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Joule Heating - Resistive Heaters
Posted 17.09.2013, 18:45 GMT-4 Low-Frequency Electromagnetics, Heat Transfer & Phase Change, Parameters, Variables, & Functions, Studies & Solvers 3 Replies
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I've built a COMSOL model that models the joule heating of electrodes that are designed to heat up channels in a microfluidic device. I am able to choose a V0 (input voltage) run a transient study and get back temp values very close to what I expect so I think my model is sound.
What I want to do now is vary the voltage applied over time. Lets say some type of square function that applies 5V for 2 second 2V for 2 sec and see how that will affect the heat in my system over time. When I try using the function: V0 = 5V*(sin(2*pi*t/4)>0) + 2V*(sin(2*pi*t/4)<=0) to define the input voltage my model does not solve giving me the following error: "Repeated error test failures. May have reached singularity at time: 0. Last time step is not converged." I tried this first because I have used this technique before with a boundary temperature source to apply a varying temperature.
This is obviously not the best way to vary the voltage within the model. Is there a better way to do this? Would it be some kind of periodic condition set on the boundary heat source? I am new to COMSOL so detailed explanations would be greatly appreciated.
Thanks
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I think Comsol is right, there is a singlarity at t=0. The way you have defined
the voltage that are jumps.
I suggest to use a smooth function. The "step" function in Comsol allows for
smooth step-function. The step can be very fast, but smooth is better.
Also from my experience it is better not to start a transient simulation at the
time of such an event, start shortly before.
Regards
Jens
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I am trying to build an analytical function that combines 4 steps to define my voltage cycling. However I can't figure out how to normalize the function. The steps go from 0 - 1, 1 - 0.4 , 0.4 - 0.7, and then 0.7 - 1.0, and when I add them it normalizes 2.1 - 3.1. How can I normalize this back to 0 - 1 on the y-axis?
Also, I noticed that you can add a periodic extension to an analytical function. Does this mean that I can make the function repeat itself because ultimately I want this cycle to repeat itself several times. The help in COMSOL doesn't really help and the parameters don't really make sense. Does anyone have any insight on this feature?
Thanks,
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