Will it Blow? Joule Heating in a Fuse on a Circuit Board, Chapter 3

In this final video chapter that investigates the joule heating of a fuse using COMSOL Multiphysics, you will see how the solved model depicts the temperature profile of the fuse ranging from room temperature to the maximum temperature in the fuse. Will it melt? Will the fuse blow?

Transcript

00:00:01 [Music] in the first two parts of this tutorial I set up and solved this model of a fuse I sent a current through it and the console computed the temperature increase In this part we'll find out how you can improve the simulation by introducing temperature dependent material properties Let's get straight to the

00:00:23 materials and uh have a look at what I used last time So we have F FR4 copper and aluminum The fuse itself is made out of aluminum So that's what I'll focus on You can see here what properties we have assumed for this aluminum There's for example the heat capacity equal to 900 jou in per kilogram in Kelvin and so forth Uh these properties are all constant values Uh keep in mind

00:00:48 especially that we have an electric conductivity of roughly 3.8 * 10 7th zmons per meter This happens to be a perfectly fine value for aluminum at room temperature Now what happens in reality when we heat it up is a whole different story and we should capture that in the model So let me see if I can find a more extensive version of aluminum in our material

00:01:13 library I'll browse down to material library elements and scrolling down just a little bit we'll find aluminum Let me add that to the model and apply it to the same domains um where we had the old version of aluminum before the version with just constant material properties Um you'll notice that we no longer have constant values for these properties Instead we have these funky

00:01:40 looking expressions What are they well let's find out uh for example the electrical conductivity is now specified as this peacewise function uh we'll focus on the uh part of the function that is for the relevant range of temperatures from 200 up to melting point and I'll plot that So what does that look like well remember that we had this uh constant conductivity of uh 3.8

00:02:08 8 * 10 7th at room temperature and that's what we see here too just below 300 kel right this is the temperature and this is the conductivity now for higher temperatures the conductivity decreases quite rapidly and we actually end up at less than 1 * 10 7th just before melting so this is quite a difference uh versus what we had before and we should adapt the current to that

00:02:33 so before with this constant connectivity we needed a 15 amp current to melt the fuse Now that we take into account the decreased conductivity at higher temperatures this should mean that we will need less current before it melts Right well that's something you may want to think about for a second But let's just try it out Um I'll send in 9 amps instead of 15 amps as we had before

00:02:56 I'll just browse down to the terminal button and uh I'll send in 9 amps instead of 15 amps And we'll solve the model again by clicking compute And we have the result a temperature distribution with a maximum just below 900 Kelvin which is just a little little tiny bit less than the melting point So making this a two-way coupled multifysics model taking in account the

00:03:24 true material dependency on the temperature turn this presumed 15 amp fuse into something closer to a 9 amp fuse That's quite remarkable