1. Helium gas at 8108R, 45 lbf/in.2, and a velocity of 10 ft/s enters an insulated nozzle operating at steady state and exits at 6708R, 25 lbf/in.2 Modeling helium as an ideal gas with k 5 1.67, determine (a) the velocity at the nozzle exit, in ft/s, (b) the isentropic nozzle efficiency, and (c) the rate of entropy production within the nozzle, in Btu/8R per lb of helium flowing.
2. Air modeled as an ideal gas enters a one-inlet, one-exit control volume operating at steady state at 100 lbf/in.2, 9008R and expands adiabatically to 25 lbf/in.2 Kinetic and potential energy effects are negligible. Determine the rate of entropy production, in Btu/8R per lb of air flowing,
(a) If the control volume encloses a turbine having an isentropic turbine efficiency of 89.1%.
(b) If the control volume encloses a throttling valve.