Modelling the motion of cylindrical particles in a nonuniform flow

The models currently used in computational fluid dynamics codes to predict solid fuel combustion rely on a spherical shape assumption. Cylinders and disks represent a much better geometrical approximation to the shape of bio-fuels such as straws and woods chips. A sphere gives an extreme in terms of the volume-to-surface-area ratio, which impacts both motion and reaction of a particle. For a nonspherical particle, an additional lift force becomes important, and generally hydrodynamic forces introduce a torque on the particle as the centre of pressure does not coincide with the centre of mass. Therefore, rotation of a nonspherical particle needs to be considered. This paper derives a model for tracking nonspherical particles in a nonuniform flow field, which is validated by a preliminary experimental study: the calculated results agree well with measurements in both translation and rotation aspects. The model allows to take into account shape details of nonspherical particles so that both the motion and the chemical reaction of particles can be modelled more reasonably. The ultimate goal of such a study is to simulate flow and combustion in biomass-fired furnaces using nonspherical particle tracking model instead of traditional sphere assumption, and thus improve the design of biomass-fired boilers.     

Charge transfer and SEIRAS studies of 1,4-benzoquinone functionalized mixed monothiol/dithiol self-assembled monolayers

Although substantial information can be obtained from electrochemical measurements, much greater detail concerning molecular structure can be obtained by coupling such measurements with molecular spectroscopy. To this end, electrochemical and in situ surface enhanced infrared spectroscopy (SEIRAS) was performed to analyze 1,4-benzoquinone (BQ) terminated self-assembled monolayers. Monolayers were derived via the Michael addition of BQ to a pre-formed mixed monolayer composed of methyl and thiol terminated functionalities. This approach resulted in relatively robust but non-ideal redox-active monolayers. Spectroscopic and electrochemical measurements have allowed us to determine the pH dependence of both the apparent formal potential and the heterogeneous standard rate constant for proton coupled electron transfer (PCET) for this 2e⁻/2H⁺ redox system. While the former is in excellent agreement with predictions of step-wise PCET, the latter deviates from the expected kinetic response.     

A Fixed-Bed Reactor Study of Catalytic Partial Oxidation over Rh/Al2O3: An Indication of a Direct Pathway to CO

Catalytic partial oxidation (CPO) of CH₄ in air was investigated over Rh/Al₂O₃ catalysts (0.01, 0.05, 0.1 and 1 wt% Rh⁰) in co-feed modus in laboratory scale fixed-bed reactors. Main focus was on catalyst stability and selectivity at low temperatures (<700 °C). A particularly high selectivity to CO was observed, indicating existence of a direct pathway.     

Oxygen reduction at a water-1,2-dichlorobenzene interface catalyzed by cobalt tetraphenyl porphyrine - A fuel cell approach

Oxygen reduction at the polarized water-1,2-dichlorobenzene interface, catalyzed by 5,10,15,20-tetraphenyl 21H,23H-porphine cobalt(II), is utilized in a novel type of flow fuel cell. In this fuel cell, hydrogen is oxidized at the anode as usual, but oxygen reduction takes place at the water-1,2-dichlorobenzene interface by a redox mediator, which is regenerated at the cathode. Oxygen reduction is coupled with proton transfer from water to the organic phase to form hydrogen peroxide, which is extracted into an aqueous phase flowing through the cell. The advantage of the cell is that no platinum catalyst is required at the cathode for O₂ reduction. Furthermore, recombination of H⁺ and O₂ at the cathode, like in a conventional fuel cell, is not possible, because the Gibbs free energy of transfer of protons from water to an organic phase is very high, 50-60 kJ/mol. The experiments reported here demonstrate that proton transfer is possible only by the facilitation of the catalyst.     

Application of three-dimensional electrical resistance tomography to characterize gas holdup distribution in laboratory flotation cell

Flotation is a separation process in which a hydrophobic material is separated from a hydrophilic one. It is commonly used in several branches of processing. The purpose of this paper was to use three dimensional Electrical Resistance Tomography (ERT) for the measurement of the spatial distribution of gas holdup in a mechanical flotation cell. Using an array of metal electrodes installed on the wall of the cell, a set of electric currents was injected to the cell and the resulting voltages were measured. The electrical conductivity within the cell was estimated based on the known currents and measured voltages. The gas holdup distribution was computed based on Maxwell model. The method was tested in a 50 dm³ mechanical flotation cell filled with water. The gas holdup distribution is presented at various values of the rotor speed and gas superficial velocity in non-frothed and frothed cases. Moreover, the performance of two rotor-stator mechanisms was compared. The results indicate that the 3D gas holdup distribution in a mechanical flotation cell under different conditions can be estimated using ERT. Moreover, differences in the gas holdup distribution can be detected depending on which rotor-stator mechanism is in use.     

The TRPA1 Agonist Cinnamaldehyde Induces the Secretion of HCO3− by the Porcine Colon

A therapeutic potential of the TRPA1 channel agonist cinnamaldehyde for use in inflammatory bowel disease is emerging, but the mechanisms are unclear. Semi-quantitative qPCR of various parts of the porcine gastrointestinal tract showed that mRNA for TRPA1 was highest in the colonic mucosa. In Ussing chambers, 1 mmol·L⁻¹ cinnamaldehyde induced increases in short circuit current (ΔI_sc) and conductance (ΔG_t) across the colon that were higher than those across the jejunum or after 1 mmol·L⁻¹ thymol. Lidocaine, amiloride or bumetanide did not change the response. The application of 1 mmol·L⁻¹ quinidine or the bilateral replacement of 120 Na⁺, 120 Cl⁻ or 25 HCO₃⁻ reduced ΔG_t, while the removal of Ca²⁺ enhanced ΔG_t with ΔI_sc numerically higher. ΔI_sc decreased after 0.5 NPPB, 0.01 indometacin and the bilateral replacement of 120 Na⁺ or 25 HCO₃⁻. The removal of 120 Cl⁻ had no effect. Cinnamaldehyde also activates TRPV3, but comparative measurements involving patch clamp experiments on overexpressing cells demonstrated that much higher concentrations are required. We suggest that cinnamaldehyde stimulates the secretion of HCO₃⁻ via apical CFTR and basolateral Na⁺-HCO₃⁻ cotransport, preventing acidosis and damage to the epithelium and the colonic microbiome. Signaling may involve the opening of TRPA1, depolarization of the epithelium and a rise in PGE2 following a lower uptake of prostaglandins via OATP2A1.     

Continuous-time interface for a micromachined capacitive accelerometer with NEA of 4 g and bandwidth of 300 Hz

A continuous-time accelerometer interface is feasible when a high dynamic range together with a wide signal band is required. In this paper the implementation of a continuous-time force-feedback loop for a capacitive sensor element with a full-scale signal of ±1.5 g is presented. The interface is measured to attain a noise equivalent acceleration (NEA) density of 500  at 30 Hz for the on-chip digitized output and 300  at 30 Hz for the analog output using a capacitive half-bridge sensor element with a single pair of electrodes. The essential circuit structures of the closed-loop sensor will be presented and analyzed in detail.