Hi guys. Without going into too much detail. Basically I have a counter-flow heat exchanger problem where I need to find one of the outlets temps only given the inlet temps of each fluid. I have no idea how to do it though as I'm not given a value for over heat transfer coefficient (U) or surface area (A). However, in a previous example the same heat exchanger was used and one of the outlet temps was given which allowed me to calculate the value of the product of the overall heat transfer coefficient and the surface area (U*A). I was wondering if I can use this value again for the 2nd example? I know A is probably constant but is U constant too? All that has been changed for the 2nd example is flow rate of one of the fluids (same inlet temps and fluid properties). Any help would be greatly appreciated as my understanding of U isnt all that great. Mark.