Experimental investigation of heat conduction in polyester-Al2O3 and polyester-CuO nanocomposites

This paper presents an experimental analysis of the thermal conductivity of nanocomposite systems composed of unsaturated polyester resin (UPR) as matrices and two different metal-oxides nanoparticles as fillers: alumina (aluminum oxide) and tenorite (copper oxide). The nanoparticles used were alpha-Al₂O₃ (30-40 nm) and CuO (30-50 nm). Samples were fabricated using simple molding and homogenization using magnetic stirring. Thermal conductivities were measured using a device that complies with ASTM norms C518-04 and E1530-06. Measurements were taken at three different temperatures (0 °C, 25 °C and 50 °C), for different sets of samples, varying the nanoparticle fraction used in composite systems. Finally, the experimental data are compared with traditional models for predicting the thermal conductivity of composite materials, showing that the traditional models underestimate the measured values.     

Measurement of the concentration diffusion coefficient for Ne-Ar,Ne-Xe,Ne-H2, Xe-H2, H2-N2 and H2-O2 gas systems

The concentration diffusion coefficient, D ₁₂, is measured for the equimolar mixtures of Ne-Ar, Ne-Xe, Ne-H₂, Xe-H₂, H₂-N₂ and H₂-O₂ binary gas systems in a two-bulb metal apparatus in the temperature range 0 C to 100 C. These values are compared with the existing data on these systems and with the predictions of the kinetic theory in conjunction with the modified Buckingham exp-six potential. Unlike the thermal diffusion coefficient, with the simple theory it is possible to predict D ₁₂ within a few percent even for systems involving polyatomic gases. The smoothed experimental D ₁₂ values are also used to obtain data for the coefficients of viscosity and thermal conductivity at round temperatures and compositions for these systems.     

Role of interfacial layer and clustering on the effective thermal conductivity of CuO-gear oil nanofluids

Copper oxide nanoparticles (∼40 nm) are dispersed in gear oil (IBP Haulic-68) at different volume fractions (0.005-0.025) with oleic acid added as a surfactant to stabilize the system. Prepared nanofluids are characterized by Fourier Transform Infrared spectroscopy (FTIR) and Dynamic light scattering (DLS) measurements. DLS data confirmed the presence of agglomerated nanoparticles in the prepared nanofluids. Thermal conductivity measurements are performed both as a function of CuO volume fraction and temperature between 5 and 80 °C. An enhancement in thermal conductivity at 30 °C of 10.4% with 0.025 volume fraction of CuO nanoparticle loading is observed. Measured volume fraction dependence of the thermal conductivity enhancement at room temperature is predicted fairly well considering contributions from both nanolayer at the solid-liquid interface and particle agglomeration in the suspension, as visualized by Feng et al.     

Transport properties in mixtures involving carbon dioxide at low and moderate density: test of several intermolecular potential energies and comparison with experiment

It is the purpose of this paper to extract unlike intermolecular potential energies of five carbon dioxide-based binary gas mixtures including CO₂–He, CO₂–Ne, CO₂–Ar, CO₂–Kr, and CO₂–Xe from viscosity data and compare the calculated potentials with other models potential energy reported in literature. Then, dilute transport properties consisting of viscosity, diffusion coefficient, thermal diffusion factor, and thermal conductivity of aforementioned mixtures are calculated from the calculated potential energies and compared with literature data. Rather accurate correlations for the viscosity coefficient of afore-cited mixtures embracing the temperature range 200 K < T < 3273.15 K is reproduced from the present unlike intermolecular potentials energy. Our estimated accuracies for the viscosity are to within ±2%. In addition, the calculated potential energies are used to present smooth correlations for other transport properties. The accuracies of the binary diffusion coefficients are of the order of ±3%. Finally, the unlike interaction energy and the calculated low density viscosity have been employed to calculate high density viscosities using Vesovic–Wakeham method.     

Experimental determination of the diffusion coefficients of wood in isothermal conditions

The diffusion coefficients of frake (Terminalia superba) were determined in the radial, tangential, and longitudinal directions at tree different temperatures: 30°C, 35°C an 40°C. The longitudinal diffusion coefficient is larger than the transverse diffusion coefficient. In addition the radial coefficient is larger than the tangential coefficient.     

Chapman–Enskog solutions to arbitrary order in Sonine polynomials III: Diffusion,thermal diffusion,and thermal conductivity in a binary,rigid-sphere,gas mixture

The Chapman–Enskog solutions of the Boltzmann equation provide a basis for the computation of important transport coefficients for both simple gases and gas mixtures. These coefficients include the viscosity, the thermal conductivity, and the diffusion coefficient. In a preceding paper (I), for simple, rigid-sphere gases (i.e. single-component, monatomic gases) we have shown that the use of higher-order Sonine polynomial expansions enables one to obtain results of arbitrary precision that are free of numerical error and, in a second paper (II), we have extended our initial simple gas work to modeling the viscosity in a binary, rigid-sphere, gas mixture. In this latter paper we reported an extensive set of order 60 results which are believed to constitute the best currently available benchmark viscosity values for binary, rigid-sphere, gas mixtures. It is our purpose in this paper to similarly report the results of our investigation of relatively high-order (order 70), standard, Sonine polynomial expansions for the diffusion- and thermal conductivity-related Chapman–Enskog solutions for binary gas mixtures of rigid-sphere molecules. We note that in this work, as in our previous work, we have retained the full dependence of the solution on the molecular masses, the molecular sizes, the mole fractions, and the intermolecular potential model via the omega integrals. For rigid-sphere gases, all of the relevant omega integrals needed for these solutions are analytically evaluated and, thus, results to any desired precision can be obtained. The values of the transport coefficients obtained using Sonine polynomial expansions for the Chapman–Enskog solutions converge and, therefore, the exact diffusion and thermal conductivity solutions to a given degree of convergence can be determined with certainty by expanding to sufficiently high an order. We have used Mathematica® for its versatility in permitting both symbolic and high-precision computations. Our results also establish confidence in the results reported recently by other authors who used direct numerical techniques to solve the relevant Chapman–Enskog equations. While in all of the direct numerical methods more-or-less full calculations need to be carried out with each variation in molecular parameters, our work has utilized explicit, general expressions for the necessary matrix elements that retain the complete parametric dependence of the problem and, thus, only a matrix inversion at the final step is needed as a parameter is varied. This work also indicates how similar results may be obtained for more realistic intermolecular potential models and how other gas-mixture problems may also be addressed with some additional effort.     

The thermal conductivity of dialkylphthalates

The thermal conductivity of liquids poorly absorbing heat radiation depends considerably on the thickness of the sample in the direction of heat flux. This arises from the radiative component of thermal conductivity which shows a size effect just for such sample sizes which are mostly chosen for experimental reasons. Therefore, only values of strongly absorbing liquids should be selected for reference purposes because the radiative term is much smaller in such liquids. This is important in particular at elevated temperatures because the radiative component increases very considerably with temperature. In the range from about 0 °C to 300 °C dialkylphthalates seem to be suitable reference materials. As a first contribution to the problem of obtaining appropriate standard reference data the thermal conductivity of six compounds of this type was measured between + 10 °C and 85 °C. The measurements show that the size effect is not larger for these compounds than for alcohols.

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Zusammenfassung Die Wärmeleitfähigkeit von Flüssigkeiten, welche die Wärmestrahlung wenig absorbieren, wie Kohlenwasserstoffe oder chlorierte Kohlenwasserstoffe, hängt schon bei Raumtemperatur erheblich von der Schichtdicke der Probe ab. Dies liegt an dem Strahlungsanteil der Wärmeleitfähigkeit, der bei den aus experimentellen Gründen meist gewählten Probenabmessungen einen Größeneffekt aufweist. Als Bezugswerte sollten daher nur solche von stark absorbierenden Flüssigkeiten ausgewählt werden, weil bei ihnen der Strahlungsanteil viel kleiner ist. Da dieser mit der Temperatur stark ansteigt, ist dies besonders wichtig für den Bereich höherer Temperaturen. Zwischen etwa 0 °C und 300 °C scheinen Dialkylphthalate geeignete Bezugsflüssigkeiten zu sein. Als Beitrag zur Gewinnung brauchbarer Normalbezugswerte wurde die Wärmeleitfähigkeit von sechs Verbindungen dieses Typs zwischen +10 °C und 85 °C gemessen.

     

Polymer contribution to the thermal conductivity and viscosity in a dilute solution (Fraenkel Dumbbell model)

The phase-space kinetic theory for polymeric liquid mixtures is used to obtain an expression for the polymer contribution to the thermal conductivity of a nonflowing, dilute solution of polymers, where the polymer molecules are modeled as Fraenkel dumbbells. This theory takes into account three mechanisms for the energy transport: diffusion of kinetic energy (including the Öttinger-Petrillo term), diffusion of intramolecular energy, and the work done against the intramolecular forces. This paper is an extension of previous developments for the Hookean dumbbell model and the finitely-extensible dumbbell model. A comparison among the dumbbell results suggests that the thermal conductivity increases with chain stiffness. In addition, the zero-shear-rate viscosity and first normal-stress coefficient are also given for the Fraenkel dumbbell model.Dedicated to Prof. John D. Ferry on the occasion of his 85th birthday.     

Chapman–Enskog solutions to arbitrary order in Sonine polynomials V: Summational expressions for the viscosity-related bracket integrals

The Chapman–Enskog solutions of the Boltzmann equations provide a basis for the computation of important transport coefficients for both simple gases and gas mixtures. These coefficients include the viscosity, the thermal conductivity, and the diffusion coefficient. In a preceding paper on simple gases (I), we have shown that the use of higher-order Sonine polynomial expansions enables one to obtain results of arbitrary precision that are free of numerical error. In two subsequent papers (II–III), we extended our original simple gas work to encompass binary gas mixture computations of the viscosity, thermal conductivity, diffusion, and thermal diffusion coefficients to high-order. In a fourth paper (IV) we derived general summational representations for the diffusion- and thermal conductivity-related bracket integrals and provided compact, explicit expressions for all of these bracket integrals needed to compute the diffusion- and thermal conductivity-related transport coefficients up to order 5 in the Sonine polynomial expansions used. In all of this previous work we retained the full dependence of our solutions on the molecular masses, the molecular sizes, the mole fractions, and the intermolecular potential model via the omega integrals up to the final point of solution via matrix inversion. The elements of the matrices to be inverted are, in each case, determined by appropriate combinations of bracket integrals which contain, in general form, all of the various dependencies. Since accurate expressions for the needed bracket integrals have not previously been available in the literature beyond orders 2 or 3, and since such expressions are necessary for any extensive program of computations of the transport coefficients involving Sonine polynomial expansions to higher orders, we have investigated alternative methods of constructing appropriately general bracket integral expressions that do not rely on the term-by-term, expansion and pattern matching techniques that we developed for our previous work. It is our purpose in this paper to report the results of our efforts to obtain useful, alternative, general expressions for the bracket integrals associated with the viscosity-related Chapman–Enskog solutions for gas mixtures. Specifically, we have obtained such expressions in summational form that are conducive to use in high-order viscosity coefficient computations for arbitrary gas mixtures and have computed and reported explicit expressions for all of the orders up to 5.     

Chapman–Enskog solutions to arbitrary order in Sonine polynomials IV: Summational expressions for the diffusion- and thermal conductivity-related bracket integrals

The Chapman–Enskog solutions of the Boltzmann equations provide a basis for the computation of important transport coefficients for both simple gases and gas mixtures. These coefficients include the viscosity, the thermal conductivity, and the diffusion coefficient. In a preceding paper on simple gases, we have shown that the use of higher-order Sonine polynomial expansions enables one to obtain results of arbitrary precision that are free of numerical error. In two subsequent papers, we have extended our original simple gas work to encompass binary gas mixture computations of the viscosity, thermal conductivity, diffusion, and thermal diffusion coefficients to high-order. In all of this previous work we retained the full dependence of our solutions on the molecular masses, the molecular sizes, the mole fractions, and the intermolecular potential model via the omega integrals up to the final point of solution via matrix inversion. The elements of the matrices to be inverted are, in each case, determined by appropriate combinations of bracket integrals which contain, in general form, all of the various dependencies. Since accurate, explicit, general expressions for bracket integrals are not available in the literature beyond order 3, and since such general expressions are necessary for any extensive program of computations of the transport coefficients involving Sonine polynomial expansions to higher orders, we have investigated alternative methods of constructing appropriately general bracket integral expressions that do not rely on the term-by-term, expansion and pattern matching techniques that we developed for our previous work. It is our purpose in this paper to report the results of our efforts to obtain useful, alternative, general expressions for the bracket integrals associated with the diffusion- and thermal conductivity-related Chapman–Enskog solutions for gas mixtures. Specifically, we have obtained such expressions in summational form that are conducive to use in high-order transport coefficient computations for arbitrary gas mixtures and have computed and reported explicit expressions for all of the orders up to 5.     

A cryostat for use with a thermal conductivity hot wire system

Summary A cryostat for use with a thermal conductivity hot wire system is described in which temperatures between –70°C and –130°C can be maintained constant to within (0.01°C). Control of temperature is made by adjusting the vacuum between a five component mixture and liquid oxygen. Extra control is made by adjusting the current through a heating coil immersed in the cryostat mixture. The temperature indicator is a platinum wire surrounding the tubes.     

The macroscopic coefficients of thermal conductivity and diffusion in microinhomogeneous solids

A method is given for calculating the macroscopic coefficients of thermal conductivity and diffusion for microinhomogeneous solids whose local coefficients of thermal conductivity (or diffusion) form an ergodic homogeneous stray field. In the case of marked isotropy of the field of the local coefficients, the calculations are taken to a conclusion. The final formulas for the structure are not much more complicated than the corresponding first-approximation formulas. The results of calculations for certain other cases are also given. The effect of anisotropy of the crystallites in polycrystalline material on the coefficients of thermal conductivity and diffusion is discussed.One of the main problems in the mechanics of microinhomogeneous bodies is the determination of the macroscopic constants from the corresponding microscopic characteristics. The assumption regarding the small inhomogeneity used by a number of authors [1, 2] is not applicable in the case of isotropic polycrystalline aggregates consisting of substantially anisotropic crystallites, stochastic reinforced media media, etc. The so-called self-consistent field method [3] opens up some interesting prospects, but this method is an approximate one and its errors have not yet been assessed. Nevertheless, by making certain fairly general assumptions about the correlation properties of the inhomogeneity, it is possible to obtain final accurate formulas for such macroscopic properties of the solids as the coefficients of thermal conductivity, diffusion, elasticity, and thermal expansion. Below we consider some of the simplest problems involved in determining the macroscopic constants which form a second-order tensor and which characterize the distribution of a certain scalar quantity in a microinhomogeneous body.     

Measurement of temperature-dependent thermal conductivity and viscosity of TiO2-water nanofluids

Nanofluid is an innovative heat transfer fluid with superior potential for enhancing the heat transfer performance of conventional fluids. Many attempts have been made to investigate its thermal conductivity and viscosity, which are important thermophysical properties. No definitive agreements have emerged, however, about these properties. This article reports the thermal conductivity and dynamic viscosity of nanofluids experimentally. TiO₂ nanoparticles dispersed in water with volume concentration of 0.2–2 vol.% are used in the present study. A transient hot-wire apparatus is used for measuring the thermal conductivity of nanofluids whereas the Bohlin rotational rheometer (Malvern Instrument) is used to measure the viscosity of nanofluids. The data are collected for temperatures ranging from 15 °C to 35 °C. The results show that the measured viscosity and thermal conductivity of nanofluids increased as the particle concentrations increased and are higher than the values of the base liquids. Furthermore, thermal conductivity of nanofluids increased with increasing nanofluid temperatures and, conversely, the viscosity of nanofluids decreased with increasing temperature of nanofluids. Moreover, the measured thermal conductivity and viscosity of nanofluids are quite different from the predicted values from the existing correlations and the data reported by other researchers. Finally, new thermophysical correlations are proposed for predicting the thermal conductivity and viscosity of nanofluids.     

Thermal stress analysis of a silicon carbide/aluminum composite

Thermal deformations and stresses were studied in a silicon-carbide/aluminum filamentary composite at temperatures up to 370°C (700°F). Longitudinal and transverse thermal strains were measured with strain gages and a dilatometer. An elastoplastic micromechanical analysis based on a one-dimensional rule-of-mixtures model and an axisymmetric two-material composite cylinder model was performed. It was established that beyond a critical temperature thermal strains become nonlinear with decreasing longitudinal and increasing transverse thermal-expansion coefficients. This behavior was attributed to the plastic stresses in the aluminum matrix above the critical temperature. An elastoplastic analysis of both micromechanical models was performed to determine the stress distributions and thermal deformation in the fiber and matrix of the composite. While only axial stresses can be determined by the rule-of-mixtures model, the complete triaxial state of stress is established by the composite cylinder model. Theoretical predictions for the two thermal-expansion coefficients were in satisfactory agreement with experimental results.     

Measurement of the concentration diffusion coefficient for Ne-Ar, Ne-Xe, Ne-H2, Xe-H2, H2-N2 and H2-O2 gas systems

The concentration diffusion coefficient, D ₁₂, is measured for the equimolar mixtures of Ne-Ar, Ne-Xe, Ne-H₂, Xe-H₂, H₂-N₂ and H₂-O₂ binary gas systems in a two-bulb metal apparatus in the temperature range 0 C to 100 C. These values are compared with the existing data on these systems and with the predictions of the kinetic theory in conjunction with the modified Buckingham exp-six potential. Unlike the thermal diffusion coefficient, with the simple theory it is possible to predict D ₁₂ within a few percent even for systems involving polyatomic gases. The smoothed experimental D ₁₂ values are also used to obtain data for the coefficients of viscosity and thermal conductivity at round temperatures and compositions for these systems.Nomenclature C ₂ ^t relative amount of a gas in the mixture in the bulb 2 at an instant t - C ₂ relative amount of the same gas in the mixture in the bulb 2 at equilibrium - D ₁₂ diffusion coefficient - X ₁ mole-fraction of the heavier component in the mixture - _mix viscosity coefficient - _mix thermal conductivity coefficient     

Coupled model of coating formation on a cylindrical substrate

A coupled model of coating formation on the surface of a part of a cylindrical shape during deposition from the plasma is proposed. This model takes into account the phenomena of thermal diffusion, diffusive thermal conductivity, and mass transfer under the action of the stress gradient, and the formation of chemical compounds. The coating growth rate is considered to be a given function of the particle velocity and particle concentration near the surface of the growing coating. The problem is solved numerically. It is shown that diffusion cross-fluxes, diffusive thermal conductivity, and thermal diffusion during the growth process reduce the width of the transition zone between the substrate and the coating. This effect becomes most essential if the substrate has a low thermal conductivity. Accounting for stresses arising in the coating-substrate system during the deposition process changes the effective transfer coefficients and significantly affects the result of modeling the distribution of chemical elements and their compounds in the coating.     

Analytical and numerical study of natural convection heat transfer in an inclined composite enclosure

Laminar natural convection heat transfer in inclined fluid layers divided by a partition with finite thickness and conductivity is studied analytically and numerically. The governing equations for the fluid layers are solved analytically in the limit of a thin layered system with constant flux boundary conditions. The study covers of the range of Ra from 10³ to 10⁷, from 0° to 180° and the thermal conductivity ratio of partition to fluid ratioK from 10^–2 to 10⁶. The Prandtl number was 0.72 (for air). Results are obtained in terms of an overall Nusselt number as a function of Rayleigh number, angle of inclination of the system, mid layer thickness, and mid layer thermal conductivity. The critical Rayleigh number for the onset of convection in a bottom-heated horizontal system is predicted. The results are compared with the numerical results obtained by solving the complete system of governing equations, using SIMPLER method, as well as with the limiting cases in the literature.     

Structure and dynamics of ovalbumin gels

Solvent effects on dynamical and thermal behaviors of ovalbumin (OVA) gels induced by thermal denaturation at high temperature of 160°C were studied from dynamic shear modulus measurement, shear creep and creep recovery measurement, and DSC measurement. Two organic solvents, glycerin (G) and ethylene glycol (EG), and their mixtures with water (W)(G/W and EG/W) were used as solvent for preparation of gels. Stable gels formed in pure glycerin took a fractal structure at OVA concentration C range of 15–45wt% at a temperature specific to respective C, whereas a fractal structure was not observed for gels prepared in EG, G/W, and EG/W. The results were consistent with thermal denaturation behaviors of OVA in these solvents. Morphologies of two gels prepared in water and glycerin were explored using high resolution SEM, which showed that a basic unit responsible for formation of OVA gels was spheres with a diameter ranging from 20 to 40 nm, being much larger than 5.6 nm of the diameter of native OVA, and a fractal structure was related to network formation accompanied by melting of those spheres.Dedicated to Prof. John D. Ferry on the occasion of his 85th birthday.