Thermal effusivity

The heat penetration coefficient is a material-specific parameter from thermodynamics that is specified in the unit:

With

• Heat conductivity in W / ( m · K)
• Density in kg / m³
• Specific heat capacity in J / (kg K).

If two halbunendlich ausgedehnete body associated with different initial temperatures and in perfect thermal contact, the contact temperature (ie the temperature of the contact surface ) with the heat penetration coefficient and the two substances are tested for:

This formula can also be the initial contact temperature finite field well estimated.

Practical experience is the heat penetration coefficient when touching different fabrics the same temperature with the bare hand:

• Substances with a high heat penetration coefficient (eg metals) are perceived as particularly cold, when its temperature is below that of the skin.
• Materials with a low heat penetration coefficient (eg insulation or wood ), however, found to be warmer at the same temperature.

A related quantity is the thermal diffusivity.