High Water Flow Rates Research Articles

Impacts of environmental conditions and management of sluice gates on glass eel migration

Anthropogenic barriers such as tidal gates impair animal migration and ecological continuity. For migratory fishes, barriers may alter or impeach both upstream and downstream migrations. Juveniles of European eels, namely glass eels, have to pass those barriers when migrating upstream, whereas they have limited swimming capacities and are dependent on several environmental variables. Hydrological conditions, which can be modified by barrier management, are critical for glass eels. Here, we investigated the links between hydrological conditions and barrier management and the recruitment of glass eels at a connection between the Mediterranean Sea and a lagoon. To do that, we modeled the recruitment of glass eels over ten seasons accounting for temporal variations and co-variable effects. We modeled three aspects of recruitment: presence, level, and composition. We found that monthly and inter-annual effects explained the main part of the variations in glass eel recruitment but accounting for environmental effects improved our models, with a positive effect of temperature, for instance. We associated low levels of catches and recruitment of rather old individuals to high water flow rates when water flows out of the lagoon. Those results call for further studies on how sluice gate management may improve glass eel recruitment and seem to indicate that local stakeholders should adjust the number of open gates depending on the water level on both sides of the barrier.

Ion rejection performances of functionalized porous graphene nanomembranes for wastewater purification: A molecular dynamics simulation study

Performances of small- and large-pore, porous graphene nanomembranes (PGNMs) (pristine and functionalized by amide, sulfonic acid, thiourea, and carbamate functional groups) for purification of heavy metal ions and nitrate-contaminated wastewater were determined using molecular dynamics (MD) simulation. At the operational conditions of the simulated membrane (150 and 0.1 MPa pressure on the left and right piston sides at 300 K), higher water flow rates were obtained in the functionalized PGNMs possessing large pores, as opposed to the non-functionalized and small-pore ones. Amide-functionalized PGNM provided the highest flow rate (380 and 330 molecules/ns for large and small pores, respectively). Cu2+ and As3+ ions were rejected at a level of 100% in the small-pore PGNMs, while the rejection level of the NO3- ions was about 95%. For large-pore PGNMs, As3+ ions were rejected at a level of 100%, while a few Cu2+ and NO3- ions could pass through the pores with no discernible dependence on the graphene surface chemistry. A radial distribution function (RDF) analysis revealed two hydration radii for all ions interacting with the surrounding water clusters. Overall, graphene surface chemistry modification did not significantly affect the ion rejection performance.

Experimental study on the effect of metal foams pore size in a phase change material based thermal energy storage tube

It is well known that latent thermal energy storages can help in store large quantities of energy in small volumes, but that their charging and discharging periods are prohibitively long. In this work it was experimentally demonstrated that the addition of a foam can drastically shorten the phase change materials charging and discharging times up to 10 and 5 times, respectively. A tube-in-tube heat exchanger, where water flows in the tube with an aluminum foam-saturated Phase Change Material inserted in the annulus, was experimentally tested and new data was added to the open literature. Testing three different foam samples, the influence of the foam pore density (10, 20, and 40 Pores per Inch), sample orientation as well as that of water flow rate (from 2 to 8 l min−1) and inlet temperature (from 45 to 55 °C), on charging and discharging processes was investigated. Few researchers investigated the influence of sample orientation, while published results do not agree on the pore size influence. In this work it was found that the 20 Pores per Inch sample showed the best performance leading to fastest charging and discharging processes. Moreover, it was observed that with foam-saturated Phase Change Materials, the charging and discharging times are not affected by the inclination angle. On the contrary, they are affected by water flow rate and temperature. A high inlet water temperature and a high water flow rate can shorten both phase transfers.

Effect of Installation Conditions of Water Mist Nozzle on Thermal Radiation Attenuation Performance

In this experimental study, the effect of installation conditions of a water mist nozzle on thermal radiation attenuation performance was investigated. Two types of nozzles (Small_nozzle and Large_nozzle) were used. Experiments were conducted under conditions in which the nozzle was installed near the heater and heat flux sensor (Position_NH and Position_NS, respectively), and water mist was discharged from one and two nozzles (Case_ID and Case_SD, respectively). To characterize the water mist spray, the water supply pressure and droplet size were measured, and visualization of the sprayed water mist was performed. The thermal radiation attenuation performance improved with an increase in the water flow rate, and Small_nozzle showed higher thermal radiation attenuation performance than Large_nozzle. Moreover, Case_SD showed lower thermal radiation attenuation performance than Case_ID_Sum (that is, the Sum of Case_ID & Position_NS and Case_ID & Position_NH) and the difference in thermal radiation attenuation performance between Case_SD and Case_ID_Sum at a higher water flow rate was more significant than that at a lower water flow rate. These might be attributed to the wide overlapping area of water mist discharged from two nozzles in Case_SD and at a higher water flow rate, narrowing the overall width of the water mist.

Investigation on plugging prediction of multiphase flow in natural gas hydrate sediment with different field scales

The change in water–gas flowrate ratio is one of the main reasons to induce plugging occurrence in the natural gas hydrate (NGH) exploitation process, which significantly influences gas production efficiency. However, there was still no judgment factor to predict multiphase flow plugging in different field scales. Therefore, two sizes cylindrical reactors (Ф50, Ф15) were used in this study, and the difference in effective sectional velocity of water phase (vew) between the two reactors was about 12 times. The entire hydrate re-formation process was directly observed by magnatic resonance imaging (MRI), and the results proved that hydrate re-formation was the main factor for plugging in water–gas flow process. Moreover, the methane concentration gradient across the water and hydrate decreased with the decreasing water flowrate. Thus, the faster mass transfer process on water-hydrate interface enhanced the amount of hydrate re-formation in the two-phase flow process. After validation, the hydrate re-formation amount increased by 11.75% when the vew was reduced by 0.75 m/s. In other words, the higher water flowrate can effectively prevent the plugging of hydrate sediment under the same gas flowrate. Based on the above, the effective sectional velocity was first used to judge plugging occurrence for different scales hydrate sediment. At a given gas effective sectional velocity of 0.23 m/s, the flow plugging phenomenon did not appear when the effective sectional velocity of the water phase was higher than 3.59 m/s for two different scales of hydrate sediment. The results effectively evaluated the plugging occurrence in hydrate sediment with different scales during the water–gas flow process, and further established a bridge between the laboratory investigation and hydrate actual production test.

A novel approach for wettability estimation in geological systems by fluid–solid interfacial area measurement using tracers

Wettability plays a vital role in many applications of flow in porous media and affects Darcy scale flow parameters by influencing the fluid–solid interfacial area. Therefore, quantifying the fluid–solid interfacial area can provide a way to measure wettability at the Darcy scale. Here, we experimentally explore a dual-tracer method, which can also be scaled to large geological reservoirs to quantify the fluid–solid interfacial area during the multiphase flow through a porous medium for different wetting conditions. Using our experiments, we demonstrate the influence of different saturations, wettability and flow conditions on the solid–liquid interfacial area. When oil is in the residual phase, we observe that the solid–water interfacial area increases with the increase in water saturation for the water-wet and mixed-wet cases. However, the water–solid interfacial area decreases with an increase in water saturation for the oil-wet case. We increase the water saturation by increasing the water flow rate; therefore, the anomalous behaviour seen in the oil-wet case can be attributed to the rearrangement of oil and water at higher water flow rates. When both oil and water are flowing, the solid–water interfacial area increases with water saturation for all the wettability cases and increases in water wettability as anticipated.Synopsis: Wettability measurements at Darcy-scale give a broad idea of overall subsurface wetting conditions for application in CO2 sequestration, ground-water remediation or oil recovery.

Experimental characterization of the coupling and heating performance of a CO2 water-to-water heat pump and a water storage tank for domestic hot water production system

This work presents an experimental study of the dynamic performance of a CO2 water-to-water heat pump in a domestic hot water production system. A facility was developed and used to characterize the time evolution of the COP of this heat pump, the heating and stratification processes of the hot-water storage tank, and the global COP of the system. Results showed that, when heating the water storage tank, strategies based on promoting stratification to reach Ri ∼40, such as the use of vertical tank filling velocities v ∼ 10-4 m·s−1 with low water flow rates between the tank and the heat pump gas cooler, permits an increase of ∼12.4% in the system global COP and a reduction of ∼16% of the compressor energy consumption compared to other strategies. However, strategies based on considering higher water flow rates (i.e. Ri ∼1) increase the thermal energy available in the tank (∼6% when flow rate and v increases a factor 3.6) but enhance the water mixing and extend the heating time which reduces the global COP of the system. Besides, an increase of the evaporator inlet water temperature from 5 °C to 20 °C increases the system global COP by 59% and reduces the heating time ∼40%.

차량용 납전지 전극 제조 금형의 유로 설계를 위한 수치 연구

A numerical study is conducted on a die-casting process to produce the lead electrodes employed in car batteries. The primary concern is to reduce the processing time by enhancing cooling performance. The proposal is to employ a recursive cooling passage characterized by dual spiral channels, which overcomes the spatial restriction in the mold. A three-dimensional CFD model based on the ANSYS package is constructed to simulate the transient cool-down process from the molten-state lead to a solid product, in which the solidification process is included. The turbulent flow of water in the cooling channel and the conjugate heat transfer in the mold are examined. The preliminary computations for the mold with the conventional straight cooling channels illustrate that the required cool-down performance is hardly attainable even for high flow rate of water. The computations for the mold with spiral channels show that the spiral passage provides an augmentation of cooling performance even for a moderate flow rate. The cooling performance increases and the temperature uniformity decreases as the inclination angle of the spiral cooling passage. This suggests that an optimal selection of the inclination is needed to satisfy the both requirements for processing time and temperature uniformity.

THE PROBLEM OF SAND-WATER MANİFESTATİON IN OIL PRODUCTION

Sand manifestation has been observed in both deep and shallow wells in areas with abnormally low pressure formations. In all cases, the appearance of sand and water creates complex problems. As a result of the collapse of the bottom whole zone, there are cases of bending and failure of pipelines in and above the filter. All this leads to long repairs. From the development of the well to its subsequent operation a number of processes occur, all of which affect the stability of the rocks weakens and creates conditions for the formation of sand manifestation. As a result of sand movement in the filter area, holes are formed, and the rock, which acts as a support for the operational pipeline, is destroyed and enters the pipeline through the perforated channels. The results of all these processes lead to deformation of the production pipeline, in some cases to the loss of the well. During the development and operation of wells to prevent the destruction of the filter zone and simultaneous sand plugging in the belt, are shown the conditions of the well flow rate. One of the most effective measures against sand-water manifestation is sand plug washing. It has been shown that during washing of sand plugs in production wells, small sand grains are carried out by the flow, but big sand grains sedimentation at the bottom of the well. The distribution of the particles in the flow is carrying out under the force of the earth's gravity at the Bolstmann distribution. It is explain with the increasing of the concentration of particles at the bottom of the well and decreasing at the top of the well. For the first time their hydrodynamic model of sedimentation in suspension has been given by the accepting of the participation of sand particles in the washing at the Bolstmann distribution. İt has been noted that ,although the effective washing of sand plug is an important measures, preventing of formation of sand plug remains as big challenge. After an effective washing of sand plug, it is necessary to applied measures against water manifestation. Otherwise, it is impossible to prevent of sand manifestation. Since high water flow rate (10 ÷ 20 m3/day) gradually destroys the borehole bottom-hole zone and in the filter zone a hole is formed, the wall of the well is destroyed. And this becomes a cause of huge complications. This is because that the water flow cannot destroy the isolation mass,which is applied against water to the layer. Thus, the most effective measure against sand-water manifestation should be consist of three successive integrated measures. Complex measures against sand and water appearance are suggested, which have found application in production. Keywords: well, sand manifestation, sand plug, cement solution, washing process.

An innovative unit for water desalination based on humidification dehumidification technique

An innovative humidification – dehumidification (H-D) system, consisting of two primary components, a humidifier, and a condenser, was designed and built, together with its various accessories, to generate desalinated water from seawater simply and cost-effectively. The experimental work was split into two parts. The first was concerned with the humidification of ambient air in a specifically designed and developed humidifier. The influence of significant factors on the % relative humidity of the humidified air, as well as the temperatures of the exiting air and water, was examined using the natural draft and air-blown forced convection. The second part pertained to combined H – D of air to produce desalinated water. The findings revealed the presence of a hydrophilic plant (Loofa Egyptiaca) as packing that has never been utilized previously, is branching and mimics structured packing to a large extent. The presence of four stages, each with just a shallow Loofa bed height, was enough to create exit air with 100 % relative humidity. The unit's daily productivity was highest (133.72 kg water per total volume of packed section) at high water flow rates and temperatures (60 °C), as well as when using cold water in the condenser, with a condensation efficiency of 93.5 % without the need for more complicated and expensive coil-type or finned tube-copper condensers. Furthermore, completely desalinated water was produced, which was superior to potable water.

Fluctuation-induced quantum friction in nanoscale water flows.

The flow of water in carbon nanochannels has defied understanding thus far1, with accumulating experimental evidence for ultra-low friction, exceptionally high water flow rates and curvature-dependent hydrodynamic slippage2-5. In particular, the mechanism of water-carbon friction remains unknown6, with neither current theories7 nor classical8,9 or ab initio molecular dynamics simulations10 providing satisfactory rationalization for its singular behaviour. Here we develop a quantum theory of the solid-liquid interface, which reveals a new contribution to friction, due to the coupling of charge fluctuations in the liquid to electronic excitations in the solid. We expect that this quantum friction, which is absent in Born-Oppenheimer molecular dynamics, is the dominant friction mechanism for water on carbon-based materials. As a key result, we demonstrate a marked difference in quantum friction between the water-graphene and water-graphite interface, due to the coupling of water Debye collective modes with a thermally excited plasmon specific to graphite. This suggests an explanation for the radius-dependent slippage of water in carbon nanotubes4, in terms of the electronic excitations of the nanotubes. Our findings open the way for quantum engineering of hydrodynamic flows through the electronic properties of the confining wall.

Feed Digestion, Growth and Disease Prevalence in Nile Tilapia (Oreochromis niloticus) Cultured at Different Water Exchange Rates in a Recirculating Aquaculture System

The quality of culture water and the rate of water flow within a culture system can affect fish growth and health. In this study, the effects of different water flow rates on digestion efficiency, growth and welfare of juvenile Nile tilapia (Oreochromis niloticus) (Initial weight: 25.75±0.47 g) were investigated. Fish (15 per tank) were randomly stocked into twelve 150 L thermoplastic tanks of a recirculating aquaculture system and subjected in quadruplicate groups to water flow rates of 50 Lh-1 (Low exchange; LE), 100 Lh-1 (Medium exchange; ME) and 150 Lh-1 (High exchange; HE) for 72 days. Water quality parameters including total ammonia nitrogen, nitrate and alkalinity, dry matter, protein and lipid digestibilities, somatic growth and some welfare indicators including haematology and disease prevelance were monitored. There were no significant differences in growth among the treatments. Higher prevalence of cataract, fin erosion, oral and dermal lesions were observed in the LE and ME treatments indicating compromised welfare. There were no statistical differences among the treatments in terms of nutrient digestibility. This study has shown that culturing Nile tilapia under moderately high water flow rates of at least 100% tank water replacement per hour in RAS ensures good growth and feed utilization.

Numerical simulation of multi-size bubbly flow in a continuous casting mold using population balance model

A population balance model based on the multiple-size-group (MUSIG) approach was developed to investigate the multi-size bubbly flow in a slab continuous casting mold. Firstly, effects of the bubble size group number, the initial bubble diameter, and the calibration factors for breakage and coalescence in MUSIG model on the multi-size bubbly flow were discussed in detail. Then, effects of both the water and gas flow rates on the bubble size distribution, the gas volume fraction, and the turbulence intensity of liquid phase were investigated. A relatively high water flow rate intensified the turbulence in the upper recirculation region of the mold and also eased the turbulence near the submerged entry nozzle (SEN) by promoting the breakage and horizontal transportation of bubbles; thus, an appropriate water flow rate is essential for better stability with a lower turbulence intensity near the SEN to prevent exposed slag eye formation and slag entrainment. With increase in the gas flow rate, the mean bubble diameter and gas volume fraction increased significantly, the turbulence near the SEN was also significantly increased, but this effect was much weaker in the region away from the SEN.

Modelling the effects of water chemistry and flowrate on clay erosion

Clay buffer is a key component of the engineered barrier system (EBS) for geological disposal of higher activity radioactive waste. Experimental observations indicate the possibility of buffer erosion at the interface with host rock due to interactions with groundwater. Existing models for clay erosion are very limited in terms of addressing the hydro-chemical effects, while the assessment of the long-term performance of clay buffer requires robust predictive models covering expected environment conditions and multiphysics phenomena involved in the erosion process. The work presented here is a step towards such a predictive capability, which considers clay expansion, detachment of clay particles and transport of detached particles by groundwater within a single modelling framework. The effects of solution chemistry and flowrate on the penetration, extruded mass and particle release rate of clay buffer are investigated in this paper. A series of experimental data are used to validate the swelling and erosion model developed in this study. The results show that the extrusion distance, which is controlled by both clay swelling and detachment processes, is nearly linearly dependent on the water flowrate irrespective of the water chemistry. Similar linear dependence of the erosion rate on water flowrate is observed for flowrates less than 10−5 m/s. Higher water flowrates are shown to induce nonlinearly increasing erosion rates in accordance with experiments. A flowrate threshold is found above which the erosion behaviour of compacted bentonite can be significantly affected. A concept of tolerance time for clay buffer is introduced as a failure criterion. The results indicate that the coupled effect of water chemistry and velocity requires further investigation for ionic concentrations below 1 mM.

Model-Based Analysis of Low Stoichiometry Operation in Proton Exchange Membrane Water Electrolysis.

Proton exchange membrane water electrolysis cells are typically operated with high water flow rates in order to guarantee the feed supply for the reaction, the hydration of the ionomer phase and to homogenize the temperature distribution. However, the influence of low flow rates on the cell behavior and the cell performance cannot be fully explained. In this work, we developed a simple 1+1-dimensional mathematical model to analyze the cell polarization, current density distribution and the water flow paths inside a cell under low stoichiometry condition. The model analysis is in strong context to previous experimental findings on low water stoichiometry operations. The presented analysis shows that the low water stoichiometry can lead to dry-out at the outlet region of the anode channel, while a water splitting reaction is also present there. The simulation results show that the supply with water in this region is achieved by a net water transport from the cathode to the anode catalyst layer resulting in higher local proton resistances in the membrane and the anode catalyst layer.

Microplastic and microfiber fluxes in the Seine River: Flood events versus dry periods

Studies on the influence of hydrodynamic conditions on anthropogenic microfiber (MF) and microplastic (MP) distributions in freshwater environments are sparse. In this study, we evaluated the influence of urbanisation gradient on the spatial variability of MFs and MPs. Temporal variability was also assessed by comparing the concentrations and fluxes of MFs and MPs under low flow conditions with those during the January–February 2018 flood event. For each period, Seine river water was collected upstream and downstream of Greater Paris and filtered through an 80 μm net at three different sampling sites. MFs were counted using a stereomicroscope, while MPs were analysed using micro-Fourier transform infrared spectroscopy coupled with siMPle analysis software. The highest concentrations of MFs and MPs were reported at the furthest downstream sites during both periods. However, high water flowrates and urbanisation gradient did not significantly impact MF and MP concentrations, sizes, or polymer distributions. The median MF and MP concentrations were 2.6 and 15.5 items/L and their interquartile ranges were 1.6 and 4.9 items/L (n = 10), respectively, illustrating relatively stable concentrations in spite of the urbanisation gradient and variations in the flowrate. In contrast to the concentration, size, and polymer distribution characteristics, MP mass fluxes were strongly affected by river flow. MF and MP fluxes show increases in the number and mass of particles from upstream to downstream. The downstream site presents high MP mass fluxes, which range between 924 and 1675 tonnes/year. These results may indicate significant MP inputs from the Paris Megacity through wastewater treatment plant effluents and untreated stormwater. The January–February 2018 flood event, which represented 14.5% of the year (in terms of time), contributed 40% of the yearly MP mass fluxes. Thus, flood events contribute strongly to MP fluxes.

Development and experimental analysis of a novel dual-mode counter-flow evaporative cooling device

The recent energy demand for cooling increases rapidly, which has forced researchers to think about the technological shift. Evaporative cooling is an eco-friendly option, uses much less energy. Direct evaporative coolers are used worldwide and effective for arid climates. Regenerative evaporative coolers can cool up to dew point without adding moisture to the supply air. The dual-mode evaporative cooler is a novel idea that can operate in both regenerative and direct modes. In this work, the testing unit of this novel cooler is fabricated and experimentally investigated in both direct and regenerative modes. The important operating parameters (extraction ratio, inlet air temperature, inlet air velocity, inlet air specific humidity, water flow rate and water inlet temperature) are varied to get their effect on energy and environmental performance parameters (supply air temperature, cooling capacity, dew-point effectiveness, COP and CO2 emission). Technical comparison with conventional vapor compression air-conditioner is presented as well. The water inlet temperature affects regenerative mode more as compared to direct mode. The high water flow rate decreases the COP sharply in both modes. Comparison shows that direct mode can be used for higher cooling capacity (lower carbon emission) and COP while regenerative mode can be used for higher effectiveness.

Біотестування нафтових сорбентів на основі відходів полімерів

Introduction. Biotesting is considered to be an effective method of assessing the potential hazard of chemical, physical or biological effects on an ecosystem. Biotesting is carried out experimentally using, as a rule, standardized laboratory test systems, by recording changes in biologically important indicators (test reactions) under the influence of the studied samples. Hydrobionts act as biologically sensitive sensors: protozoa, algae, crustaceans, mollusks, fish, etc. Biotic indicators can provide information about the transformation of the ecosystem, the state of organisms and the degree of acceptability of influences to preserve the diversity of life forms and their balanced development. During the bioremediation of oil-contaminated water bodies at low temperatures and at high water flow rates (mountain streams) there are significant difficulties and traditional approaches and sorbents can not always be applied. Therefore, it is necessary to develop new non-traditional sorbents. At the same time, it is ecologically expedient to use multi-ton waste of packaging polymeric materials extracted from solid household waste, which are biologically and chemically inert, have unique sorption properties and are suitable for multiple use. Two ecologically dangerous problems have been solved - water pollution by oil products and the growth of polymer packaging in the share of household waste. The goal is to biotest the change of oil-contaminated environment during purification in model conditions with the use of polymer hydrophobic sorbents from raw materials extracted from solid household waste as bioremediators. Research objectives: to establish biological and toxicological safety of the use of secondary polymer raw materials from packaging waste as oil sorbents; to investigate the safety of using environmentally friendly surfactants from vegetable raw materials common in Ukraine to increase the extraction of petroleum products from water. Methods and techniques: toxicological - determination of water toxicity on Daphnia magna acute according to DSTU 4173: 2003 (ISO 6341: 1996, MOD) and chronic according to DSTU 4166: 2003 (ISO 10706: 2000, MOD), photometric method for determining the amount of oil in water according to GOST 17.1.4.01-80. The research results show the effectiveness of hydrophobic polymer sorbents made from secondary polymer raw materials extracted from solid waste in water contaminated with petroleum products to ensure their localization-sorption. The mortality rates of daphnia in all samples with sorbents at the beginning of the experiment were much lower than in the control, because the bulk of the contaminant was adsorbed on the surface of hydrophobic sorbents. At the end of the experiment, the best result in terms of the number of viable daphnia was observed in the cut of a sorbent made of polypropylene, the surface of which is covered with surfactants extracted from Milnyanka medicinal (Saponaria officinalis L). In this sample, the mortality of the test culture is 23%, which is 32% less than the control - 72%. Conclusions. Studies of the impact on aquatic ecosystems and the toxic effect of developed petroleum sorbents on Daphnia magna Straus have established the effectiveness of hydrophobic polymeric sorbent in water contaminated with petroleum products, ensuring their localization-sorption. The mortality rates of daphnia in all studied samples of sorbents except the sorbent from PVC waste were significantly lower than in the control, because the bulk of the contaminant was adsorbed in the polymeric sorbent. Biotesting showed that the sorption material based on polymeric secondary raw materials did not have a toxic effect in the process of purification of water from hydrocarbons. Therefore, it can be considered promising as a basis for bioremediators and for further use in the purification of water bodies from dissolved and spilled petroleum products. However, further in-depth toxicological studies require PVC-based sorbents, although their effects have not gone beyond what is acceptable and it is necessary to study their behavior under the influence of temperature changes and the reaction of other test organisms.

The synthetic effect of traditional-thermodynamic-factors (temperature, salinity, pressure) and fluid flow on natural gas hydrate recovery behaviors

The commercial exploitation of natural gas hydrates (NGHs) has been a growing research focus due to its features of enormous reserves and clean fuel. To guarantee the safe and efficient production of NGHs, we have proposed a novel strategy of water flow erosion to promote methane hydrate (MH) decomposition based on the tremendous seawater resource and the fundamental process of water-gas flow during NGHs exploitation. In this study, the synthetic effects of traditional-thermodynamic-factors (temperature, salinity, pressure) and fluid flow on MH decomposition characteristics, which is known little about yet, are comprehensively analyzed via in-situ magnetic resonance imaging (MRI). The temporal-spatial behaviors of MH decomposition are visually investigated. The results indicate that the pressure, salinity, temperature and water flow synergistically increased MH decomposition efficiency. Additionally, the propagation of the decomposition front along the interface between MH and ambient phase shows that the water flow rate and heat transfer are two crucial factors for accelerating MH decomposition. The higher water flow rate also efficiently complements the insufficient decomposition driving force due to the heat loss during MH decomposition process. The highest average decomposition rate (1.1%/min) and the relatively less water injection volume (320 mL) can be archived in this study. Furthermore, the decomposition rate has a significant dependence on temperature under lower water flow rate.

An Experimental Analysis of Water–Air Two-Phase Flow Pattern and Air Entrainment Rate in Self-Entrainment Venturi Nozzles

For self-entrainment venturi nozzles, the effects of nozzle shapes and operating conditions on the water–air two-phase flow pattern, and the characteristics of the air entrainment rate have been investigated. A rectangular venturi nozzle with width and height dimensions of 3 mm and 0.5 mm was used with a vertically downward flow direction. The pressure ratio, which is the ratio of the inlet and outlet pressures, water flow rate, and diverging angle were set as experimental parameters. From the flow visualization, annular and bubbly flows were observed. In the case of bubbly flow, the more bubbles that are generated with a higher water flow rate, the smaller the pressure ratio. In the case of annular flow, the increased pressure ratio and water flow rate induce the breakup of air core in the diverging area and make the interfacial oscillation stronger, which finally causes the flow transition from annular to bubbly flow, by accompanying a sharp increase in the air entrainment rate. During this flow transition, the frictional pressure drop of the two-phase flow is reduced, showing that a two-phase multiplier gets smaller.