Investigation of boiling hydrogen flow characteristics under low-pressure conditions - Flow regime transition characteristics

Understanding the thermal-fluid characteristics of boiling hydrogen is of great significance for applications of liquid hydrogen, such as alternative clean energy and space vehicles. The boiling temperature of liquid hydrogen under atmospheric pressure is 20.3 K; thus, it is easy to boil to form a gas–liquid two-phase flow. Fuel transfer under the boiling state has been avoided in the space industry because of its unstable flow characteristics; precise control of the fuel, including the boiling flow, is necessary to improve the space-vehicle performance. This study aims to understand the flow-regime transition characteristics of boiling hydrogen through experimental investigation. The experimental conditions were as follows: the flow direction was horizontal, the inner diameter of the heating pipe was 15 mm, the mass flux ranged from 50 to 110 kg/m²s, and the pressure ranged from 250 to 300 kPa A. The flow-regime transition characteristics were obtained by a high-speed camera. Fully liquid phase (LP), dispersed bubbly flow (DB), intermittent flow (IN), and annular flow (AN) were observed during the experiment. Each flow-regime boundary model is constructed using two dominant forces from the experimental result based on a Taitel–Dukler model. For the DB/IN boundary, a large-bubble sustainable condition is derived by the balance between the shear and buoyancy forces acting upon the bubble; for the IN/AN boundary, a droplet-sustainable condition is derived in terms of the force balance between the drag and gravity acting on the droplet. The semi-theoretical model predicts the experimental data with 96.7% accuracy.     

Can a humanoid robot continue to draw attention in an office environment?

This study focuses on the use of humanoid robots in office environments, and investigates whether a robot can maintain the attention of passersby after initiation of face-to-face contact. Drawing attention can be considered as a first step in improving the continuity of use of robots; such continuity is one factor in validating their social acceptance, which must be considered when disseminating robots in offices. In this study, we assume that the robot approaches and greets users in order to make the users aware of its presence and encourage them to use it. In particular, the robots used in this study convey various greetings along with three nonverbal indicators (no motion, random motion, and face-to-face contact) when a passerby at the office is close to the robot. For a one-week period, we validated the social acceptance of the robot by examining how these robot motions influenced the rate and continuity of a passerby's attention. The results revealed that face-to-face contact can draw a high degree of attention, and that the presence of the robot affects the continuity with which attention is drawn. Finally, the paper discusses implications for future robot design, in terms of drawing and maintaining high rates of attention from users.     

Experiment of cryo-compressed (90-MPa) hydrogen leakage diffusion

To improve safety regulations for fuel cell vehicles and hydrogen infrastructures, experiments on cryo-compressed hydrogen leakage diffusion were conducted. The experimental apparatus can supply 90 MPa hydrogen at various temperature conditions (50 K–300 K) at a maximum flow rate of 100 kg/h. The hydrogen leakage flow rate was measured using pinhole nozzles with different outlet diameters (0.2 mm, 0.4 mm, 0.7 mm, and 1 mm). It was confirmed that the hydrogen leakage flow rate increases as the supply temperature decreases. To evaluate the hydrogen flow rate including the cryogenic condition, the orifice equation for liquid was found to be appropriate. The orifice flow coefficient converged to a constant value of 0.6 on the high-density condition side. The hydrogen concentration distribution was measured by injecting high-pressure hydrogen from the 0.2-mm pinhole for 10 min under a constant pressure/temperature condition. The axial hydrogen concentration distribution obtained by the ambient temperature (～300 K) hydrogen injection test well agreed with the experimental formula based on previous research studies. In addition, as the hydrogen injection temperature decreased, it was found that the hydrogen concentration increased, and an empirical formula of the 1% concentration distance for the cryogenic hydrogen system was newly presented. Additional tests were conducted using pinholes of different diameters, and a 1% concentration distance was confirmed to be proportional to the hydrogen leakage flow rate to the 0.5th power.     

Porous plug and superfluid helium film flow suppressor for the soft X-ray spectrometer onboard Astro-H

Suppression of superfluid helium flow is critical for the Soft X-ray Spectrometer (SXS) onboard Astro-H, to achieve a life time of the liquid helium over 5 years. The superfluid film flow must be sufficiently small, compared to a nominal helium gas flow rate of the SXS . For this purpose, four devices composed of a porous plug, an orifice, a heat exchanger, and knife edge devices will be employed based on the experience of the X-ray microcalorimeter (XRS for X-Ray Spectrometer) onboard Suzaku. The porous plug is a phase separator of the liquid and gas helium. A potential film flow leaking from the porous plug is suppressed by the orifice. Almost all the remaining film flow evaporates at the heat exchanger. The knife edge devices stop the remaining film flow by using atomically sharp edges. In this paper, we describe the principle and design of these four devices.     

An on-line method to monitor bwr core stability based on an autocorrelation method

An on-line monitoring method is introduced for BWR core stability. The method utilizes only autocorrelation values for two delay time intervals. Its simplicity makes it suitable for an on-line monitor. Accuracy of the core decay ratio calculated by the method improves as the core condition approaches instability. The error in the decay ratio for regional limit cycle oscillations is 0.2% when calculated from local signals in the most unstable region, and 4% when calculated from core averaged signals.     

Relation between the Three-dimensional Flow Structure and Aerodynamic Sound Generated from Inclined Circular Cylinder

The major causes of the sound pressure level (SPL) variation due to the changes of the inclined angle of a circular cylinder and the aspect ratio (ratio of distance between endplates to cylinder diameter) were investigated. The velocity fluctuation of the wake and the surface pressure fluctuation of the cylinder were measured in a low noise wind tunnel to find the correlation length, coherent output power and Strouhal number. The results show that the changes of these values qualitatively correspond with the change of SPL. Flow visualization tests are performed to clarify the variation of wake in relation with inclined angle and aspect ratio. It is found that the spanwise structure of Karman's vortex street is broken down by the upward flows generated around the bottom endplate, and the degree of the interference between the upward flow and Karman's vortex street is smaller when the aspect ratio is larger.     

Synthesis and UV-shielding properties of silica-coated calcia-doped ceria nanoparticles via soft solution processes

White nanoparticles of calcia-doped ceria were prepared from the precipitate by reacting CeCl₃-CaCl₂mixed solution with NaOH solution at pH 12 and the oxidation with hydrogen peroxide solution at 40^∘C, followed by the calcination at 700^∘C for 1 h. The sample before calcination contained significant amount of OH⁻ in the lattice and was yellow, but the powders calcined above 700^∘C were white, indicating that cation defect formed by replacing O^{2 −} with OH⁻ played as the color center. It is confirmed that calcia-doped ceria showed much lower photocatalytic activity as well as lower generation of singlet oxygen under UV light irradiation than those with titania and zinc oxide. Calcia-doped ceria particles were coated with amorphous silica by means of sol-gel reaction technique using hydrolysis of tetraethylorthosilicate (TEOS) or acid hydrolysis of sodium silicate. The silica coating by sol-gel reaction with TEOS was much more efficient for the reduction of catalytic activity of ceria for the oxidation of organic materials without loss of UV-shielding ability than that by acid hydrolysis of sodium silicate.     

Collision-activated infrared multiphoton dissociation in a quadrupole ion trap mass spectrometer

We propose and demonstrate a new method for multiple-stage mass spectrometry (MSn), collision-activated infrared multiphoton dissociation (CA-IRMPD), which is very effective for the quadrupole ion trap mass spectrometer (QITMS). CA-IRMPD uses a combination of focused laser irradiation (beam radius, approximately 0.4 mm) and collisional activation by a supplemental AC voltage between endcap electrodes. This combination enables IRMPD, which has conventionaLly been ineffective above 10(-4) Torr, to be used under a standard bath gas pressure of 2-8 mTorr. CA-IRMPD can produce richer spectra of product ions than CID or IRMPD while maintaining high sensitivity and mass resolution; thus, it will contribute to an accurate determination of peptide sequences.     

para-Selectivity of silicalite-1 coated MFI type galloaluminosilicate in aromatization of light alkanes

Journal of Porous Materials - MFI type galloaluminosilicates (GaAlMFI) were coated with inert silicalite-1 layers. The silicalite-1 coating could improve the para-selectivity for xylene production...