Mixed Convection of Water at 4°C Along a Wedge with Variable Surface Flux in a Porous Medium

In this study, the mixed convection of water at 4°C along a wedge in a porous medium is investigated numerically using finite difference method. In order to explore the effect of mixed convection, both forced and free convection-dominated regimes are considered. Non-similarity solutions are obtained for the variable wall flux boundary condition. Velocity and temperature profiles as well as local dimensionless skin friction and Nusselt number are obtained and compared with the available numerical results for various values of different parameters. The wedge angle geometry parameter m and mixed convection parameter ξ are ranged from 0 to 1 in both regimes whereas different values of λ are considered for the purpose of comparison of heat transfer results.     

A simple and facile route for the synthesis of 2H-1,4-benzoxazin-3-(4H)-ones via reductive cyclization of 2-(2-nitrophenoxy)acetonitrile adducts in the presence of Fe/acetic acid

A simple route for the synthesis of 1,4-benzoxazin-3-(4H)-ones is described herein. This method involves the reductive cyclization of 2-(2-nitrophenoxy)acetonitrile adducts in the presence of Fe/acetic acid in good to excellent yields. This system was compatible with various other functional groups.     

A ‘tree’ for generation and identification of the colour symmetry point groups

A flow chart (inverted ‘tree’) for generating and identifying the 58 magnetic and 18 polychromatic point groups using a classification for the 32 generating crystallographic point groups is suggested. The idea of colour generator is explored for generating the colour symmetry point groups. The advantages in presenting the identification of colour groups through a tree are discussed.     

On proper dissociation configurations of a molecule

An analytical procedure is presented for the determination of the proper dissociation configurations of a molecule. We illustrate this procedure by determining the proper dissociation configurations of many electronic states of the first-row diatomic molecules and ozone. Finally, a few simple guidelines are provided to help in the identification of the important configurations needed for proper dissociation of a molecule.     

Influence of protonation on physico-chemical properties of metal extractants

Summary The protonation constants of several metal extractants, especially hydroxamic acids have been determined by a solvent extraction method. The influence of the acidity on the solubility and the distribution ratio has been studied. A plot correlates the protonation behaviour of these metal extractants with the Hammett Acidity Function, H_o. The protonation constant is useful to explain the acid catalysed hydrolysis rate of these metal extractants and to determine the extraction coefficients of their metal chelates.     

Instabilities and transition in boundary layers

Some recent developments in boundary layer instabilities and transition are reviewed. Background disturbance levels determine the instability mechanism that ultimately leads to turbulence. At low noise levels, the traditional Tollmien-Schlichting route is followed, while at high levels, a ‘by-pass’ route is more likely. Our recent work shows that spot birth is related to the pattern of secondary instability in either route.     

Free convection from a vertical plate with nonuniform surface heat flux and embedded in a porous medium

An analysis is presented for the calculation of heat transfer due to free convective flow along a vertical plate embedded in a porous medium with an arbitrarily varying surface heat flux. By applying the appropriate coordinate transformations and the Merk series, the governing energy equation is expressed as a set of ordinary differential equations. Numerical solutions are presented for these equations which represent universal functions and several computational examples are provided.     

Sonic discontinuities in a relaxing gas

Following Elcrat [1] the phenomena associated with the sonic discontinuities in non-equilibrium gasdynamics have been studied here. The sonic wave in non-equilibrium gaseous medium propagates with the frozen speed of sound. The magnitude of discontinuities of the first derivatives of flow quantities in the unsteady flow of relaxing gas are shown to satisfy Riccatti equations along the orthogonal trajectories of surface S(t). In order to integrate them in full generality, they are transformed to an equation along the bicharacteristic curve in the characteristic manifold S(t). These equations have been solved completely. The criteria for decay or blow up of sonic discontinuities are given and the particular cases of plane and spherical waves existing in an ideal dissociative gasdynamics have been discussed. In the case of planewave for uniform propagation, it is shown that the dissociating character of the gas is to decrease the critical time. Other cases of shock formation have been studied in detail.