Examinando por Autor "Casado, Cintia"

Mostrando 1 - 9 de 9

Evaluation of new photochemical systems for water disinfection by the integration of particle tracking into kinetic models for microbial inactivation
(Elsevier, 2023) Casado, Cintia; Yunta, Verónica; Marugán, Javier
This work presents the development of a novel methodology for the simulation of photochemical processes for water disinfection using computational fluid dynamics (CFD). A new approach was implemented to calculate and visualise the disinfection performance as the microorganisms move along the photoreactor. Hydrodynamics and microorganism’s statistical trajectories were computed using the discrete phase model, which also provides the distribution of microbial residence times. The distribution of radiation in the reactor was calculated using the discrete ordinate method. The local values of incident radiation were integrated over each statistical trajectory path to get the accumulated dose received for each microbial particle. The coupling in situ of the cumulative radiation dose with the inactivation kinetics allows monitoring of the disinfection process concurrently with the particle tracking. This methodology introduces significant advantages over the traditional estimation of the microorganism inactivation sequentially after calculating the dose histograms estimated from the statistical trajectories. The developed tool enables evaluating the photoreactor efficiency in each reactor position, a useful capability for optimising and scaling up complex geometries. It also allows the easy, intuitive visualisation of microbial inactivation trajectories, improving the understanding of the influence of the reactor features on the disinfection process. Application of this computational approach to two different photoreactor geometries using a virus as a representative target microbe is presented.
Evaluation of the uniformity of UVA LED illumination on flat surfaces: Discrete ordinate method, single axis, and surface scanning radiometry
(Elsevier, 2023) Reddick, Conor; Casado, Cintia; Reynolds, Ken; Stanley, Simon; Pablos, Cristina; Marugán, Javier
Uniform illumination from UVA LED lamps is a crucial design characteristic for a range of industries including photocatalytic applications. In this work, radiometry and the discrete ordinate method (DOM) are used to determine the ideal target surface size and working distance from a UVA LED lamp for highly uniform illumination. Horizontal incident radiation and full surface incident radiation measurements were conducted using a scanning radiometry technique. It is shown that horizontal incident and full surface incident radiation measurements show good agreement for uniformity measurements over a range of working distances, with maximum uniformity (2.6% and 3.6% standard deviation respectively) over the measured range found at 15 mm working distance. DOM simulation results showed good agreement with radiometry for power and incident radiation measurements, whilst indicating a maximum uniformity at 20 mm working distance. These results demonstrate that DOM simulations can be used as a fast, low cost, and reliable indication of surface uniformity, peak surface irradiance, and power measurements in the design of UV lamps for industrial and academic applications.
Mechanistic modelling of wastewater disinfection by the photo-Fenton process at circumneutral pH
(Elsevier, 2020-07-22) Casado, Cintia; Moreno-San Segundo, José; De la Obra, Irene; Esteban García, Belén; Sánchez-Pérez, José Antonio; Marugán, Javier
This work focuses, for the first time, on the mechanistic modelling of wastewater disinfection by the solar photo- Fenton process using controlled solar simulated radiation. At circumneutral pH, iron precipitates forming hydroxides and significantly affecting the optical properties of the water. In this regard, radiation transfer in the reactor has been taken into account. The proposed model considers that the solar inactivation of bacteria follows a serial n-event mechanism with n reversible steps of photonic attacks leading to the bacterial inactivation. Dark Fenton cyclic process of hydroxyl radical formation from hydrogen peroxide is considered to be mediated mainly by precipitated iron species, prevailing at circumneutral pH. Finally, the photo-Fenton process was modelled using a multiple target – multiple hit mechanistic approach that accounts for the synergistic effect between the photonic and the hydroxyl radical attacks to the bacteria. Model predictions successfully reproduce experimental data of solar disinfection, hydrogen peroxide consumption, and photo-Fenton disinfection at circumneutral pH.
Novel procedure for the numerical simulation of solar water disinfection processes in flow reactors
(Elsevier, 2018) García-Gil, Ángela; Casado, Cintia; Pablos, Cristina; Marugán, Javier
A novel procedure for the simulation of solar water disinfection (SODIS) processes in flow reactors is presented. The modeling approach includes the rigorous description of hydrodynamics, radiation transfer, mass transport and bacterial inactivation phenomena within the reactor by means of a computational fluid dynamics (CFD) software. The methodology has been evaluated in a tubular reactor coupled with a compound parabolic collector (CPC). Velocity profiles have been validated versus theoretical fully developed flow, and radiation fields versus both ray tracing and experimental actinometrical measurements. Incorporation of the solar vector calculation significantly improves the model capabilities for prediction of the potential performance of the SODIS process at different geographical coordinates and operation time. A mechanistic kinetic model was used for the description of the bacterial inactivation rate with explicit radiation absorption effects, coupling the radiation field with the mass balances of viable bacterial species. Model predictions successfully reproduce the experimental data of E. coli inactivation under different irradiances of both simulated and natural solar light with a normalized root mean squared logarithmic error (NRMSLE) of 6.65% and 9.72%, respectively. Therefore, this novel methodology is confirmed as a useful tool for the scaling-up of the SODIS process to large volume systems to be installed in remote communities where safe drinking water is not available.
Optimization and parallelization of the discrete ordinate method for radiation transport simulation in OpenFOAM: Hierarchical combination of shared and distributed memory approaches
(Open Research Europe, 2021-01-01) Marugán, J; Moreno-Sansegundo, José Ángel; Casado, Cintia; Concha, David; Sanz, Antonio
This paper describes the reduction in memory and computational time for the simulation of complex radiation transport problems with the discrete ordinate method (DOM) model in the open-source computational fluid dynamics platform OpenFOAM. Finite volume models require storage of vector variables in each spatial cell; DOM introduces two additional discretizations, in direction and wavelength, making memory a limiting factor. Using specific classes for radiation sources data, changing the store of fluxes and other minor changes allowed a reduction of 75% in memory requirements. Besides, a hierarchical parallelization was developed, where each node of the standard parallelization uses several computing threads, allowing higher speed and scalability of the problem. This architecture, combined with optimization of some parts of the code, allowed a global speedup of x15. This relevant reduction in time and memory of radiation transport opens a new horizon of applications previously unaffordable.
Photocatalytic NOx removal: Rigorous kinetic modelling and ISO standard reactor
(Catalysis Today, 2019) Muñoz, Vanesa; Casado, Cintia; Suárez, Silvia; Sánchez, Benigno; Marugán Aguado, Angel Javier
An air purification reactor working under the standard ISO 22197-1 is studied and used for the determination of the intrinsic kinetic parameters of the NOx photocatalytic removal. A new mechanistic kinetic model considering explicitly the radiation step is proposed. The derived reaction rate expressions for NO and NO2 include the dependence on the concentration of NO, NO2 and the local superficial rate of photon absorption. The air purification reactor was modelled using a numerical simulation methodology to validate homogeneity of the light distribution reaching the catalyst surface and go deep in the knowledge of fluid dynamic behaviour. Based on these results, general guidelines of the reactor behaviour working under the ISO 22197-1 standard can be stablished, being the first time that this reactor is modelled with a global predictive approach. Radiation intensity over the catalyst surface was confirmed to reach the specified value of 10 ± 0.5 W m−2. Plug flow can be applied in the studied reactor with an axial dispersion module lower than 0.001. However, the diffusion of chemical species in the reactor was also studied, as well as the impact of mass transfer phenomena on the accuracy of the calculated kinetic parameters. A comprehensive simulation model of the ISO reactor, including fluid dynamics, radiation, photochemical reaction and mass transfer was developed. The simulation results confirm that the kinetic parameters obtained without considering mass transfer limitation fail to reproduce the experimental data, whereas a global error lower than a 17% was achieved including the diffusion of the species in the reactor. The proposed methodology, experimentally validated, could be successfully applied to the pre-diction of the performance of different type of photocatalytic reactors or even open systems for NOx pollutants.
Removal of diclofenac by UV-B and UV-C light-emitting diodes (LEDs) driven advanced oxidation processes (AOPs): Wavelength dependence, kinetic modelling and energy consumption
(Elsevier, 2023) Pizzichetti, Raffaella; Reynolds, Ken; Pablos, Cristina; Casado, Cintia; Moore, Eric; Stanley, Simon; Marugán, Javier
In this study, the degradation of diclofenac (DCF), a frequently detected non-steroidal pharmaceutical, was evaluated by using UV-B and UV-C (265, 285, and 310 nm) light-emitting diodes (LEDs) alone and in combination with hydrogen peroxide (UV/H2O2) and free chlorine (UV/FC). The degradation of DCF followed a pseudo first-order kinetic, and their trend reflected the pattern of the molar absorption coefficients of the DCF and the oxidants. A positive synergistic factor was found for the UV-LED driven advanced oxidation processes in almost all cases, but despite the higher degradation rates, the overall electricity demand is similar to UV alone due to the oxidants’ energy cost. The rigorous kinetic degradation mechanisms at different wavelengths were proposed for the two processes, UV/H2O2 and UV/FC, where the predicted values were respectively kHO = 9.12 ⋅ 109 M− 1 s − 1 and kCl = 1.30 ⋅ 1010 M− 1 s − 1 . No significant synergy (p > 0.05) was found for the dual-wavelength system (265 + 285 nm), and the time-based constants in all cases changed linearly with lamp intensity. Finally, dissolved organic carbon and phytotoxicity analysis revealed low mineralisation (around 20–30%) associated with the formation of stable dimers and a decrease in toxicity towards tomato and radish seeds. In the main, this work shows the great potential of implementing wavelength-specific LEDs in water treatments and effectively designing the reactor playing with adjustable intensities and kinetic degradation rates.
Use of Kahoot! to keep students’ motivation during online classes in the lockdown period caused by Covid 19
(Elsevier, 2021) Martín-Sómer, Miguel; Moreira, Judite; Casado, Cintia
COVID 19 lockdown forced a general move of teaching activities from their on-site mode to remote producing different negative consequences for students. In this work, the use of Kahoot! platform was studied to keep students’ interest during online teaching. For this, Kahoot! games were carried out for the different topics of a university subject. The data analysis revealed that a high participation implies an improvement in the final marks. Additionally, questions response time was also extracted serving as a reference for remote exams. On the other hand, two surveys were carried out in which the students showed that the transfer from face-to-face to remote teaching had produced a general decrease in interest that can be mitigated by performing Kahoot! games.
Utilising interactive applications as educational tools in higher education: Perspectives from teachers and students, and an analysis of academic outcomes
(Elsevier, 2023) Martín-Sómer, Miguel; Casado, Cintia; Gómez-Pozuelo, Gema
Our students belong to a highly digitised generation with easy and rapid access to information. They are dependent on technology and tend to become bored quickly. There is an ongoing debate regarding the need to reconsider our teaching methods in order to capture the attention of our students. This study surveyed both students and teachers on the subject of online teaching and its impact on university education. Additionally, it explored issues related to integrating interactive applications in education. These applications are considered essential tools in combating student boredom and disinterest. They also enable teachers to receive valuable feedback, which was highlighted as critically important by educators in the survey. In this context, we conducted a study within a chemical engineering program at a Spanish university. We examined the use of four different interactive applications (Kahoot!, Wooclap, Classflow, Moodle) and compared the results with those from previous years when only one of these applications was employed. This study aimed to determine how using multiple applications led to increased student participation, driven by avoiding monotony, resulting in improved academic performance.