Mixed Convection Boundary-Layer Flow Along a Vertical Cylinder Embedded in a Porous Medium Filled by a Nanofluid

The steady mixed convection boundary-layer flow on a vertical circular cylinder embedded in a porous medium filled by a nanofluid is studied for both cases of a heated and a cooled cylinder. The governing system of partial differential equations is reduced to ordinary differential equations by assuming that the surface temperature of the cylinder and the velocity of the external (inviscid) flow vary linearly with the axial distance x measured from the leading edge. Solutions of the resulting ordinary differential equations for the flow and heat transfer characteristics are evaluated numerically for various values of the governing parameters, namely the nanoparticle volume fraction ${\phi}$ , the mixed convection or buoyancy parameter ?? and the curvature parameter ??. Results are presented for the specific case of copper nanoparticles. A critical value ?? _c of ?? with ?? _c <?0 is found, with the values of | ?? _c| increasing as the curvature parameter ?? or nanoparticle volume fraction ${\phi}$ is increased. Dual solutions are seen for all values of ?? >??? _c for both aiding, ?? >?0 and opposing, ?? <?0, flows. Asymptotic solutions are also determined for both the free convection limit ${(\lambda \gg 1)}$ and for large curvature parameter ${(\gamma \gg 1)}$ .     

Unsteady mixed convection boundary-layer flow with suction and temperature slip effects near the stagnation point on a vertical permeable surface embedded in a porous medium

The unsteady mixed convection boundary-layer flow near the two-dimensional stagnation point on a vertical permeable surface embedded in a fluid-saturated porous medium with suction and a temperature slip effect is studied numerically. Similarity equations are obtained through the application of a similarity transformation technique. The shooting method is used to solve these similarity equations for different values of the mixed convection, wall mass suction, the unsteadiness and the slip parameters. Results show that multiple solutions exist for certain ranges of these parameters. Some limiting forms are then discussed, namely strong suction, the free convection limit, the situation when there is a large temperature slip and when the time dependence dominates.     

On the Temperature Slip Boundary Condition in a Mixed Convection Boundary-Layer Flow in a Porous Medium

A problem derived previously (Rohni et?al., Transp Porous Media 92:1?C14, 2012) for unsteady mixed convection flow in a porous medium involving a ??temperature slip?? boundary condition and fluid transfer through the boundary is considered. It is shown that the solution to this problem can be directly related to the solution of the corresponding problem for a prescribed surface temperature, involving a mixed convection parameter ??, an unsteadiness parameter A and transpiration parameter s. This latter problem is discussed in detail, particular attention being given to the steady analogue, A?=?0, allowing for fluid transfer through the surface, and to the unsteady problem, A?>?0, for an impermeable surface, s?=?0. Asymptotic results are obtained for large fluid transfer rates, ${s \gg 1}$ and ${s <0 , |s| \gg 1}$ and for large A. Particular attention is given to deriving asymptotic results for the critical points which determine the range of existence of solutions.     

In vitro assessment of pediococci- and lactobacilli-induced cholesterol-lowering effect using digitally enhanced high-performance thin-layer chromatography and confocal microscopy

The cholesterol-lowering properties of 12 lactic acid bacteria (LAB) in the absence or presence of 0.3% bile salts were assessed and compared quantitatively and qualitatively in vitro. A new, more sensitive and cost-effective high-performance thin-layer chromatography method combined with digital image evaluation of derivatised chromatographic plates was developed and validated to quantify cholesterol in LAB culture media. The performance of the method was compared with that of the o-phthalaldehyde method. For qualitative assessment, assimilated fluorescently tagged cholesterol was visualised by confocal microscopy. All LAB strains exhibited a cholesterol-lowering effect of various degrees (19–59% in the absence and 14–69% in the presence of bile salts). Lactobacillus plantarum LAB12 and Pentosaceus pentosaceus LAB6 were the two best strains of lactobacilli and pediococci. They lowered cholesterol levels by 59% and 54%, respectively, in the absence and by 69% and 58%, respectively, in the presence of bile salts. Confocal microscopy showed that cholesterol was localised at the outermost cell membranes of LAB12 and LAB6. The present findings warrant in-depth in vivo study.

(A) 3D plots based on scan at 525 nm of (B) derivatized HPTLC plate of separated cholesterol and (C) confocal microscopic image showing the localisation of NBD-cholesterol assimilated by LAB

     

A Further Note on the Unsteady Mixed Convection Boundary Layer in a Porous Medium with Temperature Slip: An Exact Solution

The aim of this Letter is to show that a further exact solution of the problem on unsteady mixed convection boundary layer in a porous medium with temperature slip can be obtained in addition of that reported very recently by Fang et al. (2012).