Inlet Water Pressure Research Articles

Effect of parameter optimization on the flow characteristics of venturi-self-excited oscillation mixer based on response surface model and multi-island genetic algorithm

The present study focuses on the development of a novel venturi-based self-excited oscillation mixer that effectively utilizes the venturi effect to facilitate efficient abrasive intake while simultaneously ensuring effective prevention of backflow through the utilization of the systolic section within the venturi tube. It not only ensures uniform mixing of water and abrasive but also transforms the continuous jet into a pulsed one, thereby significantly enhancing exit velocity. The orthogonal experimental design method and single factor experiment method were employed to investigate the effects of inlet water pressure, water nozzle diameter, abrasive inlet angle, aspect ratio of the self-excited oscillation mixer, and abrasive pipe inlet diameter on the inlet pressure of the abrasive pipe and the velocity of the jet exit in the new mixing device. Approximate response surface models for these parameters were constructed using lsight optimization software, combining the results of orthogonal experimental simulation. By employing a multi-island genetic algorithm, we have globally optimized this innovative mixing device to determine its optimal performance parameters. Subsequently, comparative experiments were conducted to validate the performance of different mixing devices in descaling applications. Through experimental verification, it was found that the venturi-self-excited oscillation mixer exhibits excellent rust removal capabilities in steel plate tests compared to traditional self-excited oscillation mixers. These findings provide valuable guidance for the subsequent design and enhancement of abrasive water jet mixers.

Development of a spray-ejector condenser for the use in a negative CO2 emission gas power plant

One promising solution for developing low-emission power technologies is using gaseous fuel combustion in pure oxygen when the exhaust gas mixture is composed of H2O and CO2, and where CO2 is separated after steam condensation. The paper presents the results of computational analyses providing to the Spray-Ejector Condenser (SEC) development, which is one of the crucial components of the negative CO2 gas power plant (nCO2PP) cycle development. The proposed design of the ejector-condenser to ensure the high effectivity of vapor condensation and CO2 compression with preparation to separation, ready for application in gas power cycle, is a novelty of this research. Different computational techniques leading to the development and better understating of ejector operation were applied. The main operating conditions in the characteristic connected with the developed nCO2pp cycle points were investigated to evaluate the impact of the operating conditions on SEC performances. The amount of motive water needed for the cooling purpose is susceptible to the inlet water pressure and temperature and strongly affects the generated pressure of the suction stream. The preliminary results confirm that the SEC's basic design and geometrical dimensions can be applied in the negative CO2 power plant cycle. Results from CFD modeling give the possibility to investigate the turbulent flow of water/steam/CO2 mixture together with the condensation process occurring at this same time. It is found that the average droplet diameter and motive water supplying method significantly effects the condensation intensity. The further direction of the presented computational research activities and results is to test various designs of Spray-Ejector Condensers that will enable the evaluation of the direct contact condensation process and develop the final geometrical design.

An open superhydrophilic microchannel heat sink for thin film boiling with a high coefficient of performance

Currently, the existing two-phase boiling heat transfer technologies have limitations in extremely narrow spaces and cannot satisfy the high heat flux dissipation requirements of highly integrated and ultrathin devices. In this study, a high-efficiency and low-cost open superhydrophilic microchannel heat sink with a micro/nanocomposite structure, negligible pumping energy, and a high coefficient of performance (COP) was achieved. The wettability and microscopic morphology of the different heat sinks as well as the variation in the critical heat flux (CHF) and heat transfer coefficient (HTC) at different mass fluxes were discussed. When the mass flux was 0.05 kg/m2⋅s, the CHF of the microgrooved composite nanostructured copper (MCNC) heat sink was 173.90 W/cm2, which was 182.80% higher than that of the smooth copper (SC) heat sink and 20% higher than that of the microgrooved copper (MC) heat sink. In addition, the highest CHF of 325.90 W/cm2 was obtained for the MCNC at a 0.15 kg/m2⋅s mass flux. The high CHF of thin film boiling was achieved at a low inlet water pressure. This resulted in a COP of 695,600 for this boiling method, which is a larger value than that in most reports thus far. This study provides a preliminary investigation of the thin film boiling performance for an open microchannel. This may provide a new solution to the challenge of high heat flux dissipation in extreme spaces.

Experimental Study on the Effects of Shear on Co‐Currently Swirling Steam‐Water Flow Instabilities

AbstractThe shear effect of co‐currently flowing water on the flow instabilities induced by swirling steam was investigated. With shear, a 22–27 % decrease in velocity fluctuation amplitude was observed. The decrease was 29–41 % on an exponential and 12–17 % on a proportional basis. Shear reduced the layer thickness on increasing the inlet water pressure from 1 to 2 bar by 1.9–2.9 and 6.35–12.89 % at steam inlet pressures of 1 and 2 bar, respectively. The ratio of the swirl intensity along the dimensionless axial length scale and the initial swirl intensity was changed from < 1 to > 1 across critical point due to the nearly equal values of buoyancy and rotational frequencies. A critical limit of the initial swirl intensity within the control plane was investigated wherein the swirl‐induced instabilities can be attenuated uniformly and the rotational effects dominate over the gravity waves and buoyancy.

Study on the Influence Rule of High-Pressure Water Jet Nozzle Parameters on the Effect of Hydraulic Slotting

In order to get the appropriate nozzle parameters, numerical simulation and field tests are used to investigate the influence of high-pressure water jet nozzle parameters on the effect of hydraulic slotting. A nozzle model is created by using FLUENT software. For different nozzle contraction angles, outlet diameters, and straight column section lengths, the distribution rules of the velocity of the water jet and dynamic pressure on the central and vertical axes are obtained, and the parameters for the best nozzle effect are determined. The relationship between the nozzle contraction angle gradient, the inlet water pressure, and the nozzle outlet water velocity is discovered. A mathematical model of the nozzle outlet water velocity of the water jet is established. The depth, width, and volume of the hole generated by the nozzle impact are employed as indications for inquiry, and field measurements are used to derive the results of nozzle geometry parameter optimization. The field tests validate the numerical simulation conclusions, and the results have theoretical and practical guidance for hydraulic slotting in coal mines and get the appropriate nozzle parameters specially.

Characteristics of a Cavitating Spoiler Mixing Device and Its Performance in a Foam Dust Suppression System.

The unsteady foaming-agent mixing ratio in traditional foam-dust-suppression technology limited the dust suppression efficiency. Recent studies proved that the steady mixing ratio could be guaranteed by keeping the jet pumps or Venturis working under cavitation conditions, but the pressure loss of the current devices was over 50%. To decrease the pressure loss under cavitation conditions, we proposed a new mixing device by introducing a spoiler in the Venturi structure. Through computational fluid dynamics (CFD) simulation, the spoiler structure influence on the downstream flow field and the cavitation cloud structure, which affected the total pressure loss of the device, were revealed. For structure optimization, the effect of the other geometric parameters, including the throat length and divergent angle, on the pressure loss was also studied. The proposed device enhanced the cavitation on the suction tube side of the throat; meanwhile, the cavitation in other parts of the device was avoided. Therefore, the cavitation zone in the proposed device was much smaller than that in current devices, and the pressure loss was reduced significantly. When the flow ratio was 0.5–1%, the critical pressure ratio of the proposed mixing device was 0.71–0.68, which indicated that the pressure loss was only 29%–32%. The laboratory experiment verified that when the proposed device worked under cavitation conditions, the accurate and steady mixing ratio was guaranteed. The field experiment indicated that due to the reduced pressure loss of the proposed device, the required water inlet pressure decreased to 0.29 MPa, and the dust suppression rate increased dramatically. This study was of important value in manipulating cavitation cloud structure using a spoiler, clarifying the influence of the cavitation cloud structure on the liquid mixing performance and expanding the application field of the cavitating mixing method.

A novel permeability prediction model for coal based on dynamic transformation of pores in multiple scales

Schlumberger-Doll research (SDR) model is popular in predicting rock permeability, however the intrinsic defects constrain its applicability in coal. Pore structure in coal is complicated while SDR model assumes it is homogeneous. To solve this problem, we conducted water flushing experiments to simulate coalbed methane (CBM) drainage process using nuclear magnetic resonance (NMR) on durain (DHB-9-3), clarain (HP-5-3) and semi clarain (MD-6-6). Through comparative analyses on stress sensitivity, adsorption pores in DHB-9-3, non-adsorbed pores in HP-5-3 and seepage pores in MD-6-6 show a greater sensitivity. The non-adsorbed pores, which are responsible for reservoir permeability, become more complicated under increasing effective stress. The fractal dimension of non-adsorbed pores in DHB-9-3 and HP-5-3 increases from 2.93 to 2.97, and from 2.92 to 2.93 in MD-6-6 when the inlet water pressure reduces from 8 MPa to 3 MPa, indicating a more complicated pore geometry and a longer water flow pathway. As a result, the permeability shows a downward trend. A novel coal permeability prediction model is constructed with a factor of fractal dimension embedded in. Compared with SDR model, the new model is verified to have 0.79 times, 0.16 times and 0.08 times less error rates in DHB-9-3, HP-5-3 and MD-6-6, respectively.

Experimental testing on the influence of shaft rotary lip seal misalignment for a marine hydro-kinetic turbine

Tidal energy has received considerable attention over the past decade due to its predictability and high power density. The research in the tidal turbine area has concentrated primarily on the improvement of the energy conversion efficiency. In contrast, the testing of the tidal turbine’s mechanical components has received less attention. In particular, the reliable operation of rotary seals is crucial to prevent water ingress into mechanical and electrical components. This paper outlines an experimental test campaign to investigate the effect of shaft misalignment. Both instantaneous temperature and pressure measurements were recorded from two rotary seals. It was shown the temperature inside the aligned seal increased until the seal chamber pressure became equal with the inlet water pressure. The wear on the lip seal rings was examined and the difference found to be between 3.28% and 19.61%. Inspection of the seal liners, showed the presence of strong wiping effects for the misaligned seal with maximum track width differences of between 52.94% and 97.60% being noted. The misaligned seal liner experienced wider wear tracks but were not as deep as the aligned seal with differences of between 37.55% and 103.13% being recorded.

Analysis of compression in uniform and non-uniform GDL microstructures on water transport

ABSTRACT A 3D compressed gas diffusion layer (GDL) microstructure is developed based on the finite volume method (FVM) and used to evaluate water transport behavior. The compressed GDL microstructure and two-phase flow VOF model are developed and validated on the OpenFOAM CFD platform. The models are compared to experimental data, with good agreement. Consequently, the reconstructed GDL microstructures are subjected to compressive stresses. The water uptake behavior in the compressed samples with different (CR) compression ratios (10% CR, 20% CR, and 40% CR) is compared to that in an uncompressed GDL microstructure. Also, the effects of GDL wettability, water pressure, and non-uniform fiber diameter arrangement in GDLs are investigated. In GDL microstructures, two-phase interaction is influenced by the GDL contact angle, compression ratio, water inlet pressure and capillary pressure. It is found that excessive compression on GDLs constricts the pores, thereby restricting access of water through the pores. As such, 10% CR was found to be the safe limit with just 8% saturation drop. On the other hand, altering the fiber structural arrangement through unequal-sized fiber diameter had very little impact on water saturation in the through-plane direction of both the uncompressed and compressed GDL microstructures. As such, the excessive introduction of the unequal-sized fibers may not be the right choice, especially under compressive forces. Thus care must be taken in the treatment of GDL carbon papers and clamping force during assembly since these significantly influences water patterns in them.

The Effectiveness of Microbubble Technology in The Quality Improvement of Raw Water Sample

An experimental study to observe the performance of microbubble generator (MBG) and microbubble-generating nozzle on water is carried out under laboratory conditions. The MBG is used to treat wastewater from water bodies which was impacted by domestic and industrial wastewater. The study uses MBG with a spherical body and a drilled hole, along with a dispersing nozzle placed at the bottom of microbubble reactor tank. The MBG used is considered to be more applicable for water bodies rather than other types. Two types of pressure gauges are installed around the MBG and the nozzle in order to examine and configure the inlet water pressure and the inlet gas pressure based on the best microbubble size produced from a prior experiment. Biological Oxygen Demand (BOD), Chemical Oxygen Demand (COD), Dissolved Oxygen (DO), Total Suspended Solids (TSS), and Turbidity has been analyzed in the beginning and every 10 minutes of a 60 minute detention time to examine the effectiveness of MBG. The results of study shows the MBG have a high rate of removal percentage in a 60-minute retention time with 60 to 90% for TSS, up to 90% for Turbidity, 74 to 96% for BOD, and 41 to 59% for COD.

Spatiotemporal Evolution Characteristics of Fluid Flow through Large-Scale 3D Rock Mass Containing Filling Joints: An Experimental and Numerical Study

This study analyzes the spatiotemporal evolution characteristics of seepage through a large-scale rock mass containing a filling joint. Firstly, a conceptual model was established to characterize the geomechanical occurrence of a typical water-resistant slab adjacent to a water-bearing structure. Then, a special apparatus was developed to conduct a hydromechanical test of a 3D large-scale rock mass. For a certain boundary stress and inlet water pressure, the pore water pressure in the joint first experiences a dramatic increase before approaching a constant value, and the steady pore water pressure presents a linear decrease along the joint length. A water inrush phenomenon happens as a result of connected flowing channels induced by migration of fillings. Using the finite element of COMSOL multiphysics, the influences of filling joint permeability, matrix permeability, and joint thickness as well as the inlet water pressure on seepage evolution in the jointed rock mass were, respectively, investigated. The pore water pressure increases with all these factors, and the stable pressure values increase with the inlet water pressure but decrease along the joint length. The flow velocity undergoes an increase with both the joint permeability and inlet water pressure but presents constant values independent on the matrix permeability or joint thickness. The water pressure contour planes distributed along the flowing path generally transfer from a “long funnel” shape to a “short funnel” shape before reaching a series of parallel pressure planes perpendicular to the joint direction. By using the genetic algorithm, the coupling influences of these factors on the pore water pressure and flow velocity were investigated, and the decision parameters were optimized. The calculated values show a good agreement with the numerical results, indicating a good prediction of the seepage evolution through the filling joint.

An Experimental Investigation on the Mechanism of Contact Erosion in Levee Foundations Considering the Characteristics of Particle Shape and Flow Field

Abstract Internal erosion is one of the most critical contributing factors for levee failures. Contact erosion, as a type of internal erosion, dominants when the seepage flow direction is parallel with the interface between coarse and fine soil layers. As is often the case beneath the foundation of a levee or at the top of clay core in an embankment dam, contact erosion can induce continuous transport of fine particles. Consequently, these water-retaining structures may collapse. To mitigate such potential hazards, the condition for initiation and progression of contact erosion should be investigated. In this research, the characteristics of contact erosion within cohesionless soils are presented visually by means of a newly devised apparatus. Two types of transparent coarse particles, namely quartz rubble and glass bead, are incorporated in two tests to study the effect of hydraulic conditions and particle shape on the initiation of contact erosion. The occurrence of contact erosion is captured qualitatively by snapshots, and the variation of soil sample configuration and flow lines are monitored by a stationary camera. Quantitative measurements are also conducted. Hydraulic gradients, turbidity, eroded mass, and inlet water pressure are recorded. The results provide insight into the influence of flow condition and particle shape on the occurence of contact erosion. The initiation and progression of contact erosion are governed by both hydraulic conditions and pore morphology. The latter is more crucial.

Experimental investigation on the shell-side heat transfer performance of molten salt steam generator

In this study, an experiment was conducted to obtain the heat flux and heat transfer coefficient of a mixed molten salt (60% NaNO3, 40% KNO3) and water at subcritical pressure in a tube in tube heat exchanger. The control variable method was used in this study. The experimental parameters included the molten salt and water mass fluxes of 38.7–54.1 kg/m2s and 212.8–259.6 kg/m2s, respectively, water pressure of 15–19 MPa, water and molten salt inlet temperatures of 200–400 °C and 440–500 °C, respectively, and heat flux of 12–160 kW/m2. The heat transfer performances of the molten salt and water in the subcooled, subcooled boiling, saturated boiling, dryout and superheated regions were analysed with respect to the molten salt and water mass flow rate, inlet salt temperature, water pressure, and inlet water temperature. The fitting correlation of the thermal performance of molten salt to the subcooled boiling or vapor-liquid two-phase flow was presented; the fitting values demonstrated good consistency with the experimental data, with a maximum deviation of –6% and +8%.

Study on flow field and temperature field characteristics of gas-liquid two-fluid snowmaking nozzle

A snowmaking nozzle based on the principle of supersonic speed of Laval nozzle is proposed, and the influence of its operation and structural parameters on flow field and temperature field characteristics is analysed. The results show that the gas-liquid mixture velocity outside the nozzle outlet increases with the increase of air inlet pressure, water inlet pressure and throat diameter, decreases with the increase of distance between water inlet and nozzle outlet. The gas-liquid mixture temperature outside the nozzle outlet increases as water inlet pressure and distance between water inlet and nozzle outlet increases, decreases as air inlet pressure and throat diameter increases. As gas-liquid pressure ratio increases, the gas-liquid mixture velocity outside the nozzle outlet tends to decrease first, then increase and then decrease, while its temperature tends to increase first, then decrease and then increase. When gas-liquid pressure ratio α = 3, this nozzle has the best performance.

Development and assessment of a water pressure reduction system for lining invert of underwater tunnels

To efficiently reduce the secondary lining external water pressure on underwater tunnels, the feasibility of a novel bottom-up drainage and water pressure reduction system for reducing has been validated by conducting laboratory evaluations. Critical factors of underwater tunnels, including the surrounding environment, lining, bottom drainage system, and other supplementary components have been represented by such system to investigate the drainage mechanism and efficiency of the designed system. The drainage system has been further optimized by analyzing the measured water pressure and flow rate. Experimental results indicate that the designed draining system is feasible for reducing the secondary lining external water pressure in the bottom of tunnels and the water pressure has been reduced significantly with high efficiency. The capacity of the proposed system to control the rapid water inflow in tunnel construction regions can be guaranteed. The factors affecting the performance of the system such as the diameter of the drainage pipe and the inlet water pressure are also discussed.

Experimental Study of Water Infiltration in Unsaturated Horizontal Sand Columns under Various Air Confinement Conditions

The process of water infiltration into initially dry sand was studied in horizontal sand columns under various airtight conditions. To investigate the interrelations among water inflow behavior, air pressure, air confinement effect, and vent effectiveness in unsaturated porous media experiencing dynamic infiltration, a total of five dynamic infiltration experiments with fixed inlet water pressure were performed with different air vents open or closed along the column length. Visualizations of the infiltration process were accompanied by measurements of water saturation, air pressure, and accumulated water inflow. In a column system with an open end, the absence of air pressure buildup reveals that the vent at the column end can significantly reduce the internal air pressure effects during infiltration, and the air phase can be ignored for this case. However, in columns with a tight end, the coupled air and water flow processes can be divided into two completely different periods. Before the water front passed by the most distant open vent, the internal air pressure effects on retarding dynamic infiltration are negligible, similar to the open end case. After this period, the open vents can certainly influence the inflow behavior by functioning as air outlets while they cannot equilibrate pore air pressure with the atmospheric pressure. The remaining air ahead of the front will be gradually confined and compressed, and the significant increase in air pressure highlights the great role of air pressure buildup in reducing the water infiltration rate. The closer the last open vent was to the water inlet, the higher was the increase in air pressure and the greater was the delaying effect on water infiltration. This work may extend the experimental study of water infiltration into the unsaturated soils with different airtight conditions and provide experimental evidence on these coupled mechanisms among the water and air phases in soils.

Improved foam application at the tunnel face with large ventilation volume and low pressure supplied water

Due to large energy loss, current foam technology for dust suppression requires high inlet water pressure, but performance is poor where ventilation volume is high. This paper proposes modifying key foam device components, including the agent mixing device, foam generator, and nozzle, to address these problems. A cavitating jet pump was simultaneously employed for accurate agent mixing and flow meter, guaranteeing accurate agent flow and low energy loss. A vertical foam generator was designed to increase foam volume and ensure even foam distribution among the foam nozzles. The two-layered foam nozzles were designed and fabricated using 3D printing to ensure even and thick foam impact area on the dust source, effectively blocking dust escape passages. Experiments were performed in the laboratory and on a real heading face. Ventilation volume was 560–570 m3/min for the field experiment with initial total dust concentration 589–679 mg/m3. The proposed system reduced required inlet water pressure to 0.87 MPa, while achieving 86.8% average total dust suppression efficiency and reducing long-term time average respirable dust concentration to 3.9–5.7 mg/m3. This study will help improve performance and expand application fields for foam dust suppression technology.

Experimental Investigation on Heat Transfer Mechanism of Air-Blast-Spray-Cooling System with a Two-Phase Ejector Loop for Aeronautical Application

This paper presents an air-oriented spray cooling system (SCS) integrated with a two-phase ejector for the thermal management system. Considering its aeronautical application, the spray nozzle in the SCS is an air-blast one. Heat transfer performance (HTP) of air-water spray cooling was studied experimentally on the basis of the ground-based test. Factors including pressure difference between water-inlet-pressure (WIP) and spray cavity one (PDWIC) and the spray volumetric flow rate (SVFR) were investigated and discussed. Under a constant operating condition, the cooling capacity can be promoted by the growth factors of the PDWIC and SVFR with the values from 51.90 kPa to 235.35 kPa and 3.91 L ⋅ h − 1 to 14.53 L ⋅ h − 1 , respectively. Under the same heating power, HTP is proportional to the two dimensionless parameters Reynolds number and Weber number due to the growth of droplet-impacting velocity and droplet size as the increasing of PDWIC or SVFR. Additionally, compared with the factor of the droplet size, the HTP is more sensitive to the variation in the droplet-impacting velocity. Based on the experimental data, an empirical experimental correlation for the prediction of the dimensionless parameter Nusselt number in the non-boiling region with the relative error of only ± 10 % was obtained based on the least square method.

Simulations and experimental validation of Pico conduit pressure hydropower systems with battery storage

Abstract An increase in the world's population has led to an increased energy demand. Sustainable renewable energy sources must be broadly executed to fulfil the continuous need for energy. Amongst different renewable energy technologies, hydropower generation proved to be the most feasible solution. A portion of small hydropower can be acquired by recovering the energy inside water supply networks. This may lead to a sustainable electrification solution and reduced electricity bills for the water utility companies. Hence, the procedure of energy recovery using conduit hydro technology must be a part of the water cycle. Numerous nations have started with the improvement of this innovative conduit hydro technology. However, very little has been exploited. Hence, this study focuses on developing a simulation tool that can be used to analyse conduit hydropower generation system with a battery storage. Subsequently, this paper exhibits the modelling and performance analysis of a small conduit hydropower system in MATLAB/Simulink software. This will assist the conduit hydropower developers to quantify the available energy and evaluate the viability of the conduit hydropower projects. Furthermore, the performance of the modelled conduit hydropower system is compared to the performance of a prototype setup in a laboratory environment. Inlet water pressure was assessed to observe how the system reacts to the variation of the water pressure. This data was used to simulate the performance of the model in MATLAB/Simulink in comparison with the laboratory prototype. The results revealed that the developed model reacted viably under variable pressure. The conduit hydropower was just dynamic when the excess pressure was accessible, this is because of the pressure distinction between Pressure Reducing Valve (PRV) pre-set pressure and the system pressure. Hence, the excess pressure is used to drive the generator and the generated energy is then stored in the battery.

Turbulence dissipation & its induced entrainment in subsonic swirling steam injected in cocurrent flowing water

Subsonic swirling steam induced turbulence, its dissipation, and entrainment inside the concurrent flowing water has been investigated on an experimental basis. Pressure fluctuations of dissimilar amplitudes have been observed which have been attributed to the vortices and hence instances for entrainment on a spatial basis. The extent of turbulence dissipation has been measured by the rate of decrement of the smallest pressure fluctuation of amplitude 0.04 bars. It has been observed that the turbulence dissipation along radial direction rises from 2.3 to 6.3 fluctuations/cm with rising in the inlet pressure of steam & till 12.5 fluctuations/cm in case of rising in rpm of the swirler. On a temporal scale, the turbulence dissipation varies from 0.7 fluctuations/sec at initial conditions which rise till 1.9 fluctuations/sec with the rise in inlet pressure of steam & 3.7 fluctuations/sec in case of rising in rpm of the swirler. Effect of rising in compressibility & rpm on sheer layer transformation into vortices imparted in terms of spatial dislocation along the axial axis, which ranges from 64–66% to 35–41% respectively. The extent of entrainment has found to be influenced by an increase in the compressibility, the rpm of the swirler and the surrounding water inlet pressure, which has been represented by the number of occurrences of the vortices across radial and axial directions. Effects imparted by the given conditions on fluctuations, entrainment, and non-dimensionalized flux has also been investigated.