Two or Three Dimensional for a coil
 

Hi all;

I have a coil with a circular cross section according to the following attached pattern . Just As anybody observes, this pattern has two returns (two elbow couple). My question is if I can model this problem by a two dimensional model or I have to model this example by a three dimensional one. The boundary conditions are same for every cross section. If your answer is ok, Please lead me how to consider this configuration.

Thanks a lot for any help.
M.asghari

Attachment 7919

Again,Suppose , a gas within the coil is my model being heated by a liquid fluid. Which boundary condition is suitable for outlet Temperature?
Diricleh or nueman ,d()/dn=0.0 or another one?
What's your opinion?
What about should we take for other outlet boundary condition,too ? For example, the pressure or velocity.

Also, consider a semi-cylinder surrounds this coil. How can I mesh this three dimensional pattern by subtracting this semi-cylinder from coil?
Actually, which mesh type with which quality can be used for this problem?
Thx again for any help and consult.