Sensitivity Study of S-CO2 Compressor Design for Different Real Gas Approximations

2016 ◽  
Author(s):  
Jekyoung Lee ◽  
Seong Kuk Cho ◽  
Jae Eun Cha ◽  
Jeong Ik Lee
Keyword(s):  
Thermodynamic Property ◽  
Critical Point ◽  
Technology Development ◽  
Static Condition ◽  
Sensitivity Study ◽  
Ideal Gas ◽  
Brayton Cycle ◽  
Real Gas ◽  
Compressor Design ◽  
Turbomachinery Design

With the efforts of many researchers and engineers on the Supercritical CO2 (S-CO2) Brayton cycle technology development, the S-CO2 Brayton cycle is now considered as one of the key power technologies for the future. Since S-CO2 Brayton cycle has advantages in economics due to high efficiency and compactness of system, various industries have been trying to develop technologies on the design and analysis of S-CO2 Brayton cycle components. Among various technical issues on the S-CO2 Brayton cycle technology development, treatment of thermodynamic property near the critical point of S-CO2 is very important since the property shows non-linear variation which causes large error on design and analysis results for ideal gas based methodologies. Due to the special behavior of thermodynamic property of CO2 near the critical point, KAIST research team has been trying to develop a S-CO2 compressor design and analysis tool to reflect real gas effect accurately for better design and performance prediction results. The main motivation for developing an in-house code is to establish turbomachinery design methodology based on general equations to improve accuracy of design and analysis results for various working fluids including S-CO2. One of the key improvements of KAIST_TMD which is an in-house tool for S-CO2 turbomachinery design and analysis is the conversion process between stagnation condition and static condition. Since fluid is moving with high flow velocity in a compressor, the conversion process between stagnation and static condition is important and it can have an impact on the design and analysis results significantly. A common process for the conversion is based on the specific heat ratio which is typically a constant from ideal gas assumption. However, specific heat ratio cannot be assumed as a constant for the case of S-CO2 compressor design and analysis because it varies dramatically near the critical point. Thus, in this paper, sensitivity study results on the state condition conversion between stagnation and static conditions with different approaches will be presented and further analysis on impact of the selected approaches on the final impeller design results will be discussed.

The Effect of Real Gas Approximations on S-CO2 Compressor Design

2018 ◽  
Vol 140 (5) ◽  
Author(s):  
Jekyoung Lee ◽  
Seong Kuk Cho ◽  
Jeong Ik Lee
Keyword(s):  
Critical Point ◽  
High Efficiency ◽  
Technology Development ◽  
Static Condition ◽  
Component Technology ◽  
Brayton Cycle ◽  
Real Gas ◽  
Compressor Design ◽  
The Future ◽  
The Impact

From the efforts of many researchers and engineers related to the S-CO2 Brayton cycle technology development, the S-CO2 Brayton cycle is now considered as one of the key power technologies for the future. Since the S-CO2 Brayton cycle has advantages in economics due to high efficiency and compactness of the system, various industries have been trying to develop baseline technology on the design and analysis of the S-CO2 Brayton cycle components. According to the previous researches on the S-CO2 Brayton cycle component technology, the treatment of a thermodynamic property near the critical point of CO2 is one of the main concerns since conventional design and analysis methodologies cannot be used for the near critical point region. Among many thermodynamic properties, the stagnation to static condition conversion process is important since the flow in a compressor is at high flow velocity. In this paper, the impact of various stagnation to static conversion methods on the S-CO2 compressor design near the critical point will be evaluated. From the evaluation, the limitation of a certain stagnation to static conversion method will be discussed to provide a guideline for the future S-CO2 compressor designers.

Numerical Approach for Real Gas Simulations: Part I — Tabular Fluid Properties for Real Gas Analysis

2017 ◽  
Author(s):  
Francisco Moraga ◽  
Doug Hofer ◽  
Swati Saxena ◽  
Ramakrishna Mallina
Keyword(s):  
Equation Of State ◽  
Error Analysis ◽  
Critical Point ◽  
Ideal Gas ◽  
Phase Region ◽  
System Level ◽  
Component Level ◽  
Power Cycles ◽  
Real Gas ◽  
Fluid Properties

Recently there has been increased interest in the use of carbon dioxide (CO2) in closed loop power cycles. As these power cycles capitalize on the non-ideal gas behavior of CO2, their analysis both at the system level and at the detailed component level requires an advanced equation of state. Commonly used analytical equations of state as BWRS (BenedictWebbRubin equation of State) or Peng-Robinson are known to have high errors near the critical point and are thus unsuitable for the analysis of cycles or components where the flow conditions approach the critical point. An accurate equation of state is required at all phases of the development process from high level cycle calculations to the detailed component CFD. The NIST RefProp software package provides accurate CO2 fluid properties across the thermodynamic space but suffers from high computational over-head. This study is presented in two parts. Part I (this part) of this paper describes an approach to creating a tabular representation of the equation of state that is applicable to any fluid. This approach is applied to generating an accurate, fast and robust tabular representation of the RefProp CO2 properties and an error analysis is performed to meet the accuracy requirements. The paper also discusses two approaches used to define speed of sound in the two-phase region and their sensitivity analysis on the 3D compressor flow. Part II of the paper details the numerical simulations of a supercritical CO2 centrifugal compressor using the tabular approach. This paper shows that table resolution can be tailored to match the accuracy requirements while minimizing the time used to evaluate the tabulated thermo-physical functions. Error analysis are shown to demonstrate the level of accuracy possible with this approach.

scholarly journals Design of a Centrifugal Compressor Stage and a Radial-Inflow Turbine Stage for a Supercritical CO2 Recompression Brayton Cycle by Using 3D Inverse Design Method

2017 ◽  
Author(s):  
Jiangnan Zhang ◽  
Pedro Gomes ◽  
Mehrdad Zangeneh ◽  
Benjamin Choo
Keyword(s):  
Centrifugal Compressor ◽  
Supercritical Co2 ◽  
Design Method ◽  
Ideal Gas ◽  
Inverse Design ◽  
Brayton Cycle ◽  
Real Gas ◽  
Radial Inflow Turbine ◽  
Inverse Design Method ◽  
The Ideal

It is found that the ideal gas assumption is not proper for the design of turbomachinery blades using supercritical CO2 (S-CO2) as working fluid especially near the critical point. Therefore, the inverse design method which has been successfully applied to the ideal gas is extended to applications for the real gas by using a real gas property lookup table. A fast interpolation lookup approach is implemented which can be applied both in superheated and two-phase regimes. This method is applied to the design of a centrifugal compressor blade and a radial-inflow turbine blade for a S-CO2 recompression Brayton cycle. The stage aerodynamic performance (volute included) of the compressor and turbine is validated numerically by using the commercial CFD code ANSYS CFX R162. The structural integrity of the designs is also confirmed by using ANSYS Workbench Mechanical R162.

SCO2PE Operating Experience and Validation and Verification of KAIST_TMD

2013 ◽  
Author(s):  
Jekyoung Lee ◽  
Jeong Ik Lee ◽  
Yoonhan Ahn ◽  
Seong Gu Kim ◽  
Jae Eun Cha
Keyword(s):  
Research Team ◽  
High Efficiency ◽  
Operating Experience ◽  
Ideal Gas ◽  
Operating Conditions ◽  
Inlet Temperature ◽  
Brayton Cycle ◽  
Validation And Verification ◽  
Pump Design ◽  
Turbomachinery Design

Supercritical carbon dioxide (S-CO2) Brayton cycle has gaining attention due to its compactness and high efficiency at intermediate temperature range of turbine inlet temperature. Thus, many research groups have been trying to develop their own S-CO2 Brayton cycle technology or component design technology. KAIST research team has been trying to develop a S-CO2 turbomachinery design methodology. As a part of this effort, In-House code KAIST_TMD (KAIST Turbomachinery Design) was developed based on open literatures. KAIST_TMD can reflect real gas effect since it uses precise equations and property database rather than ideal gas assumptions. Most special characteristic of KAIST_TMD is that KAIST_TMD can design both of radial type and axial type turbomachineries so it can compare performance of both radial and axial turbomachineries under the same operating conditions. KAIST_TMD provides geometry of turbomachinery and off design performance map also. This research team built a S-CO2 Pump Experiment facility (SCO2PE) to experience the S-CO2 loop operation and to perform validation and verification of KAIST_TMD in near future. Canned motor pump and shell and tube type heat exchanger were installed as the main components of SCO2PE. Main objectives of this paper are to present preliminary experimental data and share the operating experience and troubleshooting of the facility. Data analysis and detailed discussions about an experimental procedure and major issues when pump operates near the critical point will be presented in the paper. As a result, preliminary data were obtained that can be used for improving the facility to increase accuracy of the data for future validation and verification of KAIST_TMD for radial compressor/pump design.

Review of evolution of compressor design process and future perspectives

2006 ◽  
Vol 220 (6) ◽  
pp. 761-771 ◽  
Author(s):  
M Molinari ◽  
W N Dawes
Keyword(s):  
Design Process ◽  
Preliminary Analysis ◽  
Technology Development ◽  
Fluid Dynamic ◽  
Advisory Council ◽  
Jet Engines ◽  
Future Perspectives ◽  
Current Generation ◽  
Compressor Design ◽  
Turbomachinery Design

Having virtually reached the asymptote of the technology development in turbomachinery design, the challenge is now to find and implement new design methodologies and tools, capable of applying the current technology more quickly and reliably. This article first reviews the different approaches historically used in turbomachinery design, with the aim of understanding what has triggered improvements in the design up to the present day and how the trend can be maintained and accelerated. By recognizing the problems encountered in turbomachinery design, the aim is to identify the features of a new design process, which designers should follow to meet the objectives set by the Advisory Council of Aeronautical Research in Europe - to generate innovative and affordable solutions and, fundamentally, to break the asymptote for the current generation of large civil jet engines. In particular, it is believed that computational fluid dynamic tools should be more highly integrated in the design process by making them fully available from the preliminary analysis.

Preliminary Aerodynamic Design of a S-CO2 Axial Turbine

2021 ◽  
Author(s):  
R. Senthil Kumaran ◽  
Dilipkumar B. Alone ◽  
Abdul Nassar ◽  
Pramod Kumar
Keyword(s):  
Mass Flow ◽  
Brayton Cycle ◽  
Cfd Simulations ◽  
Fluid Medium ◽  
Axial Turbine ◽  
Real Gas ◽  
Axial Turbines ◽  
Turbine Design ◽  
Turbomachinery Design ◽  
Line Design

Abstract Axial turbines are gaining prominence in supercritical carbon-di-oxide (S-CO2) Brayton cycle power blocks. S-CO2 Brayton cycle power systems designed for 10 MW and upwards will need axial turbines for efficient energy conversion and compact construction. The real gas behavior of S-CO2 and its rapid property variations with temperature presents a strong challenge for turbomachinery design. Applying gas and steam turbine philosophies directly to S-CO2 turbine could lead to erroneous designs. Very little information is available in the open literature on the design of S-CO2 axial turbines. In this paper, design of a 10 MW axial turbine for a simple recuperated Brayton cycle waste heat recovery system is presented. Three repeating stages with nominal stage loading coefficient of 2.3 and flow coefficient of 0.37 were designed. An axial turbine mean-line design method tuned to S-CO2 real gas fluid medium is discussed. 3D blade design was made suing commercial turbomachinery design software AxSTREAM. The turbine was designed for inlet temperature of 818.15 K, pressure ratio of 2.2, rotational speed of 12000 rpm and mass flow rate of 104.5 kg/s. 3D CFD simulations were carried out using the commercial RANS solver ANSYS CFX 2020 R2 with SST turbulence model for closure. S-CO2 was modelled as real gas with Refrigerant Gas Property tables generated over the appropriate pressure and temperature ranges using NIST Refprop database. CFD studies were carried out over a range of mass flow rates and speeds, covering the design and several off-design conditions. The performance maps generated using 3D CFD simulations of the turbine are presented. The geometrical parameters obtained with the mean-line design matched well with that of the 3D turbine design arrived using AxSTREAM. It was observed that the turbine produced 10 MW power at the design condition while passing the required mass flow. CFD studies also showed that the preliminary turbine design achieved a moderate total-to-total efficiency of 80 % at the design condition. The design has potential for further optimization to obtain improved efficiency and for reducing the number of stages from three to two.

Centrifugal Compressor Design for Near-Critical Point Applications

2018 ◽  
Vol 141 (3) ◽  
Author(s):  
Alireza Ameli ◽  
Ali Afzalifar ◽  
Teemu Turunen-Saaresti ◽  
Jari Backman
Keyword(s):  
Critical Point ◽  
Centrifugal Compressor ◽  
Compressibility Factor ◽  
Design Procedure ◽  
Operating Conditions ◽  
Brayton Cycle ◽  
Compressor Design ◽  
Lower Temperature ◽  
The Individual ◽  
Line Design

The supercritical CO2 (sCO2) Brayton cycle has been attracting much attention to produce the electricity power, chiefly due to its higher thermal efficiency with the relatively lower temperature at the turbine inlet compared to other common energy conversion cycles. Centrifugal compressor operating conditions in the supercritical Brayton cycle are commonly set in vicinity of the critical point, owing to smaller compressibility factor and eventually lower compressor work. This paper investigates and compares different centrifugal compressor design methodologies in close proximity to the critical point and suggests the most accurate design procedure based on the findings. An in-house mean-line design code, which is based on the individual enthalpy loss models, is compared to stage efficiency correlation design methods. Moreover, modifications are introduced to the skin friction loss calculation to establish an accurate one-dimensional design methodology. Moreover, compressor performance is compared to the experimental measurements.

Centrifugal Compressor Design for Near-Critical Point Applications

2018 ◽  
Author(s):  
Alireza Ameli ◽  
Ali Afzalifar ◽  
Teemu Turunen-Saaresti ◽  
Jari Backman
Keyword(s):  
Critical Point ◽  
Centrifugal Compressor ◽  
Compressibility Factor ◽  
Design Procedure ◽  
Operating Conditions ◽  
Brayton Cycle ◽  
Compressor Design ◽  
Lower Temperature ◽  
The Individual ◽  
Line Design

The supercritical CO2 (sCO2) Brayton cycle has been attracting much attention to produce the electricity power, chiefly due to its higher thermal efficiency with the relatively lower temperature at the turbine inlet compared to other common energy conversion cycles. Centrifugal compressor operating conditions in the supercritical Brayton cycle are commonly set in vicinity of the critical point, owing to smaller compressibility factor and eventually lower compressor work. This paper investigates and compares different centrifugal compressor design methodologies in close proximity to the critical point and suggests the most accurate design procedure based on the findings. An in-house mean-line design code, which is based on the individual enthalpy loss models, is compared to stage efficiency correlation design methods. Moreover, modifications are introduced to the skin friction loss calculation to establish an accurate 1-D design methodology. Moreover, compressor performances are compared to the experimental measurements.

Numerical Simulation of the Performance of an Axial Compressor Operating With Supercritical Carbon Dioxide

2018 ◽  
Author(s):  
Jinlan Gou ◽  
Wei Wang ◽  
Can Ma ◽  
Yong Li ◽  
Yuansheng Lin ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Numerical Simulation ◽  
Supercritical Carbon Dioxide ◽  
Critical Point ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Axial Compressor ◽  
Brayton Cycle ◽  
Supercritical Carbon

Using supercritical carbon dioxide (SCO2) as the working fluid of a closed Brayton cycle gas turbine is widely recognized nowadays, because of its compact layout and high efficiency for modest turbine inlet temperature. It is an attractive option for geothermal, nuclear and solar energy conversion. Compressor is one of the key components for the supercritical carbon dioxide Brayton cycle. With established or developing small power supercritical carbon dioxide test loop, centrifugal compressor with small mass flow rate is mainly investigated and manufactured in the literature; however, nuclear energy conversion contains more power, and axial compressor is preferred to provide SCO2 compression with larger mass flow rate which is less studied in the literature. The performance of the axial supercritical carbon dioxide compressor is investigated in the current work. An axial supercritical carbon dioxide compressor with mass flow rate of 1000kg/s is designed. The thermodynamic region of the carbon dioxide is slightly above the vapor-liquid critical point with inlet total temperature 310K and total pressure 9MPa. Numerical simulation is then conducted to assess this axial compressor with look-up table adopted to handle the nonlinear variation property of supercritical carbon dioxide near the critical point. The results show that the performance of the design point of the designed axial compressor matches the primary target. Small corner separation occurs near the hub, and the flow motion of the tip leakage fluid is similar with the well-studied air compressor. Violent property variation near the critical point creates troubles for convergence near the stall condition, and the stall mechanism predictions are more difficult for the axial supercritical carbon dioxide compressor.

Numerical Approach for Real Gas Simulations: Part II — Flow Simulation for Supercritical CO2 Centrifugal Compressor

2017 ◽  
Author(s):  
Swati Saxena ◽  
Ramakrishna Mallina ◽  
Francisco Moraga ◽  
Douglas Hofer
Keyword(s):  
Critical Point ◽  
Centrifugal Compressor ◽  
Supercritical Co2 ◽  
Operating Conditions ◽  
Inlet Guide Vane ◽  
Thermodynamic Quantities ◽  
3D Flow ◽  
Real Gas ◽  
The Real ◽  
Operating Range

This paper is presented in two parts. Part I (Tabular fluid properties for real gas analysis) describes an approach to creating a tabular representation of the equation of state that is applicable to any fluid. This approach is applied to generating an accurate and robust tabular representation of the RefProp CO2 properties. Part II (this paper) presents numerical simulations of a low flow coefficient supercritical CO2 centrifugal compressor developed for a closed loop power cycle. The real gas tables presented in part I are used in these simulations. Three operating conditions are simulated near the CO2 critical point: normal day (85 bar, 35C), hot day (105 bar, 50 C) and cold day (70 bar, 20C) conditions. The compressor is a single stage overhung design with shrouded impeller, 155 mm impeller tip diameter and a vaneless diffuser. An axial variable inlet guide vane (IGV) is used to control the incoming swirl into the impeller. An in-house three-dimensional computational fluid dynamics (CFD) solver named TACOMA is used with real gas tables for the steady flow simulations. The equilibrium thermodynamic modeling is used in this study. The real gas effects are important in the desired impeller operating range. It is observed that both the operating range (minimum and maximum volumetric flow rate) and the pressure ratio across the impeller are dependent on the inlet conditions. The compressor has nearly 25% higher operating range on a hot day as compared to the normal day conditions. A condensation region is observed near the impeller leading edge which grows as the compressor operating point moves towards choke. The impeller chokes near the mid-chord due to lower speed of sound in the liquid-vapor region resulting in a sharp drop near the choke side of the speedline. This behavior is explained by analyzing the 3D flow field within the impeller and thermodynamic quantities along the streamline. The 3D flow analysis for the flow near the critical point provides useful insight for the designers to modify the current compressor design for higher efficiency.

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