Unsteady Mixed Convection in a Vented Enclosure Partially Filled with Two Non-Darcian Porous Layers

Mixed convection in a ventilated rectangular cavity with a horizontal strip occupied by two media of different permeability is studied by using the finite-volume method. The effect of the parameters that govern the problem, the Reynolds number (200–500), the Richardson number (0.1–10), the Darcy number (1.E–6–1.E–2), permeability ratio (0.01–100), aspect ratio of the cavity (1–1.5), and direction of flow with or against gravity, is investigated. From the numerical results, the influence of Darcy and Reynolds numbers on the fluid mechanics can be inferred. When the cold fluid flow is descending, the fluid–porous medium heat transfer increases because the hotter fluid is located in the upper zones of the cavity. As the aspect ratio (height/width) increases from 0.67 to 1.5, both the Nusselt number (7.5 < Nu < 27) and the friction coefficient increase. The friction coefficient on the walls is greater when Re = 500 and Ri = 10 in the two directions of flow. As the Darcy number increases, the velocity gradients increase near the walls, causing an increase of the friction coefficient (0 < Cf Re < 47).     

LocalBoost: A Parallelizable Approach to Boosting Classifiers

Neural Processing Letters - We are introducing a new type of membrane, called neuro-skin or neuro-membrane. It is comprised of neurons embedded in a plastic membrane. The skin is smart and adaptive...     

Introducing disjoint spectral translation in spectral multiple-valued logic design

A new form of expansion of multiple-valued logical functions in generalised Fourier series in terms of the Chrestenson functions is presented. It is shown that this expansion exhibits the property of `disjoint spectral translation? known in binary spectral logic design. This allows extending the possibility of low complexity realisation to a large class of multiple-valued logical functions.     

A stream function implicit finite difference scheme for 2D incompressible flows of Newtonian fluids

The development of a new algorithm to solve the Navier–Stokes equations by an implicit formulation for the finite difference method is presented, that can be used to solve two‐dimensional incompressible flows by formulating the problem in terms of only one variable, the stream function. Two algebraic equations with 11 unknowns are obtained from the discretized mathematical model through the ADI method. An original algorithm is developed which allows a reduction from the original 11 unknowns to five and the use of the Pentadiagonal Matrix Algorithm (PDMA) in each one of the equations. An iterative cycle of calculations is implemented to assess the accuracy and speed of convergence of the algorithm. The relaxation parameter required is analytically obtained in terms of the size of the grid and the value of the Reynolds number by imposing the diagonal dominancy condition in the resulting pentadiagonal matrixes. The algorithm developed is tested by solving two classical steady fluid mechanics problems: cavity‐driven flow with Re=100, 400 and 1000 and flow in a sudden expansion with expansion ratio H/h=2 and Re=50, 100 and 200. The results obtained for the stream function are compared with values obtained by different available numerical methods, to evaluate the accuracy and the CPU time required by the proposed algorithm. Copyright © 2002 John Wiley & Sons, Ltd.     

Identification of Lags in Nonlinear Autoregressive Time Series Using a Flexible Fuzzy Model

This work proposes a method to find the set of the most influential lags and the rule structure of a Takagi–Sugeno–Kang (TSK) fuzzy model for time series applications. The proposed method resembles the techniques that prioritize lags, evaluating the proximity of nearby samples in the input space using the closeness of the corresponding target values. Clusters of samples are generated, and the consistency of the mapping between the predicted variable and the set of candidate past values is evaluated. A TSK model is established, and possible redundancies in the rule base are avoided. The proposed method is evaluated using simulated and real data. Several simulation experiments were conducted for five synthetic nonlinear autoregressive processes, two nonlinear vector autoregressive processes and eight benchmark time series. The results show a competitive performance in the mean square error and a promising ability to find a proper set of lags for a given autoregressive process.     

Combined Drying Technologies for High-Quality Kiwifruit Powder Production

Freeze-drying is a dehydration technique which, from a sensory, nutritional and functional point of view, provides high-quality powder products. Nevertheless, both long processing times and high economic costs are required. In this study, pre-drying the samples using hot air or microwave has been considered in order to reduce the initial product’s water content thereby shortening the freeze-drying time so as to obtain high value products at a reduced cost. The effect of dehydration pre-treatments on the kinetics, antioxidant activity and solubility of freeze-dried kiwifruit products was evaluated. Nine different thin-layer semi-theoretical models were used to fit the drying data. According to the obtained results, the pre-treated samples exhibited higher drying rates than the fresh sample. In turn, the dehydration pre-treatments used did not affect the solubility or the antioxidant activity of the samples.     

Coupled 3D heat and mass transfer model for numerical analysis of drying process in papaya slices

An experimental and numerical study for the drying process of a solid food, Chilean papaya slices, was carried out in a range of air temperatures from 40 to 80 °C. The unsteady temperature and moisture distributions results inside the sample were predicted by using an unsteady tri-dimensional coupled heat conduction and mass diffusion mathematical model. The validation procedure includes a comparison with experimental and numerical temperature and moisture content results obtained from experimental data. The samples thermophysical properties as density, specific heat, and thermal conductivity are assumed to vary non-linearly with temperature. The convective heat and mass transfer coefficients were found by the analytical model. The water effective diffusion coefficient, the drying curves and the center temperature were measured by physical experiments. It was found from the experimental results that slices of papaya present an isotropic behavior with an uncertainty between 6.0% and 9.0%. According to statistical test results (RE%), the finite volume method based calculations gave a very good fit quality.     

UNSTEADY THREE-DIMENSIONAL NATURAL CONVECTION OF WATER COOLED INSIDE A CUBIC ENCLOSURE

Three-dimensional unsteady natural convection of cooling water inside a cubical cavity at Ra = 10⁵ is investigated. The finite-volume method with the SIMPLE algorithm is used to solve the nonlinear coupled continuity, momentum, and energy equations. All physical water properties—density, viscosity, thermal conductivity, and specific heat—are allowed to change with temperature. The numerical results for the 3-D geometry show that the side effects are relevant in fluid mechanics and in heat transfer, with larger differences than with the 2-D predictions in the region where the density anomaly of water is important.