Natural convection- properties calculation by polynomial eqn
I need urgent help for my following problem:
*I am using fluent 6.3.26 and want to simulate tube in tube type (double pipe) heat exchanger. Fluid in internal pipe is co2 and in outer pipe water. for the properties of co2 I have put polynomial of 6 order in the material list. water properties are const. co2 is in close loop driven by Natural convection. water is in open loop- forced convection. when I run the simulation, solution does not converge for any steady or unsteady k-e model. I set the limits of temperature (290-350K) for which I fit polynomial for properties and my operating temp range is 310-330K. I am using Pressure based solver,k-e, unsteady, SIMPLE algorithm for pr-vel coupling, PRESTO for pressure discretization, 1st order upwind scheme for remaining descretization.
When I run simulation with boussinesq and const properties, solution gets converged for same setup.
*In K-e model, to get turbulent intensity (TI) I used the formula given in fluent manual which gives the value for TI is lower for higher reynold no. Is it correct? TI=0.16*(Re)^(-1/8)
Please advice me in this regard.
Thanks and regards
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