Many new turbine designs may take large timelines to prove their worth. For getting duty condition at optimum efficiency, one can always scale speed, diameter, if a very efficient benchmark is available. This paper examines the similarity-based scaling strategy to develop radial inflow turbines for different compressible fluids from a well-established NASA radial flow turbine designed and experimentally tested with air as the working fluid. The NASA 1730 air turbine experimental data have been used as the benchmark here and adopted multiple fluids to understand scaling. The considered fluids are supercritical carbon dioxide for the Brayton cycle, helium for the cryogenic liquefaction cycle, and R143a for the organic Rankine cycle. The uniqueness here is to have three types of cycles, viz. closed-loop Brayton cycle, organic Rankine cycle, and cryogenic helium liquefaction cycle, which employ different working fluids, adapting the same NASA turbine geometry. This paper has described the scaling methodology and presented the simulated turbine performance of SCO2, helium, and R143a using computational fluid dynamics. The dimensionless curves for these fluids are plotted on the corresponding experimental characteristics of the NASA turbine. Out of the three fluids, SCO2 showed the perfect Mach number matching for the flow and torque coefficient curves. The Mach number deviations in the case of helium were small, and the variations were slightly higher for R143a. The efficiencies were the highest for R143a, followed by SCO2 and helium. Thus, the scaling was found to be effective in all cases. Thus, the standard turbomachinery space developed for air as fluid can be used effectively for the development of turboexpanders for various cycles with different working fluids without redesigning the entire shape using similarity-based scaling. The benchmark NASA 1730 turbine has proven this in three special cases. This paper is not against designing new machines but is only trying to say that when such good benchmark machines like NASA 1730 turbine is available; designers must use the power of similitude to adapt it to match new fluids and new conditions.
Performance evaluation of solar flat plate collector using different working fluids through computational fluid dynamics
