Modeling heat and mass transfer in the gas-phase chemical deposition of polycrystalline ZnSe layers

Heat and mass transfer in the gas-phase deposition of zinc selenide in the zinchydrogen selenide—argon system with separate injection of reagents into a reactor by local jets has been studied. The effects of technological parameters, design, and the geometric dimensions of the reactor on the distribution of the deposition rates of the zinc selenide layers formed have been considered.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1625–1631, July, 1996.     

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.     

Composite materials based on zeolite 4A for adsorption heat pumps

Some additives and binders were chosen for the preparation of 4A-zeolite-based composites with high equivalent thermal conductivity for heat pumps application. Additives (SiC, Si₃N₄, graphite) and binders (PTFE, Al(OH)₃) were tested for their effectiveness in terms of equivalent thermal conductivity and maximum water adsorption capacity of the composites. The influence of the equivalent thermal conductivity of the composite adsorbents on the specific power of the heat pump was also calculated. Results show a significant improvement in the equivalent thermal conductivity of the composite samples which are prepared using aluminum hydroxide as binder, over that of zeolite pellet beds. Such composite materials could be used to build adsorption heat pumps with higher specific power and, consequently, with lower investment cost.     

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。     

Adsorption properties of low-silica zeolite ZK-5

Water vapor, methanol, and argon adsorption isotherms, as well as the heat of adsorption of ammonia, methanol, and carbon dioxide have been determined on zeolite types A, ZK-4, and ZK-5. The results are explained by the distribution and the bond lengths of cations in the zeolite crystal lattice. It was shown that the exchange of 10–15% of the Na⁺ ions with Li⁺ in zeolite ZK-5 leads to a deformation of the 8-membered ring impeding the diffusion of adsorbed molecules. Cations contained in the 8-membered ZK-5 zeolite ring are bound more strongly to the framework, than in zeolite NaA, resulting in their smaller adsorption capacity.I. V. Grebenshchikov Institute of Silicate Chemistry, Russian Academy of Sciences, 199164 St. Petersburg, Russia. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 11, pp. 2494–2500, November, 1992.     

Influences of acid and heat treatments on the structure and water vapor adsorption property of natural zeolite

Natural zeolite was first acid treated and then heat treated. The influences of acid and heat treatments on the structure and water vapor adsorption property of natural zeolite were investigated. X‐ray photoelectron spectroscopy (XPS), X‐ray diffraction (XRD), thermogravimetric analysis (TG), and Brunauer‐Emmett‐Teller (BET) surface areas were employed to investigate the structure changes of the zeolite samples. Water vapor adsorption property of the samples was investigated in order to determine wettability of the samples. The results showed that nitric acid treatment could remove Al from the structure, decrease relative crystallinity, and significantly increase specific surface area of the zeolite samples. Heat treatment could change or even destroy the structure, effectively remove water molecules from the surface/structure, and decrease the specific surface area of the zeolite samples. Water vapor adsorptions on the acid‐treated zeolite samples were significantly lower than that for the zeolite sample, and the adsorptions further reduced for the heat‐treated zeolite samples. The increase of Si/Al ratio, decreases of silanol groups, and specific surface area of the samples were major reasons related to the reductions of water vapor adsorptions on the zeolite samples.     

Electrochemical mass transfer modeling of a complex two phase heat transfer problem: Case of a prototype slagging gasifier

The local and averaged forced-convective heat transfer coefficients were estimated from measured local and averaged mass transfer coefficients in a model slagging-gasifier hearth pool using the Chilton-Colburn analogy. A solution of ferri/ferrocyanide and buffer with addition of CMC (carboxymethylcellulose) was used for the electrochemical mass transfer measurements. This solution had similar properties to those of the slag in the real gasifier. The influence of natural convection due to the differences in temperatures in the hearth was also estimated. Values of heat transfer coefficient similar to those estimated by British Gas for the prototype Westfield gasifier were found using the mass transfer modelling method. Published in Russian in Elektrokhimiya, 2008, Vol. 44, No. 4, pp. 447–458. The text was submitted by the authors in English.     

Evaluation of energy distribution on a heterogeneous surface from heat of adsorption and its application to the ammonia/Na-Y zeolite system

The— function (energy level function) which represents surface heterogeneity was derived from theq— function (experimental heat function) in the case of reversible adsorption. The Langmuir equation was extended and applied to the procedure of calculations. An iterative calculation led to the most probable— function by setting theq— function and adsorption temperature. As an example for actual cases, the— function of Na-Y zeolite was calculated from theq— function obtained by the measurement of heats of adsorption of ammonia at 373 K. The— function thus derived seemed to be consistent with the positional distribution of sodium ions.     

Adsorption of helium on zeolite NaA

Isotherms of helium adsorption on zeolite NaA were measured by the volumetric method under static conditions at 23–50 K and pressures from 1 Pa to 65 kPa. The Henry constants and the initial heat of helium adsorption were calculated; the isosteric heat was calculated, and its dependence on the adsorption was determined.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1291–1292, May, 1996.     

A study of heat and mass transfer of Non-Newtonian fluid with surface chemical reaction

Considering the significance of non-Newtonian fluid usage in manufacturing such as molten plastics, polymeric materials, pulps, and so on, significant efforts have been made to investigate the phenomenon of non-Newtonian fluids. In this article the influences of heat and mass transfer on non-Newtonian Walter's B fluid flow over uppermost catalytic surface of a paraboloid is encountered. An elasticity of the fluid layer is considered in the freestream together with heat source/sink and has the tendency to cause heat flow in the fluid saturated domain. The flow problem of two-dimensional Walter's B fluid is represented using Law of conservation of mass, momentum, heat, and concentration along with thermal and solutal chemical reactive boundary conditions. The governing equations are non-linear partial differential equation and are non-dimensionalized by employing stream function and similarity transformation. The final dimensionless equations yielded are coupled non-linear ordinary differential equations. Furthermore, shooting technique along with RK-4th order method is used to get the numerical results. Graphs and tables are modeled by using MATLAB software to check the effects of Walter's B parameter, Chemical reaction parameter and Thickness parameter on temperature, velocity, and concentration profiles. Tabular analysis shows the results of some physical parameters like skin friction coefficient, Nusselt number and Sherwood number due to the variation of Walter's B parameter, thickness parameter and chemical reactive parameter.     

Validity of energy distribution derived from heat of adsorption in an ammonia/cation-exchanged Y zeolite system

The validity of- functions (energy level functions) which were derived from experimentalq- functions (heat functions) was examined in an ammonia/cation-exchanged Y zeolite system. The- functions of Na-Y zeolite and Cs-Na-Y zeolite were respectively calculated from theirq- functions measured by ammonia adsorption at 373 K. The heat of adsorption of ammonia was also measured on a mixture of these two zeolites at a certain mixing ratio at 373 K. The- function of the mixture was likewise calculated on the basis of this measurement. The- function thus calculated was in good agreement with the synthesized- function derived by linearly combining two- functions of each zeolite mentioned above. The- function derived from experimental- function thus proved to be valid in an actual adsorption system.     

NaX zeolite,carbon fibre and CaCl2 ammonia reactors for heat pumps and refrigerators

The key elements of solid sorption machines are the chemical compressors-adsorbers. Two categories of the solid sorption system are analyzed: adsorbents NaX zeolite, carbon fibre Busofit with NH₃, and complex combinations that undergo chemical reaction and physical adsorption (CaCl₂ + carbon fibre Busofit with NH₃).Two phase ammonia motion inside the adsorbent bed was checked. That accompanied NH₃/CaCl₂ solution redistribution between the cold and hot surfaces of the sorbent bed, resulting in a rich CaCl₂ concentration at the boundaries.Solid sorption heat pump and refrigerator technology utilizing heat pipe heat recovery with a condensing/evaporating refrigerant holds considerable promise for bivariant (space and domestic) applications due to the variable temperature and variable load capabilities of such machines.     

A lubricated stagnation point flow of nanofluid with heat and mass transfer phenomenon: Significance to hydraulic systems

The improved thermal association of heat transfer is considerably observed due to interaction of nanoparticles in recent days. The lubrication phenomenon with heat and mass transfer effects plays a key role in the hydraulic systems. In current research, the thermal impact of nanofluid over a lubricated stretching surfaces near a stagnation point analytical has been studied. A thin layer of lubricating fluid with a variable thickness provides lubrication. The inspection of thermophoresis and Brownian motion phenomenon is illustrated via Boungrino model. The analytical finding of refurbished boundary layer ordinary differential equations is obtained by a reliable and proficient technique namely variational iteration method (VIM). The Lagrange Multiplier is a potent tool in proposed technique to reduce the computational work. In addition, a numerical comparison is presented to show the effectiveness of this study. The range of flow parameters is based on theoretical flow assumptions. Physical inspection of involved parameters on velocities, temperatures, concentrations, and other quantities of interest when lubrication is presented. The current results present applications in polymer process, manufacturing systems, heat transfer and hydraulic systems.     

Effect of heat transfer on the oscillatory behavior in partial oxidation of methane over nickel catalyst

Monte Carlo method was applied to simulate the oscillatory behavior during partial oxidation of methane under non-isothermal condition. The simulation was performed to examine the influences of heat transfer constant and particle size on the kinetic oscillation. The oscillatory period and amplitude were observed to increase with the increase of heat transfer constant. The increase of catalyst particle size was found to result in short oscillatory period and more or less regular oscillations combined with the formation of oxide down to L=100.     

Enhancement of oxygen gas–liquid mass transfer with colloidal gas aphron dispersions

In this work, an attempt was made to enhance gas–liquid mass transfer of oxygen with the aid of colloidal gas aphron (CGA) dispersion. The gas–liquid volume mass transfer coefficients (k_La) of oxygen in CGA dispersions were measured and related to stirring velocity, type and concentration of surfactants, and temperature. Four surfactants, sodium dodecyl sulfate (SDS), hexadecyltrimethyl ammonium chloride (HTAC), nonylphenol ethoxylate (NP-10), and potassium mono lauryl phosphate (MAPK), were examined in forming CGAs and thereby affecting the mass transfer of oxygen in the dispersions. It was found that effects of surfactants on the oxygen gas–liquid mass transfer were type-dependent. As concentrations rose, the k_La of oxygen increased evidently for SDS and an enhancement of k_La by a factor of three was observed at the concentration of 2.75 g/L. However the k_La decreased for MAPK. Nonylphenol ethoxylate was found to have little effect on k_La and HTAC showed mixed behavior. In SDS dispersion, it was found that the mass transfer reached a maximum value at a stirring velocity of 8000 r/min, but further benefit was not observed afterwards. With the increase of temperature, the mass transfer of oxygen was intensified but no much benefit was observed above 308 K.     

固体粒子对板式膜吸收过程的传质强化

分别采用纯CO2-去离子水和不同浓度的NaOH溶液为实验体系,在板式膜器中研究了第三相固体粒子对膜吸收过程传质效果的影响．分别考察了在不同粒子种类、搅拌转速、传质体系、化学反应强度、膜孔隙率等因素下固体粒子对传质强化的影响．结果表明,随着粒子固含率的增大,传质系数和增强因子均有所提高,当粒子固含率增大到一定范围后,传质系数和增强因子的变化趋于平缓．在固含率一定的条件下,不同种类的固体粒子对膜吸收过程的强化效果随着固体粒子密度的增加而减小．传质系数随着搅拌转速的增大而增大,但高搅拌转速下固体粒子的强化作用减弱．膜吸收过程的传质系数和增强因子随着化学反应强度的增强而增加．随着粒子固含率的增大,不同膜孔隙率对传质效果的差异减小,且孔隙率越小,固体粒子对膜吸收传质过程的强化效果越好．其中,对于纯CO2-去离子水体系,当孔隙率为20％,粒子固含率为1．5gL^（-1）时,固体粒子的加入可使传质系数提高1．45倍,增强因子可达2．45．     

CuNaY分子筛的有效吸附位与其脱硫性能的关联性研究

以液相离子交换法制备了一系列不同Cu负载量的CuNaY分子筛;采用XRD及N₂吸附-脱附表征分子筛的微观结构和织构性质,采用动态吸附法考察其对噻吩模拟油的吸附脱硫性能,结合NH₃-TPD和Py-FTIR方法对CuNaY分子筛的酸量和有效Cu⁺物种进行定量分析,研究了CuNaY分子筛的表面酸性和铜物种形态结构对其吸附脱硫性能的影响机制。结果表明,通过改变铜负载量可有效调控改性Y分子筛的表面酸性以及铜物种化学形态;适量铜物种的引入可以最大限度的形成有效吸附位,从而获得最优吸附脱硫性能,而过量的Cu物种会在Y分子筛笼内形成多核铜物种结构,导致有效吸附位点的减少,影响其对噻吩的吸附能力。     

Thermodynamics of CO<Subscript>2</Subscript> adsorption on zeolite NaX in wide intervals of pressures and temperatures

The dependences of the differential molar isosteric heat of adsorption and entropy of adsorption of CO₂ on zeolite NaX were determined in wide temperature (196–423 K) and pressure (0.1 Pa to 5.4 MPa) intervals. In the initial region of adsorption (a < 1 mmol g^–1), the differential molar heat of adsorption increases from 40 to 43 kJ mol^–1 and then decreases to 33 kJ mol^–1. The heat of adsorption remains virtually unchanged at 3 mmol g^–1< a < 6.5 mmol g^–1 and decreases sharply at high fillings of zeolite micropores (a > 7 mmol g^–1). The heat of adsorption was found to be temperature-dependent. The region with the constant heats shrinks with the temperature increase, and the heats begin to decrease at lower fillings of micro pores. The dependences of the change in the differential entropy of the adsorption system on the amount adsorbed were calculated at different temperatures. The specific features of the behavior of the thermodynamic functions of this adsorption system in the initial and medium region of fillings kre associated with interactions of adsorbate molecules with Na⁺ cations and walls of large cavities. For high fillings, an increase in repulsion forces between adsorbed molecules results in a sharp expansion of the adsorbent and a decrease in the heat of adsorption.Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1570–1573, August, 2004.     

A study on the heat transfer geometry in MBDTA

This paper presents the quantitative application of the Metal Blocked Differential Thermal Analysis (MBDTA). Calibrations have been electrically carried out by using three types of calibration heaters (pen, ring and spiral), which are placed inside the sample. By means of this arrangement, thermophysical properties of the samples make the quantitative evaluation of the results easy. The influence of the size and sample diameter, the types of heater, the space between heater and thermocouple, in other words, the factors affecting calibration and the effect of the heat transfer geometry on the determination of the fusion heat have been investigated.

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Zusammenfassung Vorliegende Arbeit stellt eine quantitative Anwendung der Metallblock-DTA (MBDTA) dar. Es wurden elektrisch Kalibrationen mit verschiedenen, innerhalb der Probe befindlichen Kalibrationserhitzern (Stift, Ring, Spirale) durchgeführt. Mit Hilfe dieser Anordnung wird die Auswertung der Ergebnisse durch die thermophysischen Eigenschaften der Probe erleichtert. Es wurde der Einfluß von Größe und Probendurchmesser, von Erhitzertyp, von Abstand zwischen Erhitzer und Thermoelement, mit anderen Worten von denjenigen Faktoren, die die Kalibration beeinflussen sowie der Einfluß der Wärmetransportgeometrie auf die Bestimmung der Schmelzwärme untersucht.