Mikio Kumita

Heat and mass transfer from a flat plate of finite thickness to a boundary layer flow with transpiration

Abstract Cooling a flat plate by evaporation of a volatile liquid from the surface to a laminar boundary layer flow past the plate is theoretically analyzed, taking into account both injection effect due to the vaporization and two-dimensional thermal conduction in the plate, with convective thermal-boundary condition on the other plate surface. The thermal effect of the volatile liquid supply to the plate is neglected and all of the physical properties are assumed to be constant in spite of the changes in concentration and temperature in the boundary layer. Representative calculations were performed for air-water system with various thermal conditions of the plate and flow conditions. The temperature fields and distributions of the local Nusselt and Sherwood numbers are estimated for a parallel flow case. The effects of parameters related to the wall conduction on the injection parameter are discussed. Comparison of results calculated for air-methanol and air-water systems shows that in the former case the injection gives more significant influence on the heat and mass transfer characteristics.

Mass transfer enhancement during electrolysis with cylindrical electrodes by magnetic field exposure and its dependency on electrode positions

Abstract Electrolytic mass transfer rates under diffusion-controlled conditions were extensively measured for cylindrical cathodes in various positions relative to applied horizontal and static magnetic field using the limiting current technique with electrochemical reduction of Fe(CN) 6 3− with an excess of supporting electrolyte. To establish a more generalized dimensionless regression equation for the mass transfer coefficient, the modification of the equivalent diameter in relevant dimensionless parameters was discussed based on flows induced around cylinders. The resulting experimental data were well correlated by modifying the diameter d to d/( cos θ cos α) , where θ is the inclination angle of the cathode from the horizon and α is the depth angle from the magnetic field direction. Similar experiments for α = π /2 were also carried out under further extensive experimental conditions as a limiting case of the preceding one and the obtained data were well correlated by additionally introducing the new term of “aspect ratio of cathode” in the regression equation and using the characteristic length d /(sin θ ) or L in the relevant dimensionless parameters, Sherwood number, Rayleigh number and magneto-diffusion factor, where L is the cathode length.

Centrifugal Filter for Aerosol Collection

Air filters collect particles by the mechanical collection mechanisms, namely, inertia, interception, gravitational settling, and Brownian diffusion. There exists the most penetrating particle size (MPPS) in submicron size range for which none of the collection mechanisms work effectively. In this study, we propose a new type of filter named as “centrifugal filter,” which collects aerosol particles by centrifugal force together with the conventional mechanical collection mechanisms. The centrifugal filter proposed in the present work may be rotated by a motor or compressed air. Air passes through the filter in the axial direction of filter rotation. The filter rotates so does the air embedded in the filter, and therefore centrifugal force exerts on particles. In addition to the mechanical collection mechanisms, small migration of particles due to the centrifugal force enhanced the collection efficiency of submicron particles significantly without increasing the pressure drop. The performance tests of centrifugal filter were conducted by changing the fiber diameter, the air flow velocity and the rotation speed. We found that the collection efficiency of filter is enhanced significantly by rotating the filter without increasing the pressure drop and that the filter efficiency is well predicted by the conventional filtration theory accounting for the centrifugal force. Copyright 2015 American Association for Aerosol Research

Enhancement of Electrolytic Mass Transfer Around Cylinders by Exposure to Switching Magnetic Fields

The effect of alternating magnetic fields, from 20 to 200 mHz and up to 250 mT in the horizontal direction with a symmetrical or asymmetrical rectangular waveform, on the mass transfer rate during diffusion-controlled electrolysis was experimentally investigated for a K3Fe(CN)6 - K4Fe(CN)6 system. The experiments were performed using inclined cylindrical Pt cathodes on a plane parallel to the magnetic field direction.

Application of centrifugal filter to aerosol size distribution measurement

ABSTRACT In the present work, the centrifugal filter proposed by the authors was applied to classify aerosol particles followed by the detection of total mass or number concentrations so as to measure the size distribution of aerosol particles. The structure and operating condition of the centrifugal filter were optimized in order to attain sharp separation curves with various cut-off sizes between 0.3 and 10 μm. The aerosol penetrating the centrifugal filter at various rotation speeds was measured with a photometer to determine the total mass concentration. The virtue of this system is that the cut-off size is varied just by scanning the rotation speed of filter and that it can be applied to the measurement of high concentration aerosols without dilution by choosing an appropriate filter medium. As a result, the centrifugal filter was successfully applied to measure the size distribution of solid particles in size ranging from 0.3 to 10 μm. Copyright

Sieving of aerosol particles with metal screens

ABSTRACT Metal screens with uniform micrometer-sized opening were employed to sieve aerosol particles by suppressing the adhesion of particles smaller than the openings. The collection efficiencies of monodispersed polystyrene latex (PSL) particles were experimentally determined using the metal screens with 1.2, 1.8, 2.5, and 4.2 μm openings at various filtration velocities. The particles smaller than the mesh opening adhered on the metal screen at a low filtration velocity, but the bounce-off of particles on the mesh surface suppressed the adhesion at a high velocity. As a result, we found that the adhesion of PSL particles larger than 0.3 μm mostly suppressed at a filtration velocity higher than 10 m s−1 and therefore we can sieve aerosol particles according to the opening size of metal screens. We also found that the particle number concentration could be determined by measuring the increase in pressure drop since the clogging of metal screen openings takes place by the individual particles.

Breathing simulator of workers for respirator performance test

Breathing machines are widely used to evaluate respirator performance but they are capable of generating only limited air flow patterns, such as, sine, triangular and square waves. In order to evaluate the respirator performance in practical use, it is desirable to test the respirator using the actual breathing patterns of wearers. However, it has been a difficult task for a breathing machine to generate such complicated flow patterns, since the human respiratory volume changes depending on the human activities and workload. In this study, we have developed an electromechanical breathing simulator and a respiration sampling device to record and reproduce worker’s respiration. It is capable of generating various flow patterns by inputting breathing pattern signals recorded by a computer, as well as the fixed air flow patterns. The device is equipped with a self-control program to compensate the difference in inhalation and exhalation volume and the measurement errors on the breathing flow rate. The system was successfully applied to record the breathing patterns of workers engaging in welding and reproduced the breathing patterns.

Focused Deposition of Nanoparticles on Polymer Film with an Improved TSI-Nanoparticle Sampler (Model 3089)

A two-dimensional array of spots of deposited nanoparticles as small as 7 × 7 μm was fabricated on a polymer film using a modified commercial nanometer aerosol sampler (NAS; TSI-model 3089) coupled with a surface-discharge microplasma aerosol charger (SMAC). The charged aerosol particles were electrostatically focused by a metal mesh (electrically grounded) on the polymer film (insulator) and electrode (3 kV). The effect of mesh geometry on the concentration ratio (focusing ratio × collection efficiency) was evaluated using monodisperse polystyrene latex particles with diameters of 48, 100, and 300 nm. The electrostatic focusing effect was also analyzed by a numerical simulation of the electrostatic field. The two-dimensional patterning of nanoparticles is an effective method in concentrating particles for the subsequent observation and chemical analysis of aerosol particles. In our experiments, the SMAC-NAS system achieved a net concentration ratio of more than 20 times for 48- and 100-nm particles, which would significantly shorten the aerosol-sampling time. The particle deposition patterns formed on a transparent polymer film may provide samples for analyzing the transmittance, luminescence, and other optical characteristics of deposited nanoparticles. Copyright 2015 American Association for Aerosol Research

Sorption Dynamics of Cr(VI) on Used Black Tea Leaves

Sorption efficiency of Cr(VI) on used black tea leaves from aqueous solutions was evaluated. Kinetic studies were conducted using a batch process, and the effects of Cr(VI) concentration, solution pH and temperature on the adsorption and reduction performance were investigated. The adsorption kinetics follows pseudo‐second order rate equation better than pseudo‐first order one. The rate constant of pseudo‐second order adsorption decreases with increasing an initial concentration of Cr(VI), up to a certain limit, then becomes steady. The maximum value of the rate constant was observed at an initial solution pH = 1.3. The rate constant was found to linearly increase with an increase in temperature, showing that the process is endothermic. The activation energy of adsorption calculated from Arrhenius plot is 16.3 kJ/mol, indicating that the adsorption occurred easily.