Volumetric Transfer Coefficient Research Articles

Experimental and modeling study of bubble absorption-based deep dehumidification using the ionic liquid: Parametric analysis on heat and mass transfer

Conventional liquid desiccant dehumidification is good at humidity control with energy conservation and stable operation, but is limited by corrosion and crystallization in deep dehumidification. Thus, it is necessary to broaden the humidity adjustment range of liquid desiccant deep dehumidification as well as avoid corrosion. Ionic liquids (ILs) with deep dehumidification potential (e.g., extremely low vapor pressure and non-corrosion) are a promising alternative to traditional salt solutions. Meanwhile, the bubble absorption-based mode can obtain a huge gas–liquid specific interfacial area, which is expected to solve the low wettability and insufficient gas–liquid transfer efficiency in traditional falling-film/packed dehumidifiers using IL. In this work, the bubble absorption-based deep dehumidification using IL (BADD-IL) is investigated. Meanwhile, the heat and mass transfer mathematical model of BADD-IL is established, and a bubble column dehumidifier using the novel IL is experimentally examined under different conditions. The results indicated that the deep dehumidification performance is strongly dependent on operating parameters, and the minimum outlet air humidity ratio is around 1.2 g/kgda. In particular, it is most sensitive to inlet air humidity ratio, followed by liquid height and superficial velocity, and the effect of solution temperature is the least. Notably, the influential mechanism of superficial velocity and solution temperature on volumetric transfer coefficient is different. The increase of superficial velocity promotes both gas–liquid specific interfacial area and heat and mass transfer coefficient. For the IL with lower temperature, its higher heat and mass transfer coefficient makes up for the poor specific interfacial area caused by high viscosity. Additionally, the Lewis factor of bubble column dehumidifier using the novel IL is basically less than 0.6, which is important for the device design and scale-up. This study clarifies the heat and mass transfer mechanism of BADD-IL, and provides guidance for the development of ILs deep dehumidification technology.

Oxygen and hydrocarbon volumetric transfer coefficients in the production of an oil-degrading bacterial consortium: emulsifying activity and surface tension in a bioreactor.

Our work shows that in multiphase systems, it is more important to take into account the mass transfer of oil rather than that of just oxygen. The oxygen volumetric transfer coefficient is important in aerobic bioreactor design. However, in multiphase systems with non-soluble substrates, oil transfer can impose larger restrictions but is usually not considered. Emulsification and surface tension could play an important role due to effects on oil droplet size and interfacial transfer area. Petroleum oil and is derivates such as diesel can negatively affect living organisms. This study evaluated the effects of the volumetric transfer coefficients (kLa) of hydrocarbons and oxygen on the production of an oil-degrading consortium in an airlift bioreactor relative to emulsifying activity and surface tension, which play important roles in the biodegradation of non-soluble substrates such as diesel due to a combined mass transfer constraint. Our results showed a clear difference in kLa values, which ranged from 15 to 91h-1 for oxygen and from 0 to 0.0014h-1 for diesel. Most aerobic biodegradation studies focus on the oxygen volumetric transfer coefficient (kLaoxygen), but our results indicated that non-soluble constraints, such as the volumetric transfer coefficient of diesel (kLadiesel), could be more important. Additionally, d32diesel decreased as superficial gas velocity (Ug) increased. Lower Ug rates (0.15cms-1) resulted in higher values of d32diesel (0.38cm-1), whereas higher Ug rates (2.7cms-1) resulted in lower values of d32diesel (0.21cm-1) at the beginning of the cultivation.

Characteristics of air-liquid heat and mass transfer in a bubble column humidifier.

Bubble columns are recently used for the humidification of air in water treatment systems and fuel cells. They are well applicable due to their excellent heat and mass transfer and their low technical complexity. To design and operate such devices with high efficiency, the humidification process and the impact of the operating parameters need to be understood to a sufficient degree. To extend this knowledge, we use a refined and novel method to determine the volumetric air–liquid heat and mass transfer coefficients and the humidifier efficiency for various parametric settings. The volumetric transfer coefficients increase with both of the superficial air velocity and the liquid temperature. It is further shown that the decrease of vapor pressure with an increase of the salinity results in a corresponding decrease in the outlet humidity ratio. In contrast to previous studies, liquid heights smaller than 0.1 m are investigated and significant changes in the humidifier efficiency are seen in this range. We present the expected humidifier efficiency with respect to the superficial air velocity and the liquid height in an efficiency chart, such that optimal operating conditions can be determined. Based on this efficiency chart, recommendations for industrial applications as well as future scientific challenges are drawn.

Methods for Oxygenation of Continuous Cultures of Brewer’s Yeast, Saccharomyces cerevisiae

Maintaining steady-state, aerobic cultures of yeast in a bioreactor depends on the configuration of the bioreactor system as well as the growth medium used. In this paper, we compare several conventional aeration methods with newer filter methods using a novel optical sensor array to monitor dissolved oxygen, pH, and biomass. With conventional methods, only a continuously stirred tank reactor configuration gave high aeration rates for cultures in yeast extract peptone dextrose (YPD) medium. For filters technologies, only a polydimethylsiloxan filter provided sufficient aeration of yeast cultures. Further, using the polydimethylsiloxan filter, the YPD medium gave inferior oxygenation rates of yeast compared to superior results with Synthetic Complete medium. It was found that the YPD medium itself, not the yeast cells, interfered with the filter giving the low oxygen transfer rates based on the volumetric transfer coefficient (KLa). The results are discussed for implications of miniaturized bioreactors in low-gravity environments.

Gas transfer management by membrane contactors in an oenological context: Influence of operating parameters and membrane materials

Oxygen management in wine is one of most challenging issue for winemakers. Indeed, an excess of dissolved oxygen (O2) can prematurely age wine and leads to organoleptic deviation.Membrane contactors composed of hydrophobic hollow fiber are becoming a relevant technology especially for gas-liquid mass transfer operations. Nevertheless, their utilization in an oenological context to manage oxygen in wine has not been comprehensively studied. Fouling phenomena could be problematic and may limit their utilization during winemaking.The aim of this study is to develop (i) a simple and rapid method to characterize membrane contactors and (ii) to investigate the effects of two types of membrane contactor composed either of polypropylene (PP) or of PP with a dense coat layer (Teflon). The specific methodology proposed using volumetric transfer coefficient (KL·a) is used to investigate the performance of the membranes on gas transfer in terms of wetting and fouling, as well as the effect of the membrane material. After liquid flow rate optimization, which was necessary to determine a suitable value (300 mL·min−1), the membrane contactors’ performances were characterized with water, a wine model solution and two red wines with different fouling index. After several hydrodynamic optimization operations, we consider that the membrane contactors studied could remove oxygen while carbon dioxide is dissolved with KL·aCO2 close to 20 × 10−5 s−1 for both prototypes. The addition of a dense coat layer in an oenological context may be necessary for a non-prepared wine with a high fouling index.

Application of Mathematical Models Using Volumetric Transfer Coefficients in Fluidized Bed Dryers

Fluidized bed dryers are often used in several industrial processes to dry wet granular solids with high moisture contents. During the drying process, simultaneous heat- and mass transfer occurs between the material and drying gas. Drying is an extremely energy intensive process, therefore the invested energy should be mitigated during planning the operation, granting optimal geometric and operational parameters of the device. During the planning, sufficiently accurate thermal models provide an opportunity to increase the effectiveness of dryers. The purpose of our work is to develop mathematical model to investigate the influence of operating parameters describing the simultaneous heat- and mass transfer in a fluidized bed dryer. The input parameters of the model are the volumetric transfer coefficients between the drying gas and the granules, due the uncertain heat- and mass transfer surface. A pilot plant fluidized bed dryer device is developed to determine the volumetric transfer coefficients and to study the heat- and mass transfer phenomena during the drying processes. The goal of our work is to model the fluidized bed drying process more accurately using volumetric transfer coefficients.

Effect of viscosity-inducing factors on oxygen transfer in production culture of bacterial cellulose

Bacterial cellulose (BC) production culture requires high oxygen transfer rate (representatively kLa) at a low shear force. Considering that oxygen exhaustion is observed at the latter half of the exponential growth phase where BC production actually begins, it is highly probable that the drastic reduction of kLa (oxygen volumetric transfer coefficient) is caused by the drastic increase of the soluble and insoluble viscous materials. Therefore, we examined the apparent viscosity-inducing materials generated during BC culture and investigated their effects on kLa. Using the saccharified liquid from food waste as the culture medium, we discussed the relationship between the concentration of the generated solid matters, especially BC and the viscosity, the relationship between the BC concentration and kLa, and the correlation between the viscosity and kLa. The relationship between the solid matter (BC), which is the insoluble viscosity-inducing material, and kLa showed that the BC concentration and kLa were in exponentially reciprocal proportion with the linear regression equation. In case of using agar as the soluble viscosity-inducing material, the correlation between the viscosity and kLa showed that the viscosity depending on the agar concentration was in exponentially reciprocal proportion with kLa in both tap water and the saccharified liquid medium. The results indicated that the effect of the BC concentration on kLa was not great in the saccharified liquid medium. As the agar concentration increased in tap water and the saccharified liquid medium, the viscosity was increased and kLa was decreased gradually, showing a linear relation between the logarithm of the viscosity as agar and kLa. In conclusion, the effect of the soluble viscosity on kLa was greater than that of solid matter (BC). Also, it was suggested that the soluble viscosity-inducing matters like agar were rather more effective than kLa in BC production.

Adaptation of the “Dynamic Method” for measuring the specific respiration rate in oxygen transfer systems through diffusion membrane

Monitoring the specific respiration rate (Q(O2)) is a valuable tool to evaluate cell growth and physiology. However, for low Q(O2) values the accuracy may depend on the measurement methodology, as it is the case in animal cell culture. The widely used "Dynamic Method" imposes serious difficulties concerning oxygen transfer cancellation, especially through membrane oxygenation. This paper presents an improved procedure to this method, through an automated control of the gas inlet composition that can minimize the residual oxygen transfer driving force during the Q(O2) measurement phase. The improved technique was applied to animal cell cultivation, particularly three recombinant S2 (Drosophila melanogaster) insect cell lines grown in a membrane aeration bioreactor. The average measurements of the proposed method reached 98% of stationary liquid phase balance method, taken as a reference, compared to 21% when the traditional method was used. Furthermore, this methodology does not require knowledge of the volumetric transfer coefficient k(L)a, which may vary during growth.

Modelling gas–liquid and liquid–gas transfers in vinegar production by genetic algorithms

The transfer of oxygen from aeration flow to the fermentation medium and the transfers of ethanol, ethyl acetate, acetoin, acetic acid and water from the fermentation medium to aeration flow were modelled for the industrial production of vinegar. The study was developed in a pilot fermentor, working with continuous processes and industrial fermentation mediums. The cores of the proposed models were the semi-empiric correlations for the volumetric transfer coefficients k L a for oxygen transfer and k A,G a for the liquid–gas transfers. The main novelty was the introduction of the effect of pressure on the fermentation medium, together with the expression proposed for k A,G a, with the same structure as the expression for k L a. A genetic algorithm was developed to calculate the parameters of the models, with a four composed desirability function as the evaluation function. The optimised sets of parameters provided models with good predictive ability. The models can be applied for any fermentor with the same agitation and aeration system design and the same geometry.

Influence of oxygen availability on cell growth and xylitol production by Candida guilliermondii.

Oxygen availability is the most important environmental parameter in the production of xylitol by yeasts, directly affecting yields and volumetric productivity. This work evaluated the cell behavior in fermentations carried out with different dissolved oxygen concentrations (0.5-30.0% of saturation), as well as a limited oxygen restriction (0% of saturation), at several oxygen volumetric transfer coefficients (12 < or = kLa < or = 70 h(-1)). These experiments allowed us to establish the specific oxygen uptake rate limits to ensure high yields and volumetric productivity. When oxygen availability was limited, the specific oxygen uptake rate values were between 12 and 26 mg of O2/of g cell x h, resulting in a yield of 0.71 g of xylitol/xylose consumed, and 0.85 g/[L x h] for the volumetric productivity. According to the results, the effective control of the specific oxygen uptake rate makes it possible to establish complete control over this fermentative process, for both cell growth and xylitol production.

Oxygen transfer characteristics of a centrifugal, packed-bed reactor during viscous xanthan fermentation

The oxygen transfer properties of a novel, centrifugal, packed-bed reactor (CPBR) during viscous xanthan fermentation were determined with respect to the effects of the arrangement of the centrifugal, packed bed (CPB) and the recirculation loop (RL). Characterized by the maximum volumetric transfer coefficient (k L a) in xanthan broth, the aeration efficiency of CPBR was compared to those in stirred-tank reactors (STR) equipped with disc turbines (DT) or marine propellers (MP), and to that in a water-in-oil emulsion (WIO). As expected, STR-WIO showed the highest k L a (0.038 s–1 at 2%) among all systems studied due to reduced broth viscosity; however, practical difficulties exist in product recovery. It was found that, at 3.5% xanthan the k L a in CPBR (0.018 s–1) was higher than that of STR (0.005 s–1) and close to that of STR-WIO (0.020 s–1), indicating improved oxygen transfer at such a xanthan concentration. The exterior baffles along the rotating fibrous matrix offer additional agitation in the viscous broth. A gas-continuous arrangement, in which the CPB was kept above the broth, was able to elevate k L a to 0.023 s–1, higher than that of STR-WIO. The external RL operated by a peristaltic pump was found to play an important role in CPBR aeration by providing better gas–liquid contact. With the improved oxygen transfer efficiency in CPBR at high xanthan concentrations, the CPBR system is practically the preferred system for xanthan fermentation. The characteristic roles of CPB arrangement and the RL should be considered primarily during scale-up operation.

Theoretical prediction of the mass transfer coefficients in bubble columns operating in churn-turbulent flow regime. Study in Newtonian and non-Newtonian fluids under different operation conditions

A comprehensive experimental study of the volumetric transfer coefficient kLa with Newtonian and non-Newtonian fluids in bubble columns using CO2 as gas phase is the objective of this work. The evaluation of the hydrodynamic characteristics of the bubble columns and delineated the different hydrodynamic regimes considering column geometry, gas flow, liquid height and type of fluid (Newtonian and non-Newtonian) suggest a general applicability of the proposed model. An explanation about of the kLa values in non-Newtonian fluid is offered take into account shear rate, column geometry, viscosity and results reported in the literature previously.

Volumetric heat transfer coefficients in solid–fluid porous media: closure problem, thermal analysis and model improvement with fluid flow

This paper presents a detailed investigation on the volumetric transfer coefficient (VHTC) model in solid–fluid porous media based on the volume averaging method (VAM). The VHTC is obtained by solving the closure problem with the control-volume finite difference method. A thermal analysis is conducted to illustrate the thermal nature of the VHTC, based on which, an improved VHTC model has been proposed by taking into account the effects of the thermal entrance and the non-uniformity of the velocity field. With this model, the applicability of the VAM has been extended to large Peclet number laminar regime for convection heat transfer in porous media characterized by straight ducts.

Effect of the oxygen transfer coefficient on xylitol production from sugarcane bagasse hydrolysate by continuous stirred-tank reactor fermentation.

The effect of the oxygen transfer coefficient on the production of xylitol by bioconversion of xylose present in sugarcane bagasse hemicellulosic hydrolysate using the yeast Candida guilliermondii was investigated. Continuous cultivation was carried out in a 1.25-L fermentor at 30 degrees C, pH 5.5, 300 rpm, and a dilution rate of 0.03/h, using oxygen transfer coefficients of 10, 20, and 30/h. The results showed that the microbial xylitol production (11 g/L) increased by 108% with the decrease in the oxygen volumetric transfer coefficient from 30 to 20/h. The maximum values of xylitol productivity (0.7 g/[L.h]) and yield (0.58 g/g) were obtained akLa 20/h.

Model based in neural networks for the prediction of the mass transfer coefficients in bubble columns. Study in Newtonian and non-Newtonianian fluids

A comprehensive study for the prediction of the volumetric transfer coefficient k L a with Newtonian and Non-Newtonian fluids in bubble columns is the objective of this work. The evaluation of the hydrodynamic characteristics of the bubble columns and delineated the different hydrodynamic regimes considering column geometry, gas flow, liquid height and type of fluid (Newtonian and non-Newtonian) suggest a general applicability of the proposed model. A new learning pattern based in the design parameters of the bubble columns is proposed.

Determination of the reaction yield during biotransformation of the volatile and chemically unstable compound beta-ionone by aspergillus niger

Biotransformation of beta-ionone by Aspergillus niger IFO 8541 was a complex system, due to the low precursor solubility in water (0.88 mol/m(3)) which gave a two-phase liquid system, its high volatility (vapor pressure 7.2 Pa), and its poor chemical stability. A dynamic model, considering transfers between organic, aqueous, and gas layers, was established. It also took into account the decrease in organic layer area exchange during a process, due to progressive precursor disappearance. Its solving needed separate determination of two parameters. The first-order kinetic constant for chemical degradation, K(1), was estimated from side experiments involving a model system at thermodynamic equilibrium; its value was found to be close to 4.17 x 10(-)(6) s(-)(1). The volumetric transfer coefficient between gas and aqueous phase was estimated by analogy with results obtained for oxygen transfer. Results obtained demonstrated high liquid-gas transfer rates, while liquid-liquid transfers were severely limited. These data were then used to estimate the true yield of a biotransformation experiment, which was found to be close to unity.

Direct contact heat transfer with change of phase: Spray‐column studies of a three‐phase heat exchanger

AbstractTransfer characteristics are presented for a perforated plate‐spray column in which a volatile dispersed phase evaporates while rising in the continuous, counterflowing, immiscible phase. Optimal column heights, volumetric transfer coefficients, holdup, and foam heights are reported as functions of flow rate and temperature approach for a pentane‐water system, A comparison with related studies is presented.