Band 76, Heft 7

The current study addresses the influences of Brownian motion and thermophoretic force on non-Newtonian fluid flow. Eyring–Powell fluid serves as the base fluid for heat and mass transfer through a porous channel. Buongiorno model for nanofluid is incorporated into the convection–diffusion equation to investigate the random motion of tiny spherical particles. Additional contributions of viscous dissipation and thermal radiation have also been applied by formulating two different types of flows. A system of nonlinear coupled differential equations is solved with the help of the “regular perturbation method”. For the limiting case, a numerical solution is obtained to validate the computational results with existing literature and it is found to be in complete agreement. Eventually, it is inferred that the heat transfer rate dominates in nanofluid flow due to the moving plate, while the mass transfer is more prominent in generalized Couette nanoflow of Eyring–Powell fluid.

In this study, we have constructed a viable cosmological model characterized by the presence of the Gauss–Bonnet four-dimensional invariant, higher-order corrections to the low energy effective action motivated from heterotic superstring theory and a general exponential potential comparable to those obtained in higher dimensional supergravities. The field equations were studied by assuming a particular relation between the Hubble parameter and the time derivative of the scalar field. It was observed that, for specific relations between the free parameters in the theory, the universe is cyclic, expands and contracts alternately without singularity with an equation of state oscillating around −1. The model is found to fit the recent astrophysical data.

The thermal entrance problem (also known as the classical Graetz problem) is studied for the complex rheological Carreau fluid model. The solution of two-dimensional energy equation in the form of an infinite series is obtained by employing the separation of variables method. The ensuing eigenvalue problem (S–L problem) is solved for eigenvalues and corresponding eigenfunctions through MATLAB routine bvp5c. Numerical integration via Simpson’s rule is carried out to compute the coefficient of series solution. Current problem is also tackled by an alternative approach where numerical solution of eigenvalue problem is evaluated via the Runge–Kutta fourth order method. This problem is solved for both flat and circular confinements with two types of boundary conditions: (i) constant wall temperature and (ii) prescribed wall heat flux. The obtained results of both local and mean Nusselt numbers, fully developed temperature profile and average temperature are discussed for different values of Weissenberg number and power-law index through graphs and tables. This study is valid for typical range of Weissenberg number We≤1$\left(We\le 1\right)$ and power-law index n<1$\left(n{< }1\right)$ for shear-thinning trend while n>1$\left(n{ >}1\right)$ for shear-thickening behaviour. The scope of the present study is broad in the context that the solution of the said problem is achieved by using two different approaches namely, the traditional Graetz approach and the solution procedure documented in M. D. Mikhailov and M. N. Ozisik, Unified Analysis and Solutions of Heat and Mass Diffusion, New York, Dover, 1994.

In the present work, semiconducting cadmium sulfide (CdS) nanoparticles have been synthesized by co-precipitation method. X-ray diffraction (XRD), UV–visible (UV/Vis) absorption spectroscopy, and high-resolution transmission electron microscopy (HRTEM) have been used for the characterization of the synthesized nanoparticles. Two-step technique has been used to formulate stable polyvinyl alcohol (PVA)-based CdS nanofluids at room temperature. Thermal conductivities of nanofluids at different temperatures have been measured using Hot Disc Thermal Constants Analyzer. Significant enhancement in thermal conductivity is noted at very low nanoparticle loading. Ultrasonic velocity and ultrasonic attenuation in the prepared nanofluids have been investigated using ultrasonic interferometer and Acoustic Particle Sizer (APS-100), respectively. APS-100 has been also used for the analysis of particle size distribution (PSD) of CdS nanoparticles in the prepared nanofluids. The PSD result of APS-100 is in good agreement with that of HRTEM. The characteristic behavior of CdS nanofluid is illustrated on the basis of its ultrasonic and thermal properties. The thermal conductivity enhancement increases with the temperature and reaches up to 61.6% for 1.0 wt% particle loadings at 80 °C. Our analysis shows that CdS nanofluids have potential application for effective heat transfer management in various cooling industries.

The present work is focused on the determination of elastic, mechanical, ultrasonic and thermal properties of ScRu intermetallic under the variation of pressure 0–60 GPa and particle size 5–40 nm. Initially, the second order elastic constants (SOECs) have been computed under a potential model approach, in which interaction potential is defined by Coulomb and Born–Mayer potentials. Later on, the estimation of mechanical, ultrasonic and thermo-physical parameters has been performed using SOECs. The ultrasonic velocities are estimated in the same pressure/particle size range for wave propagation along 〈100〉 crystallographic direction. It is found that elastic constants, ultrasonic velocities, Debye average velocity, specific heat at constant volume, thermal energy density, thermal conductivity and melting point enhance with increase in pressure and decay in particle size in chosen intermetallic. The analysis of the obtained results reveals that the elastic, mechanical and thermal properties of ScRu intermetallic shall enhance effectively under pressure in comparison to decay in particle size.

The two-parameter van der Waals (vdW) equation of state is generalized, by adding another two parameters to the attractive term. General relations between thermodynamic functions of the generalized vdW equation and the hard sphere gas are derived. The cubic equation of the generalized vdW is solved and the critical points ( P c , V c , T c ) are obtained for general k . The critical properties of the vdW real gas such as the isothermal compressibility K T , the isobaric expansion coefficient α and the isobaric heat capacity C P are calculated exactly. The temperature dependence of K T , α and C P is investigated close to the critical point on the critical isobar path P r = 1( P = P c ). Numerical calculations for K T and C P are presented above and below P r .

According to classical and statistical thermodynamics, a well-mixed fluid mass has a uniform temperature and is at thermodynamic equilibrium. It independent of the gravitational field. However, large well-mixed fluid masses, for example, in atmospheres and oceans, often are isentropic. One has attributed that to the influence of gravity. This has raised the question if such masses can go to a different restricted thermodynamic equilibrium with uniform entropy. Discussions on this issue have continued for three centuries without finding a final answer. This paper presents another analysis of the question if a fluid mass under the influence of gravity may go to a restricted equilibrium state with uniform entropy. At first, it analyses previous work as a background study. Then, it describes a kinetic model for the motion of fluid parcels in a vertical fluid column. This model is the tool for studying if and how the column may go to an isentropic equilibrium. The kinetic model supports the hypothesis that a fluid column under the influence of gravity may go to a restricted equilibrium state with an isentropic temperature profile. A statically unstable column can reach that state spontaneously, while its entropy increases and gravitational potential energy decreases. The latter energy is the source of the kinetic energy for the motion of its fluid parcels, driving the internal heat transfer that results in the isentropic profile.