Quiz2_problems

Quiz2_problems - One way to improve the efficiency of a...

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Unformatted text preview: One way to improve the efficiency of a simple Brayton cycle gas turbine is to introduce a heat exchanger, known as a regenerator, into the system as shown in the diagram below. This regenerator transfers heat from the exhaust stream of the turbine to the high pressure gas exiting the compressor prior to the introduction of this gas to the combustion stage. Air at condition (1) is drawn through an adiabatic isentropic compressor, and exits at condition (2). It then enters an idealized heat exchanger, which does not have any pressure drop, and leaves at condition (a). It then enters an idealized combustion chamber which adds an amount of heat qh to the air and exits that chamber at condition (3). The heated high pressure air then enters an ideal turbine which allows it to expand to condition (4). This gas is then run through the regenerator where is transfers heat to the air at condition (2). The exhaust then exits the system at condition (b); this exhaust then mixes with ambient air and returns to condition (1), forming a closed cycle. In the ideal limit, the temperature at point a equals the turbine exhaust temperature, i.e. Ta=T4. MAE 118A QUIZ 2 Prof. G.R. Tynan UCSD MAE Department CLOSED BOOK CLOSED NOTES NO CALCULATORS OR OTHER ELECTRONIC DEVICES ARE PERMITTED. ALLOTED TIME: 15 MINUTES. A) Draw a T‐s diagram for this cycle, making sure to label conditions 1, 2, a, 3, 4, and b. Draw a horizonal line denoting Ta in terms of T4. (15 Points) B) Write an expression for the heat input in the combustion chamber, qh, in terms of the specific heat Cp and the appropriate temperatures. (5 points) C) Write a similar expression for the net work, wnet=wt‐wc where wt and wc denote the turbine work release and compressor work input. (5 points) D) Find the thermal efficiency in terms of the temperatures T1, T2, T3 and T4. (5 Points). ...
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