What I'm trying to figure out is the temperature vs. time of a aqueous nuclear reactor. I'm trying to cool 200kW of energy with metal pipes running through a working reactor. This is just a heat calc, I'm not actually building one. The reactor runs at 200kW, is liquid filled, and will be cooled with water running through pipes that run through the reactor core. Assuming we have inlet cooling water at 25*C, and we need to constantly remove heat from the reactor, what size pipes do I need? I already have figured out, by m*Cp*deltaT, I will have somewhere around 2-4 kg water flow per second. I used this to find the approx. flowrate. 200*10^3 = m*cp*deltaT So what I have is a vessel that's 125L or water solution, being chilled cold water running through pipes that penetrate the vessel. So what is the temperature of the vessels water solution vs. time? I need to calculate how much heat is transferred to the water inside the pipe. This means I can vary the area of pipes, thickness, and make. I'm thinking I'll use a 2mm wall thickness, and steel as the pipe's material. Any help is appreciated.