Droplet Deposition Rate Research Articles

Effects of application height and crosswind on the crop spraying performance of unmanned helicopters

Unmanned helicopters are increasingly used for crop protection in Asia. However, the moving mechanism of droplets from helicopters, which is strongly related to the complexity of the downwash flow, is still unclear. In this study, the lattice Boltzmann method was used to simulate the flow field and movement of the droplets released from the helicopter. The application height was set to 1.5, 2.5, and 3.5 m, while the crosswind speed was varied from −3 to 3 m/s. The vortex structures and downwash flow velocity field were found to be asymmetric, and the maximum downwash flow area was observed at the left side of the helicopter. The flow structure angle was inversely proportional to the application height and followed a second-order law with respect to the crosswind speed. The yaw angle was inversely proportional to the crosswind speed and was found to be more significantly affected by the crosswind speed at higher application heights. To study the effects of the droplet size on their movement in the downwash flow, droplets with diameters of 50, 100, 200, and 400 µm were studied. The back view of the small droplets with diameter of 50 and 100 µm has a double-peak pattern. Larger droplets, which were hardly moved up by the vortex, reached much nearer distances and floated at lower altitude. When the application height was 2.5 and 3.5 m, the droplets deposited nearly symmetrically at the cross wind with opposite direction. At an application height of 1.5 m, the droplets, especially the large ones (200 and 400 µm), deposited asymmetrically at the cross wind with opposite direction. The cross wind blew from the left side due to a stream vortex near the ground on the right side of the helicopter, which carried the big droplets and move them back into the air. When the cross wind blew from the right side, large droplets (200 and 400 µm) deposited faster and concentrated near the swath, while small droplets (50 and 100 µm) were moved by the crosswind blowing from the right side with strong non-uniform spatial distribution and floated on the far left side. This finding could help to greatly reduce the spray drift. The droplet deposition rate is more likely to be affected by the quadratic term of the droplet diameter, while the coefficient of variation of deposition is affected by the quadratic terms of the droplet diameter and cross wind speed. The results of this study will be useful to analyze and optimize the downwash flow development and droplet movement/deposition of water from plant-protection unmanned aerial vehicles.

Effects of Crop Protection Unmanned Aerial System Flight Speed, Height on Effective Spraying Width, Droplet Deposition and Penetration Rate, and Control Effect Analysis on Wheat Aphids, Powdery Mildew, and Head Blight

As a new type of crop protection machinery, the Crop Protection Unmanned Aerial System (CPUAS) has developed rapidly and been widely used in China; currently, how to use the CPUAS scientifically has become a top priority. However, the relationships between the operating parameters of the CPUAS and the effective spraying width (ESW), droplet distribution characteristics, and control effects of insect pests and diseases are not clear yet. Therefore, three levels of flight speed (FS) as 3, 4, and 5 m/s, three levels of flight height (FH) as 1.5, 2.0, and 2.5 m, and spraying volume 2.0 L/min experiments were carried out to investigate the effects of FS and FH on the ESW, droplet deposition uniformity (DDU), and droplet penetration rate (DPR) by using an electric single-rotor CPUAS CE20. Based on the obtained results, combined with the insect pests and diseases occurrence agronomic laws, the optimal operation parameters of the CPUAS were selected to control the wheat aphids, powdery mildew, and head blight. The results showed that the ESW of CE20 was not consistent, the maximum value was 5.78 m, and the minimum one was 2.51 m. The FS had a highly significant impact on ESW (p = 0.0033 < 0.01), while the FH and the interaction between FS and FH had no significant impact on ESW. The coefficients of variation (CV) of the droplet deposition were between 23.3% and 34.4%, which meant good deposition uniformity. The FH (p = 0.0019) and the interaction between FS and FH (p = 0.02) had significant impacts on the DDU. The control effects on aphids were 78.71% (1 day), 84.88% (3 days), and 90.42% (7 days), the control effects on powdery mildew were 77.17% (7 days) and 82.83% (14 days), and the control effect on head blight was 88.32% (20 days). This study proved that by the optimization of parameters and the combination of agronomy, good control effects for insect pests and diseases could be achieved by the CPUAS. The research results would provide some technical supports for CPUAS application.

Performance evaluation of a multi-rotor unmanned agricultural aircraft system for chemical application

Unmanned agricultural aircraft system (UAAS) has been widely employed as a low-cost and reliable method to apply agrochemicals to small agricultural fields in China. The performance of battery-powered multirotor UAAS has attracted considerable attention from manufacturers and researchers. The objective of this research was to design a UAAS equipping with a data acquisition system, to characterize its chemical application performance based on droplet deposition data and optimize the operating parameters. Each test was repeated three times to assess the reliability of the spraying system. Various flight parameters were also evaluated. The optimal spray pressure for the XR8001 and XR8002 (TeeJet, Wheaton, IL, USA) nozzles was found to be 300 kPa, and the latter nozzle had a higher droplet deposition rate and spray volume. Spray volume was not significantly affected by the flight speed or droplet density, and was negatively correlated with the nozzle pressure. The results of this study provide a basis for improving the efficiency of UAAS chemical application systems in terms of large-scale application. Keywords: spray characterization, unmanned agricultural aircraft system, aerial sprayer, onboard data acquisition system, effective swath width, flight parameters, chemical application, performance evaluation DOI: 10.25165/j.ijabe.20211404.6194 Citation: Zhu H, Li H Z, Adam A P, Li L J, Tian L. Performance evaluation of a multi-rotor unmanned agricultural aircraft system for chemical application. Int J Agric & Biol Eng, 2021; 14(4): 43–52.

Force balance droplet entrainment model for the horizontal stratified flow condition

Under the horizontal stratified flow condition, a droplet with a large interfacial area influences the mass, momentum, and heat transfer between the gas and liquid phases. In this study, we developed a force balance droplet entrainment rate model applicable to the horizontal stratified flow condition. This model is based on the balance of forces that act on the interfacial wave, which consists of an interfacial shear force, a surface tension force, and the force of gravity. In addition, the force balance droplet entrainment rate model includes constitutive relations for the parameters that are related to the geometry and the characteristics of the interfacial wave. This includes the wave frequency, wave height, wave slope, the wave velocity along the flow direction, and the lateral length of the interfacial wave along the circumferential direction of the flow pipe. The prediction of the onset of entrainment by the proposed force balance droplet entrainment rate model was compared to that with the existing models. Subsequently, the model was evaluated with the latest droplet deposition rate correlation from the literature against the experimental data obtained under the horizontal stratified flow condition. It showed a good prediction capability with a MAPE of 15.34%. Finally, the applicability of the force balance droplet entrainment rate model to a large-sized pipe was investigated. The force balance model showed a reasonable prediction performance. The applicable ranges of the gas and liquid Reynolds numbers (Reg and Rel, respectively) proposed by droplet entrainment rate model are 65,500–571,400 and 170–11,000, respectively.

The Flow Boiling Crisis of Saturated Water in Pipes at High Pressures

The procedures developed by the authors for calculating the distribution of the liquid over the channel cross section in the dispersed-annular flows open up opportunities for more justified modeling of the conditions for the occurrence of a boiling crisis at positive values of the relative enthalpy (quality) of the flow. However, a comparison of the calculated values of the liquid flowrate in the film with the recommended values of critical heat flux (CHF) in water flow boiling in pipes has demonstrated that, in general, there is no obvious correlation between them. An analysis confirms the well-known opinion that a unified model of the flow boiling crisis in pipes cannot be constructed. At the same time, the regularities revealed in calculating the entrainment and deposition of droplets should be considered in developing a crisis model. An increase in CHF with mass flowrate, which was discovered experimentally and accounted for in the reference tables in a wide range of high pressures and mass flowrates, gives us reasons to return to Doroshchuk’s hypothesis about the “deposition crisis.” Application of the correlation for the droplet deposition rate in a disperse-annular flow enabled us to quantitatively verify this correlation. The predictions obtained using this correlation agree well with the tabulated data at a flow quality from 0.15 to 0.40 and mass flowrates above 2000 kg/(m2 s). At the same time, it has been demonstrated that the widespread use of extrapolation of the CHF values recommended in the latest edition of these tables makes them, in fact, not only unreliable but also physically unjustified in a certain range of parameters. This paper identifies several such ranges wherein revision of the tables is essential.

Effect of Droplet Size Parameters on Droplet Deposition and Drift of Aerial Spraying by Using Plant Protection UAV

In the field of pesticide spraying, droplet size is one of the most important factors affecting droplet deposition and drift. In order to study the effect of different droplet size parameters on droplet deposition distribution and drift of aerial spraying by using plant protection UAV, an aerial spraying test with the same spraying rate and different size droplets in rice canopy was carried out by using multi-rotor unmanned aerial vehicles (UAV) and four TEEJET nozzles with different orifice sizes (these droplets with a volume median diameter (VMD) of 95.21, 121.43, 147.28, and 185.09 μm, respectively), and the deposition distribution and penetration of droplets in the target area and the drift distribution of droplets in the non-target area were compared and analyzed. The results showed that the deposition distribution and penetration of droplets in the target area and the drift distribution of droplets in the non-target area were influenced by the droplet size. The droplet deposition rate in the upper and lower rice canopies were increased in the target area with the increase of droplet size. The penetration results of droplets also increased with the increase of droplet size, and that of droplets with a VMD of 185.09 μm was the best, reaching 38.13%. The average values of the cumulative drift rate of droplets in the rice canopy in the four tests were 73.87%, 50.26%, 35.91%, and 23.06%, respectively, and the cumulative drift rate and the drift distance of droplets decreased with the increase of droplet size, which indicated that the increase of droplet size can effectively reduce droplet drift. It demonstrated that the droplet size is one of the most important factors affecting droplet deposition and drift for pesticide spraying by plant protection UAV, and for the application of plant protection UAV with extra-low volume spraying, the use of droplets with VMD less than 160 μm should be avoided and a more than 10 m buffer zone should be considered downwind of the spraying field to avoid drug damage caused by pesticide drift. The results have fully revealed the effect of droplet size parameters on droplet deposition and drift of aerial spraying. Moreover, the influence of the wind field below the rotors on the distribution of droplet deposition was surmised and analyzed from the perspective of plant protection UAV. It is important for optimizing the droplet parameters of aerial spraying, increasing the spraying efficiency, and realizing precision agricultural aviation spray.

Experimental investigation of droplet entrainment and deposition in horizontal stratified wavy flow

An experimental study of the local droplet parameters for an atmospheric horizontal stratified wavy flow was conducted in a horizontal circular pipe with an inner diameter of 40 mm and a length of 5.5 m. The local distributions of the droplet fraction, droplet velocity, droplet diameter, and droplet mass flux in the cross section of the pipe were measured using single optical fiber probes at four locations with length-to-diameter ratios of 17.5, 55.0, 80.0, and 105.0 from the inlet of the test section. The average droplet mass flow rate along the axial direction of the flow channel was also obtained from the droplet parameters. The combination of the droplet entrainment and deposition rate models of Schimpf et al. was evaluated for droplet mass flow rates obtained from five different experiments including the present experiment in the horizontal stratified flow. However, its prediction accuracy was not good for the present and REGARD data. Finally, new droplet entrainment and deposition rate models for the horizontal stratified flow were proposed based on those five experiments. The applicable ranges of the proposed models are 65,500–571,400 and 170–11,000 for the gas (Reg) and liquid (Rel) Reynolds numbers, respectively.

Development of a droplet entrainment rate model for a vertical adiabatic two-phase flow

The authors have assessed some well-known droplet entrainment and deposition rate models against a wide range of vertical annular-mist flow experiments. The results of assessment showed that the Hewitt model predicts quite well for low-pressure air-water experiments and the Hewitt and the Okawa models are reasonably good for high-pressure steam-water experiments. However, the models still have large errors and significant deviations. Especially, it is known that their entrainment rate models are inappropriate to the developing region of an annular-mist flow because they were developed using experimental data estimated with the equilibrium assumption that the entrainment rate is equal to the deposition rate. To solve these problems, a new entrainment rate model is proposed here.Key variables for droplet entrainment are deduced from the analysis of experimental data and then the basic form of the new model is suggested as an empirical correlation. For the least-square fitting of the new correlation, the experimental data set of entrainment rate versus flow condition were needed. However, the entrainment rate cannot be measured in experiments but should be estimated. In this study, the droplet entrainment rates of 349 experiments were realistically estimated by using the continuity equation of the liquid film in an annular-mist flow, where the measured axial change of the liquid film mass flux can be taken into account, that is, the equilibrium assumption is not always needed. The new model was fitted using the data set and, then, assessed against 470 annular-mist flow experiments. The results showed that the new entrainment rate model in combination with the Okawa’s deposition rate model is definitely better than the existing models in terms of both accuracy and precision.

Effect of Ga droplet deposition rate on morphology of concentric quantum double rings

For the fabrication of particular nanostructures, Stranski-Krastanov (SK) growth mode driven by strain is most widely used. Meanwhile, another technique that is used to form the complex nanostructures is the droplet epitaxy technique, which is based on the deposition of group III element nanoscale droplets onto substrate and followed by the reaction with group V element for crystallization into III-V compound nanostructures. Droplet epitaxy technique is simple and flexible, and it does not require additional complicated processing and has potential to develop various quantum nanostructures. It, unlike standard MBE growth, exploits the sequential supply of group-III and group-V elements to form quantum nanostructures. Quantum rings are a special class of quantum-confinement structure that can be fabricated by the droplet epitaxy technique and have attracted wide attention due to the Aharonov-Bohm effect, which is specific to the topology of a ring. In this paper, GaAs/GaAs (001) concentric quantum double rings (CQDRs) are prepared by droplet epitaxy technique at different Ga droplet deposition rates in monolayer per second (ML/S). The 2 μm × 2 μm atomic force microscope images are obtained to show the morphologies of CQDRs. We study the effects of Ga droplet deposition rates (0.09 ML/s, 0.154 ML/s, 0.25 ML/s, 0.43 ML/s) on CQDRs. The results show that with the increase of Ga droplet deposition rate, the density of CQDRs increases and the radius of inner ring and the radius of outer ring decrease. According to the nucleation theory, through the relationship between the maximum cluster density and the Ga droplet deposition rate, the critical number of atom nucleations is found to be 5, which suggests that the stable Ga atom crystal nucleus should contain at least 5 Ga atoms in the process of forming Ga droplet, and a nucleation state transformation diagram is drawn in order to obtain an insight into the process of forming Ga droplet according to the nucleation theory and fitting results. The research results could be instructive for preparing the GaAs concentric quantum double rings that the density can be controlled by droplet epitaxy.

Characteristics of metal droplet transfer in wire-arc additive manufacturing of aluminum alloy

The wire-arc additive manufacturing (WAAM) process applies gas metal arc welding (GMAW) technology. The wire materials of aluminum alloy are melted to form metal droplet by the arc discharge and are accumulated layer-by-layer in this process. The arc voltage and arc acoustic emission (AE) signals were detected synchronously in the experiment. According to the signal feature of arc voltage and arc AE, the droplet transfer behaviors in various transfer modes were investigated based on the GMAW-WAAM process. Furthermore, significance of parameters was analyzed and computational models of droplet size and deposition rate were developed to evaluate the quality and efficiency of WAAM. The results showed that the identification of the characteristics of droplet transfer mode can be realized by means of arc signals analysis, which is an alternative method for the analysis of droplet transfer in the GMAW-WAAM process. The interaction of arc voltage and arc current (U × I) is the most important factor to influence the droplet transfer, and the cubic polynomial regression equation is a more ideal model to describe the relationship between the frequency of droplet transfer and arc power. The droplet radius decreases exponentially with the increase of frequency of droplet transfer, and the deposition rate increases with the increase of droplet transfer frequency by cubic polynomial rule.

Droplet entrainment and deposition rates in a horizontal annular flow for SPACE code

Correlations for the droplet entrainment and deposition rates were developed to accurately predict its behavior in a horizontal annular flow. The Lopez de Bertodano et al. droplet entrainment rate correlation was evaluated and then modified based on the experimental data for both vertical and horizontal annular flows. In addition to this, a new droplet deposition coefficient correlation was proposed for a droplet deposition rate. The droplet deposition coefficient is represented by a function of dimensionless parameters considering the effects of the gas and liquid superficial velocities and the pipe inner diameter. Finally, the SPACE code was assessed against various experimental data for droplet mass flow rate of horizontal annular flows obtained from the open literature. The improved SPACE code showed better prediction capability for the droplet behavior in the horizontal annular flow than the original one.

CFD–DEM study of residence time, droplet deposition, and collision velocity for a binary particle mixture in a Wurster fluidized bed coater

ABSTRACTAn approach that combines computational fluid dynamics with the discrete element method is applied to investigate the residence time and collision velocity in different processing zones of a Wurster fluidized bed. Ideal and nonideal circulating motions of particles are distinguished to evaluate distributions of cycle times. Solid-like droplets are injected and simulated inside a predefined spray zone to study the droplet deposition rate. The simulation, conducted for a binary mixture of small and large particles, predicts the ideal cycle times and the residence times of both particle sizes in the Wurster tube are in good agreement to the available experimental results.

A Comparison of Modeling Techniques for Polydispersed Droplet Spectra in Steam Turbines

Within steam turbine flows, condensation phenomena give rise to complex droplet spectra that can span more than two orders of magnitude in size. To predict the behavior of the two-phase flow and the resulting losses, the interactions between the vapor phase and droplets of all sizes must be accurately calculated. The estimation of thermodynamic losses and droplet deposition rates, in particular, depends on the size range and shape of the droplet spectrum. These calculations become computationally burdensome when a large number of droplet groups are present, and it is therefore advantageous to capture the complete droplet spectrum in a compressed form. This paper compares several methods for reducing the complexity of the droplet spectrum: a single representative droplet size (equivalent monodispersion), the moment method (including various growth rate approximations), the quadrature method of moments (QMOM), and spectrum pruning. In spectrum pruning, droplet groups are individually nucleated, but their number is subsequently reduced by combining groups together in a manner that preserves droplet number, wetness fraction, and the shape of the initial spectrum. The various techniques are compared within a Lagrangian framework by tracking the two-phase behavior along predefined pressure–time trajectories. Primary and secondary nucleation, droplet evaporation, and a representative turbomachinery case are modeled. The calculations are compared in terms of speed, accuracy, and robustness. It is shown that both the moment methods and spectrum pruning provide an appreciable improvement in accuracy over the use of an “equivalent” monodispersion without compromising calculation speed. Although all the examined methods are adequate for primary nucleation and droplet growth calculations, spectrum pruning and the QMOM are most accurate over the range of conditions considered.

Structure modification and numerical study of the moisture-separation performance of special crossunder pipe separators for nuclear power steam turbines

The present paper investigated the enhancement of moisture-separation efficiency for ordinary special crossunder pipe separators (SCRUPSs) and proposed three structure-modified separators (combined separator, Z-shaped SCRUPSs, and spiral-type SCRUPSs). Deposition mechanisms for droplets with different sizes were considered using commercial CFD flow solver. Results show that three-structure modified separators can increase droplet deposition rate to varying degrees. Regarding flow losses, spiral-type SCRUPSs cause the highest increase, with a total pressure loss coefficient of 231%, although it has the best deposition rate improvement. Among the three structure-modified separators, "Z" shape separator has the best separation performance because of its higher moisture-separation efficiency and lower total pressure loss efficiency. Results could provide theoretical basis for research on and development of this new type of moisture separator.

F213 混合翼付きグリッドスペーサが気液環状二相流の液滴再堆積量に及ぼす影響(OS9 熱・流動(4))

The purpose of this study is to investigate the effects of a grid spacer with mixing vane (MV) on air-water two-phase annular flow in simplified center subchannel, which is seen in fuel rod bundle of a boiling water nuclear reactor (BWR). Two types of spacer, which were grid spacer with and without MV, were installed to the circular pipe of 16 mm in diameter, and deposition rate of liquid droplets in gas core of the annular flow on the channel wall was measured with double liquid film extraction method. From the deposition rate data, it was seen that deposition mass transfer coefficient was much higher for the spacer with MV than the spacer without MV.

Deposition Evaluation of Aerial Electrostatic Spraying System Assembled in Fixed-Wing

<abstract> <bold><sc>Abstract. </sc></bold>There are many difficulties involved with controlling pests and diseases on corn, not least of which include efficiencies relating to process, spraying chemicals, and labor. This study proposes an aerial electrostatic spraying method for the disease and pest control of corn, which is more efficient and economic than previous methods. An aerial electrostatic nozzle embedded with a conical tubular electrode was specifically designed to attach to the fixed-wing aircraft Y5B. Laboratory studies have been conducted to examine the distribution of droplet deposition on the modeled crop targets. Meanwhile, field experiments have also been conducted on the three spray treatments using the aircraft Y5B: electrostatic, non-electrostatic, and rotary sprays. The results showed that compared with non-electrostatic and rotary sprays, the size of the electrostatic spray droplet reduced and the uniformity increased. Also, the coverage of the droplet on the canopy of simulated lab targets increased by 20 and 42 drops·cm^-2. Likewise, the coverage increased 3.71 and 4.33 times on the field targets, when compared to the non-electrostatic and rotary sprays. In particular, there was a significant increase in the number of deposits in the back of the targets. The distribution of the droplet deposition on the vertical canopy showed that the droplet more successfully penetrated the field canopy compared to the same in the lab; and the droplet deposition rate on the middle and bottom of the targets increased significantly. The volume deposition on the middle was highest when using the electrostatic spray application, up to 0.046 μg.cm^-2. The mean deposition calculated was 5.64, 4.26, 3.81 L·ha^-1 for electrostatic, non-electrostatic, and rotary sprays, respectively. The pest control test demonstrated that the cumulative mortality of armyworms was as high as 95.4% under the electrostatic spray treatment, which had better control effects and was more economic than the other two treatments. This study will significantly improve the understanding of the Y5B aircraft aerial electrostatic spraying technique and contribute to the prevention of crop disease and damage.

CFD modelling of stratified/atomization gas–liquid flow in large diameter pipes

A CFD model of stratified flow with atomization has been developed to study the transport of water droplets in gas–liquid multiphase systems in 38in. diameter pipes. Entrained droplets may deposit onto the wall surface, forming a thin draining film associated with an effective interfacial roughness. Secondary flows related to large gas flow rates may enhance the transport of droplets in the top region of the pipe. Gas–liquid surface tension also appears as an important parameter; it is shown to affect the entrainment rate and subsequently, the droplet deposition rate. This work involving water droplets extends the initial study performed with oil droplets entrainment in the gas phase, validated for 8in. pipes, and scaled-up on larger diameter pipes.

Effect of contact angle and drop spacing on the bulging frequency of inkjet-printed silver lines on FC-coated glass

The morphologies of inkjet-printed narrow silver lines on fluorocarbon film-coated glass substrates were measured with varying contact angles and drop spacing to study the actual stability of line printing by using a practical inkjet system. From a practical stability point of view, three types of the lines were observed: stable, unstable, and meta-stable. The stable lines were free from any bulging or breaking; the unstable lines had repetitive and periodic instabilities; and the meta-stable lines had no repetitive instability but had irregular bulges that appear sparsely. Unstable line printing resulted from either the dynamic or static instability of bead flow, which arose when the pressure-driven bead flow was too large or too small compared with droplet deposition rate, respectively. Whether the printing would be stable or meta-stable was determined by the anti-bulging stability of the flow against other disturbances. The anti-bulging stability increased when the bead flow rate was balanced with the printing rate, whereas it decreased for the present system when the flow-balance became sensitive to drop spacing.

On Kinematic Relaxation and Deposition of Water Droplets in the Last Stages of Low Pressure Steam Turbines

In the first part of the paper steady two-phase flow predictions have been performed for the last stage of a model steam turbine to examine the influence of drag between condensed fog droplets and the continuous vapor phase. In general, droplets due to homogeneous condensation are small and thus kinematic relaxation provides only a minor contribution to the wetness losses. Different droplet size distributions have been investigated to estimate at which size interphase friction becomes more important. The second part of the paper deals with the deposition of fog droplets on stator blades. Results from several references are repeated to introduce the two main deposition mechanisms which are inertia and turbulent diffusion. Extensive postprocessing routines have been programmed to calculate droplet deposition due to these effects for a last stage stator blade in three-dimensions. In principle the method to determine droplet deposition by turbulent diffusion equates to an approach for turbulent pipe flows and the advantages and disadvantages of this relatively simple method are discussed. The investigation includes the influence of different droplet sizes on droplet deposition rates and shows that for small fog droplets turbulent diffusion is the main deposition mechanism. If the droplets size is increased inertial effects become more and more important and for droplets around 1 μm inertial deposition dominates. Assuming realistic droplet sizes the overall deposition equates to about 1% to 3% of the incoming wetness for the investigated guide vane at normal operating conditions.

Tailored surface roughnesses for enhanced deposition of fine liquid droplets from a flowing gas

Separating fine liquid droplets from a gas stream is an important operation in many industrial applications. In this paper, the effect of surface roughness on the deposition of droplets was investigated in a series of wind tunnel experiments. The roughness was modelled by 2-D rectangular ridges oriented at 45° to the flow direction. The rate of droplet deposition onto the surface was measured by a conductivity method. It was found that the deposition of droplets onto the roughened surface was enhanced by the roughness and the enhancement increased with ridge size-based Reynolds number. The maximum enhancement of droplet deposition on roughened surfaces over that of the smooth surfaces was observed to be around 150%. Data obtained for droplets with different sizes also indicated that the deposition rate of fine droplets was more dependent on the Reynolds than that of the large droplets. For relatively larger droplets, the enhancement of deposition is mainly caused by momentum-dominated impact. However, for fine droplets this is mainly due to the enhancement of local turbulence.