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ElectroHydroDynamische Atomisatie (EHDA) wordt ook wel “electrospraying” genoemd. Atomisatie is het proces van het uit elkaar vallen van een vloeistof in kleine druppeltjes. Een elektrisch veld wordt toegepast om het proces van druppelvorming (grootte van de druppels) te beïnvloeden en de druppeltjes een elektrisch lading mee te geven. De geladen druppeltjes stoten elkaar af waardoor een nevel ontstaat. Deze wordt aangetrokken door het gewas. Drie methoden van toepassen van gewasbeschermingsmiddelen zijn met elkaar vergeleken met behulp van een fluorescerende stof (Tinopal) op de bladeren van potplanten en chrysantenstek en bloemknoppen van roos: EHDA, conventioneel en een pulverisateur (rugketel). De verdeling van druppeltjes over de bladeren bij toepassing van EHDA is goed zowel bij de rozen als bij de potplanten en chrysantenstekken. Op de onderkant van de bladeren zijn echter geen druppletjes terecht gekomen. Dit heeft te maken met de grootte van de druppels, 200 micron. Deze zijn te zwaar om af te buigen naar de onderkant van de bladeren. Onderzoek in het verleden heeft aangetoond dat druppels met een kleinere diameter wel op de onderkant van de bladeren terecht komen. Bloemknoppen zijn opengemaakt om te kijken in hoeverre de druppeltjes in de knoppen zijn doorgedrongen. Bij toepassing van EHDA blijkt dit dieper te zijn dan bij de andere methoden.

ElectroHydroDynamische Atomisatie (EHDA) wordt ook wel “electrospraying” genoemd. Atomisatie is het proces van het uit elkaar vallen van een vloeistof in kleine druppeltjes. Een elektrisch veld wordt toegepast om het proces van druppelvorming (grootte van de druppels) te beïnvloeden en de druppeltjes een elektrisch lading mee te geven. De geladen druppeltjes stoten elkaar af waardoor een nevel ontstaat. Deze wordt aangetrokken door het gewas. Drie methoden van toepassen van gewasbeschermingsmiddelen zijn met elkaar vergeleken met behulp van een fluorescerende stof (Tinopal) op de bladeren van potplanten en chrysantenstek en bloemknoppen van roos: EHDA, conventioneel en een pulverisateur (rugketel). De verdeling van druppeltjes over de bladeren bij toepassing van EHDA is goed zowel bij de rozen als bij de potplanten en chrysantenstekken. Op de onderkant van de bladeren zijn echter geen druppletjes terecht gekomen. Dit heeft te maken met de grootte van de druppels, 200 micron. Deze zijn te zwaar om af te buigen naar de onderkant van de bladeren. Onderzoek in het verleden heeft aangetoond dat druppels met een kleinere diameter wel op de onderkant van de bladeren terecht komen. Bloemknoppen zijn opengemaakt om te kijken in hoeverre de druppeltjes in de knoppen zijn doorgedrongen. Bij toepassing van EHDA blijkt dit dieper te zijn dan bij de andere methoden.

Crop protection products are usually applied as sprays. These spray droplets have a certain size distribution. Fine droplets are often required to achieve a good coverage of the plant and to guarantee the biological efficacy of an agrochemical product. At the same time very fine droplets in spray are not desirable. Due to their low mass and velocity, these droplets can be carried from the application site by crosswind and e.g. can contaminate surface water. Droplet drift can be minimized by reducing the number of very fine droplets in spray. Dilute emulsions produce coarser sprays compared to water when atomized through a standard flat fan nozzle. For this reason dilute emulsions can reduce drift risk. The mechanism of spray formation of dilute emulsions has been investigated in this thesis. The proposed mechanism also describes spray formation in more complex mixtures of dilute emulsions with surfactants or polymers.

Membrane emulsification is a relatively new technique to produce emulsions. In this method the oil phase is pushed through a membrane, a sieve with very small holes, and forms droplets in the water phase at the other side of the membrane. The most important advantage of this technique is that all the formed droplets have the same size and the emulsion has therefore a better quality. In this research, the influence of surfactants on the droplet formation and detachment process has been studied with the help of experiments and computer simulations.The results showed that both the concentration surfactant and the velocity of the oil phase flowing through the membrane influence the droplet size.

Membrane emulsification is a relatively new technique to produce emulsions. In this method the oil phase is pushed through a membrane, a sieve with very small holes, and forms droplets in the water phase at the other side of the membrane. The most important advantage of this technique is that all the formed droplets have the same size and the emulsion has therefore a better quality. In this research, the influence of surfactants on the droplet formation and detachment process has been studied with the help of experiments and computer simulations.The results showed that both the concentration surfactant and the velocity of the oil phase flowing through the membrane influence the droplet size.

In chemical crop protection, the amount of deposition and drift is the cumulative result of a large number of individual drops travelling through air. When investigating the flow of drops through air, one has to be aware of kinetic aspects as well as evaporation of water from the drops. A theoretical discussion of kinetic aspects is carried out for sedimentation of drops in still air. The presented theory can be used for windy situations as well, with basically straight- forward adaptations. The theoretical discussion of evaporation deals with aqueous drops in air. This derivation bears considerably on the kinetic aspects of drops in air. A major application for both kinetic aspects and evaporation is their implementation in the IDEFICS spray drift model. However, the kinetic and evaporation models are presented in a general way, and can be implemented in other applications as well. Extension to systems based on solvents other than water can be performed easily.

With membrane emulsification in principle monodisperse emulsions can be produced, requiring a relatively low energy density which implies that the shear stress exerted on the ingredients is low. In membrane emulsification the to-be-dispersed phase is pressed through the membrane pores; under certain conditions droplets are formed at the membrane surface. In cross-flow membrane emulsification the droplets are detached by the continuous phase flowing across the membrane surface. A limiting factor for emulsion production on a commercial scale will be a low disperse phase flux. Better knowledge of how membrane parameters affect the disperse phase flux would enable the targeted development of membranes, optimal for the process of cross-flow membrane emulsification for a given application. Therefore, the objective of this research is to gain a fundamental understanding of the mechanism of droplet formation at the membrane surface and of the flow of the disperse phase through the membrane as a function of the membrane characteristics.Droplet formation was studied at a microscopic level with computational fluid dynamics (CFD) simulations and by microscopic experiments of droplet formation at a very thin microsieve with uniform pores. Since these membranes are extremely well defined, they are a good model system for detailed study. Results from both simulations and experiments indicate that to prevent coalescence and steric hindrance of droplets, the membrane porosity should be very low. Steric hindrance resulted in polydisperse emulsions and led to coupling of droplet detachment from neighboring pores. Furthermore, although the pores all had the same diameter, the number of pores at which droplets were formed only increased gradually with increasing transmembrane pressure. This effect was further studied with a scaled-up analogon and could be modeled by taking the resistance of the pores and the resistance of a membrane substructure into account. This model is compared with a model for flow through an isotropic membrane with interconnected uniform pores and extended to describe flow through a membrane with a pore size distribution. This model is used to show that in most cases the estimation of a membrane pore size distribution by using the liquid displacement method is not correct. Just as in membrane emulsification, pores become active at higher transmembrane pressures than expected. Finally, the effects of several membrane parameters on membrane emulsification performance are summarized. As an example, the membrane area required for a typical industrial application is estimated using the models mentioned above, for different types of membranes.

In chemical crop protection, the amount of deposition and drift is the cumulative result of a large number of individual drops travelling through air. When investigating the flow of drops through air, one has to be aware of kinetic aspects as well as evaporation of water from the drops. A theoretical discussion of kinetic aspects is carried out for sedimentation of drops in still air. The presented theory can be used for windy situations as well, with basically straight- forward adaptations. The theoretical discussion of evaporation deals with aqueous drops in air. This derivation bears considerably on the kinetic aspects of drops in air. A major application for both kinetic aspects and evaporation is their implementation in the IDEFICS spray drift model. However, the kinetic and evaporation models are presented in a general way, and can be implemented in other applications as well. Extension to systems based on solvents other than water can be performed easily.