Joule heat, thermal resistance

・In Japanese
Premise knowledge
・Relational expression between heat quantity and temperature

■Joule heat

Joule heat is the amount of heat generated when current flows through a conductor, and is represented by the following formula. The principle of heat generation is that the atoms vibrate when electrons moving in the conductor collide with the atoms.

■Conductor resistance

The resistance of the conductor is represented by the following formula from the length and cross-sectional area of the conductor.



＜Relationship between resistance and temperature＞
As the temperature of the copper wire rises, the resistance value increases, and the following formula is obtained.



When the temperature rises, the resistance rises, and when the resistance rises, the temperature rises further. The state in which the loop goes too far is called thermal runaway. One of the causes of such thermal runaway is an increase in resistance due to a decrease in contact area with the copper wire caused by stress changes due to thermal expansion of the crimped portion of the connector.

■How to calculate the temperature of copper wire

If the calorific value is known above, the temperature can be obtained from the following relational expression between the calorific value and temperature.



By substituting formula (1) into the above formula,

■What is thermal resistance?

Thermal resistance means the temperature rise value for calorific value [W], and the temperature of the conductor can also be obtained using the thermal resistance.



When obtaining the temperature of a long conductor, the thermal resistance value per unit length may be used. At that time, the form of the formula does not change, but the unit must be changed as follows.

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