Wall Spray Research Articles

New thinking for filth fly control: residual, non-chemical wall spray from volcanic glass.

Filth flies are of medical and veterinary importance because of the transfer of disease organisms to animals and humans. The traditional control methods include the use of chemical insecticides. A novel mechanical insecticide made from volcanic glass and originally developed to control mosquitoes (Imergard™ WP; ImG) was investigated for control of adult grey flesh flies, Sarcophaga bullata (Parker), secondary screwworms, Cochliomyia macellaria (F.), and house flies, Musca domestica L. In a modified WHO cone test device, the time to 50% mortality (LT50 ) when applied at 5 g/m2 (tested at 30 °C and 50% relative humidity (rH)) was 7.1, 4.3 and 3.2 h, respectively. When knockdown was included, the LT50 s were 5.5, 1.5 and 2.8 h, respectively. Application rates of 1.25 and greater g/m2 had the shortest LT50 s. The time to the LT50 increased for M. domestica as rH increased, but ImG was still active at the highest rH tested of 70%. Scanning electron micrographs showed ImG was present on all body parts, unlike that for mosquitoes where it was found mostly on the lower legs. These first studies on the use of Imergard WP against flies suggest this could be an alternative method for filth fly control.

ImergardTMWP: A Non-Chemical Alternative for an Indoor Residual Spray, Effective against Pyrethroid-Resistant Anopheles gambiae (s.l.) in Africa

Malaria is the deadliest mosquito-borne disease and kills predominantly people in sub-Saharan Africa (SSA). The now widespread mosquito resistance to pyrethroids, with rapidly growing resistance to other insecticide classes recommended by the World Health Organization (WHO), may overturn the successes gained in mosquito control in recent years. It is of utmost importance to search for new, inexpensive, and safe alternatives, with new modes of action, that might improve the efficacy of current insecticides. The efficacy of a novel mechanical insecticidal mineral derived from volcanic rock, ImergardTMWP, was investigated to determine its efficacy as a stand-alone residual wall spray and as a mixture with deltamethrin (K-Othrine® Polyzone) in experimental huts in Cove, Benin. The evaluation was conducted with susceptible (Kisumu) and wild-type Anopheles gambiae (s.l.). Deltamethrin applied alone demonstrated 40–45% mortality (at 72 h post-exposure) during the first four months, which declined to 25% at six months for wild An. gambiae from Cove. ImergardTMWP alone and mixed with deltamethrin, under the same assay conditions, produced 79–82% and 73–81% mortality, respectively, during the same six-month period. ImergardTMWP met the 80% WHO bio-efficacy threshold for residual activity for the first five months with 78% residual activity at six months. ImergardTMWP can be used as a mixture with chemical insecticides or as a stand-alone pesticide for mosquito control in Africa.

Microencapsulation of Bacillus megaterium NCT-2 and its effect on remediation of secondary salinization soil

Aim: To prolong the shelf life of Bacillus megaterium NCT-2 by preparing microcapsules through spray drying, and evaluate their efficiency in secondary salinisation soil remediation.Methods: The wall material and spray drying conditions were optimised. Morphological characteristics of microcapsule were measured, and soil remediation effects were tested under field conditions.Results: A relatively higher survival rate of B. megaterium microcapsule was obtained with 1:1 of chitosan/maltodextrin (w/w) when spray drying was performed at 150.0 °C, with the feed flow rates of 800 mL h−1 and 1000 mL h−1, respectively. The span value of 0.93 ± 0.01 was obtained under above conditions. Microcapsule survival rate was 64.09 ± 0.12% after 6 months of storage. Moreover, microcapsule successfully decreased NO3− and EC value in strongly saline soil by 46.5 ± 1.48% and 45.2 ± 1.51%, respectively.Conclusion: Bacillus megaterium NCT-2 microcapsules have application potential in the remediation of secondary salinisation soil.

Modeling of Aqueous Urea Solution Injection with Characterization of Spray-wall Cooling Effect and Risk of Onset of Wall Wetting

The definition of a sufficiently resolved heat transfer model with spray cooling effect as a function of each droplet kinetic and thermal parameters is a key factor in the numerical simulation of aqueous urea (AUS) based Selective Catalytic Reduction (SCR) exhaust after-treatment systems.A consolidated spray-wall interaction model [1] has been implemented on the open source 3D finite volume software OpenFOAM and a critical investigation of its behaviour in engine representative conditions is reported.A simplified test case is used to highlight the influence of the chosen model on the numerical simulation of the system, reducing the importance of the other spray sub-models in the Lagrangian-Eulerian computational framework. The coupling between the droplet evaporation heat flux and the gas-solid interface thermal boundary condition has been studied, pointing out the significance of each contribution.The main focus of this work is to present reference conditions to simulate the spray-dry wall spray impingement behavior to determine the ‘onset of wall wetting’ thermal conditions.

Determination of Pomegranate Juice Powder Properties Produced by a Pilot Plant Spray Dryer with a Two-Fluid Nozzle

The ingredients in pomegranate juice are invert sugars, citric acid, and a small amount of malic acid, all of which have low glass transition temperatures. Due to this characteristic, the particles stick to the dryer wall upon their collision with it. In order to solve the stickiness problem, maltodextrin DE12 and silicon dioxide were used as carriers to reach a suitable drying condition. A cool chamber wall spray dryer was employed in order to decrease the probability of particles stickiness on the wall. A suitable two-fluid nozzle was selected based on the feed rate of the dryer. The nozzle accessories were built in order to assemble the nozzle on top of the spray dryer. Our investigation revealed that the addition of 3% silicon dioxide and 35% maltodextrin DE12 to pomegranate juice was the optimum amount for complete and successful drying of pomegranate juice. The powder particles were amorphous and did not have a crystalline structure, so the powder solubility was high. By increasing the air temperature of the dryer, the solubility of the pomegranate powder decreased. Increasing the feed rate from 0.16 to 0.3 L/min resulted in increasing solubility from 80 to 95%. By increasing the powder storage period, color specifications (L, a, and b) decreased. Increasing the inlet air temperature caused some reduction in color specifications and decreasing the feed rate led to decreasing color specifications. Adsorption isotherms of pomegranate powder samples had a sigmoid shape, which is typical of hygroscopic materials. Kuhn's and Iglesias and Chirife's models fitted very well with the experimental moisture content data.

Transient fuel spray impingement at atmospheric and elevated ambient conditions

This study analyses detailed temporally resolved full flow field data for pre- and post-impingement fuel sprays under atmospheric and elevated ambient conditions. A comprehensive suite of diagnostic techniques is utilised comprising of phase-resolved Phase Doppler Interferometry—employing a very fine grid and velocity signature to differentiate between pre- and post-impingement droplets—high-speed imaging (utilising Mie-scattering), high-magnification shadowgraphy and an adapted instantaneous mass-rate tube. Raised ambient conditions are achieved in a high-temperature, high-pressure constant volume rig affording large optical access. Temporal data for the free and impinging sprays is compared and analysed within three phases—early, mid and late injection—defined by the mass-rate tube data. All experimental techniques employed present consistent temporal and spatial trends at atmospheric and elevated ambient conditions, and global trends are consistent with the phenomenological flow structure originally proposed by Ozdemir and Whitelaw. Detailed analysis close to the piston surface reveals approximately a threefold increase in the D50 mean spray diameter for the post-impingement droplet size distribution at the wall spray tip. It is suggested that this is due to droplet coalescence, with some supporting evidence from high-speed imaging. Comparison of transient mass deposited on the surface with model predictions show reasonable agreement with the ‘Wet’ model assumption.

Prediction of the Rate of Heat Release of Mixing-Controlled Combustion in a Common-Rail Engine with Pilot and Post Injections

A one-dimensional model for the prediction of the rate of heat release (ROHR) in common-rail direct-injection diesel engines with pilot, main, and post injections is developed. The model is an improvement on the previously developed mixing-controlled combustion model extended by including the effect of the wall jet. The decay of the ROHR curve has been improved in the second regime of combustion. It was observed that the input kinetic energy of the wall spray is retarded only after the growth of spray along the bowl wall exceeds the diameter of the spray cone. It is shown that this model can be extended for engines with multiple injections, i.e. pilot, main, and post injections. The ROHR was modelled as a function of the turbulence kinetic energy of the fuel mass and the dissipation rate of this energy in different stages of spray propagation. The inputs required for the model are the nozzle discharge coefficient, the injection pressure, the injection timing, and the injected fuel quantity for each injection stage that are readily controlled in common-rail engines. The predicted heat release histories corresponding to the pilot injection, the main injection, and the post injection were found to be in agreement with the experiments.

Mosquito Biting and Movement Rates as an Emergent Community Property and The Implications for Malarial Interventions

Malaria, a mosquito-vectored disease, continues to be one of the most important scourges afflicting humankind. In this paper, we take a mosquito-centric approach by studying mosquito states (i.e., energy, neurological health, and toxin information state) to demonstrate how key parameters of malaria, biting and movement rates and mosquito survival, are all emergent properties of those states when considered in the context of the background community interactions. We do so as follows: First, we develop a dynamic state variable model of mosquito biting and movement decisions that maximize mosquito expected reproductive success (fitness), and then we embed those optimal policies in a Monte Carlo simulation wherein mosquitoes attempt to feed on human hosts at domiciles where insecticide-treated bednets (ITNs) and insecticidal residual wall sprays (IRSs) are used. We find that biting rates, at the domicile level, are not impacted by mosquito state but that emigration rates from domiciles are determined by an interaction between mosquito energy state, information state, and risk of predation. This means that malaria incidence, at the village level at least, may be best understood as a response of mosquitoes to their ecological community that includes nectar-bearing plants, predators, the spatial arrangement of homes, and the protection of humans in those homes.

Numerical investigation of the effect of fuel injection mode on spray/wall interaction and emission formation in a direct injection diesel engine at full load state

The effect of three injection rate modes on fuel spray-wall impingement and combustion process in a direct injection diesel engine is investigated in present work. A three-dimensional computational fluid dynamics model for flow field, spray, spray-wall interactions, combustion, and emission formation processes have been used to carry out the computations. The optimized omega combustion chamber geometry was used in the diesel engine model instead of baseline cylindrical geometry and the results were verified for this improved combustion chamber geometry. Results for different injection modes indicate that using the ramp injection rate curve, the spray-wall impinging is increased due to higher injection rate at the end of injection duration. Also the increased in-cylinder temperature, piston surface temperature and higher turbulence intensity leads to enhanced wall-film evaporation. Soot mass fraction also decreases due to improved air-fuel mixing and evaporation of wall-film by reduction of the fuel rich zones especially in the impingement regions. Results for different injection modes indicate that using the ramp injection rate shape slightly retards the combustion process and improves combustion characteristics while maintaining lower NOx and considerably lower soot emissions compared to the boot and rectangle injection modes. Also, in this injection mode, because of the high pressure injection, higher spray droplet velocities (higher Weber number) and increased wall spray height than the other modes, it could be said that the dominant impingement regime may be the splashing regime. The results of model for baseline diesel engine are compared with the corresponding experimental data and show good levels of agreement.

Atomized non-equilibrium two-phase flow in mesochannels: Momentum analysis

Two-phase pressure drop measurements are very difficult to make while the fluid is in non-equilibrium condition, i.e. while phase change is taking place. This is further complicated when an atomized liquid is introduced in the system at much higher velocity than other components such as liquid layer, vapor core, and entrained droplets. The purpose of this paper is to develop a model to predict the two-phase pressure characteristics in a mesochannel under various heat flux and liquid atomization conditions. This model includes the momentum effects of liquid droplets from entrainment and atomization. To verify the model, an in-house experimental setup consisting of a series of converging mesochannels, an atomization facility and a heat source was developed. The two-phase pressure of boiling PF5050 was measured along the wall of a mesochannel. The one-dimensional model shows good agreement with the experimental data. The effects of channel wall angle, droplet velocity and spray mass fraction on two-phase pressure characteristics are predicted. Numerical results show that an optimal spray cooling unit can be designed by optimizing channel wall angle and droplet velocity.

Validating the Phenomenological Smoke Model at Different Operating Conditions of DI Diesel Engines

A new phenomenological model that was published in Aghav et al. (2005, “Phenomenology of Smoke From Direct Injection Diesel Engines,” Proceedings of ICEF2005, ASME Paper No. 1350) encompasses the spray and the wall interaction by a simple geometrical consideration. The current study extends this earlier work with investigations made on 16 different engines from six-engine families of widely varying features, applied to off-highway as well as on-road duty. A dimensionless factor was introduced to take care of the nozzle hole manufactured by hydroerosion, as well as the conical shape of the nozzle hole (k factor) in the case of valve-closed-orifice type of nozzles. The smoke emitted from the wall spray formed after wall impingement is the major contributor to the total smoke at higher loads. As the fuel spray impinges upon the walls of the combustion chamber, its velocity decreases. This low-velocity jet contributes to the higher rate of the smoke production. Therefore, the combustion bowl geometry along with injection parameters play a significant role in the smoke emissions. The new model is one dimensional and based on the recent phenomenological description of spray combustion in a direct injection diesel engine. The satisfactory comparison of the predicted and observed smoke over the wide range of engine operation demonstrated applicability of the model in simulation study of combustion occurring in direct injection (DI) diesel engines.

An Experimental Investigation of Lime Juice Drying in a Pilot Plant Spray Dryer

One of the major problems in spray drying of fruit juices such as lime juice is stickiness and thermoplasticity of their compositions. Lime juice consists of invert sugars and citric acid, which have low glass transition temperatures. Due to this characteristic, the particles stick on the dryer wall upon their collision with it. As a result, drying of these materials is very difficult. In order to solve this problem, various percent of silicon dioxide and maltodextrin (DE5), based on total soluble solid content of lime juice, have been used to reach a suitable drying condition. A cool chamber wall spray dryer was used in this investigation in order to decrease the probability of particles stickiness on the wall. Our investigation revealed that an addition of 10% silicon dioxide and 20% maltodextrin (DE5) to lime juice is the optimum amount for a complete and successful drying of lime juice. Sampling of particles from different longitudinal distances in the dryer tower is carried out to find the particle moisture contents as they fly downward in the dryer. The results show a very fast decrease in entrance moisture contents. Based on our experimental data, the variation of moisture contents are presented as a function of radial distance from central line and longitudinal distance from the entrance region.

Modeling of diesel spray impingement on a flat wall

To understand the transient behavior of droplets after impingement in a diesel engine, a numerical model for diesel sprays impinging on a flat wall is newly developed by the proposition of several mathematical formulae to determine the post-impingement characteristics of droplets. The new model consists of three representative regimes such as rebound, deposition and splash. The gas phase is modeled in terms of the Eulerian conservation equations, and the dispersed phase is calculated using a discrete droplet model. To validate the new model, the calculated results are compared with several experimental data. The results show that the new model is generally in good agreement with the experimental data. Therefore, it is thought that the new model is acceptable for the prediction of transient behavior of wall sprays.

Modelling and experiment of impingement and atomization of a liquid spray on a wall

An experimental and computational investigation of spray impingement on a flat surface is presented. Different angles of incidence are studied, namely 30, 45 and 60°C measured from the normal to the surface. Back-lit photographs of the wall spray taken at various times during the impingement period give a qualitative view of the secondary atomization process. A stochastic model based on the sampling of velocity and size distributions of secondary droplets is used to simulate the creation of incident droplet fragments created by the numerous splashing events occurring during the impingement period. Size characteristics of the secondary droplet cloud are computed at various points in the impingement region and these are compared against phase/Doppler particle analyser (P/DPA) measurements yielding reasonable agreement. The effect of surface roughness is incorporated into the model and is found to play a major role in affecting the splashing threshold and the sizes of splashing fragments. The secondary droplet distributions are virtually unchanged among the different angles of incidence. This behaviour is explained by considering the shift in the splashing droplet distribution as a function of incident angle.

Numerical studies of an impingement-conditioned small direct-injection diesel engine

Numerical studies are performed to identify an optimal range of geometric parameters in connection with the design of an impingement-conditioned small direct-injection diesel engine. The parametric studies were made in a pressure chamber with a circular protrusion on to which sprays are directed to impinge. Computational runs were made for 24 cases carefully chosen to allow examination of the effects on post-impingement spray characteristics of the following parameters: (a) the nozzle-plate distance and (b) the size and geometry pattern of the protrusion. An optimal range of these parameters has been identified through an analysis of the calculated results in terms of vapour concentration, the Sauter mean diameter of the wall spray and the dispersed wall spray volume. The results obtained also reveal that, by just changing the size of the impingement surface and the impingement distance, local fuel vaporization efficiency can be increased as high as 40 per cent under the same injection and ambient conditions. This raises the possibility that spray impingement may be conditioned in a manner ensuring good fuel distribution and a sufficient fuel-air mixing rate without even resorting to swirling air, thus improving substantially the engine efficiency.

96/06331 Comparison of wall spray impaction models with experimental data on drop velocities and sizes

96/06331 Comparison of wall spray impaction models with experimental data on drop velocities and sizes

Comparison of wall spray impaction models with experimental data on drop velocities and sizes

This paper describes the testing of several spray/wall impaction models developed by the authors and colleagues. A previously unpublished model is described in detail. Most models of spray impaction onto solid surfaces have previously been assessed by comparing the wall spray penetration rates and spray shapes with experimental data. There is a need to establish the ability of models to predict the internal structure of the sprays, because this will influence such parameters as heat transfer and fuel evaporation. Here, therefore, the models are further tested by comparing computer predictions against phase-Doppler anemometry data on spray velocities and drop sizes within the wall spray. The results show that the latest model described here is generally superior to earlier wall impaction submodels in describing these features of the spray. However, the agreement is far from complete, and it is evident that further work is required to enhance the predictive capabilities of the model.

The Effect of Boundary Conditions on the Downstream Penetration of Pulsed Sprays After Impaction on a Flat Surface

An experimental study has been conducted of the wall sprays produced after impaction on a flat surface by the pulsed spray from a single hole nozzle. The experiments are of relevance to direct injection diesel engines and they extend the range of boundary conditions covered in previous work, with variation of gas density, spray wall angle, gas cross-flow velocity and cross-flow turbulence level. The initial and boundary conditions are documented to provide a database which is suitable for computational fluid dynamics (CFD) model validation of an important aspect of diesel engine in-chamber flow. Previous work in the area is described and published empirical correlations are reviewed. The measurements of wall spray penetration as a function of time are presented and described and a correlation equation is proposed which fits the data with good accuracy.

Modeling wall impaction of diesel sprays

A model for diesel spray wall impaction is presented, which is assessed against experiments for a number of test cases, including normal or angled injection to a wall into a quiescent space or a cross-flowing gas at various gas pressures. New relationships are given for the velocities of the droplets rebounding from the wall. These relationships take into account the wall roughness and the possible break-up of the droplets during their impingement. The impingement model was incorporated in a spray model based on the stochastic particle technique (Dukowicz 1980) and accounts for the phenomena of droplet injection, break-up, collision and coalescence, turbulent dispersion, and evaporation. The spray model was incorporated in a recently developed three-dimensional (3-D) computational fluid dynamics (CFD) code that simulates the unsteady compressible flow of the gas in internal combustion engines by solving the full Navier-Stokes equations. It was found that the motion of the surrounding gas caused by the spray injection plays a minor role on the predicted results. The latter concern the wall spray radius and the wall spray height. The validity of the spray model is demonstrated through extensive comparisons with experiments over a wide range of gas conditions.

Numerical modeling of diesel spray wall impaction phenomena

A model for diesel spray impaction on walls is presented that is based on experimental observations. The model, which is incorporated into a two-phase CFD code employing a discrete droplet model for the liquid spray and the implicit noniterative PISO algorithm for gas equations, is assessed against experiments for a number of test cases including normal or angled injection into a quiescent space or a cross-flowing gas. In most of the cases studied, the wall spray radius is reasonably well predicted, but the wall spray height is always underpredicted. In order to capture the dispersive nature of the wall spray that contributes to the wall spray height, the original drop-drop collision model of O'Rourke and Bracco is extended to allow for the effects of multicollisions between two drop parcels in a the thick spray. The extended collision model works well in two-dimensional cases but is not fully assessed in three-dimensional cases. The wall impaction model is also implemented in the three-dimensional EPISO engine code. Preliminary results on the simulation of diesel spray impingement in an actual engine suggests that the model is there also capable of producing reasonable wall sprays.