents experimental results for flat plate regenerators made of gadolinium and sintered compounds of La(Fe,Co,Si)13 and experimentally investigates the effect of thermal conduction through the regenerator housing walls. Each regenerator was tested over a range of hot reservoir temperatures under no load conditions for a regenerator comprised of gadolinium. The test machine was also tested with two different compositions of La(Fe,Co,Si)13 compounds. Test results are presented for a regenerator made of a single La(Fe,Co,Si)13 material and a two-material regenerator, and the results are compared to the same system using gadolinium.

Keywords - experiment, magnetic refrigeration, gadolinium, regenerator

Paper's information

Strojniški vestnik - Journal of Mechanical Engineering 58(2012)1, 3-8
DOI:10.5545/sv-jme.2010.151

Experiments on a Modular Magnetic Refrigeration Device (.pdf 513KB)

 

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Dynamic 1D Model of an Active Magnetic Regenerator: A Parametric Investigation

Authors - Giulio Tagliafico ‒ Federico Scarpa ‒ Luca Antonio Tagliafico

Abstract

A one dimensional dynamic model of a reciprocating active reciprocating magnetic regenerator (AMR) was developed and a parametric analysis of its behavior at near room temperature conditions was carried out. The investigation is focused on the thermal behavior of the regenerator alone, regardless of the apparatus in which it could work. The parametric investigation aims at evaluating the influence on the AMR performances of the operating frequency and fluid mass flow rate, that is the parameters that can be tuned in a given actual device. The performance parameters analyzed are refrigeration capacity, temperature span, coefficient of performance and second law thermodynamic efficiency. A standard geometry of the AMR was assumed, while the results are given in a non-dimensional form with reference to a conventional operating condition.
Simulations show that the refrigeration capacity is very sensitive to the utilization factor, that causes a 20% refrigeration capacity reduction with a variation of -20% or +10%. The coefficient of performance (COP) is poorly influenced by Φ. Frequency variations induce a linear variation in refrigeration capacity, and a decrease in COP due to friction in the intermediate fluid. The second law thermodynamic efficiency trends show that friction and heat transfer irreversibility dominates at low and high temperature spans, respectively.

Keywords - magnetic refrigeration, active regeneration, modelization, parametric investigation

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 58(2012)1, 9-15
DOI:10.5545/sv-jme.2010.112

Dynamic 1D Model of an Active Magnetic Regenerator: A Parametric Investigation (.pdf 536KB)

 

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Comparison of Thermo-Hydraulic Properties of Heat Regenerators Applicable to Active Magnetic Refrigerators

Authors - Alen Šarlah – Jaka Tušek – Alojz Poredoš

Abstract

This paper describes passive heat regenerators appropriate for active magnetic refrigerators (AMR) and evaluates them from the point of view of thermo-hydraulic characteristics and magnetic properties. A dimensionless numerical model for the determination of the heat transfer coefficient is used together with experimental data for the evaluation of six different regenerator geometries using heat transfer, pressure drop and thermal efficiency as evaluation criteria. An existing numerical model was upgraded with magnetic properties and employed in the computer programme for an active magnetic regenerator in which the magnetic properties are obtained using molecular field approximation. The model was tested for thermodynamic consistency and verified using available experimental data.

Keywords - magnetic refrigeration, active magnetic regenerator, thermo-hydraulic properties

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 58(2012)1, 16-22
DOI: 10.5545/sv-jme.2010.250

Comparison of Thermo-Hydraulic Properties of Heat Regenerators Applicable to Active Magnetic Refrigerators (.pdf 1.7MB)

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Correlation between Incident Angle, Measurement Distance, Object Colour and the Number of Acquired Points at CNC Laser Scanning

Authors - Nikola Vukašinović – Janez Možina – Jože Duhovnik

Abstract

In this paper the results of research about the influences of the incident angle, the measurement distance and object colour and reflectivity on the number of acquired points while using a laser-triangulation scanner on CNC-machines, are presented. The number of points is an essential parameter of a successful 3D surface reconstructio, although it is rarely considered as a subject of research. In this research we identified the scanning parameters to acquire a sufficient number of points for any surface reconstruction. The causes of the results are also identified and could be considered when creating automatic-measurement strategies for CNC-machines. Finally,, the equation for an estimation of the number of acquired points in the optimal area of measuring parameters for the case example is also introduced.

Keywords - point cloud, point density, reverse engineering, laser scanning, laser triangulation

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 58(2012)1, 23-28
DOI:10.5545/sv-jme.2011.053

Correlation between Incident Angle, Measurement Distance, Object Colour and the Number of Acquired Points at CNC Laser Scanning (.pdf 1.0MB)

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Thermal Load of Multidisc Wet Friction Assemblies at Braking Regime

Authors - Zlatomir Živanović ‒ Miodrag Milić

Abstract

The paper presents the results of thermal load investigations of multidisc friction assemblies used as service brakes of a high speed tracked vehicle. By simulating the corresponding braking regimes and measuring the characteristic quantities on an inertial test stand, the relevant parameters of the braking process have been determined. The obtained results have been analyzed and compared to the permitted values of thermal load of the material of the tested friction discs. After a certain number of braking cycles by visual inspection of the brakes the state of the friction elements have been determined. The speed limits for braking the vehicle at higher transmission gear ratios, which may result in a permanent damage of the brakes, have been determined.

Keywords - track vehicle, wet friction assembly, thermal load

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 58(2012)1, 29-36
DOI:10.5545/sv-jme.2009.111

Thermal Load of Multidisc Wet Friction Assemblies at Braking Regime (.pdf 1.0MB)

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Control of Separation Flow over a Wind Turbine Blade with Plasma Actuators

Authors - Erik Potočar ‒ Branko Širok ‒ Marko Hočevar ‒ Matjaž Eberlinc

Abstract

This paper analyses the effects produced by a plasma actuator on flow around a turbine blade profile at Re 7600 and Re 10500. The analysis is undertaken with flow visualizations. The experiments indicate that for low Reynolds number plasma has a significant influence on flow around the blade and that the effects of actuation depend on power added to flow and relative distance between the electrode and the separation line of the actuator.

Keywords - wind turbine blade, plasma actuator, flow control, electrohydrodynamic actuator

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 58(2012)1, 37-45
DOI: 10.5545/sv-jme.2011.016

Control of Separation Flow over a Wind Turbine Blade with Plasma Actuators (.pdf 1.0MB)

 

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Design and Feasibility Analyses of Morphing Airfoil Used to Control Flight Attitude

Authors - Sha Du ‒ Haisong Ang

Abstract
Morphing technology, inspired by bat and bird flight can enable an aircraft to adapt its shape to enhance mission performance and optimize flight attitude controlling efficiency. A morphing airfoil concept is proposed to replace the traditional flap, ailerons, elevator and rudders in order to improve aerodynamic efficiency in this paper. A procedure is used to virtually simulate a morphing wing to perform fast, relatively accurately and efficiently. A set of optimal airfoil shapes obtained are aimed at minimizing the aerodynamic drag character by optimizing morphing configurations at different Cl under the twodimensional steady-flow simulation. These airfoil shapes are used to maneuver flight attitude, minimize drag and take place of traditional control surfaces of different rolling, yawing and pitching moment. Then, the basic relationships between optimized morphing airfoil and the traditional control element on rolling, pitching and yawing moment are simplified to the relationship of Cl. The morphing airfoil shapes at different Cl are represented. The configuration of traditional airfoil and morphing airfoil at different Cl are compared. It is proved that morphing wing can be used to take the place of a traditional wing.

Keywords - morphing wing, deformation institutions, traditional control surface, aerodynamic character, optimal design, compare

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 58(2012)1, 46-55
DOI: 10.5545/sv-jme.2011.189

Design and Feasibility Analyses of Morphing Airfoil Used to Control Flight Attitude (.pdf 704KB)

 

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Dynamic Model for the Stress and Strain State Analysis of a Spur Gear Transmission

Authors - Vera Nikolić ‒ Ćemal Dolićanin ‒ Dejan Dimitrijević

Abstract
A gear transmission dynamic model for the gear dynamic contact loading, dynamic contact stress state and dynamic contact strain state analysis is presented. A dynamic model of the transmission with four degrees of freedom is used. The transmission is analyzed using nonlinear finite elements contact formulation, using a novel software modules developed by the author used for the generalized analysis of the geared transmissions in the environment of the open source finite elements framework CODE-ASTER/SALOME.

Keywords - stress and strain state analysis, tensor invariants, finite element method, geared transmissions

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 58(2012)1, 56-67
DOI: 10.5545/sv-jme.2009.128

Dynamic Model for the Stress and Strain State Analysis of a Spur Gear Transmission (.pdf 3.6MB)

 

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