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This study presents a rapid and cost-effective method for fabricating microchannels for rarefied gas flow applications using maskless photolithography. The geometrical characteristics of the microchannels were characterized via optical microscopy and profilometry, while their fluidic performances were characterized for gas flows at varying levels of rarefaction. The fluid conductance of the fabricated microchannels was measured and compared with theoretical predictions, demonstrating excellent agreement, thus confirming the precision of the fabrication process. Our findings indicate that the microchannels maintain dimensional integrity across different pressure levels, validating the reliability of the chosen materials and methods. Through this research, we have established a robust, low-cost, and rapid fabrication process based on maskless photolithography for producing affordable microfluidic devices for rarefied gas flow applications. [ABSTRACT FROM AUTHOR]

Geosynthetic clay liner (GCL) is commonly used in cover system of engineered landfill to limit migration of gases and infiltration of water. In engineered landfill, gas transfer occurs by advection and diffusion, which may take place at different time frames or simultaneously depending on placement conditions. Hence, efficacy of GCL as a gas barrier under advection and diffusion needs to be assessed at various geoenvironmental settings. In the present study, the gas flow response of GCL under advection and diffusion were evaluated at various apparent degrees of saturation, distortion levels, hydrating fluids, and wet-dry cycles using custom-designed test apparatus. Gas permeability and gas diffusion coefficient of GCL were found to decrease by four and three orders of magnitude respectively with an increase in apparent degree of saturation from 7% to 80%. Gas permeability and gas diffusion coefficient were increased with an increase in distortion levels. With an increase in wet-dry cycles 1 to 5, gas permeability and gas diffusion of GCL were increased marginally when hydrated with distilled water while increased by one order of magnitude for hydrated with 0.0125 M CaCl2 solution. The obtained results were compared with published results and found to be in good agreement. [ABSTRACT FROM AUTHOR]

High indium-content group-III nitrides are of interest to further expand upon our ability to produce highly efficient optical emitters at longer visible/IR wavelengths or to broaden bandgap engineering opportunities in the group-III nitride material system. Current synthesis approaches are limited in their capabilities, in part due to the low decomposition temperature of indium nitride. A new high-pressure spatial chemical vapor deposition (HPS-CVD) has been proposed which can operate at pressures up to 100 atmospheres, thereby significantly raising the growth temperature of indium nitride more than 100 kelvins and permitting the investigation of the impact of pressure on precursor stability and reactivity. This study systematically analyzes an HPS-CVD reactor design using computational fluid dynamic modeling in order to understand favorable operating conditions for growth of group III nitrides. Specifically, the relationship between inlet gas type (nitrogen, hydrogen, or ammonia), inlet gas velocity, gas flow rate, and rotational speed of the wafer carrier is evaluated for conditions under which a smooth and dominant vortex-free flow are obtained over the wafer. Heater power was varied to maintain a wafer temperature of 1250–1300 K. Favorable operating conditions were identified that were simultaneously met for all three gas types, providing a stable operating window for a wide range of gas chemistries for growth; at one atmosphere, a disk rotational speed of 50 rpm and a flow rate of 12 slm for all gas types is desired. [ABSTRACT FROM AUTHOR]

Aerobreakup of fluid droplets under the influence of impulsively generated high-speed gas flow using an open-ended shock tube is studied using experiments and numerical simulations. Breakup of millimeter-sized droplets at high Weber numbers was analyzed for water and two-phase nanofluids consisting of dispersions of Al 2 O 3 and TiO 2 nanoparticles in water with high loading of 20 and 40 wt%, respectively. Droplet breakup is visualized using high-speed imaging in the experimental setup, where an open-ended shock tube generates impulsive high-speed flow impinging on a droplet held stationary using an acoustic levitator. Axisymmetric simulations using the volume-of-fluid technique are conducted to capture the gas dynamics of the flowfield and droplet deformation at the initial stages. Fluid droplets are subject to a transient flowfield generated by the open-ended shock tube, characterized by a propagating incident shock wave, a recirculating vortex ring, and standing shock cells. Droplet breakup for all fluids proceeds through an initial flattening of the droplet followed by generation of a liquid sheet at the periphery in the presence of a curved detached shock front at the leading edge. The breakup appears to follow a sheet stripping process whereby stretched ligaments undergo secondary atomization through viscous shear. Mist generated in the wake of the droplet appears to expand laterally due to the unconstrained expansion of the high-speed gas jet. The breakup morphology of droplets for all fluids appears consistent with previous observations using conventional shock tubes. Lateral deformation of the coherent droplet mass is observed to be higher for nanofluids as compared to water. This is attributed to higher viscosity and Ohnesorge number of nanofluid droplets, which results in delayed breakup and increased lateral stretching. When plotted as a function of non-dimensionalized time, the same effects are also attributed to generate the highest non-dimensional velocities for the TiO 2 nanofluid, followed by Al 2 O 3 nanofluid, and water, which mirrors the order of viscosity and Ohnesorge number for the three fluids. An area of spread, which can be interpreted as a measure of dispersion, plotted as a function of non-dimensionalized time also shows the highest value for the TiO 2 nanofluid, followed by Al 2 O 3 nanofluid, and water. Overall, current results indicate that droplet breakup for two-phase fluids appears to be similar to those for single-phase fluids with effectively higher viscosity. Furthermore, an open-ended shock tube proves to be an effective tool to study droplet aerobreakup, with some differences observed in the droplet wake due to the unconfined expansion of gas flow. [ABSTRACT FROM AUTHOR]

An elegant and easy-to-implement numerical algorithm for simulating flows of homogeneous gas mixtures with component temperatures and velocities assumed to be equal is constructed and tested. The algorithm yields monotone density profiles for the components even if their specific heat ratios are widely different. The algorithm can be used to simulate some flows of gas–liquid mixtures. [ABSTRACT FROM AUTHOR]

Although two-phase flows containing gas and water have received extensive attention, the pulsating pressurization effect of a two-phase fluid in a pipe is unclear and the influence of the gas-phase content has not been revealed. This paper discusses the pulsating pressurization of such a two-phase fluid. First, the two-phase Navier–Stokes equations are derived and an algorithm is developed based on MacCormack's method. The reliability of the algorithm is examined and validated using Poiseuille's theory and existing experimental two-phase flow data. Finally, the influence of several key factors is discussed, including the gas-phase fraction and pipe slenderness. Our results show that a significant pulsating supercharging phenomenon occurs when the gas-phase fraction is less than 10−3. When the gas-phase fraction is greater than this critical value, the pulsating supercharging effect decreases significantly with the increasing gas-phase fraction. The equivalent elastic modulus of the two-phase fluid rapidly decreases as the gas-phase fraction increases, and the pressure disturbance is absorbed by the gas bubbles, causing an apparent weakening of the pulsating supercharging effect. Thus, decreasing the gas-phase content can enhance the pulsating supercharging effect. The pipe slenderness has a very limited influence on the pulsating pressurization process, and the maximum reduction is only 7.3% for slenderness ratios of up to 2000. Moreover, we derive and propose a new mathematical expression for the inlet boundary that is applicable to gas–liquid two-phase flows. To our knowledge, this paper extends the pulsating pressurization range from the single-phase to two-phase fluid for the first time and reports different physical phenomena and regularity. The present research clarifies the pulsating pressurization phenomenon in two-phase flows, providing a valuable reference for pulsating pressurization design. [ABSTRACT FROM AUTHOR]

The gas and water flow behavior in rough-walled hydrophilic fractures at the pore scale is crucial for understanding the gas production characteristics of naturally fractured formations. This paper presents a systematic analysis of the gas and water flow characteristics in both the single-fracture and Y-shaped junction fracture models using the volume of fluid (VOF) method. Numerical simulations showed that the gas/water rate ratio is the most significant factor influencing gas bubble/slug geometry, phase distribution, and saturation. The effect of fracture roughness and tortuosity is less significant than the gas/water ratio, whereas the total fluid rate has a negligible effect. For Y-shaped junction models, the phase distribution and referential pathways are predominantly controlled only by the channel aperture ratio, whereas the effect of the intersecting angle and fluid flow rate can be neglected. [ABSTRACT FROM AUTHOR]

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This work presents a Direct Ghost Fluid Method (DGFM) as part of a two-fluid numerical framework suitable to model explosive gas and water flows resulting from underwater explosion (UNDEX). Due to the presence of explosive gas and water with shock waves in the modeling domain, classic Eulerian methods with inherent diffusion may not be effective. Numerical diffusion occurs due to nonphysical diffused density at material interfaces, which creates spurious pressure oscillations and significantly degrades the quality of the numerical results. To eliminate or minimize numerical diffusion, sharp interface methods having no mixed elements may be used in multifluid flow computations. The Direct Ghost Fluid Method (DGFM) described in this paper uses direct extrapolation of density (vice pressure) and tangential velocity from real to ghost fluid. The spurious pressure oscillations near the material interface are therefore minimized. One-, two-, and three-dimensional computational fluid dynamics (CFD) solvers that have DGFM as an essential part in their framework to model UNDEX interface conditions are developed, explored, and applied to the simulation of a series of benchmark problems. Excellent agreement is obtained among the simulations, the analytical solutions, and the experiments. [ABSTRACT FROM AUTHOR]

Droplet separators, or mist eliminators, are a very important internal part of fluid separation columns. They remove liquid droplets or mist from the gas stream and are installed at the top of the column with vertical gas or vapor flow. They reduce emissions to the atmosphere or to subsequent process steps. Droplet separators even can increase the separation efficiency of fluid separation processes, like absorption, desorption, distillation, evaporation etc. In this work the approach to develop a new vane type droplet separator for separation columns based on experimental investigation and CFD analysis is presented. The new droplet separator has a higher separation efficiency at the same pressure drop compared to state‐of‐the‐art standard droplet separators. [ABSTRACT FROM AUTHOR]

The precise fluid and gas energy flow equations (FEFEs) are difficult to formulate due to the uncertain parameters. This paper proposes a data-driven approach to fit the FEFEs by polynomial functions through experimental data. Furthermore, a convex optimization model is set up to find the solution of the FEFEs, and a tight reformulation is proposed to exactly reformulate the proposed model as a second-order cone programming (SOCP) that can be tractably solved. Numerical results on several test systems show the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

When a gas-liquid two-phase jet is discharged from a nozzle, its surface is fairly smooth for a certain distance from the nozzle exit. Then, deformation develops to cause jet breakup eventually. The deformation length that is defined as the length required for the jet deformation to develop is of industrial importance since significant splashing occurs when deformed jet impinges on a solid surface. The present work investigated the deformation length experimentally using air and water as the test fluids. The flow direction was vertical downward, and annular liquid film was formed at the nozzle exit. It was shown that the deformation develops faster with an increase in the gas flow rate. The measured deformation lengths were about 28.5 times the liquid film thickness estimated at the nozzle exit and no noticeable influence of the Weber number was found. [ABSTRACT FROM AUTHOR]

An analytical model has been developed to determine how effectively the temperature of a flowing hot gas can be reduced through the introduction of cold liquid droplets. The hot gas flows through a venturi-shaped mixer where the cold liquid is introduced into the mixer at the throat, vaporizes, and mixes with the hot gas resulting in a cooler gas temperature at the exit of the mixer. The cold liquid droplet residence time, evaporation time, and mixing with the hot gas determine the extent to which the hot gas temperature can be reduced. The model is used to predict the achievable gas cooling of hot hydrogen, nitrogen, and oxygen with cryogenic droplet coolant of the same species. Temperature and pressure along the mixer for these different fluids are calculated, and trends are presented using a non-dimensional number analogous to the Damköhler number in reaction chemistry. The model can be used to predict the minimum mixer length required to achieve specified amount of hot gas cooling or to assess the cooling efficacy of a mixer of given length for various hot gas and cold liquid flow rates. [ABSTRACT FROM AUTHOR]

The hydrodynamic performance of a gas-stirred ladle is analyzed experimentally, through a factorial experimental design, through physical modeling and particle image velocimetry techniques, to find the effects of the nozzle position, and its number, the gas flow rate and the presence or not of an oil layer on the flow velocity field,the turbulent kinetic energy distribution,and the open eye area,A. Flow patterns changed drastically in the presence of one or two plugs and as a result of the nozzle’s positions. The turbulent flow fields showed significant differences under the presence or absence of an oil layer and the open eye area strongly depends on the gas flow rate, the position and the number of nozzles. Responses,, andAwere statistically processed to identify the relevant effects of each variable on,, andA. These responses were used to calculate the optimum process conditions that minimizeAand maximize bothand, and then improve mixing efficiency in ladles using multi-objective optimization through the genetic algorithm (GAmultiobj). A Pareto characterization and its analysis were performed to reveal the embedded operation rules allowing optimum performances of the ladle for specific production goals. [ABSTRACT FROM AUTHOR]

Fluid, when running through pipes, makes a complex sound emission whose parameters change nonlinearly with respect to flow speed. Especially, in household pipe systems, there may be spraying effects and resonance effects which make the emission more complex. We present a novel approach for predicting flow speed based on wavelet packet analysis of sound emissions rather than traditional time and frequency domain methods. Wavelet packet analysis, by providing arbitrary time-frequency resolution, enables analyzing signals of stationary and non-stationary nature. It has better time representation than Fourier analysis and better high-frequency resolution than wavelet analysis. Wavelet packet analysis subimages are further analyzed to obtain feature vectors of norm entropy. These feature vectors are fed into a multilayer perceptron for prediction. Prediction accuracy of 98.62%, with 3.99E−04 L/s mean absolute error and its corresponding 1.85% relative error is achieved. Time sensitivity is ±0.453 s and is open to improvement by varying window width. The result indicates that the proposed method is a good candidate for flow measurement by acoustic analysis. [ABSTRACT FROM AUTHOR]

This investigation presents both theoretical and experimental studies on the size of a growing bubble in power-law non-Newtonian liquids. At first, some previous works on the prediction of bubble size in Newtonian liquids have been extended by considering the balance of forces acting on the bubble at the moment of separation. Predicted bubble sizes were validated against the experimental results for a wide range of operating conditions, including different gas flow rates and needle diameters as well as a wide range of physical properties of the Newtonian liquids. Furthermore, in order to determine the size of the bubbles formed in power-law non-Newtonian liquids with a similar analysis, the effective shear rate of bubble growth was calculated in which the rheological properties of fluid were taken into account and subsequently the viscosity of the fluid was modified. Theoretically obtained bubble sizes for non-Newtonian liquids are in a good agreement with our experimental high-speed video observations of three carboxyl methyl cellulose (CMC) solutions. [ABSTRACT FROM AUTHOR]

A generalized coupled level set/volume-of-fluid/ghost fluid method for the detailed simulation of gas-liquid flows is proposed in this paper. The interface is captured by the coupled level set and volume-of-fluid method, where the level set method is used to compute normal vector and curvature accurately, and the volume-of-fluid method is used to conserve the global volume or mass. The ghost fluid method is also used for discretization across the interface. The novelty of the present approach lies in that a generalized formulation for the conversion between the level set function and the volume-of-fluid function is proposed in a simple and efficient manner. Three benchmarks, including Zalesak's disk, two-dimensional deformation and three-dimensional deformation, are used for validation and verification. It shows that excellent agreement is achieved, and the present method has first-order accuracy. The current method is further applied to the simulations of droplet dynamics, rising bubbles, head-on droplet collision and liquid jet breakup, demonstrating the capability to accurately capture the interface. • A generalized coupled level set/volume-of-fluid/ghost fluid method for detailed simulation of gas-liquid flows is proposed. • The present work utilizes level set method and volume-of-fluid method to capture the interface. • A generalized formulation for the conversion is proposed in a simple and efficient manner. • The present framework has been validated by several cases. • The coupling procedure is easy to be implemented in the existing interface capturing method. [ABSTRACT FROM AUTHOR]

Present two-fluid models are mainly for dense gas-particle flows and combustion in fluidized beds, where the particle-flow behavior, like the particle stress is determined only by inter-particle collision based on kinetic theory. For gas-particle flows and combustion in pulverized solid-fuel combustors and furnaces, where the particle dispersion is determined by its turbulent fluctuation, the mainly used approach is Lagrangian treatment of the particle phase—trajectory models, which needs large computational effort for giving detailed information of the particle flow field in the three dimensional space. An alternative approach is the two-fluid modeling. However, for taking this approach it is necessary to develop the models of particle turbulence and particle history effect. A k-ε-k p model and a unified second-order moment (USM) two-phase turbulence model were proposed by the present author. Regarding to the particle history effect, a two-fluid-trajectory (TFT) model (a continuum-trajectory model of particle phase) and a full two-fluid (FTF) model were developed by the present author. Both TFT and FTF models have been applied to simulate combusting gas-particle flows. The simulation results are validated by experiments. Besides, a LES of swirling combusting particle flows was also made by the present author to study the interactions among the turbulence, particles and combustion. In this paper, a review is given for developing these models by the present author and his colleagues. [ABSTRACT FROM AUTHOR]

A series of fine-grid simulation with two-fluid model (TFM) is performed for bubbling, turbulent and circulating fluidized beds (CFB) with Geldart A particles. The results show that the fine-grid TFM with homogeneous drag seems feasible for simulation of low-velocity, bubbling fluidized beds. However, the fidelity of fine-grid TFM declines with the increase of gas velocity. In particular, the solids flux predicted deviates much from the experimental data of CFB though the clustering phenomenon can be captured with refinement of grid. In contrast, the structure-dependent approach as exemplified by the energy-minimization multi-scale (EMMS)-based multi-fluid model gives better agreement with experimental data. This discrepancy raises the question of the applicability of the local equilibrium assumption underlying the TFM. It also sheds light to the necessity of meso-scale modeling and the critical role of solids flux to evaluate the simulation of CFB. [ABSTRACT FROM AUTHOR]