Insulated Tube Research Articles

Modeling for the Fabrication Process of a ϕ1185 mm C/C Composite Thermal Insulation Tube in an Isothermal Chemical Vapor Infiltration Reactor

The large-size chemical vapor infiltration (CVI) of the carbon/carbon (C/C) composite thermal insulation tube is a key component for drawing large diameter monocrystalline silicon rods. However, the CVI densification process is complex, and the cost of experiment optimization is extremely high. In this article, a multi-physics coupling simulation model was established and validated based on COMSOL Multiphysics v.5.6 software to simulate the fabrication process of an isothermal CVI process for a Φ1185 mm C/C composite thermal insulation tube. The influence of process parameters on densification was explored, and a method of optimization was proposed. Our modeling results revealed that the deposition status in areas of low densification was effectively and significantly enhanced after process optimization. At the monitoring site, the carbon density was no less than 1.08 × 103 kg·m−3, the average density of the composite-material thermal insulation tube improved by 5.7%, and the densification rate increased by 26.5%. This article effectively simulates the CVI process of large-sized C/C composite thermal insulation tubes, providing an important technical reference scheme for the preparation of large-sized C/C composite thermal insulation tubes.

Geothermal Energy Extraction Using a Novel Combined Coaxial and U-Shaped Closed-Loop System

In the present study, a novel combined coaxial and U-shaped closed-loop system was proposed to enhance the thermal performance of the U-shaped geothermal system. The proposed geothermal system consists of two separate energy extraction units, called primary and secondary systems. The primary system consists of an insulated U-shaped tube heat exchanger. In order to extract more thermal energy, a coaxial double-pipe heat exchanger was coupled to the primary system as the secondary system. A conjugate heat transfer (CHT) module incorporating a k-ε turbulent model was employed to simulate the heat extraction and fluid flow within the proposed system. Further, the study extended to analyse the effect of various individual parameters on the thermal performance of the proposed closed-loop system. The results depicted that the proposed system can extract up to 42% higher thermal power than that of an insulated U-shaped tube heat exchanger. Further, the coefficient of performance (COP) of the combined system ranges between 1.03 to 1.22 depending upon the operational parameters. Overall, the proposed geothermal system effectively utilized both the heat loss from the hot primary fluid as well as the thermal energy available in the rock surrounding the insulation of U-shaped geothermal heat exchangers. The outcomes of the present study may be productive for researchers and industries interested in the extraction of clean and renewable energy.

Finite Element Modeling for HEAT Transfer of FORCED CONVECTION in INSULATED TUBE With EES Analytical Validation at different Operating conditions

Finite Element Modeling for HEAT Transfer of FORCED CONVECTION in INSULATED TUBE With EES Analytical Validation at different Operating conditions

Safety Simulation Analysis of Supporting Structure for Live Working Used Insulation Platform on 10KV Lines

The insulation platform mainly comprises insulation tubes, carrying personnel for live working at high altitudes. The structure is prone to deformation, fracture, and vibration under stress. The model of supporting structure is established by Solidworks software. Ansys Workbench is used for static and modal analysis of supporting structures. The results show that the connection between the supporting and front insulation tubes is weak with the maximum stress, and the maximum deformation and vibration occur at the supporting and main platforms. The change of the angle between the supporting insulation tube and the front insulation tube and the angle between the two supporting insulation tubes will cause the maximum stress of the structure to change. The optimal range of the angle is determined finally. The results can be used for the structural optimization of the insulation platform, which is significant for improving its safety performance.

Water Skating Miniature Robot Propelled by Acoustic Bubbles.

This paper presents a miniature robot designed for monitoring its surroundings and exploring small and complex environments by skating on the surface of water. The robot is mainly made of extruded polystyrene insulation (XPS) and Teflon tubes and is propelled by acoustic bubble-induced microstreaming flows generated by gaseous bubbles trapped in the Teflon tubes. The robot's linear motion, velocity, and rotational motion are tested and measured at different frequencies and voltages. The results show that the propulsion velocity is proportional to the applied voltage but highly depends on the applied frequency. The maximum velocity occurs between the resonant frequencies for two bubbles trapped in Teflon tubes of different lengths. The robot's maneuvering capability is demonstrated by selective bubble excitation based on the concept of different resonant frequencies for bubbles of different volumes. The proposed water skating robot can perform linear propulsion, rotation, and 2D navigation on the water surface, making it suitable for exploring small and complex water environments.

Compaction technology development for ITER In-vessel coil joints

Two types of ITER In-vessel coils (IVCs) are installed inside the vacuum vessel inner wall, behind blanket shield modules (BSMs), and near the plasma, namely: edge localized mode (ELM) and vertical stabilization (VS) coils. Overall, 27 ELM coils are distributed around the vacuum vessel inner wall, while one VS coil each is mounted above and below the plasma. Moreover, 176 IVC joints are used for joining the IVC coils, feeders, and feedthroughs, while 144 and 32 joints are used for joining the 27 ELM and two VS coils, respectively.The joints, which constitute a stainless steel (SS) sleeve, MgO insulation, and copper tube, show comparable performance to that of the conductor and can thus withstand severe conditions. Furthermore, the minimum available space for joint manufacturing is limited to 60 mm, which is a major obstacle. In joint manufacturing, two adjacent copper conductors are first welded via tungsten inert gas (TIG) welding, then the MgO insulation and sleeve will be applied. To maintain the insulation performance, the MgO insulation and SS sleeve should be compacted. Since compaction is one of the most important processes for joint manufacturing, this paper elucidates the development of compaction technology for IVC joints.

Flow Simulator Optimizes Geothermal Heat Extraction From End-of-Life Wells

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 208928, “Optimizing Geothermal Heat Extraction From End-of-Life Oil and Gas Wells Using a Transient Multiphase Flow Simulator,” by David Sask, SPE, David Sask Technology; Peter Graham, Algar Geothermal; and Carlos Nascimento, SPE, Schlumberger. The paper has not been peer reviewed. _ The complete paper presents results from evaluation of the rate of thermal energy that can be extracted under various completion scenarios using a transient flow simulator. This evaluation was conducted on closed-loop systems wherein the fluids are contained within the wellbore and surface facilities and do not involve any formation fluids. The use of a multiphase flow simulator for this study provides a road map for understanding thermal energy potential and important variables when considering extraction of geothermal energy from existing oil and gas wells. Introduction In Western Canada, there are, at the time of writing, more than 130,000 inactive and suspended wells. This includes more than 3,000 orphan wells but excludes an additional 115,000 abandoned wells. For some of these wells, end-of-life liability can be turned into an asset. This paper presents an overview of one system for extracting geothermal energy from a single well configuration using a closed-loop mode of operation. Equipment and Processes The technology described in the paper calls for inserting an insulated inner tubing inside the existing production casing immediately above the sealed base of the well. Cooler water is injected down the annulus of the coaxial configuration. As the water descends, it collects heat from zones where the adjacent rock is hotter. At the base of the well, the heated water is then redirected to surface from the open base of the insulated inner tubing. At surface, the heat is recovered, and the resulting cooled water is reinjected into the well to complete the circuit. This closed-loop process has little pump demand because there is no hydraulic head. This technology was developed in the late 1990s but did not gain much traction because of the excessive cost of drilling, inadequate and expensive insulated tubing, and poor heat and temperature recoveries. The technology has developed enhancements to overcome the latter limitation. One key enhancement is to operate the well in two different modes. The first mode operates as a storage mode during periods when no heat demand exists. Water is pumped into the annulus of the well and returned to surface within the insulated inner tube. Once the heated water reaches the surface, it is reinjected directly into the same well without any heat being recovered at surface. As the returning hot water descends, it transfers heat to the adjacent cement and rock, which creates a heat jacket in the upper sections of the well. When heat demand returns, the second mode, referred to as extraction mode, commences. The only change is that the ascending heated water is redirected to a heat exchanger, which extracts only heat sufficient to meet demand; then, the partially heated water is returned to the well to collect additional heat.

Mathematical Modeling and Simulation of a Compound Parabolic Concentrators Collector with an Absorber Tube

CPC solar collectors are a combination of new technologies that make it possible to generate heat from radiant solar energy by transferring heat between the absorber and the fluid. This study was performed based on heat transfer equations by proposing a mathematical model, as reported in the literature. A compound parabolic concentrators solar collector (CPC) numerical model was simulated and coded in Aspen HYSYS and MATLAB software and validated by comparing its results with other researchers and experimental results. The simulated mathematical model includes a two-dimensional numerical model to describe the thermal and dynamic behavior of the fluid inside the CPC solar collector absorber tube. Numerical simulations of the fluid flow equations inside the CPC solar collector absorber tube, along with the energy equation for the absorber tube wall, coating, insulation and reflector, and solar collector heat analysis, were performed repeatedly in MATLAB and Aspen HYSYS software. This method is the most appropriate and reliable method for solving equations for numerical convergence. The experimental results of the parabolic concentrated solar collector (CPC) were used to evaluate and validate the numerical model. A solar compound parabolic concentrators collector (CPC) with short reflectors was used. This collector includes a cylindrical absorber with a real density ratio of 1.8, a reception angle of 22 degrees and a length of 2.81 m, a width of 0.32 m, and an opening of 0.1764 m. Analysis and uncertainty of the proposed model were performed with the measured sample. In the thermal efficiency analysis, the average deviation of the model from the experimental results of other researchers was equal to 7%, for increasing the temperature by 9 °C. According to these results, a good correlation between numerical results and experimental results for this proposed model has been obtained.

Research on Active Cooling Technology of Measuring Instrument While Drilling Based on Insulation Tube in High Temperature Well

Research on Active Cooling Technology of Measuring Instrument While Drilling Based on Insulation Tube in High Temperature Well

Influences of low temperature on internal gas-filled cavity discharges in EPR cable termination and its feature factors analysis

Ethylene–propylene rubber (EPR) cable is the most commonly used type in high-speed railway. Several flashover accidents take place in cable termination in an extremely cold environment. In this study, EPR cable terminations were tested in a simulated low-temperature system with varied applied voltages. The results showed that the differences in elastic modulus and free space volume between EPR insulation and stress control tube (SCT) in a frigid environment would lead to structural defects between them. Damages on the EPR insulation occurred in the form of flashover point when the ambient temperature declined to −30°C and below, with the growth rate of discharge and resulting extent of damage across the EPR/SCT interface being non-linearly related to ambient temperature. Besides, the partial discharge (PD) initial voltage and PD extinction voltage under low-temperature conditions reduced by >40% compared with those at 20°C. The flashover probability of EPR terminations increased significantly, and the shape characteristics of PD patterns have also changed obviously at low temperatures. It can be verified that under the high-voltage and low-temperature conditions, the EPR/SCT interface is prone to organisational mismatch, which will lead to the PD phenomenon and seriously affect the stable operation of EPR cable terminations.

Cycle Stability of All-Solid-State Lithium-Ion Batteries with Nanoporous Si Composite Anodes Prepared from SiO2 Fume

A lot of anode materials have been reported to enhance the storage capacity and energy density of lithium-ion batteries (LIBs). Among such advanced candidates, Si is the most promising, mainly for the following reasons: 1) high theoretical capacity, 2) low operating potential, and 3) abundance in nature. However, the cycle life is short because the decomposition proceeds by the large volume change (> 300%) with the storage and release of Li+ ion. Very recently, we have found that sulfide-based all-solid-state LIBs (ASSLIBs) with Si composite anodes exhibited high capacity retention [1,2]. Here, nanoporous-Si particles, which were prepared through the air-oxidation of Mg2Si, were adapted as the anode active material. In the present study, the reaction of Mg2Si and SiO2 fume under vacuum was used to obtain the nanoporous-Si particles. In PRiME, we will report the cycle stability of ASSLIB comprising new Si composite anode.The nanoporous-Si particles were prepared as follows under Ar atmosphere, unless otherwise specified. Mg2Si (382.9 mg), SiO2 fume (300.0 mg), and Mg (12.1 mg) were mechanically milled at 1800 rpm for 15 min by using a high-speed mixer. The mixture was heated to 700 oC with a ramp rate of 100 oC min-1, and it was held at 700 oC for 12 hours in vacuum. The products were soaked in 1M HCl to remove MgO and unreacted Mg2Si, and then collected by centrifugation. Finally, the precipitates were rinsed by deionized water and ethanol three and two times, respectively. Anode composite material was comprised of the nanoporous-Si particles (36wt%), Li3PS4 electrolyte (55wt%), and acetylene black (9wt%). In an electric insulation tube with 10 mm diameter, the Li3PS4 powder (80 mg) and the anode composite material (2 mg) were pressed under 330 MPa to make two-layered pellet. As the counter electrode, Li-In foil was attached on the electrolyte side. Finally, the three-layered pellet was compressed at ca. 75 MPa using stainless-steel disks to prepare the all-solid-state half cells. By a charge/discharge measurement device (BTS-2004, Nagano), electrochemical tests were conducted in the constant current mode of 0.127 mA cm-2 (0.033 C) for initial 3 cycles and 0.3 mA cm-2 (0.077 C) for the following cycles at 30 oC. The cut-off voltages were 0.88 and -0.58 V vs Li-In, corresponding to 1.50 and 0.04 V vs Li+/Li.All the peaks in XRD pattern of the nanoporous-Si particles were indexed to a diamond cubic Si. The calculated lattice constant of a = 0.544 nm was close to the reported value of a = 0.543 nm (JPCDS 27-1402). By using Scherrer equation, the crystallite size was estimated to be about 39.8 nm. In the Raman spectrum, there was a broad peak at 496 cm-1. Compared with the strong scattering at 520 cm-1 in single crystal Si, assignable to the k~0 transverse optical (TO) mode, the signal shifted to lower frequency with broadening. This is due to the decrease in the crystallite size. As shown in Figure 1, the disordered nanometer pores were observed in TEM image. Based on Brunauer-Emmett-Teller analysis, the specific surface area and pore size were found to be approximately 213 m2 g-1 and 5.9 nm, respectively. These experimental results indicate that the nanoporous-Si particles were successfully prepared by the reaction of Mg2Si and SiO2 fume under vacuum. Figure 2 shows the cycle characteristics of the half cell with the nanoporous-Si composite anode. The measurement result on the cell with the composite anode containing commercially available non-porous Si particles is also exhibited to compare the features. Though the initial discharge capacities were similar in both cells, there were large difference in the cycle stability. Namely, the nanoporous-Si cell maintained the capacity retention of 78% at 50th cycle, while 17% in the non-porous Si cell. These results strongly suggest that the volumetric expansion is buffered by the shrinkage of pores in the Si particles. Our finding provides a novel and unique process to improve the cycle stability, and valuable information about the design of composite anodes for ASSLIBs.

Numerical study of geothermal district heating from a ground heat exchanger coupled with a heat pump system

Two important problems are often encountered in the application of middle-deep geothermal heat pump (MD-GHP) systems: (1) large deviations between the operating and design conditions and (2) the lack of a theoretical basis for parameter control during actual operations. Accurate heat transfer and energy conversion models of MD-GHP must be established to solve these problems.The novelty of this work lies in its establishment of a complete unsteady heat transfer model of a ground heat exchanger (GHE) and the coupling of this model with the energy conversion model of a heat pump. The influences of key design and control parameters on the coefficient of performance (COP) of MD-GHP are then studied. The use of vacuum insulated tubes as central pipes can increase the COP of the system by approximately 10%. When the well depth increases from 2000 m to 3000 m, the maximum heating load increases nearly linearly from 500 kW to 960 kW. At the bottom 20% of the well, insulation of the central pipe does not obviously increase the COP of the system. An optimal circulation rate occurs in MD-GHP, and this rate increases with the well depth. When the well depth increases from 2000 m to 3000 m, the optimal circulation rate increases from 6.7 kg/s to 9.9 kg/s. When the average heating load is kept constant, the intermittent heating mode slightly affects the average COP of the system. The thermal conductivity of the cement sheath exerts minimal effects on the COP of the system.The overall merit of this work is that a mathematical relationship between the heating load and formation temperature distribution is established to predict the energy efficiency of the whole system. This study provides important theoretical guidance for the design and control of MD-GHP.

ПОЛНОЕ ОПИСАНИЕ МЕХАНИКИ ТУРБУЛЕНТНОСТИ В ТЕКУЩЕЙ ЖИДКОСТИ

The conditions and mechanisms of events in a moving fluid are analyzed, leading to the apparent disorder of unsteady flow, known as turbulence. The method of analysis is the use of different forms of equations of motion and transfer of characteristics, the selection of stable formations in the flow structure and a description of the interaction between them. The non-trivial results of previous works are used. The transfer and transformation of disturbances of a vortex distributed in the flow is analyzed, the conditions under which insulated tubes with a helical flow appear inside the shear flow. An important condition is the short duration of vortex disturbances. Equations are obtained that describe the interaction of the main shear flow and the vortex tube, the features of which lead to flow instability. The existence of two mechanisms for the development of turbulence is shown - the autogeneration of local decelerations and the instability of stretching of vortex tubes. The self-generation mechanism is the transfer of kinetic energy from the main flow to an annular vortex with the generation of a new annular vortex. This is the main mechanism that ensures the propagation of instability downstream, arises first when the Re number increases. The tensile instability leads to the splitting of the vortex tube into independent sections, the generation of many annular vortices that fill the space and drift in it. The vortex multiplication factor in each generation increases with the Re number and can reach many thousands. The role of ordered unsteady flows in the initiation of turbulence is shown.

Optimization of a solar water heating system for vapor absorption refrigeration system

AbstractIn this work, the optimization study of the solar collector integrated, with a thermal energy storage tank for the vapor absorption refrigeration system, was studied using TRNSYS. The performance of the integrated system was evaluated considering major contributing parameters such as solar collector area, the mass flow rate of the operating fluids, storage tank volume and height, absorber plate thickness, tube spacing, absorber tube diameter, insulation thickness, and glass thickness/properties, respectively. A physical model of the complete solar water heating (SWH) and refrigeration system was developed followed by simulation studies of the major components for optimization, and finally, the obtained results were compared with the reported data for validation. The results indicated that, by using the solar power with a serpentine tube type flat plate collector of area 24 m2 and a storage volume to a specific collector area of about 60 Lm−2, the optimized system could meet 65% of the annual thermal energy requirement for the refrigeration unit. Further, the annual performance of the optimized solar collector in terms of collector efficiency, heat removal factor, and overall heat loss coefficient was found to be about 0.32, 0.87, and 2.99 W m−2 K, respectively. In addition, the optimization approach that is adopted using TRNSYS in the present study could be used for optimizing the solar‐based energy system for various applications.

Study on inner insulation tube for ITER axial insulation breaks

Inner insulation tube as a key component of ITER insulation break, its fabrication process was designed, and the specimen type was designed and made. Fibres and void content was tested, and thermal coefficient was measured. The results showed that it is reasonable to use R glass fibres in filament wet winding as inner tube for ITER IB because the thermal shrinking measure of this composite fabricated by this process technology is so close to the one of stainless steel 316L that it is good to reduce the thermal stress in the insulation structure of IB

Electrochemical Study on Porous Silicon Anodes in Sulfide-Based All-Solid-State Lithium-Ion Batteries: II

All-solid-state lithium-ion battery (LIB) with high safety and reliability is the dominant power source for electric and hybrid vehicles. Here, to meet the energy demands of near-future automobile technology, the anode materials should possess high energy density and long cycle life. Though Si with a high theoretical capacity (4200 mAh g-1) is the most attractive choice, there are few applications for the all-solid-state LIBs. This is because the large volumetric fluctuation (>300%) in lithiation/delithiation causes the drastic capacity loss and low coulombic efficiency. Very recently, sulfide-based all-solid-state LIBs with porous Si composite anodes have exhibited high capacity retention [1]. We proposed the following mechanisms to consistently explain the experimental results [2]: (a) the volumetric expansion is buffered by the shrinkage of Si pores and (b) the stress arising from the Si particles is relieved by the elastic deformation of solid electrolyte (SE). In the present study, to provide further insight into these findings, the electrochemical characteristics were evaluated for the porous Si composite anodes with different SEs.Porous Si particles were prepared through air-oxidation demagnesiation of Mg2Si. The details have been described in our previous paper [1]. Anode composites were comprised of Si particles, SE, and acetylene black. Here Li3PS4 (LPS) and Li10GeP2S12 (LGPS) were adopted as sulfide-based SE. In an electric insulation tube, the anode composite and LPS powder were pressed to make two-layered pellet. As the counter electrode, Li-In foil was attached on the SE side. Finally, the three-layered pellet was compressed using stainless-steel disks. AC impedance of the half-cells thus prepared was measured in the range from 0.002 to 1 MHz.Figure 1 shows the cycle characteristics of LPS- and LPGS-cells. The LPS composite anode cell exhibited an initial discharge capacity of 1240 mAh g-1. On the other hand, a discharge capacity of 924 mAh g-1, which was about 30% lower than that of LPS-cell, was observed in the LGPS-cell. The maximum discharge capacity was 1532 mAh g-1 for LPS-cell and 1269 mAh g-1 for LGPS-cells, respectively. As the results, the capacity retention of LPS-cell was calculated as 95% at 50th cycle, compared to 83% in LGPS-cell. It is worthy to note that these values were extremely larger than those of non-porous Si anode cells. As shown in Cole-Cole plots, Figure 2, in the LPS composite anode cell, there was few changes in the arc size between 1st and 5th cycles. On the other hand, the arc of LPGS-cell became large with the increase of cycle number.The Young's modulus of LPS is known to be about 10% lower than that of LGPS [3]. Based on this fact, the above results are described as follows. Though the volumetric expansion is buffered by the shrinkage of pores, the porous Si particles slightly become large during lithiation. In LPS-cell, the stress should be relieved by the elasticity of surrounding SE. On the other hand, in LPGS with higher rigidity, voids are probably formed between the Si particles and the deformed SE, resulting in the lower capacity retention and higher interfacial resistance. In these considerations, we should note that LGPS with narrow potential window is prone to decompose in long cycles.

Fast and Automatic Control of a Frequency-Tuned Radiofrequency Plasma Source

A frequency-tuned radiofrequency (rf) plasma source is automatically controlled to minimize the rf power reflection and to maintain the constant net rf power corresponding to the forward power minus the reflected power. The experiment is performed with a power amplifier operational for the frequency of 37 - 43 MHz and a compact helicon source consisting of a loop antenna, a solenoid, and an insulator tube. The rf power is supplied to the rf antenna via an impedance matching circuit consisting of only fixed small ceramic capacitors. It is demonstrated that the reflection coefficient of the rf power is minimized within ~10 msec and the net power is successfully maintained at constant.

A Novel Experimental Approach to the Applicability of High-Sensitivity Giant Magneto-Impedance Sensors in Magnetic Field Communication

This article presents a new application field of a giant magneto-impedance (GMI) sensor. It shows valuable findings for the GMI sensor on the possibility of a new receiving element in magnetic field communication. The proposed GMI sensors serve as antennas and mixers in receiver systems. They have the advantage of being easily implemented and in terms of mass production and manufacturing processes due to the manufacture base on a printed circuit board (PCB). Their smaller size, lower cost, and higher sensitivity have more advantages than conventional magnetic sensors, such as the magneto-inductive, anisotropic magneto-resistive, and giant magneto-resistive sensors. Two types of PCB-based GMI sensors are proposed. The first type of GMI sensor is directly wound around the solenoid-shaped pickup coil onto an alumina insulation tube inserted with an amorphous microwire. The second type of GMI sensor has a patterned pickup coil that does not require the winding of the coil, similar to the patterned pickup coil of a micro electro-mechanical system-based GMI sensor. This GMI sensor provides a new geometry that can be easily manufactured with two PCB substrates. The proposed GMI sensors achieve the equivalent magnetic noise spectral density to the high-sensitivity characteristics of the pT/√Hz level. The equivalent magnetic noise spectral density of 1.5 pT/√Hz at 20.03 MHz is obtained for the first type of GMI sensor, and 3 pT/√Hz at 3.03 MHz is achieved the second type. The analyzed results of the bandwidth and the channel capacity for the two types of GMI sensors are acceptable. This first analysis confirms the possibility of the implementation of GMI sensors in magnetic field communication. The results of this experiment confirm the high performance of the proposed GMI sensors and their applicability in magnetic field communication. The detailed experimental results of the proposed GMI sensors are presented and discussed.

Retarding the decay of temperature in the air flow field during the melt blowing process using a thermal insulation tube

During melt blowing, most of the polymer jet attenuation occurs in the area within 2 cm from the die, due to the rapid decrease of polymer jet temperature. Therefore, keeping the polymer jet temperature above melting point for a longer time is beneficial for its attenuation. Here, a thermal insulation tube with heating ability was introduced into the air flow field during the melt blowing process. The computational fluid dynamics technique was employed to investigate the effects of the thermal insulation tube on the air flow field. It was found that the thermal insulation tube has enhancing effects on the temperature, velocity, and turbulence kinetic energy of the air flow field. Experiments were conducted to examine the fiber diameters of the final nonwovens, the results of which indicates that a die with a thermal insulation tube can achieve a higher polymer jet attenuation and that the heating effect can further enhance the attenuation. Based on the computational fluid dynamics technique, the effects of the tube diameter and length on the temperature, velocity, and turbulence kinetic energy of the air flow field were investigated.

Electrochemical Study on Porous Silicon Anodes in Sulfide-Based All-Solid-State Lithium-Ion Batteries

All-solid-state lithium-ion battery (LIB) with high safety and reliability is the dominant power source for electric and hybrid vehicles. To meet the energy demands of near-future automobile technology, the anode materials should possess high energy density and long cycle life. Though Si with a high theoretical capacity (4200 mAh g-1) is the most attractive choice, there are few applications for the all-solid-state LIBs. This is because the large volumetric fluctuation (>300%) in lithiation/delithiation causes the drastic capacity loss and low coulombic efficiency. Very recently, we have found that sulfide-based all-solid-state LIBs with porous Si anodes exhibited high capacity retention [1,2]. In the present study, the electrochemical impedance was measured to provide further insight into the stable cyclability. Porous Si particles were prepared through air-oxidation demagnesiation of Mg2Si. The details have been described in our previous paper [1]. Commercially available non-porous Si particles were also used as a reference active material. Anode composite was comprised of Si particles, Li3PS4 solid electrolyte (SE), and acetylene black. We adopted two mixing methods, ball milling and mortar milling, to vary the dispersion degree of Si particles. In an electric insulation tube, the anode composite and SE powder were pressed to make two-layered pellet. As the counter electrode, Li-In foil was attached on the SE side. Finally, the three-layered pellet was compressed using stainless-steel disks. AC impedance of the half-cells thus prepared was measured in the range from 2×10-3 to 1×106 Hz. The ball-milled porous Si anode cells exhibited the capacity retention over 80% up to 150 cycles. In contrast, the lower retention, 40%, was observed for the mortar-milled porous Si anode cells. The ball-milled and mortar-milled non-porous Si anode cells possessed the poorer cycle stability with the capacity retention of 10% or less. As shown in the Cole-Cole plots, in the ball-milled porous Si anode cell, there was few changes in the arc size between 1st and 20th cycles. On the other hand, the arc of the mortar-milled porous Si anode cell became gradually large with the increase of cycle number. In addition, huge arcs were observed in the non-porous Si anode cells, regardless of the mixing method. The experimental results described above can be explained as follows. By utilizing the ball milling, Si particles are highly dispersed in the SE matrix. In this case, a lot of pores on the porous Si surface are exposed to the electrolyte. As the result, surface electrolyte interface (SEI) is easily formed at 1st cycle. However, SEI become hardly thick with the increase of charge/discharge cycle. This is because SE possesses high stability and low fluidity. In addition, the volumetric expansion is buffered by the shrinkage of Si pores. Therefore, the slight stress arising from the Si particles is relieved by the elastic deformation of SE. These findings strongly suggest that almost constant interfacial resistance causes the cycle stability of the ball-milled porous Si anode cells.