Second-order slip MHD flow and heat transfer of nanofluids with thermal radiation and chemical reaction

The effects of the second-order velocity slip and temperature jump boundary conditions on the magnetohydrodynamic (MHD) flow and heat transfer in the presence of nanoparticle fractions are investigated. In the modeling of the water-based nanofluids containing Cu and Al₂O₃, the effects of the Brownian motion, thermophoresis, and thermal radiation are considered. The governing boundary layer equations are transformed into a system of nonlinear differential equations, and the analytical approximations of the solutions are derived by the homotopy analysis method (HAM). The reliability and efficiency of the HAM solutions are verified by the residual errors and the numerical results in the literature. Moreover, the effects of the physical factors on the flow and heat transfer are discussed graphically.     

Characteristic and microstructure of the microarc oxidized TiO2-based film containing P before and after chemical- and heat treatment

Chemical- and heat treatment was performed to modify the surface of the microarc oxidized TiO₂-based (TOB) film containing P to produce nano-scale compounds containing Na, Ti and O elements. In the TOB film, anatase and rutile nanocrystals were randomly distributed in P-doped matrix. On the surface of the chemically treated TOB (C-TOB) film, amorphous titanium oxide containing Na shows nano-scale ribbonlike morphology. Na, Ti and O show uniform distribution in the outer layer of the C-TOB film along surface depth. Chemical treatment did not alter the surface roughness of the TOB film obviously; however, it improved its hydrophilic property. Heat treatment has no influence on the chemical states of Ti, Na and O, as well as wetting ability, elemental composition and atomic concentration in the outer layer of the C-TOB film. However, the phase compositions and surface morphology of the C-TOB film after heat treatment are dependent on the heat treatment temperature.     

The role of Pb ions doping in the mechanism of chromate adsorption by goethite

Pure and 0.384% Pb²⁺ ions doped goethite samples were prepared in the laboratory by the coprecipitation method. The laboratory-prepared goethite samples were characterized for pH of point of zero charge (pH_pzc), surface area, XRD, TG-DTA, TEM, SEM and FTIR analysis, which suggest that the Pb²⁺ ions are incorporated into the crystals of goethite and are also present on the surface in the hydroxylated form. Chromate adsorption studies were carried out in the concentration range 0.25-2.01 mmol L⁻¹ at pH 3, 5 and 7, which show that maximum chromate is adsorbed at the lowest pH of 3 by both the samples of goethite. Effect of temperature on the adsorption of chromate, in the range 303-323 K, shows that the process of adsorption is endothermic in case of pure goethite and exothermic in case of Pb-doped goethite. The values of isosteric heat of adsorption were positive for pure goethite and negative for Pb-doped goethite, which are consistent with the effect of temperature on the process of adsorption. Langmuir isotherm was found applicable to the experimental data. FTIR analysis and equilibrium pH changes reveal that at pH 3 outersphere while at pH 5 and 7 innersphere complexation is the dominant mechanism for chromate adsorption by both the samples of goethite.     

关于克劳修斯方法对可逆和不可逆过程(循环)的处理

介绍了克劳修斯方法对可逆和不可逆过程(循环)的处理,提出了处理不可逆过程的方法,论证了处理方法与克劳修斯方程的一致性,论述了克劳修斯方法的实质和意义;简单介绍了熵的另一个导出方法,比较了两种方法对绝热过程的处理,指出克劳修斯方法存在一个假设条件.     

Exergy analysis of ramjet

An exergy analysis of possible regimes of energy supply to the air flow in the ramjet duct is carried out. A condition for the supply of a given heat amount to supersonic flow and a condition of the passage across the sound velocity are obtained for a duct with variable cross-sectional area. An analysis of the flow in a model ramjet duct at a pulsed-periodic energy supply is carried out. For a clear demonstration of possible schemes of heat supply in such a duct, a diagram in the temperature-exergy coordinates is proposed. A duct configuration in which the heat supply to supersonic flow is realized with regard for the limitation of the gas static temperature is proposed.     

Study of plasma technology for silicate refractory melts production

Herein the fundamentally new unit for production of silicate refractory melts with the use of high-concentrated heat fluxes is considered. Mathematical model describing temperature fields in skull layer in the process of the plasma flow interaction with the particles of refractory silicate material has been developed. Typical numerical results of temperature distribution in various sections of the skull layer are presented. Numerical and experimental data have been compared, and their fair agreement is obtained. The work was financially supported by RF President (Grant No. MK 1110.2008.8).     

Dependence of the critical heat flux at boiling on the coolant physical properties

It has been experimentally proved that heat transfer at boiling appears to be the problem with the conjugated boundary conditions. Heat transfer and critical heat fluxes at boiling depend both on physical properties of the boiling liquid and on the number of characteristics of the heat transferring wall. Various experimental data of the problem of boiling liquid with various physical properties have been analysed. To eliminate or minimize influence of the properties of the cooled wall on the value of critical heat transfer, the data obtained at boiling on the thick cooled wall only from the stainless steel or nichrome are considered. To eliminate effect of capillary forces specific linear size of heat transferring wall satisfied the condition ≥ 2.0.     

Mathematical modelling of complex heat transfer in a rectangular enclosure

Numerical simulation of convective-radiative heat transfer in an enclosure with a heat source in the presence of heat-conducting walls of the finite thickness was carried out. The distributions of both local (streamlines, temperature fields) and integral (mean Nusselt numbers at typical interfaces) characteristics describing specific features of the investigated process in a real range of the variation of determining parameters were obtained. The radiation influence scales at thermal modes formation were determined. The effect of transient factor on the fields development of both hydrodynamic and thermodynamic characteristics was analysed. Correlation ratios for determining the mean Nusselt number at solid-gas interfaces were obtained depending on the Grashof number. The work was financially supported by the Russian Foundation for Basic Research (Grant No. 08-08-00402-a).     

Magnetic properties of (Ce1−xLax)PdIn2

We report on results of X-ray powder diffraction, magnetization and specific heat measurements of the pseudo-ternary (Ce_1−xLa_x)PdIn₂ system with x=0; 0.2; 0.4 and 0.6. The results show a linear increase of the unit cell volume and a reduction of the ferromagnetic transition as La content increases. The Debye temperature, Sommerfeld coefficient and crystal field parameters were estimated from specific heat data, and are found to be weakly dependent of the Ce concentration. Also, the variation of magnetic entropy at T_C is only weakly dependent on x (ΔS≅0.92Rln2) indicating that T_K/T_C is approximately constant along the series. The T_C and T_K behaviors are explained by the variation of the exchange parameter due to the volume change when Ce is replaced by La. Our results indicate that the chemical pressure is the dominant effect rather than the chemical disorder for determining the physical proprieties of the (Ce_1−xLa_x)PdIn₂ system.     

Crystal electric field excitations in ferromagnetic CeTX compounds

A ferromagnetic ground state was identified for the compounds CeCuGe (T_C=10 K), CeCuSi (T_C=15 K) [F. Yang, et al., J. Appl. Phys. 69 (1991) 4705] and CeAuGe (T_C=10 K) [R. Pottgen, J. Magn. Magn. Mater. 152 (1996) 196]. The observed saturation magnetic moment values at low temperatures for all three compounds are considerably less than the theoretically expected value g_JJ=2.14μ_B for the free Ce³⁺ ion involving the entire six-fold J=5/2 multiplet, and thus provide a first indication of partial lifting of the f-electron level degeneracy in these compounds. Specific heat data yield crystal electric field (CEF) excitation energies (Δ_Sch) equivalent to 140 K for CeCuGe, 110 K for CeCuSi and 280 K for CeAuGe. To confirm the presence of CEF excitations directly, we have carried out inelastic neutron scattering (INS) measurements on all three compounds, using the HET spectrometer at ISIS Facility. Here, we present a detailed analysis of the INS spectra of CeCuSi on the basis of a CEF model and the detailed analysis of the INS of the other two compounds will be reported elsewhere.