Design, Analysis, and Fabrication of Heat Exchangers and Auxiliary Components of a Novel Supercritical Carbon Dioxide Brayton Cycle for Power Generation

Date
2021
Authors
Bass, Diego C.
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Abstract

Based upon the unique properties of supercritical carbon dioxide (sCO2), the sCO2 Brayton cycle, when compared to a steam Rankine cycle or a helium Brayton cycle, can achieve higher thermal efficiencies with lower turbine inlet temperatures. Carbon dioxide's ability to reach the supercritical phase (7.37 MPa, and 31 °C) with low thermal energy input is a desirable feature in power generation design, allowing for the use of various types of heat sources. The scope of the current research is to analyze, design, and fabricate heat exchangers and auxiliary components to an sCO2 Brayton cycle using a reciprocating piston expander. Design concepts were evaluated based upon capital costs, ease of fabrication, and effectiveness. One-dimensional heat transfer calculations were conducted for the heat source (heat introduced to the cycle) and heat exchanger (heat dissipated from the cycle) to determine required length of each component and their heating/cooling performance. Based upon analytical results, the heat source can produce a maximum heat rate of 16.7 kW, while the heat exchanger can dissipate a maximum heat rate of 13.5 kW. The heat exchanger is mostly limited by the capacity of water storage that is to be placed within the laboratory facility. For the sCO2 Brayton cycle to operate for periods of 5 to 10 minutes, the amount of heat dissipated by the heat exchanger must be kept minimum, and therefore, the amount of heat added to the system is controlled to maintain an 85 °C expander inlet temperature. With an inlet temperature of 85 °C to the piston expander, 4.45 kW of power is anticipated to be produced under isentropic conditions with an overall thermal efficiency of the cycle to be 12.75 %. Maintaining the inlet temperature of the compressor to 37 °C and the inlet temperature to the piston expander to 85 °C, the thermal efficiency of the cycle is maximized with the decreased heat addition requirement of the cycle. With completed fabrication, preliminary testing showcases that each component (the heat exchangers, compressor cooling, and dry ice installation) are ready for integration into the Brayton cycle as preparations are made to transition into full system testing.

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Keywords
Brayton cycle, Turbine inlet temperatures, Heat transfer calculations
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Department
Mechanical Engineering