Effects of various configurations of an inserted corrugated conductive cylinder on MHD natural convection in a hybrid nanofluid-filled square domain

Journal of Thermal Analysis and Calorimetry - This paper aims to understand the characteristics of heat transfer and flow by natural convection of Al2O3–Cu/water-based hybrid nanofluid-filled...     

Natural convection flow from a continuously moving vertical surface immersed in a thermally stratified medium

 Natural convection boundary layer flow over a continuously moving isothermal vertical surface immersed in a thermally stratified medium has been investigated here. The non-linear coupled partial differential equations governing the non-similar flow have been solved numerically using an implicit finite difference scheme. For small values of the streamwise distance the partial differential equations are solved by using a perturbation expansion procedure and also using the Shanks transformation. The results indicate that the thermal stratification significantly affects both the surface shear stress and the surface heat transfer. The buoyancy parameter and the Prandtl number increase significantly, both the surface shear stress and heat transfer. Also the buoyancy force gives rise to an overshoot in the velocity profile. Received on 1 February 2000     

Entropy generation and MHD natural convection of a nanofluid in an inclined square porous cavity: Effects of a heat sink and source size and location

The effects of a heat sink and the source size and location on the entropy generation, MHD natural convection flow and heat transfer in an inclined porous enclosure filled with a Cu-water nanofluid are investigated numerically. A uniform heat source is located in a part of the bottom wall, and a part of the upper wall of the enclosure is maintained at a cooled temperature, while the remaining parts of these two walls are thermally insulated. Both the left and right walls of the enclosure are considered to be adiabatic. The thermal conductivity and the dynamic viscosity of the nanofluid are represented by different verified experimental correlations that are suitable for each type of nanoparticle. The finite difference methodology is used to solve the dimensionless partial differential equations governing the problem. A comparison with previously published works is performed, and the results show a very good agreement. The results indicate that the Nusselt number decreases via increasing the nanofluid volume fraction as well as the Hartmann number. The best location and size of the heat sink and the heat source considering the thermal performance criteria and magnetic effects are found to be D?=?0.7 and B?=?0.2. The entropy generation, thermal performance criteria and the natural heat transfer of the nanofluid for different sizes and locations of the heat sink and source and for various volume fractions of nanoparticles are also investigated and discussed.     

Hydromagnetic simultaneous heat and mass transfer by mixed convection from a vertical plate embedded in a stratified porous medium with thermal dispersion effects

The problem of steady, laminar, hydromagnetic simultaneous heat and mass transfer by mixed convection flow over a vertical plate embedded in a uniform porous medium with a stratified free stream and taking into account the presence of thermal dispersion is investigated for the case of power-law variations of both the wall temperature and concentration. Certain transformations are employed to transform the governing differential equations to a local similarity form. The transformed equations are solved numerically by an efficient implicit, iterative, finite-difference scheme. The obtained results are checked against previously published work on special cases of the problem and are found to be in excellent agreement. A parametric study illustrating the influence of the magnetic field, porous medium inertia effects, heat generation or absorption, lateral wall mass flux, concentration to thermal buoyancy ratio, and the Lewis number on the fluid velocity, temperature and concentration as well as the Nusselt and the Sherwood numbers is conducted. The results of this parametric study is shown graphically and the physical aspects of the problem are discussed. Received on 17 November 1998     

Double-diffusive natural convection in inclined porous cavities with various aspect ratios and temperature-dependent heat source or sink

Laminar double-diffusive natural convective flow of a binary fluid mixture in inclined square and rectangular cavities filled with a uniform porous medium in the presence of temperature-difference dependent heat generation (source) or absorption (sink) is considered. Transverse gradients of heat and mass are applied on two opposing walls of the cavity while the other two walls are kept adiabatic and impermeable to mass transfer. The problem is put in terms of the stream function-vorticity formulation. A numerical solution based on the finite-difference methodology is obtained for relatively high Lewis numbers. Representative results illustrating the effects of the inclination angle of the cavity, buoyancy ratio, Darcy number, heat generation or absorption coefficient and the cavity aspect ratio on the contour maps of the streamline, temperature, and concentration as well as the profiles of velocity, temperature and concentration at mid-section of the cavity are reported. In addition, numerical results for the average Nusselt and Sherwood numbers are presented for various parametric conditions and discussed.     

Generalized Plain Couette Flow and Heat Transfer in a Composite Channel

An analytical study of fluid flow and heat transfer in a composite channel is presented. The channel walls are maintained at different constant temperatures in such a way that the temperatures do not allow for free convection. The upper plate is considered to be moving and the lower plate is fixed. The flow is modeled using Darcy–Lapwood–Brinkman equation. The viscous and Darcy dissipation terms are included in the energy equation. By applying suitable matching and boundary conditions, an exact solution has been obtained for the velocity and temperature distributions in the two regions of the composite channel. The effects of various parameters such as the porous medium parameter, viscosity ratio, height ratio, conductivity ratio, Eckert number, and Prandtl number on the velocity and temperature fields are presented graphically and discussed.     

Et3B-mediated palladium-catalyzed direct allylic substitution reactions of Morita–Baylis–Hillman alcohols with aromatic amines

An efficient, direct allylic amination of both cyclic and acyclic Morita–Baylis–Hillman alcohols with aromatic amines, in tetrahydrofuran (THF) at room temperature, catalyzed by Pd(0)/Et₃B, is reported herein. The corresponding amines are obtained with a high α -regioselectivity in 65–87% yields.     

Experimental study of an earth-to-air heat exchanger coupled to the solar chimney for heating and cooling applications in arid regions

Journal of Thermal Analysis and Calorimetry - Arid regions around the world are characterized by hard summer and winter seasons, which leads to thermal discomfort. The southwest of Algeria is...     

Synergistic Effect of Polyoxometalate and Single Walled Carbon Nanotubes on Peroxidase‐like Mimics and Highly Sensitive Electrochemical Detection of Hydrogen Peroxide

A novel Keggin‐type metatungstate hybrid POMs ((APy)₆[H₂W₁₂O₄₀])/carboxylic acid functionalized single‐walled carbon nanotube based amperometric sensing platform was successfully constructed for the sensitive detection of hydrogen peroxide. A simple and reliable procedure was implemented for the synthesis of new composite materials obtained by the covalent grafting of (APy)₆[H₂W₁₂O₄₀] onto the surface of (SWCNT‐COOH). The synergistic effect of single walled carbon nanotubes on the electrochemical behavior of (APy)₆[H₂W₁₂O₄₀] was evidenced through the increase of the oxidation and reduction peaks of the polyoxometalate. The sensitivity of hydrogen peroxide detection was increased by a factor of 38.5 in presence of SWCNTs, showing their high influence on peroxidase‐like mimics of (APy)₆[H₂W₁₂O₄₀]. The detection limit, the response time, the repeatability and the shelf lifetime were respectively 0.4 μM, 10 s, <4%, 60 days.