Supercritical carbon dioxide as a working fluid in a Brayton power cycle has benefits but also faces unique challenges in implementation. With carbon dioxide, turbomachinery is much more compact and potentially more cost effective. The primary impediments to cycle component performance are the high pressures required to bring the fluid to a supercritical state and the wildly varying fluid properties near the critical point. Simple design models are often used as a quick starting point for modern turbomachinery and heat exchanger design. These models are reasonably accurate for design estimate, but often assume constant properties. Since supercritical carbon dioxide varies not only in temperature, but also in pressure, the models must be evaluated for accuracy. Two key factors in cycle design, aerodynamics and heat transfer, are investigated through the modeling of the performance of the first stage of the turbo-expander and the recuperative heat exchangers. Lookup tables that define the change in fluid properties relative to changes in pressure and temperature are input into the fluid dynamics software. The results of the design models are evaluated against each other. The simpler models and the fluid dynamics simulations are found to have acceptable agreement. Improvements to the simple models are suggested.
Master of Science in Mechanical Engineering (M.S.M.E.)
College of Engineering and Computer Science
Mechanical and Aerospace Engineering
Mechanical Engineering; Thermo-Fluids Track
Length of Campus-only Access
Masters Thesis (Open Access)
Schmitt, Joshua, "Comparison of Modeling Methods for Power Cycle Components Using Supercritical Carbon Dioxide as the Operating Fluid" (2015). Electronic Theses and Dissertations. 5034.