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The heat sink thermal resistance model consists of two resistances, namely the resistance in the heat sink base, , and the resistance in the fins, . The heat sink base thermal resistance, , can be written as follows if the source is a uniformly applied the heat sink base. If it is not, then the base resistance is primarily spreading resistance:
typical thermal power, which is measured under normal load (for instance, AMD's average CPU power) maximum thermal power, which is measured under a worst-case load; For example, the Pentium 4 2.8 GHz has a 68.4 W typical thermal power and 85 W maximum thermal power. When the CPU is idle, it will draw far less than the typical thermal power.
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.
So that practical clothing may be described conveniently by a range of small integers, the unit of thermal resistance, to be called the “tog”, is the resistance that will maintain a temperature difference of 0.1°C. with a flux of 1 watt per square metre, or in more practical terms, 10°C. with a flux of 1 watt per square decimetre.
The thermal conductivity of a material is a measure of its ability to conduct heat.It is commonly denoted by , , or and is measured in W·m −1 ·K −1.. Heat transfer occurs at a lower rate in materials of low thermal conductivity than in materials of high thermal conductivity.
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 ...
This article uses the term absolute thermal resistance for the temperature difference per unit of heat flow rate and uses the term R-value for the temperature difference per unit of heat flux. In any event, the greater the R-value, the greater the resistance, and so the better the thermal insulating properties of the barrier.
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).