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With the increasing emphasis on reducing the CO2 emission while improving power generation efficiency, new power cycles are being developed. One of those promising power cycles is a supercritical CO2 (S-CO2) power cycle. To generate over 10MW electricity with S-CO2 power cycle, a magnetic bearing can be a good option for the hermetic type turbomachinery. However, from several studies on the magnetic bearing, the instability issues under high density fluid and high speed operating conditions were repeatedly mentioned. The instability in the magnetic bearing was observed to be related to the fluid conditions, mostly pressure and density. Because of this issue, the magnetic bearing sometimes cannot maintain enough clearance for the rotor leading to physical contact and consequently damaging the system. Thus, these instability issues should be thoroughly studied and be resolved for the successful and steady operation of the power system. The instability due to fluid force around the rotating shaft can be modeled with the Reynolds lubrication equation. The steady lubrication force analysis model is developed based on this equation. The model results imply that the lubrication performance is quite sensitive to the thermal condition of the CO2 especially density gradient around the shaft. Based on the modeling results, an experimental system is designed to investigate the issue. To study the instability issues experimentally, an impeller of the operating S-CO2 compressor is removed and the discharge line is blocked. Therefore, the main instability factor in this experiment will be the interaction between the rotor and the bearing only. The shaft position can be measured with inductive sensors. The forces exerted from the electromagnet is calculated from the electric current data which is applied by the controller. From these experimental data, the lubrication force is calculated. These results are compared with the analytical lubrication model to verify the model. From this study, it is expected that it will be possible to define the unstable operating conditions and suggest the required magnetic bearing performance for S-CO2 conditions.

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.

Nowadays Small Modular Reactors (SMRs) have been receiving considerable attentions worldwide for potential advantages of an excellent flexibility for siting, low capital investment, and advanced safety. In Korea, a new research project has launched for the development of a conceptual design of a further advanced SMR which aims for a naturally-safe and autonomous operation, so called Autonomous Transportable On-demand reactor Module (ATOM). Major design objectives of the ATOM system are focused on the soluble boron-free (SBF) primary coolant system which enables the SMR to operate automatically in a load following mode. For the secondary system, the SCO2 power conversion cycle with air-cooling system as a final heat sink is being considered. The air-cooling system is expected to show flexible response even to extreme environmental conditions, such as a desert where utilization of cooling water is limited. The objective of this study is a feasibility assessment for applying the air-cooling system as a final heat sink of the ATOM by means of experimental work. As a 1st phase of the ATOM development, we first conducted the experiments using a typically considered primary coolant, water-steam, to verify that air flow has enough cooling capability to remove developed heat which the coolant carries. An Integrated Condensation Loop with Air-cooling System (ICLASS) experimental facility with three pressure boundaries (Steam, coolant, and air) was established. The cooling capability of the air-cooling system was evaluated by varying steam mass flow rate, coolant flow rate, and air environment temperature as experiment variables. Overall heat transfer rate by condensation was compared with numerical simulations of a 1D thermal-hydraulics analysis code, using the MARS model of the ICLASS facility.

From the observation of previous experimental results, it was recognized that the amount of external losses at the external flow paths can be substantial. Understanding the external loss mechanisms, and reducing the external losses are crucial to the design of a high performance S-CO2 compressor. Therefore, this study first focused on verifying the existing external loss models by estimating the internal loss accurately through a high fidelity CFD calculation and then substituting from the total losses. By analyzing the CFD result and energy balance data obtained from the experiment, the authors are suggesting the best combination of the external loss models for the S-CO2 compressor. This is followed by the investigation of the condensation effect in the impeller by utilizing a two-phase VOF model with metastable properties. As a result, it is re-confirmed that there is a negligible amount of condensation effect.

The Supercritical CO2 power cycle (S-CO2 cycle) is the power cycle that adopts CO2 as a working fluid and is designed to have a compression process near the critical point of CO2. Due to the non-linearity of CO2 pyhsical properties near the critical point, the S-CO2 cycle needs relatively less compression work. Therefore, the efficiency of the S-CO2 cycle is higher than traditional gas cycles. Furthermore, because of the relatively high system minimum pressure (near the critical point, ∼7.39 MPa), an S-CO2 cycle can be composed of smaller turbomachines. Considering these advantages, nowadays, there are many attempts to apply S-CO2 cycles to various fields, such as waste heat recovery, nuclear, coal, concentrated solar power plant and so on. These non-linear pyhsical properties become the cause of some unique issues. One of the most significant issues is the internal pinch point problem in a recuperator. Unlike the traditional gas-to-gas heat exchanger, each hot and cold side of the S-CO2 recuperator goes through the severe change of specific heat. This dramatic change of specific heat may cause the internal pinch point of the recuperator. When the internal pinch point phenomenon occurs, the performance of the recuperator may not able to be evaluated from the pre-fixed effectiveness. This can be an issue when the compressor inlet temperature decreases to transcritical or subcritical region. This may alter the optimal point of the S-CO2 power cycle. In this paper, optimal design points and optimal performance of the S-CO2 power cycle are tracked with the consideration of the internal pinch point phenomenon. While changing the system boundary conditions, the optimal point variation due to internal pinch point phenomenon is evaluated and compared with a traditional methodology. This research is progressed with an in-house integrated S-CO2 power cycle analysis code, which is named KAIST – ESCA (Evaluator for Supercritical CO2 Cycle based on Adjoint method). The target cycle layouts are Simple Recuperated, Intercooling, Recompression and Recompression with intercooling layouts. Both of the S-CO2 Rankine and Brayton cycles conditions are considered.

Supercritical CO2 (S-CO2) has the potential to be used as the working fluid in a power cycle since S-CO2 shows a density value high as its liquid phase while the viscosity value remains closer to its gaseous phase. Thus, it requires much less work to compress due to its low compressibility as well as relatively small flow resistance. However, the S-CO2 leakage flow from turbo-machinery via seal becomes one of the important issues since not only it influences the cycle efficiency due to parasitic loss but also it is important for evaluating the system safety under various operating conditions. In the previous turbo expo paper, the effect of the tooth length on the critical flow and comparing the results to the existing two phase system analysis code calculation were presented. In this paper, the gap effect, which is simulated by changing the diameter of a orifice and the number of tooth effect in a labyrinth seal geometry nozzle are presented by using the same experimental facility described in the previous paper. In addition, this paper includes the experimental results under various conditions including not only single phase flow such as supercritical, and gaseous state only but also two phase flow condition.

The supercritical carbon dioxide (S-CO2) Brayton power cycle has been receiving worldwide attention due to the high thermal efficiency and compact system configuration. Because of the incompressible liquid like characteristic (e.g. high density, low compressibility) of the CO2 near the critical point (30.98 °C, 7.38MPa), an S-CO2 Brayton cycle can achieve high efficiency by reducing compression work. In order to utilize the S-CO2 power conversion technology in various applications, such as distributed power generation and marine propulsion, air-cooled waste heat removal system is necessary. However, the critical temperature of CO2 (30.98 °C) is an intrinsic limitation on the system minimum temperature. Because of the small difference with atmospheric temperature, a large amount of cooling air flow or a very large heat exchanger is required to reach the target minimum temperature. In this paper, to improve the system efficiency and ease the problem of air-cooled waste heat removal system, the mixture of supercritical CO2 with other fluids has been studied. Also, the preliminary performance test results of CO2 mixture with pre-existing experimental facility are evaluated.

As a part of Sodium-cooled Fast Reactor (SFR) development, the supercritical CO2 (S-CO2) Brayton cycle is considered as an alternative power conversion system to eliminate sodium-water reaction (SWR) from the current conventional steam Rankine cycle is utilized with SFR. The leakage flow of S-CO2 from turbo-machinery via seal becomes one of important issues since not only it influences the cycle efficiency due to parasitic loss but also it is important for evaluating the system safety under various operating conditions. Thus, a transient simulation for estimating the critical flow in a turbo-machinery seal is essential to predict the leakage flow rate and calculate the required total mass of working fluid in a S-CO2 power system. This paper briefly reviews the advantages of supercritical CO2 Brayton cycle relative to a typical steam Rankine cycle used in the Sodium-cooled Fast Reactor. In addition, this paper describes the test data using a CO2 critical flow experimental facility with three orifice configurations to model the flow resistance of a rotating shaft labyrinth seal. This data is used for validation of an existing transient analytical tool developed for transient hydraulic system analysis. Contained within this code is the analysis approach of Henry/Fauske from 1971 for two phase critical flow of one-component mixtures. This paper presents prediction of transient pressure, temperature, and flow profiles for critical and sub-critical flows of CO2 relative to blowdown test data to show that reasonable results are obtained. Similar analyses relative to test results of three orifice configurations are conducted and it shows that multiple orifices increase the time to equalize pressure in the blowdown system and therefore equates to higher flow resistance and lower leakage.

For the concentrating solar power (CSP) applications, the supercritical carbon dioxide (s-CO2) power cycle is beneficial in many aspects, including higher cycle efficiencies, reduced component sizing, and potential for the dry cooling option, in comparison to the conventional steam Rankine cycle. Increasing number of investigations and research projects are involved in improving this technology to realize the s-CO2 cycle as a candidate to replace the conventional power conversion systems. In this conceptual 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 compared to that of the conventional compressor under varying compressor inlet conditions. Furthermore, the recompression Brayton cycle layout using s-CO2 as a working fluid is evaluated for the CSP applications. Results show that for compressor inlet temperatures (CIT) near the critical point, the simple recuperated Brayton cycle with an isothermal compressor performs better than the given reference recompression cycle by 6–10% points in terms of cycle thermal efficiency. For higher CIT values, the recompression cycle using an isothermal compressor can perform above 50% in thermal efficiency. Adopting an isothermal compressor in the s-CO2 layout, however, can imply larger heat exchange area for the compressor which requires further detailed design for realization in the future.

As the demand to develop more efficient energy systems increases, ways to generate power from waste heat are under investigation. The supercritical carbon dioxide recovery cycle (S-CO2 cycle) has been considered a viable candidate as a bottoming cycle for “waste heat to power” (WHP) applications, such as the utilization of gas turbine outlet heat. One major limitation to the system is that the S-CO2 cycle operates at a low expansion ratio, which leads to a higher turbine outlet temperature. This waste heat should be recuperated in order for the overall cycle efficiency to increase. Such limitation leads to a larger recuperator, higher volume flow rate, lower temperature gradient at the heater, and more complex cycle layouts for WHP applications. These constraints ultimately lead to the increase of hardware costs, which can degrade economics of the system. To solve the existing problems regarding the use of S-CO2 cycle for WHP applications, the possibility of using an isothermal compressor in place of a conventional compressor in a simple Brayton cycle is investigated. This solution, named the iso-Brayton cycle, though the compressor technology is still under development, seems promising because it does not require an additional heat exchanger as one of the cycle components. Furthermore, the compressing work is minimized during an isothermal compression process. To analyze the cycle performance of the iso-Brayton cycle, it is compared with a reference cycle, the simple recuperated Brayton cycle. The parameters of cycle net efficiency and cycle net work (or net usable work) are calculated using the KAIST-CCD in-house code.

A Sodium-cooled Fast Reactor (SFR) has receiving attention as one of the promising next generation nuclear reactors because it can recycle the spent nuclear fuel produced from the current commercial nuclear reactors and accomplish higher thermal efficiency than the current commercial nuclear reactors. However, after shutdown of the nuclear reactor core, the accumulated fission products of the SFR also decay and release heat via radiation within the reactor. To remove this residual heat, a decay heat removal system (DHRS) with supercritical CO2 (S-CO2) as the working fluid is suggested with a turbocharger system which achieves passive operational capability. However, for designing this system an improved S-CO2 turbine design methodology should be suggested because the existing methodology for designing the S-CO2 Brayton cycle has focused only on the compressor design near the critical point. To develop a S-CO2 turbine design methodology, the non-dimensional number based design and the 1D mean line design method were modified and suggested. The design methodology was implemented into the developed code and the code results were compared with existing turbine experimental data. The data were collected under air and S-CO2 environment. The developed code in this research showed a reasonable agreement with the experimental data. Finally using the design code, the turbocharger design for the suggested DHRS and prediction of the off design performance were carried out. As further works, more effort will be put it to expand the S-CO2 turbine test data for validating the design code and methodology.

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.

A supercritical carbon dioxide (S-CO2) Brayton cycle has received attention as one of the future power conversion systems because of its high thermal efficiency at relatively low turbine inlet temperature. However, the design process of the S-CO2 compressor is known to be difficult because the fluid properties vary significantly near the critical point. This paper discusses about the design methodology of a S-CO2 compressor on the basis of the existing design practice and performance map of Sandia National Laboratory, which is the only reported experimental data for the S-CO2 compressor. Five parameters are mainly used for verifying the turbomachinery similarity. When all of 5 parameters coincide with the prototype and the conceptually designed turbomachinery, similar performance can be assumed. As a result, the data of SNL are insufficient to design a single stage compressor which is able to compress from near critical point to 20MPa. The optimum cycle pressure ratio is reported to be around 2.6∼2.7 in the previous S-CO2 Brayton cycle research works. The minimum number of stages is required at least two to utilize the existing data in the compressor design. So this study focuses on two main purposes. The first is to check whether the SNL data can be extended for the larger scale S-CO2 system. Second, the performance map obtained from KAIST_TMD, which is from an in-house code developed by the Korea Advanced Institute of Science and Technology (KAIST) research team, was compared to the SNL data, so that KAIST_TMD can be used as a design tool for a larger scale S-CO2 power conversion system in the future.

The supercritical CO2 (S-CO2) power cycle has been receiving attention as one of the future power cycle technology because of its compact configuration and high thermal efficiency at relatively low turbine inlet temperature ranges (450∼750°C). Thus, this low turbine inlet temperature can be suitable for the bottoming cycle of a combined cycle gas turbine because its exhaust temperature range is approximately 500∼600°C. The natural gas combined cycle power plant utilizes mainly steam Rankine cycle as a bottoming cycle to recover waste heat from a gas turbine. To improve the current situation with the S-CO2 power cycle technology, the research team collected various S-CO2 cycle layouts and compared each performance. Finally, seven cycle layouts were selected as a bottoming power system. In terms of the net work, each cycle was evaluated while the mass flow rate, the split flow rate and the minimum pressure were changed. The existing well-known S-CO2 cycle layouts are unsuitable for the purpose of a waste heat recovery system because it is specialized for a nuclear application. Therefore, the concept to combine two S-CO2 cycles was suggested in this paper. Also the complex single S-CO2 cycles are included in the study to explore its potential. As a result, the net work of the concept to combine two S-CO2 cycles was lower than that of the performance of the reference steam cycle. On the other hand, the cascade S-CO2 Brayton cycle 3 which is one of the complex single cycles was the only cycle to be superior to the reference steam cycle. This result shows the possibility of the S-CO2 bottoming cycle if component technologies become mature enough to realize the assumptions in this paper.

The supercritical carbon dioxide (S-CO2) Brayton power conversion cycle has been receiving worldwide attention because of high thermal efficiency due to relatively low compression work near the critical point (30.98°C, 7.38MPa) of CO2. The S-CO2 Brayton cycle can achieve high efficiency with simple cycle configuration at moderate turbine inlet temperature (450∼650°C) and relatively high density of S-CO2 makes possible to design compact power conversion cycle. In order to achieve compact cycle layout, a highly compact heat exchanger such as printed circuit heat exchanger (PCHE) is widely used. Since, the cycle thermal efficiency is a strong function of the compressor inlet temperature in the S-CO2 power cycle, the research team at KAIST is focusing on the thermal hydraulic performance of the PCHE as a precooler. The investigation was performed by first developing a PCHE in-house design code named KAIST-HXD. This was followed by constructing the designed PCHE and testing it in the KAIST experimental facility, S-CO2PE. The test results of the PCHE were compared to the test results of a shell and tube type heat exchanger as well.

The CO2 compressor control is one of the most important issues to operate a Supercritical CO2 (S-CO2) Brayton cycle with a high thermal efficiency because it is operated near the critical point to reduce the compressing work. Therefore, our research team has accumulated the CO2 compressor data from the S-CO2 compressor test facility called SCO2PE (Supercritical CO2 Pressurizing Experiment). The data can be obtained under various compressor inlet conditions, especially near the critical point of CO2. Despite the growing interest in the S-CO2 Brayton cycle, research on the cycle transient analysis, especially in case of CO2 compressor inlet condition variation, is still in its early stage. So, in this study, the validation and verification of the gas system transient analysis code GAMMA+ is carried out by utilizing the experimental data of SCO2PE. To simulate the SCO2PE by the GAMMA+ code, the code was revised to reflect the compressor performance and add an expansion valve option. Moreover, the NIST database was connected to the GAMMA+ code for more accurate CO2 properties near the critical point. Prior to the transient analysis with the whole SCO2PE loop, major components such as a compressor and a heat exchanger were separately tested with the steady state data of SCO2PE. The loss of cooling water accident was assumed as the transient situation by observing the operating condition variations of the SCO2PE while the mass flow rate of water loop was decreased. Thus, the experimental data of SCO2PE was compared with the revised GAMMA+ code under the planned transient.

The Supercritical Carbon Dioxide (S-CO2) Brayton cycle has been receiving a lot of attention because it can achieve compact configuration and high thermal efficiency at relatively low temperature (450∼750 °C). However, to achieve high thermal efficiency of S-CO2 Brayton cycle, it requires a highly effective recuperator. Moreover, the temperature difference in the heat receiving section is limited for the S-CO2 Brayton cycle to achieve high thermal efficiency results in high mass flow rate and potentially high pressure drop in the cycle. Thus, to resolve these problems while providing flexibility to match with various heat sources, authors suggest a hybrid system of S-CO2 Brayton and Rankine cycle. This hybrid system utilizes the waste heat of the S-CO2 Brayton cycle as the heat input to the Carbon Dioxide (CO2) Rankine cycle. Thus, the recuperator effectiveness does not always have to be high to achieve high efficiency, which results in reduction of the recuperator volume reduction. By controlling amount of the heat transfer from the cooler of the S-CO2 Brayton cycle to the Rankine cycle, the total system can be compact and can achieve wider operating range. Thus, the hybrid system of S-CO2 Brayton cycle and CO2 Rankine cycle can be coupled to various heat sources with more flexibility without trading off the performance. In this paper, Molten Carbonate Fuel Cell (MCFC) system is selected to demonstrate the feasibility of the proposed hybrid cycle system while comparing the proposed system’s performance to that of other cycle layouts as well.

The concern about the global climate change and the unstable supply of fossil fuels stimulate the research of the new energy source utilization and the efficient energy system design. As the interests on the future energy sources and renovating the conventional power plants grow, an efficient and widely applicable power conversion system is required to satisfy both requirements. S-CO2 cycle is considered as a promising candidate with the advantages of 1) relatively high efficiency in the modest temperature (450–750°C) region because of non-ideal properties near the critical point, 2) effectively reduced size of the total cycle with compact turbo-machines and heat exchangers, 3) potential for using in various applications with competitive efficiency and simple layout. The S-CO2 cycle was originally considered as an attractive candidate for the power conversion cycle of the next generation nuclear reactors. However, due to many benefits of the S-CO2 cycle, it is recently considered in other conventional and renewable energy system applications including fossil fuel power plant system, ship propulsion application, concentrated solar power system, fuel cell bottoming power cycle and so on. This paper will discuss about the design of S-CO2 cycle for the various energy system applications over different temperature range. Unlike a large size power plant which usually focuses more on maximizing the cycle efficiency, a small capacity energy system is seriously concerned about the total size of the cycle. In this manner, several preliminary S-CO2 cycle designs will be compared in terms of the efficiency and the physical size. Various layouts and components of S-CO2 cycle are compared to find the optimum cycle for each energy systems. The in-house codes developed by the KAIST research team are used to evaluate the various cycle performances and component preliminary designs. The obtained results will be compared to the conventional power conversion systems along with its implication to other existing designs.Copyright © 2013 by ASME

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.

The supercritical CO2(S-CO2) Brayton Cycle is gaining attention due to its high thermal efficiency at relatively low turbine inlet temperature and compactness of turbomachineries. For designing turbomachineries of the S-CO2 Cycle, however, most of existing codes based on ideal gas assumption are not proven yet to be accurate near the supercritical condition. Furthermore, many of existing design computer programs usually focuses on a specific type of turbomachinery, e.g. axial or radial, which makes hard to compare performance of both types at the same design condition. Since both axial and radial types of turbomachineries were pointed out as an equally possible candidate for the S-CO2 Brayton cycle, in order to compare and determine the best effective type of turbomachinery requires considering both types under the same design conditions. Taking into consideration of these facts, some modifications to the conventional design methodology of gas cycle turbomachinery are necessary to design a turbomachinery for the S-CO2 cycle. Especially, a modified design method should consider non-linear property variation of CO2 near the critical point to obtain an accurate result. Thus, the modified design method for the S-CO2 Brayton cycle turbomachineries is suggested in this paper and the method was implemented in the in-house code. In addition, some preliminary results will be discussed with the plan for validation and verification of the code.