Hi Vamsi, just running the model now.
Can you elaborate on what the results should be? Can you share the model with the straight tube and point out the differences between the 2 models? (both setup and results)
A few comments on the setup that I can see:
1. adiabatic wall, is it really 100% adiabatic on the outside? perfectly insulated?
2. i prefer to make lids myself rather than using the lid tool. this makes sure that any interferences that are found are ones that i want to eliminate. i haven't had a chance to fully check your model for interferences..etc.
3. i don't think you need to have the initial parameter velocity in the X direction. you can use that to speed along steady state solutions but this one should solve pretty quick.
4. you can remove air from the default fluid definition. because from what i can see you want to have nitrogen in the center and water on the outside. (setup looks ok)
I know the inlet conditions of the fluid and gas, for example let us say I have gas at 600K and water at 300K at the inlet, if this is the case the outlet of the gas should be <600K and water >300K with variation in velocity and slight variation in the density(as the temperature varies). I have no pressure information at inlet and outlet of heat exchanger.
Reasons for your comments
1.adiabatic wall, It is not 100% adiabatic outside, not insulated at all, but at first I was trying to do it without considering the heat loss to the environmet then add the outside air condition to compare both of the results. I just want to see whether this simulation works out well or not.
2.I tried by making own lids also, but anyway I tested with floexpress to see whether the design has any problems.
3.I haven't specified any velocity in the X direction, It automatically takes this because I gave the inlet mass flow rate.
4.I did even without the air.
The major problem that I found is when I specify the fluid subdomain as water which is flowing outside, calculation shows the density of the inside fluid is also close to density of the water, but when I specify air in the fluid subdomain, the calculation shows the density of the outside fluid close to that of the density of Air.
the results look pretty reasonable to me. the temperature drop in the inner fluid is about 60degrees. what are you expecting?
a couple other things I noticed on review of the results:
1. few goals, i would recommend setting up some "smoke test" goals where you check mass flow rate in and out. similarly things like inlet/outlet pressure and temperature. I prefer goals because it lets me evaluate many parameters at once on many locations at once rather than surface parameters that are surface by surface.
2.did you mean to set environmental pressure? since they are set at the outlets, this will define static pressure at the outlet. Are the inlet pressures ok?
3.I noticed you used level 8 mesh. did you see a difference from 3-8? you might want to try solution adaptive for your final runs.
the temperatures of my results are also reasonable but have you gone through the other parameters like density and Velocity??
Inlet and outlet densities of water and air?? If so can you tell me what are values you got?
density of water is 995,
default fluid is nitrogen, it's 0.75 at the inlet, 0.63 at the outlet
all in kg/m^3
looks good to me
checked nitrogen here: http://yeroc.us/calculators/gas-density.php
130kPa, 600K and 28g/mol
Thats great.. Looks like what I need, Can you tell me what all changes you made to the model that I have sent??
What's the version you used to simulate it?
Can you send the file please, @firstname.lastname@example.org
I'm running 2013 sp2.0, what version are you running?
I made no changes. Just looked at the setup and ran. Actually I changed from mesh level 8 to 5. Maybe yours completed because of max travels rather than converged goals and that is why your results are wrong. Try level 3 and then 5. Check why completion occurs.
Thats at 25 iterations, have you let it run to completion?
Please setup goals for pressure, temp, density and velocity all all the inlets and outlets, let it run to completion and post.