23 research outputs found
Effect of doors opening in refrigerated cabinets: phenomenological study of the thermodynamic behavior and air flow dynamics
During last years, supermarkets have increased the demand for closed refrigerated
display cabinets due to new regulations and trends on energy and sustainability. However,
the performance of this type of refrigerated display cabinets is not completely known, being
of utmost importance how the airflow distributions could affect over the temperature distributions
inside the cabinet. Consequently, this work presents a numerical evaluation of the
performance of closed display cabinets focusing on the effect of the sliding doors opening
process. The set of computational fluid dynamics (CFD) simulations served to validate the use
of immersed solid approach in order to accurately analyze and evaluate transient behavior of
the turbulent air flow distributions and temperature evolutions inside the cabinet and over
the products, and characterizing the air curtain disruptions and the warm air entrainment
during the opening process of the cabinet sliding doors (i.e. from closed doors, through doors
opening process and to doors totally open)
On the development and application of intrusive sensors for two-phase flows characterization in complez environments
Intrusive sensors are widely employed in numerous industrial applications to determine the phase fraction in gas-liquid two-phase flows. Such applications include those in the chemical, nuclear, and oil industries. This study aims to investigate the use of three distinct intrusive sensor topologies, specifically intended for underwater applications, wherein the detailed characterization of the disperse phase is the primary objective. Examples of such applications include aeration diffusers in wastewater treatment plants (WWTPs) and fish farming facilities.Peer Reviewe
Transcription of Nanofibrous Cerium Phosphate Using a pH-Sensitive Lipodipeptide Hydrogel Template
A novel and simple transcription strategy has been designed for the template-synthesis
of CePO4 xH2O nanofibers having an improved nanofibrous morphology using a pH-sensitive
nanofibrous hydrogel (glycine-alanine lipodipeptide) as structure-directing scaffold. The phosphorylated
hydrogel was employed as a template to direct the mineralization of high aspect ratio nanofibrous
cerium phosphate, which in-situ formed by diffusion of aqueous CeCl3 and subsequent drying (60 C)
and annealing treatments (250, 600 and 900 C). Dried xerogels and annealed CePO4 powders were
characterized by conventional thermal and thermogravimetric analysis (DTA/TG), and Wide-Angle
X-ray powder diffraction (WAXD) and X-ray powder diffraction (XRD) techniques. A molecular
packing model for the formation of the fibrous xerogel template was proposed, in accordance with
results from Fourier-Transformed Infrarred (FTIR) and WAXD measurements. The morphology,
crystalline structure and composition of CePO4 nanofibers were characterized by electron microscopy
techniques (Field-Emission Scanning Electron Microscopy (FE-SEM), Transmission Electron
Microscopy/High-Resolution Transmission Electron Microscopy (TEM/HRTEM), and Scanning
Transmission Electron Microscopy working in High Angle Annular Dark-Field (STEM-HAADF))
with associated X-ray energy-dispersive detector (EDS) and Scanning Transmission Electron
Microscopy-Electron Energy Loss (STEM-EELS) spectroscopies. Noteworthy, this templating
approach successfully led to the formation of CePO4 H2O nanofibrous bundles of rather co-aligned
and elongated nanofibers (10–20 nm thick and up to ca. 1 m long). The formed nanofibers
consisted of hexagonal (P6222) CePO4 nanocrystals (at 60 and 250 C), with a better-grown and
more homogeneous fibrous morphology with respect to a reference CePO4 prepared under similar
(non-templated) conditions, and transformed into nanofibrous monoclinic monazite (P21/n) around
600 C. The nanofibrous morphology was highly preserved after annealing at 900 C under N2,
although collapsed under air conditions. The nanofibrous CePO4 (as-prepared hexagonal and
900 C-annealed monoclinic) exhibited an enhanced UV photo-luminescent emission with respect to
non-fibrous homologues
A comprehensive hydrodynamic analysis of a full-scale oxidation ditch using Population Balance Modelling in CFD simulation
This work exhibits the importance of the experimental validation when full-scale computational fluid dynamics (CFD) models are developed to provide a detailed analysis of the spatial variations in 3D of the fluid flow inside aerated tanks. Single-phase and two-phase CFD models were performed to study the fluid behaviour carefully by means of the velocity profiles and the aeration pattern in a full-scale oxidation ditch. Air hold-up, bubble size distribution and interfacial area density were calculated by polydisperse models where Population Balance Model (PBM) was governed by break-up and coalescence; the free-surface approach allowed the CFD model to describe the three-dimensional effect of bubbly plumes in large scales in detail. Tracer tests were carried out to obtain the flow pattern and the hydraulic distribution of the flow into two wastewater treatment lanes in order to define the boundary conditions for the model correctly. Despite the difficulty of performing velocity measurements of the fluid in 3D, with and without air bubbles, these provided essential information to validate the CFD model. From this analysis, several simulations were performed to improve the hydrodynamics and the operation of the process by relocating the propellers
Characterization of the gas-liquid interfacial waves in vertical upward co-current annular flows
[EN] For more than fifty years, hundreds of research works have focused on the study of annular flow because of its huge importance in many industrial processes, for instance, chemical, petroleum, etc., being of particular interest in nuclear industry. Specifically, interfacial waves play a vital role in the mass, momentum and energy transference processes between gas and liquid phases. This paper describes the new experimental measurements of vertical upward co-current two-phase gas-liquid flow carried out in a tube with an inner diameter of 44 mm. The liquid film thickness and the major characteristics of the interfacial waves have been measured using a non-intrusive instrument, a conductance probe. The physical phenomenon in which this device is based is the change in the electrical conductivity between air and water, i.e., the electrical signal collected in the sensor receiver depends on the thickness of the liquid film layer. The experimental measurements range from 2000 to 3500 l/min for the gas volumetric flow rate, and from 4 to 10 l/min for the liquid volumetric flow rate. Correlation of the experimental measurements of liquid film thickness and the major properties of the interfacial waves have been analyzed using non-dimensional numbers. An important part of the document focuses on the comparison of the experimental data and the fitting correlations against several of the most widely used expressions. Throughout this paper, in addition to present all the available correlations, the existing scattering found when comparing against other expressions have been also confirmed, underlining the existence of gaps of knowledge even today. Emphasize that the proposed correlations are the ones that better fit the data of all experimental series carried out under the present study for the analyzed variables, with almost all the experimental points covered by the +/- 10% error bands of the new correlations.The authors are indebted to the plan of I+D support of the EXMOTRANSIN project ENE2016-79489-C2-1-P.Cuadros-Orón, JL.; Rivera-Durán, Y.; Berna, C.; Escrivá, A.; Muñoz-Cobo, JL.; Monrós-Andreu, G.; Chiva, S. (2019). Characterization of the gas-liquid interfacial waves in vertical upward co-current annular flows. Nuclear Engineering and Design. 346:112-130. https://doi.org/10.1016/j.nucengdes.2019.03.008S11213034
Water temperature effect on upward air-water flow in a vertical pipe: Local measurements database using four-sensor conductivity probes and LDA
Experimental work was carried out to study the effects of temperature variation in bubbly, bubbly
to slug transition. Experiments were carried out in an upward air-water flow configuration. Four sensor
conductivity probes and LDA techniques was used together for the measurement of bubble parameters. The
aim of this paper is to provide a bubble parameter experimental database using four-sensor conductivity probes
and LDA technique for upward air-water flow at different temperatures and also show transition effect in
different temperatures under the boiling point
Multi-needle capacitance probe for non-conductive two-phase flows
Despite its variable degree of application, intrusive instrumentation is the most accurate way to obtain local information in a two-phase flow system, especially local interfacial velocity and local interfacial area parameters. In this way, multi-needle probes, based on conductivity or optical principles, have been extensively used in the past few decades by many researchers in two-phase flow investigations. Moreover, the signal processing methods used to obtain the time-averaged two-phase flow parameters in this type of sensor have been thoroughly discussed and validated by many experiments.
The objective of the present study is to develop a miniaturized multi-needle probe, based on capacitance measurements applicable to a wide range of non-conductive two-phase flows and, thus, to extend the applicability of multi-needle sensor whilst also maintaining a signal processing methodology provided in the literature for conductivity probes.
Results from the experiments performed assess the applicability of the proposed sensor measurement principle and signal processing method for the bubbly flow regime. These results also provide an insight into the sensor application for more complex two-phase flow regimes
Diseño y desarrollo de un mueble frigorífico comercial con funcionamiento autónomo durante ciertos periodos de tiempo
El trabajo presentado en este artículo se basa en integrar en el interior de un
mueble frigorífico comercial un fluido caloportador con cambio de fase que permite un
funcionamiento totalmente autónomo durante un periodo de tiempo, sin necesidad de
conexión eléctrica para mantener la temperatura del alimento perecedero. En este artículo
se presenta una nueva solución para optimizar el rendimiento de los muebles frigoríficos
destinados al almacenamiento de producto perecedero en un supermercado a la vez que
se abre una nueva posibilidad de añadir servicios nuevos que hasta la fecha el mercado
desconoce. Este estudio se ha llevado a cabo a partir de la acumulación térmica de un fluido
compuesto por muestras PCM (Phase Change Material) y de la optimización de todos
los mecanismos de transmisión de calor que coexisten durante el funcionamiento de un
mueble.
El almacenamiento de calor en un momento determinado para disponerlo más tarde se
presenta como una solución sin precedentes. En este sentido, nace una manera nueva de
producir frío que nos va a permitir recargar este acumulador térmico en horario de tarificación
eléctrica más bajo y proporcionar un servicio autónomo y continuado para mantener
las condiciones que necesita el almacenamiento del producto perecedero durante el horario
de mejor coste energético y mitigando las variaciones de temperatura que pueda sufrir
el producto perecedero
An Eulerian-Lagrangian open source solver for bubbly flow in vertical pipes
Air-water two-phase flow is present in natural and industrial processes of different nature as nuclear
reactors. An accurate local prediction of the boiling flow could support safety and operation
analyses of nuclear reactors. A new Eulerian-Lagrangian approach is investigated in this contribution.
A new solver has been developed and implemented in the framework of the open source
package OpenFOAM
R
and based on the PIMPLE algorithm coupled with the Lagrangian equation
of motion has been implemented for computing incompressible bubbly flows. Each bubble is
divided in equivolumetric volumes and tracked into the Eulerian mesh for an appropriate assignment
of the effect of the bubble in the cell without resolving the interface. The coupling between
phases is done considering in the momentum equation the interfacial forces and bubble induced
contribution along the bubble path during an Eulerian time step. The bouncing of the bubbles between
themselves and the wall is modeled with a dynamic soft sphere model. The computational
results obtained for different flow conditions are validated with the recently released experimental
data on upward pipe flow. The test section used is a 52 mm pipe of 5500 mm of length maintained
under adiabatic conditions with air and water circulating fluids working with inlet velocity
ranges of 0-2 m/s and 0-0.3 m/s for the continuous and dispersed phase respectively. Averaged
results of radial distribution for void fraction, chord length, turbulence kinetic energy, dispersed
and continuous velocity profiles show a good agreement among different flow conditions.Peña Monferrer, C.; Muñoz-Cobo González, JL.; Monrós Andreu, G.; Martinez Cuenca, R.; Chiva Vicent, S. (2014). An Eulerian-Lagrangian open source solver for bubbly flow in vertical pipes. Sociedad Nuclear Española. http://hdl.handle.net/10251/71943
A CFD-DEM solver to model bubbly flow. Part I: Model development and assessment in upward vertical pipes
[EN] In the computational modeling of two-phase flow, many uncertainties are usually faced in simulations and validations with experiments. This has traditionally made it difficult to provide a general method to predict the two-phase flow characteristics for any geometry and condition, even for bubbly flow regimes. Thus, we focus our research on studying in depth the bubbly flow modeling and validation from a critical point of view. The conditions are intentionally limited to scenarios where coalescence and breakup can be neglected, to concentrate on the study of bubble dynamics and its interaction with the main fluid. This study required the development of a solver for bubbly flow with higher resolution level than TFM and a new methodology to obtain the data from the simulation. Part I shows the development of a solver based on the CFD-DEM formulation. The motion of each bubble is computed individually with this solver and aspects as inhomogeneity, nonlinearity of the interfacial forces, bubble-wall interactions and turbulence effects in interfacial forces are taken into account. To develop the solver, several features that are not usually required for traditional CFD-DEM simulations but are relevant for bubbly flow in pipes, have been included. Models for the assignment of void fraction into the grid, seeding of bubbles at the inlet, pressure change influence on the bubble size and turbulence effects on both phases have been assessed and compared with experiments for an upward vertical pipe scenario. Finally, the bubble path for bubbles of different size have been investigated and the interfacial forces analyzed. (C) 2017 Elsevier Ltd. All rights reserved.The authors sincerely thank the ''Plan Nacional de I + D+ i" for funding the project MODEXFLAT ENE2013-48565-C2-1-P and ENE2013-48565-C2-2-P.Peña-Monferrer, C.; Monrós Andreu, G.; Chiva Vicent, S.; Martinez-Cuenca, R.; Muñoz-Cobo, JL. (2018). A CFD-DEM solver to model bubbly flow. Part I: Model development and
assessment in upward vertical pipes. Chemical Engineering Science. 176:524-545. https://doi.org/10.1016/j.ces.2017.11.005S52454517