## Fluids

#### Issue of different velocities between inlet and outlet.

• Raj007
Subscriber
Hello all,nI am trying to simulate a simple two-conduit model. It is a straight double pipe with a length of 5 cm. I want to do thermal analysis at a constant velocity and check heat transfer for different velocities. But when I specify velocity inlet and outflow outlet or pressure outlet. There is an increase in the velocity at the outlet. I would like to take the suggestion to solve the issue and achieve the same velocity at the outlet as an inlet.nThank you in advancenRajn
• Rob
Ansys Employee
How does the mass balance look? n
• Raj007
Subscriber
Hey Mr. Rob,nnI found something unusual thing. I am using the VOF model. Inlet 1 has phase 1 material and inlet 2 has phase 2 material. As the two materials flow through different conduits. They should not mix. But, in both the outlets, I can see only phase 1 material (i.e, in outlets 1 and 2 there is only one material coming out). I just wanted to discuss this, as this might be a problem.nCan you help me out like, what might be the solution for this problem?nThank younRajnn
• Rob
Ansys Employee
If the materials don't interact (ie are in separate containers/pipes) you don't need a multiphase model. You just need to assign a different fluid to the two fluid domains. nAs I can't see what you're doing it's hard to diagnose: post lots of pictures. n
• Raj007
Subscriber
Hello,nI understand what you said. But, the first approach of my work is not to deal with the material interaction instead it is about constant velocities at inlets and outlets. Let us consider as you said, I will assign two different materials to two different fluid domains.nSo, keeping that into consideration. I have taken a sample model with the single fluid domain. In that case, I have taken Velocity inlet with 0.2m/s. But, I got the velocity as 0.199634 (which is almost the same). But in my working model, I am seeing a change from 0.2m/s to 0.5 m/s. (It is also a simple model).nHow can I get the same velocities for a simple cylinder at the inlet and outlet?nI cannot take the mass flow inlet because I need to change the velocities. (According to my knowledge, Ansys take velocities for MF inlet based on the Area of the inlet. So in that case, I cannot change the velocities.)n(Please excuse me if my explanation and knowledge is bad)nThank younRajnn
• Rob
Ansys Employee
Check mass weighted as that accounts for there being more mass transferred through the regions that are moving more quickly. What you're seeing is the velocity profile: the inlet is a constant, the outlet is the profile we get following the solution (ie developed flow). n