0.10 ft3/min of water is to heated from 50oF to 100oF as it flows through the inner tube (1-in ID) of a double pipe heat exchanger. 0.25lbm/s of hot water at 200oF enters the outer pipe and flows counter-current to the cold water. The overall heat transfer coefficient based on the inner tube is 100 Btu/(hr-ft-oF). Calculate tube length. Note that Q = UAΔTmean and specific heat of water is 1 Btu/lb/oF. Please draw a diagram and indicate your ΔTs on the diagram.
First calculate the flow rate of cold water in lbm/s Then find the exit temperature of the hot water Calculate the heat lost by the hot stream, Qh Calculate the heat gained by the cold stream, Qc - should be the same, obviously Calculate the mean temperature difference, ΔTmean Find A = Q / (UΔTmean) Find length from A
