Experimental Test Setup Research Articles

Establishment of Intrinsic Permeability of Coarse Open-Graded Materials: Review and Analysis of Existing Data from Natural Air Convection Tests

This paper presents a review and analysis of large-scale air convection tests and the establishment of intrinsic permeability in coarse open-graded materials. Natural air convection can make a significant contribution to heat transfer during cooling periods. In seasonally freezing environments this can result in excessive frost penetration and subsequent frost-related problems. Intrinsic permeability largely defines the onset of convective heat transfer in granular materials. Conventional methods for measuring intrinsic permeability cannot be applied to very coarse materials. Large-scale laboratory experiments on natural air convection can serve as an alternative method for determining this crucial parameter. This paper gives an overview of four different experimental test setups for measuring natural air convection, all differing in physical shape, boundary conditions and heat flux/temperature measurement devices. Comparison between these is difficult because the air convection pattern can differ and in some cases the shape and number of convection cells cannot be validated. Most of the studies available in the literature use theoretical equations to approximate intrinsic permeability. A method based on the analytical Nu-Ra number relationship is employed to establish the values of intrinsic permeability. Tests that provide enough data to enable the use of the Nu-Ra relationship are very limited. The overall results show a reasonable correlation between experiment-based intrinsic permeability and theoretical approximation. However, several issues must be addressed: first, differences may exist between the intrinsic permeability of natural and of crushed materials due to the shape effect. Second, the method used is in theory valid only for two-dimensional air convection within a square enclosure heated from below. Yet the results show that this method could be extended to other conditions with a certain degree of confidence. Third, a good estimate of intrinsic permeability is possible only with accurate experimental measurement.

Thermal performance augmentation in latent heat storage unit using spiral fin: An experimental analysis

Abstract A comprehensive experimental analysis is reported to evaluate the heat transfer augmentation in vertical shell and tube Latent Heat Storage Unit (LHSU) with installation of spiral fins. Influence of spiral fins on charging and discharging rate is evaluated. PCM and HTF used in the existing experimental test setup is stearic acid and water respectively. To obtain accurate PCM temperature in radial, angular and axial direction, total 45 temperature sensors are installed in the annulus of the shell. Simulations have been also performed to track the interface of solid-liquid during charging and discharging. Experimental findings infer that installation of the spiral fins improve melting and solidification time due to the transport of thermal energy in the middle and lower axial planes, which expedites the energy storage/retrieval process. Installation of spiral fins lead to a reduction in the charging and discharging time by 41.48% and 22.16% respectively. The total cycle (charging + discharging) rate is reduced by 31.82% due to installation of spiral fins. Simulation results also depict significant reduction in charging and discharging time.

On the impact of geomagnetically induced currents in driving series capacitor compensated power systems to ferroresonance

Solar storms cause disturbances in the Earth's magnetic field, which results in quasi-DC geomagnetically induced currents (GICs) flow in the grounded sections of the system. The flow of GICs in the power system may drive the power transformers to the saturation region. Moreover, HV transmission lines are often compensated by series capacitor units for enhancing the capability of power transmission lines. The proximity of power transformers and series capacitor compensation units during GICs may enhance the chance of the ferroresonance phenomenon in power transformers. The occurrence of ferroresonance produces extensively high voltages/currents in system apparatus, including transformers which can consequently result in severe damages. This paper puts forward the analysis of the power transformer ferroresonance phenomenon due to GICs in series capacitor compensated networks. This issue has been addressed through mathematical analysis and verified by an experimental test setup, in order to demonstrate the effect of GIC on ferroresonance. Through the employment of an example test system in EMTP-RV environment, impacts of different involving parameters such as system loading, compensation level, and substations' grounding resistances are evaluated on the occurrence of ferroresonance due to GICs. The results indicate that for series capacitor compensated power grids, GICs can profoundly enhance the vulnerability of power transformers to the occurrence of ferroresonance phenomena.

A comparison of diurnal variation of pavement albedo between vertical and horizontal surfaces under tropical climatic condition of Thailand

Albedo is an important indicator of radiation reflectance of pavement surfaces for the building envelope and on the ground level, and their resultant impacts on human comfort and the urban environment in outdoor spaces. Usually, albedo is generally accepted only for horizontal surfaces. This study developed an experimental test set-up for the albedo measurement system with pyranometers and automatic meteorological data acquisition system, which used it to conduct field measurements of albedo on horizontal and vertical surfaces of the used concrete block. The results show that albedo measured on a horizontal surface is not proportional to irradiance on a vertical surface. The albedo value between the two surfaces depend upon time of day, and the horizontal surface also received significantly more incident solar radiation than the vertical surface during all but the central hours of the day, while at reflected solar radiation on vertical irradiances were less than the horizontal. These results can help reduce the uncertainty in understanding and evaluating the thermal behaviour of the building and environmental impacts of pavement surfaces with different albedos in the outdoor urban space.

Behaviour of headed studs subjected to cyclic shear in steel frames with reinforced concrete infill walls

Headed studs are often used to facilitate composite actions between steel and concrete structures. In steel building structures, reinforced concrete walls are commonly used to ensure composite action to stiffen steel frames as a lateral resistance system against horizontal loads, such as earthquakes or wind. Such walls need to be anchored to the steel frame by headed studs, and these must be able to withstand shear and tension forces, as well as the interaction between these two. To design such anchors in concrete walls, it is necessary to describe experimentally their behaviour under monotonic and cyclic shear forces given that edge conditions and reinforcing details influence stud stiffness and strength.As very few experimental studies have examined headed studs subjected to monotonic or cyclic shear with usual boundary effects in steel frames with reinforced infill walls, a new experimental test setup and test results are presented herein. Four tests on headed studs were carried out to describe the behaviour of headed studs under monotonic and cyclic shear loading, as well as to validate the new test setup.This research shows that the behaviour of studs installed in infill walls without group effects are conservatively predicted by EC-4 and Makino’s formula under monotonic shear loading. Furthermore, a reduction factor of 0.70 is recommended to design studs subjected to cyclic shear forces.

Comparison between Digital Tone-Mapping Operators and a Focal-Plane Pixel-Parallel Circuit

In a previous work, we proposed a color extension of an existing focal-plane tone-mapping operator (FPTMO) and introduced circuit modifications that led to smaller sensing array area and simpler off-chip white-balance operations. The proposed FPTMO chip was fabricated and its experimental test setup is under development. In the present work, we systematically compare the previously proposed FPTMOs with conventional digital tone-mapping operators (DTMOs), both in terms of overall image quality and execution time. To assess the image quality, we use the Tone-Mapped image Quality Index (TMQI) metric, the Blind Tone-Mapped Quality Index (BTMQI) metric, and an image colorfulness metric. By statistically comparing the results given by both metrics, we verify that the proposed FPTMOs achieve results similar to those obtained with DTMOs, occasionally outperforming them. To compare the tone-mapping operators execution times, we perform a detailed complexity analysis. Results show that system-level software FPTMO descriptions (FPTMO functionality described in software) rank among the fastest DTMOs and that the hardware FPTMO (described in software) speed-up depends on the target frame rate. For 30-frames-per-second color image generation, the fastest FPTMO is 15 times faster than the DTMO with highest TMQI and BTMQI metric scores, and 170 times faster than the DTMO with best colorfulness metric score.

Study of the tribological properties of surface structures using ultrashort laser pulses to reduce wear in endoprosthetics

BackgroundLoosening of prostheses and functional disorders represent a far-reaching problem in the clinic, and the long-term outcomes are essentially determined by wear. Despite all advances, up to 10% of prostheses still fail after 10 years. In particular, more active patients show increased revision rates.MethodsThe objective of this thesis is to examine whether the applied microstructures of the articulating surfaces can lead to a reduction in abrasion. Three different structural geometries (dimples, offset lines, grid lines) were defined. In an experimental test setup according to DIN ISO 6474 (Deutsches Institut für Normung, International Organization for Standardization), a tribological test of metal and ceramic pairings was performed using two-dimensional ring-on-disc (RoD) tests.ResultsIn both material groups, the structuring had a positive effect on the wear behaviour. In the ceramic group, an abrasion reduction of 22.6% was achieved. However, it is important to take into account the limited informative value due to the hardness of the material. Two of the three Cobalt-Chrome-Molybdenum (CoCrMo) structure geometries (grids, offset lines) also showed a significant reduction in abrasion compared to the reference group, with a maximum wear reduction of 55.5%.ConclusionBy reducing abrasion, surface structuring could be used to extend the life of prostheses and minimise the number of revisions.

Pressure vessel priming analysis for a regulated liquid propulsion system

An investigation was performed to determine the pressure transient levels and time required to reach pressure equilibrium in a regulated liquid propulsion system due to the priming of a propellant tank during system initiation. An experimental fluid flow test setup was designed and fabricated using a pressure vessel to house distilled water as a propellant simulant for liquid hydrazine and high-pressure gaseous nitrogen as the pressurant. A snubber orifice was installed downstream of the high-pressure gaseous nitrogen bottles to protect a regulator from high-pressure transients, prior to the regulation of incoming gas to beginning of life propulsion system propellant tank conditions. Experiments were conducted to measure pressure transients and time to pressure equilibrium by varying initial system pressures, snubber orifice diameter, and system ullage volume. A mathematical model was developed and compared against the experimental regulated system priming results to predict the system pressures and time to reach system pressure equilibrium during the pressurization period for regulated propulsion systems given initial conditions.

Modelling of a hydrogen permeation process from gas phase towards liquid sodium and experimental set-up for prototype testing

Hydrogen permeation through nickel dense membrane applied to Sodium cooled Fast Reactors has been studied theoretically and experimentally. In order to investigate the coupling of nickel membrane with external gas and sodium flows, an analytical model based on mass transfer resistances is developed. A sensitivity analysis showed that, for enough thick membranes and high sodium velocities, the nickel resistance has the most important effect. A permeator prototype constituted of four Ni201 tubular membranes, has been designed: experimental tests at pilot-scale are carried out at different temperatures, gas pressures and flowrates, both in gas-vacuum and gas-sodium configuration. Results for permeation against vacuum demonstrate that hydrogen diffusion within the membrane is the limiting step, in accordance with previous literature results obtained for pure nickel permeation experiments.

Ferrofluid rotary seal with replenishment system for sealing liquids

Ferrofluid rotary seals are mechanical contact-free magnetic liquid seals that are characterised by their simple structure, low friction and ability to hermetically seal. Although ferrofluid rotary seals for sealing vacuum and gases are part of a well established industry, the sealing of liquids has not been implemented yet. Literature learns that degradation of the ferrofluid seal over time when it dynamically contacts a liquid results into premature seal failure. This paper presents a new type of ferrofluid rotary seal in which a ferrofluid replenishment system is implemented that renews the ferrofluid in the sealing ring while sealing capacity is maintained. By replacing the degraded ferrofluid in the seal at a sufficient rate, service life of the ferrofluid rotary seal can theoretically be unlimited. An analytical model and FEM analysis are used to design the ferrofluid sealing device and to predict its sealing capacity. An experimental test setup has been built on which the sealing capacity and service life of the device has been tested for different sealing conditions. It is demonstrated that the ferrofluid replenishment system successfully extends and controls the service life of the ferrofluid rotary seal that dynamically seals pressurised water.

Design and implementation of cascaded H-Bridge multilevel inverter using FPGA with multiple carrier phase disposition modulation scheme

The paper deals with design of Cascaded H-Bridge Multilevel Inverter (CHB-MLI) with separate DC source to each inverter using multiple carrier Phase Disposition PWM such as symmetric disposition, phase opposition disposition and alternative phase opposition disposition to reduce the Total Harmonic Distortion (THD) and to improve the power quality of the supply voltage and current. In early days, the multilevel inverters are controlled with high frequency PWM method. This is not suitable for high power applications due to the high switching losses. With the help of multiple carrier PWM switching losses in the inverter circuit are reduced, so it can be used for high switchi ng frequency applications. The simulation of proposed system is developed using MATLAB Simulink software. The Performance simulation results are validated through experimental test setup using SPARTAN - 6 FPGA. Simulation results and effectiveness of the proposed method is proved and validated by experimental data.

Study on effect of glazing on performance and heat dynamics of asphalt solar collectors: An experimental study

Exposure to solar irradiation for an extended period during a day causes asphalt pavements can reach to a considerable temperature. Consequently, they can be converted into an affordable solar collector by harvesting thermal energy. In recent years much effort and time have been devoted to improving the thermal performance of solar collectors. To this aim, the glazing strategy is a promising technique. The glass covers results in the reduction of heat loss and protecting the asphalt surface (absorber surface) from the outside environment. Little attention has been given to the glazing strategy in improving the performance of ASCs. The chief aim of the current investigation is a comparative assessment of the performance and heat dynamics of unglazed asphalt solar collectors with glazed asphalt solar collectors under field conditions. The evaluation was carried out using an experimental test-setup composed of an asphalt solar collector with a surface area of 1.2 m2 and a pipe network length of 12 m. Various sensors were utilized to monitor and measure the key parameters such as ambient conditions and working fluid temperature during the experimental runs. The experimental results prove that the glazing strategy is an effective method to improve the performance of ASCs. The constructed glazed ASC increases hot water temperature, meanly around 5 °C, and pavement temperature, meanly around 20 °C, while represents an improvement in the performance, near 10%, compared with the unglazed one.

Thermal performance of diffusion-bonded compact heat exchangers

This work presents an experimental and theoretical evaluation of the thermal performance of a square straight diffusion-bonded stainless steel compact heat exchanger. A one-dimensional steady-state thermal model was proposed to predict the thermal characteristics of the heat exchanger. To validate the model and to study the thermal behavior of the heat exchanger, an experimental test apparatus was developed. The heat exchanger was tested in several combinations of Reynolds ranging from 2600 to 7500, representing transition to turbulent regimes. The temperatures were varied from 70 °C to 80 °C for the water and from 25 °C to 42 °C for the air, at the inlet of the heat exchanger, respectively. A good agreement between the experimental data and the analytical model was obtained.

Performance characteristics of the Spiky Central Receiver Air Pre-heater (SCRAP)

Combined cycle concentrating solar power (CSP) plants provide significant potential to achieve an efficiency increase and an electricity cost reduction compared to current single-cycle plants. A combined cycle CSP system requires a receiver technology capable of effectively transferring heat from concentrated solar irradiation to a pressurized air stream in a gas turbine. The novel spiky central receiver air pre-heater (SCRAP) technology is proposed to overcome barriers experienced to date.The SCRAP receiver is a novel metallic receiver technology aimed at pre-heating an air stream to about 800 °C, either prior to a combustion chamber or alternatively prior to a cascaded secondary non-metallic receiver system, capable of achieving elevated temperatures.A ray-tracing analysis demonstrated that the flux imposed on the absorber assemblies is dependent on the heliostat size. A thermodynamic computer model was developed to investigate the performance characteristics of the absorber assemblies (spikes) of the SCRAP receiver. The model was validated against an experimental test setup. Satisfactory agreement at various air flow rates was obtained.The thermal efficiency of the spikes was investigated and used to approximate the receiver’s solar-thermal efficiency. The receiver is predicted to perform at solar-thermal efficiencies exceeding 80%. The geometric design of the receiver achieves a relatively low radiative heat loss, predicted at about 4–5%. A relatively large vulnerability to convective heat losses was identified. The pressure loss was found to be relatively low, compared to existing alternative receiver designs, with system pressure losses below 40 mbar achievable.

A new feature extraction approach based on one dimensional gray level co-occurrence matrices for bearing fault classification

ABSTRACT Recently, precise and deterministic feature extraction is one of the current research topics for bearing fault diagnosis. For this aim, an experimental bearing test setup was created in this study. In this setup, vibration signals were obtained from the bearings on which artificial faults were generated in specific sizes. A new feature extraction method based on co-occurrence matrices for bearing vibration signals was proposed instead of the conventional feature extraction methods, as in the literature. The One (1) Dimensional–Local Binary Patterns (1D-LBP) method was first applied to bearing vibration signals, and a new signal whose values ranged between 0–255 was obtained. Then, co-occurrence matrices were obtained from these signals. The correlation, energy, homogeneity, and contrast features were extracted from these matrices. Different machine learning methods were employed with these features to carry out the classification process. Three different data sets were used to test the proposed approach. As a result of analysing the signals with the proposed model, the success rate is 87.50% for dataset1 (different speed), 96.5% for dataset2 (fault size (mm)) and 99.30% for dataset3 (fault type – inner ring, outer ring, ball) was found, respectively.

Varying mechanical compliance benefits energy efficiency of a knee joint actuator

In the field of wearable robots, actuator efficiency and user safety are frequently addressed by intentionally adding compliance to the actuation unit. However, the implications compliance has on the actuator’s overall performance in different conditions and activities are not fully understood, largely due to single task-focused experimental evaluations of these devices. To overcome this, our paper analyzes the effects that changing mechanical compliance has on the actuator’s overall performance in different ideal conditions in an experimental test setup. The torque performance and electrical energy consumption of an orthotic, adjustable-compliance knee joint actuator are evaluated during emulated walking and sit-to-stand-to-sit movements. Furthermore, the feasibility of combined operation of a dual mechanical compliance configuration during walking is investigated, and its outcomes reported in this work. The results demonstrate that varying mechanical compliance can lead up to 50% energy savings compared to a no-compliance configuration and show that, in general, changing compliance level leads to either energy-optimal or power-optimal actuator performance, but not both.

Numerical and experimental evaluation of an alternative mechanism for wall thickness variations of hollow profiles applying a porthole die

The cross sections of conventionally extruded profiles remain constant along the length of the extrudates due to application of static, rigid dies. The profile cross section is dimensioned according to the expected loads applied during technical application. Mostly, the loads are not distributed homogeneously upon the length of a product. Thus, locally over-dimensioned profile areas are the result. In order to optimize the profile design and therefore obtain lighter products, load adapted tailored profiles should be manufactured. In this paper a mechanism for wall thickness variations of lightweight hollow profiles was investigated by finite element analysis (FEA) and experimental extrusion trials. The principle for manufacturing wall thickness variations is based on application of bending elements which work as bearing channel at the porthole die. Their deflection in direction of the die bearing would lead to wall thickness reductions. An increase of the wall thicknesses should be achieved by a deflection of the bending elements back into direction of their initial position due to the normal pressure of the flowing aluminum billet material. FEA of the material flow during extrusion was conducted in order to investigate the principle feasibility of the mechanism. The force requirements for wall thickness variations were also gained from the numeric simulations on the one hand. The force necessary for the deflection of the bending elements was also determined in an experimental test setup. The extrusion tryouts applying the developed mechanism revealed that the force of the hydraulic drive was successfully transmitted onto the moveable segments inside of the porthole die. Although subsequent to the extrusion experiments variations of the hollow profile wall thicknesses were observed, it was found out that they were not induced by the developed mechanism as intended. Instead, aluminum billet material filled even smallest voids and gaps inside of the mechanism causing deflection and failure of different components that effected the development of the wall thickness.

Stable Force Reconstruction from Acceleration Measurements - Theory and Experiment

This paper presents an unknown input observer for the estimation of external forces acting on mechanical systems from only acceleration measurements. To circumvent arising stability issues, a classical unknown input observer extended with an additional filter is proposed. The influence of the design parameter of the filter is analyzed. A guideline for the parameter tuning depending on predefined estimation goals is given. In contrast to existing methods, no prior knowledge about the unknown acting force is assumed in the design process. The performance of the presented concept is compared to a state-of-the-art approach in both simulation studies and on a experimental test setup.

Testing and Simulation of a Solar PV / Battery Storage System with and without PWM Charge Control

This paper presents an experimental and modelling study of an off-grid solar photovoltaic system using pulse width modulation (PWM) charge control and battery storage using manganese oxide as the cathode, carbon titanium phosphate composite as the anode, and alkali-ion saltwater as the electrolyte battery cells. The paper presents an experimental test apparatus, empirical data collection and numerical modelling and simulation of the system. The experimental data for charging and discharging the system is used to correlate the numerical simulation model output. Results for charging and discharging the system are subsequently used to develop transfer function models of the system's charging and discharging behaviour.

Testing and simulation of a solar PV/battery storage system with and without PWM charge control

This paper presents an experimental and modelling study of an off-grid solar photovoltaic system using pulse width modulation (PWM) charge control and battery storage using manganese oxide as the cathode, carbon titanium phosphate composite as the anode, and alkali-ion saltwater as the electrolyte battery cells. The paper presents an experimental test apparatus, empirical data collection and numerical modelling and simulation of the system. The experimental data for charging and discharging the system is used to correlate the numerical simulation model output. Results for charging and discharging the system are subsequently used to develop transfer function models of the system's charging and discharging behaviour.