In this paper, we present binary collisions of immiscible liquid drops as a promising and reliable process for encapsulating liquids in shells of other, immiscible liquids. Our current experimental ...approach describes the collision outcome according to relevant parameters. Depending on the drop size and the relative velocity, the impact parameter and liquid viscosity, density and surface tension, we observe that either the full drop of encapsulating liquid spreads around the encapsulated one, or part of it separates, while the rest remains attached. We show that the viscosities of the two liquids do not have equal importance for the stability limit of the process, especially for head-on collisions. For separation after the collision, a new mechanism is identified which does not occur with miscible liquid drop collisions. For separated drops, the thickness of the remaining liquid shell was also investigated and turns out to be independent of both liquid viscosities and relative velocity. As a consequence, we can accurately adjust the thickness of the coating layer by simply tuning the impact parameter of the collision. An interpretation of this behavior based on a geometric argument is proposed.
Bubbles rising in viscoelastic liquids may exhibit a jump discontinuity of the rise velocity as a critical bubble volume is exceeded. We carried out detailed experiments to investigate the occurrence ...of this discontinuity with single air bubble rising in various polymer solutions without influence of surfactants. The polymer solutions were characterized thoroughly by means of shear and elongational rheometry, as well as tensiometry. The experiments showed that a jump discontinuity can exist only if the non-dimensional group
λ
E(
g
3
ρ
1/
σ)
1/4, found by dimensional analysis, exceeds a critical value. A universal correlation of non-dimensional numbers for the non-dimensional critical bubble volume at the jump discontinuity was found. The non-dimensional numbers represent the relevant rheological and dynamic liquid properties. This is the first time that the prediction of the critical bubble volume as well as the potential of the solution to exhibit a bubble rise velocity discontinuity becomes possible based on liquid properties only. In the correlation found, the relaxation time of the polymer solutions in elongational flow of the viscoelastic liquid was found to play a key role.
Spray drying is widely used in pharmaceutical manufacturing to produce microspheres from solutions or suspensions. The mechanical properties of the microspheres are reflected by the morphology formed ...in the drying process. In suspension drying, solids dissolved in the carrier liquid may form bridges between the suspended primary particles, producing a microsphere structure which is resistant against mechanical loads. Experiments with individual, acoustically levitated droplets were performed to simulate the drying of suspension droplets in a spray drying process. The suspensions studied consisted of a binary liquid mixture as the carrier liquid, and primary particles of suspended lactose material which is partially soluble in the liquid. The solubility of lactose was varied by the composition of the liquid mixture. The experiments revealed longer first and second drying stages for higher lactose solubility. Electron micrographs revealed the morphology of individual microspheres produced by drying in the levitator. Microspheres with only primary particles and no visible crust were obtained for low lactose solubility, whereas higher contents of dissolved lactose resulted in a more densely packed microsphere with crust formation. To quantify the hardness of individual microspheres, the maximum breaking force upon mechanical loading was measured for a range of varying suspension compositions. These measurements confirmed that densely packed structures with a thick crust reveal high mechanical strength. It was shown that, for primary lactose particles to be conserved in spray drying, the dissolved lactose mass loading Xd must be below 5.2%.
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•Drying experiments of suspension droplets by means of acoustic levitation•Microsphere formation at different mass of suspended and dissolved lactose•Hardness tests of individual microspheres•Study of kinetics of single droplet drying with relevance for industrial processes
The international study at CERN of a possible future circular collider (FCC) considers an option for a very high energy hadron-hadron collider located in a quasi-circular underground tunnel of about ...100 km of length. The technical segmentation of the collider foresees continuously cooled sections of up to 10.4 km; throughout the entire section length, more than 600 kW of heat mainly generated by the beam synchrotron radiation must be removed from the beam screen circuits at a mean temperature of 50 K. The cryogenic system has to be designed to extract the heat load dependably with a high-efficiency refrigeration process. Reliable and efficient cooling of the FCC beam screen in all possible operational modes requires a solid basic design as well as well-matched components in the final arrangement. After illustrating the decision making process leading to the selection of an elementary hydraulic scheme, this paper presents preliminary conceptual designs of the FCC beam screen cooling system and compares the different schemes regarding the technical advantages and disadvantages with respect to the exergetic efficiency.
The cooling of the superconducting magnet cold masses with superfluid helium (He II) is a well-established concept successfully in operation for years in the LHC. Consequently, its application for ...the cooling of FCC magnets is an obvious option. The 12-kW heat loads distributed over 10-km long sectors not only require an adaption of the magnet bayonet heat exchangers but also present new challenges to the cryogenic plants, the distribution system and the control strategy. This paper recalls the basic LHC cooling concept with superfluid helium and defines the main parameters for the adaption to the FCC requirements. Pressure drop and hydrostatic head are developed in the distribution and pumping systems; their impact on the magnet temperature profile and the corresponding cooling efficiency is presented and compared for different distribution and pumping schemes.
In pressure-atomized sprays, the liquid droplets and the gas in the two-phase flow field may exhibit self-similar properties, so that the spray flow as a whole may be described as self-similar. This ...description is used to model the mass transfer from the droplets to the ambient gas by evaporation of the droplet liquid. The concentration of the vapor phase is described as the solution of the related transport equation in a self-similar form. The self-similar transform of the mass source of vapor representing the effect of droplet evaporation is compared against profiles obtained from the Frössling correlation for the Sherwood number as a function of the Schmidt and Reynolds numbers. The vapor concentration at the droplet surface depends on the droplet temperature, which converges to the wet-bulb temperature determined by the local vapor content of the ambient air and the dry-bulb air temperature. The self-similar structure of the vapor concentration field and the respective vapor source are determined.
The free oscillation of liquid droplet is one of the classical questions in science research, liquid drops play important role in a lot of engineering applications. Theory study of droplet ...oscillation mainly based on the linear method, this method is only adapted to the small-amplitude oscillatory motion of drops. Except the linear method used in this study, numerical method have been successfully applied in simulation of the free oscillation of liquid droplet.
In this paper, the finite element method is used to investigate numerically the influence of viscoelasticity on the small-amplitude oscillation of drop of polymer solutions. A spatial discretization is accomplished by the finite element method, the time descretization is carried by the Crank-Nicolson method, and the arbitrary Lagangian-Eulerian (ALE) method is used to track the change of the interface. Numerical results are compared with the ones of linear theory. The behaviors of oscillation are found to depend on the viscosity and the stress relaxation time of viscoelastic fluid, the results of numerical simulation and linear theory are identical.
The paper presents an analytical solution of the diffusion equation on a spherical domain with its surface shrinking linearly with time. The solution is given as a series expansion in confluent ...hypergeometric functions and is valid for arbitrary ratios of the rate of shrinkage of the surface of the sphere to the diffusion coefficient in the liquid phase. The field of application of the results is spray drying of solutions of solid substances with very low vapor pressure. The mathematical functions found may be used as a benchmark for numerical computations.
A method is proposed for investigating the processes in the combustion chamber of chemical heat engines. In this method, the processes in the combustion chamber and the fuel injector are considered.
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