Choking Effect Research Articles

Realization of a shock-tube facility to study the Richtmyer-Meshkov instability driven by a strong shock wave.

A shock-tube facility capable of generating a planar shock with the Mach number higher than 3.0 is developed for studying Richtmyer-Meshkov instability induced by a strong shock wave (referred to as strong-shock RMI). Shock enhancement is realized through the convergence of shock within a channel with the profile determined by using shock dynamics theory. The facility is designed considering the repeatability of shock generation, transition of shock profile, and effects of viscosity and flow choking. By measuring the dynamic pressure of the tube flow using pressure sensors and capturing the shock movement through the high-speed shadowing technique, the reliability and repeatability of the shock tube for generating a strong planar shock are first verified. Particular emphasis is then placed on the ability of the facility to study strong-shock RMI, for which a thin polyester film is adopted to form the initial interface separating gases of different densities. The results indicate that the shock tube is reliable for conducting strong-shock RMI experiments.

An initial investigation into the mental health difficulties in athletes who experience choking under pressure

This study aims to determine the frequency of choking under pressure (i.e., choking) and quantify the prevalence of psychological and behavioural consequences of choking. 165 current and retired athletes (over 18 years old) from various sporting levels completed an online survey that asked about demographics, the frequency of choking, and the psychological (e.g., negative feelings toward sport, passion/enjoyment of sport negatively affected, and suicidal ideation) and behavioural (e.g., missing/skipping sport temporarily, dropping out/quitting sport, and maladaptive, risky behaviour) effects of choking. Descriptive statistics on choking frequency indicated 127 (77%) athletes in this sample experienced choking in the last year of playing their sport, and, on average, “choked” 18.25 times during that year. Of the 65 athletes currently playing sport, 36 (55.4%) experienced choking in the past month. Furthermore, 39.4% and 7.1% of athletes in this sample did not achieve higher levels of competition and had suicidal thoughts due to choking, respectively. High-performance athletes in the current sample were more likely to engage in maladaptive behaviours after choking compared to low-performance athletes. Choking more negatively affected the passion/enjoyment for sport of currently playing (i.e., excluding all retired) high-performance than currently playing low-performance athletes. This seminal study crudely quantifies the frequency of choking in athletes, but more importantly provides crucial evidence of the psychological and behavioural consequences of choking and advocates for further research into choking and athlete mental health.

Investigating choking phenomena in CFB risers under different operating parameters

Choking phenomena in circulating fluidized bed (CFB) risers pose a significant challenge to industrial operations. To tackle this concern, multiphase particle-in-cell (MP-PIC) simulations are employed to investigate the impact of varying solids flux, bed height, and riser size on solids transport in CFB risers. The research sheds light on the complex interplay of operating parameters in CFB systems. The transition of solids holdup profiles from exponential to S-shaped curves with increasing solids inventory is observed, accurately predicting the choking point. By adjusting geometric dimensions, the choking point distance from the outlet at a fixed length-to-diameter ratio can be efficiently shifted. The findings provide a deeper understanding of saturation carrying capacity (SCC) in CFB risers, which can be leveraged to optimize industrial performance. This research is instrumental in mitigating choking effects and enhancing the design and operation of CFB systems.

Effects of excess oxidizer coefficient on RBCC engine performance in ejector mode: A theoretical investigation

This study investigates the effects of the primary rocket’s excess oxidizer coefficient (EOC) on the performance of a kerosene-fueled rocket-based combined cycle (RBCC) engine operating in ejector mode using the diffuser and afterburning (DAB) cycle. Employing complete mixing and chemical equilibrium assumptions, a quasi-one-dimensional model is developed to simulate combustion processes in the primary rocket chamber, mixer, and afterburner. Experimental data and full three-dimensional simulation validate the model’s accuracy. Results indicate that increasing EOC mitigates thermal choking effects at the mixer exit, decreasing mixing and Rayleigh losses, enhancing the entrainment ratio, and providing more oxygen for secondary combustion. However, the gas mixture’s compression ratio and total temperature decrease, rendering secondary combustion more susceptible to thermal choking in a constant cross-sectional afterburner. As the flight Mach number increases from 0.8 to 2.5, the optimum EOC for maximum specific impulse shifts from 0.725 to 2.375. While the optimum EOC for maximum thrust remains consistently around 2.0. The findings underscore the necessity of a higher EOC to fully unlock the DAB cycle’s thrust augmentation potential.

Optimization study of obstacles in T–T mixing channel at low Reynolds numbers

AbstractIn this study, numerical simulations were conducted to optimize obstacle geometry for improving mixing in T–T mixers at low Reynolds numbers (2 < Re < 100). The study considered obstacles of cylindrical and prismatic shapes and optimized their pitch and geometrical parameters for enhanced mixing. For cylindrical obstacles, the optimized configuration resulted in symmetrical recirculation zones at Re > 30, which led to larger mixing qualities of 80% and 85% for Re values above 30 and 50, respectively. However, the pressure drop increased in the optimized T–T mixer due to the larger size of the obstacles. On the other hand, in the case of prismatic obstacles, the mixing qualities of 80% and 85% were achieved only at relatively higher Re values of 70 and 90, respectively. The recirculation zone formed behind the obstacle was asymmetric due to the asymmetrical shape of the optimized prism. At higher Re, the optimized cylindrical obstacle configuration resulted in better mixing than the prismatic configuration. However, the choking effect in the former increased the pressure drop.

Does learning a skill with the expectation of teaching it impair the skill’s execution under psychological pressure if the skill is learned with analogy instructions?

ObjectiveHaving learners practice a motor skill with the expectation of teaching it (versus an expectation of being tested on it) has been revealed to enhance skill learning. However, this improvement in skill performance is lost when the skill must be performed under psychological pressure due to ‘choking under pressure.’ The present study investigated whether this choking effect is caused by an accrual of declarative knowledge during skill practice and could be prevented if a technique (analogy instructions) to minimize the accrual of declarative knowledge during practice is employed. DesignWe used a 2 (Expectation: teach/test) x 2 (Instructions: analogy/explicit) x 2 (Posttest: low-pressure/high-pressure) mixed-factor design, with repeated measures on the last factor. MethodsOne-hundred fifty-six participants were quasi-randomly assigned (based on sex) to one of four groups. Participants in the teach/analogy and teach/explicit groups practiced golf putting with the expectation of teaching putting to another participant, and analogy instructions or explicit instructions, respectively. Participants in the test/analogy and test/explicit groups practiced golf putting with the expectation of being tested on their putting, and analogy instructions or explicit instructions, respectively. The next day all participants completed low- and high-pressure putting posttests, with their putting accuracy serving as the dependent variable. ResultsWe observed an Expectation x Instructions × Posttest interaction, such that a main effect of expectation was found in the low-pressure posttest, with the teach group exhibiting superior accuracy, and an Expectation × Instructions interaction was revealed for the high-pressure posttest. This interaction resulted from the teach group showing greater accuracy than the test group exclusively when receiving analogy instructions. ConclusionResults show that participants who practiced with the expectation of teaching exhibited superior learning and indicate that they choked under pressure likely due to their accrual of declarative knowledge during practice, since the choking effect was prevented by having them practice with analogy instructions. Accordingly, having learners practice with the expectation of teaching and techniques that minimize the accrual of declarative knowledge is recommended.

Study on Sealing Characteristics of Compliant Foil Face Gas Seal under Typical Hypervelocity Gas Effects

In order to investigate the influence of typical hypervelocity gas effects on the gas lubrication performance of compliant foil face gas seal (CFFGS) end surfaces, the gas–elastic coupling lubrication theory model of CFFGS is modified by considering the choked flow and inertia effect, and the lubrication performance is solved using the finite difference method. Based on the choking effect, the effect of hypervelocity choked flow on the pressure field and velocity field of the seal is analyzed, and the influence of operating parameters on the choked flow and the mechanism of choked flow on the change in dynamic lubrication and sealing performance are explored. Furthermore, based on the inertia effect, the effect of gas inertia force on the flow field, and the correlation law between the pressure field and velocity field under the influence of operating parameters are studied. Then, the relationship between the inertia effect and sealing performance are analyzed. The results show that choked flow increases sealing outlet pressure significantly, from 0.1 MPa to a maximum of 14.25 MPa, and the sealing outlet flow velocity decreases by up to 50 times. The increase in medium pressure and balance film thickness aggravate the choking effect, resulting in a 20% maximum increase in opening force and a 99.6% maximum decrease in leakage rate. In addition, the inertia effect causes obvious centrifugal movement of the gas flow. As result, the radial flow velocity reduces by up to 50%, and the pressure distribution varies widely. Especially under high rotational speed and high medium pressure, the inertia effect is enhanced to clearly reduce the opening force (max. decrement of 3.5%) and leakage rate (max. decrement of 23%).

Dual Synthetic Jets Actuator and Its Applications—Part III: Impingement Flow Field and Cooling Characteristics of Vectoring Dual Synthetic Jets

In order to understand the impingement flow field and cooling characteristics of vectoring dual synthetic jets (DSJ), an experimental investigation was performed to analyze the parameter effects. With the variation of the slot location, the vectoring angle of DSJ can be adjusted from 34.5° toward the left to 29.5° toward the right. The vectoring function can greatly extend the length of impingement region. There are three local peaks both for the local cooling performance (Nu) and the whole cooling performance (Nuavg). Although the peak Nu at a certain location of the slider is higher than that at the center, the corresponding Nuavg is lower. As for different driving frequencies, the vectoring angle reaches its minimum of 9.7° at 350 Hz, but the Nu is obviously improved. There is one local peak of Nuavg values at 350 Hz rather than three local peaks at 250 Hz and 450 Hz. The slot locations where the Nuavg of 250 Hz and 450 Hz reach maximum are different. With the increase in driving voltage from ±100 V to ±200 V, the vectoring angle drops from 46.9° to 22.2°, but both Nu and Nuavg are improved. The maximum Nuavg of each driving voltage occurs at the center location of the slider. The choking effect and the cross flow have dominated the vectoring angle and the cooling performance of impingement DSJ. Vectoring DSJ will give impetus to the thermal management of large-area electric devices in spaced-constrained cooling and removing dynamic hotspots.

Numerical analysis of direct-current (DC) plasma processing for high-efficient steel surface modification

Nowadays, direct-current (dc) non-transferred arc plasma torch has drawn significant interest from both academia and industry due to the capability to process products in an efficient and convenient way. The core of this technology is to clarify and manipulate the arc behavior at the interior of the dc plasma torch to produce ideal plasma jets for processing. To solve this problem, a quasi-steady axisymmetric model is built to simulate and compare the arc characteristics in different operating conditions and different nozzle structures of the plasma torch. The results uncover distinct aspects of the study on arc characteristics, including the detection of the primary arc attachment region and its spatial features caused by the choking effect of torch structure. The thermal efficiency focused on processing substrate is also calculated in this paper for estimating the performance of plasma processing. The calculated results show that increasing the mass flow rate brings better thermal efficiency and the greatest promotion is at least 6% in the same current value, whereas improving the arc current value causes the opposite result. Meanwhile, two types of nozzle are compared to the original design in thermal efficiency, where the wide nozzle is chosen for torch optimization due to its best power efficiency. The secondary arc attachment on the metal substrate is discovered though its impact scope is only within a radius of 10 mm from the torch axis, its effect on the processing could be ignored for the extremely low electric current value.

Study on vapour dispersion and explosion from compressed hydrogen spill: Risk assessment on a hydrogen plant

Hydrogen produced from renewable resources is one of the cleanest fuels and could be used to store intermittent solar, wind and other energies. The main concern about using hydrogen is its hazards, such as high storage pressure, wide-range flammability, low mass density, and high diffusion. This study investigated the hazards of compressed hydrogen storage by developing a CFD model to understand the gas dispersion behaviour. The model was validated using the past experimental data and showed a good agreement, which could demonstrate the diffusion characteristics and gas stratification of a buoyant gas. A case study of an accidental release of compressed hydrogen from a storage tank was investigated to evaluate the risk of a hydrogen plant. A mathematical model of the jet spill was used to account for the choking effect from a high-pressure release to ensure the input velocity in CFD simulation is suitable for modelling gas dispersion using verified spatial and temporal scales, then the simulation results were used as inputs of vapour cloud explosions (VCEs) to investigate the potential overpressure effect. It was found the CFD model could predict a more reasonable flammable gas amount in cloud than using the bulk hydrogen release rate. The safety distance based on the overpressure prediction was reduced by 35%. The method proposed in this study can provide more validity for the consequence analysis as part of risk assessment.

Numerical simulation method of surge experiments on gas turbine engines

In order to obtain the surge margin of an aero-engine during its operation, an engine surge experiment is required. A multi-dimensional simulation method for an aero-engine is established in this paper. The simulation of a surge experiment using high-pressure air-injection is then carried out on a turbo-shaft engine to obtain the surge boundary using this method. More specifically, firstly, a body-force model is employed to calculate the compressor performance owing to its capability of capturing the main three-dimensional features of compressor surge and avoiding excessive simulation time required by the traditional fully-three-dimensional Reynolds Averaged Navier-Stokes (RANS) method. Then, a one-dimensional model combining a lumped-parameter plenum model is used for the combustor to account for the propagation of pressure waves and the heat-release process, and a zero-dimensional throttle model is used to mimic the choking effect at the turbine nozzle. Finally, the air-injection system is modeled by imposing an injection boundary condition, which can be used conveniently in changing injection parameters. Based on the established method, the influences of different test parameters, such as the air-injection location, the pressure, the orifice size, the number of injection orifices, and the injection time duration on the surge characteristics and boundary are further studied, which offer effective guidance to optimize an actual experimental design.

Banana bunching associated with climatic and nutritional variations

Choked banana presents closeness of petioles looks that allows the exit of the distal part of the inflorescence, but not the basal part is stuck up at the throat. The aim of this study was to avaluate the effect of choking on the growth of Musa spp. cv Nanica, as well as to investigate how the climatic variations and status nutritional of plants are associated whith this physiological disorder. The experiment was conducted in September/2018 in August/2019 in Registro, São Paulo state, Brazil. The experimental design adopted was completely randomized with two treatments and ten repetitions, in sub-divided plots over time (months). The evaluation consisted in determining the intensity of the symptom, number of leaves, plant height, hand number, stalk length, symptoms of nutritional deficiency and other abnormalities, leaf nutrient contents. Plant growth was not impacted by choking, only the hands number in the months of October/2018 and June/2019 to August/2019 (p< 0.05). Choking occurred throughout the year, with a predominance of severe symptoms of April in June due a redução da temperatura e radiation. The twisted fruits, united by fusion of floral parts and with different sizes occurred, respectively, in 21.67, 60.83 and 17.52% of the symptomatic plants, associated with the cool temperature during the differentiation of the female fruit. Choking and abnormalities in the bunch and fruits were associated with Zn deficiency (p< 0.05). The deficiency of Ca at low temperatures, the lower availability of radiation and the high relative humidity were also associated with the choking. The excess of P in the soil, as well, the adverse climatic conditions contributed to the limitation of these nutrients.

Do valence and effects of meta-stereotype conform to the rewarding principle?

<p id=C10>The term meta-stereotype refers to the beliefs of in-group members regarding the stereotypes that out-group members hold about them. Its valence can be positive or negative, and its effects can also be positive or negative. Previous researchers have held the view that the valence and effects of meta-stereotype conform to the “rewarding principle.” In other words, positive meta-stereotype activation would have a positive effect, and negative meta-stereotype activation would have a negative effect. However, recent studies, have found that this relationship was not consistent. Up to now, the nature of the relationship between the valence and effects of meta-stereotype is still a matter of debate. <p id=C11>For the negative meta-stereotype activation, its threat effect conforms to the rewarding principle, whereas the reactance effect does not. The threat effect of the negative meta-stereotype is that its activation could result in psychological conflict for individuals engaged in social situations. This may induce them to face a loss of cognitive balance and experience anxiety and stress, resulting in negative consequences. In contrast, it is possible for the activation of negative meta-stereotype to have a positive effect, that is, the reactance effect. When the negative meta-stereotype is activated, individuals perceive that they are being negatively evaluated by the out-group members. They may act to refute the negative evaluation. They would then display positive behaviors in a way to maintain a positive in-group image or prove their own abilities. It was found that the threat and reactance effects of negative meta-stereotype differ in the research scope, mechanism, and interventions that would eliminate the negative effects of meta-stereotype. <p id=C12>For the positive meta-stereotype activation, its boost effect conforms to the rewarding principle, whereas the choking effect does not. In general, the positive meta-stereotype reflects the positive evaluation by the out-group to the in-group members; that is, it contains a number of positive characteristics. Therefore, the activation of the positive meta-stereotype can lead to a boost effect. Specifically, when individuals feel that they are positively viewed by the out-group members, they not only feel better about themselves, but also are encouraged to give back to other out-group members in helpful, constructive way. In contrast, positive meta-stereotype activation may also have a negative effect; that is, the choking effect. If individuals perceive that the out-group members hold very high expectations of them, they may feel substantially more pressure. This can bring about undesirable outcomes. They might focus too intensely on themselves, or even feel worry and doubt their own abilities, and subsequently perform badly. After comparing previous studies of the boost and choking effects of positive meta-stereotype, it was found that the differences between them were in the research scope, mechanism, and the mode of activation. <p id=C13>Based on the analysis of the four effects mentioned above, it appears that the effects of meta-stereotype activation of different valences are influenced by a variety of factors at the individual and the group levels. Among them, the individual-level factors are the difficulty of retrieving the meta-stereotype, the internal resources, the degree of meta-stereotype personalization, and the impression management motivation; the group-level factors include group social status. <p id=C14>Although research on meta-stereotype has gradually expanded, it still mainly focuses on the threat effect of the negative meta-stereotype and the boost effect of the positive meta-stereotype respectively. Studies on the reactance effect of the negative meta-stereotype and the choking effect of the positive meta-stereotype are limited. Many issues remain to be addressed. Future research can further expand the fields and preconditions of the diverse effects activated by the negative and positive meta-stereotypes, explore the interventions to eliminate the negative effects of meta-stereotype, and investigate the role of meta-stereotype activation mode.

Air Entrainment in Drop Shafts: A Novel Approach Based on Machine Learning Algorithms and Hybrid Models

Air entrainment phenomena have a strong influence on the hydraulic operation of a plunging drop shaft. An insufficient air intake from the outside can lead to poor operating conditions, with the onset of negative pressures inside the drop shaft, and the choking or backwater effects of the downstream and upstream flows, respectively. Air entrainment phenomena are very complex; moreover, it is impossible to define simple functional relationships between the airflow and the hydrodynamic and geometric variables on which it depends. However, this problem can be correctly addressed using prediction models based on machine learning (ML) algorithms, which can provide reliable tools to tackle highly nonlinear problems concerning experimental hydrodynamics. Furthermore, hybrid models can be developed by combining different machine learning algorithms. Hybridization may lead to an improvement in prediction accuracy. Two different models were built to predict the overall entrained airflow using data obtained during an extensive experimental campaign. The models were based on different combinations of predictors. For each model, four different hybrid variants were developed, starting from the three individual algorithms: KStar, random forest, and support vector regression. The best predictions were obtained with the model based on the largest number of predictors. Moreover, across all variants, the one based on all three algorithms proved to be the most accurate.

The relationship of motive disposition and situational incentives to individual differences in choking under pressure.

Motive disposition theory posits that individuals exhibit stable differences in their achievement, affiliation, and power motives - shaping their capacity to perceive performance, social affiliative, or competitive contexts as rewarding. Whereas this approach has been employed in research on individual differences in motor performance, it has not been considered in predicting individual differences in choking under pressure. Typical pressure manipulations often use competitive or team settings which also constitute prime examples of power and affiliation incentives. Consequently, we hypothesized participants' affiliation (vs. power) motive to be related to golf putting performance in team (vs. competitive) settings. In addition, due to the performance feedback provided by the task, it should also generally appeal to participants high in achievement motivation. Specifically, after a familiarization phase a total of 115 participants completed a baseline assessment of golf putting performance, followed by an experimental block manipulating the task's incentives (competition, team, control) between participants. Analysis of participants' previously assessed motives revealed that both participants' affiliation and achievement motive were positively related to performance (variable error) under pressure. No effects emerged for the power motive. These findings highlight the role of personality differences in predicting motor performance variability in pressure situations. We discuss the specific contributions of projective and self-report motive measures and touch upon possible avenues for coaches and practitioners to counter choking effects.

Numerical investigation on the flow characteristics and choking mechanism of cavitation-induced choked flow in a Venturi reactor

For liquid mediums, choked flow is a derivative phenomenon of cavitation, which has been widely studied in engineering. Previous studies mainly focused on the suppression or application of choked flow but rarely explored its flow characteristics and choking mechanism. In this study, based on experimental research, a numerical investigation of a Venturi reactor with strong choking effect was performed through a self-developed compressible cavitation phase-change solver to determine the flow characteristics and choking mechanism of cavitation-induced choked flow. Utilizing fast Fourier transform (FFT) and data processing, combined with theoretical analysis, characteristics of flow pulsation and energy loss were studied respectively. Effects of pressure ratio and compressibility on choked flow were also studied. Results show characteristics and influencing factors of flow pulsation, as well as the root cause of choked flow. The flow in the choked condition is pulsating, with low frequency at the inlet and a combination of low and high frequency at the outlet. The periodic evolution of cavity shape causes the inlet low-frequency flow fluctuation and then affects that at the outlet. But the temporal evolution of total cavity volume is the major factor of the outlet low-frequency flow fluctuation. Mechanical energy is absorbed to realize the cavity development. In cavitating flow, as outlet pressure decreases, the increased flow energy is all spent to promote the cavity development, leading to the larger cavitation area and cavity volume rather than the increase in flow rate, which is the essence of choking. Additionally, the collapse of cavities releases mechanical energy, manifesting as the local high pressure superposed by pressure waves, under which the flow velocity is re-driven, causing the high-frequency flow pulsation at the outlet.

The theoretical prediction of the boundary-layer-blockage and external flow choking at moving aircraft in ground effects

The theoretical discoveries of the Sanal flow choking [V. R. Sanal Kumar et al., “Sanal flow choking: A paradigm shift in computational fluid dynamics code verification and diagnosing detonation and hemorrhage in real-world fluid-flow systems,” Global Challenges 4, 2000012 (2020)] and streamtube flow choking [V. R. Sanal Kumar et al., “Deflagration to detonation transition in chemical rockets with sudden expansion/divergence regions,” AIAA Paper No. 2020-3520, 2020] achieved significant contemplation in all branches of science and engineering for resolving various unanswered scientific questions brought onward from the beginning of this era [V. R. Sanal Kumar et al., “A closed-form analytical model for predicting 3D boundary layer displacement thickness for the validation of viscous flow solvers,” AIP Adv. 8, 025315 (2018)]. The applications of these flow choking phenomena are more significant in aerospace industries [V. R. Sanal Kumar et al., “Nanoscale flow choking and spaceflight effects on cardiovascular risk of astronauts—A new perspective,” AIAA Paper No. 2021-0357, 2021] and medical sciences [V. R. Sanal Kumar et al., “Lopsided blood-thinning drug increases the risk of internal flow choking leading to shock wave generation causing asymptomatic cardiovascular disease,” Global Challenges 2021, 2000076]. Herein, as an offshoot of the Sanal flow choking phenomena, the proof of the concept of boundary-layer-blockage (BLB) persuaded external-flow-choking (EFC) at aircraft-in-ground (AIG)-effect is presented. When the aircraft's ground clearance is relatively low, the evolving BLB factor from both planes (the bottom surface of the aircraft and the ground) creates a transient fluid-throat, leading to the Sanal flow choking and supersonic flow development in the duct flow region. In this physical situation, the pressure ratio (Ptotal/Pstatic) at the external flow choking region is exclusively a function of the specific heat ratio of the fluid. The EFC is more prone for the low wing aircraft flying in the near vicinity to the ground and/or sea with relatively high subsonic Mach number and low angle of attack. At this flying condition, the underside of the aircraft (fuselage and/or wing) and the ground creates the convergent-divergent duct flow effect leading to the EFC at the critical total-to-static pressure ratio. The accurate estimation of the BLB factor at the location of the EFC at AIG effect is presented in this manuscript as a universal yardstick for two-dimensional (2D) in silico simulation. For establishing the proof of the concept of external flow choking and supersonic flow development and shock wave generation, the 2D in silico results are presented for both stationary and moving airfoils in ground effect. In silico results show that the airfoil at stationary position exhibits relatively higher BLB factor and an immediate occurrence of the EFC than the same airfoil moving with the identical inflow Mach number and Reynolds number. We could establish herein that the moving vehicle simulation is inevitable for capturing actual flow physics and further precise examination of the BLB factor and the possibilities of the occurrence of the EFC for credible trajectory optimization of high-speed ground-effect vehicles.

A priori assessment of long‐term productivity of frac‐packed wells for producing natural gas from marine gas hydrate reservoirs

AbstractThis work investigates the feasibility of using frac‐packing techniques to complete wells in marine gas hydrate fields. It focuses on the long‐term well productivity under pseudo‐steady state flow conditions after the gas hydrate reservoir pressure drops to below the hydrate dissociation pressure within the well drainage area. The analytical model proposed by Shan et al. (J Energy Sci Eng, 2020, 8, 1247) for cross‐flow in the fractured region was modified in this study to include the horizontal radial flow in the non‐fractured region of the well drainage area. Methods were developed to predict the fracture geometry and to design proppant size distribution for formation sand/particle control. Sensitivity analyses with the model identified the fracture radius and permeability being the key factors affecting the productivity of frac‐packed wells. Well productivity was found to increase non‐linearly with fracture radius and permeability. The benefit of increasing fracture size drops due to the choking effect near the wellbore and pressure loss inside the fracture. The benefit of increasing fracture permeability diminishes when the fracture permeability is large due to the bottleneck of low reservoir permeability. Gas hydrate wells in the Shenhu area, northern South China Sea, can be elevated to commercial levels of greater than 10 MMscf per day with a proppant injection volume of 110 cubic feet during frac‐packing. Well productivity can be further increased by injecting higher proppant volume to enlarge fracture. This work presents a simple method for assessment of frac‐packing design to improve well productivity in marine gas hydrate reservoirs.

Hydrophilic/Hydrophobic Silane Grafting on TiO2 Nanoparticles: Photocatalytic Paint for Atmospheric Cleaning

In this study, anatase titania was utilized to prepare a durable photocatalytic paint with substantially enhanced photoactivity towards NO oxidation. Consequently, to alleviate the choking effect of photocatalytic paint and incorporate self-cleaning properties, the parent anatase titania was modified with Al(OH)3 and a number of organosilane (tetraethyl orthosilicate, propyltrimethoxysilane, triethoxy(octadecyl)silane, and trimethylchlorosilane) coatings. A facile hydrolysis approach in ethanol was employed to coat the parent titania. To facilitate uniform dispersion in photocatalytic paint and strong bonding with the prevailing organic matrix, it is necessary to avail both hydrophobic and hydrophilic regions on the titania surface. Therefore, during the preparation of modified titania, the weight proportion of the total weight of alkyl silane and trimethylchlorosilane was adjusted to a ratio of 1:1. As the parent titania has few hydrophilic portions on the surface, tetraethyl orthosilicate was coated with an organic silane having an extended alkyl group as a hydrophobic group and tetraethyl orthosilicate as a hydrophilic group. When these two silane mixtures are hydrolyzed simultaneously and coated on the surface of parent titania, a portion containing a large amount of tetraethyl orthosilicate becomes hydrophilic, and a part containing an alkyl silane becomes hydrophobic. The surface morphology and the modified titania’s optical attributes were assessed using X-ray powder diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), UV-Vis diffuse reflectance spectroscopy (DRS), and electrochemical impedance spectroscopy (EIS) analysis. Based on the advanced characterizations, the NO removal mechanism of the modified titania is reported. The modified titania coated at 20 wt.% on the ceramic substrate was found to remove ~18% of NO under one h of UV irradiation. An extensive UV durability test was also carried out, whereby the coated surface with modified titania was exposed to 350 W/m2 of UV irradiance for 2 weeks. The results indicated that the coated surface appeared to preserve the self-cleaning property even after oil spraying. Hence, facile hydrolysis of multiple organosilane in ethanol could be a viable approach to design the coating on anatase titania for the fabrication of durable photoactive paint.

A transient two-phase flow model for production prediction of tight gas wells with fracturing fluid-induced formation damage

A major concern with hydraulic fracturing in tight formation is the fracturing fluid-induced formation damage (FFIFD) for the high capillary pressure and the presence of water-sensitive clays. Analytical and semi-analytical models are good choices for formation damage evaluation comparing to computationally expensive numerical simulations, particularly in early times when there is limited information about the formation properties. However, the effects of FFIFD and two-phase flow are not addressed in many analytical models. This paper presents a semi-analytical model for this problem with the consideration of both FFIFD and two-phase flow. First, the physical model and mathematical fundamentals of the model are presented. The triple-porosity model is modified to capture the formation damage caused by fracturing fluid. A low permeability fracturing fluid invasion layer (FFIL) is used to characterize leakoff caused clay swelling and polymer adsorption in the matrix pores, and two-phase flow is assumed in the fractures to capture the choking effects. The analytical solution is obtained in the Laplace domain, and a successive iteration is used to update the dynamic parameters by coupling the flowing material balance equations. Then, the commercial numerical simulator Eclipse is used to validate the precision of the semi-analytical model, and several synthetical cases are presented to study the effects of two-phase flow, and the permeability and width of FFIL on gas production rate. Finally, a field case is provided to test the application of the proposed model. The main contribution of this paper is the provision of a simple yet versatile semi-analytical model for production prediction and analysis with the consideration of fracture networks, FFIFD, and two-phase flow. It serves as a good tool for making production prediction and production data analysis for hydraulically fractured tight gas wells.