Nozzle Loss Research Articles

Optimal design of a dual-pressure radial-inflow turbine for S-CO2 cycle based on constructal theory

Based on constructal theory, a dual-pressure turbine (DPT) model for supercritical CO2 cycle is established. Seven kinds of losses, such as the nozzle, incidence, passage, windage, tip clearance, trailing and exit velocity losses, are considered in the radial-inflow turbine. The volume fraction, wheel diameter ratio and inlet pressure of the DPT are optimized, and its power output (PO) is maximized. The parameter influences on constructal results are analyzed. It reveals that the total POs after primary and twice optimizations are 1.041 MW and 1.058 MW, and are augmented by 3.89 % and 5.62 %, respectively. The total PO after triple optimization is 1.148 MW, and the corresponding optimal volume fraction, wheel diameter ratio and inlet pressure are 0.194, 0.350 and 10600.2 kPa, respectively. The PO of DPT after optimization is improved by 14.57 %, and its performance is obviously improved by optimizing three variables. Among the discussed parameters, the total mass flow rate has a more significant effect on the triple maximum PO. The results supply valuable guidelines for the turbine designs of supercritical CO2 cycles.

Experimental study of underwater plasma arc penetration parameters for oil wellheads

Dismantling abandoned oil wellheads is a central aspect of the decommissioning of production facilities. A wellhead consists of multiple layers of conductive oil casing nested with nonconductive cement rings. Plasma-arc cutting is expected to be used in abandoned wellhead demolition owing to its high processing efficiency for conductive materials. Currently, no reports are available on the operating parameters of plasma-arc cutting in oil wellhead dismantling. This study experimentally investigated the penetration parameters of an underwater plasma arc in abandoned wellheads. The stand-off distance, penetration angle, nozzle diameter, plasma arc current, and gas flow rate were considered as the main factors affecting the penetration effect. A composite workpiece consisting of 10 mm thick mild steel and 30 mm thick cement blocks was used to simulate a small segment of an oil wellhead. The penetration depth, removal volume, penetration specific energy, and nozzle loss were used as comprehensive evaluation indicators for optimizing the penetration parameters. Based on the results, the experimental phenomena during penetration were explained and recommended values of the underwater plasma arc processing parameters were provided. This study may advance the development of plasma arc cutting for the demolition of abandoned wellheads.

Comparative analysis of energy losses in hydrogen and helium turbo-expanders for hydrogen liquefiers

Liquid hydrogen plays an essential role in the large-scale hydrogen energy development. Claude cycle is the baseline process for most industrial hydrogen liquefactions. The hydrogen turbo-expander is the crucial component, determining the system efficiency and reliability. In this paper, a hydrogen turbo-expander is designed by using a mean-line method with loss models which have been validated against experimental data of helium turbo-expanders. Geometrical and velocity field similarity can be achieved between a hydrogen turbo-expander and a helium turbo-expander by selecting the same specific speed and the characteristic ratio. CFD simulations are performed to illustrate the internal flow field and loss mechanisms in helium and hydrogen turbo-expanders. The CFD predictions of passage efficiencies agree well with that by the loss models, demonstrating the mean-line design method and loss models can be used to guide the preliminary design of hydrogen turbo-expanders. The CFD simulation results show that the passage efficiency of hydrogen turbo-expander is 1.88% higher than that of helium expander. Due to a higher sound speed and a lower viscosity, the hydrogen turbo-expander has smaller nozzle loss, incidence loss and impeller passage compared with the helium turbo-expander. The lower viscosity of hydrogen results in a higher tip leakage flow, and the tip leakage accounts for 1.09% and 1.23% of total mass flow in helium and hydrogen turbo-expanders, respectively. Since the cross flow over the blade tips can increase the vortices and secondary flow losses in impeller passages, it is necessary to reduce tip clearance in the design of hydrogen turbo-expanders.

Design Parameter Influence on Losses and Downstream Flow Field Uniformity in Supersonic ORC Radial-Inflow Turbine Stators

The design of organic Rankine cycle (ORC) turbines often requires dealing with transonic flows due to the cycle efficiency requirements and the matching of the temperature profiles with heat sources and sinks, as well as the nature of organic fluids, often featuring high molecular weight. Consequently, the use of convergent–divergent turbine stators has been widely established as a solution in the published literature for use in both axial- and radial-inflow machines. With respect to the latter layout in particular, the available design guidelines are still limited. The present work shows the results of an investigation into a series of ORC radial-inflow convergent–divergent nozzles that differ with respect to the vane count and the designed metal angle of the outlet. These stators were designed by fitting the divergent portion of a sharp-edged minimum-length nozzle, designed by means of the method of characteristics (MoC) adapted to dense gases, into a radial-inflow turbine stator. The geometries were analysed by means of steady-state RANS CFD calculations, and the results were used to assess the influence of the design parameters on the nozzle losses and downstream flow field uniformity, showing that conflicting trends exist between optimum stator efficiency and optimum downstream flow field uniformity.

МОДЕЛЮВАННЯ ДВОФАЗНОГО ПОТОКУ ПРИ ХОЛОДНОМУ ГАЗОДИНАМІЧНОМУ НАПИЛЮВАННІ

The one-dimensional gas-dynamic model for calculation of acceleration and heating of particles which takes into account space from the nozzle outlet to the substrate has been improved. One cycle of particle acceleration by a gas flow can be divided into three parts: mixing a gas flow with powder; particle movement and acceleration in the divergent part of the nozzle; the movement of gas-powder flow from nozzle outlet to substrate. It is known that cold spray coating formation depends on the normal component of particle velocity towards the surface to be sprayed. Each material obtains its value of the critical velocity when the coating formation process starts. At particle velocities above critical, they adhere to the substrate and form coating due to plastic deformation of particles, and at velocities below critical value surface erosion or spraying with low efficiency is observed. One of the features of the process of cold gas-dynamic spraying is a relatively small distance between the nozzle outlet and the deposited surface, which leads to the occurrence of the reverse flow of the gas stream (bow shock) reflected from the substrate. The reflected flow significantly inhibits the trajectory of particles of sprayed powder which need to be investigated. Impact temperature and velocity of aluminum and nickel particles with size 25 microns with a substrate for SK-20 supersonic nozzle of DIMET-405 low-pressure cold spraying machine has been calculated. Although the one-dimensional isentropic gas-dynamic model, which is usually used to calculate flow parameters, describes flow only along the axis of the nozzle, excluding heat transfer with nozzle and friction loss on the inner walls, which leads to overestimated results of calculations, its utilization allows to optimize the geometry of the nozzle channel and develop a technological process of the spraying process. Mathematical modeling of two-phase flow dynamics of the cold spraying process was performed using the MATLAB software. Comparison of simulation results with experimental data to determine the flow velocity and temperature showed that the theoretical calculations differ from the experimental ones by no more than 10 %.

Fullerene-like Nanoparticles of WS2 as a Promising Protection from Erosive Wear of Gun Bore Nozzles

Background: Erosive wear causes increase in the bore diameter of firearms barrels and nozzles. Most responsible factors for this erosion are friction and heat generated during the shot. Protection from erosive wear is very important for gun tube life cycle, and various protection methods are used: adding phlegmatizers in gunpowder composition or applying protective layers on the gun bore inner surface. Objective: In this research, a possibility is examined to protect the surface of a nozzle exposed to gunpowder erosion applying a layer of tungsten disulfide fullerene-like nanoparticles, IF-WS2, known as outstanding solid lubricant of a great mechanical resistance. Methods: Nanoparticles on the nozzle surface before and after the gunfire tests were observed using scanning electron microscopy/energy dispersive X-ray spectroscopy. Gunfire tests were performed on designed erosion device. Temperatures in the defined position near the affected surface were measured with thermocouples and compared for the nozzles with and without nanoprotection, as well as the nozzle mass loss after each round. Results: For the sample with IF-WS2 lower temperatures after firing and lower mass losses were observed. Mass loss after first round was 25.6% lower for the sample with protective nanoparticles layer, and the total mass loss was about 5% lower after five rounds. After the first round the nozzle without IF-WS2 was heated up to a temperature which was for 150.8°C higher than the nozzle with IF-WS2. Conclusion: Protective function of IF-WS2 is the most pronounced for the first round. The observed results encourage its further application in firearms gun bores protection.

Experimental and Numerical Investigation of Small-Scale Tesla Turbines

Abstract Interest in small-scale turbines is growing mainly for small-scale power generation and energy harvesting. Conventional bladed turbines impose manufacturing limitations and higher cost, which hinder their implementation at small scale. This paper focuses on experimental and numerical performance investigation of Tesla type turbines for micro power generation. A flexible test rig for Tesla turbine fed with air as working fluid has been developed, of about 100 W net mechanical power, with modular design of two convergent-divergent nozzles to get subsonic as well as supersonic flow at the exit. Seals are incorporated at the end disks to minimize leakage flow. Extensive experiments are done by varying design parameters such as disk thickness, gap between disks, radius ratio, and outlet area of exhaust with speeds ranging from 10,000 rpm to 40,000 rpm. A quasi-one-dimensional (1D) model of the whole setup is created and tuned with experimental data to capture the overall performance. Major losses, ventilation losses at end disks, and nozzle and exhaust losses are evaluated experimentally and numerically. Effect of design parameters on the performance of Tesla turbines is discussed.

Nozzle Wear and Pressure Rise in Heating Volume of Self-blast Type Ultra-high Pressure Nitrogen Arc

This paper reports on experiments with ultra-high pressure nitrogen arcs in a self-blast type switch design. The effect of filling pressure on nozzle mass loss and pressure-rise in the heating volume were investigated. An arc current peak of 130 A at 190 Hz and a fixed inter-electrode gap of 50 mm were used throughout the experiment. The arc burns inside a polytetrafluoroethylene nozzle with a gas outflow vent in the middle. Nitrogen filling pressure of 1 bar, 20 bar, and 40 bar was tested, which also covers the supercritical region. Moreover, to study the effect of vent size on blow pressure near current zero, three different vent dimensions were investigated. By increasing the filling pressure, the energy deposited in the arc increases as a result of increased arcing voltage. It was observed that the pressure-rise in the heating volume is linked to the filling pressure, while the vent size plays a crucial role in the blow pressure near current zero. The nozzle mass loss per unit energy deposited in the arc is found to be independent of the filling pressure.

CFD research on particle movement and nozzle wear in the abrasive water jet cutting head

Particle velocity and movement in the high-pressure abrasive water jet (AWJ) heading are significant jet properties which deserve a better understanding for improving AWJ machining performance. In this paper, particle acceleration and movement trajectory in the jet field within AWJ cutting head were conducted based on the Euler-Lagrange approach and the discrete particle model (DPM) from a computational fluid dynamics (CFD) simulation study. The particle inlet position, particle inlet angle, and converge angle of focus tube were taken into consideration in the physical model. The models were then assessed qualitatively and quantitatively by previous experiment data. The results indicated that a particle inlet located at a high position could increase particles’ exiting velocity and decrease nozzle wear. A steeper abrasive feed angle would improve the particle acceleration process and reduce radial velocity, resulting in less nozzle weight loss. The effects of converging part angle were analyzed as well. The obtained results would improve the machine efficiency of the workpiece, extend nozzle lifetime, and guide the future design of AWJ nozzle.

Experimental and numerical analysis of thermo-chemical erosion in gun steel

Various factors of thermo-chemical erosion process in gun steel were analysed. The factors are mainly related to the thermal load of gun barrel inside surface, characteristics of barrel surface and chemical interactions between propellant combustion products and barrel surface. The experimental simulation of conditions in gun barrel was carried out by vented vessel firings in the device based on modification of 37 mm M39 gun. The nozzle mass loss during firing was the measure of gun steel erosion. The main thermal factor of erosion is maximum nozzle inner surface temperature. This temperature was determined experimentally by micro thermocouples measurements at specified distance away from the inner surface and by numerical analysis of the inverse heat conduction problem. Modelling of two-phase flow of propellant combustion products and unburned propellant grains in the vented vessel and heat transfer to the nozzle were conducted using developed 1-D interior ballistic code and CFD simulation in FLUENT. Influence of different propellants, TiO2/wax wear reducing liner and tungsten-disulfide nanoparticles layer on nozzle erosion was analysed. Good agreement between experimental and computational results was achieved.

303 噴流推力ならびにノズル損失測定装置の製作と性能評価(流体工学I)

303 噴流推力ならびにノズル損失測定装置の製作と性能評価(流体工学I)

Performance deterioration of the governing stage nozzle caused by solid particle erosion in the steam turbine

In the steam turbine, solid particle erosion on a nozzle cascade is known to damage the profile and surface smoothness of the cascade, which increases the flow loss of steam. The present study aims to make clear the relations between nozzle loss and surface degradation, aerodynamic parameters, as well as the shape, location, and size of the erosion notch. A series of numerical simulations were conducted to model the aerodynamic performance of various existing eroded nozzles. The results indicate that the nozzle loss caused by the surface degradation shows an approximate linear decrease with an increase in notch depth. The nozzle loss caused by the erosion notch increases with either a decrease in the exit Mach number or an increase of the notch area. For the same erosion-induced weight loss of the nozzle, the asymmetric notch and local notch cause more nozzle loss than the symmetric notch and quasi-global notch. This means that the performance deterioration can be reduced to a minimum value if the erosion is uniform along the span-wise of the nozzle. In addition, a combined experimental and numerical investigation is conducted to explore the erosion damage process of the nozzle. The result suggests that the eroded nozzle should be replaced by a new nozzle before the notch begins to propagate.

The optimization of rough surface supersonic nozzles

In this work, a theoretical optimization study of compressible gases adiabatic flows was conducted for conical nozzles with internal rough surface. A mathematical model was developed for allowing the determination of thrust accounting for nozzle friction and divergence losses. In the first part of the study, it is shown that in rough surface nozzles there are critical values of the nozzle opening half angle, under which, additional increase in gas velocity is not obtained. It is also observed that the minimum nozzle opening half angle value increases as the flow velocity and the nozzle internal surface roughness increase. In the second part of the study, it is shown that there are optimal values of nozzle opening half angle for minimum hydraulic loss across the nozzle, for each combination of the hydraulic resistance caused by the internal surface roughness and the nozzle outlet cross sectional area.

Studies on ejector-venturi fume scrubber

Experimental studies on diesel fume scrubbing have been conducted in a down-flow type liquid-jet ejector-venturi scrubber. The fume particulates have been captured in the throat of the ejector-venturi by a mechanism involving inertial impaction and impingement. The effect of nozzle geometry and the motive fluid flow rates on the suction created and the volumetric fume aspiration rates have been analyzed, in order to select the optimum nozzle geometry. Using the optimum nozzle geometry the efficiency of fume collection has been experimentally investigated as function of various hydrodynamic parameters. A theoretical analysis has been performed to interpret the experimental findings and determination of nozzle loss coefficients.

Three-Dimensional Modeling of a Helixchanger® Heat Exchanger Using CFD

Detailed three-dimensional computational fluid dynamics (CFD) simulations have been performed to explore the performance of a helically baffled heat exchanger, commercially referred to as the Helixchanger ® heat exchanger. The CFD simulations employ the HEATX computer simulation program, which is designed for the simulation of shell-and-tube heat exchangers. The simulation accounts for the complex helical geometry of baffles, leakages, and nozzle entrance and exit. Three cases are presented that correspond to helix angles of 10°, 25°, and 40°, defined with respect to the radial axis. Inspection of the computed flows reveals distinct inner and outer regions, with the outer region showing a very desirable plug flow characteristic. The inner region, however, displays recirculation zones due to back mixing at the small helix angle, which suggests potential vibration problems but also creates a desirable temperature uniformity. A comparison with plug flow showed that the helically baffled heat exchanger had a fluid turn ratio of 0.64, 0.78, and 0.77 for the 10°, 25°, and 40° helix angles, indicating more overall plug-like flow for the higher helix angles. Computed pressure drops compare reasonably well with ABB Lummus Heat Transfer correlation results, although nozzle entrance and exit losses require further study.

メタン燃料を用いたロケットエンジンノズル性能特性

Performance of the methane fueled rocket nozzles are numerically investigated using computational fluid dynamics approach. A simple set of chemical reactions and kinetics for methane/oxygen nozzle flow is proposed. The chamber pressure, mixture ratio and size of the nozzle are parametrically changed to study the influence of characteristic rocket engine design parameters on nozzle losses. The amount of dissociation is high when the chamber pressure is low and the kinetic loss becomes dominant compared to the other nozzle losses. The peak specific impulse is achieved at a higher mixture ratio region as the chamber pressure increases. The chemical non-equilibrium flow appears mainly at down stream region of the nozzle throat. The influence of the chemical non-equilibrium effect decreases as the chamber pressure increases. Supersonic chemically reactive gas stays longer in the nozzle as the size of the nozzle become larger and the amount of recombination increases which decreases the kinetic loss. When the chamber pressure is high, the kinetic loss becomes small and the effect of the size of nozzle also becomes small.

The effects of system and geometric parameters on abrasive water jet nozzle wear

Nozzle wear dependence on abrasive water jet system parameters and nozzle geometry is experimentally investigated. Experimental procedures for evaluating long term and accelerated nozzle wear are discussed. Accelerated wear tests are conducted to study the effects of nozzle length, inlet angle, diameter, orifice diameter, abrasive flow rate, and water pressure on wear. An empirical model for nozzle weight loss rate is developed and is shown to correlate well with experimental measurements.

Strutjet Engine Performance

To increase the technology readiness level of hypersonic scramjet technology, an innovative strut-based dualmoderamjetenginedesign capableofpoweringa hypersonicvehicleatspeedsfrom Mach4to 8isinvestigated.Two versions of the engine are under development: a dual-mode (ramjet/scramjet )engine formissile applicationsand a rocket-based combined cycle engine for space access. This paper will discuss the features of the dual-mode engine design and how they contribute to overall engine performance. Engine component performance was evaluated using a combination of analysis and component testing. Inlet performance data (mass capture, pressure recovery, and inlet/isolator pressure ratio ) were obtained from wind-tunnel testing and correlated with model and full-scale computational e uid dynamics (CFD)analyses. Combustorperformance data (combustion efe ciency, fuel-injection performance, and pressure distributions ) were obtained from full-scale direct-connect combustor testing. Nozzle losses and efe ciency were obtained from CFD analysis. Performance parameters derived from these component tests and analyses were fed into a standard hypersonic engine cycle code to predict e ight engine performance. The demonstrated component performance values were extrapolated to determine predicted component performance at the end of engine development, which were used to compute the vision e ight engine performance.

A Study of Nozzle Wear in Abrasive Entrained Water Jetting Environment

Parameters that influence nozzle wear in abrasive water jetting environment are identified and classified. Regular and accelerated wear test procedures are developed to study wear under actual and simulated conditions, respectively. In addition to exit diameter growth, nozzle weight loss and bore profiles are shown to better characterize and explain the wear phenomenon. The effect of nozzle geometry on wear is investigated by means of the developed test procedures and measures of wear. [S0742-4787(00)00202-2]

Thrust Enhancement in Hypervelocity Nozzles by Chemical Catalysis

In the hypersonic flight regime, the air-breathing supersonic combustion ramjet (scramjet) has been shown to be a viable propulsion system. The current designs of scramjet engines provide performance benefits only up to a Mach number of 14. Performance losses increase rapidly as the Mach number increases. To extend the applicability of scram'jets beyond Mach 14, research is being conducted in the area of inlet and wave drag reduction, skin-friction and heat-transfer reduction, nozzle loss minimization, low-loss mixing, and combustion enhancement. For high Mach number applications, hydrogen is the obvious fuel choice because of its high energy content per unit mass in comparison with conventional fuels. These flight conditions require engines to operate at supersonic internal velocities, high combustor temperatures, and low static pressures. The high static temperature condition enhances the production of radicals such as H and OH, and the low-pressure condition slows the reaction rates, particularly the recombination reactions. High-temperature and low-pressure constraints, in combination with a small residence time, result in a radical-rich exhaust gas mixture exiting the combustor. At high Mach number conditions (due to low residence time), H and OH do not have enough time to recombine ; thus, a significant amount of energy is lost as these high-energy free radical are exhausted. The objective of the present study is to conduct a flowfield analysis for a typical nozzle geometry for NASP-type vehicle to assess for thrust enhancement in hypervelocity nozzles by substituting small amount of phosphine for hydrogen.