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Due to the double layer airgap configuration, the even-order harmonic components exist in the phase back electromotive force (EMF) of flux-modulation electrically-excitation double-stator synchronous machine (FMEE-DSM), thus resulting in relatively high torque ripples. To promptly and effectively suppress these torque ripples, this paper proposes and implements a second-order iterative learning control (ILC) strategy to minimize the main harmonic torque components based on the periodically repetitive characteristic of torque ripples in the FMEE-DSM. Via harmonic analysis on the torque ripples caused by the cogging torque and the non-sinusoidal induced EMFs, the dominative harmonic component, namely, the 7th order component, can be precisely identified and then involved in the proposed ILC for torque ripple suppression. To verify the feasibility of proposed control strategy, a test bench of the FMEE-DSM control system was built based on dSPACE 1103. Accordingly, both the static and dynamic performances of the FMEE-DSM were investigated under the conditions of no-load and rated load. The theoretical analysis, computer simulation and hardware experimentation are given to verify the proposed second-order ILC.

This paper presents a novel magnetic-geared direct-drive machine (MGDM) with V-shaped permanent magnets (PMs) installed on its rotor. By extending the inner rotor shaft and connecting it to a prime motor, the torque and power density of the proposed MGDM is boosted. Additionally, compared with the conventional MGDM with surface-mounted PMs, the proposed MGDM with V-shaped PMs has a more robust rotor structure to cope with extreme operating conditions. The operating principle and structure requirement of this MGDM are first derived. Then, the geometrical parameters are optimized via a three-stage multi-objective optimization method to maximize output torque and efficiency and minimize torque ripple via the genetic algorithm and finite element analysis (FEA) combined optimization strategy. Furthermore, the proposed MGDM is artfully integrated into hybrid electric ships (HESs) to construct an onboard integrated power system (OB-IPS). Since the proposed system possesses various operating modes to cope with practical operating conditions, it enjoys a high systematic efficiency and good dynamic performance. Finally, a prototype is fabricated and tested with various operating modes by referring to the practical navigation cycle of a HES. The experimental results validate the feasibility of the proposed MGDM for being applied in HESs.

This paper studies the vibration and noise analysis of flux-modulation double-stator electrical-excitation synchronous machine (FM-DSEESM) in both no-load mode and on-load mode by using the mode superposition method. First, the theoretical excitations of vibration and noise, namely the radial electromagnetic force harmonics, are deduced and classified by their sources. Second, the finite element analyses (FEA) of these radial electromagnetic force harmonics are analyzed via Fourier decomposition and compared to their theoretical results for validation. Third, to perform the vibration and noise analysis, the modal test is conducted, and the modal FEA model is established based on the tested modal results. Also, the radial electromagnetic forces are coupled with the modal FEA model to conduct the vibration and noise analysis, and the responses of sound power levels in A-weighting are calculated. By using the modal participating factors, the main contributing modes are determined in the vibration and noise responses.

In conventional model predictive torque control (MPTC), only one voltage vector (VV) is applied during a whole control period, thus causing a large torque ripple. To improve the steady-state performance, some two-vector-based control schemes have been proposed. However, the selection of the optimal VV pair is complex as well as has a large computational burden, and the improvement of performance is still limited by the direction and amplitude of the output VV. This article proposes a low-complexity three-vector-based MPTC for SPMSM drives, which can precisely determine the appropriate active voltage vectors (AVVs) with the predicted torque error. Then, a modified switching table is developed to directly select the AVVs, thus greatly reducing the complexity and computational burden of the algorithm. To obtain a better steady-state performance, a duty cycle calculation method based on torque and stator flux difference parameters is newly proposed to achieve the deadbeat control of torque and stator flux. And then, the experimental comparisons with the double-vector-based MPTC are conducted. The results show that the proposed MPTC can effectively reduce the steady-state torque ripple while maintaining a good dynamic performance as well as almost a fixed switching frequency for all speed ranges.

In the double-vector-based model predictive torque control (MPTC), two voltage vectors are applied in one control period. Due to a large number of possible combinations among voltage vectors, the determination of optimal voltage vector pair is often complicated. This article proposes a new approach to reduce the number of candidate active voltage vectors. The concept is to preselect the active voltage vectors according to the stator flux vector error. The proposed MPTC is implemented in a stationary frame and avoids the complicated coordinate transformation as well as the tangent inverse calculations. Furthermore, a promising approach is conceived for calculating the duty cycle of active voltage vector, which can contribute to the less dependence on the system model, thus alleviating the sensitivity to motor parameter variations. To further improve the steady-state performance, a modified three-vector-based MPTC is newly put forward. Meanwhile, the proposed duty cycle calculation method is used to achieve the deadbeat control of torque and stator flux. Theoretical analyses and experimental results are given to verify the effectiveness of the proposed MPTC methods.

This paper proposes and analyzes a novel radial partitioned stator HTS-excitation flux-switching (RPS-HTSFS) machine. The key is that the single ring-shaped HTS-excitation coil is independently placed in the coaxial claw-pole outer stator while the armature windings are wound around the U-shaped iron core on the inner flux-switching armature stator without permanent magnets. This solution has been explored to realize the physical isolation of armature winding and excitation winding, relieving the influence of armature field on the HTS-excitation coil. Moreover, only a single ring-shaped HTS-excitation coil is employed, therefore, reducing the HTS wires and the bending strain of the HTS-excitation coil. Also, the special refrigeration system can realize stationary seals of the double-layer ring-shaped cooling Dewar pattern, improving the cooling performance. By using the three-dimensional finite element analysis (3D-FEA), the machine performances are investigated and the validity of the proposed machine is verified.

This paper proposes a novel high-temperature superconducting stator-excited axial-flux magnetic gear (HTS-SEAFMG) for the high-torque transmitting system. The proposed magnetic gear combines the merits of both HTS-excitation and stator-excitation. By using the HTS-excitation, a high air-gap flux density can be easily obtained, thus achieving the high torque density. The HTS-excitation windings are placed on the stator with a static seal of cooling Dewar which greatly reduces the manufacturing difficulty and the cost of refrigeration system compared with the dynamic seal. Thanks to the stator-excitation pattern, both the high-speed rotor and the low-speed rotor comprise only iron, thus contributing to the high mechanical reliability. The axially sandwich structure can also simplify its assembly in the high torque transmission applications. The dimensional parameter optimization and the electromagnetic performance evaluation are conducted by using the finite element method, respectively. The results show that the torque density of the proposed HTS-SEAFMG can reach 123 kNm/m3. Theoretical analysis and results are both given to verify the feasibility of the proposed HTS magnetic gear design.

This paper proposes a new 12-slot/10-pole high-temperature superconducting excitation claw-pole doubly-salient (HTS-CPDS) machine with a single HTS-excitation unit using stationary seal cooling. The key advantage of adopting claw-pole structure is that a ring-shaped HTS-excitation coil can be easily wound and artfully placed in the claw-pole cavity to realize the design of single excitation unit, and thus the cooling Dewar design for stationary seal is easily implemented. Also, due to using HTS-excitation, the air-gap flux can be flexibly regulated by changing the HTS current, thus keeping a constant amplitude of phase back-EMF under different rotor speeds. The cooling Dewar construction and the key parameter optimization are illustrated in detail. And compared to a counterpart employing the discrete racetrack HTS coils, the proposed machine can significantly reduce the HTS wire consumption and electromagnetic stress to a certain extent, thus cutting the cost and improving the anti-quench ability. By using the finite element analysis (FEA), the machine electromagnetic performances are evaluated, and its validity is verified.

This article proposes a novel transverse-flux tubular linear switched reluctance (TF-TLSR) machine for long-stroke applications, in which the armature windings are placed on the short primary, while the long secondary is made of only low-cost iron ring. The key for the proposed machine is to innovatively introduce the complementary tooth structure into the primary salient-pole design and equip the complementary machine unit configuration in the primary construction for the purpose of minimizing the force ripple. The principle of force ripple reduction by using these complementary structure configurations is illustrated in depth. The analytical calculations of the winding inductance and thrust force of the proposed machine are developed with the air-gap magnetic path modeling. By using the 3-D finite element analysis (3-D-FEA), the sensitivity study of two key structural parameters on the force characteristics is also carried out, based on which a satisfactory TF-TLSR machine is finally determined. Consequently, a prototype is fabricated for experimentation testing, and the FEA and experimental results are comparatively demonstrated, which verifies the validity of the design ideas of using a complementary concept for minimizing force ripple in the proposed machine.

Steam to carbon ratio (S/C) determines the availability of oxygen-containing species during steam reforming, which not only affect the amount of coke formed, but also might impact physicochemical properties of the coke generated. In this study, the effect of S/C on the coke formation in steam reforming of acetic acid was assessed. The results indicated that dissociative absorption of acetic acid generated the intermediates containing both C O and C C groups even at 100 °C. At low S/C, the insufficient ∗OH reacted with carbonaceous intermediates such as CHx to form more carbonyl species, leading to significant coking and lower gas yields. Sufficient ∗OH at high S/C facilitated transformation of the carbonyl-containing species into gases, minimizing coking. The varied amount of coke showed significant effect on the diffraction of metallic nickel phase, the particle size of Ni and the absorption for the Si–O–Si functional groups on spent catalysts. The coke formed at low S/C was more aromatic with high thermal stabilities, while the coke formed at high S/C was more aliphatic with low thermal stabilities. The involvement ∗OH species in coking process determined not only properties but also morphologies of the coke. The coke formed at low S/C showed bamboo-like, dendritic or twisted rope-like structure. While the higher S/C favored the generation of the carbon nanotubes with smooth outer surface.

The generation of etch pits with clear morphology is an important prerequisite to study dislocation structures. A mixture of water and ethanol is used to etch pyramidal faces of rapidly grown KDP crystals. Vivid etch pits on {101} faces were created by the process of etching and polishing and investigated using an optical microscope and 3D confocal microscope. The formation mechanism of dislocation-related etch pits was speculated. There exists approximately a central symmetry relation between the morphology of the dislocation-related etch pits and dislocation hillocks on the same face. The arrangement order of the inclined sectors (I′ → II′ → III′) of the dislocation-related etch pits is in accordance with that of the vicinal sectors (I → II → III) of the dislocation hillocks. The inclined sectors are composed of steps with the same orientations, [ 1], [ 1 1] and [0 1 0], as the vicinal sectors on the (1 0 1) face. Due to crystal symmetry, the morphology of the dislocation-related etch pits on adjacent pyramidal faces possesses mirror symmetry. There is a central symmetry relation between the dislocation-related etch pits on the upper face and the bottom side of the same sample.

The air-gap magnetic field analysis of the field-modulation double-stator electrical excitation synchronous machine (FM-DSEESM) is complicated due to its double stator and modulation-ring rotor configuration. Aimed to investigate the influence of the each part of the machine on the magnetic fields in the air-gaps, this study focuses on the permeance function analysis of FM-DSEESM to reveal its air-gap magnetic field distribution. Due to the limited physical space, the non-ferromagnetic segments of modulation-ring rotor in FM-DSEESM cannot be regarded as infinitely deep slots. Therefore, by adding a new flux line in the non-ferromagnetic segments, a new permeance function is proposed based on the calculation of the equivalent air-gaps. Then, analytical results of flux densities in the air-gaps are calculated and verified by finite element analysis. Finally, a FM-DSEESM prototype is fabricated to prove the feasibility of the permeance functions.

This paper proposes a high temperature superconducting (HTS) double stator machine (HTS-DSM), based on the magnetic field modulation principle. In the proposed HTS-DSM, the HTS field winding and the copper armature winding are separately located on the two stators, so that it overcomes the drawbacks caused by the coupling device for cryogenic transfer, the torque tube, the carbon brushes, and slip rings in the conventional HTS synchronous machines with the rotating field winding, bringing the merits of high reliability and low maintenance cost. Moreover, a method of amounting a ferromagnetic ring outside the HTS field winding is also proposed to reduce the negative effects of the armature reaction field on the HTS field winding, since the alternating current (AC) losses induced by the armature reaction field easily cause the quench of the HTS field winding. Totally four different topologies are proposed, and the operation principle of the HTS-DSMs is analyzed based on the magnetic field modulation principle. Then the design and optimization of the HTS-DSM is discussed in detail to present the main design parameters of the four topologies. Finally, the performance of the four different topologies are compared by the finite element analysis, the results reveal that the HTS-DSM with modular dewar and iron-teeth inner stator exhibits the merits of higher power density.

This paper proposes a novel high-temperature super-conducting (HTS) claw-pole vernier machine, which combines the merits of stator HTS-excitation machine with the “magnetic gearing effect” designed for direct-drive applications. The key is to adopt claw-pole stator structure to realize the multi-pole pattern using single HTS-excitation unit with stationary seal, thus greatly simplifying the cooling Dewar architecture as well as improving the structural compactness. Moreover, the armature windings are wound around the split-teeth which are set on the surface of claw poles to achieve the physical separation from the HTS-excitation coil, thus reducing their space conflicts and impact with each other. The operation principle analysis and the initial machine design are conducted in details. By using the three-dimensional finite element analysis, the machine performances are evaluated, and its validity is verified.

This paper proposes a new high-temperature super-conducting (HTS) linear flux-controllable doubly salient machine for high-power long-stator applications, which incorporates the merits of both the HTS-excitation machine and the primary-excitation linear machine. The key is to adopt the modular mover to obtain the phase symmetric magnetic circuit as well as effectively reduce the cogging force due to module complementary effect, while the HTS-excitation windings and armature windings are physically separated to reduce space conflicts between each other and easily implement static seals of cooling Dewar. Also, the air-gap field can be flexibly regulated by changing the HTS-excitation current, thus facilitating to extend the operating speed range. The operation principle analysis, cooling Dewar design, and key parameters determination are conducted in detail. By using the finite-element analysis, the machine performances with emphasis on flux-controllable features are analyzed to verify its validity.

This paper proposes and analyzes a novel high-temperature superconducting (HTS) flux-switching transverse-flux (HTS-FSTF) machine with partitioned stator, which keeps the merits of stator-excitation HTS machine with static seals. The key is to adopt the axial partitioned stator structure to realize the independent partition arrangement of armature windings and HTS-excitation windings, as well as artfully place the flux barrier between them to minimize the impact of armature field on the critical field state of the HTS excitation. Moreover, by using the split-pole design, only a single ring-shaped HTS-excitation coil is employed, thus, easily implementing static seals of simple cooling Dewar pattern to improve the refrigeration system reliability and reduce costs. The operation principle based on the transverse-flux path analysis and the cooling Dewar design are described in details. Also, by using the three-dimensional finite-element analysis, the electromagnetic performances of the proposed machine are investigated, and its validity is verified.

A new biscarbazole-fused xanthene hybrid dye MeBCX has been prepared by CH3SO3H-promoted condensation of 4-hydroxycarbazole and o-phthalic anhydride, followed by esterification with methanol, which exhibits good cell membrane permeability. Taking advantage of the spiro-controlled xanthene platform of the dye, a Cu2+-selective fluorescence “off-on” probe BCX-Cu has been successfully prepared with excellent performances in selectivity and sensitivity, and the detection limit is calculated to be 88.7 nM. The sensing mechanism is confirmed to involve a specific cascade reactions of Cu2+-induced spirolactam ring-opening and hydrolysis. In addition, living L929 cell imaging demonstrates the probe has living cell membrane permeability and shows great potential for tracing intracellular Cu2+ through fluorescence imaging technology.

Tailoring the nanomorphology of electrochemically active materials could significantly affect their resultant catalytic and charge storage performance. In this study, the nanostructured morphology of multinary CuCo2O4 and CuCo2S4 was tuned using a different volume concentration of water and ethanol resulting in different nano-shapes maintaining similar crystal structure. The electrocatalytic performance was analyzed for all the synthesized samples as the hydrogen (HER) and oxygen evolution catalyst (OER). The HER and OER study for CuCo2S4 sample synthesized using ethanol required a low overpotential of 158 mV to reach 10 mA/cm2 and 290 mV to achieve 20 mA/cm2, respectively. Furthermore, the electrolyzer cell using symmetrical electrodes required a low overall cell potential of 1.66 V to achieve a current density of 10 mA/cm2 and maintained stable performance for over 24 h, suggesting a promising bifunctional catalytic behavior. Furthermore, the synthesized samples were studied as electrodes for high-performance energy storage systems. The CuCo2S4 electrode showed an areal capacitance of 6.3 F/cm2 (3190.8 F/g) at a current density of 2 mA/cm2. The Ragone plot for the areal energy versus power density resulted to be 265 mWh/cm2 (132 Wh/kg) and 11.9 W/cm2 (5973 W/kg), respectively. Thus, from the overall study, it can be confirmed that tailoring morphology of nanostructured material such as CuCo2S4 could be a promising way for the advancement of energy generation and storage devices.

The cracking of KDP crystals during the growth & fabrication process is a serious problem that limits their application in the large-aperture high-power laser system; furthermore, the cracking is mainly attributed to their high brittleness. In order to explore the mechanical parameters related to KDP crystal cracking in detail, we measured the fracture toughness of KDP crystals as a function of temperature using the single-edge notched beam (SENB) method up to 170 °C. Meanwhile, the effects of crystallographic orientation, annealing and loading rate on the fracture toughness values were investigated in detail. Strong orientation dependence was observed on the fracture toughness of KDP crystals, and the relationship was concluded as follows: x-cut > type II > type I > z-cut. With the increase in temperature, the fracture toughness of crystals increased and reached its maximum value at 160 °C; then, it decreased, indicating that 160 °C is the temperature at which brittle-to-ductile transition occurs. Using an optical microscope, it was observed that the fractured surfaces of the samples become gradually rough with the increase in temperature. This may offer a viewpoint for understanding the dependence of fracture toughness on temperature. Furthermore, annealing and decrease in the loading rate were conducive to the significant increase in the fracture toughness of KDP crystals.

This paper proposes and analyzes a novel high-temperature superconducting (HTS) modular flux-switching linear machine for long-stator applications, which adopts the stator with a low-cost salient-pole iron core and accommodates both the armature windings and HTS-excitation windings on the short mover, thus facilitating static seals of cooling Dewar for the HTS windings. The key of the proposed machine is to employ a modular mover structure composed of separate phase modules to achieve a complementary pattern, such that the cogging force can be significantly offset to effectively reduce the force ripple while offering the advantages of very symmetrical back electromotive force (EMF) and high fault tolerance. The operation principle and optimization analysis of the proposed machine with concern on the HTS-excitation characteristics are carried out. Also, by using the two-dimensional finite element method, the electromagnetic performances of the proposed machine are investigated to verify its validity. The results show that it can offer symmetrical and sinusoidal back-EMF, high fault tolerance, and low force ripple.

Gas sensors have been widely used to monitor leakages and control the concentrations of various gases, during the production and fabrication processes of industrials. Conventional gas sensors were based on semiconducting oxides, such as SnO2, ZnO, Fe2O3 and In2O3. Recent development revealed that nanocarbons, including carbon nanotubes (CNTs) and nanosheets of graphene nanosheets, carbon nanofibers and carbon black, exhibit strong high performance gas sensing behaviors. Furthermore, gas sensing performances the nanocarbon materials can be enhanced by forming hybrids with nanoparticles of noble metals and semiconducting oxides. This review paper was aimed to provide an overview on recent progress in the development and characterization of gas sensors based these nanocarbon materials and their hybrids.

This paper proposes to implement a segme-nted-rotor high-temperature superconducting (HTS) flux-switching generator with dual electrical ports for offshore wind power generation. The originality is both electrical ports, namely armature windings and field-excitation windings, are placed in the stator so that the stationary seal of the cryogenic cooling system can be achieved. The key lies in that the HTS field-excitation windings in the stator side provide high field excitation, and the sinusoidal electromotive force in armature windings is induced by the magnetic field modulation of the segmented rotor. A new kind of racetrack-shaped Dewar with vacuum-sandwich was proposed and fabricated to accommodate and cool the HTS coils. Based on this proposed racetrack-shaped Dewar, a cryogenic cooling system of the proposed generator was established to maintain the superconducting properties of HTS wires. Both finite element analysis and experiments were carried out to verify the validity of the proposed generator and its cryogenic cooling system.

This study proposes a new high-temperature superconductor (HTS) modular flux-switching linear machine for rail transit, in which the armature windings and HTS field windings are placed on the short mover, while the long stator is only made of segmented low-cost iron. The key is to adopt a modular mover consisting of three separate phase modules whose positions are mutually 120° electrical degrees apart to greatly offset the cogging force for suppressing the thrust force ripple, accompanied with the features of high-fault tolerance. Also, the HTS excitation can produce stronger magnetic field than permanent magnet excitation to obtain a high force density; meanwhile, it easily regulates the air-gap flux density for achieving flexible high-speed constant-power operation. The operation principle and general design method of the proposed machine with concerning the HTS-excitation pattern are described in details. By using the finite element analysis, the machine performances are comparatively analysed with its counterpart without using modular mover to verify its validity. The results show that the proposed machine can offer more sinusoidal back electromotive force, better fault tolerance, higher thrust force and smaller force ripple.

We introduce a “gelating-cutting” strategy to improve specific areal capacity and cycle life for Li-O2 cathode. Conventional Li-O2 cathode with liquid electrolyte is gelated with highly elastic crosslinked polymer and cut into 50–200 µm granules. The gaps between the packed gel granules efficiently induce oxygen to the inner part of the cathode, leading to even Li2O2 growth in thick cathode. Meanwhile, the elasticity of the polymer chain helps to keep good contact between carbon and Li2O2 nanoparticles, which facilitates the electron transfer and improves the cyclability. Without any catalyst, the granular gel cathode is able to run 170 cycles at a fixed capacity of 1000 mA h gcarbon−1, or maintains a specific capacity higher than 10,500 mA h gcarbon−1 (12.6 mA h cm−2) during 11 cycles of full discharge-charge. Since good contact is the precondition to any electrochemical reaction, our strategy is a general way to enhance the performance of Li-O2 cathodes.

By the process of etching and polishing, the dislocation-related etch pits were clearly created on the pyramidal faces for as-grown KDP crystals by rapid growth technique. Through a combination of 3D confocal microscope and optical microscope, the direction of dislocation lines were studied in pyramid section, and the corresponding morphologies of etch pits were also observed in detail. The results show that the dislocation lines are mainly located in the {0 1 0} faces, and the dislocation-related etch pits may be caused by screw dislocations. Moreover, the research indicates that the morphologies of dislocation-related etch pits are somewhat related to the direction of dislocation lines. For the inclined sectors of Iʹ and IIʹ on etch pits, the slope ratio of Iʹ/IIʹ decreases with the increases of β as an angle between the direction of dislocation line and the normal of {101} face. Therefore, the information of dislocation in crystal, especially the orientation of dislocation line, can be inferred by the spatial size characteristics of dislocation-related etch pits.

This study presents the analysis and experimental verification of a coaxial magnetic gear (CMG) for speed-change transmission. The key design of this CMG is to adopt a stationary permanent-magnet (PM) ring between the inner and outer rotors, aiming at removing the PMs and only retaining the salient-pole-iron on the outer rotor to improve its mechanical reliability. Meanwhile, due to a large equivalent magnetic clearance promoting low torque ripples, the proposed CMG can offer the advantages of achieving a consistent speed ratio and stable transmission within the entire pull-out torque range. By using the two-dimensional finite element method, the detailed parametric analysis and static characteristics of the proposed CMG are performed to set up its design criteria. Moreover, a quantitative comparison with a conventional CMG is conducted, and a prototype is also fabricated for experimentation to verify the validity of the proposed CMG.

This paper proposes a new high-temperature superconductor (HTS) dual-rotor flux-switching machine for direct-drive wind energy conversion. The key is to adopt dual-rotor structure to improve utilizations of the HTS excitation field and the machine space, thus achieving a high power density. Also, the HTS excitation can easily achieve flexible flux regulation to keep armature voltage constant under time-varying wind speeds. The operation principle, with emphasis on the effect of relative position of both rotors on the magnetic circuits, is described in details. And the initial machine design, especially the split ratio optimization, has been done. By using the finite element analysis, the machine performances are analyzed, and its validity is verified.

This paper proposes a new stator high-temperature superconducting (HTS) field-modulated machine with the merit of high torque density for direct-drive applications, which incorporates the attractive features of both stator excitation HTS machine and field-modulated machine. The key is to artfully place the HTS windings on the stator to implement static seals as well as utilizing the “magnetic gearing effect” to achieve high torque capability. Based on the geometry of the fabricated double-layer Dewar assembly for cooling the HTS excitation coil, the proposed machine is initially designed. By using the finite element analysis (FEA), the machine performances are analyzed, and its validity is verified

This paper proposes and develops a new kind of cryogenic cooling system for high-temperature superconducting (HTS) flux-switching (FS) machine using stationary seal for its cooling Dewar. Test results show that this cryogenic cooling system can offer the cryogenic operating environment around 63 k for the racetrack-shaped HTS field coils. Based on the proposed cryogenic cooling system, a new HTS-FS machine with segmented rotor is proposed. By using the finite element analysis, the machine performance is analyzed accordingly. Hence, the electromagnetic characteristics of the proposed machine are verified.

This study experimentally investigates and numerically simulates the influence of the cathode electrode open ratio (ratio of oxygen-opening area to the total electrode surface area) on the performance of Li–O2 batteries at various discharge current densities. At the current density of 0.1 mA/cm2, the maximum discharge capacity is achieved at 25% open ratio among the tested open ratios (0–100%). As the open ratio increases from 25% to 100%, the specific discharge capacity decreases from 995 to 397 mA h/gcarbon. A similar trend is observed at 0.3 mA/cm2, while the maximum discharge capacity is obtained at 3% open ratio among the tested open ratios. The model that assumes the electrode is always fully saturated by the electrolyte does not obtain similar trends with experimental results, while the model that considers electrolyte loss by evaporation and the volume change of the solid obtains the same trend with experimental observations. The open ratio governs not only availability of oxygen but also the evap...

Transient numerical calculations were carried out to predict the evolution of temperature and thermal stress in traditionally grown large-size KDP crystals during the removal process, considering two methods that are used to accomplish the crystal extraction. The influence of the crystal size and the difference of temperature between the crystal and environment on the stresses inside the KDP crystals were also investigated in detail. Results indicate that, in both processes of isolating crystals, the highest stress transfers from the crystal periphery to the internal part from the early to the later time stage. In the case of extracting the crystal from solution directly after crystallization and exposing to air, the maximum stress at the crystal periphery is larger than that inside the crystal, and the probability of failure from the outside surface of crystals is large. In the case of retaining the solution for a time after crystallization, the maximum stress in the crystal internal region is larger than that of the crystal surface, leading to a large possibility to originate cracks in the inner region. Both increased crystal sizes and increased temperature differences between the crystals and the environment at the end of crystal growth are factors which aggravate crystal cracking. The maximum stress in crystals in the case of retaining the solution is less than that in the case of extracting the solution, which brings about a decreased likelihood of cracking. Thus, retaining solution for a period of time after the growth is completed, such as 96 h, is suggested to be adopted to accomplish successful crystal extraction.

Lithium-oxygen batteries have been considered strong candidates to supersede current rechargeable batteries especially lithium-ion batteries. Despite having tremendously high theoretical energy density, the practically achievable energy density is far from commercial application till date. The oxygen electrode is one of the major bottlenecks in maximizing the battery capacity. It is comprised of a porous structure (mainly carbon) with high surface area and sufficient reaction sites. High porosity facilitates lithium ion and oxygen mass transfer and results in high storage capacity for the insoluble discharge product during discharging. The cathode electrode is fabricated by coating a catalyst layer on a porous carbon substrate. The substrate, which contacts with oxygen channels, plays a vital role in mass transfer of oxygen from outside to the reaction sites. Therefore, it is important to select a substrate that does not clog with deposition of Li2O2 particles immediately after discharging begins and allows oxygen to reach the catalyst side for longer period of time. This study investigates the effects of oxygen electrode substrates with various coating materials on the discharge capacity of lithium-oxygen battery. For this purpose, we have compared the discharge capacity of plain carbon cloth, plain carbon paper and carbon cloth or carbon paper coated with carbon catalysts including Vulcan XC, Super P and Graphene Oxide. 1.5mg/cm2 (+/-0.3mg/ cm2) is used as catalyst loading. The electrolyte used in this study is 1M LiTFSI in TEGDME. PTFE (30wt%) is used as a binder. All experiments are conducted at room temperature with pure oxygen supply. With carbon cloth as a substrate, the discharge capacities obtained were 3 to 6 times higher (depending on the carbon catalysts coated) than the capacities obtained with carbon paper. The bare carbon cloth, Vulcan XC, Super P and Graphene oxide with carbon cloth as a substrate have discharge capacities of 0.11 mAh/mg, 13 mAh/mg, 6.8 mAh/mg, 1.5 mAh/mg respectively. On the other hand, the discharge capacities achieved with bare carbon paper, Vulcan XC, Super P and graphene oxide with carbon paper as substrate were 0.02 mAh/mg, 2.4 mAh/mg, 2.7 mAh/mg, 0.28 mAh/mg respectively. The results clearly indicate that the cathode with carbon cloth as a substrate yields significantly higher discharge capacity with all the coating materials as compared with the carbon paper. The different performances of two substrates can be attributed to their structure and pore size distribution. Carbon cloth is composed of flexible woven threads with longer lengths ( ̴ 30µm) and broader pore size distribution (5-200 µm) with peaks at 10, 70 and 100 µm. This type of structure is favorable in reducing tortuosity, enhancing mass transport of oxygen and lithium ion and improving ionic conductivity. On the other hand, the structure of carbon paper comprises of non-woven short carbon fibers ( ̴ 15µm) and smaller pore size distribution range (10-70 µm) with a peak at 50 µm. This renders poor transport of oxygen from outside to the reaction sites leading to lower discharge capacity. The primary function of coating materials is to increase surface area of cathode thereby providing more reaction sites and creating tri-phase boundaries for reaction to take place. These catalysts also have different pore size distributions and resistance to mass transfer. Therefore, various carbon catalysts used yield different discharge capacity with same substrate.

Cu2ZnSn(S, Se)4 (CZTSSe) device is fabricated with Zn1−xSnxO (ZTO) buffer layer deposited by atomic layer deposited (ALD). The ALD process results in a precise control of thickness and Sn/(Sn+Zn) ratio of the buffer layer. The performance of the CZTSSe device with ZTO buffer layer has been enhanced by adjusting proper Zn and Sn ratio during the ALD process. The optimized Sn/(Sn+Zn) pulse ratio is found to be around 0.167, with a thickness of around 50 nm. The champion device with a ZTO buffer layer has an efficiency of 8.60% (active area efficiency 9.20%) compared with 8.14% (active area efficiency 8.70%) of the reference solar cell with chemical bath deposited CdS buffer layer. The optimum device performance is a result of optimized band alignment between CZTSSe absorber and the ALD ZTO buffer as shown by ultraviolet photoelectron spectroscopy (UPS).

Zr 57 Co 27 Al 16 and La 57 Co 27 Al 16 alloys with excellent glass-forming ability (GFA) were adopted to synthesize new phase-separated bulk metallic glasses (BMGs) upon rapid solidification. (Zr x La 1 − x ) 57 Co 27 Al 16 (x = 0.2, 0.4, 0.6, and 0.8) melts separate into ZrCo-rich and La-rich liquids upon cooling due to the existence of a miscibility gap in Zr-La liquids. The intrinsic and extrinsic mechanisms for the formation of phase-separated alloys under different casting conditions were analyzed in detail. The GFA of the studied alloys changes in the following order: Zr 57 Co 27 Al 16 > La 57 Co 27 Al 16 > Zr 11.4 La 45.6 Co 27 Al 16 > Zr 22.8 La 34.2 Co 27 Al 16 > Zr 34.2 La 22.8 Co 27 Al 16 > Zr 45.6 La 11.4 Co 27 Al 16 . The quaternary Zr-La-Co-Al phase-separated metallic glasses (MGs) are shown to experience double glass transition, crystallization and melting events, which could be regarded as possible model materials to study the glassy transition and structural relaxation behavior of BMGs.

The urea oxidation reaction (UOR) is a possible solution to solve the world&rsquo, s energy crisis. Fuel cells have been used in the UOR to generate hydrogen with a lower potential compared to water splitting, decreasing the costs of energy production. Urea is abundantly present in agricultural waste and in industrial and human wastewater. Besides generating hydrogen, this reaction provides a pathway to eliminate urea, which is a hazard in the environment and to people&rsquo, s health. In this study, nanosheets of CuCo2O4 grown on nickel foam were synthesized as an electrocatalyst for urea oxidation to generate hydrogen as a green fuel. The synthesized electrocatalyst was characterized using X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy. The electroactivity of CuCo2O4 towards the oxidation of urea in alkaline solution was evaluated using electrochemical measurements. Nanosheets of CuCo2O4 grown on nickel foam required the potential of 1.36 V in 1 M KOH with 0.33 M urea to deliver a current density of 10 mA/cm2. The CuCo2O4 electrode was electrochemically stable for over 15 h of continuous measurements. The high catalytic activities for the hydrogen evolution reaction make the CuCo2O4 electrode a bifunctional catalyst and a promising electroactive material for hydrogen production. The two-electrode electrolyzer demanded a potential of 1.45 V, which was 260 mV less than that for the urea-free counterpart. Our study suggests that the CuCo2O4 electrode can be a promising material as an efficient UOR catalyst for fuel cells to generate hydrogen at a low cost.

This paper has proposed a high temperature superconducting (HTS) field-modulation double-stator (HTS-FMDS) machine with a stationary seal for low-speed and direct-drive applications. The originality of this paper lies in the HTS field-excitation windings, which were fed with a direct current in order to offer strong field excitation, were placed in the inner stator, while the armature windings were installed in the outer stator so that the stationary seal of the cryogenic cooling system could be achieved. Moreover, a ferromagnetic ring was mounted on the top of each HTS coil to prevent the quench of the HTS wires resulting from the armature-reaction magnetic-field. By using finite-element analysis (FEA), the influence of the armature-reaction magnetic-field on the critical current and the electromagnetic properties were carried out so as to verify the validity of the proposed machine.

In this paper, the loss of a new type of high temperature superconducting (HTS) flux-switching (FS) machine with stationary seal is analyzed, and the loss in the HTS windings is analyzed emphatically. Two-dimensional time-step finite element method is used to analyze iron loss and furthermore compared with the calculated data. The magnetic field of HTS winding was tested by three-dimensional finite element method to evaluate the HTS heat loss. No-load calculated loss and FEM analyzed loss are basically the same, verifies the correctness of the loss calculation method. Finally, the change of loss and efficiency under different load conditions and the influence of rotor speed on the efficiency are studied.

This paper presents an effective permanent-magnet vernier (PMV) machine for direct-drive applications, in which the low-speed outer rotor employs a spoke-magnet arrangement with flux focusing to improve air-gap flux density, and the stator adopts an open-slot structure to enable the stator teeth to achieve field modulation. Using the finite element analysis, the performance characteristics of the proposed machine are investigated and compared with the split-slot surface PMV machine. A prototype is also built for experimentation to verify the validity. Both simulation and experimental results show that the proposed machine can offer the advantages of improved torque capability and low voltage regulation.

This paper presents a field-modulated permanent magnet (FMPM) machine using spoke-magnet-array outer rotor for direct-drive applications. The operating principle with detailed theoretical derivation is analyzed to reveal the evidence for high torque capability of the proposed machine, just due to the utilization of effective harmonic flux adding to the contribution of air-gap fundamental flux for energy conversion. Using the finite element analysis, the performance characteristics of the proposed machine are assessed and compared with permanent magnet synchronous machine counterparts to verify the theoretical analysis. A prototype machine is also fabricated for experimental validation of the proposed machine. The analytical discussions also form an important foundation for research in various high-performance FMPM machines.

In this study, a new organic lithium oxygen (Li–O2) battery structure is proposed to enhance battery capacity. The electrolyte is forced to recirculate through the cathode and then saturated with oxygen in a tank external to the battery. The forced convection enhances oxygen transport and alleviates the problem of electrode blockage during discharge. A two dimensional, transient, non-isothermal simulation model is developed to study the heat and mass transfer within the battery and validate the proposed design. Results show that this novel active cathode design improves the battery capacity at all discharge current densities. The capacity of the Li–O2 battery is increased by 15.5 times (from 12.2 mAh g−1 to 201 mAh g−1) at the discharge current of 2.0 mA cm−2 when a conventional passive electrode is replaced by the newly designed active electrode. Furthermore, a cathode with non-uniform porosity is suggested and simulation results show that it can reach a higher discharge capacity without decreasing its power density. Detailed mass transport processes in the battery are also studied.

This paper presents the design and experimental verification of a field-modulated permanent-magnet (FMPM) machine using spoke-magnet outer rotor for direct-drive wind turbines. The fundamental operation and optimised design process of the proposed machine are elaborated and discussed in detail. The electromagnetic analytical calculation is used for the initial determination of the prototype design, mainly concerning the special constraints of wind power generation, and the two-dimensional finite element analysis is also applied to optimise and investigate the detailed characteristics. A 5 kW prototype is constructed, and the measured performances have verified the analysis and design, justifying that the proposed machine can offer significant advantages of high-torque capability and low-voltage regulation. Experience gained from this study has led to develop a general design guideline for the open-slot FMPM machine using spoke-magnet outer rotor for direct-drive applications.

In this work, an effective field-modulated permanent-magnet (FMPM) machine was investigated, in which the spoke-magnet outer rotor and open-slot stator were employed. The objective of this paper is to provide the mathematical modeling analysis that was performed for the purpose of control research on this type of FMPM machine. The simulation results by means of finite element analysis (FEA) are given to verify the theoretical analysis and the validity of mathematical model. A prototype machine was also fabricated for experimentation. Both the analytical model and the FEA results are validated by experimental tests on the prototype machine.

Supercapacitors, also known as electrochemical capacitors, are considered the most promising energy storage devices owing to their high power densities and long lifespan. [ 3–5 ] The fast charge and discharge capability make supercapacitors favorable for applications in hybrid vehicles, portable electronics, and backup energy systems. [ 6–10 ] Carbonaceous materials, including carbon nanotubes and graphene, are being widely studied as alternatives to conventional graphites. [ 2 , 11–14 ] However, carbon-based materials usually show low energy density as they store charges electrostatically at their surfaces, so they have intrinsically low specifi c areal capacitance ( C a ) in the range of 10 − 40 μ F cm − 2 . Transition metal oxides/hydroxides store charges with surface faradaic (redox) reactions, which enable higher energy density compared to carbon. Metal oxides/hydroxides such as MnO 2 , NiO, Ni(OH) 2 , CoO x and their compounds have recently come into focus in the design of high-energy-density charge-storage materials. [ 15–27 ] Despite these efforts, practical energy storage applications still require higher specifi c capacitance. One way out is to design nanometer-scale electrode materials with very large surface areas and structural stability. In this context, porous nanostructures are of great interest because they can reduce ionic and electronic diffusion distance and provide large electrode/electrolyte contact area. For example, porous Ni and Au electrodes as current collectors have recently been reported, which signifi cantly improve the specifi c capacitance when covered with the pseudoactive material MnO 2 . [ 28 , 29 ] Also, nanoporous graphene electrodes with ∼ 4 nm pores drastically enhance the specifi c capacitance up to 166 F g − 1 . [ 30 ] For metal oxides

A two-dimensional, transient, and non-isothermal model was developed in this work to study the mass transfer properties of the Li-air battery. Special attentions have been paid to the cathode carbon electrode and the distributions of oxygen, lithium ion, lithium peroxide, and temperature in the carbon electrode have been calculated in the model. The effects of discharge current, electrode thickness, porosity distribution in the electrode, and cathode open ratio on the discharge capacity of the battery have been investigated. Modeling results showed that the discharge capacity of a Li-air battery was primarily determined by the oxygen supply. Most of the available pores deep in the electrode were not utilized because Li2O2 accumulated at the electrode/air interface and blocked the oxygen. It was also found that the utilization rate of the electrode was lower when the electrode was thick, the cathode open ratio was low, and the discharge current was high. A unique design of the carbon electrode with a non-uniform porosity distribution was proposed, and the discharge capacity of the battery was increased by more than 25% after implementing the new electrode. © 2012 The Electrochemical Society. [DOI: 10.1149/2.043210jes] All rights reserved.

A novel approach has been proposed to improve the water management of a passive direct methanol fuel cell (DMFC) fed with neat methanol without increasing its volume or weight. By adopting perforated covers with different open ratios at the cathode, the water management has been significantly improved in a DMFC fed with neat methanol. An optimized cathode open ratio could ensure both the sufficient supply of oxygen and low water loss. While changing the open ratio of anode vaporizer can adjust the methanol crossover rate in a DMFC. Furthermore, the gas mixing layer, added between the anode vaporizer and the anode current collector to increase the mass transfer resistance, can improve the cell performance, decrease the methanol crossover, and increase the fuel efficiency. For the case of a DMFC fed with neat methanol, an anode vaporizer with the open ratio of 12% and a cathode open ratio of 20% produced the highest peak power density, 22.7 mW cm−2, and high fuel efficiency, 70.1%, at room temperature of 25 ± 1 °C and ambient humidity of 25–50%.

A passive vapor-feed direct methanol fuel cell (DMFC) was experimentally investigated to improve its water management and cell performance when neat methanol was directly used. The effects of different water management approaches, including the addition of a water management layer (WML) and a hydrophobic air filter layer (AFL), and the use of thinner membrane on the cell performance, internal resistance, and fuel efficiency were investigated. The transient discharging behavior and long-term stability of the passive vapor-feed DMFC with the optimized water management were also studied. The results showed that by adding a WML and an AFL, or thinning the membrane thickness, the water management capability can be highly improved, not only enhancing the water recovery from the cathode to the anode, leading to a lower internal resistance and better cell performance, but also curbing the methanol crossover, increasing the fuel efficiency. It is also seen from the long-term constant-voltage test that the discharged current varied with the methanol concentration in the tank and the ambient temperature, while no evident permanent performance degradation was encountered after the 150 h test.

Passive Q-switching laser operation of Nd:GdxY1−xVO4 mixed crystals at 671 nm has been compared in the same V-shape folded cavity. Based on our comparative analysis, the best laser characteristics – the highest pulse energy and peak power and the shortest pulse width – were demonstrated by Nd:Gd0.63Y0.37VO4 crystal. At the same time, this crystal possesses the lowest thermal conductivity in comparison with the other Nd:GdxY1−xVO4 crystals, which could result in decreasing the average laser output power. To verify this assumption we also measured the focal lengths of thermal lens induced in the crystals during the laser operation.

In a high-concentration direct methanol fuel cell (HC-DMFC), the methanol crossover is typically decreased to an acceptable level by two main mechanisms: high methanol transport resistance between the anode reservoir and the membrane electrode assembly (MEA), and high water back flow from the cathode to the anode. Based on the semi-passive HC-DMFC fabricated in this work, the effects of methanol barrier layer (MBL) thickness and electrolyte membrane thickness on cell performance, methanol and water crossover, and fuel efficiency have been studied. The results showed that a thicker MBL could significantly decrease the methanol and water crossover by increasing the mass transport resistance between the anode reservoir and the MEA, while a thinner Nafion ® membrane could also significantly decrease the methanol and water crossover by enhancing the water back flow from the cathode through the electrolyte membrane to the anode. Using Nafion ® 212 as the electrolyte membrane, and a 6.4 mm porous PTFE plate as the MBL, a semi-passive HC-DMFC operating at 70 °C produced the maximum power density of 115.8 mW cm −2 when 20 M methanol solution was fed as the fuel.

The methanol barrier layer adopted for high-concentration direct methanol fuel cells (HC-DMFCs) increases water transport resistance, and makes water management in HC-DMFCs more challenging and critical than that in the conventional direct methanol fuel cell (DMFC) without a methanol barrier layer. In the semi-passive HC-DMFC used in this work, oxygen was actively supplied to the cathode side while various concentrated methanol solutions, 4 M, 8 M, 16 M, and neat methanol, were passively supplied from the anode fuel reservoir. The effects of the cathode relative humidity, cathode pressure, and oxygen flow rate on the water crossover coefficient, fuel efficiency, and overall performance of the fuel cell were studied. Results showed that electrolyte membrane resistance, which was determined by its water content, was the predominant factor that determined the performance of a HC-DMFC, especially at a high current density. A negative water crossover coefficient, which indicated that water flowed back from the cathode through the electrolyte membrane to the anode, was measured when the methanol concentration was 8 M or higher. The back flow of water from the cathode is a very important water supply source to hydrate the electrolyte membrane. The water crossover coefficient was decreased by increasing the cathode relative humidity and back pressure. Water flooding at the cathode was not severe in the HC-DMFC, and a low oxygen flow rate was preferred to decrease water loss and yield a better performance. The peak power density generated from the HC-DMFC fed with 16 M methanol solution was 75.9 mW cm −2 at 70 °C.