Cycle Helium Research Articles

Thermoeconomic analysis for hybrid solar Brayton cycles operating with different working fluids

A Brayton cycle analysis with regeneration fed by heat input from a central concentration solar energy tower and a combustion chamber that uses natural gas is presented. The thermodynamic model includes the irreversibility of the different components of a conventional Brayton cycle system and a solar concentration system through energy and exergy considerations. The environmental conditions of Barranquilla are used for the plant analysis using different working fluids throughout the day, where the carbon dioxide cycle presents an overall efficiency of 28.8 %, the cycle with air efficiency is 26.6 %, and the Helium cycle is 20.2 %. The model considers the energy flows within the plant and the exergy destruction. In this sense, the solar concentration system contributes an energy fraction of 0.209 when operating with air, while the exergy destruction fraction is 0.189 when operating with carbon dioxide when solar radiation is maximum. Finally, an estimation of the Levelized Cost of Energy is presented.

The investigation of thermo-economic performance for dry-cooled closed Brayton cycle coupled to nuclear microreactors using different coolants

Dry-cooled closed Brayton cycle (CBC) coupled to gas-cooled nuclear microreactors offers a compact structure and can be deployed in water-deficient areas. The gas-cooled reactor utilizes coolants including supercritical carbon dioxide (S–CO2), helium, and He–Xe mixture. The choice of working fluids for CBC strongly affects its size and performance, where smaller plant sizes, higher thermal efficiency, and lower investments are preferred. This study investigates the thermo-economic performances of dry-cooled CBC coupled to nuclear microreactors using different coolants. A design method for dry-cooled CBC is developed based on the integration of thermodynamic modeling and component preliminary design. Baseline designs are first established, followed by an analysis of the effects of key design parameters. Furthermore, a multi-object optimization is conducted to compare the Pareto frontiers of CBC using different working fluids. The results demonstrate that the helium simple cycle exhibits superior efficiency and precooler size due to its higher reactor outlet temperature, though with a larger capital cost. The Pareto frontier of the He–Xe cycle is worse than that of the helium cycle. The S–CO2 recompression cycle has a comparable efficiency with a smaller capital cost at mediate reactor outlet temperatures but suffers from large precooler sizes. The findings revealed that the S–CO2 recompression cycle is a more promising choice if the reactor outlet temperature can be further elevated.

Thermodynamic Analysis and Comparison of Power Cycles for Small Modular Reactors

Small nuclear power plants can provide a stable, carbon-free energy supply to civil infrastructure and industrial enterprises in remote regions isolated from unified energy systems. More than 70 projects of small modular reactors are currently being developed by IAEA member countries; several low-power power units are already supplying thermal and electrical energy to consumers. One of the main limitations standing in the way of widespread dissemination of this technology is the high specific capital cost of a low-power nuclear power plant; therefore, new scientific and technical solutions are needed in this industry. Increasing the thermodynamic efficiency of power cycles of small modular reactors can become a driver for reducing the cost of supplied electrical energy. This paper presents the results of a comprehensive thermodynamic analysis of existing and promising power cycles for small modular reactors. In addition to traditional steam power cycles, cycles using non-traditional working fluids, including carbon dioxide, freons, and helium cycles, are considered. Optimal sets of thermodynamic parameters were determined to ensure maximum net efficiency of electricity production. For water-cooled reactor plants, a maximum efficiency of 33.5% at an initial temperature of 300 °C could be achieved using a steam turbine cycle. It was revealed that for reactor plants with liquid metal and liquid salt coolant in the range of initial temperatures above 550–700 °C, the maximum thermal efficiency was provided by the Brayton recompression cycle with a carbon dioxide coolant: the net electrical efficiency exceeded the level of steam turbine plants, with intermediate superheating of the steam, and could reach a value of 49.4% at 600 °C. This makes the use of these cycles promising for low-power nuclear power plants with a high initial temperature. In small gas-cooled reactor plants with a helium coolant, the use of a binary cycle consisting of a helium Brayton cycle and a steam-powered Rankine cycle provided an efficiency of 44.3% at an initial helium temperature of 700 °C and 52.9% at 1000 °C. This was higher than in the Brayton cycle with a recuperator, with a minimum temperature difference in the heat exchanger of 20 °C: the efficiency was 40.2% and 52%, respectively. Also, the transition to power cycles with non-traditional working fluids will lead to a change in the operating conditions of turbomachines and heat exchangers.

Numerical investigation on the heat transfer of air/helium precooler for air-breathing pre-cooled engine

Installing a precooler behind the intake is an effective approach for hypersonic air-breathing pre-cooled engine to cool the hot incoming air. Synergetic air-breathing rocket engine is a revolutionary hypersonic air-breathing pre-cooled engine with complex thermodynamic cycle i.e. air cycle, helium cycle. Air/helium precooler is a key component and its configuration and operating condition have great effect on the performance characteristics of air-breathing pre-cooled engine. Thus, the minimum periodic flow and heat transfer model of the precooler are established. The effects of key parameters on the heat transfer performance of precooler are numerically studied. The results indicate that: when the tube row number increases from 7 to 15, the average heat transfer coefficient of air side decreases by 57%, the heat exchange rate increases by 19%, and effectiveness increases by 18.4%. The tube transverse pitch can enhance the heat transfer coefficient of air and helium side, while the heat exchange rate decreases by 33 % when the tube transverse pitch increases from 1.5 to 3.5. The helium inlet velocity can improve the heat transfer performance of precooler and reduce the flow resistance of air side.

Effects of key parameters on performance of a pre-cooled core engine based on the closed helium cycle

A pre-cooled combined engine based on a closed helium (He) cycle offers high specific thrust and high specific impulse. Therefore, evaluation of the performance of such an engine is crucial for engine applications and key technology research. This study employs an analytical approach to investigate the effects of key parameters on the performance of a pre-cooled core engine, assuming a perfect gas model. The findings revealed that the specific thrust and specific impulse of the pre-cooled core engine are related to the pressurized coefficient of the airflow passage and equivalence ratio (ER). An increase in the pressurized coefficient leads to an increase in both specific thrust and specific impulse. However, within a certain range, although the specific thrust is positively correlated with the ER, the specific impulse is greatly reduced. With specific component parameters and a fixed thermodynamic cycle, a minimum ER exists, which satisfies the cycle-matching requirement. Moreover, the value of the minimum ER is related to the closed-cycle efficiency. For a pre-cooled core engine with a simple closed He cycle, the minimum ER is approximately 2.5–3.5.

Alternatives to Improve Performance and Operation of a Hybrid Solar Thermal Power Plant Using Hybrid Closed Brayton Cycle

Hybrid solar thermal power plants using the Brayton cycle are currently of great interest as they have proven to be technically feasible. This study evaluates mechanisms to reduce fuel consumption and increase the power generated, improving plant efficiency. An energy and exergy model for the hybrid solar plant is developed using an estimation model for the solar resource to determine the plant operation under specific environmental conditions. The effect of using different working fluids in the Brayton cycle, such as air, and helium in transcritical conditions and carbon dioxide in subcritical and supercritical conditions, is evaluated. Additionally, the plant’s exergy destruction and exergy efficiency are evaluated. In those, it can be highlighted that the helium cycle in the same operating conditions compared to other working fluids can increase the power by 160%, increasing fuel consumption by more than 390%.

Model for analyzing the energy efficiency of hydrogen liquefaction process considering the variation of hydrogen liquefaction ratio and precooling temperature

The energy efficiency of the hydrogen liquefaction process is studied, and a general model of the hydrogen liquefaction process is built for analyzing the energy efficiency and the influence of multiple parameters. Energy and exergy analysis models of the typical single-pass cycle and multiple-pass cycle are developed. The specific relationships among the parameters and energy efficiency of the total liquefaction system are deduced. A hydrogen liquefaction process with precooling nitrogen and cryogenic helium cycles is studied. For the precooling and cryogenic cycles, the SEC and net power consumption of the cryogenic helium cycle have different variation trends along with the precooling temperature and hydrogen liquefaction ratio. Their optimal values are identified to be −194 °C and 0.9453, and the corresponding SEC, exergy efficiency, total capital expense, and total annual cost are 3.619 kWh/kgLH2, 33.44%, 82.58%, 8.263 M$, and 531.62 M$/yr, respectively. The proposed model can be used in the design and operation stages to analyze the variation of energy efficiency along with multiple parameters of the hydrogen liquefaction process.

Thermodynamic analysis of key parameters on the performance of air breathing pre-cooled engine

Synergetic Air-Breathing Rocket Engine is a revolutionary air breathing pre-cooled engine with complex circuits and multiple components. The performance of Synergetic Air-Breathing Rocket Engine depends on the key design parameters among subsystems, i.e. air cycle, helium cycle and propellant system, and for which the performance of key design parameters on engine and the design criteria have not been well established. On account of this purpose, a component-level model was proposed as the basis for thermodynamic analysis. The calculation of engine performance was adopted by the method of combination of solving equations of a component-level model and numerical calculation for precooler, in which several constraint equations were considered. The results show that the helium flowrate and distribution ratio in branch have little impact on the thrust and thermal efficiency of the engine, but the enlargement of total hydrogen consumption and distribution ratio significantly increases total hydrogen consumption. Moreover, with helium inlet temperature increasing by 140 K, the specific thrust decreases by 3.6%, and the total efficiency decreases by 5.6%. Besides, with combustion chamber pressure increasing by 1 MPa, the specific thrust increases by 5.9%, and total engine efficiency decreases by only 2%. Some suggestions are also proposed for engine design and operation. The helium flowrate, distribution ratio and helium inlet temperature should be designed as small as possible, within the range of parameters considered. A compromised design is needed for combustion chamber pressure to balance its impacts to structural design.

The performance and efficiency of novel oxy-hydrogen-argon gas power cycles for zero emission power generation

This study investigates the performance and efficiency of closed-loop oxy-hydrogen Brayton power cycles through numerical modelling and simulation. Coupled with storage hydrogen and oxygen produced by a water-electrolysis system, these cycles have the potential to produce flexible electrical power at high thermal efficiency whilst producing zero exhaust gas emissions. The efficiency and power output of the cycles are investigated using a thermodynamic model. A standard Argon Power Cycle (APC) fuelled by hydrogen is explored which yields an efficiency of 19% under typical operating conditions. To improve the performance, the cycle is modified by including an intercooler, reheater and regenerator, which has the potential to increase the efficiency to 64% when operating under the same conditions. In addition, the potential use of helium and air as the working fluid is explored, as well as a methane fuelled cycle. It is found that the hydrogen–helium cycle is more efficient over all pressure ratios but the most expensive to operate.

Comprehensive comparison of various working media and corresponding power cycle layouts for the helium-cooled DEMO reactor

The main goal of this study is to propose a comprehensive view of the benefits of using various working media and thermal cycle layouts for efficient conversion of thermal energy from the helium-cooled DEMO reactor for electricity production. A four-source boundary condition proposed by Bubelis (2018) [1] is used in the power cycle optimization process. Selected power cycle layouts are optimized through a specialized computational optimization code to achieve maximum net power output with variable blanket helium outlet temperature in the range from 380 up to 520 °C. The selected working media are water-steam, supercritical CO2, and helium. The Rankine cycle layout is based on the layout proposed by Rovira (2019) [7] and optimized in the full range of blanket outlet temperature. Investigated S-CO2 cycles are simple Brayton cycle, re-compression cycle, and pre-compression cycle. In the case of the indirect helium cycle, the only reasonable layouts are the simple Brayton cycle and the pre-compression cycle. Study results compare suitability of using the water-steam, S-CO2, and helium cycles for different outlet temperatures of the source as well as a view of their complexity in terms of size and number of components. Presented results show, that the Rankine cycle is the most effective solution from thermodynamics point of view, but S-CO2 cycles can compete with it in size, complexity, cost, and operational flexibility.

Preliminary Analysis and Design of the Energy Conversion System for the Molten Salt Fast Reactor

The unique design features of the molten salt fast reactor (MSFR) should enable higher coolant temperatures than in conventional water reactors, with a significant improvement in the achievable thermodynamic performance. The use of a molten salt as both fuel and coolant, however, poses several advanced heat transfer challenges, such as the design of innovative heat exchangers and energy conversion systems. In this work, we address a preliminary but quantitative analysis of the energy conversion system for the MSFR, based on reference design data from the SAMOFAR H2020-EURATOM project. We consider three main technologies, i.e., the supercritical steam cycle, the closed helium cycle and the helium/steam combined cycle. Preliminary design results are presented for each technology, based on a simplified modelling approach. The considered cycles show promising efficiency improvements, with the best performance being proven by the supercritical steam cycle. The analysis also highlights the critical issue related to the risk of freezing of the molten salts within the secondary heat exchangers, due to the low inlet temperatures of the working fluids. Results show potential incompatibility between the freezing point of molten salts and the temperatures typical of steam cycles, while helium cycles offer the best chances of freezing avoidance. The combined cycle promises intermediate performance in terms of thermodynamic efficiency and thermal compatibility with molten salts comparable with closed helium cycles.

Thermodynamic and economic aspects of the Nelium Turbo-Brayton refrigerator development for the FCC-hh

Within the conceptual design study for the Future Circular Hadron Collider (FCC-hh) it was shown, that a large part of the total cryogenic heat load falls into the temperature range between 40 to 60 K. Thus, additional cryogenic refrigerators for this temperature level are specified for each of the 10 foreseen cryoplants. Such a cryogenic system was developed at the TU Dresden and is based on a Brayton cycle working with a neon-helium mixture as refrigerant and using multistage centrifugal compressors. The duty requirements comprise a 6.2 MW total heat load at 40 to 60 K for beam screens and shielding, additional 2.7 MW at 300 to 40 K for the pre-cooling of the helium cycle and a turndown ratio of up to 3.8. The optimisation of the referenced system was performed in order to obtain a high efficiency of the cryogenic cycle and tolerable costs for system components at the same time. An analysis of the mixture composition influence on the components and on the total gas mass was performed. Restrictions for industrially existing hardware were taken into consideration. Updated cycle parameters are subsequently described.

Development of pressure acquisition system for cryogenic receiver

Receiver system is an indispensable signal receiving equipment for radio astronomical observation. By refrigeration, the noise temperature of the receiver is reduced to a great level, and the sensitivity of the receiver is improved. Therefore, the refrigeration link is particularly important. The cryogenic receiver system of radio astronomy usually adopts compressor compressed helium cycle refrigeration mode. When the compressor is in normal operation, the injected helium high pressure is between 280-300 Psi and the low pressure is between 70-100 Psi. The two pressure values will directly affect the refrigeration efficiency of the receiver. Because the compressor and cryogenic receiver system are both on the radio telescope, engineers are unable to check the pressure state at any time during the observation process. Sometimes, because of temporary power failure or pressure reduction, the receiver warms up and so on, which affects the whole receiving system. Combining with the refrigeration system of Nanshan 26-meter antenna, we have established 6 channels of helium pressure acquisition and remote monitoring, which can better ensure the operation of cryogenic receivers.

An integrated mixed refrigeration cycle for pre-cooling of refrigeration below 25 K

Two trends can be found in current large-scale cryogenic projects. The first is the ever-increasing capacity requirements, while also a shift towards cooling demands at higher temperatures is observed. Conventional helium cycles require the use of oil flooded screw compressors, which are limited in efficiency, capacity, and reliability. Reverse-Brayton cycles with neon-helium mixtures deliver efficient refrigeration at a temperature above the dew point of neon, but cannot be applied to the cooling of conventional superconductors. This paper describes an approach where oxygen as a heavier gas allows the use of turbo-compressors viable. The oxygen is separated and used for providing refrigeration at higher temperature levels.

Study of the cooling systems with S-CO2 for the DEMO fusion power reactor

The power conversion system is one of the key parts of the fusion power plant. The DEMO fusion power reactor features multiple heat sources, like the first wall, blanket, divertor and vacuum vessel, on different temperatures and power levels. The heat addition into a thermodynamic cycle from different heat sources is disadvantageous in terms of efficiency of steam Rankine or helium cycles. However, it is advantageous for the S-CO2 cycles as it resolves the real S-CO2 property issues. S-CO2 is thus an option for conversion of heat into electricity and might have overall better performance than the steam Rankine or helium Brayton cycles. Therefore, it should be considered as an option for the DEMO fusion power reactor. The paper focuses on the application of S-CO2 for the European DEMO fusion power plant. The higher net efficiency of the S-CO2 cycles for the DEMO fusion power plant in comparison with the Rankine steam cycles is presented.

Design and experimental investigation of a cryogenic system for environmental test applications

This paper is concerned with the design, development and performance testing of a cryogenic system for use in high cooling power instruments for ground-based environmental testing. The system provides a powerful tool for a combined environmental test that consists of high pressure and cryogenic temperatures. Typical cryogenic conditions are liquid hydrogen (LH2) and liquid oxygen (LO2), which are used in many fields. The cooling energy of liquid nitrogen (LN2) and liquid helium (LHe) is transferred to the specimen by a closed loop of helium cycle. In order to minimize the consumption of the LHe, the optimal design of heat recovery exchangers has been used in the system. The behavior of the system is discussed based on experimental data of temperature and pressure. The results show that the temperature range from room temperature to LN2 temperature can be achieved by using LN2, the pressurization process is stable and the high test pressure is maintained. Lower temperatures, below 77K, can also be obtained with LHe cooling, the typical cooling time is 40min from 90K to 22K. Stable temperatures of 22K at the inlet of the specimen have been observed, and the system in this work can deliver to the load a cooling power of several hundred watts at a pressure of 0.58MPa.

Study of various Brayton cycle designs for small modular sodium-cooled fast reactor

Many previous sodium cooled fast reactors (SFRs) adopted steam Rankine cycle as the power conversion system. However, the concern of sodium water reaction has been one of the major design issues of a SFR system. As an alternative to the steam Rankine cycle, several closed Brayton cycles including supercritical CO2 cycle, helium cycle and nitrogen cycle have been suggested recently. In this paper, these alternative gas Brayton cycles will be compared to each other in terms of cycle performance and physical size for small modular SFR application. Several new layouts are suggested for each fluid while considering the turbomachinery design and the total system volume.

Speech alarm and cycle helium gas monitoring of helium refrigerator

Two helium liquefiers are running round-the-clock in parallel. One of them is always connected to the Superconducting Cyclotron in refrigeration mode. EPICS based alarm system is running with alert sound in computer speaker. But the fault cannot be located without opening the fault screen. An audible English speech alarm system was envisaged and implemented in EPICS platform. Voice message are now being played in relation to faults or alarms. In continuously operating refrigeration system pure helium gas inventory is an important parameter to log. We need to calculate total pure equivalent helium cycle inventory. Now, we have put these calculations together in EPICS controller. This continuously calculates displays and archives the pure equivalent cycle helium gas. If any leak develops in the process, this trend gives a quick indication.

Numerical modeling and design of supercritical CO2 pre-cooler for fusion nuclear reactors

One of the key issues of fusion technology is the efficient recovery of the fusion power extracted by heat transfer fluids in the breeding blanket. The Spanish National Program TECNO_FUS is exploring a dual-coolant breeding blanket design concept and its plant auxiliary systems for a future power reactor (DEMO), with liquid lead–lithium as main primary nuclear power recovering fluid. Supercritical CO2 is chosen for the secondary circuit, since its high efficiency at significantly lower required temperatures than for the Brayton helium cycle, due to low compression work near the critical point and also because its additional major benefits in terms of tritium control. Use of printed circuit heat exchangers (PCHE) is suggested in literature due to its highly compact design and robustness for the high pressures found. This work deals with the heat exchanger devoted to release the thermal energy of the power cycle to the thermal sink. The aim of this work is analyzing how the nearness of the CO2 to its critical point affects the performance of the heat exchanger. Computer Fluid Dynamics (CFD) simulations that include the complex thermal behavior of CO2 properties at supercritical conditions are used in order to achieve an accurate approach to the design of this heat exchanger. These results are compared with others obtained through correlations found in the open literature. The behavior of CO2 close to its critical point results in an inefficient use of the exchange area, giving a temperature profile in CO2 which remembers a condensation process and an overall heat transfer coefficient 1.4 times higher than the one achieved with literature correlations design.

Closed versus open cycle energy recovery from solid oxide fuel cells

A computer model of a solid oxide fuel cell (SOFC) was implemented with a number of operational options to evaluate the best use of the cell waste heat. The simplest solution for heat recovery is represented by adopting a pressurized fuel cell with the eventual expansion of the exhaust stream in a gas turbine. Other alternatives feature the adoption of various closed cycle recovery systems: a standard steam cycle, an inter-refrigerated helium cycle, and an advanced binary cycle. Assuming a fuel energy input of 100 MW, the overall efficiency of a hybrid cell was computed, which was much higher than that of a small capacity (100 kW) existing plant (67 versus ∼53 per cent). Such high efficiency hybrid SOFC systems were taken as the reference to evaluate the performance of alternate options. Reclaiming the cell waste heat by means of a subcritical steam cycle yields a performance similar to that of a hybrid system. Similar results are obtained resorting to a closed helium cycle. Advanced binary cycles, using either potassium or cesium as working fluids, were extensively investigated in view of achieving a superior overall performance. The hot, clean stream exhausted by the fuel cell is recognized as an ideal heat source for a binary plant. The SOFC-binary cycle system was fully optimized yielding top efficiencies ∼74 per cent and an additional power output of ∼45 per cent of the cell rating (30 per cent in the case of the hybrid system). The excellent efficiency of a binary cycle combined with the large amount of oxygen that is available in the cell exhaust flow suggests that a supplementary firing of the fuel could improve the overall merit of the system. Burning 75 per cent of the additional natural gas, for example, reduces the total efficiency to a level of that of a hybrid system but makes available an extra power 1.35 times greater than the fuel cell capacity. Pushing further this concept, the fuel cell could become an auxiliary equipment of a binary cycle.