Double Pass Research Articles

Friction Stir Welding of Thick AA2519 Alloy: Defect Elimination, Mechanical and Micro-Structural Characterization

Friction stir welding (FSW) of thick aluminium sections will pave way for remarkable new defence applications, provided the accompanying challenges are successfully addressed. These challenges include elimination of tunnel defects, loss of strength in heat-treatable aluminium alloys, tool design and excessive process forces. Accounts of defect elimination, detailed micro-structural and mechanical characterization for thick section FSW are scarce in the published literature. Further, special strategies such as bobbin tool, pre-drilled hole for plunging and inverted double pass are generally deployed to overcome these challenges. This makes the process less productive and complex. In the present work, armor grade aluminum alloy AA2519-T87 plates having a thickness of 15.4 mm have been successfully joined with a joint efficiency of greater than 75% without supplementary strategies. The disparity in the effects of tool rotational speed and welding speed in the formation of a sound weld has been addressed in detail to enhance the understanding of FSW of thick sections. Micro-hardness measurements have been carried out throughout the transverse cross-section of the welds and correlated with different zones and their corresponding microstructures. Scanning electron microscopy and X-ray energy dispersive spectroscopy have been used to characterize the coarse phase particles present in the weld zones.

An experimental investigation of a double pass solar air heater performance: A comparison between natural and forced air circulation processes

This work involves an experimental study on a trapezoidal Double-Pass Solar Air Heater (DPSAH) to analyse its performance under natural and forced convection cases for the purpose of comparison. The experiments have been conducted in winter and compared for each case in same time and weather conditions. The collector has been carefully designed and constructed to prevent as possible the heat losses. A uniform fins have been fixed on both sides of the absorber plate to enhance the heat exchange rate. Effects of solar radiation and air mass flowrate on DPSAH performance have been investigated. The results show that DPSAH produces higher efficiency when the system is operated under natural convection case in comparison to forced convection case. The maximum efficiency has been found equal to 73.5% and 65% for natural and forced convection, respectively. A significant temperature difference has been obtained under natural convection case compared to forced convection. The results confirmed that DPSAH with adding fins leads to considerable performance improvement compared to conventional DPSAH due to enhance the absorbing solar energy caused by increasing surface area. The increasing in air mass flowrate has inverse influence on the performance of DPSAH. For natural circulation case, the outlet, plate and glass temperatures have been always observed higher than the forced convection case. It is evident that type of heat transfer has considerably affect the system performance and consequently, the selection of air circulation process are required to be satisfactorily chosen according to the application to achieve the desired objective.

Simulation of dual stage thulium-doped fiber amplifier using pump power distribution technique

<span>This paper shows dual stage thulium-doped fiber amplifiers (TDFAs) that use a pump power distribution technique. Simulations were done with signals ranging from 1975 nm to 2000 nm using the OptiSystem v.13 software. The results required were gathered from the software. The results of gain, noise figure, optical signal-to-noise ratio (OSNR) and output power were obtained. The highest gain and lowest noise figure results were achieved for the double pass dual stage TDFA configuration with values of 19.85 dB and 5.58 dB respectively, followed by the single pass dual stage TDFA. The OSNR and output power performances were also better for the double pass dual stage TDFA, obtaining 57.12 dB and 19.55 dBm respectively. This study shows that thulium can be used in the 2 µm region as an active gain medium and the dual stage architecture and distributed pumping technique proves to be effective techniques to obtain the desired results. Experimental work will be done in the future with the simulated results used as a reference.</span>

Performance analysis of free space optical–based wireless sensor networks using corner cube retroreflectors

AbstractAsymmetric free space optical wireless sensor networks (FSO‐WSNs) have gained momentous attention lately due to the promise of minimal energy consumption at the distributed sensors along with eminent performance. Asymmetric FSO is accomplished using corner cube retroreflector (CCR) that is mounted on each sensor node. The CCR either reflects or absorbs the received laser beam from the fusion center to indicate its local decision regarding the monitored target. In this study, a bistatic channel is assumed where the transmitter and the receiver are located at different locations such that the double pass channel is modeled as a product of two independent turbulence channels. Novel performance analysis of the CCR‐based FSO‐WSN system in terms of the average bit error rate (BER) and the average decision error rate (DER) is presented. In particular, closed‐form expressions for the BER and the DER are derived using the Fox H‐function under different bistatic turbulent channel models including negative exponential, K‐turbulence, Gamma‐Gamma, and Malaga channel models. Monte Carlo simulation results are obtained to corroborate the accuracy of the derived analytical formulas where an exact match is reported over wide range of system and channel parameters. In addition, the influence of transmit power, distance, detection threshold, and turbulence parameters on the performance of the system is investigated and thoroughly discoursed.

Diagnostics of Plasma Pencil Discharge for Chemical Analysis

We present diagnostics of plasma pencil discharge as alternative excitation source for analytical chemistry. The plasma pencil is special type of rf plasma nozzle at atmospheric pressure. Through this nozzle flows working gas argon with aerosol. The aerosol sample introduction system employed a double pass Scott spray chamber with a pneumatic concentric nebulizer. The parameters of the plasma were calculated by optical emission spectroscopy.

Experimental study on double pass solar air heater with fins at lower and upper channel

Abstract Solar air heater with a double pass configuration and rectangular longitudinal fins on one side of the absorber plate was investigated experimentally. Performance parameters outlet temperature, absorber plate temperature, output power of the air heater with fins placed in lower channel and fins placed in upper channel were presented. The effect of mass flow rate of air on the efficiency of air heater with fins in lower and upper channel were also investigated. The result shows that air heater with fins placed in lower channel is more efficient than the air heater with fins placed in upper channel.

Cracks in the 3D-printed conductive traces of silver nanoparticle ink

Printing conductive traces of sinterable metallic nanoparticle (NP) based inks is one of the key components of 3D additively manufactured (printed) electronic circuits. In this study, we employ 3D aerosol jet printing to print conductive traces of silver NP based ink and provide insights into the risk of cohesive longitudinal cracking inside the printed and sintered traces. This was investigated for a wide range of carrier and sheath gas flow rates, which implies a wide range of particle deposition rates and velocities. These cracks appear for both single and double pass traces that are several microns in height and hundreds of microns in width. We examine different sources of stress that could be the potential driver for the cracking and infer that the most likely source is the classical capillary-pressure-driven crack formation mechanism for the evaporating NP-based thin films. Most importantly, this hypothesis raises the possibility of crack formation at several locations of the NP-based conductive traces printed using an extremely popular recent technique for printed electronics, AJP.

CFD modeling and performance evaluation of multipass solar air heaters

This article investigates the impacts of flow configurations on the thermal performance of a solar heater system. Recycled aluminum cans (RACs) have been utilized as turbulators with a double pass single duct solar air collector. The CFD software of COMSOL Multiphysics V5.3a is used to model three designs: Cocurrent (model A), countercurrent (model B), and U-shape (model C). The numerical results reveal that the U-shape design offers a greater thermal performance of 5.4% and 6.5%, respectively, compared with the cocurrent and countercurrent flow models. Furthermore, an outdoor experiment is performed based on the numerical modeling of flow configurations. The experimental setup is examined for three configurations of model C, namely, solar air heater (SAH) without RAC model C-I (plain model), SAH with in-line RAC layout (model C-II), and SAH with staggered RAC layout (model C-III). We found the double pass single duct solar air collector (model C) design is in a good agreement with the experimental data, and model C-III has a better thermal efficiency of 60.2%, compared to those of model C-II, 53.1%, and model C-I, 49.4%.

Influence of the location of discrete macro-encapsulated thermal energy storage on the performance of a double pass solar plate collector system

In this work, an outdoor experimental analysis is conducted to determine the impact on the useful heat gain when discrete cylindrical energy storage units are directly integrated into the solar collector. The collector has a double-pass airflow channel pathway, and the storage is intended to serve only for a short-term. The location of storage inside the collector is always a major concern. This study seeks to determine whether the thermodynamic performance of the system is effective by the location of cylindrical energy storage (paraffin wax) capsules on the upper or the lower airflow channel pathway. The obtained results suggest that due to asymmetric channel depth, the thermodynamic performance of the collector was not greatly influenced by the placement of capsules, unlike with symmetric channel depths. The amount of useful heat gain when storage was placed in the upper (Case A) and lower (Case B) airflow pathways was 0.35 kW and 0.4 kW. For Case A and Case B, the average collector thermal efficiency was 62.9% and 73.7%, and the exergy efficiency was 44.3% and 47.5%. The energy payback time for the collector based on energy calculations is nine months, and that on exergy analysis is 34 months and 20 days.

Imaging properties of hemispherical electrostatic energy analyzers for high resolution momentum microscopy

Hemispherical deflection analyzers are the most widely used energy filters for state-of-the-art electron spectroscopy. Due to the high spherical symmetry, they are also well suited as imaging energy filters for electron microscopy. Here, we review the imaging properties of hemispherical deflection analyzers with emphasis on the application for cathode lens microscopy. In particular, it turns out that aberrations, in general limiting the image resolution, cancel out at the entrance and exit of the analyzer. This finding allows more compact imaging energy filters for momentum microscopy or photoelectron emission microscopy. For instance, high resolution imaging is possible, using only a single hemisphere. Conversely, a double pass hemispherical analyzer can double the energy dispersion, which means it can double the energy resolution at certain transmission, or can multiply the transmission at certain energy resolution.

Experimental and numerical investigations of a single and double pass porous serpentine wavy wiremesh packed bed solar air heater

This research work presents the thermal performance investigation of a porous serpentine wavy wiremesh packed bed solar air heater, experimentally and numerically. Experimental results revealed the best thermal and thermohydraulic efficiencies for 93% porous double pass serpentine packed bed solar air heater and found to be about 80% and 74%, respectively, which is about 18% and 17% high compared to single pass, respectively. Whereas, numerical investigation is carried out on a CFD tool and the results are validated with experimental data. The range of porosity from 85% to 95%, wavelength from 0.05 m to 0.075 m, amplitude from 0.012 m to 0.016 m, hydraulic diameter from 0.025 m to 0.046 m and mass flow rate from 0.01 to 0.05 kg/s is considered to obtain optimum values for geometrical and flow parameters on the basis of THPP and exergy efficiency. The numerical results present the maximum 24.33% better thermohydraulic performance for serpentine packed bed solar air heater when compared to flat packed bed solar air heater. The wavelength of 0.075 m, amplitude of 0.012 m, hydraulic diameter of 0.0835 m, porosity of 90%, and mass flow rate of 0.03 kg/s is obtained as the optimum configuration.

Improvement of Noise and Gain Characteristics of Low-Repetition-Rate Double-Pass Fiber Amplifiers

The noise and gain characteristics of pulsed double-pass (DP) amplifiers operating at low repetition rates are analyzed theoretically and experimentally. The Frantz–Nodvik equations are extended to realize rapid calculation of signal gain in DP fiber amplifiers. At the same time, the rate equations are used to compute the evolution of amplified spontaneous emission (ASE) noise. The effects of the pump scheme, the input energy, and the insertion loss on the gain and noise characteristics are discussed. Based on the simulation results, a new structure Yb-doped DP amplifier is proposed. The experimental results show that the small-signal gain of the DP amplifier can exceed 50 dB. In particular, the average ASE background of the DP amplifier at high-energy output is lower than that of the single-pass amplifier at the same output. This result is quite different from continuous-wave fiber amplifiers.

Imaging Michelson interferometer for a low-density gas jet characterization.

A new optical probing method with increased interferometric sensitivity for a low-density gas jet characterization is presented. The proposed technique employs a Michelson interferometer with a self-imaging object arm, which enables the relay imaging of the object on itself, and in this way, the phase sensitivity of the device is increased by a double propagation of the object laser beam through the gas jet. The wavelength of 405 nm was chosen to further increase the sensitivity by increasing the probe wavenumber. A low-density argon gas jet with various backing pressures was characterized by our method and by a commonly used Mach-Zehnder interferometer setup showing the expected twofold increase in the signal to noise ratio in the double pass configuration.

Investigation on thermal-hydraulic performance of the absorber plate using a piezoelectric fan in the solar air heater

This paper presents experimental and numerical research about piezoelectric fan array in solar air heater (SAH) at the frequencies 45-60 Hz by using lamp array as solar radiation simulator. The effective heat transfer coefficient (HTC) of the traditional method such as strip rib on the solar collector and the HTC enhanced by the piezoelectric fan are compared in detail with the different flow rate of the air. A prototype solar collector with a dimension of 300 mm (L)×150 mm (W) is fixed in a wind tunnel in the experiment. Three configurations of piezoelectric fan array which include through-pass and double pass mode have been tested. The results show that the piezoelectric fan can increase HTC or Nusselt number effectively. The Nusselet number is increased by 50∼100%, whereas the pressure drop is increased by no more than 5%. The additional power consumption of the piezoelectric fan is only as low as 0.96 W for 2×2 piezoelectric fan array. The maximum amplitude and the HTC or Nusselt number will be achieved at the resonance frequency, and the vertical setup is the most effective for heat transfer enhancement.

Influence of Cu powder on strength, failure and metallurgical characterization of single, double pass friction stir welded AA6061-AA7075 joints

The present work investigates the effect of copper powder addition during single pass and double pass friction stir welding (FSW) between AA6061-T6 and AA7075-T651 to appraise the formation and detailed characterization of the intermetallic compounds (IMCs) in addition to study tensile, flexural strength, material flow, and fracture behavior. The copper powder was added in three different ways namely over the plate top surface (along weld path, below the tool shoulder), inside the slots of 1 mm and 2 mm (combined slot width at faying surfaces of adjoining plates) in addition to plate top surface. Analysis was also carried out employing a quick weld stop approach keeping the tool pin inside the weld seam and sectioning through it. Small improvement in joint ultimate tensile strength and flexural load was noticed when copper powder was added on plate top surface. For joints obtained with the addition of Cu powders in slots, formations of large clusters of particulates and/or IMCs were observed. Detailed characterization revealed that the formation of IMCs in small quantity with finer size distributed evenly could be beneficial for improving joint strength. However, large chunks/lumps can promote quick and brittle failure. In double pass FSW (with second pass in the reverse direction of first pass) good material flowability and slightly finer grains in stir zone (SZ) were observed. Comparatively smaller size agglomerates were also noticed distributed on either side of the SZ after the second pass. Fractographs showed the presence of numerous micro-voids and dimples in sound joints indicating the ductile fracture. However, tearing/rupture and brittle failure were witnessed in the joints prepared with addition of Cu powder in slots.

Theoretical and experimental analysis of bidirectionally pumped 1.3 μm Pr3+-doped ASE source

We have analyzed the characteristics of 1.3 μm praseodymium (Pr3+) doped bidirectionally pumped double pass (BIP-DP) configuration amplified spontaneous emission (ASE) source theoretically and experimentally. The source’s simulation model was established and corresponding simulated results were given. The effects of pump ratio, Pr3+-doped fiber (PDF) length, total pump power and source’s optical losses were researched. The output power of BIP-DP ASE source is mainly affected by the total pump power, PDF length and source’s optical losses, while it has little relationship with the pump ratio. The BIP-DP ASE source operating at the symmetric bi-directional pump condition was constructed experimentally. The acquired output power of more than 5 mW has been obtained experimentally, which was with the quasi-gaussian output spectrum, and its 3 dB bandwidth is ~ 20 nm.

Optimization of TMCP strategy for microstructure refinement and flow-productivity characteristics enhancement of low carbon steel

Improving the mechanical properties of low carbon steel through the microstructural refinement without adding alloying elements is a complicated scientific and technical mission. This challenge can be overcome by using thermo-mechanical controlled processing (TMCP) technology. Most researches have examined the influence of TMCP on the microstructure development without shed light on the flow characteristics. The current work aims at studying the effect of applying different TMCP strategies on the microstructure refinement, flow-productivity characteristics, i.e. peak stress, flow stress, strain hardening index, Zener–Hollomon parameter and total strategy time, of low carbon steel. These TMCP strategies involve applying heavy deformation in single-pass TMCP strategy versus light deformation/pass in multi-pass TMCP strategy through applying different plane-strain hot compression regimes using Gleeble 3500 thermo-mechanical simulator. The proposed TMCP strategies have been involved application of heavy accumulative strain of 45–57% through: (1) single pass TMCP strategy at various strain rates (0.01, 0.1 and 1.0s−1), (2) double pass TMCP strategy at different strain rates and (3) multi-pass TMCP strategy at strain rate of 0.1s−1. Microstructures after the diverse TMCP strategies reveal ferrite grain refinement and the flow curves show typical strain hardening. This denotes that the working grain refinement mechanism during all TMCP is dynamic strain-induced transformation of austenite to ferrite. It has been found that the strain rate plays a considerable role in determining the flow characteristics regardless the applied TMCP strategy type. Double-pass TMCP strategy is the optimum TMCP strategy that promotes the ferrite refinement and enhances the flow and productivity characteristics.

40 dB gain all fiber bismuth-doped amplifier operating in the O-band

In this Letter, we investigate and compare the gain and noise figure characteristics of bismuth (Bi)-doped fiber amplifiers configured in both single and double signal pass implementations. A maximum gain of 25dB and a noise figure of 4dB is measured at 1360nm in the single pass configuration for -23 dBm input signal power, whereas in the double pass configuration the gain of the amplifier is improved significantly by 14dB allowing us to achieve a gain of 39dB with a noise figure of 5dB. To the best of our knowledge, this is the highest gain reported to date using Bi-doped fiber as a gain medium. Furthermore, we also study the gain and noise figure dependency on pump power, signal power, and pump wavelength for the double pass amplifier configuration. We observed similar gain and noise figure performance in the double pass configuration to that of the single pass configuration but with the benefit of less pump power and a shorter length of the Bi-doped fiber.

An effective Schmid factor in consideration of combined normal and shear stresses for slip/twin variant selection of Mg-3Al-1Zn alloy

An effective Schmid factor (ESF), as an alternative parameter to the uniaxial stress based Schmid factor, is newly proposed to account for the effects of grain orientations and general loading conditions including shear deformation on the selection of slip/twin modes of magnesium alloys. The validity of the proposed parameter is confirmed by accurately predicting twin variants developed during double pass differential speed rolling of Mg-3Al-1Zn alloy. The analysis based on the ESF concept clarifies that shear stress and their relative magnitude to the normal stress have considerable impact on the activation of the predominate slip, twin type and variants.

Tear-film dynamics by combining double-pass images, pupil retro-illumination, and contrast sensitivity.

Tear-film dynamics were analyzed by a synchronizing recording of double-pass (DP) and pupil retro-illumination (RI) images with contrast sensitivity (CS) measurements. Simultaneous DP and RI images were acquired in three subjects wearing contact lenses while keeping the eye open. Changes in contrast sensitivity for an 18 c/deg green grating were also estimated. From the DP retinal images, the effect of the tear film is described through the objective scattering index (OSI). This presented a negative correlation with the increase in CS during tear-film deterioration (as observed by RI imaging). These results show a relationship between visual outcome degradation due to tear-film breakup and the increase in intraocular scattering. This work shows a combined methodology for the evaluation of tear-film dynamics.