Consider a heat exchanger that uses hot air to heat cold water. Air enters this heat exchanger at 20 psia and 200°F at a rate of 100 ft3 /min and leaves at 17 psia and 100°F. Water enters this unit at 20 psia and 50°F at a rate of 0.5 lbm/s and exits at 17 psia and 90°F. Determine the total flow power, in hp, required for this unit and the flow work, in Btu/lbm, for both the air and water streams.

It is common knowledge that the temperature of air rises as it is compressed. An inventor thought about using this high-temperature air to heat buildings. He used a compressor driven by an electric motor. The inventor claims that the compressed hot-air system is 25 percent more efficient than a resistance heating system that provides an equivalent amount of heating. Is this claim valid, or is this just another perpetualmotion machine? Explain.

Steam flows steadily through a turbine at a rate of 45,000 lbm/h. It enters at 1000 psi and 900°F and leaves at 5 psi as saturated vapor. If the power generated by the turbine is 4 MW, determine the rate of heat loss from the steam.

Water is stored in a large, well-insulated storage tank at 21.0°C open to atmosphere. It is pumped at a rate of 40 m3/h to another tank 25 m above, which is also open to atmosphere. The motor driving the pump supplies energy at the rate of 9.5 kW. The water passes through a heat exchanger where 255 kW of heat is added to the water. The total friction loss (ΣF) in the system is 90.25 J/kg. Determine the final temperature of the water at the second tank