Droplet Spectra Research Articles

The Effects of Crosswind Speed on the Droplet Deposition Distribution of Thrush 510G Aircraft

HighlightsThe penetration ability of droplet in the crop canopy was in a negative correlation with wind speed.The high wind speed was conducive to the deposition of droplet on the crop canopy in the deposition area.The smaller the wind speed was, the more uniform the distribution of droplets became, and the worse the uniformity of droplet penetration.Abstract. Large plant protection fixed-wing aircrafts are widely used for crop spraying in Northeast China, because their working efficiency matches farm size. However, the spray droplet deposition and drift associated with manned fixed-wing aircraft has not been fully understood in China. The objectives of this study were to quantify effects of the small gradient crosswind speeds of 1.10, 0.83, and 0.58 m/s on the distribution and drift of droplets on soybean in the field. Water-sensitive paper (WSP) was used to collect the droplets on the upper canopy and lower parts of the plant. The results showed that the percentage of droplet deposition (the percentage of droplet deposition on the lower layer to that on the canopy of soybean plant) negatively correlated with the crosswind speeds. The crosswind speed had a significant influence on the deposition of droplets on the canopy and penetration performance. When the crosswind speed was 1.10 m/s, the deposition of droplet on the canopy was maximum and the average value of droplet penetration percentage was minimum, which was 6.11 µL and 50.6%, respectively. The average volume median diameters (VMD or DV0.5s) from all in-swath WSPs of three treatments were all smaller than that of droplet spectrum. The variation coefficients of droplet density in three treatments were 46.8%, 39.6%,and 34.1%, respectively, which indicated that the smaller the wind speed was, the more uniform the distribution of droplets became. The results revealed the influence of crosswind speed on the droplet distribution of large fixed-wing aircraft, which was of great significance to improve the operation. Keywords: Droplets distribution, Penetration, Uniformity performance, Wind speed.

Effect of Cloud Droplet Spectrum Distribution on Retrievals of Water Cloud Optical Thickness and Effective Particle Radius by AGRI Onboard FY-4A Satellite

Effect of Cloud Droplet Spectrum Distribution on Retrievals of Water Cloud Optical Thickness and Effective Particle Radius by AGRI Onboard FY-4A Satellite

HOW DO THE DROPLET SPECTRUM UNIFORMITY AND SPRAY VOLUME OF FLAT-FAN NOZZLES INFLUENCE FUNGICIDE SPRAY DISTRIBUTION QUALITY IN SOYBEANS?

Droplet spectrum quality is essential to effectively control crop pests and diseases. This study aimed to characterize the droplet uniformity of the eight most popular flat-fan nozzles used by Brazilian farmers and relate it to their spraying quality. The method consisted of using a laser-diffraction-size analyser to determine droplet-size distribution for three fungicide spray solution compositions and at two flow rates. Our goal was to identify the nozzle models with the highest and lowest Span values for each fungicide spray solution. In the first stage, the results confirmed differences in uniformity and droplet size for both nozzle models and flow rates applied. However, these differences were not the same for both flow rates nor constant for all fungicide spray solution compositions. Through field experiments, we could understand how the combination of flow rate, nozzle model, and spray solution composition provides different results and application efficiencies. Based on our results, we can state that Span has an impact on the number of droplets prone to drift and quality of canopy coverage. Therefore, this droplet-quality parameter should be considered and displayed in nozzle catalogues to improve nozzle selection and sprayer configuration, thus enhancing application quality.

Microphysical characteristics of precipitating cumulus cloud based on airborne Ka-band cloud radar and droplet measurements

Based on cloud-probe data and airborne Ka-band cloud radar data collected in Baoding on 5 August 2018, the microphysical structural characteristics of cumulus (Cu) cloud at the precipitation stage were investigated. The cloud droplets in the Cu cloud were found to be significantly larger than those in stratiform (STF) cloud. In the Cu cloud, most cloud particles were between 7 and 10 μm in diameter, while in the STF cloud the majority of cloud particles grew no larger than 2 μm. The sensitivity of cloud properties to aerosols varied with height. The cloud droplet effective radius showed a negative relationship with the aerosol number concentration (Na) in the cloud planetary boundary layer (PBL) and upper layer above the PBL. However, the cloud droplet concentration (Nc) varied little with decreased Na in the high liquid water content region above 1500 m. High Na values of between 300 and 1853 cm−3 were found in the PBL, and the maximum Na was sampled near the surface in August in the Hebei region, which was lower than that in autumn and winter. High radar reflectivity corresponded to large FCDP (fast cloud droplet probe) particle concentrations and small aerosol particle concentrations, and vice versa for low radar reflectivity. Strong updrafts in the Cu cloud increased the peak radius and Nc, and broadened cloud droplet spectrum; lower air temperature was favorable for particle condensational growth and produced larger droplets.摘要在积云中, 大多数云粒子的直径在7到10微米之间, 而在层云中, 大多数云粒子的直径不超过2微米. 云滴有效半径与云中行星边界层(PBL)及PBL上层的气溶胶数浓度(Na)呈负相关. 在1500米以上的高液态水含量区域, 云滴浓度(Nc)变化不大, Na含量降低. 高雷达反射率对应于大的FCDP云粒子浓度和小的气溶胶粒子浓度. 积云中的强上升气流增加了云滴的峰值半径和数浓度, 拓宽了云滴谱; 较低的空气温度有利于粒子的凝结增长, 并产生较大的液滴.

Nozzle pressure uniformity and expected droplet size of a pulse width modulation (PWM) spray technology

Pulse width modulation (PWM) is currently implemented in agricultural sprayers to deliver the expected flowrate by managing the duty cycle and maintaining the target pressure and provide the desired droplet size. However, there are still issues about the application errors caused by the pressure variations when using this system as it may result in pesticide resistance and product loss. Field tests were conducted in a 30.0 ha (ha) and 54.0 ha fields to assess the pressure uniformity and the expected droplet size of the PWM technology. These parameters were also translated to an equivalent value if a flow-based system will be used during operation.Results showed that pressure mostly remained within the acceptable range in both fields. Pressure CV were within 10.0%, indicating the system's ability to provide acceptable pressure at varying conditions. However, nozzle pressure still varies, especially at the outer boom section where frequent duty cycle variation occurs. Pressure also deviates during acceleration and deceleration, indicating the system's latency to respond rapidly on changing conditions. In a flow-based system, the pressure varies due to varying speed as dictated by field terrain, curvilinear paths, and headland maneuvers. The droplet size also deviates from the expected droplet spectra based on the nozzle manufacturer’s specification when using a PWM system. However, the PWM system can still provide the target droplet size if a nozzle selected provides the desired droplet spectra in a wide range of pressure. In a flow-based system, the droplet size was expected to vary because of the fluctuation in application pressure due to speed changes during operation.

Influence of nozzle enabling strategy on spray deposition of crop protection unmanned aerial system

Proper nozzles arrangement is significant to improve spray deposition of crop protection unmanned aerial system (UAS). Besides fuselage structure, the control strategy is another nozzle location changing method when there are multiple sets of nozzles. A four-rotor crop protection UAS equipped with four centrifugal nozzles was used to conduct a field experiment in the rupturing stage of rice. Two sets of nozzles in the front and rear of the fuselage were enabled independently to investigate spray deposition, including spray coverage and droplet density on the sampling cards. Various nozzle rotating speeds and flight speeds were employed in the experiment to study the influence of nozzle location on the deposition. With different nozzle rotating speeds, the droplet spectrum could be controlled. The results show that the average coverage and average cumulative droplet density are negatively correlated with flight speed. Average droplet density is also negatively correlated with the droplet size. Spray deposition of front nozzles is significantly reduced compared with that of the rear nozzles under the same spray parameters, especially when the droplet size is too large or the flight speed is too fast. The reduction is mainly concentrated in the center area of the spray swath. As a result, the average cumulative droplet density of the front nozzles decreases by 25.96% in total. The average droplet density decreases by 18.54% when the droplet size is smaller than 100 μm, decreases by 25.02% when between 100 μm and 200 μm, and decreases by more than half when larger than 200 μm. This research can provide guidance for the installation of UAS nozzles and spray control strategy design. Keywords: crop protection, unmanned aircraft system, nozzles arrangement, spray coverage, droplet density DOI: 10.25165/j.ijabe.20211403.5922 Citation: Gu W, Xue X Y, Chen C, Zhou Q Q, Zhang S C, Peng B. Influence of nozzle enabling strategy on spray deposition of crop protection unmanned aerial system. Int J Agric & Biol Eng, 2021; 14(3): 53–61.

Comparison of UAV and fixed-wing aerial application for alfalfa insect pest control: evaluating efficacy, residues, and spray quality.

Integrating unmanned aerial vehicles (UAV) as a new method of pesticide application into existing commercial crop protection systems requires extensive research and comparison to conventional, proven application technology. Pest control expressed as efficacy against target pests, and spray quality expressed as coverage and chemical residue are three key criteria. We investigated and compared these quantitative parameters between a multi-rotor UAV and conventional piloted airplanes in two commercial alfalfa production systems. Effective and equivalent control of leaf-feeding insect pests was achieved by both methods of aerial application when delivering chlorantraniliprole at the same labeled use rate in different spray volumes (46.8 and 93.5L ha-1 ) on commercially grown alfalfa in California. Residue levels and spray coverage were also comparable and consistent between the UAV and airplane applications across three sampling techniques, specifically residue levels on alfalfa, insecticide recovery from filter paper, and spray coverage on water sensitive cards. Differences in droplet size and deposit characteristics were more variable for the UAV than airplanes based on analysis of deposition images. The results of this study provide confidence supporting the use of small-scale multi-rotor UAVs for pesticide application on agricultural crops. According to the parameters tested, UAV application quality and crop protection performance were comparable to that of the conventional fixed wing airplane application. However, the droplet spectrum and the short-term fate of droplets from unmanned aerial spray system require further optimization for effective and efficient crop protection with minimal risk to the environment.

Modelling the Condensation Phenomena within the Radial Turbine of a Fuel Cell Turbocharger

Radial turbines used in automotive fuel cell turbochargers operate with humid air. The gas expansion in the turbine causes droplets to form, which then grow through condensation. The associated release of latent heat and decrease in the gaseous mass flow strongly influence the thermodynamics of the turbine. This study aims to investigate these phenomena. For this purpose, the classical nucleation theory and Young’s growth law are integrated into a Euler–Lagrange approach. The main advantages of this approach are the calculation of individual droplet trajectories and a full resolution of the droplet spectrum. The results indicate an onset of nucleation at the blade tip and in the tip gap, followed by nucleation over the entire blade span, depending on the humidity at the turbine inlet. With a saturated turbine inflow, condensation causes the outlet temperature to rise to almost the same level as at the inlet. In addition, condensation losses reduce the efficiency and the latent heat released by condensation leads to significant thermal throttling.

Droplet characteristics in monsoon clouds before rain as observed over a high altitude site in Western Ghats, India

The cloud droplet size distribution (CDSD) and microphysical properties prior to monsoon rain events is studied using in-situ ground observations over a high altitude site in Western Ghats, India. The cloud microphysical properties, such as cloud droplet number concentration (CDNC), liquid water content (LWC), cloud droplet spectrum, droplet effective diameter (ED), droplet mean radius (Rm), spectral width (σ), and relative dispersion (ε) showed a considerable variation. A detailed analysis of CDSD before rain events showed single and multi-mode patterns which varied from case to case. An apparent variation in cloud microphysical properties is noted for both single and multi-mode cases. Large cloud droplets were found in both single and multi-mode clouds, and analysis revealed the possibility of entrainment of aerosols into these clouds leading to multi modes in the CDSD. Observed rain event duration indirectly suggested higher warm rain depths (D*) when multi-mode cases are observed.

Coastal-Fog Microphysics Using In-Situ Observations and GOES-R Retrievals

The objective of this work is to evaluate GOES-R (Geostationary Operational Environmental Satellites-R series) data-based fog conditions which occurred during the C-FOG (Toward Improving Coastal Fog Prediction) field campaign. The C-FOG campaign was designed to advance understanding of fog formation, development, and dissipation over coastal environments to improve predictability. The project took place along coastlines and open water environments of eastern Canada (Nova Scotia, and the Island of Newfoundland) during August−October of 2018 where environmental conditions play an important role for late season fog formation. During the C-FOG field campaign, coastal instruments were mainly located at the Ferryland supersite, Newfoundland, with two main sites, and five satellite sites, as well as on the Research Vessel Hugh R. Sharp. Key in-situ measurement instruments included microphysical, meteorological, radiation, and aerosol sensors. A fog spectral probe was used for measuring droplet spectra from 1–50 µm at the Ferryland supersite. A laser precipitation monitor with 100 µm to 10 mm size range and an optical particle counter with 0.3–17 µm at 16 spectral channels provided information for fog and drizzle discrimination. Remote sensing platforms, e.g. profiling microwave radiometer, ceilometer, microwave rain radar, lidar, meteorological towers, tethered balloons, and GOES-R products for fog coverage, and droplet size and liquid water path) were used to evaluate fog over horizontal and vertical dimensions. Results suggest that effective radius, phase, liquid water path, and liquid water content values obtained from GOES-R and the profiling microwave radiometer are comparable to ground-based in-situ observations. It is concluded that integration of observations and nowcasting products may help improve short-term local fog predictions.

Insecticide spray drift reduction with different adjuvants and spray nozzles

ABSTRACT Insecticide spray drift can lead to reduced control efficiency and loss of product to the environment. Thus, we conducted a study to evaluate the effect of different spray nozzles and the addition of adjuvants in insecticide spray on the resulting droplet spectrum and wind tunnel drift. All experiments were conducted in a completely randomized design with four repetitions using a 5 × 3 factorial scheme. Five spraying solutions were studied; one contained only water and the other four comprised thiamethoxam + lambda-cyhalothrin (no adjuvant, Oro-solve, Wetcit Gold, and Orobor N1), in combination with three spray nozzles (AXI, JFC, and J3D). The droplet spectrum was evaluated through the volumetric median diameter, relative amplitude, and percentage of the droplet volume with diameter ≤ 100 µm. The drifts were evaluated in a wind tunnel at 5, 10, and 15 m. Data were subjected to analysis of variance and means were compared using the Tukey’s test. In addition, a principal component analysis was performed. Application of the insecticide with the adjuvants combined with the different nozzles changed the droplet spectrum and the risk of drift. The AXI nozzle and the J3D associated with the Oro-solve and Wetcit Gold adjuvants resulted in a greater volumetric median diameter of the droplets and drifts were observed at 5 m.

Scattering resonances observed in the lasing emission spectrum of large dye-doped droplets

High-resolution spectrum analysis of the lasing emission of mm3-sized pendant droplets that contain aqueous solutions of the Rhodamine 6G (Rh6G) dye is reported. Pumping was performed with a 532 nm pulsed laser beam. The lasing emission demonstrates a complex spectral structure that contains mode-cluster peaks spaced 2 nm apart and a ripple structure formed by periodic resonances, which are superimposed on the peak closest to the maximum of the dye gain curve. The periodic resonances are associated with the light-scattering resonances on a large sphere when light absorption in the sphere occurs.

Microphysics of fog bursting in polluted urban air

The goal of this work is to study sudden fog visibility (Vis) changes called fog bursting occurred during polluted urban air conditions. Fog bursting refers to a sudden drop of fog Vis below 500 m over 30 min. A comprehensive field observational campaign called Costal City Fog Microphysical Research (CCFMR) was carried out over the city of Tianjin, China during winter of 2016–2017. The six fog bursting cases occurred during the project suggest that droplet number concentration (Nd) and liquid water content (LWC) were higher than these of other conditions. The mass concentration of PM2.5 (NPM2.5) was also higher before the fog bursting events. The fog droplet spectra (FDS) followed a Junge distribution. During fog bursting events, Vis, surface air temperature (Ta) and dew point depression (Ta-Td) exhibited decreasing trends. On the other hand, mean and turbulence kinetic energy (MKE and TKE), as well as friction velocity (u∗) had increasing trends in time. After the fog bursting, environment stability changed from the neutral stage to weakly unstable stage, and fog became deeper and optically thicker. The FDS broadened drastically between 20 and 35 μm diameter, and smaller Nd increased up to 1 order of magnitude. It is concluded that fog bursting is positively affected by combination of decreasing Ta by radiative cooling, increasing RH, turbulence mixing, and high value of NPM2.5. Results from this work suggest that fog bursting conditions need to be studied in detail by numerical weather forecast (NWP) models that currently lack of these conditions.

The Influence of Hygroscopic Flare Seeding on Drop Size Distribution Over Southeast Queensland

AbstractThis study presents measurements of the initial cloud‐base droplet spectra of seeded and unseeded clouds observed during the Queensland Cloud Seeding Research Program field campaign. The measurements were stratified by the aerosol regime that the cloud formed within, and then analyzed statistically as well as compared to parcel model simulations. Initial droplet spectra were obtained within 300–600 m of cloud base to identify the spectra resulting from nucleation and to avoid effects from collision‐coalescence broadening processes. The goal of this study is to assess the impact of hygroscopic flare seeding on cloud‐droplet growth as a first step toward understanding the effect of hygroscopic seeding on rainfall. Results indicate that initial droplet spectra are altered by seeding, such that the mean diameter and tail of drops larger than 20 µm increased in seeded clouds within a given aerosol regime. This effect is most pronounced in the continental‐influenced aerosol regime, that generally lacked coarse mode aerosols, but was also observed to occur in the maritime‐influenced regime. To further investigate if the observational results were supported by theory, a parcel model was used to improve the process‐level understanding of the seeding impact on the initial evolution of the droplet spectra. The simulated results qualitatively agree with the observations that noted the seeding effect is more prominent in the continental‐influenced regime.

A stochastic closure for two-moment bulk microphysics of warm clouds: part I, derivations

We propose a mathematical methodology to two-moment parameterization of bulk warm cloud microphysics based on a stochastic representation of the high-order moment terms. Unlike previous bulk parameterizations, the stochastic closure approach proposed here does not assume any particular droplet size distribution, all parameters have physical meanings which are recoverable from data, and the resultant parameterization has the flexibility to utilize arbitrary collision kernels. Our strategy is a new twofold approach of approximating the kinetic collection equation (KCE). First, by partitioning the droplet spectrum into two large bins representing cloud and rain aggregate particles, we are able to represent droplet densities as the sum of mean and random fluctuation terms. Second, we use a Taylor approximation for the collision kernel around the centres of masses of bulk cloud and rain aggregates which allows the derivation of bulk rate equations for the cloud and rain aggregate droplet numbers and mixing ratios that are independent of the collision kernel. Detailed numerical simulations of the KCE demonstrate that the high-order (quadratic and cubic) stochastic fluctuation terms can be neglected which results in a closed set of equations for the mean bulk cloud and rain aggregates with only five parameters. Considerations of consistency of cloud number concentration and mass conservation constraints further reduce the parameter set to three key entities representing, respectively, the strength of cloud self-collection, the strength of auto-conversion, and the strength of rain self-collection, relative to auto-conversion. In an accompanying paper, bounds on the parameters’ space are derived and the mean bulk two-moment parameterization is validated against direct simulation of the KCE and compared to an existing competitor parameterization.

Effect of angled spray nozzle designs on spray distribution and droplet spectrum

ABSTRACT New technologies have been developed to promote uniform, sustainable, safe and effective application of phytosanitary products. In this scenario, spray nozzles of different designs and jet angles can optimize application. Therefore, we aimed to analyze the effect of angled flat fan spray nozzles on spray pattern uniformity and droplet spectrum formation. The spray volumetric distribution of standard flat fan, double flat fan and the new angled flat fan spray nozzle, using two spray volumes were assessed. For that, the spray pattern distribution and the coefficient of variation (CV) were determined. The droplet spectrum characterization produced by the same treatments was performed in a real-time particle size analyzer. Also the effect of adding a fungicide mixture associated with an adjuvant on droplet formation was evaluated. All spray nozzles, regardless of design and spray volumes evaluated, produced CV values below 7%, considered acceptable by international uniformity standards. There was a difference in spray pattern according to the spray nozzle design and spray volume. It was evidenced that the main differences found in droplet spectrum occurred due to spray nozzle type, spray mixture and nominal flow rate, with little influence of spray jet angled or spray volumes.

Сomparative analysis of disperse characteristics of single-type flat spray cone nozzles

Research and development work related to the study and use of water spray must certainly be based on the most accurate determination of the dispersion composition of spray droplets. It is just this parameter that forms the basis for all further calculations of the effect of water spray on the process cycle components. The introduction of the method for restoring the original sizes of spray droplets and the most accurate measurement of their disperse characteristics will allow coming close to solving the problem of optimizing the operation of spray technology, as well as will make it possible to predict and possibly regulate the dispersed characteristics of droplet flows. Therefore, it is the foundation for the development of breakthrough and environmentally sustainable resource-saving technologies in the agricultural sector. We have developed a method for restoring the original size of the droplet spectrum (Patent No. 2709402 titled “A method for determining the size of droplets”). Based on this method, a test bench was developed and manufactured to assess the quality of spraying of working fluids. An aerosol chamber design was developed and the chamber was assembled, in which an aerosol sample was taken under conditions of equal probability of deposition and preservation of droplets of all sizes. Software for high-speed measurement of the dispersion characteristics of the spectrum of spray droplets has been developed. In general, the studies performed have demonstrated the appropriate professional capabilities of the experimental facilities when testing sprayers. This gives us an opportunity to come up with a proposal to create centers for testing sprayers for their compliance with the declared performances based on the experimental facilities.

Simultaneous measurement of cloud microphysical parameters based on digital holographic interferometry

Investigation of cloud microphysical is of great significance in deepening the understanding of the radiation energy budget, water cycle process, and precipitation mechanism, and improving the scientificity and effectiveness of artificial precipitation. Especially under the action of turbulence, in addition to shear and inertia, the turbulence in the cloud will accelerate the collision of cloud droplets through vortex superposition. The above process will further complicate the cloud microphysical characters. At present, the methods of measuring cloud microphysical parameters based on light scattering, collision and imaging theories encounter bottlenecks: the inversion process needs to make the assumptions about cloud droplet spectrum and particle characteristics, the impact process will destroy particle characteristics, and the three-dimensional characteristics of cloud particles cannot be obtained. Because of its many advantages, such as fast, real-time, non-destructive, non-invasive, high-resolution, full-field optical measurement, etc., in-line digital holographic interferometry is considered as a new potential tool for the dynamical measurement of cloud microphysical property. In particular, the mutual interference between the particle image and twin image is small under far-field recording conditions. In this paper, the measurement method of the on-line digital holographic interferometry based on interference theory, combining optical information processing, depth of field compression, and gray gradient variance technology of fusion holograms, is investigated. This method, with a <i>z</i>-axis position accuracy of 0.01 mm and system resolution of 2 μm, is employed for simultaneously and finely detecting the cloud droplet spectrum, cloud particle diameter, and number concentration. In the experiment, the liquid droplet with a median diameter of 3.9 μm, produced by the ultrasonic atomizer, is used as an example of the cloud particle. The measurement results are consistent with realistic scenario. By using a high speed charge coupled device or complementary metal oxide semiconductor camera, this method can solve the technical bottleneck of three-dimensional fine characteristics of cloud particle in airborne measurement by using cloud droplet spectrometer. It can provide effective support for the research of liquid water in the cloud, entrainment, condensation, collision, and temporal and spatial evolution laws. In addition, it has reference significance for the study of particle dynamics. Simultaneously, this method provides a feasible solution for the measurement of cloud in land-based and airborne platforms.

Comparison of Eulerian Bin and Lagrangian Particle-Based Microphysics in Simulations of Nonprecipitating Cumulus

AbstractA single nonprecipitating cumulus congestus setup is applied to compare droplet spectra grown by the diffusion of water vapor in Eulerian bin and particle-based Lagrangian microphysics schemes. Bin microphysics represent droplet spectral evolution applying the spectral density function. In the Lagrangian microphysics, computational particles referred to as superdroplets are followed in time and space with each superdroplet representing a multiplicity of natural cloud droplets. The same cloud condensation nuclei (CCN) activation and identical representation of the droplet diffusional growth allow the comparison. The piggybacking method is used with the two schemes operating in a single simulation, one scheme driving the dynamics and the other one piggybacking the simulated flow. Piggybacking allows point-by-point comparison of droplet spectra predicted by the two schemes. The results show the impact of inherent limitations of the two microphysics simulation methods, numerical diffusion in the Eulerian scheme and a limited number of superdroplets in the Lagrangian scheme. Numerical diffusion in the Eulerian scheme results in a more dilution of the cloud upper half and thus smaller cloud droplet mean radius. The Lagrangian scheme typically has larger spatial fluctuations of droplet spectral properties. A significantly larger mean spectral width in the bin microphysics across the entire cloud depth is the largest difference between the two schemes. A fourfold increase of the number of superdroplets per grid volume and a twofold increase of the spectral resolution and thus the number of bins have small impact on the results and provide only minor changes to the comparison between simulated cloud properties.

Polydispersed droplet spectrum and exergy analysis in wet steam flows using method of moments

In steam turbine flow, the complex droplet spectrum caused by nonequilibrium condensation is necessary to be modeled accurately to predict the droplet behavior and estimate the exergy destruction and erosion rate. This study built and validated a polydispersed model with Quadrature method of moments (QMOM), consisting of transition SST model, the moments and entropy generation. A spline-based algorithm was used to reconstruct the shape of the probability density function (PDF) of radius. It’s proved that the polydispersed model has a better prediction result for Sauter radius compare with monodispersed model. Then, the distributions of moments and droplet spectra in the nozzle with effects of asymmetric lambda shock and evaporation were investigated. The shape of droplet spectrum is closer to gamma distribution in nucleation zone and log-normal distribution in growth zone when outflow is supersonic. In the turbine, because the oblique shock induces complex evaporation and secondary condensation, the reconstructed shape is closer to gamma distribution. Finally, the obtained maximum exergy destruction is 25.293 kJ/kg. The rate of exergy destruction increases from 1.04% to 4.45%. The range of Baumann factor is 0.574–1.312. Besides, the erosion rate in polydispersed model is only 58.4–64.3% of monodispersed model. The polydispersed model used in this study can predict the droplet spectrum and energy loss of the turbine systems more accurately.