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What Happens if a Power Source Partially Intersects with a Domain?

Question

What happens if a power source only partially intersects with a domain, rather than completely taking up space inside the domain?

Solution

Power sources can be assigned as a part or as a geometry primitive. If an absolute power source [w] is assigned to the geometry, this means absolute power will be dissipated from the volume of the selected entity. In other words, heat generation from every cells within the entity will be:

Defining absolute power source on a geometry primitive

If the entity is not completely intersecting with the domain, the domain cannot receive full power. This is explained in the following example:

Example – Heat source inside a fluid domain

In this example, we are testing two setups. In the first setup, a geometry primitive is completely inside the fluid domain. In the second one, only half of if lies outside. In each setups, walls of the fluid domain are adiabatic and 0.38288W of absolute power is assigned to the geometry primitives. The Simulation type is transient conjugated heat transfer. Initial temperature for both cases are 293K and the simulation takes place for 10 seconds.

As stated before, power is dissipated as volumetric heat flux. Therefore, the second domain will only receive half of the absolute power, which is generated by the geometry primitive. Based on energy balance, one should expect the temperature change in the second setup to be half of the first one:

Where, P is the power [W * s], m is the mass of the fluid volume [kg]. cp is the specific heat capacity of the fluid [J/kg-K], and ΔT is the difference between initial and final average fluid temperature. Results of the stated example validates the theory.

Note

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Last updated: July 2nd, 2020

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