Session: 30-12 Testing 2

Paper Number: 122604

122604 - Experimental Investigation of Rotor Passage Loss in S-CO2 Radial Turbine 

The Brayton cycle, which uses supercritical carbon dioxide (S-CO₂) as the working fluid, has high efficiencies over a wide range of heat source temperatures. This is because the compressor inlet conditions are near the critical point, 304 K and 7.38 MPa. Near the critical point, S-CO₂ has a large density and specific heat capacity, and a small compressibility factor, so the compression work can be minimized. Low compression work is better than a high turbine inlet temperature from a cycle efficiency perspective. Additionally, the high density allows compressors, turbines, and pre-coolers to be designed compact.

Since S-CO₂ turbomachinery has different physical behavior than ideal gas turbomachinery, the existing design methodology has to be revisited and modified if necessary. Basic research was conducted worldwide based on the component analysis codes. Initial demonstration units were built and tested in many institutions such as SNL, SWRI, BMPC, and KAERI, and the behavior of the compressor and recuperator was analyzed and correlated with performance curves. The performance curves of radial compressors of various sizes and blade angles have been presented, and a number of loss models have been identified or new loss models have been proposed for the S-CO₂ compressors. However, less attention was given to the S-CO₂ turbine compared to the S-CO₂ compressor. This is because the operating conditions of the S-CO₂ turbine are far from the critical point compared to the operating conditions of the compressor, resulting in reduced real gas effects. However, due to the high density which is about 200 kg/m³ and the nonlinear properties of S-CO₂, the loss models for radial turbine should be also evaluated sufficiently for commercialization of small S-CO₂ power unit.

In this study, the calibration of the rotor passage loss in a radial turbine was performed. This loss is expected to contribute about 40% of the total enthalpy loss in a radial turbine. The rotor passage loss is the combination of irreversible losses such as skin friction, blade loading, separation, wake and mixing that occur in the rotor section of a radial turbine. Loss models have been presented by Benson, H. Moustapha and Wasserbauer. Currently, H. Moustapha’s loss model, which is considered to be the most accurate, is widely used in the turbine design. However, this loss is difficult to evaluate with CFD because it occurs in the rotor. Therefore, loss models generated in the rotor need to be experimentally validated and calibrated.

A S-CO₂ Turbine-Alternator-Compressor (TAC) has been installed at Korea Advanced Institute of Science and Technology (KAIST) and is being utilized for measuring various physical quantities to further calibrate the existing model or to develop a new model if necessary. Using this TAC, the performance map of the radial turbine has been derived and the regression analysis is performed for the existing loss models. By utilizing the experimental data, the best-fitted model is further calibrated and it will be presented in the paper.

Presenting Author: Seungkyu Lee Korea Advanced Institute of Science and Technology

Presenting Author Biography: Presenting Author: Seungkyu Lee
Email: lsk629@kaist.ac.kr
Short CV of Presenting Author:
Affiliation: Department of Nuclear and Quantum Engineering, Korea Advanced Institute of Science and Technology (KAIST)

Research Area
1. S-CO2 turbomachinery
2. S-CO2 power cycle for nuclear fission energy
3. Auxiliary component of S-CO2 power cycle

Education
1. Korea Advanced Institute of Science and Technology, Daejeon, Korea
Candidate for Ph.D of Science in Engineering: Nuclear and Quantum Engineering
2. Yonsei University, Seoul, Korea
Bachelor of Engineering: Mechanical Engineering, August 2022

Authors:

Seungkyu Lee Korea Advanced Institute of Science and Technology
Jeong Ik Lee Korea Advanced Institute of Science and Technology
Gihyeon Kim Korea Advanced Institute of Science and Technology
Jeong Yeol Baek Korea Advanced Institute of Science and Technology