Spray dispersion, properties

During the formation of a spray, its properties vary with time and location. Depending on the atomizing system and operating conditions, variations can result from droplet dispersion, acceleration, deceleration, coUision, coalescence, secondary breakup, evaporation, entrainment, oxidation, and solidification. Therefore, it may be extremely difficult to identify the dominant physical processes that control the spray dynamics and configuration. 

Spray Drying Detailed descriptions of spray dispersion dryers, together with apphcation, design, and cost information, are given in Sec. 17. Product quality is determined by a number of properties such as particle form, size, flavor, color, and heat stability. Particle size and size distribution, of course, are of greatest interest from the point of view of size enlargement. 

By examining the dispersion properties of surface acoustic waves, the layer thickness and mechanical properties of layered solids can be obtained using the SAM. It can be used to analyze the wear damage progress [104], and detect the defects of thermally sprayed coatings [105]. 

Additional research to find a suitable carrying agent having low explosive and flammability properties is urgently needed as we increase the control of adult mosquitoes by fogs and sprays dispersed by the new types of applicators. 

The key properties of the spray dispersion that influence the size of the droplets formed are its dynamic surface tension and its viscosity (Elliott and Wilson, 1983 Dexter and Huddleston, 1998) although it should be noted that poor spray machinery setup and use can play a more important role than the physical properties of the spray dispersion (Spray Drift Taskforce, 1977). 

The spray-dried powders have a small particle size (10-100 pm) with poor handling properties. Very often in the food industry, at the outlet of the spray-drying chamber, the spray-dried particles are modified by additional treatment such as agglomeration, allowing the modification/increase of powder size/porosity and improvement of solubility/dispersibility properties (i.e., instant powder, decrease of fine particles proportion) (Buffo et al., 2002). 

Figure 15.11 Dispersibility properties of dried nanocrystaUine cellulose with regard to counterion and moisture content. Drying refers to evaporation, freeze-drying and spray-drying [126].

Uses Primary dispersant In wettable powds., suspension cones., and waler-dlsp. granules formulated at low pH or with high salt loadings tec. for use with low pH, low temp., and high Ionic str. spray media Properties Free-flowing bm. powd. complete sol. In water m.w. 3200 bulk dens. 34 Ib/tP (packed) surf. tens. 52.5 dynes/cm (1% aq.) pH 7.5 (15% aq.) 9.8% total sulfur < 0.5% NajSOj 8% moisture Use Level 3-12%... 

Uses Pigment dispersant, surfactant, vise, reducer and wetting agent for latex paints compatibilizer for universal colorants in latex and alkyd paints resist, reducing agent for electrostatic spray paints Properties Gardner 1 cl. liq. sp.gr. 1.0 dens. = 1000 kg/m vise. 100 mPa.s ... 

STEPSPERSE DF-300 [Stepanj Chem. Descrip. Surfactant blend Ionic Nature Anionic/nonionic Uses Dispersant for agric, flowables and dry flowables Properties Brn, powd, sol, in water STEPWAX Emulsifier [Stepanj Ionic Nature Cationic/nonionic Uses Hydrocarbon emulsifier for car wash spray wax Properties Liq, 30% act,... 

In this chapter, novel method for microencapsulation by coacervation is presented. The method employs polymer-polymer incompatibility taking place in a ternary system composed of sodium carboxymethyl cellulose (NaCMC), hydroxypropylmethyl cellulose (HPMC), and sodium dodecylsulfate (SDS). In the ternary system, various interactions between HPMC-NaCMC, HPMC-SDS and NaCMC-(HPMC-SDS) take place. The interactions were investigated by carrying out detailed conductometric, tensiometric, turbidimetric, viscosimetric, and rheological study. The interactions may result in coacervate formation as a result of incompatibility between NaCMC molecules and HPMC/SDS complex, where the ternary system phase separates in HPMC/SDS complex rich coacervate and NaCMC rich equilibrium solution. By tuning the interactions in the ternary system coacervate of controlled rheological properties was obtained. Thus obtained coacervate was deposited at the surface of dispersed oil droplets in emulsion, and oil-content microcapsules with a coacervate shell of different properties were obtained. Formation mechanism and stability of the coacervate shell, as well as stability of emulsions depend on HPMC-NaCMC-SDS interaction. Emulsions stabilized with coacervate of different properties were spray dried and powder of microcapsules was obtained. Dispersion properties of microcapsules, and microencapsulation efficiency were investigated and found to depend on both properties of deposited coacervate and the encapsulated oil type. 

Systematic investigation on HPMC-SDS, HPMC-NaCMC, and (HPMC-SDS)-NaCMC interaction were carried out. The interactions were used to obtain coacervate of controlled rheological properties in ternary HPMC/NaCMC/SDS system consisting of 0.7% HPMC, 0.3% NaCMC and different SDS concentrations. Thus obtained coacervate was deposited at surface of emulsified oil droplets. Emulsion stability was tested. Emulsions were spray drayed in order to obtain powder of oil-containing microcapsules. Dispersion properties of microcapsules and microencapsulation efficiency were investigated. 

Emulsions stabilized with coaceravate of different rheological properties were spray dried in order to obtain powder of microcapsules. Dispersion properties of suspension of microcapsules in water, encapsulation efficiency, and influence of emulsified oil type on microcapsules properties were investigated. 

Emulsions of different oils in ternary HPMC/NaCMC/SDS mixture having 0.7% HPMC, 0.3% NaCMC and three characteristic SDS concentrations i.e. 0.00% (no HPMC-SDS complex formation), 0.35% (maximum of HPMC/SDS interaction), 1.00% (end of HPMC-SDS interaction) were prepared and spray dried. Dispersion properties (mean diameter and standard deviation) of the emulsions and suspensions of microcapsules in water are shown in Table 1. As it can be seen in Table 1 oil type influences dispersion properties of emulsions, and thus suspensions. Largest droplet diameter in all emulsions is obtained at 0.00% SDS, i.e. where no HPMC/SDS complex and coacervate formation takes place. On the other hand, largest diameter of suspended microcapsules occurs at 1.00% SDS. 

Spray Correlations. One of the most important aspects of spray characterization is the development of meaningful correlations between spray parameters and atomizer performance. The parameters can be presented as mathematical expressions that involve Hquid properties, physical dimensions of the atomizer, as well as operating and ambient conditions that are likely to affect the nature of the dispersion. Empirical correlations provide useful information for designing and assessing the performance of atomizers. Dimensional analysis has been widely used to determine nondimensional parameters that are useful in describing sprays. The most common variables affecting spray characteristics include a characteristic dimension of atomizer, d Hquid density, Pjj Hquid dynamic viscosity, ]ljj, surface tension. O pressure, AP Hquid velocity, V gas density, p and gas velocity, V. ... 

Pesticides. Many pesticides are highly concentrated and are in a physical form requiring further treatment to permit effective appHcation. Typically carriers or diluents are used (see Insectcontroltechnology). Although these materials are usually considered inert, they have a vital bearing on the potency and efficiency of the dust or spray because the carrier may consist of up to 99% of the final formulation. The physical properties of the carrier or diluent are of great importance in the uniform dispersion, the retention of pesticide by the plant, and in the preservation of the toxicity of the pesticide. The carrier must not, for example, serve as a catalyst for any reaction of the pesticide that would alter its potency. 

Finely divided aluminium powder or dust forms highly explosive dispersions in air [1], and all aspects of prevention of aluminium dust explosions are covered in 2 recent US National Fire Codes [2], The effects on ignition properties of impurities introduced by recycled metal used to prepare dust were studied [3], Pyrophoricity is eliminated by surface coating aluminium powder with polystyrene [4], Explosion hazards involved in arc and flame spraying of the powder are analysed and discussed [5], and the effect of surface oxide layers on flammability was studied [6], The causes of a severe explosion in 1983 in a plant producing fine aluminium powder are analysed, and improvements in safety practices discussed... 

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