Control Systems & PLC's

Nichrome Wire

Electric Heating Element Calculation

This article helps you design a heating element, including wire and strip heating elements. you can easily calculate the diameter of wire or width and thickness of strip under different conditions. Common used heating element can be made from nichrome alloys,FeCrAl heating alloys of Copper Nickel alloys.

Heating Wire Calculation

The following two formulae will help you to calculate the diameter of wire under certain Capacity and Voltage.

Where:

d — Diameter of heating wire, mm
p — Resistivity of heating wire，Ω· mm2/m
P — Power per phase, KiloWatts
U — Voltage，Volts
W — Surface loading，W/ cm2
L — Length of heating wire, m

For Example:

1, Supposing the condition is 800W/240V and resistance per meter you required is 8.7 Ω/m, you are going to use Nichrome 80 as the heating wire because of its high and stable performance. Refer to Nichrome Wire Data Table, you will find that dia. 0.4mm is what you need. Here according to technical data of Nichrome 80, p is about 1.09 Ω·mm2/m. So according to the formula 2, L is 8.3 m. To verify the surface loading, W is 7.68 W/cm2,  you can check whether it is ok for you. If your calculated surface loading is too high or too low, please change the grade of alloy.

2, Surface loading is related with heat transfer and element's service life. If you have requirement on surface loading such as W is 5 W/cm2，then you can know d is 0.46mm under the same condition as 1.

Heating Strip Calculation

We have two formulas to define the width and thickness of strip heating element.

t—thickness of strip (mm)

Kt—coefficient of thickness

b—width of strip

Kb—coefficient of width

P—capacity/power (W)

ω—surface area loading (W/cm2)

U—Voltage (V)

Ct—Temperature-Resistance Factor

Use following two formulas to calculate Kt and Kb:

n=b/t is the ratio of width and thickness

So Kb=n·Kt

You can find common used figure of Kt and Kb in the following table:

For Example:

Material: Nichrome 80/20

Power: 10KW

Voltage: 220V

Surface area loading: 1.05W/cm2

Temperature: 1100℃

 

According to the formula above:

b=Kb×13

According to the table, choose b/t=8:

b=0.708×13=9.20

t=9.20÷8=1.15

so the size of strip is 9.20mm×1.15mm which is not regular size,

we can change b/t to b/t=10

then:

b=0.769×13=10

t=10÷10=1

The strip size is 1mm×10mm

About the Author

Engineer of NiWire Industries Co., Ltd.

why is it HCl is used to clean the nichrome wire after the flame test?

we are asked to know what is the color of magnesium baruim copper but i wonder why we used nichrome

and we have to clean it by HCl

Not sure but I suspect that the salt will combine with and remove any metal residue that would contaminate the next tests. I further suspect that Ni Chrome is used because it does not form a metal salt when heated with H Cl.

nichrome wire