Effect of Nozzle Outlet Type On the Flow Field Velocity and Impact Pressure of High Pressure Water Jet Peening

Water jet peening can effectively improve the fatigue strength of metal materials, and the outlet shape of nozzle greatly affects the effect of water jet peening. In this paper, the effects of nozzle outlet shape on water jet velocity and impact pressure is studied by numerical simulation, and the jet velocity and dynamic pressure for different standoff distances are also discussed. The results show that the water jets of square, circular and triangular nozzles are highly concentrated, and the water jet of elliptical nozzles is the most divergent. The axial velocity attenuation of the square nozzle along the axis is slower than that of the other three nozzles. The water axial velocity of the elliptical nozzle attenuates fastest and the length of the core segment of the water jet is the smallest. Within a certain axial distance, the dynamic pressure area in the central area of the elliptical water jet is obviously larger than that of the other three nozzles, and the effective treatment range is large, which is more suitable for the welding surface strengthening operation.

Effect of Nozzle Outlet Shape on Cavitation Behavior of Submerged High-Pressure Jet

A submerged high-pressure water jet is usually accompanied by severe cavitation phenomenon. An organ pipe nozzle can greatly improve the cavitation performance of the jet, making use of the self-excited oscillation of the flow. In order to study the effect of organ pipe nozzles of different nozzle outlet shapes on cavitation behavior of submerged high-pressure jet, in this paper we build a high-pressure cavitation jet experiment system and carried out a high-speed photography experiment to study cavitation cloud characteristics of a high-pressure submerged jet. Two organ pipe nozzles with and without a whistle were compared. The dynamic characteristics of the cavitation cloud was extracted through the POD method, it was found that the result effectively reflect the dynamic characteristics of the cavitation jet. The reconstruction coefficients of mode-1 obtained by the POD can better reflect the periodic time-frequency characteristics of cavitation development. The effect of the nozzle outlet shape on the cavitation behavior of organ pipe nozzle was analyzed based on unsteady numerical simulation, and it was found that the jet generated by the nozzle with a divergent whistle had a larger vorticity in the shear layer near the outlet. Further, stronger small-scale vortex and much severe cavitation occurred from the nozzle with a divergent whistle.

Numerical Study on Effects of Geometric Parameters on the Release Characteristics of Straight Sudden Expansion Gas Extinguishing Nozzles

In order to guide the optimization design of the nozzle of the aircraft-fixed gas fire extinguishing system, we studied the influence of nozzle geometric parameters including outlet–inlet area ratio, length–diameter aspect ratio, and wall roughness on the distribution of pressure and velocity in the nozzle on the basis of CFD simulations. Although the structure of the nozzle is axisymmetric, the spatial distribution of the pressure and velocity during the flow and release of gas extinguishing agent is not completely symmetric. It was found that both of the outlet–inlet area ratio (δ) and the length–diameter aspect ratio (ξ) had a significant impact on the distribution characteristics of the pressure and axial velocity in the nozzle. With the increase of δ, the average pressure at the outlet cross-section of the nozzle decreased monotonically, while the average axial velocity at the outlet increased approximately linearly. When ξ≥2, the uniformity of the pressure and velocity distribution at the nozzle outlet was significantly improved. Moreover, with the increase of ξ, the average pressure and the average axial velocity of the outlet both showed a non-monotonic change trend, and the optimal value of ξ should be about 3.0. Compared with δ and ξ, the influence of the nozzle wall roughness (εN) on the flow and release characteristics of the extinguishing agent was weak. With the increase of εN, the average pressure of the nozzle outlet increased slightly, while the average axial velocity at the nozzle outlet decreased slightly.

Analysis on Inlet Nozzle Design Geometry of Tesla Turbine

Tesla turbine is a bladeless turbine that uses a set of discs arranged at a certain distance to rotate and one of the parameters controlling turbine performance is the inlet parameter. The purpose of this study is to optimize the design of the inlet nozzle and analyse its effects on the flow of the fluid. A total of four nozzle designs have been proposed using CATIA while the Solidworks Flow Simulator is used to analyse the fluid flow at various inlet velocities. Then, the most efficient design is then fabricated via 3D printing and put to test by connecting it with the actual Tesla turbine model. Through the results obtained from the analysis, it is observed that Design 4 is the most efficient of all tested nozzles and the highest RPM and output voltage achieved from the nozzle is 7940 RPM and 13.56 V. The difference in velocity and pressure increases as the area of the nozzle outlet reduces, whereas nozzle efficiency decreases as the inlet velocity increases. The result of this study is a source material for increasing the effectiveness of an alternative power turbine in generating electricity by manipulating the inlet design geometry.

Design and Experiment of Hydraulic Scouring System of Wide-Width Lotus Root Digging Machine

In response to the problems of small working width and low operating efficiency of existing hydraulic scouring lotus root harvesters, a wide-width hydraulic scouring system was designed based on a wide-width self-propelled lotus root harvester. The main parameters of the key components were determined through theoretical analysis of the water flow energy of the hydraulic scouring system pipelines. An experimental study was also carried out on the main factors affecting the working performance of this hydraulic scouring system. Through hydrodynamic simulation tests, the effect of nozzle type and constriction section structure on the turbulence intensity at the nozzle outlet and the pressure loss per unit mass of fluid between the nozzle inlet and outlet sections were compared and analysed. The test yielded conical-cylindrical nozzle geometry parameters for nozzle inlet diameter of 40 mm, shrinkage angle of 30°, nozzle outlet straight section length of 20 mm, nozzle outlet diameter of 16 mm, the nozzle had better flushing performance. Single-factor tests were carried out with nozzle outlet pressure, scouring angle and nozzle height from the mud surface as influencing factors. Based on the optimum effective scour depth, a three-factor, three-level Box–Behnken central combination design test was completed. The primary and secondary factors affecting the effective scouring depth were obtained in the following order: nozzle height from the mud surface, nozzle outlet pressure, and scouring angle. Finally, the performance test of the hydraulic scouring system was completed. Results showed that when the nozzle outlet pressure of 0.30 MPa, the scouring angle of 60° and the nozzle height from the mud surface of 0 mm, the effective scouring depth was 395 mm, the lotus root floating rate was 90% and the damage rate was 5%, which meet the requirements of lotus root harvesting operations.

Hotspot Cooling Performance for Submerged Confined Two-Phase Jet Impingement Cooling

Jet impingement can be particularly effective for removing high heat fluxes from local hotspots. Two-phase jet impingement cooling combines the advantage of both the nucleate boiling heat transfer with the single-phase sensible cooling. This study investigates two-phase submerged jet impingement cooling of local hotspots generated by a diode laser in a 100 nm thick Hafnium (Hf) thin-film on glass. The jet/nozzle diameter is ∼1.2 mm and the normal distance between the nozzle outlet and the heated surface is ∼3.2 mm. Novec 7100 is used as the coolant and the Reynolds numbers at the jet nozzle outlet range from 250 to 5000. The hotspot area is ∼ 0.06 mm2 and the applied hotspot-to-jet heat flux ranges from 20 W/cm2 to 220 W/cm2. This heat flux range facilitates studies of both the single-phase and two-phase heat transport mechanisms for heat fluxes up to critical heat flux (CHF). The temporal evolution of the temperature distribution of the laser heated surface is measured using infrared (IR) thermometry. This study also investigates the nucleate boiling regime as a function of the distance between the hotspot center and the jet stagnation point. For example, when the hotspot center and the jet are co-aligned (x/D = 0), the CHF is found to be ∼ 177 W/cm2 at Re ∼ 5000 with a corresponding heat transfer coefficient of ∼58 kW/m2.K. While the CHF is ∼ 130 W/cm2 at Re ∼ 5000 with a jet-to-hotspot offset of x/D ≈ 4.2.

Investigation on gas induction of liquid–gas ejector in jet loop reactor

Liquid–gas ejector as a key component of jet loop reactor (JLR), plays an important role in the continuous production of gas–liquid mixing reaction. In this paper, a formula for estimating the gas induction of the ejector is presented. The effects of nozzle radius and mixing length on gas induction of liquid–gas ejector for gas–liquid mixing are simulated, and the formula is verified. Focusing on the efficiency and gas induction, the geometrical parameters are analyzed for the same cases, so that the performance of the ejector can be thoroughly understood. The results show that the optimum mixing section length to diameter ratio (LDR) is about 5–7, and the decrease of nozzle outlet radius can increase the gas induction, which provides a reference for the evaluation of gas induction for liquid–gas ejector and has crucial guiding significance for the design of nozzle and mixing section of liquid–gas ejector in industry.

Performance Prediction of a Multi-Stage Ammonia-Water Turbine Under Variable Nozzle Operation via Machine Learning

This study proposes machine learning models to predict the performance of a multi-stage ammonia-water radial turbine using variable nozzle operation under different operating conditions. A 1.2 MW four-stage ammonia-water radial turbine is firstly designed. Then, the one-dimensional off-design simulation model is developed based on the geometric parameters to mainly evaluate the effects of different nozzle outlet angles and turbine inlet temperatures on the turbine performance. A set of data, which consists of 10,000 training points based on one-dimensional model, is used to train the proposed two high-dimensional model representation (HDMR) methods. The forward HDMR model predicts the mass flow rate, turbine outlet temperature, turbine power and turbine efficiency for any combination of turbine nozzle outlet angle and turbine inlet temperature, while the reverse HDMR model predicts the mass flow rate, turbine outlet temperature, turbine efficiency and turbine nozzle outlet angle for any combination of turbine power and turbine inlet temperature. The two HDMR models are validated using 238 sets of separated test data. The results show that the minimum coefficients of determination (R2) of forward HDMR model and reverse HDMR model are 0.9837 and 0.9953, respectively. The maximum relative errors of two HDMR models are below 1.6822%, so the quality of the proposed machine learning methods is high. The overall performance maps of multi-stage ammonia-water radial turbine under the variable nozzle operation method are constructed based on the reverse HDMR model. The reverse HDMR model is helpful in monitoring the healthy operation state of turbine.

Influence of nozzle outlet diameter on the atomization process of zirconia dry granulation

In order to predict the atomization characteristics of the atomization process of zirconia dry granulation accurately, the influence of nozzle outlet diameter on the atomization characteristics of the atomization process of zirconia dry granulation is analyzed. The VOF method and RNG k-ε turbulence model are applied to numerically analyze the flow field of pressure-swirl nozzles with different outlet diameters of the atomization process of zirconia dry granulation, and the effects of outlet diameters on the spray cone angle, liquid film thickness, pressure distribution and velocity distribution are analyzed. The result shows that when the outlet diameter is increased from 3 to 4 mm, the diameter of air core and the outlet velocity of atomized liquid are increased, the spray cone angle is increased from 30.5° to 59.7° while the liquid film thickness is decreased, but when the outlet diameter is increased to 5 mm, the diameter of air core and the outlet velocity of atomized liquid are decreased, the spray cone angle is decreased to 27.6°, while the thickness of liquid film is decreased. The spray cone angle, moisture content of zirconia particles corresponding to nozzles with different outlet diameters are measured by the design of atomization experiment platform and the microstructure of zirconia particles are observed, which verifies the correctness of numerical analysis. Taking the atomization performance of nozzle into consideration, the pressure-swirl nozzle with the outlet diameter of 4 mm is better suitable for the atomization process of zirconia dry granulation.

Numerical investigation on the performance of impeller back seal configuration in a supercritical CO2 radial-inflow turbine

Radial-inflow turbine is a core component in supercritical CO2 (SCO2) Brayton cycle. The leakage from the nozzle outlet towards the impeller back brings a great challenge to the efficiency and security of the power system. In this paper, the labyrinth seal (LS) and dry gas seal (DGS) are arranged on the impeller back of a SCO2 radial-inflow turbine and the influence on the comprehensive performance is investigated. Results demonstrate that both LS and DGS configurations can significantly reduce leakage of the impeller back and DGS configuration performs better. Compared with the configuration without leakage, the power and efficiency of DGS configuration are only reduced by 0.27% and 0.35% respectively. The seal clearance and the inlet width have a greater effect on LS configuration. The thermo-mechanical seal deformation values of DGS configurations are all less than 8 μm, which verifies the feasibility. Finally, a novel combined seal configuration with both LS and DGS is proposed and excellent performance is achieved, providing a potential approach for the sealing problem of SCO2 radial-inflow turbine.