Effect Of Water Spray Research Articles

Suprathreshold Water Spray Stimulus Enhances Plant Defenses against Biotic Stresses in Tomato.

Mechanical stimuli can affect plant growth, development, and defenses. The role of water spray stimulation, as a prevalent mechanical stimulus in the environment, in crop growth and defense cannot be overlooked. In this study, the effects of water spray on tomato plant growth and defense against the chewing herbivore Helicoverpa armigera and necrotrophic fungus Botrytis cinerea were investigated. Suprathreshold water spray stimulus (LS) was found to enhance tomato plant defenses against pests and pathogens while concurrently modifying plant architecture. The results of the phytohormone and chemical metabolite analysis revealed that LS improved the plant defense response via jasmonic acid (JA) signaling. LS significantly elevated the level of a pivotal defensive metabolite, chlorogenic acid, and reduced the emissions of volatile organic compounds (VOCs) from tomato plants, thereby defending against pest and pathogen attacks. The most obvious finding to emerge from this study is that LS enhances tomato plant defenses against biotic stresses, which will pave the way for further work on the application of mechanical stimuli for pest management.

Effect of water spray on tip leakage flow in a inlet stage of high-speed compressor

Water spray can reduce the inlet air temperature of the compressor inlet stage of the high-altitude high-speed turbine engine. In this paper, the Euler-Lagrange method is used to simulate the gas-liquid two-phase flow with droplet evaporation in NASA Stage 35. The effects of water spray on the heat and mass transfer characteristics of the stage, the tip leakage vortex structure, the unsteady characteristics of tip leakage flow and compressor performance are analyzed. The results show that the water spray increases the inlet mass flow and tip leakage flow rate of the stage, decreases the tip temperature. The inlet mass flow and tip leakage flow rate increase with the growth of inject mass flow rate and the decrease of droplet size. Water spray increases the scale of the main tip leakage vortex, and deflects the secondary leakage flow in the flow direction. Water spray increases the amplitude of pressure fluctuation at the blade tip. The frequency of pressure fluctuation at dry air condition is 0.2BPF, which decreases to 0.15BPF after water spraying. The leakage vortex weakens the strength of shock wave which causes a decline in the diffusing ability of blade; the leakage vortex is mixed with the main stream, resulting in a large aerodynamic loss. Although the injection of droplets increases the loss of tip leakage flow, it optimizes the performance of NASA stage 35 significantly. Spray increases the total pressure ratio of the R domain from 1.835 to 1.9; the total temperature ratio of the stage reduces from 1.225 to 1.203 and decreases the rotor loss coefficient from 0.12 to 0.08.

Fire control and self-extinguishment by blocking smoke flow with water spray in a tunnel fire

This study clarified the effect of water spray on fire control and extinguishment in a tunnel fire. A series of fire experiments were conducted using a 1:10 scale model tunnel to investigate the performance of water spray for suppressing the fire and blocking the smoke produced by the fire. The water spray trapped the smoke in the fire zone and prevented the inflow of fresh air from the tunnel portal. That is, the water spray sealed off the smoke and compartmentalized it in the tunnel. A calorimetry method was developed to estimate the chemical heat release rate (HRR) in the tunnel with the sealed-off descended smoke. Within the test conditions considered in this study, the following results were obtained. First, self-extinguishment occurred in 86% of the cases tested in the fire zone sealed off by the water spray. Second, the maximum HRR of the vitiated fire induced by the water spray was reduced to one-fifth compared to that during free burning. Finally, a ghosting flame and self-extinguishment by suffocation occurred when the smoke blocking rate exceeded about 60% and 80%, respectively.

Stability of smoke stratification under the impact of water sprays with various droplet size ranges in longitudinally ventilated road tunnels

This paper presents a simplified model of tunnel smoke stratification, which can be used to study the effect of sprinkler water spray on stratified stability. The stratified flow downstream of a tunnel fire is represented by a two-layer thermal flow, with the hot upper layer representing the smoke and the cold lower layer representing the ventilation air. The dragging effects of sprays from sprinkler nozzles with various K-factors were numerically studied using FDS code (version 6.7.3). Experiment data reported in the literature successfully validated the accuracy of the CFD method. Spray-induced smoke movements, including the smoke logging distance and the horizontal movement, were determined by releasing a series of massless tracers from the smoke layer inlet. The findings of the work indicate that the dragging effect of a water spray is droplet-size-dependent. The smaller the droplets, the larger the dragging force for a given volumetric spray rate. By applying dimensional analysis and introducing the volume mean diameter into the governing parameters, some correlation models that account for the droplet size were proposed to predict the spray-induced smoke movements and smoke layer heat loss. The new correlation models help complete previous work by the authors and are of practical use for tunnel fire safety design where water sprays are included alongside a longitudinal ventilation system.

Experimental and numerical study on the flow field of longitudinally ventilated tunnels with water spray system

Experiments and numerical simulations have been conducted to study the effect of water sprays on the airflow in longitudinally ventilated tunnels. A physical model tunnel containing single and double column spray systems was built at 1:11 scale and tested in a wind tunnel. The experiments captured the velocity redistribution in the upstream area of the sprays, with the most notable feature being flow acceleration close to the zone of the ceiling. The numerical reproduction of the experiments using Fluent 2021R1 was achieved with good agreement, enabling a detailed study of the flow field. The investigation revealed that the water spray induces a water-air jet, causing blockage to the incoming air and deflecting the air stream towards the ceiling. The CFD method was also implemented to study a ceiling spray system and a side-wall spray system, whose spray properties were scaled from a practical design of water a spray system. Dimensional and theoretical analyses showed that the maximum increase in the mean velocity in the near-ceiling acceleration zone is determined by the momentum ratio of the water spray to the ventilation air and the proportions of areas occupied by the water spray in the ceiling zone and the whole tunnel cross section. A correlation model was proposed using the governing parameters, which accurately predicted the velocity increases. The developing trends of the mean ceiling velocities within and downstream of the spray zone were also discussed in detail. The findings are helpful for the coupling design of the tunnel fire fighting system and can provide guidance for the water curtain strategy, which uses water sprays to prevent smoke from spreading.

Investigating the Effects of H2O Interaction with Rainscreen Façade ACMs During Fire Exposure

Preliminary investigations into adverse reactions between aluminum alloy sheets, used as facings for aluminum composite material rainscreen panels, and water vapor (2Al + 3H2O −> Al2O3 + 3H2) contributing to high-rise façade fire events are reported. Panels containing a PE blend (70% polyethylene 30% calcium carbonate) core were characterised and subsequently exposed to a surface irradiance of 50 kW/m2 using a cone calorimeter, in modified ISO 5660:1/ASTM 1354 procedures, involving water spray. Inverse modeling techniques were applied to determine the effects of water spray on the samples’ combustion parameters. From the current study, evidence for the liberation of diatomic hydrogen (H2) contributing to peak heat release rate during combustion was not found. Observed thermal shock and subsequent degradation led to a greater surface area exposure of combustible inner core material, contributing to an increase for both peak heat release rate (from 393 kW/m2 to 1040 kW/m2) and total energy release (97 MJ/m2 to 117 MJ/m2). Findings suggest no significant increase in the combustibility of aluminum composite panels arises through reduction–oxidation reactions between aluminum-water at 50 kW/m2 irradiance. However, thermomechanical processes, brought upon by environmental conditions and external intervention, may affect the dynamic combustion behavior of aluminum composite panels.

Experimental investigation of CsI aerosol removal in containment spray system test facility of 700 MWe IPHWR

Post-accident management of the radionuclide in a nuclear reactor is always a focus point from the nuclear power plant safety point of view. A number of systems using different radionuclide scrubbing mechanisms are already deployed in the Indian nuclear reactors to safeguard the public during and post-accident scenario. However, it is always desirable to achieve “As Low As Reasonably Achievable” (ALARA) philosophy. In the same lines, to further strengthen the safety of Indian nuclear reactors, Containment Spray System (CSS) is introduced in 700 MWe Indian pressurized heavy water reactors to cater/mitigate the aftermath of the Design Basis Accidents (DBA) i.e., Loss Of Coolant Accident (LOCA) and Main Steam Line Break (MSLB). It provides the fast vapour suppression and radionuclide removal from containment during/post design basis accidents. In the present work the experimental investigation of the effect of water spray on the CsI aerosol scrubbing/CsI aerosol removal is studied in a scaled down facility. Experiments are also carried out for the CsI aerosol removal when spray is not operating. In order to encompass the containment pressures during DBA, 1.0 bar(g) initial vessel pressure is used to simulate the accident conditions. For simulation of aerosols after accident CsI nano particles (spherical) suspended in the air and CsI dry aerosols are used. The spray flow rate for all the experiment is kept constant approximately 11.3 lpm. However different Sauter Mean Diameter (SMD) (D32 = 590 µm, 745 µm, 1000 µm) are used to study the effect of droplet diameter on CsI aerosol removal. The temporal variation of the vessel relative pressure gas mean temperature and wall temperature is measured. Vessel depressurization rate with time is recorded. CsI aerosol removal/ CsI aerosol concentration variation with time is measured using two diverse measurements system namely scrubber method and Optical Particle Counter (OPC). Global decontamination factor and global collection efficiency is deduced based on the studies. Few tests without spray are also carried out to estimate the plate out effect on CsI aerosol removal.

Effects of water spray on smoke layer in buildings with natural venting

Fire safety is always an important issue in the indoor and built environment. There might be hidden conflicts among different systems such as suppression and smoke control. The effect of water spray on smoke movement in halls with natural venting system is reported in this paper. A series of scale modelling experiments were carried out to study the temperature variation under water spray. A small vent on the opposite side of fire source would intensify smoke stratification and result in a higher smoke temperature. Water spray would weaken the smoke stratification due to the cooling effect on the smoke and the downward drag on the smoke layer. The temperature development of smoke was the result of competition of these two effects on the smoke layer. When the effect of water spray was stronger, the average smoke temperature tended to be lower, and the temperature difference of the ceiling to the smoke layer interface was smaller. When the effect of the opening dominated, the results were reversed. These results would be useful for providing fire safety in indoor and built environment.

Large eddy simulation of smoke blocking by water sprays in a tunnel fire

This study presents a large eddy simulation (LES) of smoke blocking by water sprays in tunnel fires to investigate the effect of water sprays on the characteristics of the smoke flow. This study uses an LES solver – FireFOAM. In addition, fire experiments using a 1/10 scale model tunnel with two water spray nozzles are conducted to validate the LES results. The length of the model tunnel is 12 m, the height and width are 0.5 m, respectively, and the heat release rate of the fire is 7.38 kW (2.33 MW in full scale). Each spray nozzle operates at a pressure of 0.3 MPa, and the volume median diameter of spray droplets is 226 μm. First, a grid sensitivity analysis on the gas temperatures under free-burn conditions is performed. A 1.25 cm uniform mesh is chosen in the tunnel domain for all subsequent simulations. Then, FireFOAM predictions are validated against experimental data on the distribution of water spray mass flux under conditions without the fire and the gas temperatures measured under conditions with and without the water sprays. The water spray mass flux and gas temperatures predicted by FireFOAM show good agreement with the measurements. Next, the characteristics of the smoke flow are investigated in the presence of the water sprays. It is found that the water sprays block part of the smoke flowing under the ceiling and force it to descend to the ground. The descended smoke flows back in the lower part of the fire zone, and a vitiated air layer is formed. The vitiated air layer is composed of the smoke flowing back and fresh air drawn from the portal. On the other hand, some smoke leaks through the water spray zone and flows along the ceiling on the portal side. It is also found that the spray cooling delays the propagation of the leaked smoke toward the tunnel portal. Furthermore, it is quantitatively shown that the buoyant flow stratification destroyed by the water sprays becomes thermally and chemically stabilized again on the portal side, for the specific case under this study. Last, the smoke blocking performance is quantified based on the mass flow rates of the smoke flowing under the ceiling in the fire zone and the smoke flowing back toward the fire. A comparison of the smoke blocking rates between the predictions (time dependent: 40–50%) and measurements (steady: 39.4%) shows good agreement.

Explosion risk-based water spray mitigation analysis of ultra-deep-water semi-submersible platforms

Water spray is an economical and environment-friendly alternative to mitigate gas explosion. This study conducts explosion risk analysis (ERA)-based water spray mitigation analysis of ultra-deep-water semi-submersible platform. 5000 gas explosion simulations with and without water spray are conducted by using FLACS codes. The outcome demonstrates that water spray with droplet size 700 μm and water application rate (WAR) 26 L/m2 min is most effective to mitigate explosion scenarios. The droplet size is the significant factor to stimulate the mitigation effect of water spray under middle and small exceedance frequencies, e.g., 1E-05 and 1E-06. WAR becomes dominate to awaken the water spray's negative effect under large exceedance frequency, e.g., 1E-04. A precise and efficient approach of BRANN integrated with artificial bee colony optimization algorithm is used to determine the optimal water spray configuration given the desirable exceedance frequency and the expected design accidental load that the ultra-deep-water semi-submersible platform structures could resist.

Numerical investigation on the stability of tunnel smoke stratification under the effect of water spray and longitudinal ventilation

Tunnel smoke stratification has been reported to exist in the vicinity of a fire source, even under moderate ventilation conditions, which is of importance for occupant evacuation. To understand the effects of a water spray on its stability, a two-layer thermal flow model was built, and a series of scenarios considering different ventilation rates, water spray rates and smoke temperatures were numerically investigated. The ability of the Fire Dynamic Simulation (FDS) tool to predict such a two-phase problem was determined by validating against experimental and zone model data found in the literature. Then the tracer method was adopted to closely observe the smoke and droplet interactions in the two-layer model used in this paper. General effects of the ventilation flows and water spray on the maximum smoke logging distance and its corresponding horizontal displacement were observed. It was found that increasing the ventilation rate promotes the horizontal displacement but weakens the maximum downward distance, while increasing the water spray rate boosts the movements in both directions. Models based on nondimensional analysis for predicting the smoke displacements and the heat loss due to water spray were obtained. The observation of droplets indicates that a water spray globally blocks the horizontal smoke movement, and the upstream part of the water spray contributes 56.7% of the total downward drag forces. This work is helpful in revealing some of the underlying mechanisms behind the interactions of water spray and smoke stratification in the presence of longitudinal ventilation.

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.

Effect of water spray on degradation of styrene-butadiene-rubber during accelerated weathering tests

Accelerated weathering tests using a xenon lamp were performed on styrene-butadiene rubber (SBR) under two conditions: only photo irradiation (photo-irradiated condition) and the addition of intermittent water spraying to photo irradiation (photo-irradiated/water-sprayed condition). Degradation mechanisms under these conditions were evaluated based on changes in chemical structure, hardness, and morphology of the exposed surface during weathering tests. The morphology of the exposed surfaces differed significantly between the two weathering conditions. Random minute cracks, known as crazes, were clearly observed under the photo-irradiated/water-sprayed condition. To clarify the origin of such craze propagation, the temperature change accompanying water spraying was traced. A combination of temperature decrease during water spraying and subsequent increase due to water evaporation was repeated under the photo-irradiated/water-sprayed condition. Such periodic temperature change caused the sample to expand and contract; however, the exposed surface could not follow this dimensional change, resulting in craze. This result indicates that water spraying is a degradation factor for accelerated weathering tests on SBR, especially change of surface shape.

Effect of water spray in exhaust passage of steam turbine on flow field of the last stage during windage

Under the windage condition, the steam in the last stage of steam turbine absorbs energy from rotor blade, which leads to overtemperature of the exhaust steam. Water spray is an effective way to lower the temperature in exhaust passage. The Euler-Lagrange particle tracking method is used to study the heat and mass transfer of the water spray in exhaust passage. The quantity of water spray under different conditions is predicted and the effect of water spray on the last stage flow field is analyzed. The results show that there is a small temperature difference between steam and liquid in the exhaust passage and a minimum evaporation of droplets for high steam velocity. The water spray quantity has a negative correlation with the inlet steam mass flow rate under different conditions and the ratio of water spray quantity to the inlet mass flow rate (water/steam ratio) has a quadratic relationship with the operating conditions. From 20%THA (Turbine Heat Acceptance) to 7%THA, the ratio of steam evaporated by water to mixture-vapor (H2O/mixture-vapor ratio) increases from 0.05% to 0.95%, and the water/steam ratio increases from 22% to 300%. The water spray has little effect on the rotor-stator clearance vortex and the separation vortex, but the height and velocity of the back flow vortex are increased. Meanwhile, the pressure of the last stage and the pressure ratio of the rotor blade increase, which result in the dissipating shaft power of the rotor blade reduces. Water spray has an effect on the flow field of the last stage, which is of great significance to correctly predict the windage conditions and study the dynamic characteristics of the rotor blade.

Airflow driven fluid–structure interaction subjected to aqueous-based liquid spraying

Artificial saliva sprays are commonly used to remedy vocal folds surface hydration. Vocal folds surface hydration and its effect on their auto-oscillation are studied experimentally using artificial vocal folds. The airflow is used to excite the vocal folds into auto-oscillation after which the vocal folds surface is sprayed with a liquid. The validity of the findings described in a previous study [A. Bouvet, X. Pelorson, and A. Van Hirtum, “Influence of water spraying on an oscillating channel,” J. Fluids Struct. 93, 102840 (2020)] concerning the effect of water spraying is further investigated. First, artificial saliva sprays (up to 5 ml) are sprayed instead of water. It is shown that this allows us to address the effect of increased dynamic viscosity (up to 8 times compared to water) as other artificial saliva properties affecting air–liquid mixing and surface wettability remain similar to water. Second, the Reynolds number in the dry stage is systematically increased (with 60%) for constant spraying volume ≥3 ml. Regardless of the sprayed liquid and Reynolds number, oscillation cycles are characterized by an increase in mean upstream pressure, cycle-to-cycle variability, and a decrease in oscillation frequency due period doubling. Increasing the dynamic viscosity tends to reduce the magnitude of these tendencies for spraying volumes smaller than 3 ml, indicating that viscous liquid–gas mixing affects the flow regime. Systematic Reynolds number variation shows that liquid spraying increases the oscillation onset threshold pressure and that the magnitude of general tendencies is reduced. The assessed conditions and features are pertinent to human voice production after hydration with an artificial saliva spray burst.

Experimental investigation of water spray on suppressing lithium-ion battery fires

This work investigated the effects of water spray on lithium-ion battery (LIB) fires. Experiments were conducted on single cell and multi-cell batteries to study the effect of water volume and spray pressure on the fire extinguishing and the effectiveness of preventing propagation of thermal runaway in LIB's. Meanwhile, the potential hazard of water spray as a fire extinguishing method was assessed by investigating the influence of water on combustion gas production during extinguishing. It was found from these experiments that water spray can effectively extinguish 21700 LIB fires and reduce the maximum surface temperature of LIB. But the water spray has no significant difference in cooling rate after temperature recovery. The contact efficiency between the water spray and batteries decreased with the increase in water pressure. With sufficient volume of water spray and high contact efficiency, water spray can inhibit the thermal runaway propagation. With insufficient volume of water spray or low contact efficiency, the time to onset of thermal runaway was delayed. Water affects combustion gas production during thermal runaway. When water was applied, the concentration of CO, H2 and HF increased, while CO2 decreased.

Experimental Study of the Effect of Water Spray in the Air on Thermal Transfers Along a Plate of an Exchanger

Abstract This study is an experimental investigation of the oceanic environment effect on a plate heat exchanger performance. Indeed, an experiment was carried out on a single plate of the exchanger to generate a turbulent airflow in which fine water droplets were injected into a horizontal vein where a heated plate was placed. The experimental tests were conducted for different air velocities and various water concentrations of freshwater and saltwater. In fact, two plate forms were considered: The first one is flat while the second is corrugated. Three main facts were observed in this work: (i) the correlations linking the heat transfer rate to the operating conditions, (ii) the effect of fog addition and the plate form on convective heat transfers, and (iii) the impact of the formation of a salt layer on the surface of the plate in the case of salt water.

Fire cooling performance by water sprays using medium and small-scale model experiments with scaling relaxation

The fire cooling performance by water sprays is investigated in medium and small-scale fire cooling experiments. The scaling relationships considered are the fire diameter, spray height, heat release rate, spray angle, flow rate, working pressure, and droplet diameter. Full-cone-type spray nozzles of different sizes are used in both scale experiments. Although spray conditions (spray angle, flow rate, pressure, and droplet diameter) satisfying the scaling relationships are used, when the geometrical scaling of the nozzles is not sufficient, the water spray mass flux distributions generated by the nozzles do not fulfill the scaling relationship. To resolve this problem, we propose a new scaling relaxation for scaling the fire cooling effect of water sprays even under incomplete scaling conditions in the water spray mass flux distributions. In the scaling relaxation, we propose an effective plane in which the group of water droplets collides with the fire plume, and assume that only the water droplets passing through the effective plane contribute to fire cooling. Based on the experimental data, we show that scaling with sufficient accuracy is possible by normalizing with the spray flow rate directly contributing to the fire cooling. The scaling accuracy tends to decrease with the increasing spray angle.

The effect of water spray on the release of composite nano-dust.

To evaluate the collection efficiency of water spray on the release of airborne composite particles during grinding of composite materials. Composite sticks (L:35 mm × W:5.4 mm × H:1.6 mm) of seven commercial dental composites were ground with a rough diamond bur (grain size 100 μm, speed 200,000 rpm). All experiments were performed in an enclosed 1-m3 chamber with low particulate background (< 1,000 #/cm3), and airborne particles were evaluated based on their electrical mobility. The number size distribution was determined by scanning mobility particle sizer (SMPS). Particles were collected by an electrostatic precipitator (ESP), and were ultramorphologically and chemically analyzed by a transmission electron microscope equipped with energy-dispersive X-ray spectroscopy (TEM-EDS). SMPS measurements confirmed that both dry and wet grinding generated high concentrations of nanoparticles particles with the highest concentration recorded during the last minute of grinding (1.80 × 106 - 3.29 × 106#/cm3), after which a gradual decline in particle concentration took place. Nevertheless, grinding with water spray resulted in a significant reduction of the number of released particles (5.6 × 105 - 1.37 × 106#/cm3). The smallest particle diameter was recorded during the last minute of grinding followed by a continuous growth for every next measurement. TEM of composite dust revealed a high concentration of particles varying in both size and shape. Regardless of whether the water cooling spray system was used during bur manipulation of composite materials, predominately nanoparticles were released. However, the particle concentrations were significantly decreased with water spray. Since water spray might not be sufficient in nanoparticle collection, special care should be taken to prevent inhalation of composite dust.

Numerical investigation of the effects of polydisperse water sprays on extinction conditions of counterflow methane non-premixed flames

Water, sprayed in the form of tiny droplets, has emerged as a potential fire suppressant after the halon compounds such as trifluorobromomethane (CF3Br, Halon 1301) were banned by the Montreal protocol. The size distribution of the water droplet plays a crucial role in the effectiveness of the water spray in fire suppression. A numerical investigation of the influence of size distribution of a polydisperse water spray on extinction of counterflow diffusion flames is presented in this paper. This study uses laminar finite rate model with reduced CHEMKIN chemistry for numerical simulations. The discrete phase, namely the water spray, is simulated using Lagrangian Discrete Phase Modelling approach. In this work, the polydispersity of water spray is taken into account in the numerical simulation by a suitable Rosin–Rammler distribution. Results obtained from numerical simulation are validated with the experimental results reported in the literature. This study demonstrates that the representation of the polydisperse spray by a monodisperse spray (with droplet diameter same as the SMD of the polydisperse spray) in numerical simulations is not always justified and it leads to deviation from the experimental results. The effects of number mean diameter and spread parameter on the efficacy of flame suppression are investigated for polydisperse sprays. A comprehensive comparison is done between the effectiveness of monodisperse and polydisperse water sprays. An optimum droplet diameter is obtained for monodisperse sprays for which the effectiveness of the spray is maximum. The effects of evaporation Damköhler number and Stokes number of water droplets on flame suppression have also been explained.