## General Mechanical

#### Transient Thermal Analysis: Sequential Exothermic Reactions

• ShaneA
Subscriber

Hello!

I am trying to use a transient thermal analysis to model the sequential reaction of a series of reactive nanolaminate particles  (see:

for a video of a reactive nanolaminate). In essence, these particles undergo a highly exothermic reaction upon reaching a specific ignition temperature (~270 C) thereby heating adjacent particles until they react. In the model we vary the thermal conductance between particles and the geometry of the particles to determine how this affects the reaction propagating through the particles.

I see several potential ways of accomplishing this in a Transient Thermal simulation, but have not figured out if they are possible or how to accomplish them if they are. As such, I was hoping someone with more experience/expertise could weigh in on the following ideas to let me know if they are possible, and if they are how I could go about implementing them. I have already attempted to figure out ways of implementing each of these approaches and so far have not found workable solutions.

Idea 1: Use APDL commands to either tun on internal heat generation or set the internal temperature to the adiabatic temperature (max temperature reached during reaction) within the particle once the ignition temperature (270 C) is reached.

I have struggled to determine how this could be implemented, but think that if it is possible this would be the most flexible solution. Is it possible to use APDL commands to, when a solid body or a node reaches a temperature, either turn on volumetric heat generation in that node/body or set that node/body to a new temperature?

Idea 2: Set up a series of sequential transient analyses - in each analysis the next particle is set to maximum temperature during an incubation step followed by a longer heat transfer calculation step. Ideally, the temperature in the next particle would be monitored and as soon as it passes the ignition point, the simulation would be stopped. Then the final temperature profile would be imported to another transient thermal simulation as the initial temperatures and another simulation with two steps - incubation of the reacted particle & then heat transfer to adjacent particle(s) - would be run.

I have not been able to find a conclusive answer as to whether it is possible to stop a transient thermal analysis programmatically by measuring a parameter within the simulation (such as average or maximum temperature in a body). Is such a thing possible?

Thank in advance to anyone who can provide some input. I have an images of my best attempt so far - essentially I tried to implement the 2nd method by iteratively determining the end times for each step. This is a very slow approach since I want to vary some of the parameters (geometric and physical properties), but hopefully it demonstrates the geometry and helps to communicate what I am attempting.

Sincerely,

Shane