[enhox090]

Good day everyone, I'm a newbie in CFD - Fluent not sure how to determine the BC for my analysis. I have a small rectangle tank containing PCM, it just has 1 inlet to fill the PCM then it'll be capped. I need to simulate the heat transfer and thermal pressure of PCM to the tank in several temperatures but do not know how to set the BC (

I've already looked for some tutorials on youtube but they all have inlets and outlets and their shape are also different (normally is a cylinder).

If someone can help, I'll be very appreciated.

[Gert-Jan]

Better ask the fluent forum. There you have a larger audience.

Nevertheless, the simulations you found are mostly steady state, where fluid flows from inlet to outlet.
You have an inherently transient process with 2 fluids. Initially a gas is present in which a fluids is poured. So setup a transient case with gas in the domain and let fluid enter the domain. Either as a function of time, or using a step function. This can be a massflow, or a uniform velocity, or a profile. That depends on what is in front of your inlet.

Where does your gas go? Don't you need an outlet for this? Or is it just pressurized?

[enhox090]

Originally Posted by Gert-Jan

Where does your gas go? Don't you need an outlet for this? Or is it just pressurized?

For my model, an inlet also acts as an outlet for the gas to go out when I fill the PCM into the container. Furthermore, it is assumed that the tank is filled with PCM and completely sealed, no voids left. The initial condition is to set the temperature for PCM at 303K and then observe the changing of the tank’s temperature and thermal pressure caused by PCM over time.
Btw, thank you for your reply and also for mentioning the appearance of the gas which I didn’t notice. It can be another case for me to analyze this model.

[arjun]

Run the simulation as inlet bc first and then when want to switch change to outlet condition and continue

[LuckyTran]

You have PCM as well so it actually is 4 phases (a solid and liquid phase for the PCM). These problems can look deceptively simple because you encounter them everyday but end up being complex and computationally expensive when you want to take into account all the physics at the same time.



You can brute force and DNS your way through this case or you can model it further. Either way, it would vastly improve your understanding of the problem if you do some order of magnitude analysis and try to figure out what regimes you even have.

1. How long does it take for your working fluid to fill up the porous region? What is this flow timescale?
2. Next, how long does it take for the PCM to respond? Is the timescale similar or is it 100x longer?
3. Is the change in temperature of the working fluid significant during this process? Is this a high thermal capacity fluid or a low one?

You my be able to reduce the complexity of the problem (from 4 phases down to 3 or 2 or maybe even 1) by coming up with these answers.

[enhox090]

Thank you for your suggestion, I’ll try it then