I am not really a heat transfer guy so I hope someone here can help me out here. I would like to know the formula to get this. Here is what I ma facing: I have a mandrel (basically a piece of cylindrical H-11 steel). It has OD of 3.5 inches and 37” in length. It has a core hole of about 7/8” Dia and 37 “ length. Water pumped into the core hole at 10 GPM thru a 3/4” dia pipe. The H-11 steel has .110 BTU/lb specific heat capacity. I want to be able to lower the temp of the mandrel from 850 to 200 deg F. How much water do I need? Please help.