Design a simple annular flow heat exchanger. Assume both fluids are water and the cold fluid flowing in the outer tube. The pipe diameters are based in type L copper tube with dimensions: (outside diameter 1/2-inch, nominal tube is 0.625 inch, with a wall thickness of 0.04 inches and the outside diameter of the one-inch nominal tube is 1.125 inches with a wall thickness of 0.05 inches. The mass flow-rate of water through both tubes should be based on 10 ft/s of water. The inlet temperature to the cold side is 40 degree F and the inlet to the hot side is 90 degree F. what length of heat exchanger is required to achieve a hot-side outlet temperature of 60 degree F if the overall heat transfer coefficient (U) for the heat exchanger is 400 Btu/hr.ft^2 F. Also calculate the log mean difference and effectiveness.