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Defining heat source’s dissipated power
Most devices have two associated power values: input power and dissipated power. Input power is the product of electrical input current and voltage to the device. Electrical engineers primarily focus on input power.
Thermal engineers are more concerned about the dissipated power of a device. Dissipated power is the waste heat that the component cannot convert from the input power to the action the device is conducting. Any sort of thermal calculation needs this input to estimate appropriate heat sinks for your application.
An example would be an LED producing light. The LED converts its input energy into light, but some of that energy is lost as heat. Some industries, like computing, report their dissipated heat as “Thermal Design Power.”
Your device may effectively be experiencing 100 W but is only dissipating 80 W as heat. The 80 W is what the heat sink will need to dissipate. Your input into Eaton Genie should be 80 W in this case. Our example 100 W device that dissipates 80 W has a 20% efficiency.
If you have multiple devices, add each device’s dissipated heat together.
While the total dissipated heat is great for rough estimations, the heat source size is also a critical aspect in how heat is applied to your heat sink or other thermal management solution. The heat source size, in addition to the dissipated power, defines the density of a heat load. Heat density impacts how well a thermal management solution can handle the heat absorbed into the component.
High density heat sources have highly focused heat loads in smaller areas as opposed to a more spread out heat load. Most thermal management solutions rely on conduction to help move heat away from the heat load first, but if there is too much heat applied in a single area, it can accumulate and significantly raise the temperature of the surface and into the device.
High heat density, or high heat flux, components will typically need a high conductivity heat spreading technology, especially in air-cooled solutions. Eaton has several effective heat spreading technologies like heat pipe assemblies, encapsulated graphite heat spreaders or ultra thin vapor chambers.
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