## Fluids

#### phase change materials in construction by Ansys Fluent

• Jonn
Subscriber

good morning

I need help if possible

I have research to study phase change materials used in construction by Ansys Fluent

Study of the temperature change of the inner side of the wall The wall consists of a layer of insulation , brick and a layer of phase change materials on the inner side

• Karthik R
Hello Since you are running a transient simulation, I'd suggest that you pick your time-step size in such a way that the CFL number is close to 1. CFL number calculation depends on the velocity scales and grid sizes used in your problem.
Regarding the residuals, we recommend that you at least converge the solution by 3 orders of magnitude. Since this is a transient solution, attempting to converge more than 3 orders of magnitude might increase your computational time.
Karthik
• Jonn
Subscriber
Hello
So for the time-step size I can give 1s, The goal of my simulation is to follow the evolution of the temperature of the wall over a period of 7 hours, giving one second for the size of the time step and 25000 for the number of time steps but for the residual monitors I give 10e-7 or 10e-9 and I find the same problem the solution stops quickly problem of convergence of solution . see figure case 1
But when I cancel the convergence, it gives about 10-14, 10-15 and the computation takes a lot of time, see figure case 2
Should I increase the value of residual monitors? Or could the problem be in the initial conditions?

• Rob
Ansys Employee
The zero values for the continuity and momentum equations suggests something odd is going on. How is the PCM material zone defined?
• Jonn
Subscriber
Hello Mr. Rob

Zero values of continuity and momentum I think is because gravitational force is neglected. Because when I enter the value of the gravitational force, I get the following results

• Rob
Ansys Employee
Which suggests that something is moving. What does the flow field look like?
• Jonn
Subscriber
I think because the inlet temperature is variable !!