射流流化床煤气化炉中气固流动和传热、传质的CFD模拟研究

通过双流体模型对射流流化床煤气化炉进行了CFD（Computational Fluid Dynamics,计算流体力学）模拟。模拟着重分析了流化床气化炉气固流动的特性和传质、传热过程。结果表明,流化床中气固两相的传热、传质过程与气体和颗粒的运动特性密切相关。     

Dissolution of polycyclic aromatic hydrocarbons from a non-aqueous phase liquid into a surfactant solution using a rotating disk apparatus

The mass transfer of two polycyclic aromatic hydrocarbons (PAHs), naphthalene and phenanthrene from a multicomponent non-aqueous phase liquid (NAPL) into a nonionic surfactant solution, Brij 35 was investigated using a rotating apparatus. Few experimental methods have been applied to the study of solubilization kinetics in organic liquids because in those systems, the interfacial area during mixing is more difficult to maintain and measure. This challenge was overcome by permeating the NAPL through a membrane. Mass transfer experiments were conducted in the absence and presence of surfactant, and the concentrations of naphthalene and phenanthrene in the bulk aqueous phase were determined in samples collected at different time intervals from the time of initial contact of the NAPL phase with the aqueous solution phase. Experiments in pure water demonstrated that the rotating apparatus behaves as in much the same way as the Levich's rotating disk. The mass transfer coefficients and the dissolution of PAHs into the surfactant solution were measured at different doses of Brij 35. As the surfactant concentration increased, the mass transfer coefficients for both PAHs from the NAPL decreased.     

Particle dynamics and particle heat and mass transfer in thermal plasmas. Part II. Particle heat and mass transfer in thermal plasmas

This paper is concerned with a review of heat and mass transfer between thermal plasmas and particulate matter. In this situation various effects which are not present in ordinary heat and mass transfer have to be considered, including unsteady conditions, modified convective heat transfer due to strongly varying plasma properties, radiation, internal conduction, particle shape, vaporization and evaporation, noncontinuum conditions, and particle charging. The results indicate that (i) convective heat transfer coefficients have to be modified due to strongly varying plasma properties; (ii) vaporization, defined as a mass transfer process corresponding to particle surface temperatures below the boiling point, describes a different particle heating history than that of the evaporation process which, however, is not a critical control mechanism for interphase mass transfer of particles injected into thermal plasmas; (iii) particle heat transfer under noncontinuum conditions is governed by individual contributions from the species in the plasma (electrons, ions, neutral species) and by particle charging effects.     

Distribution of local heat transfer coefficient values in the wall region of an agitated vessel

Experimentally found local heat transfer coefficients are analyzed as a function of the measuring point on the heat transfer surface area of the agitated vessel wall and of the impeller eccentricity. Eccentric Rushton turbine and A 315 impeller are considered. Local heat transfer coefficients were measured by means of the computer-aided electrochemical method. The measurements were performed in an agitated vessel with inner diameter 0.3 m, filled with liquid up to the height equal to the vessel diameter. The experiments were carried out within the turbulent regime of the Newtonian liquid flow in the agitated vessel. The results were compared with the data obtained for the agitated vessel equipped with an eccentrically located axial flow propeller or an HE 3 impeller. Experimental studies show that the distributions of the heat transfer coefficient values depend on the impeller eccentricity, impeller type and the direction of the liquid circulation in the agitated vessel. Presented at the 34th International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 21–25 May 2007.     

Heat transfer coefficient and pressure drop during refrigerant R-134a condensation in a plate heat exchanger

The condensation heat transfer coefficient and the two-phase pressure drop of refrigerant R-134a in a vertical plate heat exchanger were investigated experimentally. The area of the plate was divided into several segments along the vertical axis. For each of the segments, local values of the heat transfer coefficient and frictional pressure drop were calculated and presented as a function of the mean vapor quality in the segment. Owing to the thermocouples installed along the plate surface, it was possible to determine the temperature distribution and vapor quality profile inside the plate. The influences of the mass flux and the heat flux on the heat transfer coefficient and the pressure drop were also taken into account and a comparison with previously published experimental data and literature correlations was carried out. Presented at the 34th International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 21–25 May 2007.     

Modeling Biomass Gasification Using Thermodynamic Equilibrium Approach

In this paper, the thermodynamic equilibrium models for biomass gasification applicable to various gasifier types have been developed, with and without considering char. The equilibrium models were then modified closely matching the CH₄ only or both CH₄ and CO compositions from experimental data. It is shown that the modified model presented here based on thermodynamic equilibrium and taking into account local heat and mass considerations can be used to simulate the performance of a downdraft gasifier. The model can also be used to estimate the equilibrium composition of the syngas. Depending on the gasifier type and internal fluid flow, heat and mass transfer characteristics, with proper modification of the equilibrium model, a simple tool to simulate the operation and performance of varying types of biomass gasifier can be developed.     

Mass transfer performance for hollow fibre modules with shell-side axial feed flow: using an engineering approach to develop a framework

For several membrane separation processes, hollow fibre modules are either an already established or a promising type of module. Based on the analogy between mass and heat transfer, an engineering approach is proposed to estimate the shell-side mass transfer coefficient for axial flow in hollow fibre modules with due allowance for the void fraction. The approach enables one to take the entrance effects of the hydrodynamic and concentration profile into account. The trends obtained by this generalised approach are similar to those of empirical correlations found in the literature over a wide range of Reynolds numbers and module packing densities. The empirical correlations differ significantly one from the other. The differences between the mass transfer coefficients obtained by the empirical correlations compared to those obtained following the approach proposed in this study are discussed. The different effects influencing mass transfer in hollow fibre modules are identified and discussed as a function of void fraction. Further, an approach to reflect the influence of maldistribution on mass transfer performance is provided.     

T形微通道中气泡分散流的传质性能

在T形微通道中,以错流剪切的分散方式实现了微米级分散气泡的制备,并以NaOH水溶液吸收CO2为对象,考察了气．液微分散体系的分散规律和传质性能．通过考察两相流速对气泡分散尺寸的影响,建立了预测气泡形成尺寸的数学模型．根据气泡的初始分散尺寸、流动阶段的体积变化以及传质完成后的尺寸,首次测定和区分了气泡形成阶段和运动阶段的传质量,建立了原位测定气泡分散流传质系数札的方法,并考察了两相流量对札的影响．结果表明,由于微通道中气泡的形成时间很短,形成阶段的传质量在总传质量中所占的比例很低．气泡分散流的传质系数主要受液相流量的影响,气相流量的影响基本可以忽略．基于实验结果,建立了计算传质系数鼠的无因次准数关联,计算结果与实验结果符合良好．     

Resistances for heat and mass transfer through a liquid-vapor interface in a binary mixture

In this paper we calculate the interfacial resistances to heat and mass transfer through a liquid-vapor interface in a binary mixture. We use two methods, the direct calculation from the actual nonequilibrium solution and integral relations, derived earlier. We verify, that integral relations, being a relatively faster and cheaper method, indeed gives the same results as the direct processing of a nonequilibrium solution. Furthermore we compare the absolute values of the interfacial resistances with the ones obtained from kinetic theory. Matching the diagonal resistances for the binary mixture we find that kinetic theory underestimates the cross coefficients. The heat of transfer is, as a consequence, correspondingly larger.     

Shell-side mass transfer of hollow fibre modules in osmotic distillation process

The effect of packing density of hollow fibre modules on mass transfer in the shell side of osmotic distillation process was studied. The osmotic distillation experiments were carried out with several modules of the packing densities ranging from 30.6 to 61.2%. It was found that the Reynolds number was a function of packing density and packing density affected mass transfer performance. The shell-side mass transfer coefficient increased with the brine velocity. The membrane permeability can be predicted from the experimental flux at the maximum brine velocity. The mass transfer correlation was proposed in order to determine the shell-side mass transfer coefficient in the randomly packed modules for osmotic distillation process. The empirical correlation proposed was fitted to the experimental results and it was found that the mass transfer coefficients calculated from the proposed correlation were in good agreement with those from the experimental data. Comparison of the results obtained from the proposed correlation with other correlations in the literature was discussed.     

Self-diffusion,mass transfer,and viscosity coefficients for a binary mixture in narrow slit-like pores

The concentration dependences of the dynamic characteristics of a binary mixture in narrow slit-shaped pores of different widths are considered. The local and mean partial self-diffusion, label transfer, mass transfer (mutual diffusion), and shear viscosity coefficients for binary mixtures of various compositions were calculated. The calculation was based on the lattice-gas model in the quasichemical approximation for spherical components with approximately the same size. The calculation of dynamic characteristics took into account collisions between the molecules that determine the direction of their motion. All the kinetic coefficients depend substantially on the mixture density, the direction of motion, and the distance to the pore wall. The effect of the pore width on the calculated dynamic characteristics is considered. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1726—1735, August, 2005.     

Determination of the mass transfer coefficients in direct immersion solid‐phase microextraction

Diffusion of the analytes across the diffusion boundary layers and subsequently through the fiber coatings determines the extraction kinetics of solid‐phase microextraction in aqueous matrices. Besides, the matrix effects can distort the behaviors of the analytes transferring across the diffusion boundary layers. However, these processes were always studied via certain simplification, which often left the mass transfer through the fiber coatings unconsidered and the matrix effects partially investigated. Herein, a comprehensive study on the mass transfer processes in direct immersion solid‐phase microextraction was presented. Under different agitation speeds, it was determined that the mass transfer coefficients across the diffusion boundary layers were three to six orders larger than those through the fiber coatings. However, the mass transfer across the diffusion boundary layers was generally the major rate‐limiting step. In addition, the shuttle effect and the barrier effect, which were responsible for accelerating and retarding the extraction kinetics, respectively, were found to be the dominant matrix effect alternately under different agitation speeds. This study comprehensively illustrated the major rate‐limiting step and the dominant matrix effects through recording the mass transfer coefficients.     

Influence of operating conditions and vessel size on oxygen transfer during cellulase production

The production of low-cost cellulase enzyme is a key step in the development of an enzymatic-based process for conversion of lignocellulosic biomass to ethanol. Although abundant information is available on cellulase production, little of this work has examined oxygen transfer. We investigated oxygen transfer during the growth of Trichoderma reesei, a cellulase-producing microorganism, on soluble and insoluble substrates in vessel sizes from 7 to 9000 L. Oxygen uptake rates and volumetric mass transfer coefficients (k _La) were determined using mass spectroscopy to measure off gas composition. Experimentally measured k _La values were found to compare favorably with a k _La correlation available in the literature for a non-Newtonian fermentation broth during the period of heavy cell growth.     

H2和CO在间二甲苯中的溶解度和体积传质系数的研究

使用ＩＬ搅拌釜，在温度８０～１６０℃，压力０．５～５．０ＭＰａ范围内，实测了Ｈ２和ＣＯ在间二甲苯中的溶解度和体积传质系数。结果表明，两者均随温度和压力的升高而增大。实验结果与工于正规溶液理论Ｐｒａｕｓｎｉｔｚ－Ｓｈａｉｒ法计算的气体溶解度比较相符。在相同温度、压力条件下，ＣＯ的溶解度和体积传质系数比Ｈ２大。相同温度、压力下不同液相介质中Ｈ２和ＣＯ的体积传质系数排序如下：（ｋＬａ）ＭＥＦ〉（ｋＬａ）     

Mass transfer examination in electrodialysis using limiting current measurements

The impact of electrodialysis module characteristics on mass transfer was examined using the limiting current method. The current-voltage curves of different electrodialysis modules were measured and limiting currents were determined using the derivative method. The mass transfer coefficients were calculated and the parameters of their dependence on linear flow velocity were estimated. From these the impact of spacer thickness, spacer net type, membrane type, and module geometry were evaluated. It was found that the impact of spacer thickness was almost negligible within the examined range, but a decrease in the mass transfer coefficient could be expected in the case of thicker spacers. By contrast, the spacer net type and type of membrane were found to be very important parameters able to significantly influence the mass transfer. By modifying the module geometry, the mass transfer coefficient could also be altered and, only in this case, the exponential parameter of the dependence was changing. The parameters thus determined may be used to calculate the limiting current in a wide range of operational conditions and may help predict the performance of different electrodialysis module types.     

Evaluation method for heat transfer coefficient of a contact interface across a microscale thin liquid polymer film

The research presented here evaluates the heat transfer coefficient of the contact interface of a thin liquid polymer film between a pair of columnar aluminum bodies with an initial temperature difference of approximately 160 K. We measured the unsteady temperature changes inside the columns. The heat transfer test was performed with three types of liquid polymers: squalane, oleic acid, and silicone oil. The heat transfer coefficient of the polymer films as a fitting parameter was obtained by ensuring the numerically computed time evolution of the columns’ temperature corresponded with the experimentally measured data. The interfacial heat transfer coefficients of the thin polymer films (mean thickness: 60 μm) for all three polymers used were 1.75 kW/m²·K, 2.75 kW/m²·K, and 4.10 kW/m²·K. The present estimating method for determining interfacial heat transfer coefficients was suitable for a material-polymer film-material contact model. The time evolution of the temperature at the contact surfaces was also effectively evaluated using the numerical simulation.     

A protocol for the measurement of all the parameters of the mass transfer kinetics in columns used in liquid chromatography

Band broadening in chromatography results from the combination of the dispersive effects that are associated with the different steps involved in the migration of compound bands along the column. These steps include longitudinal diffusion, trans-particle mass transfer, external film mass transfer, overall eddy diffusion, including trans-column, short-range inter-channel, trans-channel eddy diffusion, and the possible, additional mass transfer contributions arising from heat friction and the thermal heterogeneity of the column. We describe a series of experiments that provide the data needed to determine the coefficients of the contributions to band broadening of each one of these individual mass transfer steps. This specifically designed protocol can provide key information regarding the kinetic performance of columns used in liquid chromatography and explain why different columns behave so differently. The limitations, accuracy and precision of these methods are discussed. Further avenues of research that could improve the characterization of the mass transfer mechanisms in chromatographic columns, possibly contributing to the development of better columns, are suggested.     

Retention and mass transfer characteristics in reversed-phase liquid chromatography using a tetrahydrofuran-water solution as the mobile phase.

The characteristics of the retention and the mass transfer kinetics in reversed-phase liquid chromatography (RPLC) were measured on a system consisting of a C18-silica gel and a tetrahydrofuran-water (50:50, v/v) solution. These parameters were derived from the first and the second moments of the elution peaks, respectively. Further information on the thermodynamic properties of this system was derived from the temperature dependence of these moments. Some correlations previously established were confirmed for this system, namely, an enthalpy-entropy compensation for both retention and surface diffusion and a linear free-energy relationship. These results are compared with those observed in other similar systems using methanol-water (70:30, v/v) and acetonitnile-water (70:30, v/v) solutions. The contribution of surface diffusion to intraparticle diffusion in C18-silica gel particles was shown to be important. The analysis of the thermodynamic properties of surface diffusion suggests that, in these three RPLC systems, its activation energy is lower than the isosteric heat of adsorption. The nature and the extent of the influence of the mobile phase composition on the parameters describing the retention and the mass transfer kinetics are different but the chromatographic mechanisms involved in RPLC systems appear similar, irrespective of the nature of the organic modifier in the mobile phase.     

Verification of Onsager's reciprocal relations for evaporation and condensation using non-equilibrium molecular dynamics

Non-equilibrium molecular dynamic (NEMD) simulations have been used to study heat and mass transfer across a vapor-liquid interface for a one-component system using a Lennard-Jones spline potential. It was confirmed that the relation between the surface tension and the surface temperature in the non-equilibrium system was the same as in equilibrium (local equilibrium). Interfacial transfer coefficients were evaluated for the surface, which expressed the heat and mass fluxes in temperature and chemical potential differences across the interfacial region (film). In this analysis it was assumed that the Onsager reciprocal relations were valid. In this paper we extend the number of simulations such that we can calculate all four interface film transfer coefficients along the whole liquid-vapor coexistence curve. We do this analysis both for the case where we use the measurable heat flux on the vapor side and for the case where we use the measurable heat flux on the liquid side. The most important result we found is that the coupling coefficients within the accuracy of the calculation are equal. This is the first verification of the validity of the Onsager relations for transport through a surface using molecular dynamics. The interfacial film transfer coefficients are found to be a function of the surface temperature alone. New expressions are given for the kinetic theory values of these coefficients which only depend on the surface temperature. The NEMD values were found to be in good agreement with these expressions.