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Spray Dryer Designs Including Multistage
Published in Nan Fu, Jie Xiao, Meng Wai Woo, Xiao Dong Chen, Frontiers in Spray Drying, 2020
Nan Fu, Jie Xiao, Meng Wai Woo, Xiao Dong Chen
Atomization refers to the process of breaking up a bulk liquid into droplets (Masters, 1979; Chen and Mujumdar, 2008). Common home atomizers are shower heads, garden hoses, hair sprays, or perfume sprays, etc. A spray is a “cloud” of moving droplets that move in a controlled manner. A droplet is a liquid particle usually of more or less a spherical shape. The reason for its roundness is due to the liquid surface tension. Bulk liquid has to be made into thin liquid ligaments that can then be torn into a massive number of small entities such as liquid particles. Water has a surface tension of 0.073 N · m−1 at 20°C (compared with that of mercury: 0.465 N · m−1 at the same temperature). Surface tension tends to stabilize a liquid, preventing it from being broken up into small sizes. As such, if all other factors are maintained the same, increasing surface tension increases the average droplet size. Liquid viscosity has a similar effect; the greater it is, the larger the average droplet size. Higher viscosity gives a resistance to the liquid entity from being torn apart as well. Liquid density is also a parameter to consider. It makes liquids resist acceleration (perhaps), so a greater density usually leads to larger average droplet sizes. The concentration and the temperature of a liquid such as milk dictates the corresponding liquid density. A review and compilation of suitable models to describe the viscosity of liquids due to changes in temperature and concentration can be found in Chapter 2 of Quek (2011).
Moving Contact Line of Droplets on Structured Surfaces
Published in Girma Biresaw, K.L. Mittal, Surfactants in Tribology, 2019
In wetting, Young’s equation is built on the assumption that a solid surface is smooth and homogeneous, and it does not take into account the surface roughness. However, the natural solid surfaces are generally rough in microscale and macroscale. Droplet wetting on rough surfaces exhibits different wetting and spreading behaviors than on smooth surfaces. Contact angles measured on rough surfaces are usually not consistent with that calculated by Young’s equation. This phenomenon was found in many experiments and theoretical analysis in the twentieth century. Wenzel introduced a factor called “degree of roughness,” which considers the surface roughness, and this factor is defined as the ratio of solid actual surface area to the projected surface area: () ro=Asl(true)Asl(projected)
Introduction
Published in S. L. Soo, Particulates and Continuum, 2018
We note that other than the need to account for the general interface configuration in treating the nuclear reactor safety problem and surface wave problem, multiphase systems, in most cases, concern clouds of particulates in a fluid phase, liquid or vapor. The magnitudes of sizes in multiphase systems in relation to other physical quantities are shown in Fig. 1.1. Solid particles are, in general, nonspherical but often isometric; further approximations are needed for treating fibers or sticks. Small liquid droplets usually attain a spherical shape due to surface tension. When gravity or other field forces are significant, they attain shapes of smallest flow resistance such as falling rain drops or minimum potential in the case of charged droplets. Gas bubbles would retain spherical shapes due to surface tension until modified by field forces. Foams or large nonspherical bubbles are further exceptions.
Size estimation of biopolymeric beads produced by electrospray method using artificial neural network
Published in Particulate Science and Technology, 2023
Preparation of biopolymeric beads from viscid solutions with a mono-dispersed size distribution, enough mechanical strength and a suitable size is one of the main aims of the pharmaceutical industry (Khorram et al. 2015; Samimi and Moeini 2020). In addition, the formation of droplets from high viscid solutions is a serious process in many operations such as ink-jet printing, spray drying and atomization dispersion and emulsification (Moghadam et al. 2008). The application of an electrostatic field in liquid spraying provides an external force that can effectively control the droplet size. Electrospray is a simple, reliable, and facile technique in which small size-droplets can be formed from high viscous liquids depending on their conductivity (Moghadam et al. 2009). This is the method of liquid atomization in which an electrical force is applied in the direction of gravitational force on the surface of a capillary. In electro-spraying, one subjects the surface of the liquid capillary at the outlet of a nozzle to shear stress by maintaining the nozzle at a high electric potential. This leads to elongation and, consequently, separation of the droplet from the nozzle tip (Almería and Gomez 2014).
Models for Droplet Motion on Hydrophilic and Hydrophobic Surfaces
Published in Heat Transfer Engineering, 2022
Mustafa Sengul, Esra H. Isik, I. Bedii Ozdemir
Droplet motion on surfaces involves very complex multiphase flow physics and is related to a wide range of practical problems in engineering systems like cooling devices, internal combustion engines, inkjet printing, liquid heating, spray coating, microfluidic flow and fuel cells [1–5]. Once the droplets interact with the surface, they can deform by spreading, splashing or rebounding motions, which depend on parameters like the initial velocity of the droplet, the impact angle, the droplet size, material-based properties of the surface and liquid phase and the pressure [6, 7]. The droplet motion in static conditions has been studied for many years, in that the contact angle has been assumed independent of time and phase factors, which significantly degrades the accuracy of the computations. The dynamic contact angle calculations, however, take into account multiple parameters and constraints such as physical properties of phases, contact line velocity and the angles between the liquid phase and the surface both in the advancing and receding directions [8, 9]. Therefore, there is a growing interest in dynamic conditions, which have not been fully understood and present challenges to make robust computations [9–11].
Investigation of droplet size distribution for liquid-liquid emulsions in Taylor-Couette flows
Published in Journal of Dispersion Science and Technology, 2018
Reza Farzad, Stefan Puttinger, Stefan Pirker, Simon Schneiderbauer
The mixture of two immiscible liquids, where one of them is dispersed in the other, is referred to as emulsion. Emulsions play a key role in several processes employed in food, pharmaceutical, polymer, and chemical industries. Especially the droplet formation and the related interfacial phenomena, which determine the droplet size distribution, are crucial issues in liquid-liquid systems. The formation of droplets depends on several factors such as the actual flow condition (i.e., shear, the amount of turbulence) and material properties.[1] On the one hand, the stability of droplets is determined by consolidating forces such as interfacial tension and the dispersed phase viscosity. On the other hand, continuous phase forces stemming from viscous shear and turbulent velocity fluctuations act against the stability of the droplets. This, in turn, implies that the maximum stable droplet size is determined by the balance of those disruptive and consolidating forces.[2] Finally, additional surfactants may affect the interfacial properties and consequently the rheological behavior of the droplets.[3]