I need to design a concentric heat exchanger. I have steam flowing on the shell side( annular region of the heat exchanger) at 2 bar and water flowing on the inside. I am maintaining constant wall temperature with steam flow. How should i size the length of the heat exchanger and how should i decide the steam flow rate for a given heat load. Also before the water is sent into the heat exchanger i am letting it flow through a calming section. How should i size the length of the calming section. Please give me the considerations i need to do. Please cite external references for calculations.