Learning Forum

[Anuj Thakkar]

Hello! I am simulating double pipe heat exchanger with helical fins on the outer surface of the inner tube. I have selected SIMPLE scheme with second order upwind method for energy, momentum and turbulent. Also, residual for continuity has been applied as 1e-05 and for momentum, energy and k-epsilon (for turbulent) residual are applied as 1e-06. The hot and cold fluid inlet selected as velocity inlet and outlet for both fluid has been applied as pressure outlet.  In initialisation turbulent kinetic energy is 0.001 and turbulent dissipation rate is 1. I have performed 1000 iterations. The energy residual is converged however, continuity residual is not converged. Any suggestion would be appricieted. Thank you.

[SRP]

Hi,

I suggest you to adjust the under-relaxation factors for continuity, momentum, and turbulent quantities. Start with a value of 0.7 and experiment with higher or lower values based on the convergence behavior. You can also also try PISO or Coupled options to see how it affect convergence.

Hope this helps.

[Anuj Thakkar]

Hello. Thank you for your reply. I have tried as per your suggestion. I have select coupled in methods and provided different value for under-relaxation factor. However, each time kind of similar trend has beed seen. They are converging but after certain iterations or residual values they graph bcomes stagnant. Please find attached snapshot for better reference. The set-up selected for this is what I described in this massge. Kindly provide suggestions if any. Thank you. 

[SRP]

Hi Anuj,

Residual graph appears to be stagnent which means it is not diverging. For convergence, it is not always you need to depend on the residual plot, it is just one part. In addition you need to check mass and energy convergence in your system which gives you the idea whether your simulation converges or not.

you can check it from reports > fluxes

Hope this helps you.

[Anuj Thakkar]

I appreciate your help once again. I've reviewed the fluxes in the report section and attached a snapshot for your reference. Does the value of 5053.787 W signify the overall heat transfer rate of the heat exchanger? If not, could you guide me on where I can find (which boundaries to be select) the overall heat transfer rate? Additionally, I've included another snapshot of mass flow rates. Can you confirm if the values of 0.282 kg/s and 0.189 kg/s correspond to the mass flow rates of the shell side and tube side, respectively? I'm curious if ANSYS calculates these values based on the velocity (selected as velocity inlet) and the fluid properties specified during the Numerical setup. Thank you so much.