An Arbitrary Lagrangian-Eulerian formulation has been posed to solve the challenging problem of the three-dimensional Taylor bubble, within a Conservative Level Set (CLS) framework. By employing a domain optimization method (i.e. the moving mesh method), smaller domains can be used to simulate rising bubbles, thus saving computational resources. As the method requires the use of open boundaries, a careful treatment of both inflow and outflow boundary conditions has been carried out. The coupled CLS - moving mesh method has been verified by means of extensive numerical tests. The challenging problem of the full three-dimensional Taylor bubble has then been thoroughly addressed, providing a detailed description of its features. The study also includes a sensitivity analyses with respect to the initial shape of the bubble, the initial volume of the bubble, the flow regime and the inclination of the channel.
Rojo, N.; Prenafeta, F.; Illa, J.; Gallastegui, G.; Guivernau, M.; Elias, A.; Barona, A. Chemical engineering science Vol. 131, p. 304-312 DOI: 10.1016/j.ces.2015.03.062 Data de publicació: 2015-07-28 Article en revista
Black slag roman electric arc furnace (EAF) was used as an innovative inorganic co-packing material in organic biofilters for the biodegradation of CS2-polluted gases. The effect on biofilter performance of increasing the inlet concentration (IC) and reducing the empty bed residence time (EBRT) was evaluated in three Not-titers packed with different bed configurations. Macro-kinetic modelling pointed to a lower CS2 biodegradation activity related to the presence of the slag. Nevertheless, the presence of black slag improved long-term biofilter performance, and the maximum elimination capacity (43 g m(-3) 3 h(-1)) was recorded in the biofilter packed with a mixed support. Molecular profiling of the eubacterial populations demonstrated the ubiquitous presence of the potential CS2 degrading species Thiomonas intermedia. Co-packing with EAF slag also prompted the development of a more complex microbial community encompassing halophilic species involved in the metabolism of sulphur compounds (i.e. Thiohalophilus spp. and Paracoccus thiocyanatus)
In this study, simulation of solar disinfection of secondary effluents was performed, to assess the dose effects, as instructed by the reciprocity law. A full factorial experimental design on the operational parameters of the process was performed (Lime, temperature, bacterial load, light intensity) and three response variables were estimated (disinfection efficiency, regrowth after 24, and 48 h). In the 240 disinfection experiments, an erratic behavior was observed in all responses to light exposure, attributed to the combination of both irradiation intensity and temperature during treatment. As a result, the validity of the reciprocity law between light dose and irradiation intensity is challenged. The majority of the cases failed to comply with it, indicating the dependence on temperature conditions, as well as the applied intensity. Dose affected the bacterial regrowth potential after 24 and 48 h in a more conventional way. It appears that in order to attain a valid projection of the outcome of solar disinfection in secondary effluent, intensity and dose are not the only parameters to be considered, with temperature also having to be taken under consideration. (C) 2015 Elsevier Ltd. All rights reserved.
The use of nanofiltration (NF) in water treatment has been proposed to improve the quality of the produced water and extend the options of concentrate valorization, taking the benefit of its different ions selectivity patterns. However, there is a need to understand and optimize the rejection not only of major components (e.g. NaCl or MgSO4) but also of minor components specially in brackish waters. The selectivity of ion rejection by NF membranes has been studied theoretically and experimentally. Theoretical analysis has been carried out within the scope of the solution-diffusion-film model (SDFM) recently extended to electrolyte mixtures. In this study, experimental ion rejection data of typical cationic and anionic species present in surface waters at various trans-membrane pressures and cross-flow velocities have been obtained with a NF membrane (NF270). Several combinations of dominant salts (NaCl, MgCl2, MgSO4, Na2SO4) with trace ions (Na+, Cl−, Mg2+, SO42−) have been used. The rejection of ions crucially depends on their environment. The dramatic differences in the rejections can be explained by the spontaneously arising electric fields generated in the membrane phase. Their effect gives rise to negative rejections of singly charged inorganic ions present as small additions to well-rejected dominant salts. As a result of theoretical interpretation the intrinsic membrane permeabilities to ions have been estimated for different aqueous solutions compositions
During batch process scheduling, products' batch size, processing conditions as well as operating times are usually established offline and considered out of the scope of the decision making stage. In practice, process dynamics may vary from the ones forecasted, in such a manner that the predicted optimal conditions will not be the best in practice. As a result of this mismatch, the plant usually operates under sub-optimal conditions, but if the process is flexible, its processing conditions can still be adapted to the actual plant needs in order to improve the overall performance. Given this situation, there is a strong motivation for developing models and optimization tools to fully integrate process dynamics into batch scheduling. In this work, the potential of directly including control variables with time varying values and variable batch sizes in the scheduling of batch plants is explored. The optimization of process dynamics, which is time varying, along with scheduling tasks is accomplished using rigorous mixed-integer dynamic optimization techniques. Through several examples, we show that integrating both decision-making levels can lead to significant economic savings.
The characteristics of two impinging bubble jets have been experimentally studied in microgravity
conditions. The experimental setup, designed to be used in a drop tower, allows to change the gas and
liquid ¿ow rates for the jet generation, and the separation distance between the jets. A slug ¿ow with
millimetric air bubbles is created in a T-junction and injected through a nozzle in a water tank. The
formation and dynamics of the generated bubble jets have been recorded by means of a high-speed
camera. The effects of the momentum ¿ux and the separation distance on the two-phase ¿ow have been
investigated. When jets do not interact, they show a conical shape with an opening angle which decreases
from ¿ ¼631 to ¿ ¼121 as the momentum ¿ux is increased from J ¼1 g cm=s2 to J ¼88 g cm=s2. Bubble
velocities in the direction of injection decrease fromvx ¼361 cm=s to vx ¼23 cm=s in the most extreme case,
as the bubble center position reaches the impingement region. Interacting bubble jets form a cross-like shape
as the jets evolve in time. Bubble mean diameter decreases fromd ¼1:7 cm to d ¼1:3 cm, as the momentum
¿ux increases from J ¼8 g cm=s2 to J ¼43 g cm=s2. Coalescence events, occurring mainly near the nozzles
and in the impingement region, are responsible for the widening of the tail in the bubble size distribution.
The global jet behavior and the individual bubble dynamics present several differences in microgravity
compared to previous observations carried out on ground.
We present an experimental study on the bubble-slug flow pattern transition which takes place in two-phase flows in microgravity related conditions. Two different sets of experiments were performed on ground with air/water and air/ethanol mixtures in a minichannel with an internal diameter of 1 mm. We address questions regarding the existence of a critical void fraction for the bubble-slug transition to occur. Experimental data are compared to the drift-flux and Suratman models predictions. We obtain results on the extension of applicability of these models for different boundary conditions. (C) 2013 Elsevier Ltd. All rights reserved.
We present an experimental study on the bubble–slug flow pattern transition which takes place in two-phase flows in microgravity related conditions. Two different sets of experiments were performed on ground with air/water and air/ethanol mixtures in a minichannel with an internal diameter of 1 mm. We address questions regarding the existence of a critical void fraction for the bubble–slug transition to occur. Experimental data are compared to the drift-flux and Suratman models predictions. We obtain results on the extension of applicability of these models for different boundary conditions.
Habtu, N.; Font, J.; Fortuny, A.; Bengoa, C.; Fabregat, A.; Haure, P.; Ayude, A.; Stüber, F. Chemical engineering science Vol. 66, num. 14, p. 3358-3368 DOI: 10.1016/j.ces.2011.01.032 Data de publicació: 2011-07-15 Article en revista
Ayude, A.; Rodríguez, T.; Font, J.; Fortuny, A.; Bengoa, C.; Fabregat, A.; Stüber, F. Chemical engineering science Vol. 62, num. 24, p. 7351-7358 DOI: 10.1016/j.ces.2007.08.045 Data de publicació: 2007-12 Article en revista
Larruy, B.; Ayude, A.; Font, J.; Fortuny, A.; Bengoa, C.; Fabregat, A.; Stüber, F. Chemical engineering science Vol. 62, num. 18-20, p. 5564-5566 DOI: 10.1016/j.ces.2007.01.079 Data de publicació: 2007-09 Article en revista
Guardo, A.; Casanovas, M.; Ramirez, E.; Recasens, F.; Magaña, I.; Martínez, D.; Larrayoz, M. Chemical engineering science Vol. 62, num. 18-20, p. 5054-5061 Data de publicació: 2007-09 Article en revista
In this article, the design and retrofit problem of a supply chain (SC) consisting of several production plants, warehouses and markets, and the associated distribution systems, is considered. The first problem formulation modifies and extends other previously presented models, in order to include several essential characteristics for realistically representing the consequences of design decisions on the SC performance. Then, in order to take into account the effects of the uncertainty in the production scenario, a two-stage stochastic model is constructed. The problem objective, i.e., SC performance, is assessed by taking into account not only the profit over the time horizon, but also the resulting demand satisfaction. This approach can be used to obtain different kinds of solutions, that may be valuable at different levels. On one hand, the SC configurations obtained by means of deterministic mathematical programming can be compared with those determined by different stochastic scenarios representing different approaches to face uncertainty. Additionally, this approach enables to consider and manage the financial risk associated to the different design options, resulting in a set of Pareto optimal solutions that can be used for decision-making.