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The provision of atmospheric oxygen, removal of carbon dioxide and heat is essential to sustain crew health during human spaceflight missions. Microgravity and reduced gravity environments (such as a planetary surface) limit the use of bubble-forming technologies, since surface tension and inertial or viscous forces may dominate buoyancy, creating an adverse effect in the system. Gas-to-liquid contacting membranes would allow for non-bubbling mass transfer through solution-diffusion, with the potential for simultaneous heat transfer, as done in membrane distillation operations. Previously published work, with similar applications, have focused on characterizing microporous membranes. In this study, a commercially available, nonporous polydimethylsiloxane (PDMS) hollow fiber membrane separated carbon dioxide from an ambient gas stream (296 K) while deoxygenating a cooling-water feed (274 K). Control experiments were conducted with gas and water at ambient temperatures (296 K and 292 K, respectively). Results show that increasing water feed rate (0.5 to 1.5 LPM) reduced the percentage of oxygen transferred from the water to the gas stream (approximately 25% less). Also, a reduction in water temperature significantly reduced percent oxygen transferred (approximately 35% reduction). System heat transfer and carbon dioxide transfer rates were positively correlated to gas flow rates, showing gas-phase dependence. Coefficients derived from the experimental results were used to form semi-empirical mass transport models. Results of this study developed two findings, that a nonporous PDMS membrane could be used for simultaneous heat and mass transfer which could also be described from first-order principles.

The objective of this paper is to present experimental methodologies developed in the field of process engineering facilitating the quantification of the main processes involved in high rate algal ponds (HRAPs). The model presented is based on the River Waters Quality Model No. 1. The hydrodynamic system is particularly simple and the reactor is modeled with a series of perfectly mixed recirculation reactors. For the calibration of the model, one must go through the study of the main axes of this model. The hydrodynamics of the reactor fitting Voncken's model: circulation time (Tc), recirculation flow rate, water velocity (Vc), Peclet's number, etc.), the gas-liquid transfer processes for oxygen but also for NH3, CO2 and the photosynthesis-related biochemical processes were monitored. The simulation is conducted in a HRAPs pilot plant using the WEST program. The oxygenation factor was optimized and set by a series of experimental data obtained on the pilot station located in Marrakech. The obtained result show a strong link between concentration of algae and dissolved oxygen concentrations with maximum levels reached after 500 h. The maximum concentration of algae and oxygen are in the order of 500 and 16 g m-3, respectively. This is one more element to judge the consistency of our model. Additionally, the simulation of heterotrophic biomass, algae biomass, nitrogen concentration, chemical oxygen demand removal efficiency and oxygen concentrations vs. time in the HRAPs with the classical cycles due to day/night conditions show that the influence of light is clearly marked on the oxygen and algae concentrations. The methodology adopted to characterize the gas transfer coefficient is suitable for piston reactors with recirculation. [ABSTRACT FROM AUTHOR]

Nitrifying biologically active filters (BAFs) have been found to be high emitters of nitrous oxide (N 2 O), a powerful greenhouse gas contributing to ozone layer depletion. While recent models have greatly improved our understanding of the triggers of N 2 O emissions from suspended-growth processes, less is known about N 2 O emissions from full-scale biofilm processes. Tertiary nitrifying BAFs have been modeled at some occasions but considering strong simplifications on the description of gas-liquid exchanges which are not appropriate for N 2 O prediction. In this work, a tertiary nitrifying BAF model including the main N 2 O biological pathways was developed and confronted to full-scale data from Seine Aval, the largest wastewater resource recovery facility in Europe. A mass balance on the gaseous compounds was included in order to correctly describe the N 2 O gas-liquid partition, thus N 2 O emissions. Preliminary modifications of the model structure were made to include the gas phase as a compartment of the model, which significantly affected the prediction of nitrification. In particular, considering gas hold-up influenced the prediction of the hydraulic retention time, thus nitrification performances: a 3.5% gas fraction reduced ammonium removal by 13%, as the liquid volume, small in such systems, is highly sensitive to the gas presence. Finally, the value of the volumetric oxygen transfer coefficient was adjusted to successfully predict both nitrification and N 2 O emissions. Image 1 • A nitrifying BAF model was extended to describe full-scale N 2 O emissions. • Inclusion of a mass balance for the gas phase is essential to describe N 2 O emissions. • Gas phase assumptions heavily impacted the prediction of nitrifying performances. • The calibrated model successfully described nitrification and the mass transfer of O 2 and N 2 O. [ABSTRACT FROM AUTHOR]

The energy efficiency of bubble generating systems of gas-liquid contacting reactors is reviewed and analyzed quantitatively. The key metrics that emerge from a new theoretical analysis are: i) gas fraction of the output dispersion ( ε gen ), ii) interfacial area density of the output dispersion ( a gen ), iii) the energy necessary to create interfacial area ( ξ ), and iv) cost and maintenance. These metrics are then used to create a literature review of the performance of existing technologies for bubble generation. thus producing a conceptual framework for process intensification and future designs for bubble generating systems. A novel micro-ejector device is then studied within this framework, and is found to have desirable performance, hypothetically because it limits fluid shear to be located on at the gas injection site, on micron size scales. A physical model of the gas entrainment and bubble creation mechanisms in the micro-ejector is described and validated with empirical data. [ABSTRACT FROM AUTHOR]

The paper aimed to study the chemical absorption of CO 2 in monoethanolamine solvent (MEA) using high frequency ultrasonic irradiation of 1.7 MHz. The experiment was conducted at instantaneous regime in order to study the physical enhancement effect of the ultrasound. Hence, a mathematical model is proposed to justify the enhancement effects involved in the absorption process. The parameters of the experiment included ultrasonic power, MEA concentration, temperature, and CO 2 partial pressure. Results show that, a significant increase in the chemical absorption rate can be obtained by using ultrasonic power of 18 W, which is up to 60 times faster than the case without ultrasonic irradiation. Besides, the experimental data is in good agreement with the simulated data by obtaining the R 2 values ranged from 0.989 to 0.997. Therefore, this study demonstrates a new technology to improve the absorption process. Besides, the enhancement for the chemical absorption using ultrasonic irradiation is believed to be dominated by the fountain formation and also the convective dynamic. In overall, ultrasonic-assisted absorption would be one of the potential alternatives for CO 2 capture with its advantages of high mass transfer coefficient and compact design. [ABSTRACT FROM AUTHOR]

Physical absorption process is always nullified by the presence of cavitation under low frequency ultrasonic irradiation. In the present study, high frequency ultrasonic of 1.7 MHz was used for the physical absorption of CO 2 in a water batch system under elevated pressure. The parameters including ultrasonic power and initial feed pressure for the system have been varied from 0 to 18 W and 6 to 41 bar, respectively. The mass transfer coefficient has been determined via the dynamic pressure-step method. Besides, the actual ultrasonic power that transmitted to the liquid was measured based on calorimetric method prior to the absorption study. Subsequently, desorption study was conducted as a comparison with the absorption process. The mechanism for the ultrasonic assisted absorption has also been discussed. Based on the results, the mass transfer coefficient has increased with the increasing of ultrasonic power. It means that, the presence of streaming effect and the formation of liquid fountain is more favorable under high frequency ultrasonic irradiation for the absorption process. Therefore, high frequency ultrasonic irradiation is suggested to be one of the potential alternatives for the gas separation process with its promising absorption enhancement and compact design. [ABSTRACT FROM AUTHOR]

• A model that integrated force balance and mass transfer of MNB was developed. • Intensive gas dissolution results in radius reduction for small bubble. • Higher initial water depth drives high shrink potency of bubbles. • Optimum bubble size that could achieve complete gas transfer were determined. Bubble aeration has been widely applied in water/wastewater treatment, however its low gas utilization rate results in high energy consumption. Application of micro-nanobubbles (MNB) has emerged as a process with the potential to significantly increase gas utilisation due to their high relative surface area and high gas-liquid mass transfer efficiency. In this study, we demonstrate through calibrated models that MNB of an optimum bubble size can shrink and burst at or below the water surface enabling (1) all encapsulated gas to thoroughly dissolve in water, and (2) the bursting of nanobubbles to potentially generate free radicals. Through the understanding of MNB dimensional characteristics and bubble behaviour in water, a dynamic model that integrated force balance (i.e. buoyancy force, gravity, drag force, Basset force and virtual mass force), and mass transfer was developed to describe the rising velocity and radius variation of MNB along its upward trajectory. Unlike for conventional millimetre-sized bubbles, intensive gas dissolution of MNBs led to radius reduction for small bubbles, while a large initial radius triggers bubble swelling. The initial water depth was also crucial, where greater depth could drive the potential for bubble shrinkage so that they were more liable to contract. For example, the optimum bubble size of air (42–194 μm) and oxygen (127–470 μm) MNB that could achieve complete gas transfer (100% gas utilisation) for a range of specific water depths (0.5–10 m) were calculated. The modelling results for microbubbles (10–530 μm) were well validated by the experimental data (R2>0.85). However, the validation of the modelling results for nanobubble (<1 μm) aeration requires further study due to a lack of available empirical data. In this study, the proposed model and analysis provided new insights into understanding bubble dynamics in water and offered fundamental guidance for practitioners looking to upgrade bubble aeration system. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: The absorption of carbon dioxide into monoethanolamine (MEA) solution has been studied. A specific setup allowing controlling gas-liquid interface has been studied. It is based on a stirred reactor. This study presents the determination of physicochemical and kinetic parameters. Determination has been done for MEA solution with and without sulphuric acid. This acid will illustrate the accumulation of SOx present in the fumes of a typical industrial process. [Copyright &y& Elsevier]

Abstract: A model was elaborated to quantify the gas–liquid partitioning of four of the most important volatile compounds produced during winemaking fermentations, namely isobutanol, ethyl acetate, isoamyl acetate and ethyl hexanoate. Analyses of constant rate fermentations demonstrated that the partitioning was not influenced by the CO2 production rate and was a function of only the must composition and the temperature. The parameters of the model were identified in fermentations run at different temperatures, including anisothermal conditions. The prediction of the partition coefficient (k i) by the model was very accurate for isobutanol, isoamyl acetate and ethyl hexanoate. The technological potential of the model was confirmed by using it to calculate the losses of volatiles in the gas phase during fermentation and comparing them with experimental data. Up to 70% of the produced volatile compounds were lost. The difference between observed losses and losses estimated from predicted k i values never exceeded 3%. [Copyright &y& Elsevier]

Abstract: Accumulation of alkane by-products from gas to liquid fuel processes presents an attractive feed stock opportunity with potential for bioconversion to a wide variety of valuable commodity products. This review highlights the need to address the complexities of the oxygen transfer rate and overall volumetric oxygen transfer coefficient (K L a) in hydrocarbon bioprocesses so that this potential can be realised. Three markedly different K L a behavioural trends have been identified in hydrocarbon–aqueous dispersions and characterised according to the hydrocarbon type and concentration, operating conditions and geometric constraints. A fundamental conceptual understanding of the mechanisms which define the exact behaviour of K L a in response to changes in turbulence and fluid properties is provided. Further, the behaviour is quantified in terms of the parameters which underpin this response viz. bubble diameter, gas–liquid interface rigidity, gas hold up, surface tension, viscosity and diffusivity. Consideration is given to existing predictive correlations for interfacial transfer area, bubble diameter, gas hold up, oxygen transfer coefficient and K L a. It is envisaged that through the elucidation and quantification of the parameters which shape the behaviour of K L a, these correlations may be successfully extended to predict the complex behavioural K L a trends in hydrocarbon-based bioprocesses. [Copyright &y& Elsevier]

Abstract: Measurements of gas–liquid and liquid–solid mass transfer coefficients were performed in two types of three-phase laboratory reactor equipped with stationary catalytic basket and multiple impeller. Those reactors are called Robinson–Mahoney reactors. Local liquid–solid mass transfer coefficients were measured using naphtol particle dissolution in n-heptane at several agitation speeds. Experiments had shown that local coefficients depended on the particle locations in the basket and agitation speeds. The local coefficient values and profiles were quite similar for both studied reactors even though the reactor designs were different. Similar values of RM basket thicknesses might account for this phenomenon because the liquid–solid mass transfers could be correlated with the ones in packed beds with forced liquid circulation. Gas–liquid mass transfer coefficients were measured using standard dynamic absorption methods in air–water or hydrogen–gas oil system. As in stirred tanks, the gas–liquid mass transfers were linked to the impeller designs and characteristics (gas-inducing or classical impeller) and to the operating conditions such as agitation speeds and fluid properties. However, correlations applicable to stirred tank reactors can be used with Robinson–Mahoney reactors, the baskets behaving like additional baffles or reduction of tank diameters. [Copyright &y& Elsevier]

As part of contributions to code development for the simulation of a severe accident in a pressurised water reactor (PWR), an experimental programme is underway at the “Institut de Radioprotection et de Sûreté Nucléaire”, concerning the mass transfer kinetics of fission products. This programme takes place in the Sisyphe facility which represents a reduced scale (1/5000) pressurised water reactor containment.This programme is to specify the mass transfer coefficients between the sump water and the containment atmosphere using dynamic absorption methods. Measurements are carried out on a simulating volatile fission product, namely oxygen.In the studied operating conditions (isothermal containment at 90 °C), there is no difficulty about the determination of the partial mass transfer coefficient in the liquid-phase, and in the case where the aqueous and gaseous phases are macroscopically motionless, this value is of kL=3.0×10-5 m/s.The method chosen for the determination of the gas-phase transfer coefficient (the reactive absorption of oxygen by an aqueous solution of sodium sulphite, with or without catalyst), has shown that the apparent transfer coefficient depends on both the sodium sulphite and catalyst concentrations. This partial mass transfer coefficient tends to a limit value for sufficient sodium sulphite and catalyst concentrations, which is the probable value of the gas-phase transfer coefficient (kG), estimated at 10-4 m/s at 90 °C. [Copyright &y& Elsevier]

Excess O 3 is invariably used to ensure the effective oxidation of NO in the industrial simultaneous desulfurization and denitration through combined ozone oxidation and absorbent scrubbing. O 3 is difficult to fully react with NO considering the short residence time of flue gas, remaining O 3 transport into the subsequent absorption device, and even its escape into the atmosphere. To study the influence of excess O 3 on NO 2 absorption in sulfite solution, we simulated an integrative process of pre-oxidation and post-absorption. NO 2 removal efficiency was improved from 36.1% to 66.5% as the mole ratio of O 3 /NO increased from 1.0 to 1.6. Additionally, the effects of temperature, pH, and reactant concentration with the remaining O 3 on NO 2 removal were evaluated. After 5 h of steady absorption, the concentration of total N species in the adsorbent was 82.8 mmol/L at a O 3 /NO mole ratio = 1.6. However, this concentration was only 51.4 mmol/L at a O 3 /NO mole ratio = 1.0, indicating that more NO 2 was absorbed, and the gas-liquid transfer of NO 2 was enhanced by the excess O 3 via oxidizing NO 2 − into NO 3 −. This work contributes to re-utilizing remaining O 3 and reducing O 3 escape in simultaneous desulfurization and denitration technology. This research studied the role of excess O3on NO2absorption in sulfite solution and the corresponding mechanism. NO2removal efficiency was enhanced with excess O3in sulfite solution. NO2-was removed from sulfite absorption system via the oxidation ofNO2-into NO3-by excess O3. The chemical equilibrium of the reaction between NO2and SO32-was shifted by removing NO2-, resulting in the NO2absorption that containing gas-liquid transfer and chemical reaction was improved. Unlabelled Image • NO 2 absorptionwas improved with excess O 3 • Absorption equilibrium was shifted • NO 2 gas-liquid transfer was modified [ABSTRACT FROM AUTHOR]