Shell-and-tube heat exchanger
 

Hi,

I am dealing with a slightly different version of the common shell-and-tube heat exchanger. This model is just a tube encapsulated by another tube. The outter tube has chilled water flowing through it and the inner tube has hot air. The boundary conditions are inlet velocity and pressure outlets. The inner tube wall is modelled as an thin wall so I am just using the option in fluent to just give the wall a thickness for 1-D conduction without meshing it.

The trick to this model is that the tube is an elliptical twisted tube, therefore flow is likely swirling around which is supposed to enhance heat transfer and increase pressure drop.

I ran the same model using hot and cold air and the solutions at least convereged even if I have no idea if they are reliable. When I change the shell to water, it is not converging not even in first order.

Can someone please help? I am using turbulence model K-epsilon RNG.