Abnomal temperature behavior Star CCM+
 

Hello everyone,
I have to simulate the cooling of a pipe which is heated on its outer surface by R12. The pipe is heated only in the central part of its length so I have built 3 different pipes and imprinted them together.
The fact is after a certain number of iterations the temperature of the fluid R12 gets below 100 K on a certain number of cells.
I have tried to see how does it work if I heat directly the fluid without the solid pipe and in that case, the simulation goes well but when I add the pipe around the fluid and heat it from outside then this problem occurs.
I have put here also the screenshots of the situation.
Best regards
L. Singh