He-Xe Mixture Research Articles

Design optimization and performance analysis of a dry-cooled Helium-Xenon Brayton cycle for nuclear microreactor based on detailed models of the cycle components

Nuclear microreactors offer reliable, low-carbon dispatchable power and heat for various end use and applications. The gas-cooled reactor coupled with the dry-cooled closed Brayton cycle has a simple plant layout and can be deployed in water-deficient areas. To evaluate the system performance more precisely and optimize the mole fraction of the He-Xe mixture for the gas-cooled microreactor, an integrated design method based on detailed models of the cycle components was developed. Three designs using 4 g/mol pure helium, 15 g/mol, and 40 g/mol He-Xe were first established as demonstration examples, and performances of the cycle and components were compared. Furthermore, the effects of the He-Xe’s molecular weight on the system’s size and efficiency were discussed, and a parametric analysis of crucial design parameters like specific speed and pressure ratio was conducted. In contrast to the previous results obtained from simplified component models, the current results revealed that a Brayton cycle using 40 g/mol He-Xe could achieve a higher thermal efficiency of 44.42 % compared with 37.65 % of pure helium, which resulted from the improved efficiency in turbomachinery and reduced pressure loss in heat exchangers. Concerning the system size, it was recommended to use the 20∼30 g/mol He-Xe for reduced volume as the stage number of the turbomachinery decreased from 5 of pure helium to a single stage of the 20 g/mol He-Xe. Although the turbomachinery occupied a relatively small volume, increasing the compressor inlet temperature could reduce the volume of the precooler, thus significantly reducing the system volume.

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.

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 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.

Performance evaluation on radial turbines with potential working fluids for space closed Brayton cycle

The performance of radial turbines with the He-Xe mixtures, helium, argon and air are examined in this paper. The published approach pertaining to Chapman-Enskog kinetic theory and corresponding states theory is adopted to calculate the transport properties of He-Xe mixtures with two different molecular weights of 15.9 g/mol and 40 g/mol. The independent or combined effects of the flow Euler number (Eu), Reynolds number (Re) and inflow velocity on flow similarity are discussed based on flat-plate flow. Under the consistent above conditions, the flows of these fluids are similar and the flow loss is merely a function of fluids properties. The established flow similarity conditions form a procedure to calculate the boundary conditions of similar turbines and its application makes the flow similar in radial turbines passages. It is reflected in the consistent topology skeleton of flow structures and the identical parameter distributions in the flow section. The turbines with He-Xe mixtures, Ar and air shares a pretty similar tendency of efficiency line and the values differ little. The differences between these turbines under the same working point have an upper limit of 0.3% before critical state. At the design point, a similar velocity triangle instead of an identical one can guarantee the flow similarity and an approximate efficiency compared with others. Once the working condition deviates from the design point, the efficiency error between the helium and other fluids widens as the working condition deviation increases.

Influence of Structural Factors on the Performance of He-Xe Mixture Gas Volute

Influence of Structural Factors on the Performance of He-Xe Mixture Gas Volute

Computational flow and heat transfer design and analysis for 1/12 gas-cooled space nuclear reactor

The computational simulations of 1/12 full core gas-cooled space nuclear reactor have been conducted using the STAR-CCM+ code. The reactor is cooled by the He-Xe mixture and coupled with direct Brayton turbo-machines. To analyze the flow and heat transfer characteristics of the reactor, a series of calculations with complex core structures under zero gravity condition are conducted. The influences of the bypass vessel cooling, surface radiation, flow channel blockage and the fuel rods are studied. Results show that, although the bypass vessel cooling can decrease the temperature of the reactor vessels and the heat loss through surface radiation, it also increases the highest coolant temperature. Besides, the flow channel blockage will increase the uniformity of the radial temperature and velocity distribution. Finally, it is presented that the peak temperature is higher than the case without fuel rods and the fuel structure has little effects on the flow and heat transfer characteristics of the coolant region.

Preliminary control strategies of megawatt-class gas-cooled space nuclear reactor with different control rod configurations

A megawatt-class, gas-cooled fast reactor was designed to provide 2.2MWth power for space application. The reactor concept adopts 90% enriched annular UO2 rods as the fuel and He-Xe mixture as the coolant. The thermal power is converted into electric power through Brayton turbines. The neutron flux distributions of four selected reactor configurations with different control rod arrangement are calculated using Monte Carlo code. In addition, calculations with different combinations of inserted control rods are conducted to investigate their effects on the power profile. Results show that control rods arranged in the central region help reduce the neutron flux peak and the radial flux peaking factor. The outer control rods, however, show limited effects on the central power profile. Instead, they only affect the region of the control rod neighborhood. Besides, since the outer control rods will increase the radial peaking factor, they are better to be used as safety rods for emergency. Based on the calculation and analysis, three control strategy candidates are proposed considering power profile flattening and control flexibility.

EFFECTS OF COOLING SCHEMES ON THE PERFORMANCE OF SPACE CLOSED BRAYTON CYCLE

Closed Brayton cycle can efficiently convert the fission energy of the reactor into electricity, which is an ideal energy conversion system for long life, high-power and compact space reactor. In order to ensure the safe and reliable operation of turbines, compressors and generators, the space closed Brayton cycle intends to cool bearings and generators by working fluid, such as He-Xe mixture. So the cooling will inevitably affect the cycle efficiency. In this paper, three different cooling schemes for bearings and generators were proposed for the space closed Brayton cycle. They are: (1) bypassing some gas from the compressor outlet to cool bearings and generators and joining the mainstream before the reactor inlet, (2) bypassing some gas from the compressor outlet to cool bearings and generators and joining the mainstream after the reactor outlet, and (3) setting an independent cooling loop. The influence of bleeding gas flow rate on the key components was analyzed, and the three schemes were compared. The results show that the temperature difference at hot end of recuperator, molar specific power of reactor, turbine inlet temperature and molar specific work of schemes (1) and (2) decrease with increase of bleeding ratio. The scheme (3) is not effected by bleeding ratio. For a given bleeding ratio, the increasing of compression ratio will promote the space Brayton cycle efficiency of the scheme (1) and (2) at first, then the efficiency reaches its maximum value, with further increasing of compression ratio, the efficiency will reduce. But further increasing of bleeding ratio will reduce the temperature difference at hot end of recuperator, the cycle efficiency and compression ratio can not reach the maximum when the bleeding ratio increases. Therefore, there are optimal bleeding ratio, maximum cycle efficiency and corresponding compression ratio. And the maximum cycle efficiency of scheme (1) and (2) increases first and then decreases with the increase of bleeding ratio. The scheme (1) has the highest efficiency of power generation, 21.63%, because the bypass can reduce the core heat absorption and the turbine inlet temperature is the highest. The scheme (3) has the lowest efficiency which is 19.78% with the highest molar specific power which is 0.8832kJ∙mol-1 , and this scheme can reduce the core inlet temperature and the power of recuperator. The analysis provides a reference for the cooling design of the space closed Brayton cycle in the future.

Investigation of Heat Transfer of a He-Xe Mixture in Heated Channels with Different Shapes of Cross Section

Investigation of Heat Transfer of a He-Xe Mixture in Heated Channels with Different Shapes of Cross Section

圧電トランスを用いた誘電体バリア放電型エキシマランプで観測される自己組織化現象

An excimer lamp constructed by a piezoelectric transformer (PT) has been developed and studied in our laboratory. The excimer lamp is based on the excitation of dielectric barrier discharge (DBD) generated by the PT surface that induces high-voltage due to the piezoelectric effect. Spectroscopic measurement in the vacuum ultraviolet (VUV) region is performed for the excimer lamp filling with a He-Xe mixture and Ar. Emission spectra having a peak at 172 and 126 nm are found, which are respectively radiated from the Xe2* and Ar2* excimers that returns to ground states. A self-organization phenomenon (SOP) is also recognized in the He and Ar DBD. Static and time-resolved observations of the self-organized patterns are performed by a single reflex and ICCD cameras, respectively. The formation of self-organized patterns in argon requires a small amount of the air as an additive. From the time-resolved observation, we found dark spots arrayed hexagonally in a weak emission on the PT surface whose arrangement well coincides with that of bright hexagonal filaments. The dark spots are considered as the traces of the accumulated charges on the dielectric electrode, which interrupt the hexagonally filamentary discharges.

Structural and vibrational properties of condensed phases in xenon molecular binary systems: He-Xe, H2-Xe

We present both structural and vibrational (Raman) results of compressed xenon binary systems of He and H2 to a maximum pressure of 142 GPa. In the He-Xe mixture 15% vol. Xe and balance He, we observe no evidence for van der Waals compound formation. Pure fcc Xe can be crystallised from the 2-phase Xe-He fluid at 0.6 GPa. The expected fcc-hcp transition is accompanied by extensive diffuse scattering and the emergence of hcp reflections at higher pressures. There is no apparent volume expansion of the measured Xe equation of state in helium indicating a near-zero (iso-structural) solubility of He in Xe. In the H2-Xe system, X-ray diffraction revealed the presence of two solid-phase structures in a 15% by volume mixture, one of which was best indexed on an orthorhombic cell. Raman spectroscopic studies of both 15% and 7.5% Xe binary mixtures by volume in H2, showed shifted vibron frequencies relative to the normal, pure (bulk) H-H stretch mode (vibron) that soften with pressure and appear to cross the pressure-frequency trajectory of the H2 vibron. The 7.5 vol % Xe-H2 mixture freezes at 5.3 GPa to a solid occupying the bulk of the available sample volume in the DAC, indicating a close-to-stoichiometric composition for one Xe-H2 solid phase.

VUV Spectroscopic Measurement for Dielectric Barrier Discharge Excited by Piezoelectric Transformer in He–Xe Mixture

A new type of compact excimer lamp has been developed using a piezoelectric transformer (PT) which employs the excitation of dielectric barrier discharge (DBD) in a He-Xe (10.8%) mixture. To investigate the vacuum ultraviolet emission characteristics, a spectroscopic measurement is performed for the He-Xe DBD generated by the PT. The emission peak is observed at 172 nm in a high gas-pressure region, and a sharp peak is observed at 147 nm in a low-pressure region. These are derived from the radiation from the Xe2* excimers and the resonance line of the xenon atoms, respectively.

Heat transfer between parallel plates: An approach based on the linearized Boltzmann equation for a binary mixture of rigid-sphere gases

An analytical version of the discrete-ordinates method is used to develop a concise and particularly accurate solution of the heat-transfer problem for a binary gas mixture confined between two parallel plates. The formulation of the problem allows general (specular-diffuse) Maxwell boundary conditions for each of the two types of particles and is based on a form of the linearized Boltzmann equation that incorporates recently established analytical expressions for the relevant rigid-sphere kernels. Numerical results are reported for the density, the temperature, and the heat-flow profiles relative to each species in Ne-Ar and He-Xe mixtures.

A Compact Excimer Lamp Constructed by Piezoelectric Transformer

A compact excimer lamp constructed with a piezoelectric transformer (PT) has been developed in our laboratory. This excimer lamp is designed based on the excitation of a dielectric barrier discharge (DBD) in a He-Xe mixture generated by the PT, which is driven with low applied voltages of several tens of volts (15-45V). Vacuum ultraviolet (VUV) radiated from the lamp is detected by a phototube having a spectral response region ranging from 160 to 320 nm in conjunction with an optical filter to discriminate the VUV and UV regions. The VUV radiation in the wavelength range 160-200 nm is recognized in this experiment. This may be derived from the 172-nm light emission by the transitions of the Xe2 excimers to the ground state. Investigations into the radiated VUV intensity are carried out by varying the gas pressure and the gap length. The optimal condition for the present excimer lamp is determined.

Single-bubble sonoluminescence from noble gas mixtures.

Light emission intensities from single-bubble sonoluminescence at room temperature, water dissolved with admixtures of pairs of noble gases, He-Ar and He-Xe, were measured as a function of mixing ratio to search for effects of species segregation occurring during the violent bubble collapse. The observed relative effect on the light emission intensity is surprisingly greater in He-Ar than in a He-Xe mixture.

Standard gas addition: a calibration method for handling temporal drifts of mass spectrometry-based sensors.

This work describes a new method for the correction of signal drift of a MS-based sensor by standard gas addition (SGA). It consists of introducing a gaseous He-Xe mixture continuously and independently of the carrier gas into the mass spectrometer source. To mimic the disturbances generated by periodical tuning of the mass detector, three series of adjustments were made to the main acquisition parameters. The influence of the SGA signal correction on the discriminating power of the data was evaluated from the analysis of three batches of cheeses by dynamic headspace coupled to mass spectrometry. SGA afforded a good correction of the main types of drift classically observed in mass spectrometry.

Spatio-temporal characteristics of infrared and vacuum ultraviolet emission from a surface discharge type AC plasma display panel cell with He-Xe and Ne-Xe gas mixture

The spatio-temporal variations of 147 nm, 173 nm, and infrared emission images were obtained from a surface discharge type AC plasma display panel (PDP) cell with the He-Xe and Ne-Xe mixture. The differences in 147 nm, 173 nm, and infrared emission characteristics between He-Xe and Ne-Xe gas mixture were observed and explained by the differences in the xenon ion mobility and dimer reaction coefficients in two cases.

Fundamental properties of inert gas mixtures for plasma display panels

Summary form only given. A fundamental kinetic model is used to compare the luminous efficiency of different compositions of Ne-Xe, He-Xe and Ne-Xe-Ar mixtures in plasma display panels. Exact solutions of the kinetic Boltzmann equation in an homogeneous, unbounded system are used, accurately accounting for all the known processes of excitation as well as ionization and other losses. A self-sustaining condition is used to estimate the breakdown electric field E/sub k/, accounting also for Penning ionization. The excitation frequency of Xe states, which emit UV photons is calculated for applied electric field values ranging from 0.2E/sub k/ to 5E/sub k/. Light generation efficiency, defined as the ratio of the volume density of UV emission intensity per unit time versus dissipated electrical power, is an increasing function of the Xe concentration N/sub Xe/, in both the Ne-Xe and He-Xe cases, although He-Xe mixtures were found to be somewhat less efficient. For both Ne-Xe and He-Xe mixtures, a Xe concentration of /spl sim/10% provides a good balance between the conflicting requirements of high luminous efficiency and low breakdown voltage level. Addition of small amounts of Ar in Ne-Xe mixtures leads to insignificant changes in efficiency or breakdown voltage level. A one dimensional self-consistent simulation of an ac plasma display cell is also used to investigate the effect of gas mixture composition on luminous efficiency.