Injection Of Water Droplets Research Articles

Analysis of Water Droplet Interaction with Turbulent Premixed and Spray Flames Using Carrier Phase Direct Numerical Simulations

ABSTRACT Carrier-phase direct numerical simulations (DNS) of n-heptane/air combustion with water droplet injection are reported in this paper. The influence of water droplet injection has been analyzed for statistically planar gaseous premixed flames and spray flames where the fuel is supplied in the form of monodisperse fuel droplets. The effects of water injection in both types of flames are compared, including their sensitivities on the initial diameter of water droplets. The simulations are based on an Eulerian-Lagrangian-Lagrangian approach to consider the multi-phase interaction and the simultaneous effects of n-heptane and water droplets. It is shown that the two types of flames are different in terms of several aspects. In particular, the spray flames are characterized by lower temperatures, and their propagation speed is lower than for premixed flames. The main reason for these differences lies in the gaseous equivalence ratio experienced by the reaction zone. For the cases investigated here, where the overall equivalence ratio is unity, the spray combustion occurs under predominantly fuel-lean conditions. Furthermore, the flame temperature is influenced by the initial diameter of water droplets, which affects the strength of thermal expansion within the flame. This in turn influences the evaporation characteristics of both fuel and water droplets due to different residence times within the flame. Although the effects of water droplets on the combustion mode are dependent on the relative position within the spray flame, the net effect is a partial shift from non-premixed to premixed mode. At the same time, the spray combustion occurs under relatively fuel-richer conditions with water injection and these trends appear consistently in laminar and turbulent flows.

Numerical evaluation of the interaction between corona discharge and particles/droplets

Effects of density, relative permittivity, diameter and mass concentration of typical particle/droplet on the corona discharge process were numerically evaluated. Results demonstrate that the inhibition effect exerted by particles/droplets on the discharge current enhances with the decreasing density and the increasing relative permittivity of particles/droplets. Submicron sulfuric acid aerosol droplets with a concentration of several tens mg/m3 result in a current decrease of more than 20%. The injection of water droplets with a diameter of 5 µm and a mass concentration of 50 g/m3 leads to a reduction in the current by 10%− 100%. A smaller diameter and a higher mass concentration of water droplets result in a stronger inhibition effect on the discharge current. In an electrostatic precipitator containing several discharge electrodes, the inhibition effect leads to a difference in the discharge current at different discharge electrodes. Spraying water droplets near the collection electrode or from multiple surfaces results in a weaker influence on the corona discharge process than spraying from the inlet. The effect of the initial velocity of sprayed water droplets on the discharge current is negligible.

Numerical Prediction of Long-Term Droplet Erosion and Washing Efficiency of Axial Compressors Through the Use of a Discrete Mesh Morphing Approach

Abstract Online water washing represents an operation strategy commonly used to reduce compressor performance deterioration due to blade fouling. Since this kind of washing is applied when the machine operates close to full load conditions, injected droplets are strongly accelerated and consequently impact the rotor blades at high velocity, thus inducing undesirable phenomena like erosion. Here, we present a novel technique to study long-term water droplets erosion by also considering the geometry modification caused by droplets impacts. Two-phase unsteady numerical simulations were carried out, considering the injection of water droplets and their transport across the fluid flow in the first part of a real compressor, which is modeled in the region extending from the inlet to the rotor blades of the first stage. Simulations are performed on the whole machine to account for the asymmetric distribution of the spray injectors, the machine struts, inlet guide vanes (IGVs), and rotor blades. The k−ɛ realizable turbulence model with standard wall functions was coupled with the discrete phase model to track injected droplets motion. Droplets-wall interaction is modeled following the Stanton–Rutland approach aiming at detecting the effect of droplet impact (deposit, rebound, and splashing) depending on the impact conditions. Moreover, a semi-empirical erosion model developed by the authors was used to evaluate the erosion induced by the droplets injection. Material removal due to erosion is converted into nodal mesh displacement that is used by a secondary routine to implement the mesh morphing scheme. The mesh modification is applied at discrete steps to reduce the computational load. This technique is adopted to account for the blades geometry modification due to water droplet erosion leading to performance losses. Moreover, an estimation of the compressor operating life before maintenance operations is given and the water washing efficiency during the whole life of the machine is evaluated by means of proper indices. At the end of the simulation workflow, erosion phenomena are observed in all the compressor regions, especially in the rotor where erosion peaks are reached at the hub of the blades leading edge. The rotor blades wet surface was found to remain almost constant at around 50% during compressor water washing. Erosive phenomena were proved to evolve nonlinearly with time indicating the need to account for the geometry modification for obtaining an accurate prediction of the long-time process.

Effects of water droplet injection on turbulent premixed flame propagation: a direct numerical simulation investigation

The influence of water droplet injection on the propagation rate of statistically planar stoichiometric n-heptane-air flames has been analysed based on three-dimensional carrier phase Direct Numerical Simulations for different turbulence intensities and different initially mono-sized droplets. It has been found that most water droplets do not completely evaporate within the flame due to their large latent heat of evaporation for the conditions considered here. Thus, the cooling effect due to the extraction of latent heat during the evaporation of water droplets dominates over the dilution of the concentration of reactants and gives rise to smaller reaction rate of reaction progress variable and thicker flame front than in the corresponding premixed turbulent flame without droplets. These effects (a) strengthen with decreasing droplet size due to higher rate of evaporation for smaller droplets, but (b) weaken with an increase in turbulence intensity. The interaction of water droplets with the flame affects the density-weighted displacement speed through its reaction and molecular diffusion components and the magnitudes of these components remain much greater than the components due to cross-scalar dissipation rate and two-phase coupling. The flame-water droplet interaction for the parameter range considered here acts to reduce the mean density-weighted displacement speed, consumption speed and turbulent flame speed, and this reduction becomes increasingly prominent with decreasing droplet diameter. However, it has been found that the presence of water droplets does not alter the qualitative nature of the strain rate and curvature dependences of both density-weighted displacement speed and consumption speed for the range of parameters considered here, but the correlation strength is altered by the presence of water droplets.

Investigation of the effect of water droplet injection on condensation flow of different nozzles geometry

Investigation of the effect of water droplet injection on condensation flow of different nozzles geometry

Effect of water nano-droplet injection on steam ejector performance based on non-equilibrium spontaneous condensation: A droplet number study

Condensation and evaporation processes in high velocity flowing steam within ejectors profoundly influence the performance of these devices. In the current study, the effects of water droplet injection in the inlet of the primary nozzle on the condensation and evaporation processes are investigated through the wet steam model. The findings reveal that the existence of liquid droplets in the steam related to the inlet of the primary nozzle has effects on the two-phase parameters, shock waves intensity, entrainment ratio, mixing layer growth and two-phase heat, such that these parameters are minimized or maximized for a specific number of droplets. The inlet wetness in the primary nozzle provides a delay in the condensation shock, and the maximum delay happens in the wetness 0.4%. In the case of using 2.0×1017 droplets with 17.5 nm radius (wetness 0.4%), in comparison with the case of without the droplets at the inlet, the entrainment ratio, primary mass flow rate, and secondary mass flow rate reduce by 2.79%, 0.8%, and 3.72%, respectively. The novelty of this study is displaying the effects of water droplet injection in the inlet of the primary nozzle on the ejector performance.

Numerical Study of the Influence of Water Droplets on the Structure of a Detonation Wave in a Hydrogen–Air Fuel Mixture

The paper presents the results of numerical studies of the influence of water injection on the parameters of detonation and deflagration waves in gas fuel mixtures. A simplified physico-mathematical model of the process is developed. The influence of the injection of water droplets on the structure and the minimum propagation velocity of a stationary detonation wave is calculated numerically, and the mass fraction and the initial diameter of water droplets that lead to detonation damping in a hydrogen–air fuel mixture are obtained.

Numerical investigation of water droplets trajectories during natural gas dehydration inside supersonic separator

Reliable estimation of the condensed water droplets trajectories inside Supersonic separators (3Ss) during the dehydration process is essential for proper design and safe operation. Most of previous researches ignored the actual sizes of condensed droplets and predicted the particles trajectories for pre-specified diameters. In this article and for the first time, real trajectories are computed by considering the actual particle size distribution (PSD) of the condensed droplets in the presence of swirl, nucleation and growth processes during the dehydration of methane rich natural gas (MRNG) inside Laval nozzle for various diffuser angles. Furthermore, the injection of water droplets to facilitate the condensation process has not been addressed previously.Our simulation results indicate that even for the most optimal geometry and at extremely large centrifugal accelerations of 500,000 g, the condensed particles from MRNG are exceedingly small and can't reach the 3S walls for practical straight tube lengths. Our findings are verified with several previously reported experimental measurements and theoretical investigations results, borrowed from literature. To ensure proper dehumidification, sufficiently large water droplets are assumed to be injected preferably after the throat location. The computed results indicate that by injecting 5 μm diameter particles into MRNG of Khangiran refinery sweet gas stream and increasing its wetness fraction up to 0.12, the dehydration process is successfully achieved in an optimally designed supersonic separator.

Further Laboratory Experiments on Aerosol Scavenging in Mixed Clouds to Assess the Role of Phoretic Forces and Particle Solubility

Scavenging experiments have been performed in a cloud chamber inside a cold room with different aerosol particles: Paraffin particles, NaCl particles, Magnesium oxide particles, Carbon particles, Sahara dust particles. Essentially the experimental tests were carried on following the sequence of operations: the generation of the aerosol particles, their injection in the lower part of the cloud chamber, injection of water droplets in the whole chamber volume, nucleation of ice crystals, collection of ice crystals and their examination as for resulting scavenging efficiency. Evidence is given of the peculiar behaviour of soluble particles, individual and eventually inside mixed particles, leading to very much important scavenging efficiency, probably to be ascribed to aerodynamic capture. The evident peculiar behaviour of deliquescent particles can be oriented towards applications to an efficient abatement of specific effluents, on one side, and to weather modification experiments, both rain enhancement and hail prevention experiments.

Development and qualification of an innovative wet electrostatic precipitator in view of gaseous iodine filtration on laboratory-scale

An innovative method to filter gaseous iodine based on a wet electrostatic precipitator (WESP) was developed and tested. It is characterized by an ozone feed located before the WESP inlet to oxidize gaseous iodine into iodine oxide particles. Tests were carried out with titanium dioxide particles, first, and then with gaseous molecular iodine (I2) and methyl iodide (CH3I). The applied electric voltage between the electrodes, the total flow rate inside the WESP, and the injection of water droplets before the WESP were varied. The filtration efficiency based on the number of particles was calculated from ELPI and CPC measurements at the inlet and the outlet of the WESP. To determine the mass filtration efficiency for iodine, ICP-MS analyses were performed. Once the operation parameters were optimised for the tested conditions, the WESP ensured a mass filtration efficiency of 99.9% and a particle number based filtration efficiency up to 99.9% against molecular iodine. The efficiency for the filtration of methyl iodide was not as high. The filtration efficiency data are presented covering the particle size range of 0.04–2 µm.

K teorii protsessa gidratoobrazovaniia v trubchatom reaktore pri inzhektsii kapel' vody i gaza

K teorii protsessa gidratoobrazovaniia v trubchatom reaktore pri inzhektsii kapel' vody i gaza

Reduction of air flow rate for pulse-detonation-turbine-engine operation by water-droplet injection

Reduction of air flow rate for pulse-detonation-turbine-engine operation by water-droplet injection

CFD–DEM model for coupled heat and mass transfer in a spout fluidized bed with liquid injection

In this paper, we present a novel CFD–DEM model for coupled heat and mass transfer in a spout fluidized bed with liquid injection. In our CFD–DEM approach both particles and droplets are treated as discrete elements. Before actual simulations were conducted, a number of tests were performed to determine the optimum particle collision time step by analysing the error in the prescribed restitution coefficient (difference between defined and applied values). Subsequently we test the model for a selected case as a proof-of-principle. In this test case, the effect of liquid injection on dynamics of a pseudo-2D spout fluidized bed with draft plates was demonstrated for the fluidized bed-spouting-with-aeration (dispersed spout) regime with injection of water droplets. The computational results were compared with experimental results that were obtained through a unique combination of particle image velocimetry (PIV) and infrared thermography (IRT).

Numerical analysis of curved vane demisters in estimating water droplet separation efficiency

The present work deals with the numerical investigations of vaned demisters using a computational fluid dynamics tool to validate the presently adopted computational methodology. A vane demister profile identified from literature, on which experimental data is available, is chosen and water particles at the rated flow rate and distribution are injected. Discrete phase modeling approach with Rosin–Rammler size distribution is chosen for specifying the water droplet injection with a combination of break-up and/or coalescence option, along with few turbulence model recommended in the literature are tested for suitability. The walls of the demister are set to capture the water droplets impinging on them and will be removed from the numerical calculations. Various options within the solver are numerically tested to recommend an appropriate combination of solver setting. The results indicate that the Wave model is the best option among several other droplet breakup models available in the solver. It was observed that inclusion of Saffman lift force does not influence the results much. Spalart–Almaras model or Realizable k–ε model can be considered as a suitable turbulence closure for numerical prediction of vane separation efficiency in curved vane demisters.

Numerical study of the structure flow of the gas-vapor mixture in a channel with injection of water droplets

Mathematical modeling algorithm for the numerical analysis of the dynamics and evaporation of the water droplet which is injected into a gas-vapor flow is offered. The algorithm was tested with the help of the problem solution about a viscous fluid flow in a plane channel of constant cross section. It was shown that the proposed mathematical model and implementation algorithm are adequate to the physics of the investigated process. It was shown that the proposed mathematical model and implementation algorithm are adequate to the physics of the investigated process. Results of numerical study of the flow structure of the gas-vapor mixture in the channel with injection of water droplet under varying the initial droplet parameters are given.

Advancement of In-Flight Alumina Powder Spheroidization Process with Water Droplet Injection Using a Small Power DC-RF Hybrid Plasma Flow System

The correlation between plasma thermofluid characteristics and alumina powder spheroidization processes with water droplet injection using a small power DC-RF hybrid plasma flow system was experimentally clarified. Micro-sized water droplets with a low water flow rate were injected into the tail of thermal plasma flow so as not to disturb the plasma flow directly. Injected water droplets were vaporized in the thermal plasma flow and were transported upstream in the plasma flow to the torch by the backflow. After dissociation of water, the production of hydrogen was detected by the optical emission spectroscopy in the downstream RF plasma flow. The emission area of the DC plasma jet expanded and elongated in the vicinity of the RF coils. Additionally, the emission area of RF plasma flow enlarged and was visible as red emission in the downstream RF plasma flow in the vicinity below the RF coils due to hydrogen production. Therefore, the plasma flow mixed with produced hydrogen increased the plasma enthalpy and the highest spheroidization rate of 97% was obtained at a water flow rate of 15 Sml/min and an atomizing gas flow rate of 8 Sl/min using a small power DC-RF hybrid plasma flow system.

Wet Compression Analysis Including Velocity Slip Effects

Injection of water droplets into industrial gas turbines in order to boost power output is now common practice. The intention is usually to saturate and cool the intake air, especially in hot and dry climates, but in many cases, droplets carry over into the compressor and continue to evaporate. Evaporation within the compressor itself (often referred to as overspray) is also central to several advanced wet cycles, including the moist air turbine and the so-called TOP Humidified Air Turbine (TOPHAT) cycle. The resulting wet compression process affords a number of thermodynamic advantages, such as reduced compression work and increased mass flow rate and specific heat capacity of the turbine flow. Against these benefits, many of the compressor stages will operate at significantly off-design flow angles, thereby compromising aerodynamic performance. The calculations presented here entail coupling a mean-line compressor calculation method with droplet evaporation routines and a numerical method for estimating radial and circumferential slip velocities. The impingement of droplets onto blades and the various associated processes (including film evaporation) are also taken into account. The calculations allow for a polydispersion of droplet sizes and droplet temperature relaxation effects (i.e., the full droplet energy equation is solved rather than assuming that droplets adopt the wet-bulb temperature). The method is applied to a generic single-shaft 12-stage compressor. Results are presented for computed droplet trajectories, the overall effect on compressor characteristics (and how this depends on droplet size), and the effects of deposition and subsequent film evaporation. As with previously published wet compression calculations (with no velocity slip), it is found that pressure rise characteristics shift to higher mass flow and pressure ratio with increasing water injection rate and that aerodynamic efficiency falls due to the stages moving away from their design point. For droplet sizes typical of fog boosting, the overall effect of slip is to slightly increase the evaporative cooling effect through the enhanced heat and mass transfer rates.

The effects of rate of expansion and injection of water droplets on the entropy generation of nucleating steam flow in a Laval nozzle

The entropy generation due to irreversible heat transfer between vapor and liquid phases in a nucleating steam flow in a Laval nozzle is studied. To calculate the entropy generation due to self-condensation in transonic steam flow, a thermodynamic model is presented. The calculations of nucleating steam flow and the predictions of entropy generation rely on one-dimensional two-phase model. This model shows that the most of the thermodynamic losses take place during the nucleation phenomena. The effect of rate of expansion on the exergy losses is considered by decreasing the divergent angle of nozzle. Also micro-sized pure water droplets is injected theoretically to supercooled steam right after the nozzle throat at the onset of divergent section and the effects of injected droplets on thermodynamic losses and nucleation phenomena are investigated. The results indicate that decreasing the divergent angle and also injection of droplets diminishes the pressure rise in transonic steam flow and decreases the thermal entropy generation due to nucleation.

1733 マイクロガスタービン用遠心圧縮機における水噴霧冷却効果の解析(S19-7 流体機械に関連した流動現象とその解析・計測(7)流体機械に関連した諸問題,21世紀地球環境革命の機械工学:人・マイクロナノ・エネルギー・環境)

The injection of water droplets is one of the most effective ways to improve the performance of gas turbine systems. This cooling method has been applied to large-scale gas turbine systems and been expected as a powerful technology for improving the efficiency also of micro gas turbine (MGT) systems. The present study aims at establishing a water injection cooling system for the flow in the centrifugal compressor installed in MGT system. This paper provides a method of utilizing ultrasonic humidifier to produce and introduce fine water droplets into the impeller, and evaluates the validity of the proposed cooling method for improving the compressor performance, by conducting a series of experiments.

Thermodynamic and aerodynamic meanline analysis of wet compression in a centrifugal compressor

Wet compression means the injection of water droplets into the compressor of gas turbines. This method decreases the compression work and increases the turbine output by decreasing the compressor exit temperature through the evaporation of water droplets inside the compressor. Researches on wet compression, up to now, have been focused on the thermodynamic analysis of wet compression where the decrease in exit flow temperature and compression work is demonstrated. This paper provides thermodynamic and aerodynamic analysis on wet compression in a centrifugal compressor for a microturbine. The meanline dry compression performance analysis of centrifugal compressor is coupled with the thermodynamic equation of wet compression to get the meanline performance of wet compression. The most influencing parameter in the analysis is the evaporative rate of water droplets. It is found that the impeller exit flow temperature and compression work decreases as the evaporative rate increases. And the exit flow angle decreases as the evaporative rate increases.