Week 8 - Natural Convection-II

Aim: Electric voltage control panel thermal analysis.

Electric voltage control panel: it is a component of an electrical distribution system that divides an electric power to feed into branch circuits, while providing a circuit breaker.

Components of voltage panel:

Enclosure: an enclosure is a cabinet for electrical or electronic equipment.

Bus bars: a busbar is a metallic bar or strip that conducts electricity within an electronic equipment.

Circuit breaker: an electric fuse given to control the current flow through the system.

Model:

Cabinet: it creates a fluid region around the model for which the governing equations are solved.

IG block:

Block type: solid

Surface material: Paint non metallic

Solid material: Fe

Total power: 168.92 W

I1 block:

Block type: solid

Surface material: Paint non metallic

Solid material: Fe

Total power: 56.16 W

Rest of the blocks follow the same procedure.

Bus bar A:

Shape: prismatic

Surface material: Cu polished surface

Solid material: Cu pure

Total power: Joule heating

Joule heating power:

Type: constant

Current: 800amp

Resistivity: 1.72e-8 ohm

C = 0.0039

Tref: 25 degree c

Rest of the busbars follow the same procedure.

IG cable:

The cable is used to distribute the current from the busbars. The total power is distributed and is dependent on the length of the cable

Block type: solid

Surface material: Cu polished surface

Solid material: Cu pure

Total power: Joule heating

Enclosure:

Block type: solid

Surface material: paint white acrylic

Solid material: steel carbon 1020

Thermal specification: thin is set wall boundaries type and the thickness is 3mm. the radiation of all walls are activated.

Grille: grille is used for natural convection of air to keep the low voltage cool down.

Mesh:

Assemble1:

Slack settings for assembly meshing

Min x = 2mm

Max x =2mm

Min y= 0

Max y= 0

Min z = 2mm

Max z = 2mm

Mesh type

Maximum element size in x =100mm

Maximum element size in y = 80mm

Maximum element size in z = 52.5mm

Min gap x =1mm

Min gap y = 1mm

Min gap z = 1mm

To check for validation of mesh

Macros>> productivity>> validation>> automatic case check tool

It checks the assembly interface between the various objects and assembly.

Mesh display in x direction

Mesh display in y direction

Mesh display in z direction

Solid and wire mesh

Face alignment:

Measures the mesh quality by face alignment index.

The value of face alignment ranges from 0 to 1. Value greater than 0.1 is preferred and greater than 0.15 is better.

Volume:

Preferable volume mesh should be 1e-12 for single precision and 1e-15 for double precision.

Skewness:

It determines the deviation of the mesh from its ideal shape.

Physics setup:

Solver: 3D navier stokes solver is used to study the computational domain.

General set up:

Boundary conditions

Flow conditions

Temp 20 degree

Pressure 0Pa

Radiation temp 20degree

Default fluid air

Default solid extruded Al

Radiation: off

Transient setup: steady

Solution initialization:

X velocity- 0m/s

Y velocity- 0.005m/s

Z velocity- 0m/s

Natural convection bc

Gravity vector for y axis -9.81 m/s2

No of iterations: 200

Flow convergence: 0.001

Energy convergence: 1e-10

Joule heating: 1e-7

Parallel setting:

No of processors- 4

Post processing plots

Convergence plot

Temperature object contour

The maximum temperature at rthe block is 75 degree C and minimum at the cable 20 degree C.

Temperature in X axis

the temperature of the block is at max 75 degree. The air at the vicinity of the block is at 61 degree. Due to natural convection the air is hotter at the nearby zone and cooler at the outer zone which is at 24.12 degree.

Temperature in Y axis

The maximum temperature is found at the block A which is 61 degree and the heat is transferred to the outer cables by natural convection to a temperature of 41 degree. The air flow temperature is seen to vary from 46 to 36 degree C.

Temperature in Z axis

The maximum temp of 71degree C is at block A and min temperature at the cable of 47 degree C.

Velocity vector plot

Velocity in X axis

The maximum velocity of 0.3 m/s at the block A is found, where maximum joule heating is generated, while at the other place the velocity is around 0.1 m/s.

Velocity in Y axis

The velocity magnitude is very low with maximum velocity of 0.1 m/s and minimum of 0.01m/s. the air recirculates from inlet grille which carries away the heat from all the blocks and moves towards outlet grille.

Velocity in Z axis

The air enters from inlet grille with max velocity of 0.19 m/s and recirculates from the top by removing heat from the heated block to the cable surface and finally moving out from outlet grille at an avg velocity of 0.3 m/s. the velocity on other areas remain at 0.09-0.048 m/s.

Conclusion:

Due to natural convection, the circulation of air takes place from the inlet grille to outlet grille. The temperature of air at the top region of enclosure is 75 degree C and at the bottom phase it is 21.35 degree C.

The bottom portion of the voltage panel is relatively cooler and has minimum velocity, while at the upper block heat source the velocity is relatively higher to dissipate the heat from the surface.