Helium-xenon Mixture Research Articles

The Design and Performance Analysis of a 15 g/mol Helium–Xenon Mixture Centrifugal Compressor

One of the primary parts of a closed Brayton cycle that uses a helium–xenon mixture as the working medium is a centrifugal compressor. Nowadays, there has been minimal research on the theoretical underpinnings and design procedures of a helium–xenon mixture centrifugal compressors, and the internal flow mechanisms remain poorly understood. In this study, we present a redesign of the 15 g/mol helium–xenon centrifugal compressor originally developed by Bruno M, utilizing a helium–xenon mixture as the working fluid to enhance compressor performance and facilitate an in-depth analysis of the internal flow dynamics. The findings indicate a significant expansion of the stable operating range of the redesigned compressor under identical outlet conditions, with a 33.27% increase in flow margin and substantial improvements in the pressure ratio. Furthermore, under consistent inlet conditions, at an operational flow rate of 0.8657 kg/s, the redesigned compressor exhibits a pressure ratio that is 2.11% greater than that of the original design, along with a variable efficiency increase of 1.1%.

Analysis of flow heat transfer characteristics of helium-xenon gas mixtures during natural circulation

Helium-xenon(He-Xe) gas mixture is a commonly used cooling medium in fourth-generation advanced reactor systems. The thermal conductivity of a passive waste heat system is related to the safety and reliability of the reactor system. Therefore, it is crucial to explore the passive characteristics of the helium-xenon gas mixture. The passive waste heat removal characteristics of a helium-xenon gas mixture are influenced by the flow and heat transfer characteristics of the mixture. However, existing research on the flow and heat transfer characteristics of helium-xenon gas mixture mainly focuses on single tube bundles and plate bundles with fixed flow rates and high Reynolds numbers. However, existing research on the flow and heat transfer characteristics of the He-Xe mixtures mainly focuses on single tube bundles and plate bundles with fixed flow rates and high Reynolds numbers, and most empirical formulas apply to Reynolds numbers greater than 10000. However, the natural circulation flow rate under the influence of gravity varies with the variation of heating power, and in most operating conditions, the Reynolds number is less than 10000. Due to the lack of research on the convective heat transfer characteristics of the He-Xe mixtures at low Re, this paper investigates the flow and heat transfer characteristics of the He-Xe under natural circulation conditions. A three-dimensional model of the natural circulation circuit was established using numerical calculation methods. Comparing the numerical simulation results of natural air circulation with empirical formulas, it was found that the error was less than 20 %. This proves that the SST k-ω turbulence model can be used to study the flow and heat transfer characteristics of He-Xe gas mixtures in natural circulation. On this basis, natural cycle numerical simulations of He-Xe mixtures with different mixing ratios were carried out at a heat flux of 5000 W/m2, as well as natural cycle numerical simulations of 40 g/mol He-Xe gas mixture at different heating powers, to study the effects of heating power and He-Xe mixing ratio on the natural cycle heat transfer characteristics of the He-Xe gas mixture. The existing He-Xe gas mixture flow heat transfer equation was modified, and the error of the modified Nu empirical equation was less than 12 %, which can be used for the development of the passive waste heat export system program for subsequent He-Xe gas-cooled fast reactors.

The influence of turbulators on the flow and heat transfer characteristic of helium-xenon mixture inside the tight lattice rod bundles

The gas-cooled nuclear reactor combined with the closed Brayton cycle is the ideal choice for future high-power space missions. The helium-xenon mixture is a suitable working medium for the reactor due to its good compressibility and heat transfer capacity. For the further development and application of a more lightweight compact reactor, the influence mechanism of turbulator structures with different angles and layouts on the heat transfer enhancement of a helium-xenon mixture in the sub-channel of a gas-cooled nuclear reactor is numerically studied. The results show that the heat transfer is effectively enhanced due to the vortex and secondary flow induced by the turbulator, leading to periodic fluctuations in the Nusselt number. When comparing the results at different angles, it is observed that the heat transfer enhancement from the turbulator at a 90° angle is relatively small, while the pressure drop is significant. Due to the secondary flow in a narrow triangular space induced by a turbulator with a 45° angle, the mixing between high and low-temperature fluids is effectively enhanced, leading to a more significant improvement in heat transfer. The heat transfer performance and thermal efficiency index of different turbulator layouts are summarized and compared, providing a reference for the heat transfer design of gas-cooled nuclear reactors.

Efficiency and mass optimization for space nuclear power systems with closed Brayton cycle loops

Space nuclear power systems should be strictly limited in mass and size. Lack of detailed designs, mass estimation in the general design phase usually relies on simple and empirical models that leave too much design margin from the limits. Accurate mass estimation of space nuclear power systems is key to minimize the design margin and maximize the system performance in the general design phase. In this paper, new mass estimation models are proposed for the main components of space nuclear power systems, including nuclear reactor, shield, turbine, compressor, heat exchanger, and thermal radiator. The mass estimation models are more accurate by incorporating principles of nuclear physics, thermal hydraulics, and structural mechanics to the component designs. Combined with thermodynamic models and genetic algorithm, the MEGREZ code is developed to optimize the system performance by setting efficiency and mass as dual objectives. The code verification results indicate that the deviations between and the Jupiter Icy Moons Orbiter project parameters and the code calculated values are only 0.4% for system efficiency and 2.1% for system mass. The optimization for the Jupiter Icy Moons Orbiter project shows that the optimal molecular weight of helium-xenon mixture is the minimum value for single-stage turbomachinery limits. Additionally, the impacts of potential technological degradation, such as increased heat exchanger thermal resistances, higher frictional factors, and decreased turbomachinery efficiency, on system performances are discussed. The results show that turbomachinery efficiency presents the strongest influence on the system-specific mass; a 0.04 reduction in the polytropic efficiency of the compressor or turbine results in more than a 10% increase in system-specific mass.

Experimental Investigation of the Heat Transfer under Air or Helium-Xenon Mixture Flow into the Heated 7-Rod Bundle with Spaced Grids

Experimental Investigation of the Heat Transfer under Air or Helium-Xenon Mixture Flow into the Heated 7-Rod Bundle with Spaced Grids

Speed of sound in helium-xenon mixtures in wide ranges of state parameters

Speed of sound in helium-xenon mixtures in wide ranges of state parameters

Performance comparison between closed-Brayton-cycle power generation systems using supercritical carbon dioxide and helium–xenon mixture at ultra-high turbine inlet temperatures on hypersonic vehicles

Closed-Brayton-cycle (CBC) has considerable potential for power generation on hypersonic vehicles, but its power level is limited by the cold source onboard, commonly the hydrocarbon fuel. To achieve power enhancement of CBC with finite cold source, this study assessed and compared the power output and thermal efficiency of supercritical carbon dioxide (S–CO2) and helium-xenon mixture (He–Xe) CBCs at ultra-high turbine inlet temperature (TIT), taking into account the thermal cracking of hydrocarbon fuel. Results indicate that raising TIT can significantly increase the electric power output for both CBC working fluids. The electric power under per unit mass flowrate of fuel is as high as 1600 kJ/kg at the TIT of 2000 K, making it easy to achieve megawatt-level power generation. The power enhancement of He–Xe CBC is more significant than S–CO2 CBC when the TIT exceeds 2000 K. Moreover, the compressor inlet temperatures and cycle pressure of S–CO2 CBCs are much higher than those of He–Xe CBC, causing additional challenges in the aerodynamic design and component manufacture. Therefore, He–Xe CBC operating at ultra-high TITs may be more suitable than S–CO2 CBCs for high-power electricity generation mission on hypersonic vehicles.

Optimization of thermodynamic performance and mass evaluation for MW-class space nuclear reactor coupled with noble gas binary mixtures Brayton cycle

Space exploration technology is an important indicator of society's technological level. A space reactor coupled with a Brayton cycle is preferable for megawatt-scale space power systems. Noble gas binary mixtures have high chemical stability, heat transfer performance, and compressibility, making them the principal choice of working fluid for the space reactor Brayton cycle, which is also the key factor affecting the thermodynamic performance and mass of the system. This study developed thermodynamic performance and mass evaluation models for the space nuclear Brayton cycle and discovered the inherent relationship between system thermodynamic performance and mass. The effects of noble gas binary mixtures on system performance and mass were investigated. The results indicated that the elevated molar mass of noble gas binary mixtures reduced the aerodynamic load and mass of the turbomachines and increased the mass of the recuperator. There are optimal values of the total mass, specific mass of the system, and working fluid composition. Helium-xenon mixture is the optimal working fluid because it can achieve the highest thermodynamic efficiency and lowest mass. Furthermore, the optimal scheme of the helium-xenon Brayton cycle for a space nuclear power system was obtained by multi-objective optimization. Its power generation efficiency, specific mass, and helium molar fraction in the helium-xenon working fluid are 29.04%, 5.65 t∙MW−1 and 77.5%, respectively. This study provides a reference for the design and optimization of space nuclear power systems.

Numerical investigation of flow stratification and heat transfer characteristics in a strongly heated horizontal rod bundles with helium-Xenon gas mixture

The helium-xenon(He-Xe) mixture has good heat transfer characteristics with a low Prandtl number(Pr ≈ 0.2 ∼ 0.3) and is suitable for the advanced compact gas-cooled reactor. The characteristics of horizontal flow stratification in the fuel rod bundles with He-Xe mixture under gravity and buoyancy were numerically simulated. Different wall heat flux q+ suitable for the reactor operating conditions were selected for calculation and analysis. Flow stratification is observed as strongly inhomogeneous in the radial direction. With the semi-local wall coordinates and Van-Driest transformation, laminarization is manifested by velocity and temperature profile and turbulent kinetic energy changes. In the horizontal flow, where the buoyancy is orthogonal to the direction of flow development, unique characteristics appear in the flow and heat transfer, and the growing longitudinal momentum and energy transport are considered the main reasons. The influence of flow acceleration and buoyancy under different bundle structures were compared. The buoyancy effect is evident in the loosely spaced rod bundles. In contrast, the thermally-induced flow acceleration effect in the tight-lattice scheme is noticeable.

Investigation of reactivity control strategies for a micro-transportable gas-cooled thermal reactor

Micro nuclear reactors have gained increasing attention in recent years due to their high efficiency and long lifetime, making them an attractive solution for meeting the energy needs of remote and off-grid locations. Previous work has proposed a conceptual design for a micro solid nuclear reactor cooled by a helium-xenon mixture. The main aim of this study is to examine the effects of introducing burnable poisons on the neutronic performance of the designed micro nuclear reactor and to improve the design of the sliding reflector segment for reactivity control. The computational results indicate that the inclusion of burnable poisons can decrease the initial excess reactivity and radial power peaking factor, while not having a significant impact on the lifetime of the core. The use of 0.4%wt Gd2O3 and 0.75%wt ZrB2 as burnable poisons results in a reduction of 6.0 $ and 7.4 $ in the maximum reactivity of the core, respectively, while the core lifetime is reduced by 169 EFPD and 545 EFPD, respectively. By partitioning the sliding reflector, a linear introduction of reactivity can be achieved, and the influence of introducing burnable poisons on the reactivity control ability of the sliding reflector is relatively small.

Numerical investigation on flow and heat transfer characteristics of helium–xenon gas mixture in rod bundles

The helium-xenon(He–Xe) gas mixture with low Prandtl number and good heat transfer characteristics suits for the advanced high heat flux and compact gas-cooled reactors. A numerical simulation was conducted on the flow, heat transfer, and turbulent mixing characteristics of He–Xe gas mixture in a tightly arranged triangular rod bundle subchannel. The transition characteristics of He–Xe gas mixture in rod bundle structure were obtained. The friction resistance coefficient, Nusselt number(Nu), and turbulent mixing factor β was corrected within the Reynolds number(Re) range of 3 × 102 - 1.8 × 105. The research results indicate that the transition occurs at Re equal to 2000 and forms a transition zone within the Re range of 2000–5000; The Blasius correlation can describe the wholly turbulent flow precisely, but it is suitable to adopt a new formula in the transition zone; The local Nu prediction performance of the modified Peckett correlation is in good agreement with the numerical simulation results, and the Petukhov correlation with shape correction and temperature correction factors has good prediction results on global Nu; The turbulent mixing factor using Re and shape parameters can better describe the mixing characteristics. This study has reference value for the design of rod bundle reactors using He–Xe gas mixtures as working fluids.

Equation of state for helium-xenon gas mixture studied by molecular dynamics simulations

In the framework of long term behaviour of nuclear spent fuels, the performance codes need physical data base such as fission gas equation of state in order to assess the pressure inside fission gas bubbles. The high pressures expected in such bubbles require gas equation of state, which are not easily accessible in the literature. Therefore, molecular dynamics simulations are carried out to assess the helium-xenon mixture equation of state in these extreme conditions. First, we confirm that the interatomic potentials used, which are key parameter for the molecular dynamics simulations, reproduce very well the existing experimental data of the pure gases. This first study provides also new data for the melting point of pure xenon in the range of 500 K to 1500 K under high pressures. Second, the simulations of the helium-xenon mixture confirm that this mixture behaves like van der Waals compounds with the presence of a gas-gas separation in equilibrium at high densities. The miscibility gap, already known for temperatures under 333 K, was extended at higher temperatures until 800 K for high gas densities. This behaviour yields to the creation of an heterogeneous gas mix, which could curb the creation of bubble containing this mixture. Finally, we have fitted with the Happel formalism a new equation of state for the helium-xenon gas mixture, which is valid over temperatures ranging from 200 K to 1000 K and for atomic volumes higher than 0.27×10−28 m3 (i.e., densities lower than 6.1×104 mol.m−3).

Transient characteristics analysis of residual heat removal system for Helium-Xenon mixture cooled small reactor system

Helium-Xenon (He-Xe) gas mixtures are characterized by stable physical properties, easy compression, and excellent thermodynamic performance, making them suitable for thermal cycle coolant for underwater reactors. Due to the unattended deep sea, and harsh and complex operating environment, the residual heat removal characteristics are directly related to reactors’ safety characteristics and stable and reliable operation ability. Therefore, studying the He-Xe gas mixture residual heat removal characteristics can provide an essential guarantee for reactor safety analysis. This article optimizes the physical property calculation model of the He-Xe gas mixture in the Brayton Cycle Reactor System Analysis Program (BRESA) and obtains a system property analysis program suitable for calculating the natural circulation of the He-Xe gas mixture. And a natural circulation system for the He-Xe mixed gas cooling reactor was constructed using the modified BRESA. Numerical calculations and theoretical analysis were conducted on the He-Xe gas mixture’s natural circulation flow process and residual heat removal characteristics. The study of the transient factors of temperature, flow rate, and other related parameters in the system circuit found that when the reactor is shut down, relying on the natural circulation system can effectively output the residual heat of the reactor core to ensure reactor safety. The relevant research results have important theoretical and scientific significance for the safety assessment and evaluation of the Brayton cycle reactor system.

Development and verification of helium–xenon mixture cooled small reaction system

Although Helium–Xenon mixture cooled small reactor has been widely concerned, there is no mature thermal calculation software that can be applied to Helium–Xenon mixture cooled small reactor in China. In this paper, a semi empirical formula used to predict the physical properties of binary inert gas mixtures is used to establish a physical property calculation model of Helium–Xenon mixture gas mixtures, and the flow and heat transfer calculation model, turbine model and compressor model are modified and improved, so as to achieve the calculation of the Brayton cycle system. The function of the original system analysis program is expanded and improved, and the simulation program for he xenon mixed gas reactor system is developed. At the same time, the closed Brayton cycle system is established by using the system analysis program developed in this paper, and the calculation results are compared with the design values. The maximum relative error is 6.9%. The steady-state operation results of the model are in good agreement with the design operation parameters, which proves the applicability of the improved simulation model. The steady-state response characteristics analysis, the introduction of positive and negative reactivity accidents and the calculation of transient conditions such as step load drop of the reactor were carried out. The overall trend is the same as the literature survey results. The results show that the system analysis program developed in this paper is suitable for the analysis of the Brayton cycle system of Helium–Xenon mixture cooled small reactor.

Effect of induced vortex and configuration layout on heat transfer enhancement of helium-xenon mixture

The helium-xenon mixture with great heat transfer and compression performance is a marvelous choice as the coolant for the gas-cooled reactor combined with the closed Brayton cycle, which has wide application prospects in the exploration of deep space. However, due to the weight and volume limit for the space nuclear reactor, it is necessary to promote the performance of the heat exchanger significantly for further deeper space exploration missions or more lightweight compact heat exchanger loadings. Therefore, the influence of three kinds of internal novel vortex generators including the Rectangular ring rib, the Kagome lattice, and the Body-Centered Cubic (BCC) lattice on heat transfer enhancement of helium-xenon mixture has been investigated numerically. The results showed that the induced vortex system significantly promoted the heat transfer capability and enhanced the overall Nusselt number up to around 2.6 times that of the smooth tube with the acceptable pressure drop. Moreover, the configuration effects showed that, as the number of vortex generators grew, the overall Nusselt number increased with the increasing friction factor. However, the thermal efficiency index did not change monotonically with the number of vortex generators. The Rectangular ring rib performed best in heat transfer enhancement, but it also caused the greatest pressure drop, while considering the tradeoff between the pressure drop and the heat transfer enhancement, the BCC lattice array showed the best thermal efficiency.

A Review on Heat Transfer Characteristics and Enhanced Heat Transfer Technology for Helium–Xenon Gas Mixtures

As one of the most promising working substances for space nuclear power sources, research on the heat transfer characteristics of helium–xenon gas mixtures has become the key issue in focus. In this paper, through an extensive literature research, the current research results are classified and organized. The results show that there are semi-empirical formulas for physical property parameters with high prediction accuracy, and there are also Nusselt correlations with small errors. However, both lack the support of experimental data. There is no systematic research on enhanced heat transfer technologies, and the conclusions of the existing studies are not significant, so they can only make limited reference contributions to the future study of enhanced heat transfer technologies. More flow and heat transfer experiments on helium–xenon mixtures are urgently needed, through detailed analysis of the heat transfer performance of helium–xenon flow, identifying the key factors affecting the heat transfer thermal resistance, and corresponding heat transfer enhancement measures to form an optimized design method applicable to helium–xenon heat exchangers. In this way, an enhanced heat transfer theory of helium–xenon heat exchangers can be developed.

Investigation of hydraulic resistance and heat transfer in the flow of HE-XE mixture with a small Prandtl number in a quasi-triangular pipe

In this work, the process of heat transfer during the flow of gas mixtures (He-Xe) in a thin-walled quasi-triangular pipe is considered experimentally and numerically. The pipe cross-section corresponds to the shape of the channel formed by the dense packing of reactor rods for generating heat at the power plant. A helium-xenon mixture with a Prandtl number of 0.23 is used as the working fluid. Temperature distributions of the heated wall are obtained in the range of Reynolds numbers from 2860 to 39,800. The influence of the laminar-turbulent transition at the initial section of the pipe and high-velocity turbulent flow at the outlet on the wall temperature distribution along the channel is analyzed. The simulation data on heat transfer are generalized using the mass-average reduction temperature as the determining temperature, which allows correct consideration of gas compressibility at high flow velocities.

Modified Stirling cycle thermodynamic model IPD-MSM and its application

A Stirling cycle is a thermoelectric conversion method with high efficiency and reliability. The Stirling cycle applies to small- and medium-sized power space nuclear reactors or radioisotope heat sources. A high-precision and well-predicted Stirling cycle thermodynamic model is the key to optimizing and improving the Stirling engine for space. The present study modified the classical Simple model by incorporating the local pressure loss into the pressure loss. An improved second-order adiabatic model based on the Simple model, namely the Incorporated Pressure Drop-modified Simple Model (IPD-MSM), was proposed. The prediction of the IPD-MSM shows well with the changing tendency of the GPU-3 Stirling engine experimental data. Moreover, this model has better prediction accuracy at high-pressure and high-frequency conditions than other adiabatic models, such as CAFS and ISAM. The thermodynamic properties of He, H2, and Helium-Xenon mixtures in the Stirling cycle were also analyzed. Results show that the He-Xe mixture reaches the highest output power and thermal efficiency when the mole percentage of Xe is approximately 2%. The mechanism is as follows: the addition of Xe leading to the reduction in non-ideal heat transfer loss exceeds the increase in pressure loss. The addition of Xe leads the pressure loss to increase abruptly as the mole percentage of Xe exceeds 2%. The characteristics and application analysis of H2, He, and He-Xe mixture were discussed. The present study provided theoretical support for the Stirling cycle analysis for space missions and the selection of working fluids.

Experimental study of heat transfer during the flow of a gas coolant in a heated quasi-triangular channel

The paper considers experimentally the process of heat transfer during the flow of gas mixtures in a heated thin-walled quasi-triangular tube. The cross-section of the tube corresponds to the shape of the channel formed by the dense packing of the reactor rods for generating heat at a power plant. The working fluids were a helium-xenon gas mixture with a Prandtl number of 0.23 as a promising coolant for a nuclear installation generating electricity, and air with a Prandtl number of 0.71. Temperature distributions of the heated wall are obtained in a wide range of flow velocities, and the effect of laminar-turbulent transition at the initial section of the tube and high-velocity turbulent flow at the outlet on these distributions is analyzed. An approach for calculating local heat transfer coefficients for an unsteady flow, based on determining the local velocities of the coolant in the channel, is proposed. Significant non-uniformity of the heat transfer coefficient along the channel length was obtained with a decrease in its value at the inlet area and an increase towards the outlet due to flow acceleration. An increase in the heat transfer coefficient during the flow of helium-xenon mixture is more intense than in the air flow. It is shown that this circumstance should be taken into account when designing compact power plants.

Entropy change in a single Leontiev tube during energy separation of low-Prandtl gas mixture

The results of numerical studies of energy separation of a helium-xenon gas mixture in a single Leontiev tube with a central cylindrical channel are presented. On the basis of the simulation data, a T-s diagram for energy separation is constructed. The changes in the total temperature depending on the entropy change in the central subsonic channel and in the annular supersonic nozzle are shown.