Experimental investigation on synthesis, characterization, stability, thermo-physical properties and rheological behavior of MWCNTs-kapok seed oil based nanofluid

Several researchers devoted their efforts for the thermal conductivity enhancement of Carbon Nanotubes (CNTs) based nanofluids as CNTs have excellent thermal properties. However, limited research is reported on the detailed thermo-physical properties of CNTs and oil based nanofluids. In this work, the one-step method synthesis of a new MWCNTs-Kapok seed oil based nanofluid at constant nanoparticle concentration (0.1 wt./wt.) is reported. The nanofluid is characterized by FESEM, FTIR, visual stability analysis and thermophysical properties are experimentally measured. The viscosity found in the range of (0.049–10.101¿Pa·s), the thermal conductivity of (0.165–0.207¿W/m·K) and enhancement of thermal conductivity (6.1538%) were observed. Moreover, the viscosity decreases, and thermal conductivity increases with an increase in temperature. The experimentally obtained data are found in agreement with existing models and modified correlations. The rheological behavior showed that nanofluid is non-Newtonian in nature and exhibiting shear thinning or pseudo plastic behavior.Preprin

Numerical study of the fluid – structure interaction in the diffuser passage of a centrifugal pump

Reliable design of turbomachinery is a complex task. In order to gain overall efficiency in the machine performance, designers may have to reduce the gap between the impeller and the diffuser, forcing them to be as closely spaced as possible. In these situations, there may be a strong interaction between them that influences both the aerodynamics and the structural performance of blades and vanes. This phenomenon is called rotor-stator interaction (RSI), and it has a strong influence on the machine behavior. These interactions can have a significant impact on the vibrational and acoustical characteristics of the machine [1-2]. Sometimes, this interaction has led to blade or vane failure [3]. Unsteadiness and turbulence play a fundamental role in RSI [4-5], and the use of computational fluid dynamics (CFD) is becoming a usual requirement in turbomachinery design due to the difficulties and elevated cost of the experimentation required to identify RSI phenomena. Nowadays, a CFD analysis based on Reynolds–averaged Navier–Stokes equations (RANS) and a coupled eddy viscosity turbulence model (EVM) is commonly applied in turbomachinery design. Therefore, the choice of an appropriate turbulence model and the boundary layer treatment is far from trivial, and a suitable turbulence modeling plays an important role for successful CFD results. In this work, an entire stage of a diffuser pump was modeled by means of a commercial CFD code in order to study the pressure fluctuations due to the interaction between the impeller and the diffuser of the pump. The obtained numerical results were compared against the experimental results of Tsukamoto et al., [6]. Full RANS equations coupled with several EVM were solved for a diffuser pump stage in order to establish the most accurate modeling strategy for a diffuser pump. Boundary layer sensitivity tests were performed, and numerical discretization influence on results was also tested and established. Frequencies of the pressure fluctuations in the diffuser passage are also obtained with several EVM and compared against experimental results

Thermal performance of ventilated double skin façades with Venetian blinds

Peer ReviewedPostprint (published version

Efectos de la obstrucción del flujo en una turbina

El rendimiento de una turbina, está sujeto al comportamiento del flujo a través de las directrices del distribuidor y de los álabes del rodete. Para evitar que el flujo de agua procedente del embalse introduzca cuerpos sólidos en el interior de la turbina, las centrales disponen de elementos de contención de estos cuerpos como rejas y mallas. Cuando alguno de estos elementos falla, es posible que se produzca una obstrucción en los canales del distribuidor o en los canales del rodete. Esta obstrucción produce una variación del flujo en la turbina que hace disminuir su rendimiento, así como un aumento de los niveles vibratorios del sistema. En este trabajo se compara mediante Dinámica de Fluidos Computacional (CFD), el comportamiento del flujo en una turbina Francis trabajando en condiciones normales de operación y cuando se produce una obstrucción en su interior. Se presentan las fluctuaciones de presión en el distribuidor y se determinarán las frecuencias características del fenómeno de interacción rotor –estator para ambos casos.Peer ReviewedPostprint (published version

Numerical study of the fluid-structure interaction in the diffuser passage of a centrifugal pump

Reliable design of turbomachinery is a complex task. In order to gain overall efficiency in the machine performance, designers may have to reduce the gap between the impeller and the diffuser, forcing them to be as closely spaced as possible. In these situations, there may be a strong interaction between them that influences both the aerodynamics and the structural performance of blades and vanes. This phenomenon is called rotor-stator interaction (RSI), and it has a strong influence on the machine behavior. These interactions can have a significant impact on the vibrational and acoustical characteristics of the machine. Sometimes, this interaction has led to blade or vane failure. Unsteadiness and turbulence play a fundamental role in RSI, and the use of computational fluid dynamics (CFD) is becoming a usual requirement in turbomachinery design due to the difficulties and elevated cost of the experimentation required to identify RSI phenomena. Nowadays, a CFD analysis based on Reynolds–averaged Navier–Stokes equations (RANS) and a coupled eddy viscosity turbulence model (EVM) is commonly applied in turbomachinery design. Therefore, the choice of an appropriate turbulence model and the boundary layer treatment is far from trivial, and a suitable turbulence modeling plays an important role for successful CFD results.In this work, an entire stage of a diffuser pump was modeled by means of a commercial CFD code in order to study the pressure fluctuations due to the interaction between the impeller and the diffuser of the pump. The obtained numerical results were compared against the experimental results of Tsukamoto et al.,. Full RANS equations coupled with several EVM were solved for a diffuser pump stage in order to establish the most accurate modeling strategy for a diffuser pump. Boundary layer sensitivity tests were performed, and numerical discretization influence on results was also tested and established. Frequencies of the pressure fluctuations in the diffuser passage are also obtained with several EVM and compared against experimental results.Peer ReviewedPostprint (published version

Estudio mediante CFD de la interacción rotor-estator en una bomba centrífuga con difusor

Una bomba centrífuga con difusor, trabajando en diseño óptimo es estudiada por modelado numérico (CFD) con el fin de identificar y estudiar la posible amplificación de fluctuaciones de presión dentro de la máquina (RSI). Se usan resultados numéricos previos, obtenidos en álabes aislados y cascadas de álabes fijos y móviles con el objeto de validar/calibrar los modelos para la turbulencia a utilizar, comparando con los de bases de datos experimentales. Este trabajo previo luego se aplica al estudio de la bomba con difusor, que servirá para futuros estudios de turbomáquinas trabaj ando bajo condiciones fuera de diseño en donde puede aparecer el fenómeno de cavitación.Postprint (published version

Wall-to-fluid heat transfer in a catalytic reactor at supercritical conditions

Computational fluid dynamics (CFD) studies can be used for improving the understanding of fluid flow and heat transfer in packed bed systems. The objective of this work was to study the heat effects in packed bed reactor under supercritical conditions using CFD comparing the simulations with empirical correlations. Simulations were done for a geometrical model of packed bed of cylindrical catalysts at high pressure supercritical conditions. The packed bed tube was heat on the walls and fluid mixture of carbon dioxide (CO2), methanol (CH3OH) and triolein (C57H104O6), is flown into the packed bed at 250 bar. The flow field is described by three-dimensional (3D) Navier-Stokes equations coupled with the energy and species governing equations, which are solved by a finite volume code. The heat transfer coefficient is obtained in terms of wall Nusselt number (Nuw) from simulation data and compared against empirical models for different flow rates.Postprint (published version

CFD study of the effects of ingested bodies on the RSI of hydraulic turbines

The ingestion of large bodies in hydraulic turbines can produce blockage in the runner and/or the distributor, modifying the amplitude and uniformity of pressure pulsations and generating large unbalanced forces. These unwanted effects can lead to reduced efficiency and increased vibration levels, which can produce significant mechanical damage. In this work, we present a characterization of the effects of flow blockages due to ingested bodies on the rotor-stator interaction (RSI) of hydraulic turbines by means of computational fluid dynamics (CFD). For this, a reduced-scale model of a pump turbine was implemented using Ansys® CFX v16.2, and numerical simulations were run for normal operation and blockage operation. Studied blockages included rotor and distributor blockages. Pressure pulsations in rotor and distributor were recorded in order to characterize the effect of the blockage on the RSI of the machine.Postprint (published version

Boundary layer effects on the vortex shedding in a Donaldsontype hydrofoil

Fluid - Structure Interaction (FSI) phenomena is becoming a relevant study field for the design or revamping of hydropower plants. The generalized trend of increasing flow rates and reducing rotor blades/stay vanes thickness in order to improve the efficiency of the machine together with a major push from plant owners/operators for production flexibility (partial load operation is more common nowadays) make the FSI between the vortex shedding phenomenon and the vanes/blades of the machine an area of interest. From a design point of view, the machine structure has to resist all the hydrodynamic forces generated and maintain tension stresses under the fatigue limit to ensure a machine lifetime of several decades. To accomplish that goal, designers have to assure there is no presence of strong coupling phenomena (lock-in) between the vortex shedding frequency and the eigenfrequencies of the structure. As the vortex street is directly related to the state of the boundary layer along the hydrofoil, in this paper the effect of the boundary layer on the vortex shedding in a Donaldson-type hydrofoil is studied using Computational Fluid Dynamics (CFD). The development of the boundary layer along the Donaldson trailing edge hydrofoil chord is presented under lock-off conditions. The results are validated against previously obtained experimental results. Since the Donaldson trailing edge is non-symmetric, the boundary layer velocity profiles are reported for the suction and pressure side of the hydrofoil. In addition, the effect of the Donaldson trailing edge on laminar-to-turbulent transition on both sides of the hydrofoil is studied.Postprint (published version

Memorias del paisaje nilótico: prospección, simulación y recreación de la inundación estacional en la zona del dique de Mimbal (Minia, Egipto)

Se verifican y documentan sobre el terreno los datos sobre los sistemas de control hidráulico de inundaciones registrados en la zona del rio Nilo. Este trabajo de campo ira acompañado de un estudio sedimentológico de la zona de estudio, la cual comprende las localidades de Marzouk, Mimbal, y Matay (Minia, Egipto). A partir de estos datos arqueológicos y sedimentológicos se crea un sistema de simulación y computación gráfica de alta resolución que refleje la gestión mediante cubetas y canales de irrigación, así como la irrigación perenne del Valle Medio del Nilo. Por otro lado, se pretende recoger y registrar la memoria oral sobre la inundación en el Valle Medio del Nilo en general y en la zona de estudio en particular y el impacto socio-cultural de su desaparición. A partir de los datos de la prospección sobre el terreno, los estudios sedimentológicos, el registro sobre el terreno de la memoria oral, la simulación y la visualización gráfica se quieren analizar los cambios paisajísticos inducidos por las transformaciones del siglo XIX y XX y los diversos procesos de sedimentación, así como sus efectos sobre el propio proceso de inundación y el entorno habitado de las riberas del río