topic Re: Transient Analysis problem with constant temperature in CFD Forum

Transient Analysis problem with constant temperature

Anonymous — Tue, 21 Feb 2017 07:22:45 GMT

Hello,

For Transient results for heat transfer i made first the flow to converge and than only the heat transfer to run in transient. But despite all the things, this time i cant receive results for the Temperature change. I noticed that the whole body of Soil and the Pipe are with temperature of 15 Deg. as the water. I have set initial condition of 1 Deg. It seems to me that the Software doesn't notice the Initial Condition of Temperature. I tried to check the Re-initialize box but without change in the results. I don't know what is the Trick here. I attached the .cfz file.

Please for feedback.

Dalibor Mishkov.

Re: Transient Analysis problem with constant temperature

Jon.Wilde — Tue, 21 Feb 2017 08:12:55 GMT

A note: you need to assign an initial temp condition to all volumes within the model (fluid and solid).

Did you already do this?

(also, that is a cfdst and not a CFZ, sorry 😉 )

Re: Transient Analysis problem with constant temperature

Anonymous — Tue, 21 Feb 2017 09:42:44 GMT

I did assigned initial conditions only to the Soil. But I will try now also for the Water and the Pipe.

Now when I assign initial conditions also to the Water and Pipe, do I have to restart also the flow analysis or I will only continue with the Heat transfer analysis?

here is the .cfz (sorry)

Please give me opinion about the converged solution in the picture below.

Thanks Jon.

Dalibor.

Re: Transient Analysis problem with constant temperature

Jon.Wilde — Tue, 21 Feb 2017 12:38:33 GMT

Just the transient 🙂

Although... your Boundary Conditions (BC's) are not OK.

The inlet should have a flow rate and temp

The outlet should have a P=0

What is the Total Temp for? This is only used in a compressible analysis - nothing that we need here I don't think.

Just assign the normal ambient temp to the volumes 🙂

Re: Transient Analysis problem with constant temperature

Anonymous — Tue, 21 Feb 2017 12:52:40 GMT

Hello Jon.

Ok for the Temperatures. I will change them to Static.

But you want to tell me that when I run Transient I need only the Temperatures to set on Transient and the Flow velocity and the pressures to leave at Steady?

Pump with 1.5m/s sucks the water from this pipe. The outlet should have lower pressure than the Inlet, or the flow will be suffocated.

Thanks, Dalibor.

Re: Transient Analysis problem with constant temperature

Anonymous — Tue, 21 Feb 2017 12:54:26 GMT

Hello Jon,

also for the Initial Conditions - The Total Temperatures to change into Static???

Thanks, Dalibor.

Re: Transient Analysis problem with constant temperature

Jon.Wilde — Wed, 22 Feb 2017 09:18:55 GMT

Hello, yes do not use total temp, only static.

Unless values are changing, they can all just be constant. No need to switch to transient settings within boundary conditions.

Yup, that is fine. You will still have a P=0 on outlet and the flow and temp at the inlet.

CFD will predict the inlet pressure for you (which will be higher than 0, or the flow will have to reverse 🙂 )

Thanks,

Jon

Re: Transient Analysis problem with constant temperature

Anonymous — Thu, 23 Feb 2017 09:17:08 GMT

Hello Jon,

In my model (Buried pipe in Soil) there is Soil from outside the Pipe, Pipe and Water Volume. I know the Inlet Temperature of water, I know the temperature of Soil, but I don't know the temperature of the pipe. Because of that, can I leave the pipe without Initial and Boundary Conditions, so that the Software can solve that? Or I will not receive any data from the Heat Transfer Analysis (Transient) afterwards?

Please clarify These things because I'm little confused.

Thanks in advance, Dalibor.

Re: Transient Analysis problem with constant temperature

Jon.Wilde — Thu, 23 Feb 2017 11:05:46 GMT

Hey Dalibor,

Somehow, all volumes must have an initial temperature condition applied to them.

If you are not sure, maybe just start with the mid point between the hot water and the soil?

Thanks,

Jon

Re: Transient Analysis problem with constant temperature

Anonymous — Thu, 23 Feb 2017 11:45:37 GMT

Thanks for the Info Jon.

Have a nice day, Dalibor.