A 50-kg iron block and 20-kg copper block, both initially at 80 oC, are dropped into a large lake at 15 oC. Thermal equilibrium is established after a while as a result of heat transfer between the blocks and the lake water. Determine the total entropy change of this process in kJ/K.

Apreheater involves the use of condensing steam at 100°c on the inside of a bank of tubes to heat air that enters at 1 atm and 25°c. the air moves at 5 m/s in cross flow over the tubes. each tube is 1 m long and has an outside diameter of 10 mm. what is the minimum value of nl needed to achieve an outlet temperature of t 75 c? what is the corresponding pressure drop across the tube bank?