Gas flow into a reactor

Hi. I'm new to COMSOL and am puzzled on where to start. I would like to model the flow of a gas into a reactor. The gas would be at a temperature T1 and the contents of the reactor would be at T2 (T1 > T2).I can assume that the reactor is a cylinder as well as the pipes carrying gas in and out of the reactor. What I'm interested in learning is what is the heat exchange in the reactor, i.e. by how much does T2 increase as a function of time At what point does it reach steady state? How do I account for the liquid in the reactor being stirred?

Thank you!