Pressure drop and flow distribution characteristics of single and parallel serpentine flow fields for polymer electrolyte membrane fuel cells

This study numerically investigates pressure drop and flow distribution characteristics of serpentine flow fields (SFFs) that are designed for polymer electrolyte membrane fuel cells, which consider the Poiseuille flow with secondary pressure drop in the gas channel (GC) and the Darcy flow in the porous gas diffusion layer (GDL). The numerical results for a conventional SFF agreed well with those obtained via computational fluid dynamics simulations, thus proving the validity of the present flow network model. This model is employed to characterize various single and parallel SFFs, including multi-pass serpentine flow fields (MPSFFs). Findings reveal that under-rib convection (convective flow through GDL under an interconnector rib) is an important transport process for conventional SFFs, with its intensity being significantly enhanced as GDL permeability increases. The results also indicate that under-rib convection can be significantly improved by employing MPSFFs as the reactant flow field, because of the closely interlaced structure of GC regions that have different path-lengths from the inlet. However, reactant flow rate through GCs proportionally decreases as under-rib convection intensity increases, suggesting that proper optimization is required between the flow velocity in GCs and the under-rib convection intensity in GDLs.     

Reciprocating Sliding Friction and Wear Property of Fe<Subscript>3</Subscript>Si Based Alloys Containing Cu in Water Lubrication

Fe₃Si, Fe₃Si alloys containing Cu were fabricated by arc melting followed by hot-pressing. The friction and wear behaviors of Fe₃Si based alloys with and without Cu addition against Si₃N₄ ball in water-lubrication were investigated. The friction coefficient and the wear rates of Fe₃Si based alloys decreased as the load increased. The wear rate of Fe₃Si was higher than that of AISI 304. The addition of Cu can significantly improve the friction and wear properties of Fe₃Si based alloys and substantially reduce the wear rates of Si₃N₄ ball. The wear rate of Fe₃Si–10%Cu was 2.56 × 10⁻⁶ mm³ N⁻¹ m⁻¹ at load of 20 N and decreased to 1.64 × 10⁻⁶ mm³ N⁻¹ m⁻¹ at load of 90 N. The wear rate of Si₃N₄ ball against Fe₃Si–10%Cu was 1.41 × 10⁻⁶ mm³ N⁻¹ m⁻¹, while the wear rate of Si₃N₄ ball against AISI 304 was 5.20 × 10⁻⁶ mm³ N⁻¹ m⁻¹ at load of 90 N. The wear mechanism was dominated by micro-ploughing. The combination of mechanical action (i.e., shear, smear and transference of Cu) and tribochemical reaction of Si₃N₄ with water was responsible for the improved tribological behavior of Fe₃Si alloys containing Cu under high loads.     

A device for sublimation molecular beam deposition of erbium-doped silicon films

The device described contains a source of Er vapors in the form of a rectangular erbium strip heated to a temperature of 800–950°C by a current passing through it. The base material (Si) flow was produced by sublimation of a silicon bar cut from a single-crystal ingot. The device was used for growing epitaxial Si layers with an Er concentration of 5×10¹⁸–10²¹ cm⁻³.     

A three-axes-compensated inductive magnetometer for measurements in high pulsed magnetic fields

A high-sensititity magnetometer intended for studying the magnetic properties of materials in pulsed magnetic fields of up to 43 T is described. A distinctive feature of the magnetometer is its method for compensating pickups generated in the magnetometer sensing element by a pulsed field. The commonly used uniaxial high-order compensation is replaced by a triaxial compensation of the lowest (quadrupole) order, combined with a transverse arrangement of the main probe coils. This method has allowed us to achieve a compensation level of the signal in the working coil (with an inner diameter of 1.4 or 1.75 mm) of the magnetometer without a sample of up to 10⁻⁶ for the longitudinal and 10⁻⁴ for the transverse field components. The magnetic moment sensitivity of the magnetometer is 10⁻⁴ mA·m² in fields below 10 T and 10⁻³ mA·m² at a field pulse amplitude of 35 T. A deviation of the compensation is below 2×10⁻⁴ for a temperature increase from 77 to 300 K and below 5×10⁻⁵ after sample replacement. The sample temperature is controlled by a fast-acting temperature control system in a range of 6–300 K to an accuracy of 0.3–0.05 K.     

Effect of Fluoride Content on Friction and Wear Performance of Ni<Subscript>3</Subscript>Al Matrix High-Temperature Self-Lubricating Composites

The self-lubricating composites Ni₃Al–BaF₂–CaF₂–Ag–Cr, which have varying fluoride contents, were fabricated by the powder metallurgy technique. The effect of fluoride content on the mechanical and tribological properties of the composites was investigated. The results showed that an optimal fluoride content and a balance between lubricity and mechanical strength were obtained. The Ni₃Al–6.2BaF₂–3.8CaF₂–12.5Ag–10Cr composite showed the best friction coefficients (0.29–0.38) and wear rates (4.2 × 10⁻⁵–2.19 × 10⁻⁴ mm³ N⁻¹ m⁻¹) at a wide temperature range (room temperature to 800°C). Fluorides exhibited a good reduced friction performance at 400 and 600°C. However, at 800°C, the formation of BaCrO₄ on the worn surface due to the tribo-chemical reaction at high temperatures provided an excellent lubricating property.     

A technique for measuring permeability of samples of anisotropic rocks for water and gas

A technique, equipment, and software for measuring permeability (including anisotropic) of rock samples for water and gas, taking variations of density and dynamic viscosity of the flowing medium into account, is described. The proposed method is intended to determine permeability with a high accuracy (up to 3–5%) in a range of 10⁻²² to 10⁻¹⁵ m² at efficient pressures up to 50 MPa and temperatures up to 300°C. In the course of one experiment on a single sample, the developed equipment and technique ensure the simultaneous determination of the axial and radial permeability components of the sample for water and Klinkenberg’s parameter which characterizes a pore space of the rock.     

Nanocomposite Microstructure and Environment Self-Adapted Tribological Properties of Highly Hard Graphite-Like Film

Graphite-like carbon (GLC) nanocomposite films were fabricated by DC magnetron sputtering using high pure graphite target at ambient temperature. Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) investigation showed that the as-deposited GLC films have high concentration of sp²-hybridized carbon. High-resolution transmission electron microscopy (HRTEM) images and selected area diffraction patterns (SADP) indicated a complex nanocomposite microstructure of the GLC films. As well as nanocrystalline graphite, a face-center cubic (fcc) diamond with a grain size in the range of 3–8 nm were dispersed in the amorphous carbon matrix inhomogenously and integrally. The nanocomposite GLC film had high hardness of 23 GPa, which was attributed to the mutual strengthening effect of nanoparticles and amorphous matrix. More importantly, the as-deposited nanocomposite GLC film exhibited excellent self-adapted tribological properties in different environments of ambient air, different relative humidity and water. The friction coefficients were 0.053 in ambient air and 0.046 in distilled water, while specific wear rates were 4.5 × 10⁻¹⁶ m³ N⁻¹ m⁻¹ and 1.6 × 10⁻¹⁶ m³ N⁻¹ m⁻¹, respectively. The friction regimes and mechanisms in different environments were elaborated. This film is foreseen to high potential in protecting and solid lubricating material in humidity or water environment.     

NiAl Matrix High-Temperature Self-Lubricating Composite

A high-temperature self-lubricating composite NiAl–Cr–Mo–CaF₂ was fabricated using the powder metallurgy technique, and the tribological behavior of the composite at a wide range of temperatures (room temperature to 1000 °C) was investigated. The results showed that the composite had a favorable friction coefficient of about 0.2 and an excellent wear resistance of about 1 × 10⁻⁵ mm³N⁻¹m⁻¹ at the high temperatures tested (800 and 1000 °C). The excellent self-lubricating performance was attributed to the formation of the glaze film on the worn surface consisting mainly of CaCrO₄ and CaMoO₄ as high-temperature solid lubricants.     

A two-frequency pulse refractometer for measuring the electron density in tokamaks

An instrument for fringe-jumps free measurements of the electron concentration and estimations of the peaking factor of density distributions in magnetic confinement plasma devices with probing at frequencies close to the cutoff is described. The instrument is intended to perform measurements in a 5 × 10¹⁸–10²⁰ m⁻³ density range (while probing by the extraordinary wave) with time resolution ∼10 μs.     

Microwave drying and moisture diffusivity of white mulberry: experimental and mathematical modeling

The literature surveyed revealed that drying kinetics of white mulberry under microwave treatment has not been investigated. In present study, both experimental study and mathematical modeling on microwave drying of white mulberry was performed. The microwave drying process which reduced the moisture content of mulberry from 3.76 to 0.25 (g water/g dry matter) was carried out at 90, 180, 360, 600, and 800 W in a modified microwave drying set-up. The effects of microwave drying technique on the moisture ratio and drying rate of white mulberry were investigated experimentally. Both the effects of microwave power level (under the range of 90–800W) and initial sample weight (50–150g) were studied. No constant rate period was observed. Mathematical modeling of thin layer drying kinetics of white mulberry under microwave treatment was also investigated by fitting the experimental drying data to eight thin layer drying models. Among the models proposed, Midilli et al. model precisely represented the microwave drying behavior of white mulberry with the coefficient of determination higher than 0.999 and mean square of deviation (χ²) and root mean square error (RMSE) lower than 1.1×10⁻⁴ and 8.9×10⁻³, respectively for all the microwave drying conditions studied. The effective moisture diffusivity (D_eff) of white mulberry varied from 0.45×10⁻⁸ to 3.25×10⁻⁸ m²s⁻¹. Both the drying constant (k) and D_eff increased with the increase of microwave power level.     

Mathematical modelling and experimental investigation on sun and solar drying of white mulberry

The drying kinetics of white mulberry was investigated in a solar dryer with forced convection and under open sun with natural convection. The constant rate period is absent from the drying curve. The drying process took place in the falling rate period. The drying data were fitted to the different mathematical models. The performance of these models was investigated by comparing the determination of coefficient (R), reduced chi-square (χ ²) and root mean square error (RMSE) between the observed and predicted moisture ratios. Among these models, the drying model developed by Logarithmic model showed good agreement with the data obtained from the experiments in the solar dryer with forced convection drying mode. The Verma et al. model has shown a better fit to the experimental mulberries data for open sun drying with natural convection mode than the other models. The effective moisture diffusivity values were estimated from Fick’s diffusional model. These values were 3.56×10⁻⁹ m²/s for solar drying and 2.40×10⁻⁹ m²/s for open sun drying.     

Multichannel wire gas electron multipliers with 1- and 3-mm gaps

The operation of multichannel wire gas electron multipliers (MWGEMs) with gaps between electrodes δ = 1 and 3 mm, when the chamber is filled with commercial neon under a 0.4- and 1.0-atm (abs.) pressure and irradiated with α and β particles, is studied. The following maximal proportional electron multiplication coefficients are obtained: 6 × 10³ (α, irradiation, δ = 3 mm, 1 atm, and 20% streamers), 1.2 × 10⁴ (β⁻, 3 mm, 1 atm, and 50% streamers), 6 × 10³ (α, 3 mm, 0.4 atm, and 20% streamers), and 10⁵ (β⁻, 3 mm, 0.4 atm, and 50% streamers). The maximal proportional electron multiplication coefficients are obtained in the MWGEM and its anode (induction) gap in the sequential electron multiplication mode: 1.08 × 10⁵ (β⁻, 1 mm, 0.4 atm, 50% streamers), 2 × 10⁶ (β⁻, 3 mm, 0.4 atm, 20% streamers), and 1.12 × 10⁵ (α, 3 mm, 0.4 atm, 50% streamers).     

Numerical determination of the elastic compliance of roller bearings using the hertz theory

Analytical determination of the elastic compliance of roller bearings using the Hertz theory is presented. It is revealed that this parameter depends on the external load q and is varied from 15 × 10⁻⁶ up to 35 × 10⁻⁶ mm²/N for the wide range of q variation.     

An experimental study on the pumping performance of molecular drag pumps

The pumping performance of molecular drag pumps (MDP) has been investigated experimentally. The experimented MDPs are a disk-type drag pump (DTDP), helical-type drag pump (HTDP) and compound drag pump (CDP), respectively. In the case of the DTDP, spiral channels of a rotor are cut on both upper surface and lower surface of a rotating disk, and the corresponding stator is a planar disk. In the case of the HTDP, the rotor has six rectangular grooves. The CDP consists with the DTDP, at lower part, and with the HTDP, at upper part. The experiments are performed in the outlet pressure range of 0.2–533 Pa. The inlet pressure and compression ratio are measured under the various conditions of outlet pressure and throughputs, and nitrogen is used for the test gas. At the outlet pressure of 0.2 Pa, the ultimate pressure has been reached to 1.0 × 10⁻² Pa for the HTDP, 1.3 × 10⁻⁴ Pa for the DTDP, and 3.6 × 10⁻⁵ Pa for the CDP. The maximum compression ratio of the CDP is much higher than those of the DTDP or HTDP. Consequently, the ultimate pressure of the CDP is the lowest one.     

An analysis of the signal-to-noise ratio of a current amplifier

The signal-to-noise ratio of the current amplifier that includes a differenting delay line (50 ns) and an RC integrator is analyzed. The amplifier is intended for use in conjunction with charge-, curret-, or voltage-pulse detectors, including those with large capacitances or low ohmic resistances. The amplifier and detector can be connected with a long (in this work, up to 100 m) radio-frequency cable. The root-mean-square intrinsic noise charge of the amplifier is 2.8×10³ e ⁻ when the input is nonloaded and 13.7×10³ e ⁻ when a 20-meterlong 3 cable is connected to the input. If the charge produced by the detector is constant and the pulse duration decreases, then both the signal-to-noise ratio and the equipment speed performance can be increased.     

An automatic system for controlling the UV-radiation dose

A photodetector based on an ⁺-GaAs/n-ClInPc heterojunction, photosensitive in the 200- to 1000-nm wavelength range, is described. The ClInPc absorbtance is high:K _λ=2×10⁷ m⁻¹ for λ=220 and 380 nm. The photosensitivity of the photodetector is 2250 V/W (S=1 cm²). An automatic system for controlling the UV-radiation dose was developed on the basis of this photoreceiver.     

Elevated temperature deformation behavior in an AZ31 magnesium alloy

An AZ31 magnesium alloy was tested at constant temperatures ranging from 423 to 473 K (0.46 to 0.51T _m ) under constant stresses. All of the creep curves exhibited two types depending on stress levels. At low stress (σ/G<4×10⁻³), the creep curve was typical of class A (Alloy type) behavior. However, at high stresses (σ/G>4×10⁻³), the creep curve was typical of class M (Metal type) behavior. At low stress level, the stress exponent for the steady-state creep rate was of 3.5 and the true activation energy for creep was 101 kJ/mole which is close to that for solute diffusion. It indicates that the dominant deformation mechanism was glide-controlled dislocation creep. At low stress level wheren=3.5, the present results are in good agreement with the prediction of Fridel model.     

Estimation of the state of rod structural elements based on recording of deformation responses to serial impact excitations

Based on the example of welded and one-piece-cut steel (Steel 10) frame triangular elements (4 × 8 × 245 mm) using the methods of thermal unloading up to the temperature T _max = 625°C, serial impact testing of parent (stressed) and unloaded elements, and comparative analysis of Fourier images of deformation responses with respect to unloaded elements, it was found that a nonlinear region of the Fourier image degenerates into a linear one and the maximum of the linear regions of the Fourier image shifts up to 2 Hz. The dynamic deformation responses of the elements were recorded using superbroadband (from 10⁻² to 10⁸ Hz) ferroelectric microsensors based on thin Pb(Zr_0.53Ti_0.47)O₃ films with a thickness of ∼2.0 μm with a 0.8 mm² contact pad. The results can provide a the signal for distinguishing stressed states of structures and their elements.     

A laser spectrometer of field-asymmetric ion mobility

A method for analyzing a substance has been experimentally tested. The method combines the field-asymmetric ion mobility spectrometry and laser ionization of molecules under atmospheric pressure. Pulsed radiation of the fourth harmonic of an YAG: Nd³⁺ laser (λ = 266 nm) and a spectrometer with a cylindrical analysis camera were used. The results of detecting nitrocompounds—trinitrotoluene, cyclotrimethylenetrinitramine (hexogen, RDX), etc.—are presented. The experimental detection limits of the spectrometer are 5 × 10⁻¹⁵ g/cm³ (cyclotrimethylenetrinitramine) and ≤3 × 10⁻¹⁵ g/cm³ (trinitrotoluene).     

Analysis of viscosity effect on turbine flowmeter performance based on experiments and CFD simulations

Viscosity effect is one important factor that affects the performance of turbine flowmeter. The fluid dynamics mechanism of the viscosity effect on turbine flowmeter performance is still not fully understood. In this study, the curves of meter factor and linearity error of the turbine flowmeter changing with fluid viscosity variations were obtained from multi-viscosity experiments (the viscosity range covered is 1.0×10^–6 m²/s–112×10^–6 m²/s). The results indicate that the average meter factor of turbine flowmeter decreases with viscosity increases, while the linearity error increases. Furthermore, Computational Fluid Dynamics (CFD) simulation was carried out to analyze three-dimensional internal flow fields of turbine flowmeter. It was demonstrated that viscosity changes lead to changes of the wake flow behind the upstream flow conditioner blade and the flow velocity profile before fluid entering turbine rotor blade, which affect the distribution of pressure on the rotor blades, so impact the turbine flowmeter performance.