Back Flow Channel Research Articles

Optimization and Application of Coal Pillar in Fully Mechanized Mining Face based on Energy Analysis

Based on the theory of energy dissipation, a numerical model of goaf excavation was established by FLAC3D based on the backflow channel of Heilong Coal Industry 2202. The dissipative energy distribution characteristics of coal pillars with different widths were studied, and the dissipative energy evolution law of surrounding rock of goaf roadway was analyzed. With the increase of the width of coal pillar, the width of elastic core zone is positively correlated with the bearing capacity. The peak value of dissipated energy density decreases with the increase of the width of coal pillar, and the concentration degree and region of dissipated energy density on the side of coal pillar are greater than that on the side of solid coal pillar. The project is applied to Heilong 2201 working face, and the optimum width of coal pillar and its supporting scheme are given. The practice results show that when the width of coal pillar is 5m, the deformation of surrounding rock can be effectively controlled and the demand for safe and efficient production can be met.

Numerical and Experimental Investigation on the Performance of Backflow Channel Aerostatic Bearings with Shunt Injection

Simultaneously increasing the load capacity and stiffness of aerostatic bearings is highly significant for ultraprecision machining. To achieve this goal, this study presents a novel method of using backflow channels to divert high-pressure air from the feed pocket to the low-pressure region of the clearance. Different shunt injections are coupled at the end part of the backflow channels. The effects of distribution and structure of the shunt injections are systematically analyzed. Moreover, the experimental data are used to compare and validate the numerically predicted characteristics. Results show that the backflow channels simultaneously enlarge the high-pressure region and improve the load capacity and stiffness of the bearings. The pressure difference between the inherent orifice shunt injections is still evident, which is not beneficial in exploring the potentialities of backflow channels in terms of increasing the load capacity and stiffness of bearings. High-pressure air can be stored under the pocket orifice shunt injection to decrease the pressure difference. Slot shunt injections shaped similar to ramparts can surround the high-pressure air, resulting in a more apparent effect on decreasing the pressure difference. Finally, the load capacity, stiffness, and mass flow rate of the backflow channel bearings are evidently larger than those of pocket orifice bearings. Thus, the growing demand of mass flow rate must also be considered when using backflow channel bearings for their larger load capacity and higher stiffness.

CFD-based investigation and experimental study on the performances of novel back-flow channel aerostatic bearings

Pocketed orifice-restricted aerostatic bearings (PORABs) are broadly used in ultraprecision machining. Increasing the load capacity, stiffness and stability of PORABs is the continuing need for the development of ultraprecision machining. Traditionally, the load capacity and stiffness of PORABs are improved by optimizing the pocket. However, the vortex, which is a critical reason to decrease the bearing stability to influence the precision of machining, always exists in the pocket. Thus, increasing the load capacity, stiffness, and stability of the aerostatic bearings simultaneously is difficult. This paper presents a novel aerostatic bearing with back-flow channels, which are designed to connect the feed pocket and low-pressure region of the bearing clearance directly. Numerical results of air flow show that the high-pressure region of back-flow channel aerostatic bearings (BCABs) can be increased coupling with the vortex in the feed pocket being disappeared. The theoretical load capacity and stiffness of BCABs are larger and higher than those of PORABs. Two experimental test-beds are designed to test the bearing performances. Experimental results of load capacity obtain agree with the predictions greatly. The micro vibration of BCABs measured from the experiments is smaller than that of PORABs. The numerical and experimental results prove that the load capacity, stiffness, and stability of PORABs are increased simultaneously relative to BCABS.

Correction to: Development of graphene nanoplatelets-reinforced thermo-responsive shape memory nanocomposites for high recovery force applications

The development and large-scale implementation of multifunctional advanced materials with smart and intelligent properties like shape memory are very topical. In the present work, we report the development of multifunctional graphene nanoplatelets (GNPs)-reinforced thermo-responsive shape memory composites, in ether type shape memory polyurethane (SMPU) matrix. A unique twin screw co-rotating microcompounder with a back flow channel was operated to ensure proper dispersion of GNPs in the SMPU matrix for developing different compositions of nanocomposites, namely SMC0, SMC1, SMC2, and SMC3, respectively. The detailed characterizations and properties of the above developed nanocomposites were studied using various complementary techniques for spectroscopy, morphology, mechanical, thermal, shape memory, DMA, etc. The dynamic thermomechanical properties of all the developed nanocomposites were studied at 0.1 and 10 Hz, respectively. Structure of SMP and developed composite were also analyzed using various spectroscopic methods. The addition of GNPs to the SMP matrix improved the mechanical and shape memory properties, although a noticeable impact on thermal property is also reported. The fractured microphotographs reveal the uniform dispersion of GNP in SMPU. Addition of 1 phr GNPs increased storage modulus of SMPU from 3.14 to 4.11 GPa and the value of tan δ peak was decreased from 0.81 to 0.53, respectively. The GNPs in SMPU matrix influences the shape recovery, which is improved with the addition of GNPs in the experimental range.

Development of Graphene Nanoplatelets-Reinforced Thermo-Responsive Shape Memory Nanocomposites for High Recovery Force Applications

The development and large-scale implementation of multifunctional advanced materials with smart and intelligent properties like shape memory are very topical. In the present work, we report the development of multifunctional graphene nanoplatelets (GNPs)-reinforced thermo-responsive shape memory composites, in ether type shape memory polyurethane (SMPU) matrix. A unique twin screw co-rotating microcompounder with a back flow channel was operated to ensure proper dispersion of GNPs in the SMPU matrix for developing different compositions of nanocomposites, namely SMC0, SMC1, SMC2, and SMC3, respectively. The detailed characterizations and properties of the above developed nanocomposites were studied using various complementary techniques for spectroscopy, morphology, mechanical, thermal, shape memory, DMA, etc. The dynamic thermomechanical properties of all the developed nanocomposites were studied at 0.1 and 10 Hz, respectively. Structure of SMP and developed composite were also analyzed using various spectroscopic methods. The addition of GNPs to the SMP matrix improved the mechanical and shape memory properties, although a noticeable impact on thermal property is also reported. The fractured microphotographs reveal the uniform dispersion of GNP in SMPU. Addition of 1 phr GNPs increased storage modulus of SMPU from 3.14 to 4.11 GPa and the value of tan δ peak was decreased from 0.81 to 0.53, respectively. The GNPs in SMPU matrix influences the shape recovery, which is improved with the addition of GNPs in the experimental range.

FDM 3D printing of MWCNT re-inforced ABS nano-composite parts with enhanced mechanical and electrical properties

This work presents significant mechanical and electrical property enhancement of 3D printed parts through dispersion of multiwall carbon nanotubes (MWCNTs) using twin-screw micro-compounding extruder having a backflow channel facility. The composite structure obtained has been further processed in a single screw extruder to produce 3D printing filaments, 1,7 mm in diameter. The mechanical, electrical and melt flow properties of the MWCNT reinforced ABS matrix composite parts, with loading percentages up to 10% has been presented for the first time in this work, using a commercial 3D printer. Moreover effects of raster angle on tensile properties such as tensile strength, ductility and the elastic modulus as well as the electrical conductivity are also studied. The tensile strength of 3D printed parts has increased considerably (up to 58 MPa equaivalent to 288% increase) with 7 wt.% addition of MWCNTs in ABS. However ductile to brittle transition was observed with increasing MWCNT concentraion. Micro Raman spectroscopic and scanning electron microscopic analysis made on the 3D-printed MWCNT parts supports the enhanced mechanical properties. Electrical conductivity of the composites has also shown dramatic increase (∼ 7 fold increase), owing to the existance of MWCNT particles. A 3 wt.% MWCNT loading percolation threshold found for the linear printing direction shifted to 5 wt.% for the crossed layered samples.

Dielectric and impedance properties of three dimension graphene oxide-carbon nanotube acrylonitrile butadiene styrene hybrid composites

In this work, comparison of dielectric and impedance studies of multi-walled carbon nanotube (MWCNTs), graphene oxide-carbon nanotube (GCNTs) reinforced acrylonitrile–butadiene–styrene (ABS) composites prepared by twin-screw extruder with back flow channel have been carried out. The dielectric relaxation and impedance behavior of these polymer composites have been studied with varying wt. % of MWCNTs and GCNTs reinforced ABS matrix in the frequency range of 102–106 Hz. The results showed that the real part of the impedance of the composites with MWCNTs content of 7 wt % or higher exhibits frequency independent behavior at the low-frequency region, and GCNTs-ABS demonstrates frequency dependent. Also, the relaxation time decreases with increase in wt. % of carbon nanofillers due to the formation of an interconnecting path within the polymer matrix. The Nyquist plots for MWCNTs-ABS composites showed the appearance of a single semicircular arc, whose radius of curvature decreases with increase in MWCNTs loading, suggest the decrease in overall impedance of the composite with high amount of filler loading. The radius of arc in impedance spectra decreases with increasing the percentage of fillers indicating the occurence of conducting behavior. In GCNTs-ABS composites Nyquist plots showed the appearance of a single straight line. The dielectric responses of MWCNTs, GCNTs reinforced ABS composites were investigated. The dielectric constant of MWCNTs-ABS composites gets enhanced significantly with addition 0 to 3 wt % MWCNTs. Room temperature AC conductivity increased with increase in the wt. % of MWCNTs and GCNTs from 10−12 S/cm for the unfilled polymer to 10−5 S/cm for 10 wt % of MWCNTs-ABS and 10−7 S/cm for 10 wt % of GCNTs-ABS composites. The decrease in impedance and enhancement of dielectric properties were due to the interfacial polarization between MWCNTs and ABS. Improved conductivity of MWCNTs-ABS and GCNTs-ABS composites may be useful in electromagnetic interference (EMI) shielding and antistatic materials.

Synergetic effect of graphene oxide-carbon nanotube on nanomechanical properties of acrylonitrile butadiene styrene nanocomposites

Herein, multiwall carbon nanotubes (MWCNTs), reduced graphene oxide (rGO), graphene oxide-carbon nanotubes (GCNTs) hybrid reinforced acrylonitrile butadiene styrene (ABS) nanocomposites have been prepared by micro twin screw extruder with back flow channel and the effect of different type of fillers on the nanomechanical properties are studied. The combination of both graphene oxide and CNT has enhanced the dispersion in polymer matrix and lower the probability of CNTs aggregation. GCNTs hybrid have been synthesized via novel chemical route and well characterized using Raman spectroscopic technique. The nanoindentation hardness and elastic modulus of GCNTs-ABS hybrid nanocomposites were improved from 211.3 MPa and 4.12 GPa of neat ABS to 298.9 MPa and 6.02 GPa, respectively at 5wt% GCNTs loading. In addition to hardness and elastic modulus, other mechanical properties i.e. plastic index parameter, elastic recovery, ratio of residual displacement after load removal and displacement at the maximum load and plastic deformation energy have also been investigated. These results were correlated with Raman and X-ray photoelectron spectroscopic (XPS) techniques and microstructural characterizations (scanning electron microscopy). Our demonstration would provide guidelines for the fabrication of hard and scratches nanocomposite materials for potential use in, automotive trim components and bumper bars, carrying cases and electronic industries and electromagnetic interference shielding.

Confinement-Induced Instabilities in a Jet-Stabilized Gas Turbine Model Combustor

Self-sustained jet flapping is observed in a confined, premixed and preheated methane-air turbulent flame, generated in a single-nozzle jet-stabilized gas turbine model combustor designed based on the FLOX Ⓡ concept. The flapping frequency and its complex motion within the confinement of the combustor are characterized in detail using proper orthogonal decomposition (POD) of the flow fields measured by particle imaging velocimetry (PIV). The influence of jet flapping on combustion stability is examined using simultaneous PIV/OH chemiluminescence imaging and PIV/planar laser-induced fluorescence of OH radicals (OH PLIF) at 5 kHz repetition rate. By influencing the size and location of the recirculation zones, jet flapping modifies the flame shape and flame lift-off height. It also controls the amount of hot gas entrainment into the recirculation zones. In extreme cases, jet flapping is found to cause temporary local extinction of the flame, due to jet impingement on the combustor wall and partial blockage of burned gas entrainment. The flame is only able to recover after the jet detaches from the wall and reopens the back flow channel. The results suggest that jet flapping could play a key role in the stabilization mechanisms in similar jet-stabilized combustors.

Detailed dynamic rheological studies of multiwall carbon nanotube-reinforced acrylonitrile butadiene styrene composite

Dynamic rheological properties of multiwalled carbon nanotubes-(MWCNTs) reinforced acrylonitrile butadiene styrene (ABS) composites prepared by micro twin-screw extruder with back flow channel (used for proper dispersion) are reported. Scanning electron microscopic and high-resolution transmission electron microscopic studies showed that the nanotubes were uniformly dispersed in the ABS polymer matrix. MWCNT forms a network throughout the polymer matrix and thus promotes the reinforcement. The rheological studies showed that (for 3 wt% of MWCNTs loading) the material undergoes viscous to elastic transition. At a higher MWCNTs concentration nematic gel-like phase is observed where both storage and loss modulus (G′ and G″) are nearly independent of frequency. van Gurp–Palmen plot has been used to determine the viscoelastic properties. Dynamic intersection frequency has been used to correlate the rheological properties with different wt% of MWCNTs loading in ABS. Dynamic rheological measurements revealed the viscous-like (G″ > G′) behaviour at a lower MWCNTs loading ( 3 wt%).

Superior mechanical and electrical properties of multiwall carbon nanotube reinforced acrylonitrile butadiene styrene high performance composites

In-house synthesized multiwall carbon nanotubes (MWCNTs) have been dispersed in acrylonitrile butadiene styrene (ABS) using a micro twin-screw extruder with back flow channel. The electrical and mechanical properties of MWCNTs in ABS with different wt% have been studied. Incorporation of only 3 wt. % MWCNTs in ABS leads to significant enhancement in the tensile strength (up to 69.4 MPa) which was equivalent to 29% increase over pure ABS. The effect of MWCNTs on the structural behaviour of ABS under tensile loading showed a ductile to brittle transition with increase concentration of MWCNTs. The results of enhanced mechanical properties were well supported by micro Raman spectroscopic and scanning electron microscopic studies. In addition to the mechanical properties, electrical conductivity of these composites increased from 10−12 to 10−5 Scm−1 showing an improvement of ∼7 orders of magnitude. Due to significant improvement in the electrical conductivity, EMI shielding effectiveness of the composites is achieved up to −39 dB for 10 wt. % loaded MWCNTs/ABS indicating the usefulness of this material for EMI shielding in the Ku-band. The mechanism of improvement in EMI shielding effectiveness is discussed by resolving their contribution in absorption and reflection loss. This material can be used as high-strength EMI shielding material.

Mechanical and electrical properties of high performance MWCNT/polycarbonate composites prepared by an industrial viable twin screw extruder with back flow channel

High performance multiwall carbon nanotube (MWCNT) reinforced polycarbonate (PC) composites were prepared using an industrially viable fast dispersion process by a micro twin screw extruder with back flow channel and their mechanical and electrical properties were investigated for EMI shielding applications. A uniformly dispersed MWCNT/PC composite system was observed through SEM and TEM investigations. Incorporation of a small amount of MWCNT (2 wt%) led to enhancements in the tensile strength (up to 79.6 MPa) and flexural strength (up to 110 MPa), which were equivalent to 19.6% and 14.6% increases over the neat PC. The effect of MWCNTs on the failure mechanism of the PC under tensile loading showed a ductile to brittle transition with increasing concentration of MWCNTs. The results of enhanced mechanical properties were well supported by micro Raman spectroscopic studies. In addition to the mechanical properties, significant improvement in the electrical conductivity (0.01 S cm−1 at 10 wt% MWCNT) of these composites was observed which yielded the EMI shielding of −27.2 dB in the Ku band suggesting their possible use as a high strength EMI shielding material.

The novel use of phase change materials in a refrigerated display cabinet: An experimental investigation

In this paper, the performance of a refrigerated open-type multi-deck display cabinet with integrated phase change material (PCM) was investigated experimentally. The PCM (water gel) was purposely selected and made by mixing different compositions at specific mass ratios to obtain the appropriate melting and freezing temperatures for this particular application. It was then charged into two single panel radiators, installed immediately after the cabinet evaporator in the main back flow channel, such that the cooled air flow could pass through both external radiator sides. The display cabinet, with or without PCM integration, was then mounted in an air-conditioned chamber and tested at the same operating condition to measure and compare the performances of the system and components. The tests results showed that by installing the PCM radiators, up to 5% of energy savings and lower cabinet temperatures could be achieved. Further benefits could also be obtained, such as a greater stabilization of product temperatures during the defrost period for the modified display cabinet.

COMPUTATIONAL INVESTIGATION OF THERMAL PLASMAS IN A SF6 CHAMBER WITH DIFFERENT APPLIED CURRENTS

In this study, we predicted the thermal breakdown of high-voltage interrupter with the characteristics of thermal plasmas such as temperature, pressure and concentration of the ablated material by using a commercial CFD program. The results showed that the pressure build-up inside the chamber was proportional to the magnitude of applied current because the quantities of heat energy and ablated mass also increase together with the current during the compression process. During the decompression process, the reverse flow found did not coincide with the magnitude of current due to the compressibility of the gas through backflow channel. The present method is expected to be useful for the design of guideline and interruption capacity on the thermal breakdown of a PASB chamber.

MiniLab - Compounder and Reactor

Abstract The use of a conical twin screw extruder with backflow channel combines aspects of mixing and extrusion in a batch process. Tests and results of the new MINLAB mircocompounder are discussed in the following paper. With a total filling volume of 7 ml and a built in slit capillary die the applications focus on compounding and reactions of small amounts of polymers in molten stage.