Numerical Investigation of the Flow Behavior Inside a Supercritical CO2 Centrifugal Compressor

2018 ◽  
Vol 140 (12) ◽  
Author(s):  
Alireza Ameli ◽  
Teemu Turunen-Saaresti ◽  
Jari Backman
Keyword(s):  
Critical Point ◽  
Centrifugal Compressor ◽  
Supercritical Co2 ◽  
Flow Behavior ◽  
Liquid Density ◽  
Flow Solver ◽  
Real Gas ◽  
Fluid Behavior ◽  
Test Loop ◽  
Fluid Properties

Centrifugal compressors are one of the best choices among compressors in supercritical Brayton cycles. A supercritical CO2 centrifugal compressor increases the pressure of the fluid which state is initially very close to the critical point. When the supercritical fluid is compressed near the critical point, wide variations of fluid properties occur. The density of carbon dioxide at its critical point is close to the liquid density which leads to reduction in the compression work. This paper explains a method to overcome the simulation instabilities and challenges near the critical point in which the thermophysical properties change sharply. The investigated compressor is a centrifugal compressor tested in the Sandia supercritical CO2 test loop. In order to get results with the high accuracy and take into account the nonlinear variation of the properties near the critical point, the computational fluid dynamics (CFD) flow solver is coupled with a look-up table of properties of fluid. Behavior of real gas close to its critical point and the effect of the accuracy of the real gas model on the compressor performance are studied in this paper, and the results are compared with the experimental data from the Sandia compression facility.

Numerical Investigation of the Flow Behavior Inside a Supercritical CO2 Centrifugal Compressor

2016 ◽  
Author(s):  
Alireza Ameli ◽  
Teemu Turunen-Saaresti ◽  
Jari Backman
Keyword(s):  
Critical Point ◽  
Centrifugal Compressor ◽  
Supercritical Co2 ◽  
Flow Behavior ◽  
Lookup Table ◽  
Liquid Density ◽  
Flow Solver ◽  
Real Gas ◽  
Fluid Behavior ◽  
Fluid Properties

Centrifugal compressors are one of the best choices among compressors in supercritical Brayton cycles. A supercritical CO2 centrifugal compressor increases the pressure of the fluid which state is initially very close to the critical point. When the supercritical fluid is compressed near the critical point, wide variations of fluid properties occur. The density of carbon dioxide at its critical point is close to the liquid density which leads to reduction in compressor work. The investigated compressor is a centrifugal compressor tested in the Sandia supercritical CO2 compression loop. In order to get results with the high accuracy and take into account the non-linear variation of the properties near the critical point, the CFD flow solver is coupled with a lookup table of properties of fluid. Behavior of real gas close to its critical point and the effect of the accuracy of the real gas model on the compressor performance are studied in this paper and the results are compared with the experimental data from the Sandia compression facility.

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.

Numerical Simulation of Non-Equilibrium Condensation in Supercritical CO2 Compressors

2019 ◽  
Author(s):  
Kevin W. Brinckman ◽  
Ashvin Hosangadi ◽  
Zisen Liu ◽  
Timothy Weathers
Keyword(s):  
Critical Point ◽  
Residence Time ◽  
Supercritical Co2 ◽  
Equilibrium Phase ◽  
Nucleation Theory ◽  
Classical Nucleation Theory ◽  
Working Fluid ◽  
Modeling Framework ◽  
Test Loop ◽  
Non Equilibrium

Abstract There is increasing interest in supercritical CO2 processes, such as Carbon Capture and Storage, and electric power production, which require compressors to pressurize CO2 above the critical point. For supercritical compressor operation close to the critical point there is a concern that the working fluid could cross into the subcritical regime which could lead to issues with compressor performance if condensation was to occur in regions where the fluid dropped below the saturation point. Presently, the question of whether there is sufficient residence time at subcritical conditions for condensation onset in supercritical CO2 compressors is an unresolved issue. A methodology is presented towards providing a validated simulation capability for predicting condensation in supercritical CO2 compressors. The modeling framework involves the solution of a discrete droplet phase coupled to the continuum gas phase to track droplet nucleation and growth. The model is implemented in the CRUNCH CFD® Computational Fluid Dynamics code that has been extensively validated for simulation at near critical conditions with a real fluid framework for accurate predictions of trans-critical CO2 processes. Results of predictions using classical nucleation theory to model homogeneous nucleation of condensation sites in supersaturated vapor regions are presented. A non-equilibrium phase-change model is applied to predict condensation on the nuclei which grow in a dispersed-phase droplet framework. Model validation is provided against experimental data for condensation of supercritical CO2 in a De Laval nozzle including the Wilson line location. The model is then applied for prediction of condensation in the compressor of the Sandia test loop at mildly supercritical inlet conditions. The results suggest that there is sufficient residence time at the conditions analyzed to form localized nucleation sites, however, droplets are expected to be short lived as the model predicts they will rapidly vaporize.

Numerical Investigation of a Centrifugal Compressor for Supercritical CO2 Cycles

2020 ◽  
Author(s):  
Renan Emre Karaefe ◽  
Pascal Post ◽  
Marwick Sembritzky ◽  
Andreas Schramm ◽  
Francesca di Mare ◽  
...  
Keyword(s):  
Experimental Data ◽  
Thermodynamic Properties ◽  
Flow Field ◽  
Numerical Simulations ◽  
Centrifugal Compressor ◽  
Supercritical Co2 ◽  
Solution Method ◽  
Three Dimensional ◽  
Solution Procedure ◽  
Test Loop

Abstract In this work, the performance characteristics and the flow field of a centrifugal compressor operating with supercritical CO2 are investigated by means of three-dimensional CFD. The considered geometry is based on main dimensions of the centrifugal compressor installed in the supercritical CO2 compression test-loop operated by Sandia National Laboratories. All numerical simulations are performed with a recently developed in-house hybrid CPU/GPU compressible CFD solver. Thermodynamic properties are computed through an efficient and accurate tabulation technique, the Spline-Based Table Look-Up Method (SBTL), particularly optimised for the applied density-based solution procedure. Numerical results are compared with available experimental data and accuracy as well as potentials in computational speedup of the solution method in combination with the SBTL are evaluated in the context of supercritical CO2 turbomachinery.

Impact of Uncertainty On Prediction of Supercritical CO2 Properties and Nusselt Numbers

2021 ◽  
Author(s):  
Neil Sullivan ◽  
Yang Chao ◽  
Sandra Boetcher ◽  
Mark Ricklick
Keyword(s):  
Heat Transfer ◽  
Critical Point ◽  
Supercritical Co2 ◽  
Transfer Rates ◽  
Nusselt Numbers ◽  
Property Data ◽  
Highly Sensitive ◽  
Fluid Properties ◽  
Temperature And Pressure ◽  
The Impact

Abstract The impact of measurement uncertainty on heat transfer coefficient correlations for supercritical CO2 is investigated. Selection of appropriate temperature- and pressure-dependent reference quantities for these correlations, such as thermal conductivity, appears to have a large effect on predicting heat transfer rates. Supercritical CO2 work heavily depends on tabular real fluid property data, which show that fluid properties have very large gradients with respect to temperature and pressure near the critical point. The sharp gradients imply heat transfer predictions are highly sensitive to the accuracy of temperature and pressure experimental measurements in this region. Root sum of squares (RSS) uncertainties of various property values indicate predictably large (on the order of 1000%) uncertainties in calculated Reynolds, Prandtl, and Nusselt numbers near the critical point. Interestingly, uncertainties remain several times the calculated value for operating pressures (between 7.5 and 8.5 MPa) common in the experimental literature, highlighting a need for careful application of correlations near the pseudocritical line, and the benefits of presenting dimensional data in the literature.

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.

Design and Test Plan of the Supercritical CO2 Compressor Test Loop

2008 ◽  
Author(s):  
Takao Ishizuka ◽  
Yasushi Muto ◽  
Masanori Aritomi
Keyword(s):  
High Pressure ◽  
Critical Point ◽  
Thermal Efficiency ◽  
Supercritical Co2 ◽  
Thermal Power ◽  
Low Pressure ◽  
Fiscal Year ◽  
Pressure Side ◽  
Test Loop ◽  
Pressure Compressor

Supercritical carbon dioxide (CO2) gas turbine systems can generate power at a high cycle thermal efficiency, even at modest temperatures of 500–550°C. That high thermal efficiency is attributed to a markedly reduced compressor work in the vicinity of critical point. In addition, the reaction between sodium (Na) and CO2 is milder than that between H2O and Na. Consequently, a more reliable and economically advantageous power generation system can be created by coupling with a Na-cooled fast breeder reactor. In a supercritical CO2 turbine system, a partial cooling cycle is employed to compensate a difference in heat capacity for the high-temperature — low-pressure side and low-temperature — high-pressure side of the recuperators to achieve high cycle thermal efficiency. In our previous work, a conceptual design of the system was produced for conditions of reactor thermal power of 600 MW, turbine inlet condition of 20 MPa/527°C, recuperators 1 and 2 effectiveness of 98%/95%, Intermediate Heat Exchanger (IHX) pressure loss of 8.65%, a turbine adiabatic efficiency of 93%, and a compressor adiabatic efficiency of 88%. Results revealed that high cycle thermal efficiency of 43% can be achieved. In this cycle, three different compressors, i.e., a low-pressure compressor, a high-pressure compressor, and a bypass compressor are included. In the compressor regime, the values of properties such as specific heat and density vary sharply and nonlinearly, dependent upon the pressure and temperature. Therefore, the influences of such property changes on compressor design should be clarified. To obtain experimental data for the compressor performance in the field near the critical point, a supercritical CO2 compressor test project was started at the Tokyo Institute of Technology on June 2007 with funding from MEXT, Japan. In this project, a small centrifugal CO2 compressor will be fabricated and tested. During fiscal year (FY) 2007, test loop components will be fabricated. During FY 2008, the test compressor will be fabricated and installed into the test loop. In FY 2009, tests will be conducted. This paper introduces the concept of a test loop and component designs for the cooler, heater, and control valves. A computer simulation program of static operation was developed based on detailed designs of components and a preliminary design of the compressor. The test operation regime is drawn for the test parameters.

Uncertainty Analysis of a Polytropic Compression Process and Application to Centrifugal Compressor Performance Testing

2005 ◽  
Author(s):  
Jose´ L. Gilarranz
Keyword(s):  
Uncertainty Analysis ◽  
Centrifugal Compressor ◽  
Equations Of State ◽  
Pressure Ratio ◽  
Ideal Gas ◽  
Isentropic Compression ◽  
Real Gas ◽  
Compression Model ◽  
Test Loop ◽  
Real Gas Equations

In recent years, several papers have been written concerning the application of uncertainty analyses for isentropic compression processes under the assumption of ideal gas behavior. However, for high-pressure ratio machines, the ideal gas model fails to capture the physics of the process. Still, the estimation of test uncertainty for polytropic processes is hindered by the complexity of the equations used to calculate the performance parameters and by the incorporation of real gas equations into the models. This paper presents an uncertainty analysis developed to estimate the error levels in data gathered during factory aero-performance tests of single- or multi-stage centrifugal compressors. The analysis incorporates the effects of the variation and uncertainty levels of every parameter used to calculate centrifugal compressor aero-thermal performance. Included are the variables used to define the thermodynamic states of the fluid inside the compressor, as well as geometric and operational parameters associated with the machine and test loop. Two different methods have been utilized and the results compared to evaluate the advantages and drawbacks of each. The first method is based on the direct use of the Monte Carlo simulation technique combined with real gas equations of state. The second method employs uncertainty propagation equations and the methodology included in the ASME PTC-19.1 (1998) Test Code. Both approaches utilize the polytropic compression model and equations for performance evaluation that are included in the ASME PTC 10 (1997) Power Test Code for compressors and exhausters. The methods and results from this work may be easily extended to the isentropic compression model as well. The use of real gas equations of state make the methods applicable to virtually any gas composition. Although the analysis was intended to be applied to ASME PTC 10 Type 2 tests, the method can be extended to evaluate Type 1 and/or on-site field tests, as long as certain considerations are addressed. The uncertainty analysis presented is then used to evaluate data from several machines, ranging from a low-pressure ratio gas pipeline compressor to an eight-stage machine used for natural gas processing. Comments are offered concerning the effects of machine pressure ratio on the levels of uncertainty, as well as the importance of proper selection of instrumentation to minimize the error level of the test data. Special emphasis is placed on the benefits of using this analysis during the planning phase of the test program, to determine the optimal combination of instruments, to guarantee acceptable levels of uncertainty.

scholarly journals Stabilizing Effects of Supercritical CO2 Fluid Properties on Compressor Operation†

2019 ◽  
Vol 4 (3) ◽  
pp. 20
Author(s):  
Alexander Johannes Hacks ◽  
Sebastian Schuster ◽  
Dieter Brillert
Keyword(s):  
Critical Point ◽  
Supercritical Co2 ◽  
Cooling Power ◽  
Inlet Temperature ◽  
Stabilizing Effect ◽  
Fluid Properties ◽  
Compressor Inlet ◽  
Applicable Range ◽  
Temperature And Pressure ◽  
Inlet Conditions

This paper aims to give an understanding of an effect which stabilizes the inlet conditions of compressors for supercritical CO2 (sCO2) operating close to the critical point. The effect was observed during testing of the turbomachine within the sCO2-HeRo project, and is caused by the sCO2 real gas properties close to the pseudocritical line. Under theoretical consideration, strong gradients in the fluid properties around this line—dependent on the static temperature and pressure of sCO2—can result in strong variation of compressor performance and finally lead to unstable cycle behavior. However, this paper demonstrates reduced gradients in density at the compressor inlet when varying the cooling power and taking advantage of a stabilizing effect. The applicable range and the significance of this stabilizing effect depended on the cooler inlet temperature and pressure, and was used to evaluate the relevance for individual cycles. Controlling the cooling power and the measurement of the inlet density allowed control of the compressor inlet conditions equally well, independent of the operating point, even close to the critical point.

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