HX Please HELP

NTM

Hi All,

I'm modelling a 3D cross flow heat exchanger with a simple hex mesh less than 200,000 cells. I'm running on default convergence criteria of 3 orders of magnitude residual decay. The boundary conditions specified are for the exhaust air into HX and fresh air into HX both at a certain temp and mass flow rate, however the exhaust flow rate is double the fresh air supply flow rate. Outlets are pressure outlets.

The heat exchanger efficiency I'm getting simply by ratio of two temps is about 40% higher than my experimental values which are quite accurate. I'm just using the energy equation and shell conduction, not any specific heat exchanger models.

Is there any way to bridge the gap in simulation and experimental efficiencies? I assume that if I use a denser mesh and stricter convergence criteria it will simply become more efficient in CFD...?

Thanks for reading this