Studies of a mixing process induced by a transverse rotating magnetic field

This study reports on research results in the field of a mixing process under the action of a transverse rotating magnetic field (TRMF). The main objective of this paper is to present the effect of this type of a magnetic field on the mixing time. The proposed dimensional analysis of Navier–Stokes equation including the Lorentz force allows describing the analyzed process by means of the relationships basing on the dimensionless numbers (the mixing time number, the magnetic Taylor number, and the rotational Reynolds number). The possibility of using the magnetic particles (Fe₃O₄) as active micro-stirrers under the influence of a TRMF for active enhancement of a mixing process was considered. Moreover, the effect of a particle content on homogenization efficiency by applying a TRMF was also investigated. The obtained experimental results suggest that the mixing time under the TRMF and MDF conditions may be worked out by using the relation between the mentioned mixing time number and the modified Reynolds number (particle Reynolds number). Important conclusions referring to the discussion of experimental studies of a mixing process are also specified.     

Distributions of respiratory contaminants from a patient with different postures and exhaling modes in a single-bed inpatient room

This study investigated contaminant transport and evaluated the ventilation performance in a single-bed inpatient room. The study performed comparative experimental analysis on the distributions of respiratory contaminants breathed out and coughed out by a patient in a full-scale chamber, which simulated a single-bed inpatient room. The contaminant exhaled by the patient was simulated by an SF₆ tracer gas and 3-μm particles at steady-state conditions. The differences in the contaminant distribution between the coughing and breathing cases were insignificant for the mixing ventilation case, while for the displacement ventilation, the contaminant concentrations in the upper part of the room were higher for the coughing case. The contaminant concentrations in the inpatient room for the case with the patient sitting on the bed were lower than those for the patient supine on the bed for the displacement ventilation under the same supply airflow rate. The SF₆ tracer gas and 3-μm particles released at a notable initial velocity for simulating a cough could give similar contaminant distributions in the inpatient room. Therefore, the experimental data can be used to validate a CFD model, and the validated CFD model can be used to investigate transient coughing and breathing processes.     

水泥搅拌桩在城市道路软基处理中的应用

城市道路在软基处理技术上的要求比普通公路要求高,因为城市道路在建设过程中会同步埋设雨污水、强弱电、自来水和燃气等管线,其中雨污水管道因常采用重力流设计,因此对路基沉降要求比较高。水泥搅拌桩作为技术较为成熟的软基处理方式,在科学的施工方法和有效的质量控制措施下,可有效提高软土地基的承载能力、抗震液化能力和控制路基沉降,保证路基稳定性,满足城市道路管线工程对路基工后沉降的要求。本文通过工程实例,介绍水泥搅拌桩在城市道路软基处理中的施工方法和质量控制措施。     

GYCBL200型厂拌冷再生设备

GYCBL200型厂拌冷再生设备可以对旧沥青路面材料进行厂拌冷再生,具有配料计量精准,全自动,效率高,可连续生产等优点,其搅拌主机采用具有自主知识产权的"连续式"、"强制"、"角度"和"沸腾"的搅拌技术,搅拌力度大,搅拌效率高,混合均匀,搅拌能力最大可达250t/h.介绍GYCBL200型厂拌冷再生设备的工作原理、结构...     

阳离子明胶蛋白衍生物浆料性能及应用研究

研究阳离子明胶蛋白衍生物浆料的上浆性能及调浆工艺。自制了阳离子明胶蛋白衍生物浆料,测试了该浆料的浆液黏度和浆膜性能,将其用于纯棉14.6tex纱和涤/棉65/35 13tex混纺纱的上浆,并对阳离子明胶蛋白衍生物浆料的煮浆时间、温度和浓度进行了优化。试验表明:阳离子明胶蛋白衍生物浆料浆液浓度7%,95℃煮浆30min对纯棉纱的上浆效果较好;浆液浓度5%,95℃煮浆30min对涤/棉65/35 13tex混纺纱的上浆效果较好。认为:阳离子明胶蛋白衍生物浆料可以完全或部分替代难降解的PVA浆料。     

HEAT AND MASS TRANSFER WITH MULTIPLE PARTICLE INTERACTIONS PART I. DROPLET EVAPORATION

A generalized treatment of heat and/or mass transport between an assemblage of particles and a surrounding continuum is presented. The unsteady state diffusive transport is shown to depend on the size and positions of the particles, and the rate processes are found to be radically different from single particle rates because of particle interactions. A three dimensional model has been developed to predict global concentration or temperature distributions by treating the particles as point sources or sinks. The conditions for which particles can be treated as isolated or as interactive members of a group are established, and correction factors are presented from which multiple particle mass transfer rates can be calculated from single isolated particle mass transfer rates. For finite assemblages the correction factors are shown to be in close agreement with results computed previously using the method of images.     

FREE OBJECT MOTION IN A GAS FLUIDIZED BED

The presence probability, the characteristic motions and the velocity of various “light” objects freely immersed in a gas fluidized bed of “heavy” fine particles have been investigated as a function of superficial fluid velocity, powder characteristics and bed height. The displacement of objects through the bed has been shown to result from both a “deterministic” dynamic force equilibrium and a “stochastic” stirring effect due to bubbles. A specific gas velocity exists at which a deep change in mixing occurs: above it the stirring effect is fairly noticeable, while below it pseudo-hydrostatic effects prevail. A method has been proposed to estimate this characteristic value.     

INVESTIGATION OF A NOVEL MICROREACTOR FOR ENHANCING MIXING AND CONVERSION

A novel microreactor with a network of omega-shaped microchannels has been designed, fabricated, and tested for enhanced chemical species mixing and reaction conversion. Fluidic and mixing properties of the omega channel reactor have been investigated by means of computational fluid dynamic (CFD) simulation. Also, a stochastic model describing particle transport in the axial direction was applied to characterize the residence time distribution or the cumulative probability of a particle exiting the microreactor over time. Both fluidic simulation and stochastic model approaches revealed the advantage of the omega-shaped microchannels as compared to straight or zigzag-shaped microchannels. Fischer-Tropsch reactions were carried out using sol-gel encapsulated iron and cobalt catalysts in the omega-shaped microchannels. The experimental results showed that the conversion rate for the omega-shaped microchannels was considerably higher than that for the conventional straight microchannel or for the zigzag-shaped microchannels. These results were consistent with the fluidic simulation and the stochastic modeling results.     

IDENTIFICATION AND CORRELATION OF MIXING TIMES IN OPPOSED-JET MIXERS

This article deals with the theoretical investigation of the effect of suspended particles on the marginal stability of a double-diffusive ferrofluid layer with internal angular momentum heated from below subjected to a transverse uniform magnetic field. For a flat fluid layer contained between two free boundaries, an exact solution is obtained using a linear stability analysis theory and normal mode analysis method. For the case of stationary convection, the effect of various parameters like suspended particles, solute gradient, magnetization, coupling parameter, spin diffusion parameter, and heat conduction parameter has been analyzed. The critical magnetic thermal Rayleigh number for the onset of instability is also determined numerically for sufficiently large values of magnetic parameter M₁ and results are depicted graphically. It is observed that the critical magnetic thermal Rayleigh number is reduced because the heat capacity of clean fluid is supplemented by that of the suspended particles. The principle of exchange of stabilities is found to hold true for the ferrofluid with internal angular momentum in the absence of suspended particles, solute gradient, coupling parameter, and microinertia. Oscillatory modes are introduced due to the presence of the suspended particles, solute gradient, coupling parameter, and microinertia, which were nonexistent in their absence. The sufficient conditions for the nonexistence of overstability are also obtained.     

Study air–water system in horizontal loop geometry

To enhance the understanding of hydrodynamic of air–water multi-phase flow inside a toroidal geometry, experiments were carried out in horizontal torus reactor. Compared with vertical flow, the flow in horizontal milli torus reactor was characterized by one additional flow pattern. In vertical position two flow regimes are considered: not-dispersed and dispersed flow while in horizontal position three flow regimes have been distinguished: stratified flow, dispersed flow and mixed flow regimes. The mixing time is measured by a conductimetric method as described by (Benkhelifa et al., 2000). The effect of both superficial gas velocities and impeller rotation speeds has been studied. The mixing time has been decreased by increasing both the superficial gas velocity and the impeller rotation speed and has been shorter than the one given for the horizontal configuration. The axial dispersion inside the reactor was modelled by the Zhang's model. The obtained results are in a good agreement with Zhang's model.