Analysis of Burning Candle

COMSOL Conference

October 7-9, 2010

1

COMSOL Conference 2010 Boston Presented at the

Candle Multiphysics

• Heat

– Conduction

– Radiation

– Convection

• Fluid flow

• Phase change

• Combustion

2

Simplifying assumptions

• Heat of combustion approximated by a simple heat source

• Stationary analysis

• Symmetric boundary conditions

3

Model set up

• Air flow is described by conservation of mass, momentum, and energy

• Artificial diffusion added in plume

4

0 u

gIuuuuu

3

2Tp

upcQTk

Model set up

• Conduction in the solid domains:

• Anisotropic thermal conductivity

• Convective term added in fluid domains

5

QTk

Model set up

• Surface heat flux due to radiation

• Mutual irradiation (Gm) is a function of the radiosity

• Flame surface radiation is non-locally coupled to the radiating gas volume

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44 TTFGq ambambmr

441 TTFGJ ambambm

Model set up

• Surface radiosity is a function of the average value of T4 in the radiating gas volume

• Heat flux qr is set to zero at the boundary

• Source term is included in the flame region to account for cooling due to radiation

7

V

ATQ

4

Model validation

• Temperature as function of position along wax surface

• Temperature as a function of candle height

• Location of interface between solid and liquid

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Validation

Measured (C) FEA (C) Full Candle 40 46 Half Candle 44 49

Average temperature of glass along top outer edge

S-L interface: 54 C Line: Measured Area: Predicted

Full Candle

40

45

50

55

60

65

70

75

80

85

90

0 5 10 15 20 25 30 35 40 45 50

Distance from Center (mm)

Tem

pera

ture

(deg

C)

FEAMeasured

1mm below surface Radial through wick

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Full candle

¼ “ candle

½ Full candle

Results: Temperature @ Wax surface

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1mm below surface

5mm above surface

10mm above surface

Surface

Results: Temperature

10mm above surface

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Results: Wick location

Surface Temperature along Radial Line through Wick - Full Candle

50

70

90

110

130

150

170

190

210

230

250

270

0 5 10 15 20 25 30 35 40 45 50

Distance from Center (mm)

Tem

pera

ture

on

Surfa

ce (d

egC

) Baseline0.125" Toward Center0.125" Toward Edge

Temperature 1 mm Down along Radial Line through Wick - Full Candle

50

55

60

65

70

75

80

85

90

0 5 10 15 20 25 30 35 40 45 50

Distance from Center (mm)

Tem

pera

ture

on

Surfa

ce (d

egC

) Baseline0.125" Toward Center0.125" Toward Edge

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Results: Flow

½ Full candle Full candle ¼ “ candle

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Summary

• Analysis incorporating – Conduction

– Convection

– Radiation

– Phase change

• Validated model

• Effects of candle location/height

– Temperature distribution

– Flow

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