Chromalox Big Red Book

Technical

Technical Information Allowable Watt Density & Heater Selection - Air Heating

Graph G-100S — Strip Heater (Chrome) Air Heating Allowable Watt Densities for 1000°F Sheath Temp.

Graph G-132S — Strip Heater (Iron) Air Heating Allowable Watt Densities for 700°F Sheath Temp.

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Wattage Rating of Strip Heater = W/In 2 x Heated Area Strip Heaters < 30-1/2", Heated Length = Overall Length - 4" Strip Heaters ≥ 30-1/2", Heated Length = Overall Length - 5"

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9 F.P .S. 16 F.P.S . Dis trib u ted Air Ve loc ity

15 14 13 12 11 10

1-1/2" Wide Strip Heater = 3.45 in 2 /in. 1" Wide Strip Heater = 2.31 in 2 /in.

1 F . P . S . o r F r e e A i r 4 F . P . S . 9 F.P .S. 16 F.P.S. Distri bute d Ai r Ve loci ty

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9 8 7 6 5 4 3 2 1 0 Watts Per Square Inch (W/In 2 ) 0 100

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4 F . P.S.

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16 Watts Per Square Inch (W/In 2 ) 14 12 10

1 F .P .S . or F r ee Ai r

When Calculating Heater Capacity, Use the Maximum Outlet Temperature and the Lowest Air Velocity. For Close Grouping of Heaters, Use 80% of the Calculated Value.

200

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700

Outlet Air Temperature (°F)

Graph G-107S — Finstrip ® (Iron Sheath) Air Heating Allowable Watt Densities for 700°F Sheath Temp.

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Wattage Rating of Finstrip = W/In 2 x 3.60 x Heated Length

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1 6 F . P . S . D i s t r i b u t e d A i r V e l o c i t y

1 F . P . S o r F r e e A i r 4 F . P . S . 9 F . P . S . Watts Per Square Inch (W/In 2 ) 28 24 20 16 12 8 4

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When Calculating Heater Capacity, Use the Maximum Outlet Temperature and the Lowest Air Velocity. For Close Grouping of Heaters, Use 80% of the Calculated Value.

2

0

0 100 200 300 400 500 600 700 800 900 1000 Outlet Air Temperature (°F) Notes — Strip Heaters < 30-1/2", Heated Length = Overall Length - 4" Strip Heaters ≥ 30-1/2", Heated Length = Overall Length - 5" 1-1/2" Wide Strip Heater = 3.45 in./in. 1" Wide Strip Heater = 2.31 in./in.

When Calculating Heater Capacity, Use the Maximum Outlet Temperature and the Lowest Air Velocity. For Close Grouping of Heaters, Use only 80% of the Calculated Value

0

0

100

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Outlet Air Temperature (°F)

Graph G-136S — Tubular Heater Air Heating 50

4 F.P.S. Watts Per Square Inch (W/In 2 ) Graph G-108S — Finstrip ® (Chrome Steel) Air Heating Allowable Watt Densities for 900°F Sheath Temp. Wattage Rating of Finstrip = W/In 2 x 3.60 x Heated Length 9 F.P.S. 1 F.P.S. or Free Air 16 F.P .S. Di stri but ed Air Ve loc ity 36 32 28 24 20 16 12 8

Sheath Temperature of Tubular Elements at Various Watt Densities in Free or Forced Air at 80°F

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1 6 F . P . S .

9 F . P . S .

1 F . P . S .

4 F . P . S .

S t i l l A i r

30 Watts Per Square Inch (W/In 2 ) 20 10

When Calculating Heater Capacity, Use the Maximum Outlet Temperature and the Lowest Air Velocity. For Close Grouping of Heaters, Use 80% of the Calculated Value.

4

0

0

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800 1000 1200 1400

0

Sheath Temperature (°F)

0

100

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700

Outlet Air Temperature (°F)

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