Experimental Parametric Study Research Articles

Engineering the translaminar fracture behaviour of thin-ply composites

Bio-inspired patterns of micro-cuts perpendicular to the fibre direction in thin-ply CFRP laminates have been used to increase the translaminar fracture toughness of the material. An analytical model to predict the probability of bundle pull-out during translaminar crack propagation was developed and validated through an experimental parametric study. The model was used to design three hierarchical patterns of micro-cuts and the patterns have been tested using Compact Tension specimens. The increase in fracture toughness for the three patterns was +15%, +60% and +214% when compared with the baseline material, thereby demonstrating the potential of engineering the fracture surface in CFRPs through well-designed patterns of micro-cuts to improve the damage tolerance of the material.

Heat storage by the dehydrogenation of methylcyclohexane – Experimental studies for the design of a microstructured membrane reactor

The concept of hydrogen storage via liquid organic hydrides in cycles of hydrogenation and dehydrogenation with preferably low amount of reaction enthalpy is well known under the abbreviation LOHC, Liquid Organic Hydrogen Carrier. However, our study addresses the dehydrogenation of methylcyclohexane in a prototype microstructured membrane reactor, which is mainly devoted to the heat storage in a so-called LORC, a Liquid Organic Reaction Cycle. While using the same cycles of hydrogenation and dehydrogenation, heat shall be stored on the contrary by high reaction enthalpy in the LORC. A novel planar membrane module with an integrated catalytic fixed-bed has been developed. It is equipped with structured supports to reduce the mechanical stress on the Pd-membrane foil. Experiments investigating the membrane separation performance were conducted with operational parameters up to 400 °C and 13 bar. The ability of shifting equilibrium conditions to product side and pure H2 recovery was shown. Catalyst deactivation and regeneration was tested in order to analyze stability of the Pd-membrane. An experimental parameter study was performed to obtain a future optimized design of a large-scale prototype reactor.

Response evaluation of interconnected electrical substation equipment using real‐time hybrid simulation on multiple shaking tables

SummaryIn an attempt to quantify the conductor cable effect on substation electrical equipment, real‐time hybrid simulation (RTHS) is conducted on interconnected equipment using two shaking tables. For this purpose, the existing RTHS system with advanced control capabilities at the Pacific Earthquake Engineering Research Center structural laboratory is enhanced to accommodate the simultaneous use of two shaking tables. An experimental parametric study is conducted to investigate the conductor cable effect using this system with a two‐table RTHS setup. Post insulators of disconnect switches, important components of substations that are usually tested with conventional methods for evaluating their seismic performance, are utilized as experimental substructures for realistic representation of the electrical equipment. Various global and local response parameters, including accelerations, forces, displacements, and strains, are considered to evaluate the effect of the tested conductor cable configuration for a wide range of support structure configurations, which are modeled in the computer as analytical substructures. The experimental parametric study results indicate that the conductor cable has a significant effect on the response of the interconnected equipment over the whole range of investigated support structures and needs to be explicitly considered for seismic testing of electrical equipment. Copyright © 2016 John Wiley & Sons, Ltd.

Discrete element method study of fuel relocation and dispersal during loss-of-coolant accidents

The fuel fragmentation, relocation and dispersal (FFRD) during LOCA transients today retain the attention of the nuclear safety community. The fine fragmentation observed at high burnup may, indeed, affect the Emergency Core Cooling System performance: accumulation of fuel debris in the cladding ballooned zone leads to a redistribution of the temperature profile, while dispersal of debris might lead to coolant blockage or to debris circulation through the primary circuit. This work presents a contribution, by discrete element method, towards a mechanistic description of the various stages of FFRD. The fuel fragments are described as a set of interacting particles, behaving as a granular medium. The model shows qualitative and quantitative agreement with experimental observations, such as the packing efficiency in the balloon, which is shown to stabilize at about 55%. The model is then applied to study fuel dispersal, for which experimental parametric studies are both difficult and expensive.

Ceramic foams coated with Pt[sbnd]Ni/CeO2[sbnd]ZrO2 for bioethanol steam reforming

The catalytic activity of bimetallic PtNi/CeO2ZrO2 powders and foams, with a silicon carbide carrier and containing silica or boehmite as binder, was investigated for ethanol steam reforming in the low temperature range (400–500 °C). A parametric experimental study was preliminary performed to analyze the effect of different operative conditions (temperature, water/ethanol ratio and contact time) on coke selectivity: low temperatures and space velocities as well as high water contents in the feeding stream minimized carbon deposits formation and reactor plugging. Moreover, once analyzed the individual influence of C2H4O, C3H7OH, C4H9OH and C5H11OH, selected among the main bioethanol contaminants, on catalyst deactivation, a model mixture, containing 1% mol of all the impurities, was fed to the reformer at 15,000 h−1, T = 450 °C and water/ethanol ratio equal to 6. In order to test catalytic behavior in more stressful conditions, contact time was decreased and the stability of powder and foam catalysts was investigated at 50,000 h−1. Despite very similar H2 selectivities were recorded, the structured samples, containing boehmite as binder, showed the most interesting catalytic performance, as total ethanol conversion was assured for more than 1 day of time-on-stream. Foams geometry, in fact, enhanced coke gasification reactions, limiting, at the same time, plugging phenomena.

Parametric study of hot-melt adhesive under accelerated ageing for automotive applications

The mechanical properties of commercially available hot-melt adhesive, HMA, which is mostly used in automotive applications, have been studied under different environmental and loading conditions, paying particular attention to the ageing effects. Three laboratory accelerated ageing processes were applied to single lap joints (SLJs) of two polypropylene substrates in order to replicate the least favourable environmental conditions in automotive usage. Experimental parametric studies were performed on virgin and aged specimens, investigating the influence of two design factors, the overlap length and adhesive layer thickness, on the load carrying capacity and mode of failure of the SLJ. FT-IR was used to perform qualitative HMA polymer composition analyses. The DSC test was also performed to obtain the thermal behaviour, and the phase transition temperatures of the HMA. In addition, the sliding temperature test was performed in an electronically controlled climatic chamber to understand, by means of tests on SLJs, the temperature resistance of the HMA/polypropylene bonded systems. Results clearly show that depending on the type of ageing process, the strength of SLJ based on HMAs varies, this enhances a relevant difference with respect to the strength of SLJ based on conventional thermosetting adhesive. Furthermore, the parametric study performed revealed the correlation between the strength of the SLJ and its geometry, which might be taken as a design guideline for this kind of flexible adhesive joints.

Lightweight Concrete with an Agricultural Waste – Buckwheat Husk

This paper presents a parametric experimental study which investigates the potential use of buckwheat husk wastes (as an aggregate in concrete) and opoka combination for producing a lightweight composite. The study was carried out to investigate the influence of the buckwheat husk extract on the setting and hardening of pastes in which cement was partially replaced by 0, 33, or 50 % of natural pozzolana. The kinetics of hydration up to 48 h was studied using isothermal conduction calorimetry. Some of the physical and mechanical properties of buckwheat husk concrete with various levels of cement replacement of opoka without and with sand (part of buckwheat husk was replaced in the same volume of sand) were investigated. Experimental data on the compressive strength of concrete utilizing buckwheat husk with and without sand and cement at varying proportions are presented. The results suggest that buckwheat husk may be used as an aggregate, particularly in lightweight concrete, panel and blocks for walls at a relatively cheaper price.

In-Plane Behavior and Design of Rectangular SC Wall Piers without Boundary Elements

AbstractThis paper focuses on the in-plane behavior, analysis, and design of steel-plate composite (SC) wall piers without boundary elements. A series of SC wall pier specimens with aspect ratios (wall height-to-length ratios, h/lw) ranging from 0.6 to 1.0 were tested under cyclic loading until failure. The results include the lateral load-displacement (V-Δ) responses of the specimens along with observations of steel plate local buckling and concrete crushing. Detailed 3D finite element models of the SC wall specimens were developed and benchmarked using the experimental results. The models explicitly accounted for the effects of geometric nonlinearity and material inelasticity including steel local buckling, concrete crushing, and tension fracture. The benchmarked models were used to conduct parametric studies. The parameters included were the wall aspect ratio (h/lw), reinforcement ratio (ρ), and wall thickness (T). The experimental results and parametric studies indicated that the lateral load capacity...

Centrifugal instabilities in an experimental open cavity flow

We present an experimental parametric study of spanwise centrifugal instabilities in an open cavity flow. We show that the mode selected at threshold depends on the cavity streamwise aspect ratio. For small aspect ratio, a steady mode is enhanced, while travelling waves are observed for large aspect ratio. The bifurcation is found to be supercritical for all configurations. Sidewall effects are shown to generate secondary flows that carry the vortical patterns. Spanwise confinement enhances the family of steady modes relative to the family of oscillatory modes. These results are discussed with respect to predictions from linear stability analyses and other flows developing centrifugal instabilities.

Experimental study of cold plume instability in large Prandtl number Czochralski melt: Parametric dependences and scaling laws

A parametric experimental study of the cold plume instability that appears in the large-Prandtl-number Czochralski melt flows is reported. The critical temperature difference (the critical Grashof number) and the frequency of appearing oscillations were measured for varying Prandtl numbers, aspect ratios of the melt, and crystal/crucible radii ratio. The measurements were carried out by two independent and fully non-intrusive experimental techniques. The results are reported as dimensional and dimensionless parametric dependences, and then are joined into relatively simple empirical relations showing how the critical Grashof number and the frequency of emerging oscillations depend on other parameters.

Experimental study of a water-mist jet issuing normal to a heated flat plate

A parametric experimental study on the development of a round jet spray impacting a smooth, heated, flat plate has been accomplished. The main objective of this effort was to provide information characterizing the flow structure of a developing mist jet, issuing vertically towards an upward facing, horizontal heated plate, by means of simultaneous droplet size and velocity measurements. Phase Doppler Anemometry was used, providing also information on liquid volume flux. The fine spray of small atomized droplets (0.5-5.0 μm), was generated using a medical nebulizer. Two low Reynolds number jets (Re=2952, 3773) issuing from a cylindrical pipe have been tested. The distance between the jets’ exit and the plate was 50 cm. A stainless steel non-magnetic flat plate of dimensions 1000x500x12mm3 was used as target wall. Constant heat flux boundary conditions were established during measurements. Results indicate that the heat flux from the plate is influencing the evolution of the spray jet, diminishing its velocity and turbulence. Average droplet sizes are affected little by the heat flux, although for the non-heated sprays, droplet sizes increase at locations very close to the plate. A significant effect on droplet volume flow rate is also reported.

Durability of High Performance Concrete made with Silica Fume and Manufactured Sand

A parametric experimental study has been conducted to investigate the effect of manufactured sand on the durability properties of High performance concrete. Six HPC mixes with manufactured sand percentages of 0, 20, 40, 60, 80 and 100% with 10% of silica fume. The durability of concrete was studied through the measurement of Rapid chloride penetration test, Sorptivity Test, Saturated Water Absorption Test, Acid Resistance Test, and Corrosion Resistance-Impressed Current Test. The results indicate that the addition of manufactured sand has a positive effect on the chloride ion penetration of concrete. With the increase of manufactured sand content, the value of chloride ion penetration is decreasing gradually. However, the addition of manufactured sand has greatly improved the water impermeability, the acid resistance and Corrosion resistance of High Performance concrete.

Experimental and Numerical Studies on Lateral-Torsional Buckling of GJ Structural Steel Beams Under a Concentrated Loading Condition

GJ structural steel has been applied in many high-rise buildings and large-span structures, such as New CCTV Building and Beijing Olympic Stadium (Birds Nest). However, the design methods of GJ structural steel members are not covered by the current design codes. This paper describes the lateral-torsional buckling behavior of welded sections based on a series of flexural tests performed on H-sections fabricated from GJ structural steel plates. Six steel beams were tested under a concentrated loading condition. It was observed from the experimental tests that lateral-torsional buckling controlled the final failure modes. Numerical simulations of the experimental tests were conducted as well. The numerical simulation results agreed well with the test data. Parametric study was conducted after the validation of the numerical model. Finally, both the experimental test and parametric study results were compared with multiple design codes, including Chinese steel structure design codes (GB50017-2003, GB50017-201X), Eurocode (EC3) and American code (ANSI/AISC360-10). The comparisons indicate that GB50017-201X can predict appropriate flexural strengths of GJ structural steel beams. Also, it is found that the predictions of EC3 are too conservative, while for certain cases ANSI/AISC360-10 predictions are too high for the design flexural strength of GJ structural steel beams.

Experimental Parametric Study of Frequency and Sound Pressure Level on the Acoustic Coagulation and Precipitation of PM2.5 Aerosols

ABSTRACTThe efficiency of particle removal for PM2.5 aerosols using conventional separation systems is generally low. In this paper, acoustic precipitation and coagulation of aerosols as a preconditioning system is investigated experimentally. The results of experimental study concerning the effect of frequency and sound pressure level (SPL) on the acoustic coagulation and precipitation of PM2.5 aerosols are presented. An acoustic particle conditioning setup was used to perform experiments at the resonance frequencies of 204, 550, 650 and 749 (Hz), and SPLs 140, 150, 155, 162 dB. All experiments were performed under ambient condition and similar initial concentration. The experimental results showed that the effect of acoustics on filtration efficiency is amplified by increasing the frequency and intensity. Eventually, at the frequency of 749 (Hz) and 162 (dB) the acoustic coagulation and precipitation efficiency reaches about 83% which is significant. The results of this study (experimentally and theoretically) prove the existence of a threshold in SPL (≥ 155 dB) at which the acoustic precipitation and coagulation efficiency increase rapidly, implying the importance of turbulence coagulation interactions at high intensity acoustic waves. In addition, a new empirical correlation was developed for the acoustic coagulation and precipitation efficiency with reasonable accuracy.

Experimental investigation of stress–strain behavior of CFRP confined Low Strength Concrete (LSC) cylinders

The research presents a parametric experimental study on Low Strength Concrete (LSC) cylinders. The variables include the number of Carbon Fiber Reinforced Polymer (CFRP) layers and unconfined compressive strength of concrete. The aim is to predict the behavior of confined LSC cylinders and evaluate the enhancement in strength and ductility due to this external confinement with high strength CFRP wraps. The experimental results revealed a significant up gradation in compressive strength and ductility of CFRP wrapped LSC cylinders and showed a substantial contribution of this external confinement to the overall stability and stiffness of this composite system. The research concluded that various existing but seismic deficient concrete structures could be effectively strengthened with CFRP technique; which will not only recover their original state but also enable them to survive even larger potential earthquakes due to improved strength and ductility.

Phase-Change Materials for Transient Cooling of a Heater Array in a High Aspect Ratio Channel in the Presence of Mean Flow

This paper explores the effectiveness of phase-change material (PCM) for cooling of a discrete array of heat sources in low form factor channels in the presence of mean flow. The alkane n-Eicosane was chosen as the material for this work. A parametric experimental study was conducted on an array of heaters that simulate the heat dissipating components in a low form factor portable electronic device. The effects of the clearance at the top of the devices, thickness/volume of the PCM, as well as the mean flow velocity were studied under uniform and nonuniform patterns. It was found that the cooling effect of the PCM in the time frame considered reduces with increase in the mean flow Reynolds number due to its delayed melting. Thus, the cooling effect in a natural convection environment is higher compared to one with mean flow. The thickness of the PCM increases its effectiveness for a certain threshold value beyond which we reach a region of diminishing returns. The results are presented as design curves in terms of nondimensional parameters. The use of thin spreader inside the PCM pack improves its cooling effectiveness due to better lateral spreading. However, the cooling time for the n-Eicosane is not negligible and can be a potential challenge under repeated cyclic loads.

Experimental Study on Cyclic Response of Concrete Bridge Columns Reinforced by Steel and Basalt FRP Reinforcements

AbstractThis paper presents the seismic performance of concrete bridge columns reinforced with both steel and fiber-reinforced polymer (FRP). A bond-based parametric experimental study was conducted on five FRP steel–reinforced concrete (FSRC) bridge columns—using basalt FRP (BFRP) bars and BFRP sheets—and two steel-reinforced concrete (SRC) bridge columns served as references to investigate the fundamental characteristics of the proposed reinforcement. The investigated bond parameters included the texture of the FRP bars (smooth and ribbed), diameter of the FRP bars, location of the FRP bars with respect to the steel bars, and application of external FRP confinement. All columns were tested under the combined effect of constant axial load and reversed cyclic loading. The experimental results showed that the FSRC bridge column could realize the existence of a stable postyield stiffness (hardening behavior) as well as a reasonable displacement ductility of up to 10 before encountering strength degradation....

Drag reduction on a flat-back ground vehicle with active flow control

Active flow control is applied to the Honda Simplified Body (HSB), a flat-back ground vehicle model, for aerodynamic drag reduction. The use of small scale, steady jets (microjets) in normal and tangential injection orientations is investigated through experimental parametric studies and companion numerical simulations. Parameters such as injection location relative to separation point, jet diameter, and blowing ratio are explored. The flow response is characterized experimentally by aerodynamic force measurements and velocity field measurements. The computational effort utilizes Large Eddy Simulation (LES) to uncover how flow control with a steady microjet array modifies the wake and the corresponding drag. The impact of the microjets on the baseline flow field is discussed. The computational study introduces the actuator array on the top surface of the model body to support the experimental study that examines the effectiveness of flow control with microjets installed on multiple side surfaces. From both experimental and numerical analyses, it is observed that the wake can be modified with microjets such that the drag experienced by the HSB is reduced by nearly 3% with net reduction in power consumption.

Exergy Performance Analysis and Optimization of a Desiccant Wheel System

This paper focused on the exergy analysis and optimization of a dehumidification desiccant wheel (DW) system. A two-dimensional unsteady state numerical model was developed for simulation of the heat and mass transfer phenomena in a representative channel of a DW matrix. The DW mathematical model was validated using a series of experimental data and parametric studies were conducted to investigate the effects of operating parameters on the DW system performance. Exergy parameters were also studied and adopted to predict the total inlet–outlet exergy and exergy destruction, as well as exergy effectivenesses. Furthermore, a new exergy effectiveness parameter was introduced based on the concept of dehumidification. Parametric studies were carried out to characterize the optimal performance of the overall system regarding exergy destruction and exergy dehumidification effectivenesses. The results demonstrate that electrical power consumption, regeneration heat, and heat and mass transfer between air and desiccant are the main sources of exergy destruction. The optimization calculation shows that at the lowest process air velocity (up = 0.2 m/s), lowest DW rotational speed (NDW = 4 Rph), highest regeneration air temperature (Ta,r,in = 140 °C), and moderate regeneration air velocity (ur = 1.7 m/s), minimum exergy destruction occurs. The optimal value of the parameters proves that, when exergy destruction effectiveness is selected as the objective function, the only regeneration air velocity is decision variable of optimization and operational limits impose on the other parameters.

New insights into corona discharge surface ionization of polyethylene terephthalate via a combined computational and experimental assessment

The aim of the present work is to demonstrate the influence of corona discharge ionization on chemical and physical properties of polyethylene terephthalate (PET) fibers using computational and experimental studies. In the computational section, the vibrational frequencies of proposed models for PET before and after corona discharge treatment were predicted in the liquid phase at both the B3LYP/6-31G/COSMO and B3PW91/6-31G/COSMO level of theories using the harmonic approximation. When compared to B3LYP, the frequencies obtained for the B3PW91 show a better linear correlation with the experimental data. Furthermore, experimental studies were carried out by the use of Fourier transform infrared spectroscopy (FTIR), X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), and reflectance spectroscopy (RS). Experimental evidence indicated that the corona discharge modifies the surface of fibers and also increases the reactivity of PET toward cationic dyes. Our combined computational and experimental parametric study clearly confirms that the changes occurred on the PET surface due to corona discharge ionization.