Search Results (29)

The cavitation water jet cleaning and coating removal technique represents an innovative sustainable method for cleaning and removing coatings, with the nozzle serving as a crucial component of this technology. Developing an artificially submerged nozzle with a reliable structure and excellent cavitation performance is essential for enhancing cavitation water jets’ cleaning and coating removal efficacy in an atmosphere environment (non-submerged state). This study is based on the shear flow cavitation mechanism of an angular nozzle, the resonance principle of an organ pipe, and the jet pump principle. A dual-nozzle co-current cavitation water jet nozzle structure was designed and manufactured. The impact of the nozzle’s inlet pressure on the vapor volume percentage, as well as the axial and radial velocities inside the flow field, were examined utilizing ANSYS Fluent software with the CFD method. The dynamic change rule of the cavitation cloud is derived by analyzing the picture of the cavitation cloud in the nozzle’s outflow field utilizing pseudo-color imaging techniques. The results show that the maximum vapor volume percentage is more significant than 95% for different inlet pressures in the internal nozzle. The changes that occur in the cavitation cloud exhibit notable regularity, including the four stages of cavitation, which are inception, development, shedding, and collapse. A change period is 1.5 ms, which proves that the homemade co-current cavitation water jet nozzle can achieve good cavitation effects. Full article

With the continuous development of high-pressure water jet technology, research on the optimization of structural parameters for multi-nozzle configurations, the perforation effect of jet rotational impact rock breaking, and the impact force during rock breaking has received increasing attention. Through the development of a self-designed high-pressure water jet rotational drilling test device, rock breaking experiments were conducted on sandstone of different strengths using jet streams with different inclination angles, various combinations of nozzles, different target distances, and different rotational speeds. The parameters and structure of the multi-nozzle jet drill bit were optimized, and the impact of water jet-rock breaking effects was studied. The rationality of different inclination-angle jet streams in rock breaking was verified using the ALE-FEM coupling method. The changes in the force on the target body and the fragmentation mode during rock breaking with different inclination-angle jet streams were analyzed. The results showed that under the condition of adjustable inclination angles, a smaller inclination angle resulted in greater depth and a smaller diameter of rock breaking, while a larger inclination angle resulted in greater width and a smaller depth of rock breaking. The optimal combination of multi-nozzle jet streams was determined to be 20°, 30°, and 60°, which achieved a balance between rock breaking and borehole expansion performance. The efficiency of multi-nozzle jet rotational rock breaking decreased with increasing target distance, with the optimal range being 2 to 4 mm. The rotational speed of the multi-nozzle jet stream had a significant impact on rock-breaking efficiency. Under the same target distance conditions, as the drilling speed increased, the volume of rock breaking initially increased and then decreased, and the rate of volume attenuation increased with increasing target distance. The forms of rock breaking in multi-nozzle jet streams were not identical. Jet streams with smaller inclination angles mainly caused tensile failure through axial impact, while those with larger inclination angles primarily caused shear failure through radial impact. This study provides valuable guidance for optimizing the structural parameters of multi-nozzle jet drill bits and researching rotational rock breaking. Full article

High-efficiency rock breaking by hydraulic jetting is the key to radial horizontal drilling technology. In order to improve the drilling efficiency of hydraulic jet rock breaking in radial horizontal wells, based on LS-Dyna display dynamics, a numerical simulation model of single-nozzle jet rock breaking was established to analyze the influence of different nozzle parameters on the rock-breaking effect. Then, the numerical simulation model of the spin multi-nozzle jet bit was established, and the influence of different rotation speeds on the rock-breaking effect of the jet bit was analyzed. Finally, the rock-breaking drilling characteristics of the spin multi-nozzle jet bit and the conventional multi-nozzle jet bit were compared and analyzed. The results show that when the jet impacts the rock surface, the larger the inclination angle is, the larger the rock-breaking width formed by the jet is. The smaller the dip angle, the greater the rock-breaking depth. When the inclination angle is greater than 60°, it is difficult to meet the needs of reaming. The width and depth of the nozzle gradually increase with the increase of the diameter. When the nozzle diameter is greater than 1.3 mm, the growth rate of rock-breaking depth begins to decrease. The optimum nozzle diameter is 1.3 mm. When v = 50 m/s, the damage caused by the jet to the rock surface is very small, because the condition of rock fracture is not reached with this velocity. This shows that there is a critical value of the water jet impact velocity, and only when the velocity is reached, will the rock break. When the velocity is v = 150 m/s, v = 200 m/s, v = 250 m/s, v = 300 m/s, the rock breaks. At the same time, the higher the speed, the higher the degree of rock fracture, the greater the fracture depth, the greater the fracture area, and the better the fracture effect. The tangential and radial velocity of the jet increases the shear and tensile failure rate of the sample, and improves the rock-breaking efficiency of the jet, which has a certain guiding significance for improving the rock-breaking drilling efficiency of radial horizontal well drilling. Full article

Radial drilling-fracturing is an innovative fracturing technology that achieves superior stimulation effects. In order to study the permeability-increasing effect and main influencing factors of radial water jet drilling in the low physical section, this paper uses a fracking electrical simulation experiment, based on the principle of hydropower similarity, to simulate the reservoir conditions and well pattern in the low physical section and, at the same time, establishes the radial fracturing model of the low physical section reservoir, simulates the saturation field, pressure field, and production-change law under different drilling parameters, and studies different influencing factors. The experimental results show that when the number of drilling holes exceeds two, the effect of increasing production gradually becomes less significant as the number of drilling holes increases; Within the range of the angle between the two boreholes, the forward distance of the oil–water displacement front is the farthest and the sweep is relatively uniform. On both sides of the included angle, the forward distance of the oil–water displacement front edge is smaller than the forward distance of the displacement within the included angle range and it is clearly inclined towards the radial drilling with uneven spread. Radial drilling has an impact on the seepage field, causing changes in its streamline. The pressure inside the borehole is lower than the surrounding formation pressure and most of the flow lines change direction near the borehole location, causing deflection. As the borehole length increases, the oil-well production also increases. The optimal effect is for the borehole length to be 100 m. This study provides a reference for the on-site application of radial fracturing in low physical properties sections. Full article

The phenomenon of steam–water direct contact condensation has significance in a wide range of industrial applications. Superheated steam was injected upward into a cylindrical water vessel. Visual observations were conducted on a turbulent steam jet to determine the dimensionless steam jet length compared to the steam nozzle exit diameter and the steam maximum swelling ratio as a function of steam mass flux at the nozzle exit, with a gas steam flux ranging from 295–883 kg/m²s. The Reynolds number based on the steam jet’s maximum expansion ranged from 41,000 to 93,000. Farther above of the condensation region, the jet evolved as a single-phase heated plume, surrounded by ambient water. Mean axial central velocity profiles were determined against the steam mass flux ranging from 295–883 kg/m²s to observe the exponential drop in the mean axial velocity as the vertical distance increased. The radial velocity distribution within the spread of the jet was determined to be self-similar, and the radial distribution of the velocity profile followed the Gaussian function, after the proper scaling of the vertical distance and the axial mean velocity. Full article

The plasma jet transfer technique relies on a conductive wire at floating potential, which, upon entering in contact with a primary discharge, is capable of igniting a small plasma plume at the distal end of a long flexible plastic tube. In this work, two different long tube configurations were employed for the surface modification of polypropylene (PP) samples using argon as the working gas. One of the jet configurations has a thin copper (Cu) wire, which was installed inside the long tube. In the other configuration, the floating electrode is a metallic mesh placed between two plastic tubes in a coaxial arrangement. In the first case, the tip of the Cu wire is in direct contact with the working gas at the plasma outlet, whereas, in the second, the inner plastic tube provides an additional dielectric barrier that prevents the conductor from being in contact with the gas. Water contact angle (WCA) measurements on treated PP samples revealed that different surface modification radial profiles are formed when the distance (d) between the plasma outlet and target is changed. Moreover, it was found that the highest WCA reduction does not always occur at the point where the plasma impinges the surface of the material, especially when the d value is small. Through X-ray photoelectron spectroscopy (XPS) analysis, it was confirmed that the WCA values are directly linked to the oxygen-functional groups formed on the PP surfaces after the plasma treatment. An analysis of the WCA measurements along the surface, as well as their temporal evolution, together with the XPS data, suggest that, when the treatment is performed at small d values, the plasma jet removes some functional groups at the point where the plasma hits the surface, thus leading to peculiar WCA profiles. Full article

Due to global environmental conditions, the focus of household heating has shifted from fossil fuels towards environmentally friendly and renewable energy sources. Desuperheaters have attracted attention as a domestic provision involving steam-induced direct contact condensation (DCC)to warm the water. The present study is an attempt to investigate the hydrodynamics in the desuperheater vessel experimentally, namely, when the pressurized pulsating steam is injected into the vessel, where the steam jet interacts co-currently with the slow-moving water. Flow visualization showed a circulation region when the pulsating steam was injected into the slow-moving water, and the peaked vorticity corresponded to the steam injection duration of 10–60 s. Sevenhot film anemometers (HFAs) were traversed axially and radially to determine the velocity fluctuations at 0–20 cm from the steam’s nozzle exit. Vortical structures indicated the entrainment of the steam with the surrounding moving water. The circulation regions were thus exhibited in relation to the steam’s injection durations as well as the downstream axial distances of 2 and 15 cm from the nozzle exit, which showed that the core local circulation at 2 cm downstream of the nozzle exit lost 75–79% of its circulation at 15 cm downstream of the nozzle exit. Full article

The variable-area pintle injector has unique geometry and spray characteristics compared to traditional coaxial injectors, and is advantageous for weight lightening and deep throttling of liquid rocket engines. To obtain an accurate prediction of the spray windward distribution of a gas–liquid pintle injector with discrete radial orifices, a pintle injector element using air and water as simulants was designed for spray experiments in the atmospheric environment. The air-film injection pressure drop and water-jet injection orifice diameter were both adjusted for a wide variance range from 0.19 to 2.85 for the local momentum ratio. Backlight imaging was adopted for shooting the frozen spray pattern from one side, and a new dimensionless parameter, i.e., the spray fraction, was defined to quantitatively analyze the time-averaged windward boundary band. The dimensionless spray windward boundary band model for a circular-orifice jet and the corresponding derivative formula of the spray half angle were summarized through parameter study. The predicted results of empirical models were in good agreement with the experimental results. It was found that when the local momentum ratio was about 1, the spray distribution range basically overlapped with the coverage scope of gas film with uniform liquid mist. Full article

Experimental investigations are conducted to determine the mechanism and characteristics of a jet in an L-shape crossflow simulating the radial swirl injector of a lean premixed-prevaporized (LPP) combustor. To simplify the radial flow of the actual injector while ignoring the centrifugal effect, the L-shaped 2D-channel is used for the crossflow, and water is used as a fuel simulant. The jet breakup is captured using a high-speed camera, and the density gradient magnitude is post-processed to clarify the spray. The Sauter mean diameter (SMD) of the spray is measured via a laser diffraction method with a helium–neon laser optical system (HELOS). The characteristics of the jet in the L-shape crossflow are compared with the characteristics of the jet in a typical crossflow through the flat channel. The results for different outlet heights of the L-shape channel ($H/d_0$) and different injector positions ($L/d_0$) are presented. A dimensionless number ($\tau$) consisting of a time ratio is introduced to describe the jet characteristics. In a previous work, the spraying tendency was demonstrated for different injector positions. In addition, the effect of the recirculation area on $H/d_0$ was empirically shown. $H/d_0$ determines the size of the recirculation area, and the range of τ determines the jet breakup mechanism inside the L-shape channel. The results of this study present the breakup mechanism of the jet in the L-shape channel flow, which simulates a jet in a radial swirler injector for gas turbine engines. It is expected that these results can be used to assist in designing gas turbine engines with more combustion efficiency. Full article

The microfluid jet polishing (MFJP) process is a manufacturing technology in which small abrasive particles (such as diamond, alumina, and ceria) are premixed with a carrier fluid (typically water) to form a liquid suspension that is pressurized and expelled through a nozzle for material removal. The resulting microjet beam—with a typical nozzle exit diameter in the range from 0.1 to 1.0 mm—impinges the workpiece surface for material removal by erosion and/or abrasion and produces an ultraprecision surface. This work applies a computational fluid dynamics (CFD) model to analyze the key phenomena in the interaction of the liquid suspension and the workpiece surface. The liquid film characteristics (film height, minimum film height, positions of the minimum film height, and hydraulic jump) obtained from the CFD simulations are compared with the results derived from empirical formulations found in the literature. Subsequently, the numerical results are utilized to investigate the impact velocity, pressure distribution, and shear stress caused by the suspension on the workpiece surface. It is observed that the shear stress strongly depends on the injection pressure of the liquid suspension and is weakly dependent on the abrasive suspension concentration (the liquid suspension with different densities, viscosities, and surface tensions). Additionally, the particle behavior is investigated in order to estimate the impact velocity and to identify the impact and erosion zones of the liquid suspension on the workpiece surface. Numerical results indicate that ~50% of total particles are impinging the workpiece surface almost perpendicularly (with a mean impact angle of ~86 degrees) for the first time in the stagnation region, where they are strongly decelerated by the carrier fluid before they reach the workpiece surface. These particles, however, rebound on the surface and are reaccelerated by the carrier fluid, impinging the workpiece surface further in the radial direction. Full article

The introduction of air into a submerged annular jet will result in dispersion of the jet, which will affect the degree of enclosure of the gas–water mixing zone in the annular jet nozzle, and then have a significant impact on air suction and the formation of the foam system in the floatation process. A numerical simulation method is used to analyze the characteristics of the distribution of the axial flow velocity of annular jets, gas–phase volume, and turbulence intensity in the gas–water mixing zone in the nozzle with different air–liquid ratios, and thereby reveal the mechanism whereby gas–containing in annular jets affects the degree of enclosure of the gas–water mixing zone. The results show that as the air–liquid ratio increases, the degree of air–liquid mixing will increase and the radial flow velocity will decrease gradually, resulting in the effective enclosure of the gas–water mixing zone. Meanwhile, the dissipation of jet energy, the range of turbulent flow and the vorticity intensity will increase, but the turbulence intensity will decrease. When the gas–water mixing zone is fully enclosed, as gas–containing continues to increase, the degree of dispersion of the annular jet will further increase. Consequently, the area of the gas–water mixing zone with bounced–back water will become larger, resulting in a higher axial flow velocity, larger local turbulence intensity and larger vorticity intensity. This will lead to the dissipation of jet energy, which is not favorable for air suction. Full article

The method of drilling and blasting with explosives is widely used in rock fragmentation applications in underground construction projects, such as tunnels and caverns. However, the use of explosives is associated with rigorous safety and environmental constraints, since blasting creates toxic fumes, ground vibrations, and dust. Because of these constraints, there has been a growing interest in transitioning away from explosives-based rock fragmentation. The use of explosives-free methods could lead to continuous operation by eliminating the need for idle time with additional ventilation required to exhaust the blast fumes. This paper first presents a critical review of various methods that have been developed so far for rock fragmentation without explosives. Such methods include thermal fragmentation, plasma blasting, controlled foam injection, radial-axial splitter, and supercritical carbon dioxide. Thermal fragmentation, as the name implies, uses high heat to spall high-grade ore. However, it requires high heat energy, which requires additional ventilation as compared to normal conditions to cool the work area. Plasma blasting uses a high temperature and pressure plasma to fracture rock in a safe manner. While this method may be environmentally friendly, its usage may significantly slow tunnel development due to the need to haul one or more large energy capacitor banks into and out of the work area repeatedly. Controlled foam injection is another chemical method, whereby foam is the medium for fracturing. Although claimed to be environmentally friendly, it may still pose safety risks such as air blast or flyrock due to its dynamic nature. A radial-axial splitter (RASP) is an instrument specially designed to fracture a borehole in the rock face but only at the pace of one hole at a time. Supercritical carbon dioxide is used with the equipment designed to provide a high-pressure jet stream to fracture rock, and replaces water in these instruments. The method of soundless chemical demolition agents (SCDA) is evaluated in more detail and its merits over others are highlighted, making it a potentially viable alternative to blasting with explosives in underground excavation applications. Future work involves the optimization of SCDA for implementation in underground mines. The discussion compares the key features and limitations, and future work needs are underlined. Full article

The effects of water jet height and end dipping on cooling rate and hardenability in the Jominy end quench test were investigated to understand the Jominy test in more detail. Experimental tests were conducted under end dipping cooling condition as well as for specific water jet heights of 35, 65, and 100 mm. The thermal behavior and mechanical properties of the Jominy specimen with region were evaluated using thermocouples and hardness measurements, respectively. The effect of the water jet height on the thermal and hardness behaviors was not large; especially, the influence of water jet height was negligible when the water jet height was over 50 mm. These observations indicate that the uncertainty of the water jet height is not important during the standard Jominy end quench test. Meanwhile, during the standard Jominy test, we cannot neglect the heat flow along the radial direction of the specimen because the temperature difference between the center and surface area was not small; the maximum temperature difference was approximately 50 °C. Based on the comparative study between the standard Jominy cooling and the end dipping cooling processes, the thermal gradient along the radial direction of the specimen can be reduced with the more stable cooling condition on the Jominy end. However, the effect of temperature deviation along the radial direction of the Jominy specimen on the hardness distribution along the longitudinal direction was not large, which shows the high reliability of the Jominy end quench test. Full article

Due to the higher propulsive efficiency, lesser vibration, and better maneuverability, the water jet pump is widely applied to high-speed underwater vehicles. By taking a newly developed water jet pump system as the object, the corresponding underwater vehicle’s operating characteristics affected by different cruising speeds (15.43, 30.86, and 52.47 m/s) were investigated. The steady results reply that the cruising speed increase will result in the decline of the overall performances comprised of the head, the efficiency, the thrust, and the power. While, by using different analyzing methods, the unsteady results are listed as follows: (1) The energy loss theory denotes that the increasing cruising speed promoted the kinetic energy diffusion from the Reynolds stress and viscous stress and depress the turbulent kinetic energy production and the viscous dissipation. (2) The statistical PLS method reveals that the tip load effect on the leakage flow becomes weaker when the cruising speed becomes larger, while the effect from the scraping pressure has a completely opposite trend. (3) Further unsteady analysis implies that the increasing cruising speed makes the pressure pulsation larger and makes the radial force, the axial force, and the cloudy cavity size smaller. Full article

An experimental study on the flow pattern dynamics in a standard mixing vessel with radial baffles filled with water and induced by a pitched blade impeller pumping downward is presented. Investigation is mainly focused on detection and analysis of quasi-periodical or periodical low-frequency phenomenon connected with time- and length-scales considerably exceeding the Blade Passage Frequency (hereinafter BPF) and common turbulent eddies. This phenomenon, which is expressed as large-scale mean-flow variations, is generally known as flow Macro-Instability (hereinafter MI). It could break-down just below the liquid surface, or it crashes to the liquid surface and causes its Macro-Swelling (hereinafter MS). Our investigation was based on classical two-dimensional (2D) Particle Image Velocimetry (hereinafter PIV) measurement within 3 selected vertical planes in the vessel and subsequent analysis of the velocity field. The dominant frequencies evaluated in the selected points and overall analysis of the quasi-periodical macro-flow pattern behavior is to be shown. Identification of the quasi-periodical substructures appeared within the flow pattern was performed using the Oscillation Pattern Decomposition (hereinafter OPD) method. Observation of the macro-flow patterns confirmed presence of the macro-flow structures detected within flow pattern at the identical mixing pilot plant setup by previous investigations of the MIs phenomenon, i.e., the primary circulation loop and strong impeller discharge jet located in the lower vessel segment and the strong ascending wall current at the baffle, which break-down below the surface very often. A further important contribution of the presented work is the investigation of both flow pattern within the baffles vicinity and in the middle of the sector far from the baffle, showing a significant difference. Low-frequency periodical (or quasi-periodical) behavior of the investigated macro-structures was qualitatively confirmed by the presented results and it was quantified using the velocity dominant frequencies evaluation, as noted below. This frequency analysis brings insight into the supposed and detected interconnections between dynamics of the adjacent flow structures. Detected different flow patterns within the main plane near the baffles and in the inclined plane reveal a strong influence of the baffle presence to the local vertical flow, especially within the upper part of the vessel. Quite a different flow pattern appears tangentially in front of and behind the baffle, where a wake is revealed, indicating significant influence of the baffle on the local tangential flow. The new findings represent a contribution to better understanding the physical phenomena behind the standard mixing process. Full article