Search results for "Efficient"
showing 10 items of 1603 documents
Study of the thermodynamics and mass transfer kinetics of two enantiomers on a polymeric imprinted stationary phase
1998
The adsorption isotherms of d- and l-phenylalanine anilide (PA) on an l-phenylalanine anilide imprinted stationary phase have been determined using staircase frontal analysis. An aqueous buffer–organic solvent mixture has been used as mobile phase. The measurements were done at temperatures of 40, 50, 60 and 70°C for sample concentrations ranging between 5·10−4 to 1 g/l. It was found that the adsorption data fit well to both the Freundlich and the Bi-Langmuir isotherm models. Examination of the best values of the numerical coefficients of the Bi-Langmuir model shows that the site class representing the binding sites with the highest binding energy exhibits a very low saturation capacity for…
The scavenging of nitrogen compounds by clouds and precipitation:
1998
Model predictions of nitric acid scavenging by an air parcel model and a two-dimensional dynamic cloud model with detailed microphysics are compared with corresponding predictions for parameterized microphysics for the same initial conditions. In general the gas uptake proceeds slower in the model with parameterized microphysics than in the model with detailed microphysics and, the larger the drop size, results in a slower mass transfer. This behaviour can be explained by the inverse drop-radius dependency of the mass transfer coefficient and the time delays were a direct result of the microphysical parameterization. With the air parcel model for the scavenging of nitric acid, time delays i…
Mass transfer and hydrodynamic characteristics of unbaffled stirred bio-reactors: Influence of impeller design
2014
Abstract Unbaffled stirred tanks are increasingly recognized as a viable alternative to common baffled tanks for a range of processes where the presence of baffles is undesirable for some reason. For instance, in the case of shear sensitive cell cultivation (e.g. human cells), unbaffled tanks have been recently found to be able to provide sufficient mass transfer through the free surface vortex. As a consequence the need for bubble formation and subsequent bursting, along with relevant cells damage, is conveniently avoided. In this work the influence of impeller geometry on mass transfer performance and power demand of an unbaffled stirred vessel operating both in sub-critical conditions (t…
Simplified dynamic pressure method for kLa measurement in aerated bioreactors
2010
Abstract A simplified version of the dynamic pressure method for measuring mass-transfer coefficients in gas–liquid systems is proposed. With this method oxygen concentration in the liquid phase is monitored after a sudden change of total pressure is applied to the system. With respect to the original technique introduced by Linek [14] the simplified version here proposed greatly simplifies the data treatment, yet resulting in good accuracy for most practical purposes. In practice, with the help of a simple mathematical model, it is found that the dynamic oxygen concentration response, when plotted as residual driving force versus time in a semi-log diagram, should be expected to finally se…
Unbaffled, Stirred Bioreactors for Animal Cell Cultivation
2017
One of the main features of animal cell bioreactors is that the cultured cells lack a strong membrane and are therefore more prone to shear damage. It is widely accepted that animal cell damage in aerated bioreactors is mainly related to burst bubbles at the air–liquid interface. A viable alternative to sparged bioreactors, aimed at minimizing cell damage, may be represented by uncovered, unbaffled, stirred tanks, which are able to provide sufficient mass transfer through the deep free surface vortex that takes place under agitation. As a consequence the need for bubble formation and subsequent bursting accompanied by cell damage is conveniently avoided. In this chapter, mass transfer perfo…
Gas-liquid-solid Operation of a High Aspect Ratio Self-ingesting Reactor
2012
Gas-liquid stirred vessels are widely employed to carry out chemical reactions involving a gas reagent and a liquid phase. The usual way for introducing the gas stream into the liquid phase is through suitable distributors placed below the impeller. An interesting alternative is that of using “self ingesting” vessels where the headspace gas phase is injected and dispersed into the vessel through suitable surface vortices. In this work the performance of a Long Draft Tube Self-ingesting Reactor (LDTSR) dealing with three-phase (gas-liquid-solid) systems, is investigated. Preliminary experimental results on the effectiveness of this contactor for particle suspension and gas-liquid mass transf…
Gas-liquid mass transfer rates in unbaffled tanks stirred by PBT: scale-up effects and pumping direction
2018
Abstract Unbaffled stirred tanks are increasingly recognized as a viable alternative to common baffled tanks for a range of applications such as biochemical, food or pharmaceutical processes where the presence of baffles is undesirable for some reason. In this work, the mass transfer performance of unbaffled stirred tanks with pitched blade turbine, operating either in up-pumping or down-pumping mode, was investigated. The influence of impeller size and liquid viscosity were also investigated. The mass transfer intensity was measured by means of the Simplified Dynamic Pressure. Method The measurements concerned both coalescent and non-coalescent (viscous) batches. Results confirm that incre…
Effect of the height-to-diameter ratio on the mass transfer and mixing performance of a biotrickling filter
2017
BACKGROUND Biotrickling filters (BTFs) are among the most widely used biological technologies for air pollution control. The pollutant removal rate in BTFs relies to a large extent on its gas–liquid mass transfer performance. Therefore, knowledge of the design parameters affecting the mass transfer and mixing performance of full-scale BTFs is of paramount importance. RESULTS This work showed that the height-to-diameter (H/D) ratio is an important parameter in the design of BTFs devoted to air pollution control. The H/D ratio significantly affected the mass transfer and mixing performance of the BTF with and without additional stirring in the holding tank. It was observed that under the same…
Mass transfer and hydrodinamic characteristics of a high aspect ratio self-ingesting reactor for gas-liquid operations
2007
Abstract The mass transfer performance of a gas–liquid self-ingesting stirred reactor is reported both for coalescing and non-coalescing systems. The vessel features are a high aspect ratio and a rather narrow multiple-impeller draft tube, through which the gas phase is ingested and led down to the vessel bottom, where it is finely dispersed into the liquid rising in the annular portion of the vessel. Comparison is made between k L a values determined by several variants of the dynamic method, among which pure oxygen absorption in a previously de-gassed liquid phase. Results show that the gas–liquid mass transfer coefficient values obtained with the last approach are remarkably larger than …
Stable-Matching-Based Energy-Efficient Context-Aware Resource Allocation for Ultra-Dense Small Cells
2017
Implementing caching to ultra-densely deployed small cells provides a promising solution for satisfying the stringent quality of service (QoS) requirements of delay-sensitive applications with limited backhaul capacity. With the rapidly increasing energy consumption, in this chapter, the authors investigate the NP-hard energy-efficient context-aware resource allocation problem and formulate it as a one-to-one matching problem. The preference lists in the matching are modeled based on the optimum energy efficiency (EE) under specified matching, which can be obtained by using an iterative power allocation algorithm based on nonlinear fractional programming and Lagrange dual decomposition. Nex…