Sudden Expansion Research Articles

Computational Modeling of High-Speed Flow of Two-Phase Hydrogen through a Tube with Abrupt Expansion

Hydrogen can become a prevalent renewable fuel in the future green economy, but technical and economic hurdles associated with handling hydrogen must be overcome. To store and transport hydrogen in an energy-dense liquid form, very cold temperatures, around 20 K, are required. Evaporation affects the achievable mass flow rate during the high-speed transfer of hydrogen at large pressure differentials, and accurate prediction of this process is important for the practical design of hydrogen transfer systems. Computational fluid dynamics modeling of two-phase hydrogen flow is carried out in the present study using the volume-of-fluid method and the Lee relaxation model for the phase change. Suitable values of the relaxation time parameter are determined by comparing numerical results with test data for high-speed two-phase hydrogen flows in a configuration involving a tube with sudden expansion, which is common in practical systems. Simulations using a variable outlet pressure are conducted to demonstrate the dependence of flow rates on the driving pressure differential, including the attainment of the critical flow regime. Also shown are computational results for flows with various inlet conditions and a fixed outlet state. Field distributions of the pressure, velocity, and vapor fractions are presented for several flow regimes.

Numerical simulation of the flow in a flat suddenly expanding channel based on a two-fluid turbulence model

The article presents the results of a numerical study of the flow structure in a flat channel in the zone of its sudden expansion in the form of a ledge. The calculations are based on the numerical solution of a system of non-stationary equations using a new two-fluid turbulence model. The results of the profiles of longitudinal velocity and turbulent stress in different sections of the channel before and after the ledge, as well as the change in the coefficient of friction for the lower wall of the channel depending on the distance after the ledge are obtained. For the difference approximation of the initial equations, the control volume method was used, and the relationship between velocities and pressure was found using the SIMPLEC procedure. In this case, the viscous terms were approximated by the central difference, and for convective terms, a second-order scheme of accuracy against the flow was used. To confirm the correctness of the numerical results, a comparison was made with experimental data from the NASA database for the Reynolds number Re=36000. And the influence of the calculated grid in the results of the study was also investigated.

Исследование сжимаемых ламинарных потоков в трехмерном прямоугольном канале

The problem of the flow of compressible laminar gas flows through a three-dimensional channel with a sudden expansion in the shape of a square parallelepiped is formulated. The Navier-Stokes equations are solved. When solving equations, spatial derivatives are approximated with a high order of accuracy. The pseudo-implicit right-hand side algorithm is used to integrate equations over time. The computational process is parallelized using MPI technology and is carried out on the Uran supercomputer. The range of Reynolds numbers from 100 to 600 is considered. The changes in the coordinates of attachment points in various planes depending on the Reynolds number are shown. With increasing Reynolds number, the magnitudes of small separation zones are first increasing and then decreasing, while large zones only increase. The field of the vortex vector is analyzed for different Reynolds numbers. The center of rotation shifts, and disturbances penetrate further into the channel. The profiles of the longitudinal velocity at various points of the channel are presented. A tendency towards a symmetrical state is revealed for all Reynolds numbers considered in the work.

A first look at mitochondrial genetic diversity in Miniopterus schreibersii in Serbia

Schreiber?s bent-winged bat Miniopterus schreibersii (Chiroptera) is a widespread, cave-dwelling, regionally migrating species whose genetic diversity was studied throughout its distribution area using mitochondrial and nuclear markers. Previous studies revealed little to no structuring of populations and established Anatolia to be a single refugium during the last glacial maximum. The Balkans were well covered in these studies but usually lacked samples from Serbia. We sequenced the mitochondrial hypervariable region 1 (HV1) gene in M. schreibersii collected at seven sites in Serbia to assess their genetic relatedness to other European and Asia Minor populations and check whether the Balkans exhibit a higher genetic diversity than Western Europe due to its closeness to Anatolia. We recorded nine haplotypes from Serbia, six of which had not been previously reported, with a haplotype diversity of 0.585. The remaining three were shared with individuals from Portugal, Greece, and Turkey. A single most common haplotype was present throughout the species distribution range, pointing to a well-connected population and as indicated by the shape of the haplotype network, a common origin, and a sudden population expansion. Results complement existing data on M. schreibersii having a non-structured population, adding valuable new data from the Balkans supporting the previous hypothesis about its Anatolian origin.

Microfluidic synthesis of hemin@ZIF-8 nanozyme with applications in cellular reactive oxygen species detection and anticancer drug screening.

Zeolitic imidazolate framework-8 (ZIF-8) encapsulating enzymatically active biomolecules has emerged as a novel biocompatible nanozyme and offers significant implications for bioanalysis of various biomarkers towards early diagnosis of severe diseases such as cancers. However, the rapid, continuous and scalable synthesis of these nanozymes still remains challenging. In this work, we proposed a novel microfluidic approach for rapid and continuous synthesis of hemin@ZIF-8 nanozyme. By employing a distinctive combination of zigzag-shaped channel and spiral channel with sudden expansion structures, we have enhanced the mixing efficiency within the chip and achieved effective encapsulation of hemin in ZIF-8. The resulting hemin@ZIF-8 nanoparticles exhibit peroxidase-like activity and are capable of detecting free H2O2 with a limit of detection (LOD) as low as 45 nM, as well as H2O2 secreted by viable cells with a detection threshold of approximately 10 cells per mL. By leveraging this method, we achieved successful detection of cancer cells and effective screening of anticancer drugs that induce oxidative stress injury in cancer cells. This innovative microfluidic strategy offers a new avenue for synthesizing functional nanocomposites to facilitate the development of next-generation diagnostic tools for early disease detection and personalized medicine.

Numerical Calculations of Liquid-Metal Magnetohydrodynamic Flows in Rectangular Ducts with Sudden Expansions

Relating to the design of liquid-metal blankets in a fusion reactor, numerical calculations have been performed on liquid-metal magnetohydrodynamic (MHD) flows in rectangular ducts with sudden expansions. Conservation equations of fluid mass and fluid momentum, together with the Poisson equation for electrical potential, have been solved numerically. The numerical calculations have been performed for Hartmann (Ha) numbers up to the order of 10000 and expansion ratios up to 4. The pressure loss through the expansion has been estimated by the loss coefficient ζ divided by the interaction parameter N, i.e., ζ/N. The loss coefficient ζ/N through the expansion parallel to the magnetic field is much larger than that through the expansion perpendicular to the magnetic field. The loss coefficient ζ/N increases consistently with the expansion ratio. The loss coefficient ζ/N does not change very much with the interaction parameter N and the wall conductance ratio.

Comparative Analysis of Solar Chimney Power Plant Chimney Design: Performance Evaluation and Material Cost Comparison

Abstract: This paper investigates different configurations of solar chimney design in a solar chimney power plant system. Mathematical analysis of the system has been done in Ansys software. The results of the maximum (inlet) velocity, pressure, efficiency, and temperature of the air are obtained for base type, convergent, divergent, sudden contraction, and sudden expansion types of chimneys. Furthermore, the electrical power output of Solar Chimney Power Plants has been determined for different chimney types. In this analysis, one Solar Chimney Power Plant (SCPP) with a solar collector diameter of 258 m and a chimney height of 197 meters and outlet diameter of 10 m has been taken as the basis. It has been found that sudden expansion and divergent types of chimneys give higher output power than the other types of chimneys. Also, while calculating the cost of materials of the different types of chimneys, it has been found that the sudden expansion type of chimneys is costing less than other types of chimneys. When power output was compared, it was found that the sudden expansion type of chimney gives higher output than other chimneys. Detailed simulation, testing, and analysis are necessary to consolidate the results.

Cavitation in Internal Flows of Liquid Jet Through a Throat

The interaction of a liquid with the surrounding air produces unstable waves that disintegrate the liquid into droplets, which is known as liquid atomization. The common internal flow of a liquid atomization nozzle experiences a single-phase flow but might turn into a multiphase flow with the existence of cavitation. Cavitation in internal flow has gotten a lot of attention because of the positive and negative consequences it can have depending on the application. One such advantageous result is that cavitation has been used to promote the atomization of liquid jets by causing gas bubbles in the atmosphere to collapse. Most of the past research on cavitation has focused on the exit orifice’s constant cross-section area. The current study investigates the effect of throat location and geometry on cavitation characteristics. Filtered water was used as the simulation fluid. The high-speed shadowgraph technique was applied to record the images of the internal flow patterns. The placement of the throat was discovered to have a substantial impact on the status of the cavitation. Cavitation began at the inlet of the throat when the throat was placed at the uppermost part of the exit orifice. However, when the throat is placed in the middle of the exit orifice, the cavitation begins at the end of the throat. Four cavitation regimes were identified, namely developing, mixed, super and sudden expansion cavitation. Furthermore, it was found that the discharge coefficient depends on the cavitation’s state and length, except when the cavitation is in the supercavitation regime.

Pressure recovery model for gas–liquid two-phase flow across sudden expansions

Pressure recovery model for gas–liquid two-phase flow across sudden expansions

Deflagration evolution of premixed H2/CH4/air mixture undergoing a sudden expansion near the ignition source in a half-open duct

Experiments were carried out in a half-open duct to investigate the deflagration evolution of premixed CH4/H2/air mixtures undergoing a sudden expansion. Obstacles were located over and under the ignition source to simulate a long and narrow flat gap, and when the flame shot through the gap into the main body of the explosion duct, it would undergo a process of sudden expansion. By adjusting the spacings (S) and widths (W) of the gap, a series of sudden expansion conditions were considered, and the flame propagation behaviors and explosion characteristics were investigated. The results showed that different extent of flame front inversion was observed under different size of gap conditions, including inclined flat flame, vertical flat flame and tulip flame. Besides, results indicated that the vortex pairs near the obstacles play an essential role in the flame front inversion phenomenon. In addition, it was also found that the maximum overpressure in the sudden expansion duct was much lower than that in the smooth duct or with obstacles in the middle of duct. In addition, the maximum pressure (Pmax) exhibits a concave function with the increase of W, and the minimum value of Pmax was obtained at W = 150 mm, S = 30 mm, which was closely related to the combined effect of venting and combustion expansion.

Parametric analysis of different Al2O3 nanoparticle shapes and expansion angles for sudden expanded tube regarding the first law of thermodynamics

The thermo-hydraulic performance of Al2O3/H2O nanofluid with different nanoparticle shapes flowing in a sudden expansion tube with variable sudden expansion inclination angles and elliptical dimpled fins with different diameters were numerically investigated. Investigation of variable sudden expansion inclination angles, elliptic dimpled fins, and different nanoparticle shapes together reveals the novelty of this study. The main purpose of this study is to analyse the effect of nanofluid particle shapes, sudden expansion inclination angles, and elliptical dimpled fin on thermo-hydraulic performance for sudden expansion tube. The platelet, cylindrical, and blade nanoparticle shapes of Al2O3 nanoparticle (φ = 1.0 %) were separately mixed into base fluid to obtain working fluid. Numerical studies were carried out under laminar flow regime (500 ≤ Re ≤ 2000). Furthermore, the sudden expansion tube was assumed to have inclination angles with α = 30°, 45°, 60°, and 90°. The results presented that the highest Performance Evaluation Criterion is obtained for the case of DT6 using Al2O3/H2O with platelet nanoparticle shape at Re = 2000. Besides, the highest Nusselt number and Performance Evaluation Criterion were realized at the inclination angle of 45°. The increment rate of Nusselt number and Performance Evaluation Criterion at α = 45° were determined as 8.75 % and 10.52 % compared to α = 30°, respectively. Moreover, elliptical dimpled fins with sized as a = 6 mm and b = 12 mm presented the highest thermo-hydraulic performance, and this condition showed an increment of 153.9 % compared to case of a = 2 mm and b = 4 mm.

Ascent and decompressional boiling of geothermal liquids tracked by solute mass balances: a key to understand the hydrothermal explosions of Milos (Greece)

Hydrothermal explosions occur through the sudden expansion of fluids at or near boiling condition with little or no precursors, making any kind of forecast difficult. Here, we investigate the processes occurring within hydrothermal systems in a potential critical state for explosions through a new methodology based on mass balances of thermal water solutes. The usage of this method reveals that the pore water samples of the Paleochori Bay (Milos, Greece; <20 m depth below sea level), chosen as a case study, are binary mixtures of a geothermal component and seawater, from which steam is either added through condensation of underlying, ascending vapors or separates through boiling. This new method enables us to quantify and map both the fraction of the original geothermal liquid in each pore water sample and that of the vapor supplied or separated from the solutions. Furthermore, the method allows us to compute the composition of the geothermal endmember. The map of the fraction of supplied vapor shows that decompressional boiling of ascending liquids predominantly focuses in the central part of the Paleochori Bay. Both the estimated composition and temperature (324°C) of the geothermal liquid endmember overlap those measured in geothermal well fluids at or near-boiling condition, except SO4 and SiO2. The lower SiO2 and higher SO4 content in the pore waters may be ascribed to the current production of an impermeable cap, which enables underlying fluids to accumulate and pressure to buildup. The evidence of liquid at or near boiling conditions and self-sealing processes in the Paleochori Bay suggests that decompressional boiling during abrupt pressure drawdowns might have caused hydrothermal explosions at Milos in historical times, whose occurrence is testified by several hydrothermal craters. Finally, our work shows that similar conditions favoring explosions still affect the hydrothermal system of Milos. The new methodology described in this work can find useful applications in the study of submerged hydrothermal systems and in understanding the physicochemical conditions that favor hydrothermal explosions.

Multiple inlet sudden expansion flow of power-law fluids

Multiple inlet sudden expansion flow of power-law fluids

Analysis of Core Annular Flow Behavior of Water-Lubricated Heavy Crude Oil Transport

A possible method for fluid transportation of heavy oil through horizontal pipes is core annular flow (CAF), which is water-lubricated. In this study, a large eddy simulation (LES) and a sub-grid-scale (SGS) model are used to examine CAF. The behavior of heavy oil flow through turbulent CAF in horizontal pipes is numerically investigated. The Smagorinsky model is utilized to capture small-scale unstable turbulent flows. The transient flow of oil and water is first separated under the behavior of the core fluid. Two different conditions of the horizontal pipes, one with sudden expansion and the other with sudden contraction, are considered in the geometry to investigate the effects of different velocities of oil and water on the velocity distribution, pressure drop, and volume fraction. The model was created to predict the losses that occur due to fouling and wall friction. According to the model, increasing water flow can reduce fouling. Additionally, the water phase had an impact on the CAF’s behavior and pressure drop. Also, the increased stability in the CAF reduces the pressure drop to a level that is comparable to water flow. This study demonstrated that a very viscous fluid may be conveyed efficiently utilizing the CAF method.

Downward two-phase (Gas - Solid) turbulent flow through a vertical sudden expansion duct with a backward-facing step

Downward two-phase (Gas - Solid) turbulent flow through a vertical sudden expansion duct with a backward-facing step

Flame Front Dynamics in Flow of Hydrogen-Air Mixture in a Channel with Sudden Expansion and Polyurethane Foam

Flame Front Dynamics in Flow of Hydrogen-Air Mixture in a Channel with Sudden Expansion and Polyurethane Foam

Correlation between impact angle and corrosion-erosion damage behavior of ferritic/martensitic steel exposed to flowing oxygen-saturated lead-bismuth eutectic

Impact angle is considered to be one of the main factors that influence the damage behavior of materials exposed to flowing lead-bismuth eutectic (LBE) conditions in Gen IV LBE-cooled fast reactors, especially in the areas where the flow changes its direction sharply, such as sudden expansions or elbows. In the current study, the corrosion-erosion damage behaviors of T91 ferritic/martensitic steel under different impact angles were investigated in flowing (∼3 m/s) oxygen-saturated LBE at 500 °C. The results show that the damage behaviors of T91 steel are closely related to the impact angles. When the flowing direction is parallel to the specimen surface, i.e., 0° impact angle, the oxide scales show partially damaged features in the form of local buckling and exfoliation after exposure for 300 h. With continued exposure for 600 h and 1000 h, the specimen surface seems to be covered completely by the undamaged oxide scales again. In sharp contrast, when the flowing direction is perpendicular to the specimen surface, i.e., 90° impact angle, the oxide scales are almost totally delaminated after exposure for 600 h and 1000 h. As a consequence, the liquid LBE permeates into the T91 steel substrate along the boundaries of prior austenite to induce intergranular corrosion. Correspondingly, the possible reasons behind such phenomena are discussed. Meanwhile, the damage process models of oxide scales associated with 0° and 90° impact angles are established, respectively.

Mass-Transfer Intensification in Miniature Geometries Using Sudden Contraction and Expansion Devices

Mass-Transfer Intensification in Miniature Geometries Using Sudden Contraction and Expansion Devices

Potential Threat Assessment and Degree of Exposure in the event of an Explosion by Sudden Expansion of Boiling Liquid Vapor in the LPG Ground Storage Terminal in Monteverde, coastal Ecuador

The industrial complexes that handle dangerous products with flammable characteristics have been the cause of great misfortunes when sudden explosions are generated, either due to mechanical failures or human negligence. The Monteverde Gas Complex (MGC), located in the province of Santa Elena in Ecuador, represents a potential risk by housing close to 105,000 m3 of precursor gases such as Propane (PPN), Butane (BTN), and LPG finished product. Therefore, an analysis of the potential threat to which the population is exposed in case of the explosion of one of the tanks with the different products they contain has been carried out, considering the closest communes to the MGC, which are Monteverde and Jambelí. Tools such as the Probit method proposed by TNO (The Netherlands Organization for Scientific Research), and the ALOHA software of the EPA (Environmental Protection Agency, USA) were used, whose combinations allowed estimating the radius of influence, which were divided into zones according to the degree of impact on the community. The results demonstrated that the community of Monteverde, despite being more than 1 km away from the CGM, is within the red zone or high influence radius that corresponds to 2000 meters for propane and butane tanks. Whitin this area, a person could have fatal third-degree burns. The calculations have been performed under ideal conditions, so it is recommended to review the attenuations generated by natural elevations of the terrain or the direction of the wind in further studies

Conservation genetics of the steno-endemic Chorthippus lacustris (Orthoptera: Acrididae)

Invertebrate populations are amongst the most widespread species, inhabiting a variety of habitats, however there is limited conservation effort due to the scarce knowledge on their population genetics. Here, we assess levels of genetic diversity and population structure of the Epirus dancing grasshopper (Chorthippus lacustris), a steno-endemic species, located in Northwest Greece, exhibiting a fragmented distribution. By utilizing two mitochondrial genes and amplified fragment length polymorphisms (AFLPs), we detected moderate to high levels of genetic diversity of the focal populations. Haplotype network analysis revealed the existence of private haplotypes with low genetic differentiation suggesting a sudden expansion of the species in the study area with subsequent isolations on suitable habitats. Despite the low genetic differentiation between the studied populations, our data further suggest a subtle subdivision of the populations and the existence of three genetic clusters. Implications for insect conservation: Our study is the first to provide insights into the population genetics of the steno-endemic grasshopper C. lacustris, highlighting the importance of preserving focal populations. The species inhabits areas subject to high changes in land use and fragmentation. We argue that the preservation and management of suitable habitats is essential for the viability of the grasshopper populations.