Numerical study of chemical reaction effects in magnetohydrodynamic Oldroyd B oblique stagnation flow with a non-Fourier heat flux model

Reactive magnetohydrodynamic (MHD) flows arise in many areas of nuclear reactor transport. Working fluids in such systems may be either Newtonian or non-Newtonian. Motivated by these applications, in the current study, a mathematical model is developed for electrically-conducting viscoelastic oblique flow impinging on stretching wall under transverse magnetic field. A non-Fourier Cattaneo-Christov model is employed to simulate thermal relaxation effects which cannot be simulated with the classical Fourier heat conduction approach. The Oldroyd-B non-Newtonian model is employed which allows relaxation and retardation effects to be included. A convective boundary condition is imposed at the wall invoking Biot number effects. The fluid is assumed to be chemically reactive and both homogeneous-heterogeneous reactions are studied. The conservation equations for mass, momentum, energy and species (concentration) are altered with applicable similarity variables and the emerging strongly coupled, nonlinear non-dimensional boundary value problem is solved with robust well-tested Runge-Kutta-Fehlberg numerical quadrature and a shooting technique with tolerance level of 10−4. Validation with the Adomian decomposition method (ADM) is included. The influence of selected thermal (Biot number, Prandtl number), viscoelastic hydrodynamic (Deborah relaxation number), Schmidt number, magnetic parameter and chemical reaction parameters, on velocity, temperature and concentration distributions are plotted for fixed values of geometric (stretching rate, obliqueness) and thermal relaxation parameter. Wall heat transfer rate (local heat flux) and wall species transfer rate (local mass flux) are also computed and it is observed that local mass flux increases with strength of heterogeneous reactions whereas it decreases with strength of homogeneous reactions. The results provide interesting insights into certain nuclear reactor transport phenomena and furthermore a benchmark for more general CFD simulations

Determination of Soret coefficient and heat of transport in a binary liquid mixture using X-ray microscopy

With a laboratory built X-ray microscope, analysis of a thermal diffusion process in a KBr solution has been performed. A solution of a salt submitted to a constant temperature gradient gives rise to a stationary concentration gradient of the species after a few hours: this is the so called Soret effect. From the digital image of the liquid, acquired in the steady state of the process, it is easy to obtain the concentration map of the species in the solution. The average concentration profile then deduced permits to reach the value of the Soret coefficient and the heat of transport of the binary compound. X-ray radiography is an alternative powerful technique to analyse this kind of complicated phenomenon where composition matter fluxes are driven by both temperature and composition gradient

Influence of the surface mechanical attrition treatment (SMAT) on the corrosion behavior of Co28Cr6Mo alloy in Ringer’s solution

International audienceThe low carbon Co28Cr6Mo alloy used for artificial joints like hip and knee prostheses is subjected to a surface treatment called SMAT (surface mechanical attrition treatment). The purpose of this treatment is to modify the surface mechanical properties of the treated alloy. Since the SMAT impacts the surface of materials, its influence on the corrosion behavior of the CoCrMo alloy has to be assessed in a physiological solution as Ringer’s solution. Furthermore, a specific biomedical polishing is coupled with the SMAT in order to finalize the production of a hip prosthesis ready for use. The corresponding corrosion behavior is also studied. The corrosion behavior of CoCrMo alloy samples is investigated using electrochemical techniques (potentiodynamic polarization measurements and electrochemical impedance spectroscopy (EIS)) in physiological liquid and simulated by an equivalent circuit. The polarization results show the reduction of the corrosion current density and the increase of the corrosion potential after the SMAT. The EIS analyses also show the benefit of the SMAT on the corrosion resistance of the CoCrMo alloy. The surface morphology modification and the phase’s transformation induced by the SMAT are evaluated by scanning electron microscopy (SEM) and X-ray diffraction (XRD)