Tube inside a tube simulation
 

Hi

Iam simulating tube inside a tube 2D simulation with co-current laminar flow. water is flowing in outer tube and oil inside the inner tube. the geometry is inclined to 45 degrees. inlet conditions:
oil temp: 71 degrees C
oil velocity: 0.003m/s
water temp: 25 C
velocity: 0.00029

outlet conditions:
not known

outer tube wall is adiabatic

In gambit

created 2 D geometry. rectangle inside another rectangle. selected edges to define BC oil inlet, water inlet, oil outlet and water outlet. edges along the length as inner walls and outer walls. defined zones for fluid (oil and water).

In fluent

using steady state, laminar model, defined materials,
boundary conditions:
oil: fluid: motion type-->moving reference frame
translational velocity: x=0, y=0.003m/s
same for water with velocity of 0.00029m/s

inlet conditions: velocity magnitude n direction: x=0, y=(given vel for oil and water)
defined gravity in y=-9.81
i tried simulating using laminar and k-e model. difficult to converge.

need help and suggestions.

Rashmi