Influence Of Drop Size Distribution Research Articles

Applying forward mixing model in an L-shape pulsed packed extraction column to investigate the influence of drop size distribution on mass transfer

The objective of this work is to model the effect of drop forward-mixing on the mass transfer efficiency of a two phase countercurrent extraction process. Based on the flow mechanism and drop size distribution in extraction columns, a novel model with a simplified sequential algorithm is developed. Unlike the other models that use mean diameter of the dispersed phase droplets, this model accurately considered the effect of drop size distribution on mass transfer efficiency. On the base of this model the volumetric overall mass transfer coefficient has been investigated in a pilot plant of L-shape pulsed packed extraction column by using two liquid systems of toluene/acetone/water and butyl acetate/acetone/water. It is found that, although the mass transfer coefficient related to the large droplets is larger but the corresponding volumetric overall mass transfer coefficient is less than that related to the small droplets. Therefore, any factor that reduces the drop size can improve the efficiency of mass transfer. Furthermore, the effect of operational variables and physical properties including the dispersed and continuous phases flow rates, pulsation intensity and interfacial tension have been considered on mass transfer coefficients. It has been found out that the pulsation intensity and the continuous phase flow rate have seriously affected on mass transfer coefficient, however, the dispersed phase flow rate has a weaker effect. Finally, new correlations are proposed to accurately predict the mass transfer coefficient, axial mixing and drop size distribution. Good agreement between predictions and experiments was found for all operating conditions that were investigated.

Gasification of high viscous slurry R&D on atomization and numerical simulation

Biomass and low rank fuel gasification is a very promising process for conversion of fuels to a high quality fuel (Syngas). In the present paper research work on the design of a high pressure entrained flow gasifier for biomass based fuels is shown.Atomization quality of twin fluid nozzles as a function of gas velocity and reactor pressure is analyzed. The developed and characterized atomizers are used in an atmospheric entrained flow gasifier, to detect the influence of spray quality on gasification process. Furthermore, a CFD model of a high pressure entrained flow gasifier was developed.A significant influence of gas velocity and reactor pressure on Sauter Mean Diameter (SMD) of the produced spray was detected. Increasing gas velocity decreases the SMD, whereas increasing reactor pressure leads to the increase in drop diameter. An influence of SMD on gasification process was observed from organic carbon and methane concentration measurements as well as from the radial temperature profiles at various positions along the reactor centerline. Finally the CFD model of high pressure entrained flow gasification of biomass based slurries shows a very pronounced influence of drop size distribution on gasification quality.

An improved dynamic combined model for evaluating the mass transfer performances in extraction columns

Dispersed phase droplet behavior research is very important for the design and scaling up of extraction columns. Recently, the droplet velocities at high holdup were found to be uniform, which means the conventional concept of forward mixing needs correction. The drop size distribution only influences the mass transfer coefficients and not the residence time distribution of droplets. In this work, an improved dynamic combined model considering the influence of drop size distribution has been developed, by which the axial mixing can be easily evaluated using a one-dimension search. A typical experimental system of 30% tributyl phosphate (TBP) (in kerosene)-nitric acid–water with interfacial tension of 0.00995 N/m was used to investigate the mass transfer performances in a coalescence-dispersion pulsed-sieve-plate extraction column (CDPSEC) with 150 mm in diameter. The two-point dynamic method was used to obtain the stimulus–response curves. With these results, the axial mixing in the CDPSEC was evaluated. The calculated results showed that the response curves could be predicted by the dynamic combined model with a deviation less than 0.001. This model has marked advantages over previous models in literature because of its accuracy, simple boundary conditions, and single parameter optimization.

Combined Use of the Radar and Radiometer of TRMM to Estimate the Influence of Drop Size Distribution on Rain Retrievals

A combination of passive microwave and radar observations from the Tropical Rainfall Measuring Mission (TRMM) satellite is used to investigate the consistency between the two sensors. Rather than relying on some absolute ‘‘truth’’ to verify retrievals, this paper focuses on one assumption—namely, the drop size distribution (DSD)—and how different DSDs lead to improved or reduced consistency. Results from a case in the central Pacific suggest that a crude consistency may be achieved if a different drop size is used for the radiometer and the radar. In this particular case, a Marshall‐Palmer or a gamma distribution with the shape parameters properly set leads to similar results. Although this study offers no independent validation of its conclusions, it does demonstrate that rainfall validation need not be confined to surface rainfall measurements, which are only loosely related to the volumetric observations made by most sensors. As mean size distributions of raindrops are measured in the TRMM field experiments by disdrometers, profilers, multiparameter radars, and direct aircraft observations, the technique presented in this paper can be applied on a storm-by-storm basis, and conclusions can be verified directly.

Computational techniques for liquid‐liquid extraction column model parameter estimation, using the forward mixing model

AbstractHere is presented the first step toward the practical application of a model of liquid‐liquid extraction column performance which includes the influence of drop size distribution, or of ‘forward mixing’. The theory, previously developed and described, has been used successfully to obtain model parameter values from experimental extraction data, including drop size distributions and solute concentration profiles. The presence of a significant settling zone height complicates the theory and poses difficulties. These were overcome by the reduction of the settling zone height to an insignificant level. Values of the continuous phase mass transfer, and axial dispersion, coefficients for an assumed (Handlos‐Baron) drop‐side model are reported. The overall mass transfer coefficients are confirmed to increase with drop size.

A model for liquid‐liquid extraction column performance — The influence of drop size distribution on extraction efficiency

AbstractA precise model for predicting liquid‐liquid extraction column efficiency based upon assumed hydrodynamic, axial mixing and mass transfer behaviour has been formulated and solved numerically.The complex nature of the dispersed phase can be better described by drop‐size‐dependent residence time distribution (RTD). Both the variation of axial velocities due to drops of different sizes, i.e. forward mixing, and the axial dispersion for the drops of the same size have been considered in this model.The computed results reveal that the effects of both varying velocities and dispersion of drops on extraction efficiency are appreciable and cannot be neglected, and the efficiency may be overestimated if only a forward mixing model is adopted. The comparison of the experimental values of NODP with those predicted shows that the mass transfer data obtained in RDC agree well with the values predicted by the present model for the case of solute transfer in c→d direction, and are slightly higher than the predicted ones for the transfer in d→c direction.

Growth of yeast on n‐alkanes. II. Adsorption‐ desorption phenomena

AbstractIn the stochastic as well as in other models that describe the growth of yeast on liquid hydrocarbons, the adsorption and desorption of cells to drops influence to a very great extent the growth rate of the cells. In this paper a method is presented and equipment is described by which it was possible to measure the cell‐drop interaction directly. While analyzing the results of these measurements it was found that the adsorption and desorption of cells are rather complicated processes. The size distribution of the oil drops is one of the parameters that has to be taken into account. The analysis of the results yields a fairly accurate value for the initial adsorption rate. Departing from a somewhat speculative description of the influence of drop size distribution on the adsorption rate, the order of magnitude of the desorption rate constant could be calculated.

Experimental confirmation of the influence of drop size distribution on liquid—liquid extraction column performance

The predicted influence of drop size distribution on the performance of liquid—liquid extraction columns has been experimentally verified for non-coalescing dispersions in a rotating disc contactor. Moderate increases in drop size distribution width, at a constant average drop size ( d 32), caused reductions of up to 56% in the number of transfer units.

The influence of drop size distribution on the production of secondary ice particles during graupel growth

AbstractThe production of secondary ice particles when a moving body gathers rime in a supercooled cloud at −5°C has been studied for various drop size distributions. It is found that the rate of production of ice ‘splinters’ depends not only upon the concentration of large drops (⩾about 24 μm diameter) but also upon the concentration of small drops (⩽about 13μm) in the cloud.

The influence of drop size distribution on the production of secondary ice particles during graupel growth

The production of secondary ice particles when a moving body gathers rime in a supercooled cloud at −5°C has been studied for various drop size distributions. It is found that the rate of production of ice ‘splinters’ depends not only upon the concentration of large drops (⩾about 24 μm diameter) but also upon the concentration of small drops (⩽about 13μm) in the cloud.

An improved stagewise model of countercurrent flow liquid—liquid contactors

An improved stagewise model has been developed to represent more accurately the physical processes occurring in a liquid—liquid extraction column. The influence of drop size distribution is more realistically represented in this model. The model equations have been solved numerically with a range of parameter values in order to predict the extent of the influence of drop size distribution on extraction rates. Drop size distributions, measured in a turbine-agitated column section and inserted into the model equations, gave predictions of a considerable influence of size distribution on extraction column performance.