How to set up Volumetric Heat Generation Rate conditions as a function of the temperature field in FLOEFD
Summary
In some situations it can be very useful to set up heat generation boundary conditions as a function of the temperature field, such as in the case of the Pennes Bioheat Equation. One could think it can be easily done by creating a goal temperature for the volume, setting the condition as a function and selecting the temperature goal, but if one wants the condition to be applied to every cell in a volume so that the function is dependent on the temperature corresponding to that cell's position, then one can't simply do the same thing.
Details
FLOEFD allows us to set boundary conditions as functions of multiple variables or goals very easily. However, if we wanted to create a boundary condition in a certain space, where the boundary condition is different for every cell of the mesh depending on a property of each cell, we would need to divide the volume into various tinier volumes and use a local temperature goal to define each of their heat sources, which would be really impractical, time consuming and not as accurate. Now, cases where doing this is necessary are not that common, one example would be a cellphone resting on the palm of someone's hand, where the the hand's thermal properties vary a lot with the position on the hand and is simulated with the Pennes Bioheat equation, which is a function of temperature.
In order to do this, we first create a volume heat source and select the volume where we want to apply the condition. Then, in the parameter section, we select Volumetric Heat Generation Rate:
Then, we click on the Dependency button (fx) and select Formula Definition. This will bring up a window where we can define the formula. We write the formula, and then when we want to insert the temperature in the formula, we simply click on the Temperature button on the bottom left side of the window:
This will make it so that the heat source is dependent on the temperature in each cell of the mesh of the selected volume, which we can't do by using a goal or a parameter. After we're done we just have to click Ok on this window and the previous one. Now we've successfully defined the condition.