BUOYANCY EFFECTS ON THE FORCED CONVECTION ALONG VERTICALLY MOVING SURFACES

The buoyancy effects on the laminar boundary layer heat transfer from vertically moving flat plate and cylinder are studied by a coordinate perturbation method for the cases of prescribed surface temperature and prescribed wall heat flux. Universal expressions are given to show the temperature distributions and the increase of heat transfer rate with the increase of the buoyancy force parameter.     

EFFECTS OF FEED TEMPERATURE AND COMPOSITION ON OSCILLATIONS DURING HYDROGEN OXIDATION ON NICKEL POWDER COVERED NICKEL FOILS

Previous workers have reported self sustained rate fluctuations during hydrogen oxidation on nickel. All of the previous data was taken with catalysts with complicated surface structures, and complicated oscillations were seen. Here, measurements similar to those of the previous investigators were made using catalysts with much simpler surface structures. The system was found to oscillate between a high temperature mass transfer controlled state and a low temperature kinetically controlled state. The form of the oscillations was simple and reproducible, and there were consistent trends which could be compared to theory. No modeling of the oscillations is reported here, although modeling is strongly suggested.     

石灰石对煤炭燃烧特性影响的研究

利用NETZSCH 409C型差示扫描量热仪研究了石灰石对煤炭燃烧特性的影响．结果表明，在加入石灰石后，燃烧明显分成两个阶段，且随着石灰石混合比例的增加，前期的燃烧强度逐渐减弱，后期的燃烧强度增强．石灰石的添加量在30％(以混合样的质量百分比计)左右时，试样的着火温度比原煤降低约30℃，但随着石灰石的添加量的继续增加，试样的着火温度也随着升高．石灰石的加入使得试样的燃尽效果变差，燃尽时间延长．     

STUDIES ON HOMOGENEOUS CATALYSIS IN OXIDATION

For studying the homogeneous catalysis in oxidation our approach starts with the determination of the reaction sequence network of the non-catalytic oxidation using the KIM. The next step is the study of the effect of the catalyst complex and the transformation of the catalyst in the subsystems. The rate parameters collected (referring to the reactions of the catalyst complex with stable and short lived intermediates) can be used to simulate the subsystems and the overall catalytic system.     

高岭石对煤炭燃烧特性影响的研究

利用NETZSCH 409C型差示扫描量热仪对常见黏土类矿物高岭石对煤炭燃烧特性的影响进行了分析．结果表明，随着高岭石添加量的增加，煤样的失重曲线TG燃烧段变得逐渐平缓，失重速率曲线DTG的峰值点降低，燃烧失重速率降低；煤样的着火点逐渐升高，当高岭石的添加量在50％～60％之间时，着火温度约升高9℃～13℃，燃烧稳定性也降低；随着高岭石的添加量的增加，煤样总的折算灰分增大，差热扫描曲线DSC的放热峰宽变窄，放热量减少．     

A GENERALIZED DIFFERENTIAL TRANSFORM METHOD FOR COMBINED FREE AND FORCED CONVECTION FLOW ABOUT INCLINED SURFACES IN POROUS MEDIA

In this article, we apply the differential transform method (DTM) to obtain approximate analytical solutions of combined free and forced (mixed) convection about inclined surfaces (or wedges) in a saturated porous medium. Both aiding and opposing flows are considered. It is found that the parameter mixed convection from inclined surfaces in porous media is Gr/Re, where Gr is the local Grashof number and Re is the local Reynolds number. DTM solutions are obtained for mixed convection from an isothermal vertical flat plate as well as an inclined plate with constant heat flux having an inclination of 45°. Temperature and velocity profiles for these two cases at different values of Gr/Re are presented. The similarity transformations are applied to reduce the governing partial differential equations (PDEs) to a set of nonlinear coupled ordinary differential equations (ODEs) in dimensionless form. DTM is used to solve the nonlinear differential equations governing the problem in the form of series with easily computable terms. Thereafter a Padé approximant is applied to the solutions to increase the convergence of the given series. Excellent correlation between DTM-Padé and numerical quadrature (shooting) solutions is achieved. The DTM-Padé simulation is shown to be a robust benchmarking tool providing an excellent means of validation of numerical methods. The study has applications in geothermal energy systems, chemical engineering filtration systems, and packed beds.     

粗糙表面上的移动接触线和动态接触角

提出一个粗糙表面上移动接触线和动态接触角的数理模型：毛细数较低时表观接触线前缘存在极薄的前驱膜,表观接触线在“湿”固体表面上移动,不同于传统模型中认为表观接触线在“干”固体表面上移动.在Moffatt角区内部流动解的基础上,通过引入接触线特征参数表征表观接触线在前驱膜上的滑移程度,导出动态接触角的速度关系.与不同研究者实验数据对比发现量纲1特征参数反映固体材料特性和表面特性对动态湿润过程的影响,与液相的性质无关.结合前期提出的滞后张力模型,对动态法和静态法测量静接触角产生的差异给出合理解释.     

THERMAL-DIFFUSION AND DIFFUSION-THERMO EFFECTS ON NATURAL CONVECTION ALONG AN INCLINED STRETCHING SURFACE IN A POROUS MEDIUM WITH CHEMICAL REACTION

The steady natural convection along an inclined stretching surface in the presence of chemical reaction under thermal-diffusion and diffusion-thermo effects is studied. The governing equations for continuity, momentum, energy, and concentration are transformed by similarity transformation and then solved numerically using the Runge-Kutta integration with shooting scheme. Comparisons between the present data with previously published work are performed and found to be in very good agreement with each other. The obtained results show that the flow, thermal, and diffusion fields are influenced appreciably by the effects of endothermic or exothermic chemical reaction, angle of inclination, thermal radiation, magnetic field, and Soret and Dufour numbers. The physical phenomenon can be realized from the graphical profiles and in tabular form to depict special features of the solutions.     

辊道窑温度均匀器垂直安装对窑内温度场影响的研究

利用FLUENT软件对辊道窑垂直安装温度均匀器前后窑内温度场进行了数值模拟。通过分析模拟计算得出的温度场,发现加入温度均匀器前后窑内温度场有所不同。加入均匀器后,周围附近的烟气温度场更均匀,这有利于减少色差和变形等烧成缺陷。     

STUDY OF THE LAMINAR NATURAL CONVECTION PROBLEM ALONG AN ISOTHERMAL VERTICAL PLATE BASED ON DISCRIMINATED DIMENSIONAL ANALYSIS

The results derived from the application of “classical” dimensional analysis to the natural convection heat transfer problem are poor, particularly in the case of two- or three-dimensional problems. “Discriminated” dimensional analysis provides more precise solutions, which frequently lead to only one dimensionless monomial. The main feature of the discrimination, on one hand, is that the dimensional basis is extended, taking into account that each of the spatial coordinates of a problem is dimensionally independent. On the other hand, discrimination provides different dimensional equations (derived from the basic laws) for quantities of vectorial character according to its inherent spatial direction. As a result, the quantities that take part in the solution are related each other in a more restricted way than in the case of classical dimensional analysis, leading, in general, to a minor number of dimensionless groups. Many of the known dimensionless numbers, such as the Rayleigh, Grashof, Boussinesq, and Nusselt numbers, have dimensions in a discriminated basis and, per se, do not play an independent role in the solution of the problem. Discriminated dimensional analysis groups these numbers, both among themselves and with other quantities, forming new (discriminated) dimensionless monomials with a precise physical significance. Here, we study natural convection on an isothermal vertical plate using this technique and compare the results with those obtained by classical dimensional analysis.     

RADIATION AND NON-DARCY EFFECTS ON CONVECTION IN POROUS MEDIA

Combined conduction, convection and radiation heat transfer in a gray fluid-saturated sparsely packed porous medium is examined analytically for marginal convection using linear stability analysis. The effects of boundary and inertia which were absent in the usual Darcy model are considered. The Milne-Eddington approximation is employed to determine the solutions valid for transparent and opaque media which absorbs and emits thermal radiation. It is shown that the nature of the bounding surfaces and radiation significantly influence the critical Rayleigh and wave numbers. The mechanism for suppressing or augmenting convection is discussed in detail. The results obtained using Galerkin technique are compared with the existing results of Darcy model and of non-radiating systems and agreement is found.     

强制浓度周期振荡对丙烯部分氧化反应的影响

研究了强制浓度周期振荡对丙烯在 Mo-Co-Bi 氧化物催化剂上部分氧化制丙烯醛的影响。实验考察了在不同强制振荡周期与振幅下的丙烯转化率和丙烯醛选择性及收率的变化,并与稳态反应条件下的结果作了比较。发现丙烯浓度的各种脉冲方式及氧浓度的微量脉冲方式均可改善反应性能,但氧浓度的全脉冲方式效果不佳。对强制周期操作效应的机理作了探讨。     

MATHEMATICAL MODELING OF THERMAL RADIATION EFFECTS ON TRANSIENT GRAVITY-DRIVEN OPTICALLY THICK GRAY CONVECTION FLOW ALONG AN INCLINED PLANE WITH PRESSURE GRADIENT

We study theoretically the unsteady gravity-driven thermal convection flow of a viscous incompressible absorbing-emitting gray gas along an inclined plane in the presence of a pressure gradient and significant thermal radiation effects. The Rosseland diffusion flux model is employed to simulate thermal radiation effects. The momentum and energy conservation equations are nondimensionalized and solved exactly using the Laplace transform technique. Expressions are derived for the frictional shearing stress at the inclined plane surface and also the critical Grashof number. The effects of time (T), Grashof number (Gr), Boltzmann-Rosseland radiation parameter (K₁), and plate inclination (α) on velocity (u) and temperature (θ) distributions are studied. The flow is found to be accelerated with increasing inclination of the plane, increasing free convection effects, and for greater thermal radiation contribution but decelerated with progression of time. Temperature is found to be enhanced with progression of time and with greater thermal radiation contribution. Applications of the model arise in solar energy collector analysis and industrial materials processing.     

Catalytic Carbon Oxidation in The Presence of Cerium Oxide: Experimental Study and Modeling of The Effect of Oxygen Concentration

The catalytic combustion of carbon black (CB) used as a model of diesel soot in tight contact with a commercial ceria (CeO₂) was investigated. Oxygen mole fractions of 10, 5, and 1 % in the gas phase were tested in order to gain a better understanding of the redox properties of ceria and the mechanism of the catalytic oxidation of carbon black. Both isothermal and temperature programmed runs are performed to extract kinetic parameters, such as activation energy and reaction order with respect to oxygen partial pressure. The experimental data are used to propose a model of CB oxidation in the presence of CeO₂ allowing the simulation of carbon oxidation.     

Water delignification by advanced oxidation processes: Homogeneous and heterogeneous Fenton and H2O2 photo-assisted reactions

The oxidation of lignin in synthetic aqueous solutions as well as in the biologically treated pulp-and-paper mill wastewater with hydrogen peroxide was studied in various methods: hydrogen peroxide UV-photolysis, homogeneous, heterogeneous and UV-assisted heterogeneous Fenton reactions, catalysed by FeZSM-5 zeolite. Contrasting the low-molecular organic contaminants, the oxidation of lignin in aqueous solutions was drastically slowed down in presence of heterogeneous FeZSM-5 zeolite, showing the superior performance of acidic homogeneous Fenton and hydrogen peroxide photolysis. This is explained by steric hindrance in oxidation of lignin with OH radicals on the catalyst surface and possible deactivation of lignin molecules adsorbed on the zeolite. The hydrogen peroxide photolysis among the studied delignification methods appeared to be the most efficient one in a wide range of pH.     

碳相含量对C—SiC—TiC—TiB2复合材料结构和性能的影响

本文研究了碳相含量在１０～４０ｖｏｌ％范围内变动时对原位合成的碳／陶复合材料（Ｃ－ＳｉＣ－ＴｉＣ－ＴｉＢ２）的结构和性能的影响。结果表明：随着碳含量的增加,材料的抗弯强度下降。当碳相含量小于２０ｖｏｌ％时,材料的抗弯强度可达到４００Ｍｐａ以上。随着碳相含量的增加,应相应提高烧结温度。对材料在６００°Ｃ、８００°Ｃ、１０００°Ｃ、１２００°Ｃ下的抗氧化性能进行了研究。研究发现了在试验温度下,材料表现出优良的抗氧化能力。碳含量较少的试样表现为氧化增重,碳含量较多的试样表现为氧化失重。     

温度均匀器对辊道窑窑内温度场的影响

利用FLUENT软件对辊道窑垂直安装温度均匀器前后窑内温度场进行了数值模拟。通过分析模拟计算得出温度场,发现加入温度均匀器前后窑内温度场有所不同。加入均匀器后,周围附近的烟气温度场更均匀,这有利于减少色差和变形等烧成缺陷。     

自然对流对于熔体生长中小面化的影响

应用基于边界保角变换技术的Ｇａｌｅｒｋｉｎ有限元方法,研究熔体生长中动力学效应和自然对流的耦合作用探究了对流对生长系统中的温场分布、相界面２以及界面过冷度的影响。研究结果表明：自然对不充可使相界面的弯曲度减小,界面的相对位置降低,同时,对流使得小面端点处的夹角变得圆滑,小面域和粗糙面域的界线变得不明显,相应地,小面尺寸有所减小。     

RIB ORIENTATION EFFECTS ON HEAT TRANSFER PERFORMANCE IN FORCED CONVECTIVE BOILING

The effects of rib orientation to the direction of flow on the heat transfer performance of ribbed surfaces in forced convective boiling have been investigated experimentally. Test surfaces were manufactured from a stainless steel plate of 1.60 mm thickness on to which transverse rectangular ribs were machined. Rib height, length and spacing were kept constant at 0.50 mm, 1.00 mm and 0.50 mm respectively and rib orientation to the direction of flow was varied from 0° to 135°. In order to ensure good reproducibility of the experimental data, the effects of surface roughness were isolated by providing a constant surface micro-roughness for all test specimens and the effects of aging were also isolated. Experimental data are reported for heat transfer from ribbed surfaces to water boiling at atmospheric pressure for velocities ranging from 0.2 m/s to 1.4 m/s and inlet subcoolings from 5° to 30°C.     

EFFECTS OF GRADIENT MAGNETIC FIELDS ON THE MAGNETO-THERMAL MIXED CONVECTION OF AIR IN A HORIZONTAL PIPE

Effects of gradient magnetic fields on the mixed convection of air in a gravity field are numerically studied with 3-D model equations. The detailed characteristics of the magneto-thermal wind in a pipe are computed for the length ratios L (pipe length divided by pipe diameter) of 20, 30, 62, and 100, with diameter ratios N (diameter of an electric coil versus that of the pipe) from 2 to 200. It is found that there exists a best diameter ratio N to maximize the airflow rate for a channel with a fixed length. Detailed flow and temperature profiles are graphically presented for various values of N.