Defect and Diffusion Forum Vol. 399

Abstract: Experimental and numerical consideration is given in the present work to an inline, inclined triple elliptic jet-group discharged in cross flow, a common configuration widely present in several domains, namely environmental, industrial and even medical. The experiments were described by particle image velocimetry and hot wire anemometry measurements, and the numerical simulation was based upon the finite volume method together with a non uniform grid system tightened close to the discharging nozzles. Generally, optimizing similar configurations is meant to reach optimum mixings in terms of heat and/or mass transfers. The present work will be particularly dedicated to the heat transfers generated within the examined multiple jet in cross flow configuration, for jets emitted under an injection height equivalent to , and under a variable injection ratio. After presenting the handled geometry, a validation of the numerical model is proposed. Afterward, a discussion of the reduced static temperature is presented. This is a highly interesting parameter due to its closeness, if not similarity under some circumstances, to the cooling efficiency.

Abstract: The classical concept of diffusion characterized by Fick’s law is well suited for describing a wide class of practical problems of interest. Nevertheless, it has been observed that it is not enough to properly represent other relevant applications of practical interest. When in a system of particles their spreading is slower or faster than predicted by the classical diffusion model, such a phenomenon is referred to as anomalous diffusion. Time fractional, space fractional and even space-time fractional equations are widely used to model phenomena such as solute transport in porous media, financial modelling and cancer tumor behavior. Considering the effects of partial and temporary retention in dispersion processes a new analytical formulation was derived to simulate anomalous diffusion. The new approach leads to a fourth-order partial differential equation (PDE) and assumes the existence of two concomitant fluxes. This work investigates the behavior of the bi-flux approach in one dimensional (1D) medium evaluating the mean square displacement for different cases in order to classify the diffusion process in normal, sub-diffusive or super-diffusive.

Abstract: Nanofluids, which are suspensions of nanoparticles dispersed in a base fluid, have remarkable potential in a wide range of applications. However, the stability of the nanofluid has remained a challenge and a matter of concern. A lot of research, development work and reviews have been conducted on the preparation and stability of nanofluids. In this study, calculation of solubility parameter values using a molecular modelling software were performed to aid the screening of nanoparticles that are compatible with the base fluid. The solubility parameter is the numerical representation of the solvency behavior between two molecules. A molecular modelling software was used to study the solubility parameter values of nanoparticles to determine their compatibility with the base fluids. To validate the model, the computed values were compared against published literature and it was shown that the model has achieved more than 95% accuracy. The simulations were verified with experimental work with varying concentration of nanoparticles in brine solution and deionized water. Experimental results showed that zinc oxide nanoparticles demonstrated the best compatibility with the base fluid, which tally with the simulation.

Abstract: Mixed convection of unsteady non-coaxial rotation flow of viscous fluid over an accelerated vertical disk is investigated. The motion in the fluid is induced due to the rotating and buoyancy force effects. The problem is formulated and extended in terms of coupled partial differential equations with some physical boundary and initial conditions. The non-dimensional equations of the problem are obtained by using the suitable non-dimensional variables. The exact solutions of non-coaxial velocity and temperature profiles are obtained by using Laplace transform method which are satisfying all the initial and boundary conditions. The physical significance of the mathematical results is shown in various plots and is discussed for Grashof and Prandtl numbers as well as magnetic, porosity and accelerated parameters. It is found that, the velocity with the effect of acceleration is higher compared to constant velocity. In limiting sense, the present solutions are found identical with published results.

Abstract: This study presents a numerical investigation on the magnetohydrodynamic (MHD) stagnation point flow of a ferrofluid with Newtonian heating. The black oxide of iron, magnetite (Fe₃O₄) which acts as magnetic materials and water as a base fluid are considered. The two dimensional stagnation point flow of cold ferrofluid against a hot wall under the influence of the uniform magnetic field of strength is located some distance behind the stagnation point. The effect of magnetic and volume fraction on the velocity and temperature boundary layer profiles are obtained through the formulated governing equations. The governing equations which are in the form of dimensional non-linear partial differential equations are reduced to dimensionless non-linear ordinary differential equations by using appropriate similarity transformation. Then, they are solved numerically by using the Keller-box method which is programmed in the Matlab software. It is found that the cold fluid moves towards the magnetic source that is close to the hot wall. Hence, leads to the better cooling rate and enhances the heat transfer rate. Meanwhile, an increase of the magnetite nanoparticles volume fraction, increases the ferrofluid capabilities in thermal conductivity and consequently enhances the heat transfer.

Abstract: The second order equation (also known as Fick’s equation) is derived from a classical well-known theory, but it is not enough to model all applications of interest. Recently, fractional equations and higher order equations began to receive more attention, demanding increased research efforts. They are used to simulate the diffusion process in many important applications in sciences, such as chemistry, heat and mass transfer, biology and ecology. In this work, the sensitivity analysis is performed for a recently developed anomalous diffusion model in order to evaluate the possibility of estimating a set of parameters that are part of the fourth order equation model, including the parameters representing the variation of the fraction of particles that are allowed to diffuse using a sigmoid function. Finally, after the sensitivity analysis the Inverse Problem approach is used to estimate viable parameters that are necessary for simulation in the cases considered. The differential equation was approximated using the Finite Difference Method, and that solution was implemented in the RStudio platform. The Sensitivity Matrix was calculated and the Inverse Problem was solved using the same RStudio platform, and the Simulated Annealing Method.

Abstract: The investigation on the interaction between solid and fluid under combined convective flow has been carried out mathematically. The Jeffrey fluid model is taken as the fluid phase and the model is being embedded with the dust particles (solid phase). This two-phase model is constructed by introducing the fluid-particles interaction forces in the momentum equations of the fluid and dust phases, respectively. The natural and forced convections together with the aligned magnetic field are considered on the fluid flow. Also, the Newtonian heating as thermal boundary condition is induced on the vertical stretching sheet. In order to reduce the complexity of the model, the governing equations are transformed from partial differential equation into ordinary differential equation via suitable similarity transformation. The solutions are obtained in terms of velocity and temperature profiles for the fluid and particles phases respectively whereby the Keller-box method is utilized to obtain the desired outcomes. The influences of several significant physical parameters are visualized graphically to clarify the flow and heat transfer characteristic for both phases. The investigation found that the fluid’s velocity is affected by the presence of the dust particles which led to decelerate the fluid transference. The present flow model is able to be compared with the single-phase fluid cases if the fluid-particle interaction parameter is ignored.

Abstract: The analysis of the hydro-elastic interactions of the covering membrane of fluid-filled cavities or containers has a main importance due to the solution of practical problems founded in engineering applications. In this paper the dynamic behaviour of the bottom membrane of a rectangular container filled with a non-viscous and incompressible fluid is analyzed. The fluid velocity potential is obtained first by applying a method of separation of variables and afterwards the pressure field is calculated with the momentum’s linearized equation. Taking into account the deformation equation for the membrane in contact with the fluid and by applying a discretization procedure to the associated generalized work equation, a system is obtained, for the calculus of the membrane frequencies of vibration. The influence of different geometrical parameters such as dimension, aspect ratio, container relative height, relative thickness as well as the fluid density on these frequencies is analysed. Validation of the method is made by comparing the results with those obtained by other authors and theories.

Abstract: Significant research is being conducted in the simulation of fluid flows due to the increase in employing the physics of the fluid flow to either commercial, in-house or open source codes. The analysis of the fluid flow is mainly based on the Lagrangian or the Eulerian approach. Many of the simulation codes employ the Eulerian approach due to its simplicity. These codes are based on several numerical techniques and yet few benchmarks have been conducted. However, the codes which employ the Lagrangian approach seem to be promising and may accurately simulate fluid flow phenomena. In this paper, a comparative analysis of the Lagrangian and Eulerian approach is investigated for a water droplet in a tank. The velocity field and the total pressure of the fluid are generated for the simulation by employing Ansys Fluent for the Eulerian approach and DualPhysics for the Lagrangian approach. The fluid structure and the fluid flow development are compared in order to assess the capability of each approaches in analysing the investigated fluid flow. This study may play a significant role on the importance of employing the Lagrangian approach for fluid flows where complex fluid structure occurs.