Special features of propagation of hydrogen in a building

A three-dimensional mathematical model for calculating heat and mass transfer in propagation of hydrogen in a building that allows for gas exchange with the environment through an opening has been proposed. Based on numerical calculations performed by the proposed model, the author revealed certain features of the concentration fields of hydrogen in the case of its inflow at the floor level. It is shown that the dimensions and location of the explosion- and fire-hazardous zones change considerably during the process. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 73, No. 4, pp. 739–743, July–August, 2000.     

Experimental Analysis and Simultaneous Heat and Moisture Transfer with Coupled CFD Model for Convective Drying of Moist Object

Convective drying of rectangular-shaped moist object has been analyzed both experimentally and numerically. Transient mass of the potato sample is measured experimentally. Moisture content, diffusivity, and density of the object are calculated at different drying air temperatures from 40°C to 70°C with an air velocity of 2 m/s. A three-dimensional (3D) finite volume method (FVM) based numerical model is developed to predict the temperature and moisture distribution. A computational fluid dynamics (CFD) code is used for predicting heat and mass transfer coefficients required in the boundary conditions of the heat and mass transfer model. The experimental and numerical data are compared and good agreement is observed.     

Heat transfer coefficient measurements for mixed gas working fluids at cryogenic temperatures

The use of mixed gas working fluids has become common in Joule-Thomson type cryocoolers for a variety of applications. However, there is very little data or theory currently available regarding the heat transfer coefficient associated with these multi-component, multi-phase mixtures at cryogenic temperatures. This paper describes an experimental test facility and procedure that has been used to make careful measurements of the horizontal, flow boiling heat transfer coefficient for several hydrocarbon mixtures that are nominally optimal for small, Joule-Thomson cryocoolers in the 80 K to 120 K operating range. Data are presented over a range of temperatures from 100 K to room temperature and for several pressures and mass flow rates. The results indicate that quality and mass flux are the most important parameters governing the heat transfer coefficient among those that were varied. The experiment is verified by carrying out tests using single-phase, pure nitrogen gas and comparing the results with the Dittus-Boelter equation. The experimental uncertainty of the measurements is estimated from 1st principles; additionally, the repeatability of the experimental measurements was investigated by replicating tests at a nominal set of operating conditions and composition on separate days. The measurements presented here are intended to aid in the design of small, mixed-gas Joule-Thomson cryocoolers.     

Calculation of a Three-Dimensional Temperature Field with Allowance for the Radiation Heat Exchange in Chambers of Tubular Ovens with Acoustic Burners

A three-dimensional calculation of the heat transfer in the chamber of a technological tubular oven with the combustion of methane in air with acoustical burners of a floor flame has been carried out. The calculation method is based on the joint numerical solution of the difference analogs of the three-dimensional equations of radiation, energy transfer, and turbulent motion of flue gases and the model of methane combustion in air. The entire spectral region is divided into six bands to account for radiation selectivity. The organization scheme of three-dimensional modeling of the burner operation is shown. Some results of numerical studies of heat and mass transfer in a combustion chamber are given.     

Investigation of the performance of an optimised MicroCAT, a GEM and their combination by simulations and current measurements

A Micro compteur à Trous (MicroCAT) structure which is used for avalanche charge multiplication in gas filled radiation detectors has been optimised with respect to maximum electron transparency and minimum ion feedback. We report on the charge transfer behaviour and the achievable gas gain of this device. A three-dimensional electron and ion transfer simulation is compared to results derived from electric current measurements. Similarly, we present studies of the charge transfer behaviour of a Gas Electron Multiplier (GEM) by current measurements and simulations. Finally, we investigate the combination of the MicroCAT and the GEM by measurements with respect to the performance at different voltage settings, gas mixtures and gas pressures.     

Numerical Modeling of Heat and Mass Transfer in a Low-Temperature Heat Pipe

A mathematical model of heat and mass transfer in a low-temperature heat pipe has been formulated. Numerical modeling of the problem of heat and mass transfer has been carried out. The distributions of the velocities, the pressure, and the temperatures in the heat pipe have been obtained. The results can be employed in analyzing the efficiency and power of low-temperature heat pipes.     

Gateable nanofluidic interconnects for multilayered microfluidic separation systems

The extension of microfluidic devices to include three-dimensional fluidic networks allows complex fluidic and chemical manipulations but requires innovative methods to interface fluidic layers. Externally controllable interconnects, employing nuclear track-etched polycarbonate membranes containing nanometer-diameter capillaries, are described that produce hybrid three-dimensional fluidic architectures. Controllable nanofluidic transfer is achieved by controlling applied bias, polarity, and density of the immobile nanopore surface charge and the impedance of the nanocapillary array relative to the microfluidic channels. Analyte transport between vertically separated microchannels has three stable transfer levels, corresponding to zero, reverse, and forward bias. The transfer can even depend on the properties of the analyte being transferred such as the molecular size, illustrating the flexible character of the analyte transfer. In a specific analysis implementation, nanochannel array gating is applied to capillary electrophoresis separations, allowing selected separated components to be isolated for further manipulation, thereby opening the way for preparative separations at attomole analyte mass levels.     

CFD方法与间接蒸发冷却换热器的三维数值模拟

本文采用计算流体力学(CFD)和数值传热学方法,对间接蒸发冷却器内流体流动与热质交换过程进行简化和假设,建立了换热器内三维层流流动与传热的数学物理模型.采用交错网格离散化非线性控制方程组,编制了三维simple算法程序.对间接蒸发冷却器内的流场、温度场及浓度场进行数值模拟研究,得到换热器内的流体流动状态和热流分布,并分析了通道宽度变化对换热器内流体流动与换热的影响.     

Laser Time-of-Flight Mass Spectrometry of PAH-Picrate Complexes

The laser desorption/laser ionization time-of-flight (L2ToF), mass spectra of anthracene and the anthracene-picric acid charge transfer (C-T) complex have been compared at a desorption and ionization wavelength of 266 nm. Laser desorption/ionization spectra of anthracene were obtained at low temperatures (-30 °C) to minimize the interference from gas phase ionization. Positive ion mass spectra of the picrate C-T complex at room temperature comprise the parent ion of anthracene and were devoid of signals associated with the picric acid component. The L2ToF analyses of a mixture of volatile and involatile EPA priority PAHs in picric acid show that low molecular weight PAHs form involatile charge transfer complexes. The present method reduces the possibility of volatile PAH loss during mass spectrometric analyses in vacuo.     

Wave motion of porous particles in a pulsating gas flow in the presence of heat and mass transfer with deepening of the evaporation zone

Based on numerical solution of the dynamics equations of a monodisperse gas suspension with allowance for the interphase forces of aerodynamic drag, virtual masses, and the forces caused by nonstationary effects around particles, the influence of different forms of low-frequency harmonic and anharmonic oscillations of the gas on the motion of porous particles in the presence of heat and mass transfer accompanied by deepening of the evaporation zone has been investigated. The dependences of the solid-phase motion, kinetics of evaporation-zone deepening, and heat and mass transfer on the parameters of gas oscillations have been established. It is shown that on removal of free moisture, oscillations at certain parameters lead to enhancement of interphase heat and mass transfer. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 70, No. 5, pp. 11–19, September–October 2006.     

Some features of the heat and mass transfer in a fire within an atrium

A field method of calculating the heat and mass transfer in a fire within an atrium is proposed. Results of numerical simulation of the three-dimensional temperature, velocity, smoke optical-density, and visibility fields in the gas medium in a fire within an atrium with the use of the mathematical model developed are presented. It is shown that the mechanisms of heat and mass transfer determined by the method proposed substantially change the modern views on the dynamics of the dangerous factors of a fire within an atrium and that the pattern of thermodynamics of the gas in a fire obtained with the indicated model cannot be obtained with integral and zonal models. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 79, No. 5, pp. 135–146, September–October, 2006.     

Eulerian–Lagrangian method for three-dimensional simulation of fluidized bed coal gasification

A comprehensive three-dimensional numerical model has been developed to simulate the coal gasification in a fluidized bed gasifier. The methodology is based on the multiphase particle-in-cell (MP-PIC) model, which uses an Eulerian method for fluid phase and a discrete particle method for particle phase. Dense particulate flow, mass and heat transfer, homogeneous and heterogeneous chemistry between phases and within the fluid mixture are considered. The dynamics of the particle phase is calculated by solving a transport equation for the particle distribution function (PDF) f. Particle collisions and chemical reactions are solved on a grid cell with particle properties mapped from discrete particles to the grid. Solid mass consumed or produced in reactions changes the size of particles. Simulations were carried out in a coal gasifier with a height of 2.0 m and a diameter of 0.22 m at atmosphere. The calculated product gas compositions compare well with the experimental data. The formation of flow patterns, profiles of particle species and gas compositions, distributions of reaction rates and consumption of carbon mass were investigated under different operating conditions.     

A computational fluid dynamic model of the heat and moisture transfer during beef chilling

The unsteady heat and mass transfer process during beef carcass chilling was modelled for a three-dimensional beef carcass geometry. A three-step method was used to simulate the simultaneous heat and mass transfer process in order to reduce the computational time. In the first step, a steady state simulation of the flow field was conducted. In the second step, the local heat and mass transfer coefficients were calculated. Finally, the third step consists of the simultaneous heat and mass transfer process simulation on the meat carcass only. A separate 1-D grid was used to calculate the moisture diffusion in the meat. The simulation of a 20-h chilling run takes 5 days on a 2.5 GHz Pentium 4 computer. The model allows calculating and predicting the heat load, temperatures, weight loss and water activity. Local variations in the heat and mass transfer coefficients, temperature and water activity were found around the beef carcass. The CFD model gives temperature predictions that agree with experimental data better than any previous model. The weight loss tends to be over-predicted probably due to neglecting the resistance caused by the fat cover.     

Modelling of reinforced polymer composites subject to thermo‐mechanical loading

A coupled finite element model is developed to analyse the thermo‐mechanical behaviour of a widely used polymer composite panel subject to high temperatures at service conditions. Thermo‐chemical and thermo‐mechanical models of previous researchers have been extended to study the thermo‐chemical decomposition, internal heat and mass transfer, deformation and the stress state of the material. The phenomena of heat and mass transfer and thermo‐mechanical deformation are simulated using three sets of governing equations, i.e. energy, gas mass diffusion and deformation equations. These equations are then assembled into a coupled matrix equation using the Bubnov–Galerkin finite element formulation and then solved simultaneously at each time interval. An experimentally tested 1.09 cm thick glass‐fibre woven‐roving/polyester resin composite panel is analysed using the numerical model. Results are presented in the form of temperature, pore pressure, deformation, strain and stress profiles and discussed. The maximum normal stress failure criterion is used in order to establish the load‐bearing capability of the composite panel. Significant pore gas pressure build‐ups (to 0.8 MPa and higher) have been perceived at high thermo‐chemical decomposition rates where the material experiences a complex expansion/contraction phenomenon. It is found that the composite panel experiences structural instability at elevated temperatures up to 300°C but retains its integrity even under moderate external loading. Copyright © 2005 John Wiley & Sons, Ltd.     

Unsteady laminar incompressible second-order boundary-layer flow at a three-dimensional stagnation point

Summary The unsteadely laminar incompressible second-order boundary-layer flow at the stagnation point of a three-dimensional body has been studied for both nodal and saddle point regions. The effects of mass transfer and Prandtl number have been taken into account. The equations governing the flow have been solved numerically using an implicit finite-difference scheme. It has been found that the parameter characterizing the unsteadiness in the velocity of the free stream, the nature of the stagnation point, the mass transfer and Prandtl number strongly affect the second-order skin friction and heat transfer. The overall skin friction becomes less due to second-order effects but the heat transfer has the opposite behaviour. For large injection, the second-order skin-friction and heat-transfer results prevail over the first-order boundary layer results whereas for the case of large suction the behaviour is just the opposite.With 14 Figures     

Application of the hybrid zone/Monte Carlo method to 3-D curvilinear grids in radiative heat transfer

The zone method is applied to non-orthogonal curvilinear grids for the computation of radiative heat transfer. The interchange areas are calculated by the Monte Carlo technique which has been fitted with a generalized ray tracing procedure. The method is applied to two complex three-dimensional (3-D) cases where in homogeneities are present in the radiation space (non-uniform gas properties and/or shadowing effects), and the gas is taken as gray. For comparison purposes, the same examples are worked out with the discrete transfer method. Very small discrepancies are found between the two methods for the surface heat fluxes, but the gas volumetric radiative sources are much more sensitive to inhomogeneities in the gas phase, resulting in higher discrepancies for these terms. The method can be readily extended to incorporate real gases and scattering effects.     

Calculation of the effect of vibration on a region filled with a perfect viscous gas

The processes of heat and mass transfer in a region subjected to the vibration effect have been studied numerically. The effect of the vibration frequency on the behavior of the characteristics of gas located inside the region has been described. The one-dimensional problem has been solved.     

Features of the Heat and Mass Transfer in a Fire Within a Building of Complex Geometry

A method of calculating the heat and mass transfer in a fire within a building of complex geometry is proposed. The results of calculation of the three-dimensional temperature, velocity, and visible-range fields in the gas medium of a fire simulated in the atrium, corridors, and floors of a building with the use of the mathematical model developed are presented. The method proposed allowed us to reveal regularities of the heat and mass transfer in a fire within the building considered that substantially differ from the existing views of the dynamics of the hazardous factors of a fire in such buildings. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 78, No. 3, pp. 22–29, May–June, 2005.     

Impact of nonuniform heated plate on double-diffusive natural convection of micropolar fluid in a square cavity with Soret and Dufour effects

A numerical work has been carried out to study the effect of heated plate on double diffusive natural convection in a cavity with the presence of Soret and Dufour effects. The vertical left and right sidewalls of the cavity are maintained at constant cold temperatures while the lower and upper walls are considered insulated. The influence of pertinent parameters such as Rayleigh number, Schmidt number, vortex viscosity parameter, Soret and Dufour coefficients and plate non-uniformity parameter on the flow and heat transfer characteristics has been examined. Numerical results show that the heat and mass transfer rate increases with the rise of the Rayleigh number and Schmidt number. It is found that the heat and mass transfer rate are considerably suppressed by the vortex viscosity parameter. In addition, it is observed that the average Nusselt number increases and Sherwood number decreases with increasing Soret and Dufour effects.     

Concentration distribution of the exhaust gas near a roadway with a stochastic traffic flow

The mechanical process of transfer and dispersion of the exhaust gas near a motor road has been studied based on the hypothesis of a stochastic traffic flow on the considered roadway section, which is described by a Poisson process with a constant intensity. Using the three-dimensional diffusion equation, solutions have been obtained for problems on the concentration distribution of pollutants near an extended roadway and a road crossing. Basic stochastic characteristics of the concentration distribution of the exhaust gas from a stochastic traffic flow have been determined. Calculated results have been compared with experimental data. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 79, No. 6, pp. 128–140, November–December, 2006.