Assume a regenerator in a Brayton cycle has an efficiency of 75%. Find an expression for the second-law efficiency.

If air at 300 K is brought to 2600 K, 1 MPa, instantly, find the formation rate of NO.

A water turbine using nozzles is located at the bottom of Hoover Dam 175 m below the surface of Lake Mead. The water enters the nozzles at a stagnation pressure corresponding to the column of water above it minus 20% due to losses. The temperature is 15$^{\circ} \mathrm{C}$, and the water leaves at standard atmospheric pressure. If the flow through the nozzle is reversible and adiabatic, determine the velocity and kinetic energy per kilogram of water leaving the nozzle.

Ethane is burned with 150% theoretical air in a gas-turbine combustor. The products exiting consist of a mixture of CO2, H2O, O2, N2, and NO in chemical equilibrium at 1800 K, 1 MPa. Determine the mole fraction of NO in the products. Is it reasonable to ignore CO in the products?

The products of combustion are flowing through a heat exchanger with 12% carbon dioxide, 13%water, and 75% nitrogen on a volume basis at the rate 0.1 kg/s and 100 kPa. What is the dew-point temperature? If the mixture is cooled 10$^{\circ} \mathrm{C}$ below the dew-point temperature, how long will it take to collect 10 kg of liquid water?

At ground level in Denver, Colorado, the atmospheric pressure and temperature are 83.2 kPa and 25$^{\circ} \mathrm{C}$. Calculate the pressure on Pike’s Peak at an elevation of 2690 m above the city assuming (a) an incompressible and (b) an adiabatic atmosphere. Plot the ratio of pressure to ground level pressure in Denver as a function of elevation for both cases.

An Atkinson cycle has state 1 as 150 kPa, 300 K, a compression ratio of 9, and an expansion ratio of 14. Find the mean effective pressure.

In a heat pump that uses R134a as the working fluid, the R134a enters the compressor at 150 kPa, −10$^{\circ} \mathrm{C}$ and the R134a is compressed in an adiabatic process to 1 MPa using 4 kW of power input. Find the mass flow rate it can provide, assuming the process is reversible.

An air conditioner in the airport of Timbuktu runs a cooling system using R-410a with a high pressure of 1800 kPa and a low pressure of 200 kPa. It should cool the desert air at 45$^{\circ} \mathrm{C}$ down to 15$^{\circ} \mathrm{C}$. Find the cycle COP. Will the system work?

The air-standard Carnot cycle was not shown in the text; show the T-s diagram for this cycle. In an air-standard Carnot cycle, the low temperature is 280 K and the efficiency is 60%. If the pressure before compression and after heat rejection is 100 kPa, find the high temperature and the pressure just before heat addition.

An Atkinson cycle has state 1 as 150 kPa, 300 K, a compression ratio of 9, and a heat release of 1000 kJ/kg. Find the needed expansion ratio.

Is a Brayton cycle the same as a Carnot cycle? Name the four processes.

The human comfort zone is between 18 and $24^{\circ} \mathrm{C}$. What is the range in Kelvin? What is the maximum relative change from the low to the high temperature?

An oxygen molecule with mass m = M $\mathrm{mo}=32 \times 1.66 \times 10-27$ kg moves with a velocity of 240 m/s. What is the kinetic energy of the molecule? What temperature does that corresponds to if it has to equal (3/2) kT, where k is Boltzmann's constant and T is absolute temperature in Kelvin?