Evaluation of Supercritical Carbon Dioxide for Use in Fluid Film Bearings for Process Fluid Lubricated Machines

Power Systems ◽

High Speed ◽

Fluid Film ◽

Working Fluid ◽

Inertial Effects ◽

Fluid Film Bearings ◽

Process Fluid ◽

Advanced closed loop power generation cycles are under consideration for a variety of terrestrial and aerospace power systems [1]. High pressure closed brayton cycles (CBC) and supercritical cycles (SCS) offer an advantage where the cycle working fluid can also be used as the lubricant for the fluid film bearings that support the high speed turbomachinery. Unfortunately the use of supercritical carbon dioxide as a lubricant is not well understood. In the supercritical condition fluids that are typically thought of as ideal gases take on a significantly different characteristic. While these fluids typically maintain gas-like absolute viscosities, their densities are liquid like. The combination of these effects leads to the emergence of inertial effects in fluid film bearings. In addition to the inertial effects that are brought on by the high fluid density, the temperature of the lubricant cannot be controlled independently of the thermodynamic process. This situation leads to technical challenges in maintaining dimensional stability and clearance control between the rotating and stationary surfaces of the bearings.

An Optimization Study to Evaluate the Impact of the Supercritical CO2 Brayton Cycle’s Components on Its Overall Performance

Applied Sciences ◽

10.3390/app11052389 ◽

2021 ◽

Vol 11 (5) ◽

pp. 2389

Author(s):

Khaled Alawadhi ◽

Abdullah Alfalah ◽

Bashar Bader ◽

Yousef Alhouli ◽

Ahmed Murad

Keyword(s):

Carbon Dioxide ◽

Power Systems ◽

Working Fluid ◽

Inlet Temperature ◽

Brayton Cycle ◽

Optimization Study ◽

The Impact ◽

Sustainable Power ◽

The rising environmental problems due to fossil fuels’ consumption have pushed researchers and technologists to develop sustainable power systems. Due to properties such as abundance and nontoxicity of the working fluid, the supercritical carbon (sCO2) dioxide Brayton cycle is considered one of the most promising technologies among the various sustainable power systems. In the current study, a mathematical model has been developed and coded in Matlab for the recompression of the supercritical carbon dioxide Brayton cycle sCO2-BC. The real gas properties of supercritical carbon dioxide (sCO2) were incorporated into the program by pairing the NIST’s Refporp with Matlab© through a subroutine. The impacts of the various designs of the cycle’s individual components have been investigated on the performance of sCO2−BC. The impact of various sedative cycle parameters, i.e., compressor’s inlet temperature (T1), and pressure (P1), cycle pressure ratio (Pr), and split mass fraction (x), on the cycle’s performance (ηcyc) were studied and highlighted. Moreover, an optimization study using the genetic algorithm was carried out to find the abovementioned cycle’s optimized values that maximize the cycle’s per-formance under provided design constraints and boundaries.

DESIGN OF A 1 MWTH SUPERCRITICAL CARBON DIOXIDE PRIMARY HEAT EXCHANGER TEST SYSTEM

Journal of Energy Resources Technology ◽

10.1115/1.4049289 ◽

2020 ◽

pp. 1-34

Author(s):

Matthew Carlson ◽

Francisco Alvarez

Keyword(s):

Carbon Dioxide ◽

Heat Exchanger ◽

Technology Development ◽

Ambient Air ◽

Test System ◽

Department Of Energy ◽

Working Fluid ◽

Levelized Cost Of Electricity ◽

Abstract A new generation of Concentrating Solar Power (CSP) technologies is under development to provide dispatchable renewable power generation and reduce the levelized cost of electricity (LCOE) to 6 cents/kWh by leveraging heat transfer fluids (HTF) capable of operation at higher temperatures and coupling with higher efficiency power conversion cycles. The U.S. Department of Energy (DOE) has funded three pathways for Generation 3 CSP (Gen3CSP) technology development to leverage solid, liquid, and gaseous HTFs to transfer heat to a supercritical carbon dioxide (sCO2) Brayton cycle. This paper presents the design and off-design capabilities of a 1 MWth sCO2 test system that can provide sCO2 coolant to the primary heat exchangers (PHX) coupling the high-temperature HTFs to the sCO2 working fluid of the power cycle. This system will demonstrate design, performance, lifetime, and operability at a scale relevant to commercial CSP. A dense-phase high pressure canned motor pump is used to supply up to 5.3 kg/s of sCO2 flow to the primary heat exchanger at pressures up to 250 bar and temperatures up to 715 °C with ambient air as the ultimate heat sink. Key component requirements for this system are presented in this paper.

Dynamic simulation of the oscillation characteristics of supercritical carbon dioxide impacting jets

Journal of Vibration and Control ◽

10.1177/1077546318769558 ◽

2018 ◽

Vol 25 (1) ◽

pp. 61-71 ◽

Cited By ~ 1

Author(s):

Xinwei Zhang ◽

Yiyu Lu ◽

Jiren Tang ◽

Zhe Zhou ◽

Qian Li

Keyword(s):

Carbon Dioxide ◽

Numerical Model ◽

Oscillation Frequency ◽

High Speed ◽

Rock Breaking ◽

Target Distance ◽

Inlet Pressure ◽

Oscillation Characteristics ◽

A numerical model was established to investigate the dynamic oscillation characteristics of supercritical carbon dioxide (sc-CO2) impacting jets. The jet hydrodynamics, heat transfer, and physical properties of sc-CO2 fluid were incorporated into the model. The coupling of multiple fields with large velocity and pressure gradients was achieved using a modified SIMPLE segmentation algorithm. Laboratory experiments validated the reliability of the numerical model by detecting dynamic changes in the pressure on the centerline of the sc-CO2 impacting jet. Analysis of the flow field showed single or double high-speed sc-CO2 mass structures for the sc-CO2 impacting jet, revealing the generation mechanism of the impacting oscillation frequency and the mechanism of improved rock-breaking efficiency by sc-CO2 jet. The oscillation frequency equation was obtained through a quantitative treatment of the velocity and motion area of the sc-CO2 mass. Finally, the equation and simulation results were used to analyze the influences of the target distance, inlet pressure and temperature on the sc-CO2 jet oscillation characteristics. The results showed that the oscillation frequency and amplitude first increased and then decreased with increases in the target distance. The oscillation frequency and amplitude both increased with increasing inlet pressure; the oscillation frequency increased slowly with increasing temperature.

The Role of Turbomachinery Performance in the Optimization of Supercritical Carbon Dioxide Power Systems

Volume 9: Oil and Gas Applications; Supercritical CO2 Power Cycles; Wind Energy ◽

10.1115/gt2019-91189 ◽

2019 ◽

Author(s):

Alessandro Romei ◽

Paolo Gaetani ◽

Andrea Giostri ◽

Giacomo Persico

Keyword(s):

Carbon Dioxide ◽

Power Systems ◽

Pressure Ratio ◽

Plant Size ◽

Cycle Performance ◽

Small Contribution ◽

Compression Process ◽

Multiple Cycle ◽

Abstract The successful penetration of supercritical carbon dioxide (sCO2) power systems in the energy market largely depends on the achievable turbomachinery performance. The present study illustrates a systematic framework where both the compressor and the turbine are designed via validated (within ±2% pts against experiments) mean-line tools and the related impact on cycle performance estimates is quantitatively and qualitatively assessed. A significant effort is devoted to the analysis of centrifugal compressor performance operating close to the critical point, where sharp thermodynamic property variations may make critical the compression process. The analysis is performed for different compressor sizes and pressure ratios, showing a comparatively small contribution of compressor-intake fluid conditions to the machine efficiency, which may achieve technological competitive values (82 ÷ 85%) for representative full-scale sizes. Two polynomial correlations for both turbomachinery efficiencies are devised as a function of proper similarity parameters accounting for machine sizes and loadings. Such correlations can be easily embedded in power cycle optimizations, which are usually carried out assuming constant-turbomachinery efficiency, thus ignoring the effects of plant size and cycle operating parameters. Efficiency correlations are finally exploited to perform several optimizations of a recompressed sCO2 cycle, by varying multiple cycle parameters (i.e. maximum and minimum temperature, pressure ratio and net power output). The results highlight that the replacement of constant-efficiency assumption with the proposed correlations leads to more accurate performance predictions (i.e. cycle efficiency can differ by more than 4% pts), showing in particular that an optimal pressure ratio exists in the range 2 ÷ 5 for all the investigated configurations.

Visualization of Supercritical Carbon Dioxide Flow Through a Converging-Diverging Nozzle

Volume 9: Oil and Gas Applications; Supercritical CO2 Power Cycles; Wind Energy ◽

10.1115/gt2019-91691 ◽

2019 ◽

Author(s):

Chang Hyeon Lim ◽

Gokul Pathikonda ◽

Sandeep Pidaparti ◽

Devesh Ranjan

Keyword(s):

Carbon Dioxide ◽

Critical Point ◽

High Speed ◽

Operating Conditions ◽

Higher Plant ◽

Two Phase ◽

Pressure Profiles ◽

Flow Through ◽

Abstract Supercritical carbon dioxide (sCO2) power cycles have the potential to offer a higher plant efficiency than the traditional Rankine superheated/supercritical steam cycle or Helium Brayton cycles. The most attractive characteristic of sCO2 is that the fluid density is high near the critical point, allowing compressors to consume less power than conventional gas Brayton cycles and maintain a smaller turbomachinery size. Despite these advantages, there still exist unsolved challenges in design and operation of sCO2 compressors near the critical point. Drastic changes in fluid properties near the critical point and the high compressibility of the fluid pose several challenges. Operating a sCO2 compressor near the critical point has potential to produce two phase flow, which can be detrimental to turbomachinery performance. To mimic the expanding regions of compressor blades, flow through a converging-diverging nozzle is investigated. Pressure profiles along the nozzle are recorded and presented for operating conditions near the critical point. Using high speed shadowgraph images, onset and growth of condensation is captured along the nozzle. Pressure profiles were calculated using a one-dimensional homogeneous equilibrium model and compared with experimental data.

Research and Development of Supercritical Carbon Dioxide Coal-Fired Power Systems

Journal of Thermal Science ◽

10.1007/s11630-020-1282-6 ◽

2020 ◽

Vol 29 (3) ◽

pp. 546-575 ◽

Cited By ~ 2

Author(s):

Zhaozhi Li ◽

Xuejiao Liu ◽

Yingjuan Shao ◽

Wenqi Zhong

Keyword(s):

Carbon Dioxide ◽

Power Systems ◽

Research And Development ◽

Modeling Off-Design and Part-Load Performance of Supercritical Carbon Dioxide Power Cycles

Volume 8: Supercritical CO2 Power Cycles; Wind Energy; Honors and Awards ◽

10.1115/gt2013-95824 ◽

2013 ◽

Cited By ~ 14

Author(s):

John J. Dyreby ◽

Sanford A. Klein ◽

Gregory F. Nellis ◽

Douglas T. Reindl

Keyword(s):

Carbon Dioxide ◽

Ambient Air ◽

Working Fluid ◽

Brayton Cycle ◽

Heat Rejection ◽

Power Cycles ◽

Part Load ◽

Dry Cooling ◽

Continuing efforts to increase the efficiency of utility-scale electricity generation has resulted in considerable interest in Brayton cycles operating with supercritical carbon dioxide (S-CO2). One of the advantages of S-CO2 Brayton cycles, compared to the more traditional steam Rankine cycle, is that equal or greater thermal efficiencies can be realized using significantly smaller turbomachinery. Another advantage is that heat rejection is not limited by the saturation temperature of the working fluid, facilitating dry cooling of the cycle (i.e., the use of ambient air as the sole heat rejection medium). While dry cooling is especially advantageous for power generation in arid climates, the reduction in water consumption at any location is of growing interest due to likely tighter environmental regulations being enacted in the future. Daily and seasonal weather variations coupled with electric load variations means the plant will operate away from its design point the majority of the year. Models capable of predicting the off-design and part-load performance of S-CO2 power cycles are necessary for evaluating cycle configurations and turbomachinery designs. This paper presents a flexible modeling methodology capable of predicting the steady state performance of various S-CO2 cycle configurations for both design and off-design ambient conditions, including part-load plant operation. The models assume supercritical CO2 as the working fluid for both a simple recuperated Brayton cycle and a more complex recompression Brayton cycle.

A Study of Supercritical Carbon Dioxide Power Cycle for Concentrating Solar Power Applications Using an Isothermal Compressor

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.4038476 ◽

2018 ◽

Vol 140 (7) ◽

Cited By ~ 1

Author(s):

Jin Young Heo ◽

Jinsu Kwon ◽

Jeong Ik Lee

Keyword(s):

Carbon Dioxide ◽

Thermal Efficiency ◽

Solar Power ◽

Working Fluid ◽

Brayton Cycle ◽

Concentrating Solar Power ◽

Power Cycle ◽

Compressor Inlet ◽

For the concentrating solar power (CSP) applications, the supercritical carbon dioxide (s-CO2) power cycle is beneficial in many aspects, including high cycle efficiencies, reduced component sizing, and potential for the dry cooling option. More research is involved in improving this technology to realize the s-CO2 cycle as a candidate to replace the conventional power conversion systems for CSP applications. In this study, an isothermal compressor, a turbomachine which undergoes the compression process at constant temperature to minimize compression work, is applied to the s-CO2 power cycle layout. To investigate the cycle performance changes of adopting the novel technology, a framework for defining the efficiency of the isothermal compressor is revised and suggested. This study demonstrates how the compression work for the isothermal compressor is reduced, up to 50%, compared to that of the conventional compressor under varying compressor inlet conditions. Furthermore, the simple recuperated and recompression Brayton cycle layouts using s-CO2 as a working fluid are evaluated for the CSP applications. Results show that for compressor inlet temperatures (CIT) near the critical point, the recompression Brayton cycle using an isothermal compressor has 0.2–1.0% point higher cycle thermal efficiency compared to its reference cycle. For higher CIT values, the recompression cycle using an isothermal compressor can perform above 50% in thermal efficiency for a wider range of CIT than the reference cycle. Adopting an isothermal compressor in the s-CO2 layout can imply larger heat exchange area for the compressor which requires further development.

Analysis of Advanced Supercritical Carbon Dioxide Power Cycles With a Bottoming Cycle for Concentrating Solar Power Applications

Journal of Solar Energy Engineering ◽

10.1115/1.4025700 ◽

2013 ◽

Vol 136 (1) ◽

Cited By ~ 62

Author(s):

Saeb M. Besarati ◽

D. Yogi Goswami

Keyword(s):

Carbon Dioxide ◽

Solar Power ◽

Waste Heat ◽

Operating Conditions ◽

Working Fluid ◽

Brayton Cycle ◽

Concentrating Solar Power ◽

Working Fluids ◽

A number of studies have been performed to assess the potential of using supercritical carbon dioxide (S-CO2) in closed-loop Brayton cycles for power generation. Different configurations have been examined among which recompression and partial cooling configurations have been found very promising, especially for concentrating solar power (CSP) applications. It has been demonstrated that the S-CO2 Brayton cycle using these configurations is capable of achieving more than 50% efficiency at operating conditions that could be achieved in central receiver tower type CSP systems. Although this efficiency is high, it might be further improved by considering an appropriate bottoming cycle utilizing waste heat from the top S-CO2 Brayton cycle. The organic Rankine cycle (ORC) is one alternative proposed for this purpose; however, its performance is substantially affected by the selection of the working fluid. In this paper, a simple S-CO2 Brayton cycle, a recompression S-CO2 Brayton cycle, and a partial cooling S-CO2 Brayton cycle are first simulated and compared with the available data in the literature. Then, an ORC is added to each configuration for utilizing the waste heat. Different working fluids are examined for the bottoming cycles and the operating conditions are optimized. The combined cycle efficiencies and turbine expansion ratios are compared to find the appropriate working fluids for each configuration. It is also shown that combined recompression-ORC cycle achieves higher efficiency compared with other configurations.

Impact of Fluid Substitution on the Performance of an Axial Compressor Blade Cascade Working with Supercritical Carbon Dioxide

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.4045473 ◽

2019 ◽

Vol 142 (1) ◽

Author(s):

Carlos Tello ◽

Alejandro Muñoz ◽

David Sánchez ◽

Timoleon Kipouros ◽

Mark Savill

Keyword(s):

Carbon Dioxide ◽

Axial Compressor ◽

Computational Design ◽

Compressor Blade ◽

Working Fluid ◽

Local Flow ◽

Variable Boundary ◽

Turbomachinery Design ◽

Abstract Recent research on turbomachinery design and analysis for supercritical carbon dioxide (sCO2) power cycles has relied on computational fluid dynamics. This has produced a large number of works whose approach is mostly case-specific, rather than of general application to sCO2 turbomachinery design. As opposed to such approach, this work explores the aerodynamic performance of compressor blade cascades operating on air and supercritical CO2 with the main objective to evaluate the usual aerodynamic parameters of the cascade for variable boundary conditions and geometries, enabling “full” or “partial” similarity. The results present both the global performance of the cascades and certain features of the local flow (trailing edge and wake). The discussion also highlights the mechanical limitations of the analysis (forces exerted on the blades), which is the main restriction for applying similarity laws to extrapolate the experience gained through decades of work on air turbomachinery to the new working fluid. This approach is a step toward the understanding and appropriate formulation of a multi-objective optimization problem for the design of such turbomachinery components where sCO2 is used as the operating fluid. With this objective, the paper aims to identify and analyze what would be expected if a common description of such computational design problems similar to those where air is the working fluid were used.