Cr Wire Research Articles

Bush‐Shaped Vertical Graphene/Nichrome Wire for Blackbody‐Like Radiative Heating

AbstractRadiative thermal management has attracted increasing attention for the advantages of energy saving and carbon emission reduction. Infrared radiation coatings are widely adopted to alleviate the low infrared emissivity of commonly used metal alloy electrothermal materials. However, traditional infrared radiation coatings are faced with the issues of the unsteady waveband emissivity, low interfacial adhesion to substrates, and poor long‐term thermal stability. Herein, a bush‐shaped vertical graphene (BVG) grown on nichrome (Ni–Cr) wire is demonstrated, relying on which BVG/Ni–Cr wire presents a high blackbody‐like emissivity of ≈0.96 across a wide wavelength range (2.5–18 µm). When used for radiative heating, BVG/Ni–Cr wire achieves a high thermal radiation efficiency with an order of magnitude improvement compared with bare Ni–Cr wire, as well as the superior deformation and thermal stabilities. These findings reveal the impressive potentials of BVG as an excellent infrared radiation material for the energy‐efficient radiative thermal management.

Effect of AC electric field on flame spread in electrical wire: Variation in polyethylene insulation thickness and di-electrophoresis phenomenon

The effect of AC electric field on flame spread over polyethylene (PE)-insulated electrical wire was experimentally investigated by varying the applied AC voltage (VAC) and frequency (fAC) with special attention to the effect of the thickness of the PE insulation material (Tins). The diameter of the Ni–Cr wire was 0.5 mm and Tins was 0.15, 0.3, and 0.5 mm, yielding outer diameters (Dout) of 0.8, 1.1, and 1.5 mm, respectively. For the baseline cases with no electric field, the flame spread rate (FSR) (flame size) decreased (increased) with insulation thickness. Both FSR and flame size were appreciably influenced by applied AC electric fields. The FSR behaviors under applied electric fields could be classified into three sub-regimes as AC frequency increased: regime I exhibited a decreasing FSR as AC frequency increased, regime II exhibited an increasing FSR, and regime III again exhibited a decreasing FSR. Molten PE dripped from the wire (resulting in mass loss); exhibited di-electrophoresis (some molten PE moved from the main molten zone toward the burnt wire, forming globules in the process); and developed electrosprays (ejection of small droplets from the molten PE surface). For Dout = 0.8 mm, the FSR behavior was similar to that of the flame width, such that the behavior could be explained by the thermal balance mechanism. When a low voltage and high frequency were applied to wires with Dout = 1.1 and 1.5 mm, molten PE droplets detached and moved to the burnt wires continuously (although sometimes intermittently) from the main body of molten PE; the FSR behavior thus deviated from that of regime I. Droplet detachment was attributable to a di-electrophoresis. The distance moved correlated well with the difference in electric field intensities of burnt and unburned wires. Appreciable dripping of molten PE occurred at high voltages and moderate frequencies in regime II. When the frequency was excessive, flame extinction occurred via two routes: appreciable reduction of flame size when Dout = 0.8 mm in regime I and appreciable fuel mass loss via dripping of molten PE during flame spread when Dout = 0.8 and 1.1 mm in regime III. These extinction frequencies correlated well with VAC/Dout. When high voltage and frequency were applied in the Dout = 1.5 mm case, droplets detached and moved to the burnt wire via di-electrophoresis; subsequently a series of fine droplets ejected from the surface via electrospraying, while the molten PE region grew and subsequently dripped. In such cases, flame extinction did not occur because di-electrophoresis increased the flame width and thereby the FSR over the experimental ranges of VAC and fAC.

Mechanical loading leads to osteoarthritis-like changes in the hypofunctional temporomandibular joint in rats

ObjectivesTemporomandibular joint (TMJ) hypofunction secondary to feeding a liquid diet in the growing period leads to morphological hypoplasia. However, few studies have evaluated the results of mechanical loading on the hypoplastic TMJ. This study investigated whether TMJ hypofunction in rats causes osteoarthritis (OA)-like changes when exposed to mechanical loading. DesignMale 21-day-old Wistar rats were divided into four groups. The first group (C) served as the control. In the second group (W), mechanical loading was applied to the TMJ by continuous steady mouth opening (3h/day for 5 days) from 63 days of age. A jaw-opening device was used to hold the mandible open in the maximal mouth-opening position with a cobalt–chromium (Co–Cr) wire (φ: 0.9mm). Groups C and W both received a normal hard diet. The third group (L) and fourth group (LW) were fed a liquid diet and group LW were subjected to the same loading as group W. We evaluated the TMJ using micro-CT, toluidine blue staining and immunohistochemistry of matrix metalloproteinase (MMP)-13. ResultsIn group LW in the superior and posterior regions of the condyle, bone volume fraction, trabecular thickness and trabecular number were significantly decreased and trabecular spacing was significantly increased. The ratio of MMP-13 immunopositive cells was significantly higher than in the other groups. OA-like changes were also observed, including reduced thickness of the cartilage, irregularities in the chondrocytic layer, and cell-free areas. ConclusionsTMJ hypofunction in rats is likely to lead to OA-like changes when exposed to mechanical loading.

Effects of thickness of boiling-induced nanoparticle deposition on the saturation of critical heat flux enhancement

Abstract Pool boiling tests were conducted to determine the effects of nanoparticle coating thickness on critical heat flux in 0.01 vol.% alumina nanofluid under atmospheric pressure using Ni–Cr wire heaters. The thickness of nanoparticles coating layer was controlled by varying the boiling time for pre-coating in the nanofluid. The CHF enhancement curve was acquired with respect to time of pre-coating process. As the result, the CHF enhancement is remained or saturated regardless of boiling time over certain or critical pre-coating time while the CHF sharply increased in relatively shorter pre-coating time. The CHF is gradually decreased after the critical time region. The wetting characteristics and the Taylor wavelengths on the coating surfaces were investigated to explain the trend of CHF regarding the effects of coating thickness. The physical deposition characteristics such as the coating thickness and the porosity were studied to analyze the CHF trend. The porosity is a key parameter to determine the CHF saturated under conditions over a critical coating thickness.

Polypyrrole/montmorillonite nanocomposite as a new solid phase microextraction fiber combined with gas chromatography–corona discharge ion mobility spectrometry for the simultaneous determination of diazinon and fenthion organophosphorus pesticides

A novel solid phase microextraction (SPME) fiber was prepared and coupled with gas chromatography corona discharge ion mobility spectrometry (GC–CD–IMS) based on polypyrrole/montmorillonite nanocomposites for the simultaneous determination of diazinon and fenthion. The nanocomposite polymer was coated using a three-electrode electrochemical system and directly deposited on a Ni–Cr wire by applying a constant potential. The scanning electron microscopy images revealed that the new fiber exhibited a rather porous and homogenous surface. The thermal stability of the fabricated fiber was investigated by thermogravimetric analysis. The effects of different parameters influencing the extraction efficiency such as extraction temperature and time, salt addition, stirring rate, the amount of nanoclay, and desorption temperature were investigated and optimized. The method was exhaustively evaluated in terms of sensitivity, recovery, and reproducibility. The linearity ranges of 0.05–10 and 0.08–10μgL−1, and the detection limits of 0.020 and 0.035μgL−1 were obtained for diazinon and fenthion, respectively. The relative standard deviation values were calculated to be lower than 5% and 8% for intra-day and inter-day, respectively. Finally, the developed method was applied to determine the diazinon and fenthion (as model compounds) in cucumber, lettuce, apple, tap and river water samples. The satisfactory recoveries revealed the capability of the two-dimensional separation technique (retention time in GC and drift time in IMS) for the analysis of complex matrices extracted by SPME.

Vortex generation using fin-slot structures and a submerged nozzle at a wall-injected cylinder

The internal flows of solid rocket motors are not yet fully understood. Several cold-air flow experiments that simulated combustion gas flow with compressed gas wall injections have been conducted to observe the behavior of internal flows and acoustic phenomena. Direct visualization, however, has rarely been performed due to the non-transparency of the wall-injecting media. In this study, novel techniques were employed to visualize the internal flow of the cold-flow model of a solid rocket motor. The smoke, which was generated using a heated Ni–Cr wire, was used as a flow tracer, and a light penetrated through an acrylic nozzle. The head-end of the test model was made with a transparent acrylic window to record the visualized flow using a high-speed CCD camera. The results of the visualization at the nozzle entrance region showed the symmetric vortex tube structures and the transient behavior of the circumferential flow. The vortex tube generation mechanism was explained with reference to the inlet vortex phenomenon of an aircraft engine. Also, it was observed that the interaction between the adjacent vortex tubes created the circumferential flow.

Experimental study of a universal CHF enhancement mechanism in nanofluids using hydrodynamic instability

Pool boiling tests were designed and performed to confirm the relation between the enhancement of critical heat flux (CHF) in nanofluids and the development of a hydrodynamic instability on the test heater surface from the deposition of nanoparticles during boiling. These pool boiling experiments were carried out under atmospheric pressure using a 0.49mm diameter cylindrical Ni–Cr wire as a heating element with ZnO, SiO2, SiC, Al2O3, graphene oxide and CuO nanoparticles at 0.01% volume concentration. The test fluids are distilled water and R-123. The CHF value for each nanofluid is obtained and compared with the measured Rayleigh–Taylor wavelength. Higher CHF results have shorter Rayleigh–Taylor wavelengths in all cases. We propose a modified theoretical model for hydrodynamic instability that incorporates these effects and fits experimental results.

The effect of pressure on the critical heat flux in water-based nanofluids containing Al2O3 and Fe3O4 nanoparticles

Water-based nanofluids are colloidal dispersions of nanoparticles in pure water and have significantly higher critical heat flux (CHF) values compared to pure water at atmospheric pressure. This paper describes the effects of pressure on the CHF in a pool of water-based nanofluids of magnetite (Fe3O4) and alumina (Al2O3) nanoparticles using Ni–Cr wire. To evaluate the effect of pressure on the CHF enhancement of water-based nanofluids, pool boiling CHF experiments using pure water were first conducted at 101kPa (atmospheric pressure) to 1100kPa of absolute pressure. The CHF values for pure water increased with increasing system pressure, as expected. The results for pure water were compared with the CHF correlations and were found to be well matched. Based on the results for the pure water case, pool boiling CHF experiments using magnetite water nanofluid (MWNF) and alumina water nanofluid (AWNF) were performed at higher pressures within the same range as those used for the pure water case. It was found that the CHF using water-based nanofluids also can be enhanced at high pressures in a pool. Based on the obtained results, several methods (i.e., analyses of the bubble dynamics during nucleate boiling, of the contact angle with a droplet of pure water, and of the weight of deposited nanoparticles on the heating surface after CHF) were used to investigate the mechanism of CHF occurrence and the effect of pressure on the CHF in water-based nanofluids. The bubble frequency in the nanofluids was approximately 2 times higher than that for pure water. Due to the higher frequency of departing bubbles, the opportunity to rewet the hot spots on the heating surface was increased. The contact angles of the nanofluid were lower than that for the pure water cases at all ranges of pressure tested. The weight of the deposited nanoparticles on the heating surface decreased as the system pressure was increased. We discuss the effect of pressure on the surface characteristics in detail based on these analyses.

Experimental study on the pool boiling CHF enhancement using magnetite-water nanofluids

This paper described the effects of a magnetite-water nanofluid (MWNF) on the critical heat flux (CHF) enhancement using an Ni–Cr wire in pool boiling. All experiments were performed at a saturated condition under atmospheric pressure. The CHF values between the MWNF and the other nanofluids with several volume concentrations were compared to evaluate the effect of the MWNF on the CHF enhancement. The CHF values of the MWNF were enhanced from approximately 170% to 240% of pure water as the nanoparticle concentration increased. In addition, the CHF for the MWNF showed the highest value among the evaluated nanofluids. In this paper, three methods were introduced to elucidate the mechanism underlying CHF enhancement. First, scanning electron microscope (SEM) images were obtained to explain the CHF enhancement mechanism due to the deposited nanoparticles, which is related to the surface wettability of the heating surface during the pool boiling. Second, bubble formation in pool boiling was analyzed using image processing to demonstrate the relationship between bubble dynamics and CHF enhancement. Finally, the magnetic field was analytically calculated using the Biot–Savart law to evaluate the effects of the magnetic field on the CHF.

Experimental investigation of pool boiling of Fe3O4/ethylene glycol–water nanofluid in electric field

Nucleate boiling and critical heat flux (CHF) of Fe3O4/ethylene glycol–water nanofluid at atmospheric pressure on a horizontal thin Ni–Cr wire were investigated. Fe3O4 nanoparticles were dispersed in 50% (by volume) ethylene glycol/de-ionized water as base liquid in different concentrations (0.01–0.1% (by volume)). Experiments showed that boiling heat transfer coefficients deteriorate by increasing nanoparticle concentration in nanofluid. Addition of nanoparticles delays nucleate boiling incipience and increases CHF. Scanning Electron Microscope (SEM) graphs showed that porous layer of deposited nanoparticles formed on the heating surface boiled in nanofluid. The maximum CHF enhancement was obtained for 0.1% (by volume) nanofluid to be about 100%. Enhanced CHF was measured when previously boiled wire in nanofluid was used to boil the base fluid. Two different electrodes were used for applying electric field in the boiling nanofluids. Electric field applied in both configurations augmented boiling heat transfer coefficients while CHF remained almost unchanged.

Experimental studies on CHF characteristics of nano-fluids at pool boiling

To investigate the CHF characteristics of nano-fluids, pool boiling experiments of nano-fluids with various concentrations of TiO2 or Al2O3 nanoparticles were carried out using a 0.2mm diameter cylindrical Ni–Cr wire under atmospheric pressure. The results show that the CHFs of various nano-fluids are significantly enhanced over that of pure water. SEM observation subsequent to the CHF experiment revealed that a nanoparticle coating is generated on the wire surface during pool boiling of nano-fluids. The CHF of pure water was measured on a nanoparticle-coated wire which was produced during the pool boiling experiments of nano-fluids. The CHF of pure water on the nanoparticle-coated wire was similar to that of nano-fluids. This result clearly shows that the main reason for CHF enhancement of nano-fluids is the modification of the heating surface by the nanoparticle deposition. The nanoparticle-coated surface was characterized with various parameters closely related to pool boiling CHF: surface roughness, contact angle, and capillary wicking performance. Finally, CHF enhancement of nano-fluids is discussed using the parameters.

Sliding wear behavior of copper alloy contact wire against copper-based strip for high-speed electrified railways

This paper reports the study of the sliding wear behavior of the Cu–Ag–Cr wire. Cu–Ag–Cr alloy is a promising contact wire material for high-speed electrified railways, which has an excellent combination of mechanical strength and electrical conductivity. Wear tests were conducted under laboratory with a special sliding wear apparatus, which simulated the tribological conditions of sliding current collectors on overhead wires in the railway system. The Cu–Ag–Cr alloy wire was slid against a copper-based powder metallurgy strip under unlubricated conditions. The same strip as those in the train systems were used. Worn surfaces of the Cu–Ag–Cr alloy wire were analyzed by scanning electron microscopy (SEM) and energy dispersive X-ray spectrum (EDS). Within the studied range of electrical current, normal pressure and sliding speed, the wear rate increased with the increasing electrical current and the sliding distance. Compared with a Cu–Ag contact wire under the same conditions, the Cu–Ag–Cr alloy wire had much better wear resistance. Adhesive wear, abrasive wear and arc erosion were the dominant mechanisms during the electrical sliding processes.

Characterisation of NiCr wire coatings on Ni- and Fe-based superalloys by the HVOF process

Microstructural uniformity has long been considered necessary to improve the thermal, chemical and mechanical properties of materials. Metallurgists are continuously searching various processes with the intent to produce a uniform microstructure throughout the material. This study reveals the successful high-velocity oxy-fuel (HVOF) deposition of near-uniform Ni–20% Cr wire coatings, approximately 200–250 μm thick. The coatings were deposited onto Ni- and Fe- based superalloys for hot corrosion applications. The microstructural characteristics of the deposits have been studied using the combined techniques of X-ray diffraction (XRD), optical microscopy, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDAX). The coatings exhibited characteristic splat-like, layered morphologies due to the deposition and re-solidification of successive molten or semi-molten droplets. Under the employed HVOF spray conditions, a high proportion of the feedstock wire appeared to have been fully melted prior to impact on the substrate. The developed coatings have a dense and nearly uniform microstructure, with almost uniform hardness values in the range of 600–630 Hv and porosity less than 1%. XRD and EDAX results revealed that the main constituent outstanding phase of Ni–20% Cr coating is Ni. A very small fraction of Cr 2O 3 oxide phase has formed in the structure of the coating in the form of either intersplat lamellae or globules. Some partially melted particles are also observed in the structure of the coatings.

Wear behavior of Cu–Ag–Cr alloy wire under electrical sliding

The wear behavior of a Cu–Ag–Cr alloy contact wire against a copper-base sintered alloy strip was investigated. Wear tests were conducted under laboratory conditions with a special sliding wear apparatus that simulated train motion under electrical current conditions. The initial microstructure of the Cu–Ag–Cr alloy contact wire was analyzed by transmission electron microscopy. Worn surfaces of the Cu–Ag–Cr alloy wire were analyzed by scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDS). The results indicate that the wear rate of the Cu–Ag–Cr wire increased with increasing electrical current and sliding. Within the studied range of electrical current, the wear rate increases with increasing electrical current and sliding speed. Compared with the Cu–Ag contact wire under the same testing conditions, the Cu–Ag–Cr alloy wire has much better wear resistance. Adhesive, abrasive, and electrical erosion wear are the dominant mechanisms during the electrical sliding processes.

Field emission from aligned carbon nanofibers grown in situ by hot filament chemical vapor deposition

Aligned high-aspect-ratio carbon nanofibers were grown in situ using modified hot filament chemical vapor deposition. The field-emission properties were then studied. An Fe–Cr wire filament acted as a catalytic source and a heat source. Carbon nanofibers were deposited on a Si substrate with CO2 as a carrier gas through ethanol. The experimental results indicate that the flow in the horizontal direction to the substrate produces carbon nanofibers with diameters of less than 10 nm. The field-emission current of 2 V/μm was 0.54 mA/cm2; the turn-on field of the sample was 1.1 V/μm.

Sub-second thermal desorption of a micro-sorbent trap for the analysis of ambient volatile organic compounds

This study investigates a novel approach of fast thermal desorption on a micro-sorbent trap for analyzing ambient volatile organic compounds (VOCs) by gas chromatography with flame ionization detection. Unlike conventional approaches, the temperature feedback mechanism for temperature control was abandoned, which often poses a limit to the heating speed due to slow response of the sensor and the control algorithm. Instead, a series of programmed a.c. pulses was given to the Ni–Cr wire coiled around the micro-trap to perform instant heating from room temperature to 250 °C within a fraction of a second, maintained at 250 °C during injection, and subsequently to 300 °C for trap cleaning. Temperature fluctuation around a high temperature set point could be maintained within ±10 °C. Significant improvement in resolution and peak height was obtained compared to a trap with temperature feedback and control algorithm. While keeping resolution at a satisfactory level, the sub-second desorption approach allows faster chromatography and at the same time increases the sensitivity of VOC analysis.

Synthesis of multiwalled carbon nanotubes using methane/air diffusion flames

An experimental investigation has been conducted on the synthesis of multiwalled carbon nanotubes (MWCNTs) using methane/air laminar diffusion flames, with an emphasis on the effects of flame temperature and catalyst particle size on nanotube growth. The yield of MWCNTs occurred on a substrate consisting of a 0.4 mm Ni−Cr (60% Ni, 26% Cr, and 14% Fe) catalyst wire connected to a stainless steel grid. The self-formed catalyst particles in the flame were analyzed by energy dispersive X-ray to be mostly nickel oxide with some iron oxide. A high-resolution transmission electron microscope analysis indicates well-graphitized layers of MWCNTs consisting of continuous lattice fringes along the cylindrical section of the nanotube. We studied the effects of flame temperature on nanotube growth by changing the sampling location along the flame height and diluting methane with nitrogen. High temperature was found to favor the growth of large-diameter nanotubes, and nanotube growth was influenced by chemical species environment in the flame. Nitric acid treated Ni−Cr wire produced smaller sized catalyst particles that can be encapsulated within the nanotubes. The growth of well-aligned, bean-sprout-like bundles of nanotubes with catalyst particles pushed up at the tube top was found to occur: the mechanism of this unique synthesis is unknown and needs further study.

Mechanical polarization modulator using micro-turbo machinery for Fourier transform infrared spectroscopy

This paper describes the development of a mechanical polarization modulator using micro-turbo machinery for double modulation Fourier transform infrared spectroscopy (FT-IR). The modulator has a Au–Cr wire grid polarizer with a pitch of 4 μm on the backside of a φ 5 mm silicon turbine rotor. The modulator is composed of a top Pyrex glass layer and three n-type silicon layers, which were fabricated mainly by photolithography and deep reactive ion etching (deep RIE). The rotational speed was measured using nitrogen as a driving gas. This confirmed the rotational speed of about 18,000 rpm, when the volume flow rate was 8.8 l/min. The higher volume flow rate broke the edge of an air port in the second layer. We also confirmed the polarization of infrared light using a broadband infrared lamp and a fixed polarizer. The polarization was modulated according to the rotor rotation; however, the signal/noise ratio was low because of the wide pitch of the wire grid polarizer.

Nanotubes from methane flames

Entangled multi-walled carbon nanotubes with a diameter range of 20–60 nm were found to grow on a Ni–Cr wire in laminar co-flow methane-air diffusion flames. Nickel oxide particles were inside some of the nanotubes, suggesting that their particles, formed on the wire at the early stage of the synthesis, acted as catalyst. The carbon nanotubes can grow by a root-growth mechanism in a limited region inside the flame where oxygen plays an important role in the formation of nanotubes.

A FIM/AP INVESTIGATION OF A RAPIDLY SOLIDIFIED ALUMINIUM-CHROMIUM ALLOY

A rapidly solidified Al - 6 to 9wt%Cr alloy formed by vapour deposition has been studied by field-ion microscopy and atom probe microanalysis (FIM/AP). The as-deposited material was found to contain brightly imaging Cr-rich particles, both spherical and rod-shaped, of about 0.5-1nm in diameter and up to 5nm long. Random area AP analysis showed the presence of Cr-enrichment on a very fine scale, with estimated particle compositions of 30-50at%Cr. No change in particle size or composition was observed for aging at 350°C for up to 20 hours. By comparison, an Al-4wt%Cr wire formed by in-rotating-water quenching showed no indication of precipitation in its as-received state by either FIM or AP.