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Single Droplet (single + droplet)
Selected AbstractsAnalysis of supersaturation and nucleation in a moving solution droplet with flowing supercritical carbon dioxideJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 4 2005Mamata Mukhopadhyay Abstract A supercritical antisolvent (SAS) process is employed for production of solid nanoparticles from atomized droplets of dilute solution in a flowing supercritical carbon dioxide (SC CO2) stream by attaining extremely high, very rapid, and uniform supersaturation. This is facilitated by a two-way mass transfer of CO2 and solvent, to and from the droplet respectively, rendering rapid reduction in equilibrium solubility of the solid solute in the ternary solution. The present work analyses the degree of supersaturation and nucleation kinetics in a single droplet of cholesterol solution in acetone during its flight in a flowing SC CO2 stream. Both temperature and composition are assumed to be uniform within the droplet, and their variations with time are calculated by balancing the heat and mass transfer fluxes to and from the droplet. The equilibrium solubility of cholesterol with CO2 dissolution has been predicted as being directly proportional to the Partial Molar Volume Fraction (PMVF) of acetone in the binary (CO2,acetone) system. The degree of supersaturation has been simulated up to the time required to attain almost zero cholesterol solubility in the droplet for evaluating the rate of nucleation and the size of the stable critical nuclei formed. The effects of process parameters have been analysed in the pressure range of 7.1,35.0 MPa, temperature range of 313,333 K, SC CO2 flow rate of 0.1136,1.136 mol s,1, the ratio of the volumetric flow rates of CO2 -to-solution in the range of 100,1000, and the initial mole fraction of cholesterol in acetone solution in the range of 0.0025,0.010. The results confirm an extremely high and rapid increase in degree of supersaturation, very high nucleation rates and stable critical nucleus diameter of the order of a nanometre. Copyright © 2005 Society of Chemical Industry [source] Air drying of milk droplet under constant and time-dependent conditionsAICHE JOURNAL, Issue 6 2005Xiao Dong Chen Abstract Spray drying is the prime process for many years for manufacturing food powders. Dairy powders are one of the main products consumed worldwide. There has been a stream of studies published previously on both modeling the drying characteristics of a single milk droplet and the dryer wide simulations incorporating computational fluid dynamics (CFD). In CFD simulations, large numbers of particles of different sizes need be tracked to represent the size distribution; it is desirable to have an accurate yet simple model for drying of a single droplet, which does not require partial differential equation. Here for the first time, two such models are validated. One model is of the characteristic drying rate curve approach and the other (new) model is of the reaction engineering approach. The model predictions are compared against a very wide range of experimental results including isothermal and time-varying temperature conditions. © 2005 American Institute of Chemical Engineers AIChE J, 2005 [source] The Influence of Shear Stress on Crystallization in an Ultrasound LevitatorCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 10 2007S. Sacher Abstract Industrial precipitation processes often use chemical agents to influence crystal morphology and size distribution. This experimental study deals with the investigation of physical parameters including an alternative method to affect crystal growth, thus, avoiding the presence of additives as intrinsic impurities. The influence of shear stress acting on growing crystals within a droplet is investigated in an ultrasound levitator. An ultrasound levitator enables the suspension of a single droplet against gravity and the study of containerless precipitation with specific mechanical forces acting on crystals. The levitator is used as a three-phase reactor with precipitation from the gas and liquid, and as a reactor for precipitation from two different solutions. Calcium carbonate is used as a model system. The variation of temperature and the amount of applied shear stress leads to different amounts of calcium carbonate morphologies. An increase in the shear stress results in more rounded or spherical crystals. The intensity of the shear stress also influences the particle size distributions of the precipitated crystals, i.e., with increasing shear stress, particle size distributions are shifted to smaller sizes. [source] Observations of initiation stage of spontaneous vapor explosions for droplet scaleHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 1 2008Takeo Takashima Abstract In this study, the initiation stage of spontaneous vapor explosions generated by single droplets of molten tin submerged in water was investigated using a high- speed video camera operated with a reflected light system. Photographs of the formation process of vapor film, the process of vapor film disturbance, and the initiation process of the vapor explosions for different masses of molten tin and different nozzle diameters were obtained. The results demonstrate that partial thermal interaction between tin and water does not cause a vapor explosion with fragmentation. The vapor film disappears locally during the formation of the vapor film around the hot liquid droplet. Direct contact between the hot molten tin surface and water is thereby generated. However, the local disappearance of the vapor film does not progress and the vapor film is reconstructed. A vapor explosion occurs when the vapor film collapses at the local area of the bottom or edge of the disk-shaped droplet. © 2007 Wiley Periodicals, Inc. Heat Trans Asian Res, 37(1): 41,55, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20185 [source] Flow visualization and solute transport in evaporating dropletsAICHE JOURNAL, Issue 7 2010Pallippadan Johny Jaijus Abstract We have investigated the velocity field and associated particle transport in an evaporating water droplet using the tool of particle image velocimetry. Experiments were performed where single droplets containing polystyrene particles were exposed to evaporation. Our method applicable to droplets confined between two parallel surfaces differs from the conventional PIV techniques on the 3D droplets and removes many of the limitations associated with mapping of velocity field. To avoid refraction of light at the droplet surface we have studied the motion in a disc-shaped droplet which was prepared by confining the drop between two nonwetting surfaces and its base is pinned to a wetting surface. Experiments were carried out under the conditions where Marangoni flow creates convection cells and finally leading to deposition of particles toward the pinned edge. The contact angle, height of the droplet, velocity field, and the particle concentration inside the evaporating droplet was measured and its time evolution was recorded. © 2009 American Institute of Chemical Engineers AIChE J, 56: 1674,1683, 2010 [source] Sedimentation behavior of droplets for the reactive extraction of zinc with D2EHPAAICHE JOURNAL, Issue 1 2010Murat Kalem Abstract The sedimentation characteristics of the reactive standard test system zinc + D2EHPA are investigated in this work. Experiments with single droplets rising in a stagnant continuous phase have been carried out. The concentration of D2EHPA, zinc, and sulfuric acid as well as the diameter of the droplets are varied. The velocity of droplets is observed to be transient for several seconds. High mass-transfer rates increase the velocity of single droplets for the case of reactive extraction whereas for physical systems contrary behavior is observed. Therefore, droplets seem to behave principally different in reactive and physical extraction. This is explained by the interfacially active properties of D2EHPA. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] | ||||||||||