Joaquin Fernandez-Francos

The effect of the operating point on the pressure fluctuations at the blade passage frequency in the volute of a centrifugal pump

An experimental investigation is presented which analyzes the unsteady pressure distribution existing in the volute of a conventional centrifugal pump with a nondimensional specific speed of 0.48, for flow-rates from 0% to 160% of the best-efficiency point. For that purpose, pressure signals were obtained at 36 different locations along the volute casing by means of fast-response pressure transducers. Particular attention was paid to the pressure fluctuations at the blade passage frequency, regarding both amplitude and phase delay relative to the motion of the blades. Also, the experimental data obtained was used to adjust the parameters of a simple acoustic model for the volute of the pump

Numerical Prediction of the Aerodynamic Tonal Noise in a Centrifugal Fan

In this work, a numerical study about the aerodynamic tonal noise generation in an industrial centrifugal fan with backward curved blades has been carried out. A three-dimensional numerical simulation of the complete unsteady flow on the whole impeller-volute configuration has been performed. Special attention has been focused on the impeller-volute interaction phenomena, analysing the influence of the distance between the impeller and the volute tongue. The numerical results have been contrasted using previous experimental investigations carried out in the same machine.Copyright

Computational Study of Aqueous Humor Dynamics Assessing the Vault and the Pupil Diameter in Two Posterior-Chamber Phakic Lenses.

PURPOSE To compare the behavior of aqueous humor (AH) and analyze flow differences by comparing the volume and velocity of the flow after two different models of implantable collamer lens (ICL) placement. METHODS Computational fluid dynamics with numerical simulation using Ansys Fluent software was performed to compare the AH flow through a peripheral iridotomy (PI), which is typically performed after implantation of a V4b lens to the central hole of a V4c lens. The volume and flow rate in 24 scenarios were compared according to the type of lens, pupil diameter (PD) (3.5 or 5.5 mm), the vault (100, 350, and 800 μm) and the PI (single or double, 180 or 360 μm). RESULTS With a standard vault (350 μm) and a PD of 3.5 mm, the volume of AH that flows from the posterior to the anterior chamber through the PI (V4b lens: 73.4% in 360 μm and 17.3% in 180 μm) and for the central hole (V4c lens: 75.7%) is larger than in the case of a PD of 5.5 mm (13.9%, 0.91%, and 15.3% respectively). When the vault is low (100; PD 3.5 mm), the volume of AH that reaches the central hole of the V4c lens is diminished (52.0%), being 5.1% if the pupil is enlarged. CONCLUSIONS AH flow varies depending on the type of ICL implanted, whether it is implanted with an iridotomy or a central hole on the lens, the PD, and the vault.

A proposal of a modular hydroKinetic smart grid

A hydrokinetic smart grid (KSG) concept powered by modules of hydrokinetic microturbines arranged in rows is proposed in this work. A complete description of each module: mechanical design, hydropower characteristics, power electronics and control strategies have been included. A complete dynamic simulation of an example of a KSG has been performed. It considers microturbine modules, power loads, energy storage modules and a grid tie inverter that interface with the mains using a single connection. Additionally, the control and power stages of a hydrokinetic microturbine has been validated. The satisfactory technical results obtained in addition with the acceptable results of an investment analysis, encourage future implementations of KSGs.

Design and feasibility study of a microgeneration system to obtain renewable energy from tidal currents

Tidal energy to obtain electrical energy is yet an unexploited renewable energy. Existing generator designs and prototypes are not feasible due to the high investment conditioned by their high rated powers and off-shore locations. In addition, these prototypes are not readily available. This investigation presents a design of a microgeneration system with vertical axis microturbines. The design of the microturbines utilizes off-the-shelf electronic components, thus reducing the initial investment. The nominal data for selection of power electronic components and the total energy that can be obtained in a year are calculated. The investigation also studies the feasibility of an 80 kW microgeneration system to be applied in Spain, taking advantage of the actual electricity prices. The feasibility study quantifies the influence of the parameters: initial investment, tidal current speed, operation hours, turbine efficiency, price of electricity, and number of microturbines obtaining the limiting values of the...

A Study on the Unstable Coupling Between Pumps and Hydraulic Circuits With Entrapped Gas Pockets

A theoretical and experimental study has been conducted on the mass oscillation instability in hydraulic systems with entrapped gas pockets and pumps with positive slope in the head curve. The theoretical study was composed of an analysis of the critical conditions for the instability to develop, followed by the numerical resolution of the fundamental equations that govern the phenomenon, assuming unsteady one-dimensional flow, in order to simulate the limit cycle oscillations of the unstable system. Additionally a series of laboratory tests was conducted on a conventional centrifugal pump, with variation of the initial volume of an entrapped air pocket in the circuit. As expected from the predictions of the theoretical model, instability was found to developed with pressure amplitude oscillations and frequency dependent on the amount of entrapped air.Copyright