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For example, a heatsink rated at 10 °C/W will get 10 °C hotter than the surrounding air when it dissipates 1 Watt of heat. Thus, a heatsink with a low °C/W value is more efficient than a heatsink with a high °C/W value. [ 3 ]
Temperature vs. heat load diagram of hot stream (H 2 O entering at 20 bar, 473.15 K, and 4 kg/s) and cold stream (R-11 entering at 18 bar, 303.15 K, and 5 kg/s) in a counter-flow heat exchanger. "Pinch" is the point of closest approach between the hot and cold streams in the T vs. H diagram.
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:
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.
Rca (°C/W) = Thermal resistance of the Heat sink, between the case of the CPU and the ambient air. Tc = Maximum allowed temperature of the CPU's case (ensuring full performances). Ta = Maximum expected ambient temperature at the inlet of the Heat sink fan. All these parameters are linked together by the following equation:
A heat spreader transfers energy as heat from a hotter source to a colder heat sink or heat exchanger. There are two thermodynamic types, passive and active. The most common sort of passive heat spreader is a plate or block of material having high thermal conductivity, such as copper, aluminum, or diamond. An active heat spreader speeds up heat ...
The heat transfer coefficient is often calculated from the Nusselt number (a dimensionless number). There are also online calculators available specifically for Heat-transfer fluid applications. Experimental assessment of the heat transfer coefficient poses some challenges especially when small fluxes are to be measured (e.g. < 0.2 W/cm 2). [1] [2]
The Rayleigh number can be understood as the ratio between the rate of heat transfer by convection to the rate of heat transfer by conduction; or, equivalently, the ratio between the corresponding timescales (i.e. conduction timescale divided by convection timescale), up to a numerical factor.