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In physics, thermal contact conductance is the study of heat conduction between solid or liquid bodies in thermal contact. The thermal contact conductance coefficient, , is a property indicating the thermal conductivity, or ability to conduct heat, between two bodies in contact. The inverse of this property is termed thermal contact resistance.
The SI unit of absolute thermal resistance is kelvins per watt (K/W) or the equivalent degrees Celsius per watt (°C/W) – the two are the same since the intervals are equal: ΔT = 1 K = 1 °C. The thermal resistance of materials is of great interest to electronic engineers because most electrical components generate heat and need to be cooled.
Contact resistance may vary with temperature. It may also vary with time (most often decreasing) in a process known as resistance creep. Electrical contact resistance is also called interface resistance, transitional resistance, or the correction term. Parasitic resistance is a more general term, of which it is usually assumed that contact ...
A heatsink's thermal mass can be considered as a capacitor (storing heat instead of charge) and the thermal resistance as an electrical resistance (giving a measure of how fast stored heat can be dissipated). Together, these two components form a thermal RC circuit with an associated time constant given by the product of R and C. This quantity ...
The relationship between thermal conductivity and conductance is analogous to the relationship between electrical conductivity and electrical conductance. Thermal resistance is the inverse of thermal conductance. [6] It is a convenient measure to use in multicomponent design since thermal resistances are additive when occurring in series. [7]
This thermal resistance differs from contact resistance (not to be confused with electrical contact resistance) because it exists even at atomically perfect interfaces. Owing to differences in electronic and vibrational properties in different materials, when an energy carrier (phonon or electron, depending on the material) attempts to traverse ...
Perfect thermal isolation is an idealization as real systems are always in thermal contact with their environment to some extent. When two solid bodies are in contact, a resistance to heat transfer exists between the bodies. The study of heat conduction between such bodies is called thermal contact conductance (or thermal contact resistance).
The contact resistance at the inner boundary is given by = | | and during a measurement the current in the middle of the circular metallic pad is zero ((=) =). Since the modified Bessel function K 0 ( r ) {\displaystyle K_{0}(r)} tends to infinity when r {\displaystyle r} tends to zero (see figures to the right), the constant B {\displaystyle B ...