Molecular dynamics investigation on isobaric heat capacity of working fluid in supercritical CO2 Brayton cycle: Effect of trace gas

Abstract Most of the power plants operating nowadays mainly have adopted a steam Rankine cycle or a gas Brayton cycle. To devise a better power conversion cycle, various approaches were taken by researchers and one of the examples is an S-CO2 (supercritical CO2) power cycle. Over the past decades, the S-CO2 power cycle was invented and studied. Eventually the cycle was successful for attracting attentions from a wide range of applications. Basically, an S-CO2 power cycle is a variation of a gas Brayton cycle. In contrast to the fact that an ordinary Brayton cycle operates with a gas phase fluid, the S-CO2 power cycle operates with a supercritical phase fluid, where temperatures and pressures of working fluid are above the critical point. Many advantages of S-CO2 power cycle are rooted from its novel characteristics. Particularly, a compressor in an S-CO2 power cycle operates near the critical point, where the compressibility is greatly reduced. Since the S-CO2 power cycle greatly benefits from the reduced compression work, an S-CO2 compressor prediction under off-design condition has a huge impact on overall cycle performance. When off-design operations of a power cycle are considered, the compressor performance needs to be specified. One of the approaches for a compressor off-design performance evaluation is to use the correction methods based on similitude analysis. However, there are several approaches for deriving the equivalent conditions but none of the approaches has been thoroughly examined for S-CO2 conditions based on data. The purpose of this paper is comparing these correction models to identify the best fitted approach, in order to predict a compressor off-design operation performance more accurately from limited amount of information. Each correction method was applied to two sets of data, SCEIL experiment data and 1D turbomachinery code off-design prediction code generated data, and evaluated in this paper.

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Review of existing and development of a novel mathematical model for supercritical CO2 cycles working fluid

MATEC Web of Conferences ◽

10.1051/matecconf/201824001036 ◽

2018 ◽

Vol 240 ◽

pp. 01036

Author(s):

Marcin Wołowicz ◽

Jarosław Milewski ◽

Piotr Lis

Keyword(s):

Experimental Data ◽

Carbon Dioxide ◽

Mathematical Model ◽

Heat Capacity ◽

Supercritical Co2 ◽

Pressure Range ◽

Critical Conditions ◽

Working Fluid ◽

Critical Properties ◽

Area Of Interest

The paper aims to compare the models of working fluids against experimental data for carbon dioxide close to its critical conditions. Fortunately, most of the work is already done and published where the authors compared the models based on the equation of the state (EoS). There are a few other models which were not investigated, thus we would like to add a few new results here and focus only on near-critical properties where the biggest deviation between experimental and calculated properties can be observed. The area of interest was pressure range of 7.39 – 20 MPa and temperature range of 304-340 K just above fluid critical point (7.39 MPa, 304.25 K). Model validation was performed for density and heat capacity as one of the most important parameters in preliminary cycle analysis.

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Cycle Calculations of a Small-Scale Heat Removal System With Supercritical CO2 As Working Fluid

Volume 3: Nuclear Fuel and Material, Reactor Physics and Transport Theory; Innovative Nuclear Power Plant Design and New Technology Application ◽

10.1115/icone25-66084 ◽

2017 ◽

Author(s):

Marcel Strätz ◽

Jörg Starflinger ◽

Rainer Mertz ◽

Michael Seewald ◽

Sebastian Schuster ◽

...

Keyword(s):

Power Plant ◽

Supercritical Co2 ◽

Heat Removal ◽

Working Fluid ◽

Small Scale ◽

Brayton Cycle ◽

Additional Heat ◽

Decay Heat ◽

Heat Removal System ◽

Removal System

In case of an accident in a nuclear power plant with combined initiating events, (loss of ultimate heat sink and station blackout) additional heat removal system could transfer the decay heat from the core to and diverse ultimate heat sink. On additional heat removal system, which is based upon a Brayton cycle with supercritical CO2 as working fluid, is currently investigated within an EU-funded project, sCO2-HeRo (Supercritical carbon dioxide heat removal system). It shall serve as a self-launching, self-propelling and self-sustaining decay heat removal system to be used in severe accident scenarios. Since a Brayton cycle produces more electric power that it consumes, the excess electric power can be used inside the power plant, e.g. recharging batteries. A small-scale demonstrator will be attached to the PWR glass model at Gesellschaft für Simulatorforschung GfS, Essen, Germany. In order to design and build this small-scale model, cycle calculations are performed to determine the design parameters from which a layout can be derived.

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The Impeller Exit Flow Coefficient As a Performance Map Variable for Predicting Centrifugal Compressor Off-Design Operation Applied to a Supercritical CO2 Working Fluid

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

10.1115/gt2017-63090 ◽

2017 ◽

Cited By ~ 2

Author(s):

Eric Liese ◽

Stephen E. Zitney

Keyword(s):

Centrifugal Compressor ◽

Process Simulation ◽

Supercritical Co2 ◽

Flow Coefficient ◽

Working Fluid ◽

Inlet Temperature ◽

Brayton Cycle ◽

Inlet Flow ◽

Cycle Simulation ◽

Main Compressor

A multi-stage centrifugal compressor model is presented with emphasis on analyzing use of an exit flow coefficient vs. an inlet flow coefficient performance parameter to predict off-design conditions in the critical region of a supercritical carbon dioxide (CO2) power cycle. A description of the performance parameters is given along with their implementation in a design model (number of stages, basic sizing, etc.) and a dynamic model (for use in transient studies). A design case is shown for two compressors, a bypass compressor and a main compressor, as defined in a process simulation of a 10 megawatt (MW) supercritical CO2 recompression Brayton cycle. Simulation results are presented for a simple open cycle and closed cycle process with changes to the inlet temperature of the main compressor which operates near the CO2 critical point. Results showed some difference in results using the exit vs. inlet flow coefficient correction, however, it was not significant for the range of conditions examined. This paper also serves as a reference for future works, including a full process simulation of the 10 MW recompression Brayton cycle.

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Performance Characteristics of an Operating Supercritical CO2 Brayton Cycle

Volume 5: Manufacturing Materials and Metallurgy; Marine; Microturbines and Small Turbomachinery; Supercritical CO2 Power Cycles ◽

10.1115/gt2012-68415 ◽

2012 ◽

Cited By ~ 2

Author(s):

Thomas Conboy ◽

Steven Wright ◽

James Pasch ◽

Darryn Fleming ◽

Gary Rochau ◽

...

Keyword(s):

Supercritical Co2 ◽

Waste Heat ◽

Electrical Power ◽

Heat Removal ◽

Test Facility ◽

Working Fluid ◽

Inlet Temperature ◽

Brayton Cycle ◽

Compact Size ◽

Test Loop

Supercritical CO2 (S-CO2) power cycles offer the potential for better overall plant economics due to their high power conversion efficiency over a moderate range of heat source temperatures, compact size, and potential use of standard materials in construction [1,2,3,4]. Sandia National Labs (Albuquerque, NM, US) and the US Department of Energy (DOE-NE) are in the process of constructing and operating a megawatt-scale supercritical CO2 split-flow recompression Brayton cycle with contractor Barber-Nichols Inc. [5] (Arvada, CO, US). This facility can be counted among the first and only S-CO2 power producing Brayton cycles anywhere in the world. The Sandia-DOE test-loop has recently concluded a phase of construction that has substantially upgraded the facility by installing additional heaters, a second recuperating printed circuit heat exchanger (PCHE), more waste heat removal capability, higher capacity load banks, higher temperature piping, and more capable scavenging pumps to reduce windage within the turbomachinery. With these additions, the loop has greatly increased its potential for electrical power generation — according to models, as much as 80 kWe per generator depending on loop configuration — and its ability to reach higher temperatures. To date, the loop has been primarily operated as a simple recuperated Brayton cycle, meaning a single turbine, single compressor, and undivided flow paths. In this configuration, the test facility has begun to realize its upgraded capacity by achieving new records in turbine inlet temperature (650°F/615K), shaft speed (52,000 rpm), pressure ratio (1.65), flow rate (2.7 kg/s), and electrical power generated (20kWe). Operation at higher speeds, flow rates, pressures and temperatures has allowed a more revealing look at the performance of essential power cycle components in a supercritical CO2 working fluid, including recuperation and waste heat rejection heat exchangers (PCHEs), turbines and compressors, bearings and seals, as well as auxiliary equipment. In this report, performance of these components to date will be detailed, including a discussion of expected operational limits as higher speeds and temperatures are approached.

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Preliminary prospects of a Carnot-battery based on a supercritical CO2 Brayton cycle

Acta Polytechnica ◽

10.14311/ap.2021.61.0644 ◽

2021 ◽

Vol 61 (5) ◽

pp. 644-660

Author(s):

Karin Rindt ◽

František Hrdlička ◽

Václav Novotný

Keyword(s):

Energy Storage ◽

Supercritical Co2 ◽

High Efficiency ◽

Storage Systems ◽

Renewable Energy Sources ◽

Pressure Ratio ◽

Working Fluid ◽

Brayton Cycle ◽

Round Trip ◽

Weather Changes

As a part of the change towards a higher usage of renewable energy sources, which naturally deliver the energy intermittently, the need for energy storage systems is increasing. For the compensation of the disturbance in power production due to inter-day to seasonal weather changes, a long-term energy storage is required. In the spectrum of storage systems, one out of a few geographically independent possibilities is the use of heat to store electricity, so-called Carnot-batteries. This paper presents a Pumped Thermal Energy Storage (PTES) system based on a recuperated and recompressed supercritical CO2 Brayton cycle. It is analysed if this configuration of a Brayton cycle, which is most advantageous for supercritical CO2 Brayton cycles, can be favourably integrated into a Carnot-battery and if a similar high efficiency can be achieved, despite the constraints caused by the integration. The modelled PTES operates at a pressure ratio of 3 with a low nominal pressure of 8 MPa, in a temperature range between 16 °C and 513 °C. The modelled system provides a round-trip efficiency of 38.9 % and was designed for a maximum of 3.5 MW electric power output. The research shows that an acceptable round-trip efficiency can be achieved with a recuperated and recompressed Brayton Cycle employing supercritical CO2 as the working fluid. However, a higher efficiency would be expected to justify the complexity of the configuration.

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Micro Gas Turbine Integrated With a Supercritical CO2 Brayton Cycle Turbine: Layout Comparison and Thermodynamic Analysis

Volume 8: Industrial and Cogeneration; Manufacturing Materials and Metallurgy; Marine; Microturbines, Turbochargers, and Small Turbomachines ◽

10.1115/gt2020-14910 ◽

2020 ◽

Author(s):

Fabrizio Reale ◽

Raniero Sannino ◽

Raffaele Tuccillo

Keyword(s):

Gas Turbine ◽

Supercritical Co2 ◽

Waste Heat ◽

Thermal Power ◽

Energy Systems ◽

Working Fluid ◽

Small Scale ◽

Brayton Cycle ◽

Part Load ◽

Micro Gas Turbine

Abstract In an energetic scenario where both distributed energy systems and smart energy grids gain increasing relevance, the research focus is also on the detection of new solutions to increase overall performance of small-scale energy systems. Waste heat recovery (WHR) can represent a good solution to achieve this goal, due to the possibility of converting residual thermal power in thermal engine exhausts into electrical power. The authors, in a recent study, described the opportunities related to the integration of a micro gas turbine (MGT) with a supercritical CO2 Brayton Cycle (sCO2 GT) turbine. The adoption of Supercritical Carbon Dioxide (sCO2) as working fluid in closed Brayton cycles is an old idea, already studied in the 1960s. Only in recent years this topic returned to be of interest for electric power generation (i.e. solar, nuclear, geothermal energy or coupled with traditional thermoelectric power plants as WHR). In this technical paper the authors analyzed the performance variations of different systems layout based on the integration of a topping MGT with a sCO2 GT as bottoming cycle; the performance maps for both topping and bottoming turbomachinery have been included in the thermodynamic model with the aim of investigating the part load working conditions. The MGT considered is a Turbec T100P and its behavior at part load conditions is also described. The potential and critical aspects related to the integration of the sCO2 GT as bottoming cycle are studied also through a comparison between different layouts, in order to establish the optimal compromise between overall efficiencies and complexity of the energy system. The off-design analysis of the integrated system is addressed to evaluate its response to variable electrical and thermal demands.

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The Effect of Pressure on the Phase Transition of Pd3Cu Alloy

Defect and Diffusion Forum ◽

10.4028/www.scientific.net/ddf.297-301.543 ◽

2010 ◽

Vol 297-301 ◽

pp. 543-548 ◽

Cited By ~ 1

Author(s):

J. Davoodi ◽

M. Ahmadi

Keyword(s):

Molecular Dynamics ◽

Heat Capacity ◽

Thermal Expansion ◽

Melting Temperature ◽

Isobaric Heat Capacity ◽

Dynamics Simulation ◽

Interatomic Potentials ◽

Many Body ◽

Lattice Thermal Expansion ◽

Cu Alloy

In this investigation, we focused on the effects of pressure on the melting of elements Cu, Pd as well as Pd3Cu order alloy. We have performed molecular dynamics based computations of the variation of the physical properties of the elements Cu, Pd and Pd3Cu alloy with pressure and temperature. The quantum Sutton-Chen many-body interatomic potentials have been used for these elements, and the standard mixing rule has been used to obtain the parameters of this potential for the alloy state. This molecular dynamics simulation was performed in the NPT ensemble. Our study enabled us to predict the thermodynamic properties such as melting temperature, isobaric heat capacity as well as the lattice thermal expansion. The temperature dependence of energy and density were calculated at high pressure. Moreover, we presented the variation of the melting temperature, heat capacity as well as the thermal expansion of the crystal with pressure. The obtained results showed that the melting temperature increase with increasing pressure and isobaric heat capacity as well as lattice thermal expansion decrease with increasing pressure. Our computed results are in reasonable agreement with the experimental data where they are available.

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АНАЛИТИЧЕСКОЕ ОПРЕДЕЛЕНИЕ ИСТИННОЙ УДЕЛЬНОЙ ИЗОБАРНОЙ ТЕПЛОЁМКОСТИ КОМПОНЕНТ ВОЗДУХА И ПРОДУКТОВ СГОРАНИЯ С УЧЁТОМ ВЛИЯНИЯ ТЕМПЕРАТУРЫ И ДАВЛЕНИЯ И ЭФФЕКТА ТЕРМИЧЕСКОЙ ДИССОЦИАЦИИ

Aerospace technic and technology ◽

10.32620/aktt.2019.1.01 ◽

2019 ◽

pp. 4-17

Author(s):

Майя Владимировна Амброжевич ◽

Михаил Анатольевич Шевченко

Keyword(s):

Heat Capacity ◽

Gas Turbine ◽

Pressure Ratio ◽

Thermal Dissociation ◽

Combustion Products ◽

Heat Capacities ◽

Isobaric Heat Capacity ◽

Working Fluid ◽

Gas Temperature ◽

Temperature And Pressure

The basic thermophysical parameter of the working fluid of all thermal machines without exception is isobaric heat capacity (specific heat at constant pressure). Traditionally, in engineering calculations of isobaric heat capacity are determined as a tabular value for average heat capacities, or approximated with a square parabola within a given temperature range. Isobaric heat capacity is a function of temperature only. At the current level of GTE development, when the overall compressor pressure ratio is already up to 50 and the tendency of its increase remains it is unacceptable to neglect the pressure. However, the turbine inlet gas temperature also rises that will inevitably lead to the effect of thermal dissociation in the combustion products of the gas turbine engine. The studies of the thermal dissociation effect influence on the parameters of the working process of advanced GTE show that this ignoring leads to computational errors. At the present time, there are mathematical models that allow calculating the isobaric heat capacity as a function of temperature and pressure (taking into account the effect of thermal dissociation) but they are laborious, which is not always practical when estimate calculations performing and program algorithms writing. Consequently, the authors posed the problem of obtaining of simple analytic relationships that make it possible to calculate the isobaric heat capacity as a function of temperature and pressure (taking into account the effect of thermal dissociation). Based on the tabular data for the main components of the gas turbine combustion products within a given range of pressures and temperatures (nitrogen: p = 1 ... 200 bar, T = 150 ... 2870 K, oxygen: p = 1 ... 200 bar, T = 210 ... 2870 K, argon: p = 1 ... 200 bar, T = 190 ... 1300 K, the water vapor: p = 0.1 ... 200 bar, T = 640 ... 1250 K and p = 0.1 ... 400 bar and T = 1250 ... 3200 K, carbon dioxide: p = 1 ... 200 bar, T = 390 ... 2600 K), analytical dependencies were obtained for the calculation of isobaric heat capacities as functions of temperature and pressure taking into account the effect of thermal dissociation. The results of the calculations were compared with tabulated experimental data.

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