Transient Analysis of Natural Convection in a Horizontal Open Ended Cavity

2002 ◽  
Author(s):  
Assunta Andreozi ◽  
Oronzio Manca ◽  
Yogesh Jaluria
Keyword(s):  
Natural Convection ◽  
Stokes Equations ◽  
Chemical Vapor ◽  
Navier Stokes ◽  
Uniform Heat Flux ◽  
Temperature Profiles ◽  
Two Dimensional ◽  
Parallel Plates ◽  
Penetration Length ◽  
Energy Equations

The configuration of two horizontal parallel walls can be found in many applications, such as the cooling of electronic components, solar energy systems and chemical vapor deposition systems (CVD). In the present investigation a transient numerical analysis for laminar natural convection in air between two horizontal parallel plates, with the upper plate heated at uniform heat flux and the lower one unheated, is carried out by means of the finite volume method. The model was assumed to be two-dimensional. The full two-dimensional Navier-Stokes equations together with the continuity and energy equations are solved by a numerical scheme derived from a SIMPLE-like algorithm in an H-shaped domain. Results are presented in terms of velocity and temperature profiles, wall temperature profiles and the temporal behavior of several significant variables, such as the penetration length, is reported for different Rayleigh numbers and aspect ratio values.

Effect of Wall Conduction on Natural Convection in Symmetrically Heated Vertical Parallel Plates With Discrete Heat Sources

2002 ◽  
Author(s):  
Oronzio Manca ◽  
Sergio Nardini ◽  
Vincenzo Naso
Keyword(s):  
Heat Conduction ◽  
Natural Convection ◽  
Wall Temperature ◽  
Channel Wall ◽  
Stokes Equations ◽  
Vertical Channel ◽  
Navier Stokes ◽  
Temperature Profiles ◽  
Computational Domain ◽  
Parallel Plates

The effect of heat conduction on air natural convection in a vertical channel, symmetrically heated, with flush-mounted strips at the walls, was numerically analyzed. Reference was made to laminar two-dimensional steady-state flow and to full elliptic Navier-Stokes equations on a I-shaped computational domain. Solutions were carried out by means of the FLUENT code. Results are presented in terms of wall temperature profiles, air velocity and temperature profiles in the channel. The wall temperature is affected by the location of the strip on the channel wall and maximum wall temperature is far larger when the heater is located in the upper region of the channel. Heat conduction in the channel wall lowers maximum wall temperature below the heater and the thicker the wall the larger the temperature reduction.

scholarly journals Natural convection melting of nano-enhanced phase change material in a cavity with finned copper profile

2018 ◽  
Vol 240 ◽  
pp. 01006 ◽  
Author(s):  
Nadezhda Bondareva ◽  
Mikhail Sheremet
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Stokes Equations ◽  
Volume Fraction ◽  
Melting Process ◽  
Navier Stokes ◽  
Two Dimensional ◽  
Navier Stokes Equations ◽  
Dimensional Approximation ◽  
Change Material

Present study is devoted to numerical simulation of heat and mass transfer inside a cooper profile filled with paraffin enhanced with Al2O3 nanoparticles. This profile is heated by the heat-generating element of constant volumetric heat flux. Two-dimensional approximation of melting process is described by the Navier-Stokes equations in non-dimensional variables such as stream function, vorticity and temperature. The enthalpy formulation has been used for description of the heat transfer. The influence of volume fraction of nanoparticles and intensity of heat generation on melting process and natural convection in liquid phase has been studied.

Numerical Investigation of the Natural Convection Flows for Low-Prandtl Fluids in Vertical Parallel-Plates Channels

2005 ◽  
Vol 73 (1) ◽  
pp. 96-107 ◽  
Author(s):  
Antonio Campo ◽  
Oronzio Manca ◽  
Biagio Morrone
Keyword(s):  
Natural Convection ◽  
Computational Procedure ◽  
Navier Stokes ◽  
Computational Domain ◽  
Parallel Plates ◽  
Nusselt Numbers ◽  
Aspect Ratios ◽  
Rate Maximum ◽  
Induced Flow ◽  
Energy Equations

Laminar natural convection of metallic fluids (Pr⪡1) between vertical parallel plate channels with isoflux heating is investigated numerically in this work. The full elliptic Navier-Stokes and energy equations have been solved with the combination of the stream function and vorticity method and the finite-volume technique. An enlarged computational domain is employed to take into account the flow and thermal diffusion effects. Results are presented in terms of velocity and temperature profiles. The investigation also focuses on the flow and thermal development inside the channel; the outcomes show that fully developed flow is attained up to Ra=103, whereas the thermal fully developed condition is attained up to Ra=104. Further, correlation equations for the dimensionless induced flow rate, maximum dimensionless wall temperatures, and average Nusselt numbers as functions of the descriptive geometrical and thermal parameters covering the collection of channel Grashof numbers 1.32×103⩽Gr∕A⩽5.0×106 and aspect ratios 5⩽A⩽15. Comparison with experimental measurements has been presented to assess the validity of the numerical computational procedure.

Numerical Investigation on Transient Natural Convection in Vertical Channels With Heated and Cooled Walls

2007 ◽  
Author(s):  
Assunta Andreozzi ◽  
Bernardo Buonomo ◽  
Oronzio Manca
Keyword(s):  
Natural Convection ◽  
Average Nusselt Number ◽  
Fluid Motion ◽  
Uniform Heat Flux ◽  
Temperature Profiles ◽  
Computational Domain ◽  
Parallel Plates ◽  
Symmetric Motion ◽  
Transient Natural Convection ◽  
Transient Problem

A description of transient natural convection in air in a vertical parallel plates channel, with one plate heated and the other one cooled at uniform heat flux, is numerically accomplished. The transient problem is two-dimensional and laminar with constant thermophysical properties. The numerical solution is carried out employing the commercial CFD code Fluent. The computational domain is made up of the physical configuration and two reservoirs, placed downstream and upstream the channel. Results are obtained for Rayleigh number between 103 and 106 and they are presented in terms of wall temperature profiles as a function of time, velocity and temperature profiles along transversal channel sections. The simulation allows to describe the fluid motion structures inside and outside the channel. A complete skew-symmetric motion is detected. For Ra≥105 temperature profiles as a function of time show periodical oscillations. For Ra≥104 overshoots are observed along the profiles and for corresponding average Nusselt number profiles dips are present.

Numerical Simulation of Transient Natural Convection in a Channel-Chimney System

2005 ◽  
Author(s):  
Assunta Andreozzi ◽  
Bernardo Buonomo ◽  
Oronzio Manca
Keyword(s):  
Steady State ◽  
Natural Convection ◽  
Wall Temperature ◽  
Velocity Profiles ◽  
Channel Height ◽  
Uniform Heat Flux ◽  
Temperature Profiles ◽  
Parallel Plates ◽  
Transient Heating ◽  
Steady State Condition

In the present numerical investigation, a transient numerical analysis for natural convection in air, between two vertical parallel plates (channel), heated at uniform heat flux, with adiabatic parallel plates downstream (chimney), is carried out by means of the finite volume method. The analyzed transient problem is two-dimensional and laminar. Results are presented in terms of wall temperature, mass flow rate and air velocity profiles. They are given at different Rayleigh number and expansion ratios (chimney gap/channel gap) for a fixed channel aspect ratio (channel height/channel gap) equal to 10 and extension ratio (channel-chimney height/channel height) equal to 2.0. Wall temperature profiles vs time show the presence of overshoots and undershoots. The comparison among the maximum wall temperatures shows that the simple channel is the most critical configuration at steady state condition, but the best configuration during the transient heating at the first overshoot. Velocity profiles in the chimney allow for identification of some different fluid dynamic behaviors such as the vortex in lower corner and the cold inflow in the chimney. According to the temperature profiles, average Nusselt number profiles as a function of time show minimum and maximum values and oscillations before the steady state.

Internal laminar flow

2018 ◽  
Author(s):  
Marcel Escudier
Keyword(s):  
Poiseuille Flow ◽  
Stokes Equations ◽  
Circular Cross Section ◽  
Navier Stokes ◽  
Parallel Plates ◽  
Concentric Cylinder ◽  
Navier Stokes Equations ◽  
Concentric Cylinders ◽  
Constant Viscosity ◽  
Pressure Driven Flow

In this chapter it is shown that solutions to the Navier-Stokes equations can be derived for steady, fully developed flow of a constant-viscosity Newtonian fluid through a cylindrical duct. Such a flow is known as a Poiseuille flow. For a pipe of circular cross section, the term Hagen-Poiseuille flow is used. Solutions are also derived for shear-driven flow within the annular space between two concentric cylinders or in the space between two parallel plates when there is relative tangential movement between the wetted surfaces, termed Couette flows. The concepts of wetted perimeter and hydraulic diameter are introduced. It is shown how the viscometer equations result from the concentric-cylinder solutions. The pressure-driven flow of generalised Newtonian fluids is also discussed.

Direct simulation of transition in an oscillatory boundary layer

1998 ◽  
Vol 371 ◽  
pp. 207-232 ◽  
Author(s):  
G. VITTORI ◽  
R. VERZICCO
Keyword(s):  
Boundary Layer ◽  
Pressure Gradient ◽  
Stokes Equations ◽  
Navier Stokes ◽  
Turbulent Regime ◽  
Two Dimensional ◽  
Temporal Development ◽  
Direct Simulation ◽  
Navier Stokes Equations ◽  
Oscillatory Boundary Layer

Numerical simulations of Navier–Stokes equations are performed to study the flow originated by an oscillating pressure gradient close to a wall characterized by small imperfections. The scenario of transition from the laminar to the turbulent regime is investigated and the results are interpreted in the light of existing analytical theories. The ‘disturbed-laminar’ and the ‘intermittently turbulent’ regimes detected experimentally are reproduced by the present simulations. Moreover it is found that imperfections of the wall are of fundamental importance in causing the growth of two-dimensional disturbances which in turn trigger turbulence in the Stokes boundary layer. Finally, in the intermittently turbulent regime, a description is given of the temporal development of turbulence characteristics.

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