Experimental analysis of harmonic distortions in the excitation currents of double-excited three-phase transformers

This paper shows the results of experimental investigations of three-phase banks composed of single-phase transformers and three-phase three-limb core transformers under simultaneous alternating and direct current excitations, for several winding connections. Harmonic analysis of excitation currents for different de saturation levels is performed.

Numerical and experimental analysis of natural convection in a cavity heated from below

In this work, an analysis of the natural convection flow caused by heat sources dissipating energy at a constant rate simulating electronic components mounted at the bottom surface of a cavity symmetrically cooled from the sides and insulated at the top is performed. This problem was studied numerically and experimentally for several aspect ratios (height/width), for different levels of dissipation in the sources, and for different side wall temperatures. Temperature and velocity fields were determined as well as the temperature variation along the surface where the sources are mounted and the average Nusselt number in the source surfaces. Numerical and experimental results were found to agree.

Experimental analysis of heat recoveries with heat pipes operating in low inclination angle

Heat recovery devices are important in the optimization of thermal systems, since they can be used to reduce thermal losses to the environment. The use of heat pipes in these types of equipment can provide heat recoveries of higher efficiency, since both fluid flows are external and there are less contamination risks between the hot and cold fluids. The objective of this work is to study a heat recovery unit constructed with heat pipes and mainly, to analyze the influence of the inclination of the heat pipes on the performance of the equipment. For this analysis, a heat recovery unit was constructed which possesses 48 finned heat pipes in triangular geometry, the evaporator and condenser being of the same length. This unit was tested in an air-air system simulating a heat recovery process in which heat was supplied to the hot fluid by electrical resistances. The results have shown that there exists an inclination at which the system has a better performance, but for higher inclinations there is no significant increase of the efficiency of the system. This paper also presents the influence of inclination of heat pipes on effectiveness and NTU parameters which are important in heat exchanger design.

Numerical and experimental analysis of natural convection in a cavity with flush mounted heat sources on a side wall

This work considers a problem of interest in several technological applications such as the thermal control of electronic equipment. It is also important to study the heat transfer performance of these components under off-normal conditions, such as during failure of cooling fans. The effect of natural convection on the flow and heat transfer in a cavity with two flush mounted heat sources on the left vertical wall, simulating electronic components, is studied numerically and experimentally. The influence of the power distribution, spacing between the heat sources and cavity aspect ratio have been investigated. An analysis of the average Nusselt number of the two heat sources was performed to investigate the behavior of the heat transfer coefficients. The results obtained numerically and experimentally, after an error analysis, showed a good agreement.

A theoretical and experimental analysis of cold-formed steel shapes subjected to bending - Channel and simple lipped channel

Cold-formed steel shapes have been widely employed in steel construction, where they frequently offer a lower cost solution than do traditional laminated shapes. A classic application of cold-formed steel shapes is purlins in the roof panel of industrial buildings, connected to the roof panel by means of screws. The combined effect of these two elements has been the subject of investigations in some countries. Design criteria were included in the AISI Code in 1991 and 1996. This paper presents and discusses the results obtained from bending tests carried out on shapes commonly used in Brazil, i.e., the channel and the simple lipped channel, Tests were carried out on double shapes with 4.5 and 6.0 meter spans, which were subjected to concentrated loads and braced against each other on the supports and at intermediary points in three different load situations. The panel shape was also analyzed experimentally, simulating the action of wind by means of a vacuum box designed specifically for this purpose. The test results were then compared to those obtained through the theoretical analysis, enabling us to extract important information upon which to base proposed design criteria for the new Brazilian code.

Experimental analysis of heat transfer in packed beds with air flow

Heat-transfer studies were carried out in a packed bed of glass beads, cooled by the wall, through which air percolated. Tube-to-particle diameter ratios (D/dp) ranged from 1.8 to 55, while the air mass flux ranged from 0.204 to 2.422 kg/m2·s. The outlet bed temperature (TL) was measured by a brass ring-shaped sensor and by aligned thermocouples. The resulting radial temperature profiles differed statistically. Angular temperature fluctuations were observed through measurements made at 72 angular positions. These fluctuations do not follow a normal distribution around the mean for low ratios D/dp. The presence of a restraining screen, as well as the increasing distance between the temperature measuring device and the bed surface, distorts TL. The radial temperature profile at the bed entrance (T0) was measured by a ring-shaped sensor, and T 0 showed to be a function of the radial position, the particle diameter, and the fluid flow rate.

Theoretical model and experimental analysis of glulam beam reinforced with FRP

This work present a study of glulam beams reinforced with FRP. It was developed a theoretical model that calculates strength and stiffness of the beams. The model allows for the calculation of the bending moment, the hypothetical distribution of linear strains along the height of the beam, and considers the wood has a linear elastic fragile behavior in tension parallel to the fibers and bilinear in compression parallel to the fibers, initially elastic and subsequently inelastic, with a negative decline in the stress-strain diagram. The stiffness was calculated by the transformed section method. Twelve non-reinforced and fiberglass reinforced glulam beams were evaluated experimentally to validate the proposed theoretical model. The results obtained indicate good congruence between the experimental and theoretical values.

Experimental analysis of the effect of the structure area on the PZT-based SHM systems

The structural health monitoring (SHM) systems based on electromechanical (E/M) impedance technique have been widely investigated. Although many studies indicate the reliability of this technique, some practical considerations still have to be considered in real applications. This paper presents an experimental analysis of the effect of the structure area on the system's performance. The results indicate that the sensitivity of the system to detect damage decreases significantly when the host structure has large cross-section area. Copyright © 2009 by ASME.

Experimental analysis of an electromagnetic zero-sequence suppressor

The intent of this paper is to present contributions focused on the analysis and development of harmonic attenuator devices. Among these, highlights here the so-called electromagnetic zero-sequence suppressor. This arrangement consists of a filter and a blocker, both electromagnetic, whose combined operation provides paths for low and high impedance, respectively, which can be conveniently adjusted to the desired performance. In this context, here are present results related to experimental studies that show the behavior of the equipment in front of different operating conditions. The tests were performed on a low-power prototype (1kVA/220V) and the analysis results show the main motivator aspects for the use of these devices. © 2012 IEEE.

Experimental analysis of reinforced concrete block masonry spandrels using pre-fabricated planar trussed bars

Masonry spandrels together with shear walls are structural components of a masonry building subjected to lateral loads. Shear walls are the main components of this structural system, even if masonry spandrels are the elements that ensure the connection of shear wall panels and the distribution of stresses through the masonry piers. The use of prefabricated truss type bars in the transversal and longitudinal directions is usually considered a challenge, even if the simplicity of the applications suggested here alleviate some of the possible difficulties. This paper focus on the experimental behavior of masonry spandrels reinforced with prefabricated trusses, considering different possibilities for the arrangement of reinforcement and blocks. Reinforced spandrels with three and two hollow cell concrete blocks and with different reinforcement ratios have been built and tested using a four and three point loading test configuration. Horizontal bed joint reinforcement increased the capacity of deformation as well as the ultimate load, leading to ductile responses. Vertical reinforcement increased the shear strength of the masonry spandrels and its distribution play a central role on the shear behavior. (C) 2011 Elsevier Ltd. All rights reserved.

Experimental analysis of fiber reinforced cementitious matrix (FRCM) confined masonry columns

The increasing use of Fiber Reinforced methods for strengthening existing brick masonry walls and columns, especially for the rehabilitation of historical buildings, has generated considerable research interest in understanding the failure mechanism in such systems. This dissertation is aimed to provide a basic understanding of the behavior of solid brick masonry walls unwrapped and wrapped with Fiber Reinforced Cementitious Matrix Composites. This is a new type of composite material, commonly known as FRCM, featuring a cementitious inorganic matrix (binder) instead of the more common epoxy one. The influence of the FRCM-reinforcement on the load-carrying capacity and strain distribution during compression test will be investigated using a full-field optical technique known as Digital Image Correlation. Compression test were carried on 6 clay bricks columns and on 7 clay brick walls in three different configuration, casted using bricks scaled respect the first one with a ratio 1:2, in order to determinate the effects of FRCM reinforcement. The goal of the experimental program is to understand how the behavior of brick masonry will be improved by the FRCM-wrapping. The results indicate that there is an arching action zone represented in the form of a parabola with a varying shape according to the used configuration. The area under the parabolas is considered as ineffectively confined. The effectively confined area is assumed to occur within the region where the arching action had been fully developed.

Experimental analysis of coaxial jets: instability, flow and mixing characterization

The velocity and mixing field of two turbulent jets configurations have been experimentally characterized by means of cold- and hot-wire anemometry in order to investigate the effects of the initial conditions on the flow development. In particular, experiments have been focused on the effect of the separation wall between the two streams on the flow field. The results of the experiments have pointed out that the wake behind a thick wall separating wall has a strong influence on the flow field evolution. For instance, for nearly unitary velocity ratios, a clear vortex shedding from the wall is observable. This phenomenon enhances the mixing between the inner and outer shear layer. This enhancement in the fluctuating activity is a consequence of a local absolute instability of the flow which, for a small range of velocity ratios, behaves as an hydrodynamic oscillator with no sensibility to external perturbations. It has been suggested indeed that this absolute instability can be used as a passive method to control the flow evolution. Finally, acoustic excitation has been applied to the near field in order to verify whether or not the observed vortex shedding behind the separating wall is due to a global oscillating mode as predicted by the theory. A new scaling relationship has been also proposed to determine the preferred frequency for nearly unitary velocity ratios. The proposed law takes into account both the Reynolds number and the velocity ratio dependence of this frequency and, therefore, improves all the previously proposed relationships.

Experimental analysis of a separation control device based on plasma technology

In this thesis effects of plasma actuators based on Dielectric Barrier Discharge (DBD) technology over a NACA 0015 bidimensional airfoil have been analyzed in an experimental way, at low Reynolds number. Work developed on thesis has been carried on in partnership with the Department of Electrical Engineering of Università di Bologna, inside Wind Tunnel of the Applied Aerodynamic Laboratory of Aerospace Engineering faculty. In order to verify the effectiveness of these active control devices, the analysis has shown how actuators succeed in prevent boundary layer separation only in certain conditions af angle of attack and Reynolds numbers. Moreover, in this thesis actuators’ chordwise position effect has been also analyzed, together with the influence of steady and unsteady operations.

Theoretical and Experimental Analysis of micro-CHP Energy Systems

In the framework of the micro-CHP (Combined Heat and Power) energy systems and the Distributed Generation (GD) concept, an Integrated Energy System (IES) able to meet the energy and thermal requirements of specific users, using different types of fuel to feed several micro-CHP energy sources, with the integration of electric generators of renewable energy sources (RES), electrical and thermal storage systems and the control system was conceived and built. A 5 kWel Polymer Electrolyte Membrane Fuel Cell (PEMFC) has been studied. Using experimental data obtained from various measurement campaign, the electrical and CHP PEMFC system performance have been determinate. The analysis of the effect of the water management of the anodic exhaust at variable FC loads has been carried out, and the purge process programming logic was optimized, leading also to the determination of the optimal flooding times by varying the AC FC power delivered by the cell. Furthermore, the degradation mechanisms of the PEMFC system, in particular due to the flooding of the anodic side, have been assessed using an algorithm that considers the FC like a black box, and it is able to determine the amount of not-reacted H2 and, therefore, the causes which produce that. Using experimental data that cover a two-year time span, the ageing suffered by the FC system has been tested and analyzed.