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Axismmetric Transient Heat Transfer

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(1)

FEMLAB example in heat transfer

Bioprocess Laboratory Department of Chemical Engineering Department of Chemical Engineering Chungnam National University

(2)

Axismmetric Transient Heat Transfer

• This model domain is 0.3 X 0.4 meters.

• Boundary conditions

The left boundary is symmetry axis.

The other boundaries have a temperature of 1000℃. The entire domain

i t 0℃ t th t t hi h t t h i t t t

is at 0℃ at the start, which represents a step change in temperature at the boundaries.

M i l i

• Material properties

The density, ρ, is 7850 kg/m

3

. The heat capacity is 460 J/kg·℃

The heat capacity is 460 J/kg ℃.

The thermal conductivity is 52 W/m·℃.

(3)

Model navigator g

1. Execute the FEMLAB

2. Select Axial symmetry (2D) in the Space dimension list.

3. Open the Heat Transfer folder.

4. Open the Conduction node.

5. Select Transient analysis.

6 Cli k OK 6. Click OK.

(4)

Geometry modeling y g

1. Go to the Draw menu, point to Specify Object and click p y j

Rectangle.

2. In the Rectangle dialog box go to the Size area and enter 0.3 in the Width edit field and 0.4 in the Height edit field.

3. Click OK.

(5)

Model navigator and Geometry modeling g y g

3

1 4

2

(6)

Physics settings (Boundary settings) y g ( y g )

1. Go to the Physics menu and choose Boundary Settings.y g

2. Select the Select by group check box and choose boundaries 2,3 and 4 by selecting on of them.

3. Select Temperature in the Boundary condition list.

4. Enter 1000 in the Temperature dit fi ld

edit field.

5. Click OK.

(7)

Physics settings (Subdomain settings) y g ( g )

1. Go to the Physics menu and choose Subdomain Settings.g

2. In the Subdomain Settings dialog box enter the themal properties in the domain accortding to the

material properties.

3. Click OK.

(8)

Mesh generation g

1. Go to the Mesh menu and choose Initialize Mesh.

(9)

Solving the model g

1. Go to the Solve menu and choose Sover Parameters.

2. In the Time stepping area in the Solver Parameters dialog box enter 0:10:190 in the Times edit field.

3. Click OK.

4. Click the Solve button.

(10)

Solving the model g

(11)

Solving the model g

(a) (b)

Results of time stepping. (a)0:10:190 (b)0:10:1000

(12)

Postprocessing and visualization p g

1. Go to the Postprocessing menu and choose Cross-Section plot p Parameters dialog box click the Point tab.

2. Select the Point plot button.

3. Under Coordinates enter 0.1 in the X edit field and 0.3 in the Y edit field.

4 Cli k OK 4. Click OK.

(13)

Postprocessing and visualization p g

(14)

Free convection Free convection

• This example describes a fluid problem with heat transfer in the fluid.

An array of heating tubes is submerged in a vessel with fluid flow

entering at the bottom. g

(15)

Free convection(Partial differential equation) ( q )

• The incompressible Navier-Stoke equations consist of a momentum balance(a vector equation) and a mass conservation and

incompressibility condition.

0

( ⋅ ∇ = −∇ + ∇

2

+

∂ +

u )u p u F

t

u ρ η

ρ

= 0

∇ u

• The equations are following variables.

• u is the velocity field.

• p is the pressure.

• F is a volume force

• F is a volume force.

• Ρ is the fluid density.

• η is the dynamic viscosity. η is the dynamic viscosity.

• ∇ is the vector differential operator.

(16)

Free convection(continued) ( )

• The heat equation is an energy conservation equation that says that the change in energy is equal to the heat source minus the divergence of the diffusive heat flux.

Q Tu

c T

t k

c

p

T + ∇ ⋅ − ∇ +

p

=

∂ ( ρ )

ρ ∂ t

• The equations are following variables.

• C

p

is the heat capacity of the fluid.

• ρ is fluid density.

• Q is a source term

• Q is a source term.

• u is the velocity field.

(17)

Free convection(Physical constants) ( y )

C t t f d li

Constants for modeling

Property Name Expression(value)

Fluid density rho0 1e3

Fluid density rho0 1e3

Dynamic viscosity mu 1e-3

Heat capacityp y Cpp 4.2e3

Thermal conductivity kc 0.6

Volume expansion coefficient alpha0 0.18e-3

Acceleration of gravity g0 9.8

Inlet velocity vin 5e-3

Inlet temperature Tin 293

Heater temperature Theat 303

(18)

Model navigator g

1. Select 2D in the Space dimension list.

2. Click the Multiphysics button.

3. Open the Fluid dynamics and click Incompressible Navier- Stokes.

4. Click Add.

5 O th H t t f d li k

5. Open the Heat transfer and click convection and conduction and click Add.

6. Click OK.

(19)

Constants setting g

1. From the Options menu, choose Constants.

2. Enter rho0 in the Name field.

Move the cursor to the Expression field and enter 1e3.

3. Continue by adding the remaining constants.

4. Click OK.

(20)

Axes/Grid setting g

1. From Options menu, choose Axes/Grid Settings.g

2. In the Axes/Grid Settings dialog box, enter -0.01, 0.01, -0.01, 0.05 in the x min, x max, y min, y max edit field.

3. Click Ok.

(21)

Geometry modeling y g

1. Go to the Draw menu, point to Specify Object and click p y j

Rectangle.

2. In the Rectangle dialog box go to the Size area and enter 0.005 in the Width edit field and 0.04 in the Height edit field.

3. Click OK.

(22)

Geometry modeling y g

(23)

Geometry modeling y g

1. Go to the Draw menu, point to Specify Object and click Circle.p y j 2. In the Circle dialog box go to the

Size area and enter 0.0025 in the Radius edit field.

3. Go to Position area and enter 0.015 in the y edit field.

4. Click OK.

(24)

Geometry modeling y g

Click the Difference button.

(25)

Geometry modeling y g

(26)

Physics settings (Boundary settings) y g ( y g )

1. Go to the Physics menu and choose Boundary Settings.

2. Select Temperature in the

Boundary conditions list and enter Tin in the Temperature edit field at p boundary 2.

3. Select Temperature in the

Boundary conditions list and enter Theat in the Temperature edit field at boundaries 6 and 7.

4. Click the boundary 4 and select Convective flux in the Boundary

i i condition.

5. Click OK.

(27)

Physics settings (Boundary settings) y g ( y g )

1. Switch to the Incompressible

Navier-Stoke application mode by pp y selecting this mode from the

Multiphysics menu.

(28)

Physics settings (Boundary settings) y g ( y g )

1. Go to the Physics menu and choose Boundary Settings.

4. Select boundaries 6 and 7 and then select the No slip boundary y g

2. For the inflow boundary, select boundary 2 and then choose

p y

condition.

5. Other boundaries select the Inflow/Outflow velocity in the Boundary condition list. Enter vin in the y-velocity edit

Slip/symmetry boundary condition.

field(leave the x velocity 0).

3. Continue by selecting the outflow

b d 4 I th B d

6. Click OK.

boundary 4. In the Boundary condition list, select Normal

flow/Pressure. Leave the pressure at 0

at 0.

(29)

Physics settings (Subdomain settings) y g ( g )

1. Choose Subdomain Settings from the Physics menuy

2. Select the single subdomain,

number 1, and enter rho0 and mu in the Density and Dynamic viscosity fields.

3. Enter alpha0*g0*rho0*(T-Tin) in the volume force, y-dir.

4 Cli k I t t b d t th i iti l 4. Click Int tab and set the initial

value v(t0) to vin.

5 Click OK 5. Click OK.

(30)

Physics settings (Subdomain settings) y g ( g )

1. Switch to the Convection and conduction application mode by pp y selecting this mode from the Multiphysics menu.

(31)

Physics settings (Subdomain settings) y g ( g )

1. Choose Subdomain Settings from the Physics menu.y

2. Enter rho0, cp and kc in the Density, Heat capacity, and

Thermal conductivity edit fields.

3. Enter 0 in the x-velocity and y- velocity edit fields.

4. Click Int tab and enter Tin in the T(t0) fi ld

T(t0) field.

5. Click OK.

(32)

Mesh generation g

1. From the Mesh menu, choose Mesh Parameters.

2. In the Mesh Parameters dialog box, select Fine in the Predefined mesh sizes list.

3. Click OK.

4. Form the Mesh menu, choose Initialize Mesh.

(33)

Mesh generation g

(34)

Solving the model g

1. Go to the Solve menu and choose Sover Parameters.

2. In the Time stepping area in the Solver Parameters dialog box enter 0:1:30 in the Times edit field.

3. Click OK.

4. Click the Solve button.

(35)

Solving the model g

(36)

Solving the model g

1. Go to the Postprocessing menu and choose Plot Parameters.

2. Check the Arrow at the plot type at the General tab in the Plot

Parameters dialog box.

3. Click OK.

(37)

Solving the model g

(38)

Solving the model g

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