I've got a problem. I'm trying to design a reactor with internal cooling provided by water flowing through tubes directly within the reactor. Basically, it's like a shell and tube heat exchanger with an internal heat source. The problem is that the cooling water is to be evaporated within the reactor, and I don't know how to account for the resulting increase in volume. If I pump the coolant in at a standard liquid speed of 2m/s, then the exist vapour will be at several kilometers per second. This is no doubt well above the speed of sound in steam and would obviously damage the pipes. So, is it safe to just include a single expansion joint in the tubes within the reactor so that the inlet and outlet speeds are within safe range, or would that just cause other problems? I can't find anything in the literature about evaporation of coolant streams, but I'm sure it's done in industry.