Gas Expansion Research Articles

Expansion of a one-dimensional Bose gas: the role of interactions and kinetic-energy driving

We study the expansion of a one-dimensional boson gas by initialising it in a small region of a chain, and then suddenly allowing it to expand into the remainder of the chain. We consider three initial ground-state configurations: the Mott insulator, the conventional superfluid, whose momentum density is sharply peaked at zero momentum, and the cat-like state with momentum peaks at ±π/2, produced by kinetic driving, the latter being a particular case of a flat-band system. In turn, we consider three types of expansion: spectroscopic (with interactions tuned to zero), dynamic (with standard short-range repulsive interactions), and under kinetic driving. The numerical calculations are exact. We compute the momentum and real-space one-particle densities, as well as the two-particle momentum correlations. We find that the spectroscopic time-of-flight experiment reflects the initial momentum distribution except for the larger number of momentum states and at high momenta. For the dynamic expansion starting from an insulator, we recover the non-equilibrium quasi-condensation into momenta ±π/2, provide a physical explanation in terms of interacting bosons that is confirmed by the numerical simulation, and note the existence of nontrivial correlations in the momentum distribution. Under kinetic driving the expansion is comparatively slow, but we conjecture that at high densities it will be much faster. We compare various measures of the two-particle momentum correlations, noting that some of them tend to conceal the possible cat-like structure of a many-body state.

Spectroscopic plasma plume study of a non-volatile liquid-fed pulsed plasma thruster

The development of small satellites weighing as little as 1 kg has accelerated along with the miniaturization of technology. However, there is still a lack of efficient micropropulsion systems at these scales. A possible solution is the pulsed plasma thruster, which has an inherently simple structure that is conducive towards miniaturization. As these thrusters were primarily developed in an era of larger satellites, there are systematic considerations that need to be taken into account. One of these is the propellant, where the conventional solid polytetrafluoroethylene (PTFE) propellant can be replaced with a non-volatile liquid perfluoropolyether (PFPE), enabling liquid-feeding approaches for propellant feeding. The physics behind the operation of a non-volatile liquid-fed pulsed plasma thruster still remains relatively unknown compared with the well-studied solid-fed archetype. We focus here on the use of emission spectroscopy to better understand the spatial distribution and temporal behavior of plasma components within a pulsed plasma thruster using non-volatile liquid PFPE. This is directly compared with solid PTFE to give us an understanding of the similarities and differences between the two propellant types. The overall results suggest that liquid PFPE may be a useful propellant in scenarios with a high thrust-to-power requirement and lower emphasis on electromagnetic acceleration. One such use-case is in coaxial or capillary discharge miniaturized pulsed plasma thrusters, where a significant portion of thrust is obtained from thermodynamic gas expansion rather than electromagnetic acceleration.

One-step sustainable extraction of Silymarin compounds of wild Algerian milk thistle (Silybum marianum) seeds using Gas Expanded Liquids

This work reports the application of Gas Expanded Liquid (GXL) extraction to concentrate the flavonolignan fraction (silymarin) and taxifolin from Silybum marianum seeds, which have proven to be highly valuable health-promoting compounds. GXL using green solvents was used to isolate silymarin with the objective of replacing conventional methods. In one hand, the effect of different compositions of solvents, aqueous ethanol (20%, 50% or 80% (v/v)) at different CO2/liquid (25, 50 and 75%) ratios, on the GXL extraction was investigated. The obtained extracts have been chemically and functionally characterized by means of UHPLC-ESI-MS/MS (triple quadrupole) and in-vitro assays such as anti-inflammatory, anti-cholinergic and antioxidant. Results revealed that the operating conditions influenced the extraction yield, the total phenolic content and the presence of the target compounds. The best obtained yield was 55.97% using a ternary mixture of solvents composed of CO2:EtOH:H2O (25:60:15) at 40 °C and 9 MPa in 160 min. Furthermore, the results showed that obtained extracts had significant antioxidant and anti-inflammatory activities (with best IC50 value of 8.80 µg/mL and 28.52 µg/mL, respectively) but a moderate anti-cholinesterase activity (with best IC50 value of 125.09 µg/mL). Otherwise, the concentration of silymarin compounds in extract can go up to 59.6% using the present one-step extraction method without further purification, being silybinA+B the predominant identified compound, achieving value of 545.73 (mg silymarin/g of extract). The obtained results demonstrate the exceptional potential of GXL to extract high-added values molecules under sustainable conditions from different matrices.

Dynamics of expanding gas from supercritical state in conical nozzle and cluster formation

A gas dynamic model of supersonic expansion of a real (supercritical) gas flow in nozzle based on the Redlich-Kwong equation of state has been developed. The proposed model can serve as a basis for describing the expansion of the main gas (carrier gas), against which processes of interest (formation of clusters, microcapsules, condensation) occur. Specific calculations were performed for clustering in Ar and Kr flow. Experimental verification of results of the model calculations of the sizes and densities of Ar and Kr clusters using the Rayleigh scattering method was performed. The proposed model for describing cluster jets has been tested in the experiments aimed at creating X-ray sources and accelerated electron beams in the process of relativistic laser action on a krypton cluster jet.

Isobaric tanks system for carbon dioxide energy storage – The performance analysis

The paper presents the results of thermodynamic and economic analysis of a compressed carbon dioxide energy storage installation using a novel solution, i.e. isobaric carbon dioxide tanks. The solution assumes the installation of low-pressure and high-pressure vessels in such a way that they are isobaric so that during the process of compression and expansion of gas there will be no need to use throttling valves to establish a constant level of pressure before the compressor and expander. The throttling valves using decrease the round-trip efficiency of the system by generating losses in the energy balance. The article presents the results of calculations of tank main geometry features also the pressure dependence of carbon dioxide in the high-pressure tank to the low-pressure tank. Thermal energy storage and a single-stage compressor and expander are considered in the energy storage system. A thermodynamic analysis was carried out to determine the basic parameters of the installation, such as the maximum round-trip efficiency of the energy storage system, which was 76% for 220 kPa in low pressure and 28.2 MPa in a high-pressure tank. The maximum temperature calculated at the compressor outlet was 612 °C. Levelized cost of storage was determined at the level of 593.87€/MWh.

Unconventional well shut-in and reopening: Multiphase gas-oil interactions and their consequences on well performance

Recent field reports show the uplift in oil production rate (qo), after the shut-in period, referred to as “flush production”. The conventional hypotheses for explaining this phenomenon are based on water-oil-rock interactions such as counter-current oil production and water-blockage reduction due to imbibition of fracturing water. Here, we hypothesize other drive mechanisms responsible for the uplift in qo: 1) pressure buildup near matrix-fracture interface during the shut-in period, 2) increasing oil saturation (So) and compressibility (co) due to an increase in solution-gas content at higher pressures, and 3) gas expansion (solution-gas drive) during pressure drawdown after restarting the well.We analyzed the production data of two unconventional wells which were shut-in for 194 and 20 days after the primary-production period. Analysis of production data indicates that pressure buildup is the primary mechanism responsible for higher post-shut-in qo, followed by an increase in oil relative permeability (kro). The results of our compositional simulations show that by increasing the pressure near the fracture face during the shut-in period, a fraction of the free gas is dissolved in the oil phase, leading to an increase in So which is considered as the primary factor for kro enhancement. Increasing co because of increasing solution-gas content is the secondary factor that improves post-shut-in kro. However, gas relative permeability (krg) drops after the shut-in period while kroincreases. The reduction of gas saturation because of pressure buildup during the shut-in period and trapping of the gas phase due to hysteresis effect are the two reasons that explain krg reduction.

Experimental Study on Work of Adsorption Gas Expansion After Coal and Gas Outburst Excitation

Coal and gas outburst is an extremely complex dynamic phenomenon of mine gas, which is mainly manifested in a very short time. A large amount of coal and rock are thrown out from the coal body to the mining space and accompanied by a large volume of high-pressure gas. In the process of coal and gas outburst, the internal energy consumption of gas is composed of two parts: one is used to throw out broken coal and rock mass, and the other is used to pulverize broken coal. In this article, from the perspective of energy dissipation, the experiment of broken coal ejection with different coal particle sizes, different adsorption gas, and pressure is studied. The characteristics of coal ejection are studied and analyzed, and the proportion of adsorbed gas participating in the outburst work is quantitatively analyzed. The results show that after outburst excitation, residual gas will continue to desorb and work on outburst until the power is insufficient to throw coal body; compared with air, CO2 gas has a stronger ability to work on the outburst, and the outburst coal is thrown far away, and the pulverization effect is stronger. Through the energy analysis in the process of outburst, the results show that when the particle size of the coal sample is consistent, the greater the outburst pressure is, the larger the desorption amount of the adsorbed gas is, and the larger the volume involved in the outburst work is. When the test gas is consistent with the outburst pressure, the gas desorption amount of the small-size coal sample is more, the desorption gas has a stronger ability to work on the outburst, and the proportion of participating in outburst work is higher. The crushing degree of coal plays an important role in the expansion and release of gas internal energy.

Methane and helium adsorption of coal and its related deformation under different temperature and pressures

ABSTRACT In general, the adsorption/desorption of free and adsorbed gas in coal will cause the coal matrix swelling/shrinkage. However, there is no constant conclusion on how the coal deforms under the two types of gas under different temperature and pressure conditions. Herein, a self-developed constant-temperature adsorption/desorption and deformation test system is used to monitor the axial and radial deformations of coal caused by the adsorption of different gases. The effects of effective stress and gas-self adsorption on the deformation in the process of expansion of gas adsorbed–coal are studied. The results showed that at the initial stage of gas adsorption by coal, the axial deformation of coal exceeds the radial deformation. Under the same injection pressure, the volumetric strain caused by injecting He and CH4 into coal first increases and then decreases with increasing temperature. During the CH4adsorption of coal, the volumetric strain of coal caused by effective stress exceeds that caused by adsorption stress. With increasing injection pressure, coal deformations caused by adsorption stress varied insignificantly. At a constant temperature, the CH4 adsorption stress increases slightly with increasing injection pressure. Under a constant injection pressure, the decrease in the CH4 adsorption stress is large when the temperature rises from 40°C to 60°C and is small when the temperature rises from 60°C to 80°C. The effect of temperature on the CH4 adsorption stress is more significant than that of the injection pressure. Finally, the ratio of volumetric strain caused by adsorption stress to that caused by effective stress decreases with increasing temperature, and it is approximately constant at temperatures between 60°C and 80°C. In general, the volume deformation caused by adsorption stress is mainly affected when the temperature is <60°C; thus, 60°C can be regarded as the threshold temperature at which the gas adsorption of coal is significantly changed.

Drying of sodium alginate using Pressurized Gas eXpanded (PGX) liquid technology

Pressurized Gas eXpanded (PGX) liquid technology is a scalable platform technology that simultaneously purifies, micronizes and dries aqueous solutions of biopolymers into fine structured open porous materials with unique morphologies using carbon dioxide (CO2) and ethanol at mild temperatures. The objective of this study was to investigate the effect of several PGX processing parameters on the physicochemical properties of sodium alginate (SA), a water-soluble polysaccharide from brown algae. PGX-processed SA (PGX-SA) had an open porous structure with a delicate network of fibrils, compared to the irregular shaped crystal-like non-porous particles of the raw SA dried using a conventional process. Upon PGX processing, the specific surface area was increased by more than 90 times compared to the raw SA. The use of low concentration (1.0% w/w) of the SA aqueous solution as the feed material and low ethanol flow rate (15 g/min), together with the mass flow rate ratio of 1:3.75:1.25 of aqueous solution:ethanol:CO2 resulted in a specific surface area of 164.5 m2/g of the PGX-SA. The PGX process shows great potential for simultaneously purifying and drying high molecular weight biopolymers into porous morphologies with large specific surface area for bioactive delivery systems in food, cosmetic and pharmaceutical applications.

The Nigerian Petroleum Industry Act, Frontier Basins Exploration and the Global Energy Transition

The Nigerian Petroleum Industry Act (PIA) passed into Law in 2021 has the major goal to reform the Nigerian petroleum sector operations into policy, regulations and business (commercial). In the line of this, the Nigerian National Petroleum Corporation (NNPC) was transformed to NNPC Ltd to operate entirely commercially with a supervising Board and registration with the Corporate Affairs Commission. Such a commercial mandate will entail the need to explore and produce more oil and gas for export and domestic utilization. Oil is becoming less attractive as an energy source but gas is gaining momentum as a clean energy source in the global energy transition road-map. The global energy transition road-map is drawn around clean, alternative and renewable energies. The Nigerian frontier basins have recently come on board as new business opportunities with huge petroleum gas resources. These frontier basins comprise the Anambra, Benue, Bida, Chad (Nigerian sector), Dahomey, and Sokoto Basins as well as the Deep and Ultra-deep offshore. Maturing these basins through data generation and production of the gas resources therein will promote the nation’s gas utilization and gas expansion programmes meant to promote industrialization and huge employment generation, grow the economy and engender positive social transformation. The clause in the PIA that promotes frontier exploration is well-thought out. Available and required geological data needed to mature the frontier basins to producing basins are presented in this paper. The success made in Kolmani River-2 well discovery is a case study.

The Effect of Curvature on the Heat Transfer Performance of Regenerative Cooling Passages for a High-Area-Ratio Nozzle

Abstract Numerical studies on the flow and heat transfer characteristics of rectangular regenerative cooling passages with lateral curvature for a high-area-ratio nozzle are presented. Unlike regular geometries of coolant paths used in various engineering applications, high-area-ratio rocket nozzles have steeply curved surfaces over which the cooling passages are provided. Though the inherent inward curvature benefits heat transfer enhancement in the throat region, it is insufficient to circumvent peak heat dissipation demand. Hence, the heat transfer enhancement due to lateral curvature of the coolant fluid passages provided near the throat region is explored in this study. Extensive numerical simulations have been performed to analyze the effect of the geometry of the cooling channel on its flow and heat transfer characteristics. The compressible turbulent flow field inside the nozzle has been resolved to understand the realistic local wall heat transfer characteristics of the typical high-area-ratio rocket nozzle using Advection Upstream Splitting Method (AUSM) scheme-based finite volume solver. Menter’s Shear Stress Transport k–ω turbulence model is used to model the turbulent flow inside the nozzle. Simulations of the incompressible coolant flow and conjugate heat transfer in regenerative cooling passages have been performed with realistic spatially varying local heat flux profiles, resulting due to compressible gas expansion in the convergent–divergent nozzle. Secondary flow structures are formed due to the lateral curvature of the coolant fluid passages and are found to enhance the heat transfer considerably. Further, the effect of coolant flowrate and channel curvature have been examined to explore its suitability to negotiate the peak heat flux dissipation demand at the throat region of the nozzle.

Analysis of Efficiency of Beta Stirling Cycle Model in Lab View

This study strives to provide a clear explanation of the Stirling engine and its efficiency using new automation technology and the Lab View software. This heat engine was invented by Stirling, a Scottish in 1918. The engine’s working principles are based on the laws of thermodynamics and ability of volume expansion of ideal gases at different temperatures. Basically there are three types of Stirling engines: the gamma, beta and alpha models. The study focuses on a beta type engine model. The engine is coupled with a small generator for transforming heat energy to electrical energy. The heating energy is provided by a special resistor inside the cylinder. A friendly user interface has been designed so that the user can see the measured values either graphically or numerically on the screen. Main values include: input power, output power, efficiency, rpm and temperature as well as the PV diagram. Key Words: beta type engine model, input power, Lab View software output power, Stirling engine,

A new approach of CO2 separation by applying rapid expansion of supercritical CO2 rich natural gas

The previous methods for CO2 separation from CO2 rich natural gas led to expensive production costs. This work was implemented to overcome the problems utilizing a new approach economically. The cooling and rapid expansion processes were integrated for the CO2 separation from CO2 rich natural gas on the supercritical condition. The experimental apparatus was newly constructed to perform the experiments, and the results were simulated using a various equation of state. The result reveals that the inlet temperature of supercritical expansion diminished the outlet temperature and the gas condensed easily. The simulation indicated that the 70% CO2 in natural gas was condensed easier than 45% CO2. We found that the outlet temperature of −42 °C and the vapor fraction of 0.69 was attained at the CO2 composition of 70%. Besides, the pressure drop change influences the vapor fraction at various CO2 compositions. The vapor fraction under supercritical diminished significantly compared with the non-supercritical condition. The expansion coefficient determined utilizing the equation of state escalates by the enhancement of expansion inlet temperature based on CO2 composition in natural gas. The acid gas equation of state was the perfect equation to estimate the expansion coefficient with the absolute average error of 4.83%. This work suggests that the CO2 separation from CO2 rich natural gas with the cooling and rapid expansion method promotes the new approach to overcome the disadvantages of previous methods.

The Titan Haze Simulation (THS) experiment on COSmIC. Part III. XANES study of laboratory analogs of Titan tholins

We have used the Titan Haze Simulation (THS) experimental set-up at NASA Ames’ COSmIC facility to produce four laboratory analogs of Titan’s aerosols, or tholins. These tholin samples were produced from four gas mixtures of initial compositions N 2 :CH 4 (90:10 and 95:5) and N 2 :CH 4 :C 2 H 2 (89.5:10:0.5 and 94.5:5:0.5) at 150 K, using a plasma discharge in the stream of a jet-cooled gas expansion. Here we present an ex situ X-ray absorption near-edge structure (XANES) spectroscopy analysis of these four tholin samples. The C- and N-XANES spectra show the presence of various functional groups (aromatic carbon, imines, nitriles, etc.) whose abundances are correlated with (i) the relative proportions between N 2 and CH 4 , and (ii) the presence or absence of C 2 H 2 in the initial mixtures. In particular, mixtures containing C 2 H 2 result in the formation of tholins consisting of more aromatic structures and displaying larger relative amounts of imines and nitriles, but lower overall nitrogen content. XANES spectroscopy also allowed for the determination of the elemental C/N ratios for the four tholins, which were all found to be low (< 2.5) and consistent with those measured for tholins produced in other, independent experimental set-ups. The C/N ratios of tholins produced from gas mixtures that contained C 2 H 2 (2.2–2.4) were found to be about twice as large as those of tholins produced from gas mixtures that did not contain C 2 H 2 (0.9–1.3). These new results from the COSmIC/THS experimental set-up demonstrate the impact initial precursors have on the nitrogen chemistry during the formation of tholins, which may help in the interpretation of observations and the development of models of Titan’s atmosphere. • Titan aerosol analogs were produced with COSmIC/THS from four gas mixtures. • XANES spectroscopy provided chemical and elemental composition of Titan tholins. • Tholins formed from N 2 :CH 4 and N 2 :CH 4 :C 2 H 2 contain aromatics, imines, and nitriles. • C 2 H 2 resulted in more aromatics, imines, and nitriles, but lower nitrogen content. • Results show effect of initial precursors on nitrogen chemistry in tholin formation.

Climate impacts of fossil fuels in todays electricity systems

Oil, coal, and gas account for approximately 80% of global primary energy, but only a portion of total airborne CO2eq (approx. 35% at GWP20 to 65% at GWP100), even though they account for 95% of total measured CO2 emissions. The benefits of these energy sources, as well as their related costs, are not all incorporated in current energy policy discussions. Global greenhouse gas policies must include documented changes in measured airborne CO2eq to avoid spending large amounts of public funds on ineffective or sub-optimal policies. The authors examined airborne CO2, which is less than half of emitted CO2, as well as reported CH4 emissions and the global warming potential of CH4 as published by the IPCC for coal and natural gas. The surprising conclusion is that surfaced-mined coal appears 'better for the climate' than the average natural gas, and all coal appears beneficial over LNG. Therefore, current CO2-only reduction policies and CO2 taxes are leading to unintended consequences and the switch from coal to natural gas, especially LNG, will not have the desired impact of reducing predicted future global warming; in fact, quite the contrary. A large portion of anthropogenic global warming is attributed by the IPCC and IEA to CH4, but it must be noted that CH4 emissions from natural sources and from agriculture account for approximately 40% and 25% of annual global CH4 emissions respectively. Energy accounts for about 20% of documented CH4 emissions. CO2 contributes only approximately 35% of annual airborne anthropogenic GHG emissions after accounting for CH4, over a 20-year horizon. At a 100-year horizon, the contribution of CO2 increases to approximately 60%. Energy policies that do not consider all GHG emissions along the entire value chain will lead to undesired economic and environmental distortions. All carbon taxation and CO2 pricing schemes are incorrect and need to be revised. At IPCC's GWP20 an approximately 2%1 higher loss of CH4 across the value chain prior to combustion of natural gas versus coal will lead to 'climate parity' of coal with natural gas. According to public data, natural gas value chains have high CH4 and undocumented CO2 losses. On a global average, using only IEA-documented CH4 data, natural gas emits approximately 15% more CO2eq than surface-mined coal, over a 20-year horizon. This difference will increase as the use of shale gas and LNG expands. Investors should support all energy systems in a manner that avoids an energy crisis, including intermittent renewable energy systems where they make sense. If CO2 emissions need to be reduced, one of the most effective ways would be to install ultra-supercritical power plants with CCUS technology. However, the undisputed benefits of increased CO2 concentrations in the atmosphere because of its promotion of photosynthesis and plant growth effects (fertilization) need to be considered in energy policy decisions as well. The authors suggest that future research and development should concentrate on reducing net emissions from fossil fuel power plants and providing cost-effective and reliable new conventional power generation capacity, utilizing clean coal and clean natural gas technology.

Influence of temperature on gas desorption characterization in the whole process from coals and its application analysis on outburst risk prediction

With the continuing advance of deep coal mining, temperature has become an important factor affecting coal methane recovery and gas dynamic disaster prevention. However, the influence of coal temperature on the whole process of gas desorption (including initial period) and released gas energy has been rarely studied. In this paper using a self-designed gas desorption device, the gas desorption characterization, e.g. desorption capacity, desorption theoretical model and released gas expansion energy law under varied temperatures were investigated. The results show that the increased coal temperature increases the gas desorption capacity, e.g. desorption amount and rate. However, for the same coal sample, the increased effect under the same gas pressure is weaker than that under the same gas adsorption amount. Compared with exponential function, the gas desorption law at different temperatures is more in line with the power function. The ratio of initial desorption amount of gas (∼10 s) increases with the increasing temperature, even up to 50%. The initial released gas expansion energy accordingly increases with the increase of temperature, showing a linear change between them. Moreover, the change degree of initial released gas expansion energy is greater under the same gas adsorption capacity compared with the same gas pressure. Meanwhile, with the increase of desorption time the linear correlation degree between the initial released gas expansion energy and gas desorption amount decreases. This represents that shortening measurement time will make the outburst risk results more credible when the gas desorption amount is used to determine the outburst risk of coal masses.

A variable time step self-consistent mean field DSMC model for three-dimensional environments.

A self-consistent mean field direct simulation Monte Carlo (SCMFD) algorithm was recently proposed for simulating collision environments for a range of one-dimensional model systems. This work extends the one-dimensional SCMFD approach to three dimensions and introduces a variable time step (3D-vt-SCMFD), enabling the modeling of a considerably wider range of different collision environments. We demonstrate the performance of the augmented method by modeling a varied set of test systems: ideal gas mixtures, Poiseuille flow of argon, and expansion of gas into high vacuum. For the gas mixtures, the 3D-vt-SCMFD method reproduces the properties (mean free path, mean free time, collision frequency, and temperature) in excellent agreement with theoretical predictions. From the Poiseuille flow simulations, we extract flow profiles that agree with the solution to the Navier-Stokes equations in the high-density limit and resemble free molecular flow at low densities, as expected. The measured viscosity from 3D-vt-SCMF is ∼15% lower than the theoretical prediction from Chapman-Enskog theory. The expansion of gas into vacuum is examined in the effusive regime and at the hydrodynamic limit. In both cases, 3D-vt-SCMDF simulations produce gas beam density, velocity, and temperature profiles in excellent agreement with analytical models. In summary, our tests show that 3D-vt-SCMFD is robust and computationally efficient, while also illustrating the diversity of systems the SCMFD model can be successfully applied to.

Analysis of transcritical CO[formula omitted] vortex tube performance using a real gas thermodynamic model

A new real gas model is developed to estimate the cold and hot exit temperatures of a vortex tube. The effect of the Bödewadt boundary layer flow is taken into account in addition to the introduction of a correction factor to account for high cold mass fractions. The model results are validated against an ideal gas model and with experimental data available in the literature for three different working fluids, namely air, R134a and carbon dioxide. The model exhibits similar results compared to the ideal gas model for air while it substantially enhances the predictions of the cold and hot exit temperatures for R134a and carbon dioxide. In addition, a parametric study is performed to test the operation of carbon dioxide under transcritical conditions. Working under transcritical conditions, liquid droplets form after the inlet gas expansion. In effect, the hot exit temperature decreases significantly below the inlet temperature. However, the cooling and heating powers can get significantly higher up to a 1 kW compared to only 90 W under subcritical conditions. Also, the exergy efficiency increases notably by at least 88.5%.

Analysis of flame propagation mechanisms during light-round in an annular spray flame combustor: the impact of wall heat transfer and two-phase flow

Ignition in annular multi-burner combustors is marked by a succession of four phases, ending with a characteristic flame expansion from burner to burner, often referred to as light-round. During this last phase, flame propagation is prone to substantial change depending on the boundary and operating conditions. With realistic aero-engine conditions in mind, wall heat transfers can be enhanced during ignition in cold wall conditions, which aid an understanding of the main governing mechanisms of flame propagation. From a modeling perspective, several works have outlined the need for detailed descriptions of the liquid phase, turbulent combustion and wall heat transfer, which are all included in the present work for the first time. Large-Eddy Simulations of light-round are performed in the annular MICCA-Spray combustor with cold walls, Lagrangian particle tracking, a dynamic closure for the sub-grid scale flame surface wrinkling as well as a custom tabulated wall model. The predicted light-round duration from the simulation is found to be in good agreement with experimental data. It is shown that the volumetric expansion of burnt gases induces a flow acceleration in azimuthal direction which constitutes the main driving mechanism of flame propagation. Droplet accumulations in the wake of swirling jets are generated ahead of the propagating flame fronts, which in turn cause a characteristic sawtooth propagation mode of the leading point. A cooling effect of the combustor walls on burnt gases is particularly pronounced downstream, diminishing the resulting flame propagation speed. The main governing mechanisms are investigated by means of a mathematical model for the absolute turbulent flame speed to quantify their relative impact on flame propagation. Finally, a priori estimations are provided for the flame propagation speed based on different models and boundary conditions, which are directly plugged into the model.

Multiphase Flow Through Chokes - An Evaluation of Frozen, Equilibrium, and Nonequilibrium Flow Models

This work has evaluated the most common published mechanistic multiphase choke models and compared them with a newly developed model. A typical assumption for most of the models is that the flow through the choke is adiabatic because it is argued that there is limited amount of time for heat and mass transfer. Such models are often referred to as “frozen flow” models and are widely used in the industry. The new model deviates from the frozen flow concept because it includes phase transfer. The depressurization through the choke is fast; hence, thermodynamic equilibrium will not be established and a nonequilibrium coefficient will account for this intermediate state. The goal was to investigate whether frozen flow and adiabatic expansion through the choke is a reasonable simplification or whether the concept of nonequilibrium flow could provide higher predictive ability.The predicted mass rates from all models have been calculated for two experimental multiphase datasets, and the mean relative error, mean absolute percentage error, root-mean-square deviation, and standard deviation have been calculated to compare the performances. The new model seems to be more robust and performs better than the more common frozen flow models. It has better overall predictive potential with a mean absolute percentage error of 2.6% and 5.2% for the multiphase datasets.The new model is generic and can be used with any given thermodynamic process, e.g., equilibrium flow, nonequilibrium flow, or frozen flow. For frozen flow, both adiabatic and polytropic gas expansion can be used, and the model performance will then be similar to previously published frozen flow models such as Al-Safran and Kelkar or Mwalyepelo.Further, a methodology for highly viscous flow has been proposed. All the present models originally assume frictionless flow, and high viscous flow is therefore not accounted for. A Reynolds number correction has been incorporated by adjusting the choke discharge coefficient. The correction is based on a study of highly viscous flow through safety valves.