19 Due 4/14

1. You want to cool your cryogenics experiment by pumping pressurized liquid nitrogen through it. What is the power needed for a reversible pump that pressurizes 20 g/s of liquid nitrogen at 77.3 K from 200 kPa to 1MPa? Make appropriate approximations.

2. A typical specific heat ratio for the hot combustion gases entering the turbine of a jet engine is 1.25. For the gas constant, just use the one for air. Assume that the gases enter the turbine at 640 kPa and 927$\POW9,{\circ}$C, and exit at the ambient pressure of 100 kPa at a rate of 2 kg/s. Also assume that the specific heat ratio is constant going through the turbine, and that the turbine is adiabatic and reversible. Find the exit temperature, power, and heat flow. Do not compute any volumes, specific or not, when solving this question.

3. An reversible isobaric heat exchanger heats a stream of carbon dioxide at 100 kPa from 300 to 500 K. It takes in heat from a 600 K reservoir. Find the work required, the heat taken from the reservoir, and the overall entropy generation.

4. A co-flowing heat exchanger consists of two separate streams of substance that flow in the same direction while they exchange heat with each other. Assume that one entering stream consists of 0.6 kg/s of nitrogen at 150 kPa and 226.85$\POW9,{\circ}$C, and that the other entering stream consists of 0.25 kg/s of oxygen at 200 kPa and 16.85$\POW9,{\circ}$C. Also assume that the heat exchanger is long enough that the streams exit with the same temperature. The entire heat exchanger is well insulated. Find the exit temperature and rate of entropy generation. Use constant specific heats. You can write a separate first law for each stream, and then apply that the heat coming out of the nitrogen is the heat entering the oxygen. But it is simpler to write one first law for the entire thing.