The risk of Hot spots in a flexible conductive or electro heating structure

What is called a "Hot spot"?

A Hot spot of a flexible conductive or electro heating structure is a point where an abnormally hot temperature is noticed compared to the remaing parts of it.

What are the risks?

The main risk of an Hot Spot, further to the loss of functionnality of a SMART textile structure, is mainly the risk of ingnition and Fire; This one is often created by the suddent ignition of other synthetics materials in direct or close contact. (by example a defect on a car seat heater... )

example :

 Hot spot

How does an hot spot is created?

Let us come back to simple electrical power rules ! Imagine the following semi resistive yarn: 10Ω/m (Rama) I = U/R I=12/10 = 1,2A P=UI =12*1,2=14,4w

the power released wil be 0,144 Watts , We can calculate the Load ratio : (watts/cm² - power/surface unit) 0,144 / (0,138x π)= 0,33 Watt /cm²

remarq : To simplify as much as possible, we use basic rules; The load ration is depending on the echange surface; in order to have a clear idea in the case of multifilaments yarns, one should calculate the equivalent external exchange surface. It shoud stands somewhere in between the total developped surface and the surface of an equivalent round yarn.

The damaged zone can be assimilated to an equivalent much smaller cross section conductive yarn corresponding to a much finer conductiv yarn , by example of 1/10éme of its surface, but on a very short length : ex: 1mm

 Hot spot 2

thermotech answer

* Abstact of the Energy conference at the CLUBTEX

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Dangerous associations of differement metals in car seats heating structures

Example of dangerous mistake leading to major hot spot risk

During the conference, mr Tiberghien has presented the following example:
In some case people are willing to increase the strength of highly conductive materials as copper by example because they find that a stainless steel based multifilament yarn is not conductive enough for their application.

Therefore they try to associate by twisting of binding a copper yarn with a fine stainless steel yarn of 35 to 100 microns by example.

consequences in Real applications as car seat heaters by example:

dangerous conductive associations

* Abstact of the conference on hot spots risks of G tiberghien

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