ABSTRACT The performances of the Standard κ-ε, RNG, Realizable, κ-ω and RSM turbulence models to describe the behavior of the flow in agitated tank reactors were evaluated. Because most of these tanks have complex geometries, structured meshing schemes are not a practical alternative in engineering. Two particular unstructured meshing schemes composed of either Cartesian Cut-Cell (CC) or Tetrahedral elements were tested in domains larger than 3 million cells. In this work, the blade thickness, which is usually disregarded, was accounted for. The performance of the turbulence models was validated by PIV measurements. A strong dependence on the grid size and the power number was found, with CC grids having good agreement with grids > 3.6 Million. The pumping number was independent of the cell number and the values agree with experimental data. The Realizable model resolved with a tetrahedral grid presented the overall best performance.

The present work shows some applications of the software SOLEEC, which is used to get the best geometric designing features for Parabolic Trough Collectors (PTC) based on the receiver tube external diameter. Users can choose different manufacturing materials among the most used for these collectors and then make a thermal evaluation for a PTC design. Thermal evaluation is based on solar radiation for a specific place on Earth computed by Hottel's model or providing solar radiation measured data, the latitude and longitude of the place in question. Results of goemetrical features such as aperture, focal distance and colector's length, as well as thermal caracteristics such as heat gain, heat lost, mass flow rate, reciever and glazing tube temperatures and thermal and optical efficiences are presented in a friendly interface of the software. An studio was carried out for Monterrey and the versatility of the software was proved.

En el presente trabajo se muestran las aplicaciones del programa SOLEEC el cual proporciona las características geométricas de diseño para Concentradores Solares de Canal Parabólico (PTC) basados en el diámetro del tubo absorbedor. Se puede elegir entre diferentes materiales que se utilizan en la construcción de este tipo de concentradores y realizar combinaciones entre ellos. La evaluación térmica se basa en la irradiación solar para un lugar específico utilizando el modelo ideal de Hottel o bien introduciendo los datos de irradiación solar, latitud y longitud del lugar en cuestión. Los resultados que se obtienen son datos geométricos del concentrador como, apertura, distancia focal y longitud del concentrador, características térmicas como flujo de calor útil, pérdidas hacia el ambiente, flujo másico, temperaturas de los tubos absorbedor y transparente, eficiencia térmica y óptica. Se realizó un estudio para la Ciudad de Monterrey demostrando la versatilidad del software diseñado.

Laminar mixed convection over a backward-facing step is studied and presented in this work. A finite volume discretization technique is used to solve the momentum and energy equations. The SIMPLE algorithm is used to link the pressure distribution and velocity field inside the computational domain. The buoyancy forces affecting the velocity and temperature distributions are simulated for constant air flow and constant Reynold number (Re=200) for a mixed convective flow (Ri=3) and the results are compared with those of pure force convective flow (Ri=0). The results indicate that the re-circulation zones at the vicinity of the back step are reduced if the buoyancy effects are considered. It is concluded that the flow is highly tridimensional.

Se realiza un estudio sobre la convección mixta para flujo laminar sobre un conducto horizontal que encierra un escalón. Las ecuaciones de momento y energía se discretizan usando la técnica de los volúmenes finitos. Se utiliza el algoritmo SIMPLE para enlazar los campos de velocidad y presión en el dominio computacional. La influencia de las fuerzas de flotación (Ri=3) sobre los campos de velocidad y de temperaturas, se simulan para un flujo de aire y un número de Reynolds constante (Re=200) y los resultados se comparan con los de flujo a convección forzada (Ri=0). Los resultados mostraron que las zonas de recirculación adyacentes al escalón, se ven reducidas cuando se consideran las fuerzas de flotación. Se concluye que el flujo es altamente tridimensional.