Ramon Molina Valle

Numerical analysis of natural laminar convection in a radial solar heater

Abstract This paper presents a theoretical analysis of a Solar Radial Air Heater, operating on natural laminar convection in steady state, to predict the thermo-hydrodynamic behavior of the device. Temperature conditions were imposed on boundaries, so as to limit the flow in the laminar regime along the device. The mathematical model (Navier—Stokes and Energy Equations) was analyzed by the Finite Volumes Method in Generalized Coordinates. The solution was obtained in a fixed computational domain independent of the geometrical shape of the physical system. This methodology allows a detailed visualization of the effects of geometric of optimal geometric and operational characteristics for such devices.

Numerical hydrodynamic and thermal analysis of laminar flow in curved elliptic and rectangular ducts

Abstract The complete forms of the Navier-Stokes and energy conservation equations are solved for a steady, fully developed, incompressible laminar flow with constant physical properties in ducts with elliptic or rectangular cross section. The equations are solved using the finite volume method with a boundary fitted coordinate system. The curvature ratio, which is included in the conservation equations, is kept constant. Solutions are obtained for several flow rates (Dean number between 30 and 400) and cross sections (ellipses and rectangles with aspect ratio between 0.7 and 1.4). The axial and secondary velocities and temperature profiles, the heat transfer and pressure drop are analysed. Results are compared with the literature for validation of the numerical approach.

Analysis of the Airflow in a Prototype of a Solar Chimney Dryer

The development of alternative energy sources is increasingly becoming a necessity. In this context, solar energy stands out because it is a renewable and low pollutant source of energy. The solar chimney uses solar energy to generate hot airflow that can be used to dry agricultural products or generate electric power. This paper presents an experimental study of the airflow inside a solar chimney. The tests were performed in a prototype built on the campus of Universidade Federal de Minas Gerais, with appropriate dimensions to dry agricultural products. The values of temperature, velocity, solar radiation, and humidity inside and outside the device were monitored over a nine month period, allowing the characterization of the airflow and the determination of the optical properties of the materials used.

Numerical Study of the Neutral Atmospheric Boundary Layer Over Complex Terrain

We evaluate the Reynolds-averaged Navier–Stokes equations available as commercial computational fluid dynamics code for the simulation of a neutral atmospheric boundary layer and attempt to define a proper numerical simulation procedure. Four turbulence models, including two-equation and Reynolds stress models, were evaluated together with two near-wall models. Mesh and map digitization sensitivity tests were also performed. The simulations were compared to experimental field data from the Askervein Hill in Scotland. The results show that the simulations performed with ANSYS CFX 12.1 on a proper mesh and topological map with a Reynolds stress turbulence model provided the best wind-speed predictions when compared to the experimental results.

ERROR ESTIMATION AND ADAPTIVITY FOR FINITE-VOLUME METHODS ON UNSTRUCTURED TRIANGULAR MESHES: ELLIPTIC HEAT TRANSFER PROBLEMS

In this article, a simple and reliable a posteriori error estimate methodology for the finite-volume method on triangular meshes and an adaptive mesh refinement procedure are presented. The proposed error estimate employs a high-order approximation for the scalar at the triangles faces. The estimate technique does not demand expressive computational efforts and memory storage. The adaptive procedure is based on the equal distribution of the error over all the triangles, allowing for suitable local mesh refinements. The error is measured by an H 1 norm, and its convergence behavior is evaluated using four elliptic problems for which the analytical solutions are known. The error differences using analytical and estimate solutions are compared for those problems, and good performance of the adaptive procedure is verified.

Modelling and analysis of a nine-phase induction motor with third harmonic current injection

Using electric motors with a number of phases greater than three may present some advantages over conventional three phase machines in the following applications: high power levels, electric vehicles and applications that require high levels of reliability. Multiphase machines, meaning designs comprising more than three phases, also allows an increase in torque density from the injection of harmonic currents. It is shown in this paper a comprehensive approach for the derivation of equivalent circuits for steady state operation for both fundamental and third harmonic frequencies for a nine-phase motor with concentrated windings and full pitch. Besides that, simulation of the dynamic model of the machine is done to obtain the expected torque improvement.

A critical analysis of standard methods for characterization of electrical steels: Losses in high speed induction motors

The demand for high speed electrical machines has increased recently, mainly in the electric or hybrid vehicles applications. Speeds as high as 13.000 rpm may be required, demanding new grades of electrical steels with improved magnetic properties. Such magnetic properties are typically characterized using parameters such as B50 and W10/400. However, improvements in these parameters do not necessarily translate into improvements of practical significance. This paper focuses on the performance improvements from newly developed electrical steels for high speed motors. Prototype motors were built for practical validation of the performance of these steels. Practical tests and finite element analysis are used to support the conclusions of this research work.

Characterization of electrical steels for high speed induction motor applications: Going beyond the standards

The objective of the present work is to assess the impact of improvements in standard characterization figures of merit of electrical steels, typically found in manufacturers catalogs (B50 and W10/400), in the performance of high speed electrical motors. From the motor manufacturer standpoint, changing to new materials may represent a complicated and costly procedure. Besides, the motor manufacturer has to deal with process variability and building tolerances that may overcome minor improvements in the electric steel. The electrical steel manufacturer has to deal with numerous process variables and long and expensive development times to come up with new products. Hence, even a small improvement in the B50 and W10/400 figures are considered to be great achievements. In order to verify if such improvements really translate into real gains in electrical motors, a series of prototypes were constructed with newly developed electrical steels. The core losses of these prototypes were determined by the loss segregation method. Test results support the conclusion that the standard steel characterization figures of merit do not carry enough information for steel and motor manufacturers to conclude on the performance of an electrical steel grade. A datasheet of the electrical steel is proposed. Such datasheet carries useful information for the electrical motor designer and should also be used in the steel development process as a new product assessment tool.

Numerical Analysis of the Piston Crown Geometry Influence on the Tumble and Squish in a Single Cylinder Engine

The objective of this paper is to simulate the air flow (cold run) inside a single cylinder research engine for different geometries of the piston crown and investigate the influence of them on the Tumble coefficient and Squish. The study was conducted through the software star-CD, with the module esice (Expert System – Internal Combustion Engine) and simulations of the air flow with the flat piston were carried out at the first time. Once the simulation methodology was created according to its correlation with the experimental results, the geometry of the piston crown is changed and other numerical simulations are performed. Thereby, with the comparison between the obtained results for different geometries, the air flow inside the combustion chamber can be characterized, and the effects of the geometry changing on the Tumble coefficient, Squish and other flow parameters verified.

Stabilizing a photovoltaic plant power output by employing an auxiliary power source

The use of compressed air energy storage (CAES) systems instead of conventional energy storage systems in large scale grid connected photovoltaic (PV) plans has already been proposed and investigated thermo-economically, resulting to very satisfactory outcomes. On the other hand, city gate stations (CGS), in which high pressure natural gas is expanded to much lower presser levels, has been proved to be a very suitable place for producing free electricity by employing turbo-expanders instead of conventional throttling valves. In this work, the feasibility of employing a CGS power output for improving the performance of a grid connected PV plant accompanied with a CAES system and enhancing its power output stability is studied. Comprehensive energy analysis and economic assessment on the proposed configuration is carried out and the results are discussed thoroughly. Finally, the performance of this hybrid configuration is compared with the PV plant and the CGS station while working individually. Internal rate of return (IRR) method as an authentic economic evaluation approach is used for comparing the considered systems economically.