Search

AbstractThis work provides an overview of vaporization phenomena in liquid-core nuclear thermal rockets to aid in unifying modeling assumptions by characterizing the impact of vaporization. Historical variations in vapor modeling have led to reported specific impulses ranging from 1000 to 2000s following model refinements in the 1960s and the omission of vaporization consideration post 1990. The only preexisting vapor transport study to not rely on the Reynold’s analogy was performed for the radiator design.This paper performs the first such analysis for the bubbler design, given its renewed interest. Consideration is given to potential centrifugal species separation, proposed fuel mixtures, interplay between chamber pressure and vaporization, impacts on propellant thermoproperties, evaporative cooling, power requirements for vapor separation, and the complexity of hydrocarbon interactions under the proposed chamber conditions.The bubbler design is shown to be well approximated as fully saturated, whereas the radiator and droplet designs may be configured to reduce vaporization to 20% saturation. Characterization of vaporization within liquid cores is essential to early design decisions, such as overall archetype, defining the operating point, and liquid media composition. For a threshold temperature corresponding to around 10% of the propellant being vapor by mass, further increases in temperature begin reducing the specific impulse. Below this threshold temperature, the impact of vaporization on thermal modeling with the chamber is likely negligible. Above this threshold temperature, higher-fidelity thermal modeling will be required, and the work required to separate the vapor begins exceeding 100 kW/(kgH/s).Nozzle kinetics are applied to liquid cores for the first time, showing that specific impulses increase with increasing chamber pressure contrary to historical findings. Historically, modeled uranium-zirconium-carbon mixtures are predicted to reach a specific impulse up to 1260 s. A uranium-tungsten-carbon fuel mixture yielded the best theoretical specific impulse of slightly under 1400 s; however, no nucleonic or thermal analysis has been conducted with this fuel composition. [ABSTRACT FROM AUTHOR]

Pure components exhibit different phase behavior and critical properties shift when confined, primarily due to increased molecules-pore wall interactions. While extensive research has focused on modeling this behavior for pure components, there is a need to extend these models to hydrocarbon gas mixtures in tight and shale reservoirs to understand the deviation of gas properties from bulk behavior. The study utilizes the Peng–Robinson equation of state to calculate gas properties, considering the shift in critical properties of pure components due to confinement in EOS parameter calculations. Trend analysis investigates the effect of pore size reduction on gas properties, introducing the concepts of the confinement impact factor and specific pore radius. Correlation analysis explores the relationships between variables. Nonlinear regression analysis leads to the development of a new correlation that accounts for confinement effects on gas properties. The findings reveal that the deviation from bulk properties depends on the pore radius, pressure, temperature, and gas composition. The magnitude of deviation ranges from negligible to exceeding 15% under specific conditions of high pressure, low temperature, small pore radius, and rich gas composition. Gas viscosity experiences the most significant alteration, followed by density, while the gas compressibility factor also displays a noticeable impact. The isothermal gas compressibility coefficient demonstrates minimal to no response to confinement. Decreasing pore radius increases the gas compressibility factor, while gas viscosity and density decrease. The obtained results are crucial for shale and tight reservoir engineering calculations, particularly in adjusting gas properties in reservoir simulation and production modeling software. [ABSTRACT FROM AUTHOR]

In this paper, an improved multicomponent lattice Boltzmann model is employed to investigate the impact of the gas properties, specifically the gas adiabatic index, on the thermodynamic effects of cavitation bubble collapse. The study focuses on analyzing the temperature evolution in the flow field and the resulting thermal effects on the surrounding wall. The accuracy of the developed model is verified through comparisons with analytical solutions of the Rayleigh-Plesset equation and the validation of the adiabatic law. Then, a thermodynamic model of cavitation bubble composed of two-mixed gases collapsing near a wall is established to explore the influence of the gas adiabatic index γ on the temperature behavior. Key findings include the observation that the γ affects the temperature of the first collapse significantly, while its influence on the second collapse is minimal. Additionally, the presence of low-temperature regions near the bubble surface during collapse impacts both bubble and wall temperatures. The study also demonstrates that the γ affects maximum and minimum wall temperatures. The results have implications for selecting specific non-condensable gas properties within cavitation bubbles for targeted cooling or heating purposes, including potential applications in electronic component cooling and environmental refrigeration.

High-speed hydrogen turbo-expander is widely employed in hydrogen liquefaction systems due to its high efficiency. The hydrogen bearings in high-speed turbo-expander are usually applied for low viscosity and pollution-free advantages. Nevertheless, the load capacity of hydrogen bearing is low and the research on maximizing the load capacity is limited by the complicated solution process and danger hydrogen experiment. The purpose of the paper is to easily and quickly acquire the load capacity of high-speed orifice externally pressurized hydrogen journal bearing for optimization of bearing performance. A new simple load capacity predicted model, that is universal for various working fluids involving hydrogen, helium and air, was proposed through the hydrostatic and hydrodynamic analysis. In the model, the evaluation indicators of hydrodynamic and hydrostatic effects were proposed. Based on the model, no numerical analysis and computer programming are needed to calculate the load capacity of journal bearing and numerous key design variables are considered. The results from the predicted model agree very well with those obtained from the finite difference method (FDM) technique. In view of the danger of hydrogen bearing experiment, the load capacity predicted model can be used to design the equivalent experiment of load capacity through substituting air for hydrogen working fluid. • A simple performance of high-speed hydrogen bearing predicted model was established. • The predicted results show good agreement with the values calculated by numerical method. • The performance predicted model is universal for various working fluids involving hydrogen, helium and air. • The model is applied to design equivalent experiment of load capacity through substituting air for hydrogen. [ABSTRACT FROM AUTHOR]

In this work, an investigation on the fluidization behaviour of solid particles was carried out while the fluidizing agent was switched from one gas to another with an equal volumetric flow. Four different gases, namely helium, nitrogen, argon and carbon dioxide (He, N 2 , Ar and CO 2), were adopted as fluidizing agents, and fluid catalytic cracking (FCC) was used as the experimental material. When changing the gas supply a sharp decrease of the bed pressure drop and significant compression of the emulsion phase are observed, as well as the disappearing of the bubbles and the formation of channels inside the bed. However, these disturbances are temporary, and the initial fluidization conditions can be restored after a certain amount of time. Such behaviour is quantitatively described by measuring the maximum relative decrease of bed pressure drop, the time duration and the intensity of the defluidization phase. The effects of the initial powder bed height, the switching gas velocity and the gas properties are analyzed as well. Finally, a semi-empirical model was developed to predict the defluidization time based on the understanding of this physical process and analyzing the experimental data. Unlabelled Image • Defluidization phenomenon of FCC particles after switching gas is investigated. • Pressure drop intensity and time duration are described during defluidization. • Effects of powder bed height, gas velocity and gas properties are analyzed. • A semi-empirical model was developed to predict the defluidization time. [ABSTRACT FROM AUTHOR]

A series of high-temperature combined anaerobic digestion tests with different mass ratios were carried out using chicken manure and straw with a high C/N ratio as the raw materials. The changing trends of CODs, CODr, CODs/CODr and VFAs and the concentration of each component were analyzed during the high-temperature anaerobic digestion of chicken manure and straw using a sequencing batch reactor. The results showed that the CODT of the fermentation broth decreased significantly in the first 15 days, and the values of CODT decreased from 3584.45, 3132.28, 3355.45 and 2987.39 mg/L in the initial stage to 1756.28, 1532.45, 1607.28 and 1528.33 mg/L, respectively. The degradation rates of CODT15 were 51.06, 55.09, 52.11 and 48.84%, respectively. At the end of the reaction (50 d), the values of the four groups of CODT were 1223.10, 903.21, 1095.39 and 1333.46 mg/L, respectively. As the reaction proceeded to the seventh day, the maximum concentration, the VFAs of the digestive fluids from R1, R2, R3, and R7 were 3032.39, 3346.75, 3245.12 and 2794.03 mg/L, respectively. As the reaction completed, (50 d), the VFAs of the digestive fluids were 1558.34, 1547.37 and 1335.58 mg/L, respectively, in which the contents of formic acid, acetic acid, propionic acid, lactic acid, and butyric acid were 9.19-9.97%, 20.58-22.13%, 15.74- 18.44%, 22.86-25.50% and 25.56-30.02%, respectively. [ABSTRACT FROM AUTHOR]

This is the second part of a study conducted to model the aerothermodynamic impact of suction parameters and gas properties on a multi-stage centrifugal compressor’s performance. A new iterative method has been developed in the first part to derive the equivalent performance at various operating conditions. This approach has been validated to predict the compressor map at different suction pressures and temperatures using the design characteristics as reference values. A further case is included in this paper in order to emphasize the validity of the developed approach to obtain the performance characteristics at various gas compositions. The provided example shows that the performance parameters at different gas mixtures can be predicted to within ±1.34%. Furthermore, the conducted optimization in this paper reveals that the proposed method can be applied for the compressor design evaluation corresponding to the expected variation in suction conditions. Moreover, the examined case study demonstrates the effect of gas properties’ variation on the operating point and aerodynamic stability of the entire compression system. In order to achieve that, a simple approach has been established to assess the contribution of gas properties’ variation to the inefficient and unstable compressor performance based on the available operational data.

In this paper, an improved multicomponent lattice Boltzmann model is employed to investigate the impact of the gas properties, specifically the gas adiabatic index, on the thermodynamic effects of cavitation bubble collapse. The study focuses on analyzing the temperature evolution in the flow field and the resulting thermal effects on the surrounding wall. The accuracy of the developed model is verified through comparisons with analytical solutions of the Rayleigh-Plesset equation and the validation of the adiabatic law. Then, a thermodynamic model of cavitation bubble composed of two-mixed gases collapsing near a wall is established to explore the influence of the gas adiabatic index γ on the temperature behavior. Key findings include the observation that the γ affects the temperature of the first collapse significantly, while its influence on the second collapse is minimal. Additionally, the presence of low-temperature regions near the bubble surface during collapse impacts both bubble and wall temperatures. The study also demonstrates that the γ affects maximum and minimum wall temperatures. The results have implications for selecting specific non-condensable gas properties within cavitation bubbles for targeted cooling or heating purposes, including potential applications in electronic component cooling and environmental refrigeration., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2023 The Authors.)

Computational fluid dynamics (CFD) has been widely used to study the hydrodynamics of bubble column reactors. However, the interaction between the different phases, which are in fact intimately linked, and the effect of their physical properties on the dynamics of the bubbles are still not well understood. In this study, the population balance equation (PBE) is coupled with CFD model to investigate the effect of liquid and gas phases physico-chemical properties on bubbles formation and the hydrodynamic characteristics in bubble column reactors. The coupling is realized using AVL FIRE v.2017 software, and the predicted results are validated against published experimental data. User subroutines are written using FORTRAN to incorporate the scalar transport equation source term for bubble break-up and coalescence. The predicted results were in reasonable agreement with experimental observations and available literature results, since the model has been able to predict the effect of gas flow rate on the gas holdup in bubble column within the range of ±7%. The simulations showed that the average gas holdup increase with the increase in superficial gas velocity and gas phase density, and decrease with the increase in liquid phase density. It was also found that Sauter mean bubble diameter increases with the increase in liquid density and decreases with the increase in gas density. Finally, the bubble rise velocity increased when water was used as a continuous phase. On the other hand, the increase in gas density causes a decrease in the bubble rise velocity. [ABSTRACT FROM AUTHOR]

The paper reports on numerical investigation of an accelerated laminar boundary layer over a heated wall at Prandtl numbers from 0.23 to 2.39. Properties of three gases were simulated: air, helium-xenon mixture and superheated water vapor. The finite difference method was applied to solve a system of laminar boundary layer equations with variable gas properties. It has been shown that the influence of Prandtl number, viscosity, heat conductivity and heat capacity on the flow at studied conditions is secondary relative to gas density, which is the determinant factor for the overshoot magnitude and other flow parameters. Nevertheless, at insignificant differences in density distributions the overall decrease of Prandtl number and decrease of viscosity and heat capacity and increase of heat conductivity separately lead to an increase of maximal velocity within the boundary layer. [ABSTRACT FROM AUTHOR]

This is the second part of a study conducted to model the aerothermodynamic impact of suction parameters and gas properties on a multi-stage centrifugal compressor's performance. A new iterative method has been developed in the first part to derive the equivalent performance at various operating conditions. This approach has been validated to predict the compressor map at different suction pressures and temperatures using the design characteristics as reference values. A further case is included in this paper in order to emphasize the validity of the developed approach to obtain the performance characteristics at various gas compositions. The provided example shows that the performance parameters at different gas mixtures can be predicted to within ±1.34%. Furthermore, the conducted optimization in this paper reveals that the proposed method can be applied for the compressor design evaluation corresponding to the expected variation in suction conditions. Moreover, the examined case study demonstrates the effect of gas properties' variation on the operating point and aerodynamic stability of the entire compression system. In order to achieve that, a simple approach has been established to assess the contribution of gas properties' variation to the inefficient and unstable compressor performance based on the available operational data. [ABSTRACT FROM AUTHOR]

Calculation of gas and water properties are of great significance in petroleum and as well as transmission and processing industry dealing with these fluids. Because of their significance they have to be calculated quite frequently depending on composition and the existing conditions of pressure and temperature. Standard charts are available for reading the values in most cases, but that requires tremendous efforts to find the required chart and then have to interpolate, if the curve at the required conditions is not drawn. To overcome this problem, programming has been done in Visual Basic to calculate the desired property accurately and with great ease, showing the significance of in-house softwares, which at the same time are very economical. The work is divided into two parts; the first part deals with the gas properties while the second part deals with the computational calculation of water properties. The authors also give a good insight to the nonprogrammers about programming and how it can be accomplished specifically in their field. [ABSTRACT FROM AUTHOR]

Abstract: We calibrated three models of commercially-manufactured, laminar flow meters (LFMs) at four pressures (100, 200, 300, and 400 kPa) with five gases (N2, Ar, He, CO2, and SF6) over a 10:1 flow range using NIST’s primary flow standards as references. We combined three items: (1) the calibration data acquired with N2, (2) gas-property data from NIST’s database REFPROP 9.0, and (3) a physical model for each LFM that accounts for the effects of viscosity, entrance and exit effects, gas expansion, gas non-ideality, and slip. This combination predicted the calibrations for the flow of Ar, He, CO2, and SF6 with a maximum error of 0.8% for Reynolds numbers . Under these conditions, the present LFM model allows prediction of calibration results for other gases with approximately three times more accuracy than conventional approaches that plot the flow coefficient as a function of the viscosity coefficient or Re. We represented the calibration data for SF6 in the range 500 by adding an empirical quadratic function to the model for one of the LFMs. [Copyright &y& Elsevier]

Abstract: The proper orthogonal decomposition (POD) is used to reproduce absorption line black body distribution function (ALBDF). POD is a statistical technique providing an efficient way of obtaining low-dimensional approximate descriptions of a high-dimensional models. The aim of the study is to extract information about the ALBDF from large data sets defining the absorption lines. The input data are available in several databases. The output of the model is an approximation of the ALBDF expressed as a low term sum of modes multiplied by temperature and concentration dependent amplitudes. The modes are obtained by expanding an ensemble of ALBDF into a set of orthogonal vectors. The amplitudes are evaluated by fitting this expansion to the original distributions of the ALBDF. The dependence of the amplitude from temperature and concentration is postulated in a form of a linear combination of radial basis functions. The accuracy of the model has been tested in reproducing ALBDF and total emissivity against results obtained by line by line calculations. [Copyright &y& Elsevier]

• The influences of gas composition and properties on the combustion characteristics of oxy-fired pulverized coal boiler were well considered. • Except the gas mass flow rate, the flue gas composition and properties under different combustion modes also strongly affect the temperature and heat transfer distributions. • Oxy-coal combustion obtains matched furnace temperature at lower gas mass flow rate because of its higher gas specific heat. • Oxy-coal combustion obtains matched furnace wall heat absorption at higher flame temperature because of its higher gas absorption coefficient. This paper presents a numerical study on the influences of gas composition and properties on the combustion and heat transfer characteristics of pulverized oxy-coal boiler. Previous studies were primarily focused on impacts of gas mass flow rate under different flue gas recirculation (FGR) rates while the important influences of gas composition and physical properties were overlooked. The results show that the changes in the gas composition and physical properties under different combustion modes, such as density, heat capacity and gas absorption coefficient, can significantly affect the flow, temperature, and heat transfer distributions in the furnace. Specifically, due to the differences in the heat capacities of CO 2 , H 2 O and N 2 , the gas heat capacity of oxy-coal combustion is considerably higher than that of air-coal combustion. As a result, oxy-coal combustion attains furnace temperature comparable to that of air-coal combustion at remarkably lower gas mass flow rate. Moreover, because of the differences in the radiation properties of CO 2 , H 2 O and N 2 , the gas absorption coefficient of oxy-coal combustion is higher than that of air-coal combustion, especially at the near-wall region, which hinders the radiation heat transfer between the high temperature flame and furnace wall. Consequently, oxy-coal combustion needs higher furnace temperature at further lower gas mass flow rate to achieve matched wall heat absorption with that of air-coal combustion. Therefore, the differences in the gas composition and physical properties under different combustion modes need to be comprehensively considered in the design of oxy-coal combustion systems or retrofit of existing air-coal combustion systems. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a measurement of the ratio of photon to electron production and the scintillation spectrum in a popular gas for time projection chambers, carbon tetrafluoride (CF4), over the range of 200–800nm; the ratio is measured to be . This result is of particular importance for a new generation of dark matter time projection chambers with directional sensitivity which use CF4 as a fill gas. [Copyright &y& Elsevier]

• The history, microdischarge formation and application of DBD were presented. • The effect of reactor structure, power supplies, packing materials and gas properties on VOCs removal were described. • The discussion of the above factors was based on discharge behaviors, VOCs removal and mineralization rate, and by-products. • The practical implementation of DBD in VOCs abatement were examined. • Future trends on DBD for VOCs treatment were given. This review describes the history and current status of dielectric barrier discharge (DBD) non-thermal plasma (NTP) for volatile organic compounds (VOCs) abatement. Firstly, the history of DBD, the formation of microdischarge and its environmental applications were presented. Next, the status quo of DBD for VOCs removal was discussed in detail from four aspects: reactor structure (include electrode material and configuration, discharge gap and length, dielectric material and thickness, and number of dielectrics), power supplies (include applied voltage, frequency and pulsed power supply), packing materials (include packed position, properties of packing material, loaded catalyst on support and synergy of plasma and catalysis) and gas properties (include target reactants, gas flow rate, initial concentration, oxygen content and humidity level). The description of these factors is mainly based on their effects on discharge characteristics and VOCs decomposition in DBD. Subsequently, a number of aspects related to the practical implementation of DBD for VOCs treatment were described. Finally, future trends were suggested based on the existing research works. [ABSTRACT FROM AUTHOR]