Entrance Region Of Annuli Research Articles

Core Variation in the Entrance Region Flow of Casson Fluid in an Annuli

The entrance region flow of a Casson fluid in an annular cylinder has been investigated numerically without making prior assumptions on the form of velocity profile within the boundary layer region, which is determined by a cross sectional integration of the momentum differential equation for a given distance from the channel entrance. Using the macroscopic mass balance equation, the thickness of the core has been obtained at each cross section of entrance region of annuli for different values of Casson number and for various values of aspect ratio.

Developing laminar flow in the entrance region of annuli—Review and extension of standard resolution methods for the hydrodynamic problem

This paper deals with the theoretical and numerical resolution of the laminar axial developing flow in annuli. In the first part of the article, a review of the different methods of the hydrodynamic problem resolution is given. We have then extended some of the methods performed for circular ducts to annular geometry. In particular we have developed a numerical solution of the complete Navier-Stokes equations, for studying the axial momentum diffusion effect on the flow structure. In the second part of this paper we have compared the results obtained with the different methods and analysed the hydrodynamics characteristics (velocity, pressure distribution and entrance length) as a function of the annular flow parameters (radii ratio, Reynolds number and axial distance from the entrance).

Entrance region flow of blood in concentric annulus

Flow characteristics of blood obeying Casson's stress-strain relation have been investigated in the entrance region of annuli. Application of momentum-integral technique to the governing equations of flow leads to the solution of a system of two nonlinear ordinary differential equations which has been solved numerically using Runge-Kutta method. Casson fluid possesses an yield value, therefore there is a plug core formation away from the walls. The problem has been analysed by considering the two boundary layer flow regions separated by the plug core formation. Variation of the boundary layer thickness, plug core velocity, pressure drop, entrance length and the correction factor for friction-loss have been determined for all admissible yield values and for all admissible values of the aspect ratio. Assigning particular values to the aspect ratio, the corresponding results for entrance region flow in a tube and parallel-plate channel have been obtained. Calculations have been made for yield value equal to zero to get the corresponding results for a Newtonian fluid. Comparisons have been made with the available numerical solution for a Casson fluid and also for a Bingham fluid for a particular yield value. The analysis may lead to a better understanding for the flow characteristics and anomalies of blood which may be of interest in the membrane oxygenators and may help in the diagnosis of cardiovascular diseases and possibly in their treatment.

Flow behavior of power‐law fluids in the entrance region of annuli

AbstractMomentum‐integral and momentum‐energy‐integral methods are used to study the laminar entrance behaviour of power‐law fluids in annuli. The momentum‐energy method, which yields a longer entry length, appears to provide a better overall description of the entry flow behaviour. The method compares favourably with the existing Newtonian solutions for annular flow and with the non‐Newtonian flow in pipes and parallel plates in the limiting cases. The linearisation technique is also extended to power law fluids utilising the geometric parameter method. The loss coefficients predicted by the linearisation technique agree well with those obtained by the integral methods.