tutorial 1 gas power cycle
TRANSCRIPT
Tutorial 1 THERMODYNAMICS
Mohd. Hardie Hidayat b. Mohyi Taylor’s Univeristy
Copyright © The McGraw-‐Hill Companies, Inc. Permission required for reproducEon or display.
Thermodynamics: An Engineering Approach Seventh EdiEon in SI Units
Yunus A. Cengel, Michael A. Boles McGraw-‐Hill, 2011
Ques:on 1
A gas turbine has the following details, air entering the compressor at 100 kPa and 20oC, pressure ra:o of 8, maximum temperature cycle is 800oC and the cold air stream leaves the generator at 10oC cooler then the hot air stream at the generator inlet. Determine the rates of heat addi:on and rejec:on to the cycle when it produces 150 kW assuming constant specific heats
Ques:on 2
• Pressure ra:o is 7, minimum and max, temperatures are 310 and 1150 K. Assuming compressor and turbine isentropic effciciency to be 75 and 82% respec:vely, and also 65% effec:veness for the generator, find the air temperature at the turbine exit, net work output, and thermal efficiency
Ques:on 3
• Air is used as the working fluid in a simple ideal Brayton cycle that has a pressure ra:o of 12, a compressor inlet temperature of 300 K, and a turbine inlet temperature of 1000 K. Determine the required mass flow rate of air for a net power output of 70 MW, assuming both the compressor and the turbine have an isentropic efficiency of (a) 100 percent and (b) 85 percent. Assume constant specific heats at room temperature
Ques:on 4 • Air enters the compressor of an ideal gas turbine engine at 310 K and 100
kPa, where it is compressed to 900 kPa and 650 K. At the turbine, air at 1400K. a) Find the thermal efficiency and back work ra:o of the cycle above. Is it viable
to recuperate some of the exhaust energy? b) If the cycle now become an actual gas turbine engine with the efficiency of
the turbine is at 90%, find the thermal efficiency of the cycle. Is it viable to use a regenerator to recuperate some of the exhaust energy? (T-‐s diagram as below).
c) Recuperate the energy with a regenerator with 80% efficiency and find the new thermal efficiency.
d) Now, evaluate the thermal efficiencies obtained between using variable specific heats of air and constant specific heats of air at room temperature.
e) If the regenerator effec:veness is reduced to 70%, how much would the thermal efficiency vary for the case of variable specific heat capaci:es.
Answer 4
Upon comparing the thermal efficiencies it was found that the thermal efficiencies do not vary significantly (40% and 39.9%) when the standard assump:ons were changed from the air standard assump:ons to the cold air standard assump:ons