Heat Transfer and BTU Input

For more information contact Mearsecroft
Created and updated by Spiders Webs

 

 

 

 

 

 

 

 

 

 

% Available heat = (3600 - flue gas temperature (deg F) x 100) / 3600

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Heating Rate 

 

 

Heating Rate –

Kg./Hr./Sq. M. Hearth Area

Heating Rate –

Lbs./Hr./Sq. Ft. Hearth Area

Material

Heat Treatment

Penetration Rate

Min./In. Thickness

Direct

Fire

Muffle

Direct

Fire

Muffle

Iron

Forging

20

400-500

175-200

80-100

35-40

Steel

Annealing

40

250-300

175-200

50-60

35-40

 

Hardening

40

200-250

150-175

40-50

30-35

 

Drawing

120

150-175

-

30-35

-

Brass

Forging

20

350-400

200-225

70-80

40-45

 

Annealing

30

300-350

175-200

60-70

35-40

Aluminum & Magnesium

Forging

20

125-150

-

25-30

-

Solution Heat Treating

 

30

-

100-125

 

-

 

20-25

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Pot Furnaces –

Heat transfer through pot walls should not exceed about 20 to 28kW/m2 (7,000 to 9,000 Btu/hr/ft2) of exposed pot sur­face to afford good temperature control and longer pot life.

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Aluminum Dry Hearth Furnaces

Melt down zone

1.3 kWh/kg

2000 Btu/Lb.

Melting rate

400-500kg/m2/hr.

80-100 lb./sq. ft./hr.

Holding furnace

0.32kWh/kg

500 Btu/lb.

Liquid level height

0.4-0.54m

16" - 22"

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Immersion Burners  

a

Atmospheric Type

 

Heating tars

6kW/m2 

2500 Btu/sq. ft./hr.

 

Max. output

17.5kW/m2 

7500 Btu/sq. ft./hr.

 

Velocity in pipe on cold basis

1.77m/s

350 ft./min.

b

Blast or Eductor Type

 

Max. output

58kW/m2

20,000 Btu/sq. ft./hr.

 

Avg. output

44kW/m2

15,000 Btu/sq. ft./hr.

 

Velocity in pipe on cold basis

4m/s

800 ft./min

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For acid solutions

Use 300% excess air and output of 17.5kW/m2  (7500 Btu/sq. ft./hr.) 30kW/m2 (10,000 Btu/sq. ft./hr.) for lead tubes. Watch out for flame impingement

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Miscellaneous

A simple way to determine whether a flame is oxidizing or reducing is to stick a copper penny or copper wire in the flame. If reducing, the copper will shine brightly; if oxidizing, it will turn dull.

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