Thermodynamics: Isentropic Efficiency of Steady Flow Devices (22 of 25)

0:00:10 - Comments about homework
0:03:45 - Reminders about isentropic efficiency for steady flow devices
0:09:45 - Actual turbines - Typical assumptions, T-s diagram, and isentropic efficiency
0:18:35 - Actual pumps and compressors - Typical assumptions, T-s diagram, and isentropic efficiency
0:29:26 - Example: Isentropic efficiency for compressor
0:42:25 - Isentropic efficiency for steady flow devices using ideal gases with constant specific heats
0:54:30 - Example: Isentropic efficiency for turbine using ideal gas

This lecture series was recorded live at Cal Poly Pomona during Winter 2017. The textbook is Cengel and Boles, "Thermodynamics: An Engineering Approach (8th edition)."

[anajo]

thank you for helping me understand the steps to solve for isentropic efficiency.

[KnowledgeTricky]

In an open cycle gas turbine plant, air enters the compressor at 1 bar and 290 K. The pressure at the exit of compressor is 5 bar. The isentropic efficiencies of the turbine and the compressor are 90% and 85%, respectively. Air fuel ratio is 60:1. The calorific value of the fuel used is 42 MJ/kg and mass flow rate of air is 2 kg/s. Assume air as an ideal gas with specific heat at constant pressure equal to 1.005 kJ/kgK and the specific heat ratio as 1.4. Consider specific heat at constant pressure for fuel also as 1.005 kJ/kgK and specific heat ratio is 1.4. Find the following:
1). Heat supplied by fuel to the plant in kJ/s is
a) 1300
b) 1400
c) 1000
d) 900
2). Work required to drive the Compressor in kW is
a) 400
b) 309
c) 595
d) 658
3). Actual turbine outlet temperature in Kelvin is
a) 672
b) 792
c) 710
d) 590
4). Thermal efficiency of the plant in percentage is
a) 21
b) 29
c) 19
d) 39

[paulatreides]

I'm not sure where these equations are coming from, the summary sheet for this chapter of this specific book denote a completely different set of equations. Can anyone clarify? Specifically, where did he derive (T1/T2) = (P1/P2)^k-1/k. The only thing that's similar in the book is (T2/T1) = (P2/P1)^k-1/k....so, I see that relationships are inverted but normally this professor follows the book pretty closely and never goes rogue. Lastly, the pressure ratio equation is not listed at the end of the chapter as well....so, a little confused.

[-ahmedmohamedhassan]

why the entropy rises in pump and compressor and drops in turbine

[cecilkoranteng]

anyone know which book contains the homework he assigns?