Regenerative Brayton Cycle Analysis

7190 words 29 pages
MAE 336
(Power Plant Design)

Design Project 1:
Regenerative Brayton Cycle

Date Submitted: 4/02/2012

Garrett Kinsel
ID#: 003800821

Mon/Wed 9:00am-11:15am

Instructor: Dr. Torabzadeh, Ph.D.

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ABSTRACT

The purpose of this design project was to investigate the effect of various design and operating parameters on the thermal efficiency, net work output per unit mass, and back work ratio of a regenerative Brayton cycle. Specifically, these parameters include the pressure ratio, TminTmax ratio, regenerator effectiveness, and compressor and turbine efficiencies, assuming the working fluid to be air at 100kPa and 300K at the compressor inlet. Model calculations are presented
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Thus, the highly pressurized air leaving the compressor is preheated in the regenerator before it enters the combustion chamber. This results in a decrease in QH and QL by the same amount, and an increase in the overall thermal efficiency of the cycle. With this modification, it allows for the same net work output for less input. In regards to thermal efficiency, the regenerator performs best at lower pressure ratios. In the figure below it can also be seen that lower TminTmax ratios tend to generate higher thermal efficiencies:

It should also be cited that in gas turbines with a regenerator, the temperature of the exhaust gases leaving the turbine is typically higher than the temperature of the air leaving the compressor. If this requisite is not met, it will cause the heat to flow in the opposite direction causing the efficiency to decrease. The bottom line is that the thermal efficiency of a regenerative Brayton cycle depends on the pressure ratio, just as the simple Brayton cycle does, but it also depends on the ratio of the minimum temperature (T1) and the maximum temperature (T3). This reasoning is graphically depicted below:

Several assumptions are needed in order to facilitate the analysis of this problem, however all of the following simplifications are well justified. The following assumptions will be made for the regenerative Brayton cycle: * The operating fluid is air, modeled as an ideal gas.

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