Unstable Forced Convection in a Plane Porous Channel With Variable-Viscosity Dissipation

2015 ◽  
Vol 138 (3) ◽  
Author(s):  
A. Barletta ◽  
M. Celli ◽  
A. V. Kuznetsov ◽  
D. A. Nield
Keyword(s):  
Forced Convection ◽  
Flow Instability ◽  
Variable Viscosity ◽  
Wave Number ◽  
Porous Channel ◽  
Temperature Dependent Viscosity ◽  
Longitudinal Modes ◽  
Small Wave Number ◽  
Dependent Viscosity ◽  
Biot Numbers

Fully developed and stationary forced convection in a plane-parallel porous channel is analyzed. The boundary walls are modeled as impermeable and subject to external heat transfer. Different Biot numbers are defined at the two boundary planes. It is shown that the combined effects of temperature-dependent viscosity and viscous heating may induce flow instability. The instability takes place at the lowest parametric singularity of the basic flow solution. The linear stability analysis is carried out analytically for the longitudinal modes and numerically for general oblique modes. It is shown that longitudinal modes with vanishingly small wave number are selected at the onset of instability.

Laminar Forced Convection of Liquids in Tubes With Variable Viscosity

1962 ◽  
Vol 84 (4) ◽  
pp. 353-361 ◽  
Author(s):  
Kwang-Tzu Yang
Keyword(s):  
Forced Convection ◽  
Variable Viscosity ◽  
Step Change ◽  
Temperature Dependent Viscosity ◽  
Nusselt Numbers ◽  
Friction Factors ◽  
Tube Wall Temperature ◽  
Integral Procedure ◽  
Dependent Viscosity ◽  
Laminar Forced Convection

Analytical solutions for laminar forced convection of liquids flowing in circular tubes with temperature-dependent viscosity are obtained for both step change in tube-wall temperature and step change in wall heat flux by using an improved integral procedure. The accuracy of this analytical procedure is demonstrated by comparing results for the isothermal problems with that from the exact solutions. Results for the nonisothermal cases are presented in graphical forms in terms of Nusselt numbers, velocity variations at tube center line, and friction factors. Tabulated Nusselt numbers are also given.

Modulation of turbulence in forced convection by temperature-dependent viscosity

2012 ◽  
Vol 697 ◽  
pp. 150-174 ◽  
Author(s):  
Francesco Zonta ◽  
Cristian Marchioli ◽  
Alfredo Soldati
Keyword(s):  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Forced Convection ◽  
Variable Viscosity ◽  
Water Channel ◽  
Temperature Dependent ◽  
Temperature Dependent Viscosity ◽  
Systematic Analysis ◽  
Anisotropic Temperature ◽  
Dependent Viscosity

AbstractIn this work, we run a numerical experiment to study the behaviour of incompressible Newtonian fluids with anisotropic temperature-dependent viscosity in forced convection turbulence. We present a systematic analysis of variable-viscosity effects, isolated from gravity, with relevance for aerospace cooling/heating applications. We performed an extensive campaign based on pseudo-spectral direct numerical simulations of turbulent water channel flow in the Reynolds number parameter space. We considered constant temperature boundary conditions and different temperature gradients between the channel walls. Results indicate that average and turbulent fields undergo significant variations. Compared with isothermal flow with constant viscosity, we observe that turbulence is promoted in the cold side of the channel, characterized by viscosity locally higher than the mean: in the range of the examined Reynolds numbers and in absence of gravity, higher values of viscosity determine an increase of turbulent kinetic energy, whereas a decrease of turbulent kinetic energy is determined at the hot wall. Examining in detail the turbulent kinetic energy budget, we find that turbulence modifications are associated with changes in the rate at which energy is produced and dissipated near the walls: specifically, at the hot wall (respectively cold wall) production decreases (respectively increases) while dissipation increases (respectively decreases).

Elastic Effects on Rayleigh-Be´nard-Marangoni Convection in Liquids With Temperature-Dependent Viscosity

2009 ◽  
Author(s):  
G. N. Sekhar ◽  
G. Jayalatha
Keyword(s):  
Stress Relaxation ◽  
Variable Viscosity ◽  
Relaxation Parameter ◽  
Oscillatory Convection ◽  
Tight Coupling ◽  
Temperature Dependent ◽  
Temperature Dependent Viscosity ◽  
Dependent Viscosity ◽  
Viscoelastic Liquids ◽  
Retardation Parameter

A linear stability analysis of convection in viscoelastic liquids with temperature-dependent viscosity is studied using normal modes and Galerkin method. Stationary convection is shown to be the preferred mode of instability when the ratio of strain retardation parameter to stress relaxation parameter (elasticity ratio) is greater than unity. When the ratio is less than unity the possibility of oscillatory convection is shown to arise. Oscillatory convection is studied numerically for Rivlin-Ericksen, Walters B′, Maxwell and Jeffreys liquids by considering free-free and rigid-free isothermal/adiabatic boundaries. It is found that there is a tight coupling between the Rayleigh and Marangoni numbers, with an increase in one resulting in a decrease in the other. The effect of variable viscosity parameter is shown to destabilize the system. The problem reveals the stabilizing nature of strain retardation parameter and destabilizing nature of stress relaxation parameter, on the onset of convection. The Maxwell liquids are found to be more unstable than the one subscribing to Jeffreys description whereas the Rivlin-Ericksen and Walters B′ liquids are comparatively more stable. Rigid-free adiabatic boundary combination is found to give rise to a most stable system, whereas the free isothermal free adiabatic combination gives rise to a most unstable system. The problem has applications in non-isothermal systems having viscoelastic liquids as working media.

Flow of a Third Grade Fluid between Coaxial Cylinders with Variable Viscosity

2009 ◽  
Vol 64 (9-10) ◽  
pp. 588-596 ◽  
Author(s):  
Muhammad Y. Malik ◽  
Azad Hussain ◽  
Sohail Nadeem ◽  
Tasawar Hayat
Keyword(s):  
Variable Viscosity ◽  
Heat Transfer Analysis ◽  
Third Grade ◽  
Third Grade Fluid ◽  
Temperature Dependent ◽  
Temperature Dependent Viscosity ◽  
Coaxial Cylinders ◽  
Homotopy Analysis ◽  
Grade Fluid ◽  
Dependent Viscosity

The influence of temperature dependent viscosity on the flow of a third grade fluid between two coaxial cylinders is carried out. The heat transfer analysis is further analyzed. Homotopy analysis method is employed in finding the series solutions. The effects of pertinent parameters have been explored by plotting graphs.

scholarly journals Effect of Porous Medium and Copper Heat Sink on Cooling of Heat-Generating Element

Energies ◽  
2020 ◽  
Vol 13 (10) ◽  
pp. 2538 ◽  
Author(s):  
Marina Astanina ◽  
Mikhail Sheremet ◽  
U. S. Mahabaleshwar ◽  
Jitender Singh
Keyword(s):  
Energy Transport ◽  
Cooling System ◽  
Variable Viscosity ◽  
Optimal Number ◽  
Working Fluid ◽  
Heat Conducting ◽  
Temperature Dependent ◽  
Temperature Dependent Viscosity ◽  
Negative Effect ◽  
Dependent Viscosity

Cooling of heat-generating elements is a challenging problem in engineering. In this article, the transient free convection of a temperature-dependent viscosity liquid inside the porous cavity with copper radiator and the heat-generating element is studied using mathematical modeling techniques. The vertical and top walls of the chamber are kept at low constant temperature, while the bottom wall is kept adiabatic. The working fluid is a heat-conducting liquid with temperature-dependent viscosity. A mathematical model is developed based on dimensionless stream function, vorticity, and temperature variables. The governing properties are the variable viscosity, geometric parameters of the radiator, and size of thermally insulated strip on vertical surfaces of the cavity. The effect of these parameters on the energy transport and circulation patterns are analyzed numerically. Based on the numerical results obtained, recommendations are given on the optimal values of the governing parameters for the effective operation of the cooling system. It is shown that the optimal number of radiator fins for the cooling system configuration under consideration is 3. In addition, the thermal insulation of the vertical walls and the increased thickness of the radiator fins have a negative effect on the operation of the cooling system.

scholarly journals Temperature-Dependent Viscosity and Nanoparticle Effect on Wire Coating Using Third-Grade As a Polymer Liquid With Magnetic Field Flow Within Porous Die

2021 ◽  
Author(s):  
Zeeshan Khan ◽  
Prof. Dr. Ilyas Khan
Keyword(s):  
Numerical Solutions ◽  
Volume Fraction ◽  
Variable Viscosity ◽  
Numerical Technique ◽  
Wall Stress ◽  
Third Grade ◽  
Shear Forces ◽  
Temperature Dependent Viscosity ◽  
Wire Coating ◽  
Dependent Viscosity

Abstract The convective heat and mass propagation inside dies are used to determine the characteristics of coated wire products. As a result, comprehending the properties of polymerization mobility, heat mass transport, and wall stress concentration is crucial. The wire coating procedure necessitates an increase in thermal performance. As a result, this research aims to determine how floating nanoparticles affect the mass and heat transport mechanisms of third-grade fluid in the posttreatment for cable coating processes. For nanofluids, the Buongiorno model is used, including variable viscosity. The model equations are developed using continuity, momentum, energy, and nanoparticle volume fraction concentration. We propose a few nondimensional transformations that are relevant. The numerical technique Runge-Kutta fourth method is used to generate numerical solutions for nonlinear systems. Pictorial depictions are used to observe the influence of various factors in the nondimensional flow, radiative, and nanoparticle concentration fields. Furthermore, the numerical results are also verified analytically using Homotopy Analysis Method (HAM). The analytical findings of this investigation revealed that within the Reynolds modeling, the stress on the whole wire surface combined with shear forces at the surface predominates Vogel's model. The contribution of nanomaterials upon force on the entire surface of wire and shear forces at the surface appears positive. A non-Newtonian feature can increase the capping substance's velocity. This research could aid in the advancement of wire coating technologies.For the first instance, the significance of nanotechnology during wire coating evaluation is explored utilizing Brownian motion with generation/absorption slip processes. For time-dependent viscosity, two alternative models are useful.

Steady Fully Developed Mixed Convection Flow in a Vertical Channel with Heat and Mass Transfer and Temperature-Dependent Viscosity: An Exact Solution

2019 ◽  
Vol 74 (3) ◽  
pp. 235-244 ◽  
Author(s):  
Basant K. Jha ◽  
Michael O. Oni
Keyword(s):  
Exact Solution ◽  
Mixed Convection ◽  
Variable Viscosity ◽  
Vertical Channel ◽  
Convection Flow ◽  
Mixed Convection Flow ◽  
Temperature Dependent ◽  
Temperature Dependent Viscosity ◽  
Viscosity Term ◽  
Dependent Viscosity

AbstractAn exact solution for mixed convection flow with temperature-dependent viscosity in a vertical channel subject to wall asymmetric heating and concentration is obtained. The momentum, concentration, and energy equations governing the flow configuration are derived and solved exactly by incorporating the variable viscosity term, which is assumed to exponentially decrease/increase with temperature difference into the momentum equation. The roles of governing parameters are depicted with the aid of tables and line graphs. Results show that buoyancy ratio parameter can bring about the occurrence of flow reversal at the walls. It is also found that heat transfer, total species rate, skin friction, and reverse flow occurrence are enhanced in the presence of temperature-dependent viscosity.

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