Mixed convection nanofluid flow over a wedge
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Date
2023-07-26
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Department of Physics, OUAT, Bhubaneswar
Abstract
The present thesis examines boundary layer nanofluid flow over a wedge. The analytical results, which based on the assumption that the pressure gradient term is negligible in comparison to inertia and friction applies to the case of flat wall or surface parallel to uniform stream. In the case the wall or surface makes an angle ๐ฝ๐โ2 with the free stream,and then the free stream is accelerated along the x-axis which is measured from the tip of the surface. The flow which sweeps over so as to completely surround the surface making an angle ฮฒฯ is treated as inviscid (Velocity in the external flow changes so slow that viscous stresses are negligibly compared to surface shear stress). This type of flow is known as wedge flow. The inviscid flow outside the boundary layer is controlled by the balance between inertia and pressure gradient. The wedge can be a stationary wedge or non-stationary wedge. The study of many fluids over a stationary or non-stationary wedge is of the important research area in the field of fluid dynamics. The colloidal study past wedge geometry cannot be overlooked due to its extensive applications in many industrial, engineering zones. These comprised in thermal insulation, geothermal engineering, heat exchangers, and extraction of crude oil, etc. The flow of regular liquids or nanofluids over wedge geometry unlocks a new window for researchers and scientists. Therefore, researchers and scientists focused in this direction and extended the model day by day with new advances. At the outset we proposed a mathematical model for nanofluid flow over a wedge to study heat and mas transfer in presence of variable magnetic field, chemical reaction and
temperature dependent heat source. Normally researcher use internal heat generation in fluid flow analysis. In this investigation internal heat generation, which is an explicit function of local temperature in the boundary layer is taken into account. The study is completely theoretical and proposed model includes Brownian motion and thermophoresis to represent nanofluid flow. The partial differential equations relating to the flow under consideration are non-linear and hence are numerically solved after transforming them into ordinary differential equations using similarity variables. The outcome of analysis is first of all validated with previously published scientific work. The result shows an excellent agreement. The effects of physical parameters are depicted graphically. It is found that nanofluid flow along the surface of the wedge is accelerated by enhancing the Falkner-Skan parameter. The study further reveals that magnetic field has an improved effect on velocity of flow. Brownian motion has increasing effect on temperature and thermophoresis decreases concentration of nanofluid flow. Heat transfer results are interpreted physically considering the effect of temperature dependent heat source in the boundary layer. The effects are
separately discussed for positive ๐ฟ and negative ๐ฟ. For positive ๐ฟ there is a heat source in the boundary layer provided wall temperature is less than ambient and heat sink, when wall temperature exceeds the ambient temperature. This implies recombination and dissociation process in the boundary layer. In our second phase of investigation, we considered unsteady flow of viscous nanofluid over a wedge. This proposes model include combined effect of electric and magnetic field with time dependent chemical reaction. Interesting part of study is that the electrical conductivity of the medium is a power law function, which enables calculation of boundary layer thickness. Nanofluid flow includes Brownian motion and thermophoresis. Local similarity transformation is used to convert controlling partial differential equations into coupled higher order non-linear ordinary differential equations. These equations are numerically solved using an ODE boundary value solver. The results obtained are validated with previously published results and found an excellent agreement. The characteristics of physically interest quantities are depicted graphically. The quantities of technological interest are tabulated. A grid convergent test is performed to find the optimum grid size, which helps to achieve accurate results with minimum computational time. The simulation result reveals that maximum drop in the boundary layer thickness has occurred when power law index is zero.
In the third phase of investigation the thermodynamical aspect of viscous nanofluid flow over a non-isothermal wedge including the effects of non-linear radiation and activation energy is considered. Besides this the model incorporates Brownian motion and thermophoresis. Effects of thermodynamically important parameters like entropy generation number, Bejan number and augmentation entropy generation number have been discussed in great detail. This work discusses physical interpretation of heat transfer irreversibility and pressure drop irreversibility. The results are numerically computed using implicit Keller โBox method and depicted graphically. The mathematical formulation for thermal conductivity and viscosity are considered for augmentation entropy generation number in case of ๐ด๐2๐3 โ ๐ธ๐บnanofluid. We observed that adding nanoparticles tend to enhance augmentation entropy generation number. Again adding nanoparticles to the base fluid is effective only when the contribution of heat transfer irreversibility is more than fluid friction
irreversibility. The last phase of investigation describes significance of multiple slip with non-linear thermal radiation for a nanofluid flowing over a wedge. Normally liquid molecules slip at the solid surface for a length scale less than the mean free path of the molecules. Therefore, slip boundary conditions are useful to investigate fluid flow in nanoscale level. We have considered 1st and 2nd order slip conditions for velocity, temperature and concentration. Transport equations are converted into third order ODE and solved numerically using RungeKutta method. Velocity increases due to 1st order slip parameter but higher order slip parameter causes reduction in velocity. Both slip parameters tend to reduce volume fraction. Moreover, local heat transfer coefficient falls due to impact of higher order slip parameters.We have given emphasis to study nanofluid flow over a wedge with various physical quantities having applications in industry and technology. Nanofluid flows over wedge is applied in aerodynamics, power plants etc. This study finds wide applications in different cooling systems for effective heat removal. Further study can be discussed by considering hybrid nanofluid flow.