Heat exchanger results accuracy

[nehaHWSLR]

Hi,

Performing a steady state analysis of a simple model of cooling of saturated steam with water. I assigned the following conditions as inlet and outlet, and materials

Solid materials auminium and copper has constant properties followed by

Inlet conditions for one flow

Steam saturated  - material 1

Pr = 25mbar (absolute)

Volume flow rate = 3cm3/s

Quality = 0.7

Temperature = 22 degrees

Water = material 2

volume flow rate = 5m3/s, Temperature 20 degrees and Pr = 3 bar gauge and Quality = 0

applied film coefficient of 10W/m2 K at 25 degrees on the surfaces

Outlet conditon pressure = 0 is given for both steam and water flow.

The solver is run using Quality and ADV5, k-epsilon turbulence model

Currently using Autodesk CFD 2019. Are the above boundary condtions are accurate for steady state analysis?

The scalar output is fluctuating a lot. Is this accurate?

I am new to working with steam in Autodesk CFD. Any help is appreciated! 🙂

[marwan_azzam]

Hi @nehaHWSLR ,

I would set the flow rate for the Saturated Steam at the outlet and no pressure BC for outlet.

Also, for a temperature of 22C and quality of zero, the pressure is 26.452 mbar.  The program is very sensitive to the values falling on the saturated steam curves.

Marwan

[nehaHWSLR]

Hi,

Thank you for your response.

I have followed the inlet conditions for the steam for pressure 25 mbar, now temperature is 21.0776 degrees according to the saturated steam curve values you suggested.

I made the changes and ran the simulation. However now I am facing another problem. In the meshing window some of the surfaces show 'BC modifications skipped due to insufficient nodes'. Is this a meshing problem or CAD geometry problem? It is quite an easy model so I am not sure if it is a geometry problem.

For the meshing I followed a fine mesh in pipe 0.5. But still it is not fixing it. 

How to rectify it since the boundary conditions applied are not taken into the simulation?

[marwan_azzam]

Hi @nehaHWSLR ,

Insufficient nodes means that you have to refine the mesh on the surfaces in question.

I can't say more without seeing the model.

Marwan

[nehaHWSLR]

I have attached the model herewith.

Also in the simulation I want to view the quality of the steam at the outlet of the pipe/ along the pipe. I selected the scalar variable in results and used bulk calculator too along the cut plane of the model but the quality change cannot be seen in output. How to resolve this?

I am also really doubtful about the temperature results obtained. Should the mesh be further refined?

Thank you for your help.

Let me know if you can access the file.

[nehaHWSLR]

I tried simplifying the model but still has the same errors.

Does anyone know how to resolve the quality of the steam result at the outlet of the pipe?

Much appreciated, thanks a lot