ON THE EFFECTIVE CONDUCTIVITY OF A DILUTE SUSPENSION OF SPHERICAL DROPS IN THE LIMIT OF LOW PARTICLE PECLET NUMBER

In this paper we consider the effective conductivity of a dilute suspension of neutrally bouyant spherical drops which is undergoing a simple shear flow. The thermal conductivity, viscosity and specific heat capacity of the drops are assumed to be different from those of the suspending fluid, though it is assumed that the local Peclet and Reynolds numbers are small both inside and outside the drop. The analysis consists of three parts: a derivation of the relationship between bulk heat flux on the one hand and the thermal and momentum fields at the microscale of the suspended particles on the other; a calculation of the local temperature field near a single neutrally buoyant spherical drop in shear flow with an imposed transverse temperature gradient at large distances; and a synthesis of the general relationship for bulk heat flux and the calculated local temperature field to determine an effective conductivity for a dilute suspension of spherical drops.     

EFFECTIVE PROPERTIES OF POROUS AND COMPOSITE MATERIALS

Based on a previously modified version of Bruggerman's method, a dependence of the effective diffusion coefficient in porous media on the porosity is deduced and compared with available experimental data. Based on the same method, a dependency of the effective elastic coefficients of composite materials on the volume fraction of inclusions is deduced in the case of different types of inclusions. Comparison with available experimental data shows good agreement between the theory predictions and the experimental data. In the case of the elastic properties of laminated composite materials, application of the same method yields results identical to those obtained using the averaging procedure. A theory of effective viscosity of concentrated suspensions is applied for calculations of dependency of effective viscosity on applied shear rate using available experimental data.     

EFFECTIVE PROPERTIES OF POROUS AND COMPOSITE MATERIALS

Based on a previously modified version of Bruggerman's method, a dependence of the effective diffusion coefficient in porous media on the porosity is deduced and compared with available experimental data. Based on the same method, a dependency of the effective elastic coefficients of composite materials on the volume fraction of inclusions is deduced in the case of different types of inclusions. Comparison with available experimental data shows good agreement between the theory predictions and the experimental data. In the case of the elastic properties of laminated composite materials, application of the same method yields results identical to those obtained using the averaging procedure. A theory of effective viscosity of concentrated suspensions is applied for calculations of dependency of effective viscosity on applied shear rate using available experimental data.     

SINGULAR BEHAVIOR OF THE EFFECTIVE VISCOSITY IN A CONCENTRATED SUSPENSION MEDIUM

The purpose of this paper is to evaluate the effective viscosity of a concentrated Newtonian suspension via spatially periodic approximation and to clarify the results from previously published articies. It is found that singular characteristic of the effective viscosity expression does not disappear. This approximation is then extended to investigate the system of a concentrated non-Newtonian suspension fluid. The results obtained by using the spatially periodic approximation are similar to that of a quasi-steady approximation in terms of the first order of e-¹urthermore, the singular behavior also appears in the expression of the effective viscosity both for a second-order-Rivlin-Ericksen fluid at low shear rate and a Harnoy fluid at high shear rate, except that the viscoelastic effect in the low shear rate is depressed by spatially periodic approximation as compared with those orders obtained by quasi-steady approximation.     

EFFECTIVE THERMAL CONDUCTIVITY IN TRICKLE-BED REACTORS: APPLICATION OF EFFECTIVE MEDIUM THEORY AND RANDOM WALK ANALYSIS

A model for the prediction of the radial effective thermal conductivity of cocurrent down-flow trickle-bed reactors in the complete wetting trickling flow regime is presented. The radial thermal conductivity is made up of two components: that due to heat conduction and that due to radial liquid dispersion. The former is evaluated based on the effective medium theory while the latter by a random walk analysis. Comparison of the calculated values with experimental data in the literature shows good agreement.     

EFFECTIVE THERMAL CONDUCTIVITY IN TRICKLE-BED REACTORS: APPLICATION OF EFFECTIVE MEDIUM THEORY AND RANDOM WALK ANALYSIS

A model for the prediction of the radial effective thermal conductivity of cocurrent down-flow trickle-bed reactors in the complete wetting trickling flow regime is presented. The radial thermal conductivity is made up of two components: that due to heat conduction and that due to radial liquid dispersion. The former is evaluated based on the effective medium theory while the latter by a random walk analysis. Comparison of the calculated values with experimental data in the literature shows good agreement.     

测定多孔性固体催化剂颗粒有效导热系数的新方法

提出了一种测定空气中催化剂有效导热系数的方法。该方法简便、易行,实验误差小于5％.在此基础之上用woodside随机分布模型计算了反应条件下催化剂有效导热系数。误差分析表明：该模型误差较小,完全可以用于工程计算。     

EFFECTIVE THERMAL CONDUCTIVITY OF BINARY MIXTURES AT HIGH SOLID TO GAS CONDUCTIVITY RATIOS

The effective thermal conductivity of single size and binary mixtures of packed particle beds with stagnant gas at high solid/gas conductivity ratios is determined by a deterministic, unit cell approach. The model results are shown to be in good agreement with experimental data for various gas pressures and solid to gas thermal conductivity ratios up to 1300. A set of correlations for effective conductivity of binary mixtures as a function of gas pressure and particle size is derived. The effect of particle swelling on the effective conductivity of binary mixtures is studied by performing a parametric study of the contact area between the particles     

EXPERIMENTAL INVESTIGATION OF PARAMETERS AFFECTING NANOFLUID EFFECTIVE THERMAL CONDUCTIVITY

The present research reports nanofluid effective thermal conductivity enhancements (ETCE) using an accurate transient short hot wire method system. Preparation of nanofluids was carried out through a two-step method with highly powered pulses similar to that for nanoparticle dispersion in base fluids. Parameters affecting nanofluid heat conductivity such as concentration, sizes, and material of nanoparticle? type of base fluid, temperature, ultrasonic mixing time, and elapsed time after preparation were studied. In the present study, nanoparticles of Al, Al₂O₃, CuO, SnO₂, TiO₂, and SiO₂ with base fluids of water and ethylene glycol were used. Parameters like concentration, size, temperature, and the type of base fluid showed more noticeable effect on the effective thermal conductivity than the others, and mixing time had the least effect. The results showed that any increase in concentration and temperature, and also any decrease in size of nanoparticles and time elapsed after nanofluid preparation, leads to the ETCE of the nanofluid. However, the effects of nanoparticle material, base fluid, and mixing time on thermal conductivity of the nanofluid showed varying trends. Last, a number of mathematical models for prediction of thermal conductivity of nanofluids were applied.     

THE LOCAL VOLUME-AVERAGED EQUATIONS OF MOTION FOR A SUSPENSION OF NON-NEUTRALLY BUOYANT SPHERES

The local volume averages of the equations of motion as well as the appropriate boundary conditions are developed for a flowing suspension of non-neutrally buoyant, uniform spheres in an incompressible Newtonian fluid under conditions such that inertial effects can be neglected. These equations do not represent an asymptotic theory with respect to the volume fraction of solids. Higher order terms have been retained everywhere, except where it has been necessary to estimate the velocity distribution within the immediate neighborhood of each sphere by neglecting the effects of the other spheres present. The resulting local volume-averaged equations of motion and boundary conditions involve no free or undetermined parameters.

For the special case of a very dilute suspension of neutrally buoyant spheres, the total local volume average of Cauchy's first law reduces to the form of the Navier-Stokes equation with the effective viscosity computed by Einstein (1906, 1956).

In two succeeding papers, we demonstrate for several flows [in vertical tubes, in a cone-plate viscometer, between rotating concentric cylinders (Couette flow), and between rotating parallel plates] that our general theory describes more concentrated neutrally buoyant suspensions than does its limiting case of very dilute suspensions.     

THE PARTICLE VELOCITY DISTRIBUTION IN A RISER OF DILUTE CIRCULATING FLUIDIZED BED

This paper presents an experimental study on the radial and axial profiles of local particle velocity of flu-idized catalyst(FCC)particles in a circulating fluidized bed of 8000mm in height and 186mm in inside diameterwith a Fiber-Optic Probe Laser Doppler Velocimetry.It has been found that the radial profiles of local particlevelocity are parabolic,even in the centre region and steep in the region near the bed wall,and that the length ofparticle acceleration along the bed height is longer than expected.The following formula has been recommended to correlate the 1 ocal particle velocity with dilute gas-solidflow in the bed:where a,b,c and e are functions of radial positions.     

DC CONDUCTIVITY IN POLY-N-VINYLCARBAZOLE: A STUDY OF DIELECTRIC MEASUREMENTS

Dynamical dielectric measurements have been carried out on thin films of poly-N-vinylcarbazole. The dielectric response data were graphically represented in the conductivity complex plane, from which the values of the contribution of the DC conductivity were estimated. These values were in good agreement with the values obtained from DC current measurements, already reported in the literature. These results allow to conclude that the graphical representation of the complex conductivity in the complex plane represents a simple way for estimating the DC condctivity from dielectric data, without the experimental limitation to measure at very low frequencies, and without the difficulties appearing during DC current measurements.     

悬浮法成型UP微粒粒径及其分布的控制

以不饱和聚酯树脂（UP）为原料,采用悬浮成型方法制备了粒径为120～250μm的UP球形微粒,从工艺控制的角度考察了搅拌速度、搅拌器形式及反应嚣形式对UP微粒平均粒径及粒径分布的影响。结果表明,将搅拌速度控制在500～1000r／min,以4口圆柱形烧瓶为反应器,采用双层平桨、且桨叶间距为4．5cm时,所制UP微粒的粒径最小、且粒径分布最窄。     

A STRUCTURAL GENERIC MODEL TO PREDICT THE EFFECTIVE THERMAL CONDUCTIVITY OF GRANULAR MATERIALS

A generic structural model to estimate the effective thermal conductivity of granular foods is proposed based on a distribution coefficient. It is assumed that granular food materials in bulk can be considered as a two-phase system containing granules and an interstitial air phase, and while the granules are also be considered as a two-phase system containing dry mater and water. Two different distribution factors are defined, one for granular materials in bulk and another for the granules. The proposed model was applied successfully to granular starch.     

NiO掺杂对4YSZ导电性能的影响

以氧氯化锆、硝酸钇和氯化镍为原料,柠檬酸为络合剂,制备了掺NiO的4YSZ凝胶,将凝胶在500℃煅烧后,压制成圆片状,在1300℃烧结2h得到所需试样;研究NiO的不同掺量对试样的烧结性能、电导率的影响。结果表明掺NiO可提高试样的烧结性能和电导率;当Ni元素为4mol%时,试样相对密度达95.20%,其在700℃的电导率达2.40×10-3S.cm-1。     

氮化铝的室温热导率

本文导出了氮化铝室温热导率的一般表达式，对提高氮化铝陶瓷材料室温热导率的途径作了讨论。     

A STRUCTURAL GENERIC MODEL TO PREDICT THE EFFECTIVE THERMAL CONDUCTIVITY OF GRANULAR MATERIALS

A generic structural model to estimate the effective thermal conductivity of granular foods is proposed based on a distribution coefficient. It is assumed that granular food materials in bulk can be considered as a two-phase system containing granules and an interstitial air phase, and while the granules are also be considered as a two-phase system containing dry mater and water. Two different distribution factors are defined, one for granular materials in bulk and another for the granules. The proposed model was applied successfully to granular starch.     

MEASUREMENTS OF THERMAL CONTACT CONDUCTANCE FOR A PAPER/METAL INTERFACE AND EFFECTIVE CONDUCTIVITY OF MACHINE SAMPLES

ABSTRACT

The thermal contact conductance for a paper/metal interface and the effective thermal conductivity of paper samples were determined using an experimental contact conductance apparatus. The effects of pressure and moisture content on the thermal contact conductance and the effective thermal conductivity were investigated. The samples considered in the experiments consisted of paper machine samples from different sections of the drying section. The results are compared to those of the handsheets prepared in our laboratory.     

MOTION OF A CIRCULATING POWER-LAW DROP TRANSLATING THROUGH NEWTONIAN FLUIDS AT INTERMEDIATE REYNOLDS NUMBERS

The equations of motion for the flow of a power-law fluid sphere in a Newtonian continuous phase have been approximately satisfied by Galerkin's method: External and internal stream functions have been obtained for the following ranges of variables: 10-50 for Re₀, 0.1-1000 for the viscosity ratio parameters, X, and 0.6-1.0 for the dispersed phase power-law index, n_i,. It is predicted that pseudoplasticity in the dispersed phase causes a reduction in the circulation within the drop and that it has a minor effect on the drag coefficients and the rates of mass transfer in the continuous phase