Wendell de Queiroz Lamas

Laminar free and forced convection cooling of a semi permeable open cavity

Heat transfer inside a semi porous two-dimensional rectangular open cavity was numerically investigated. The open cavity comprises two vertical walls closed to the bottom by an adiabatic horizontal wall. One vertical wall is a porous and an inflow of fluid occurs normal to it. The other wall transfers a uniform heat flux to the cavity. It shows how natural convection effects may enhance the forced convection inside the open cavity. The main motivation for the work is its application for electronic equipment where frequently the devices used for the electronic equipment cooling are based on natural and forced convection. Governing equations are expressed in Cartesian coordinates and numerically handled by a finite volume method. Results are presented for both local and average Nusselt numbers at the heated wall and for the isotherms and streamlines of the fluid flowing inside the open cavity as a function of Reynolds number ranging from 1 to 100, Grashof number ranging from 0 to 10+7 and the aspect ratio number of the open cavity equal 2, 4 and 8. The results obtained show that the forced convection inside the semi-porous open cavity studied may be greatly enhanced by natural convection effects. n n xa0 n n Key words: Computational simulation, electronic equipment cooling, finite volume, natural convection, open cavity; porous media.

Notes on Steady Natural Convection Heat Transfer by Double Diffusion From a Heated Cylinder Buried in a Saturated Porous Media

This paper aims to present numerical solutions for the problem of steady natural convection heat transfer by double diffusion from a heated cylinder buried in a saturated porous media exposed to constant uniform temperature and concentration in the cylinder and in the media surface. A square finite domain 3 x 3 and acceptance criterion converged solution with an absolute error under 1 x 10(-3) were considered to obtain results presented. The Patankars power law for approaching of variables calculated T, C, and phi also was adopted. In order of method validation, an investigation of mesh points number as function of Ra, Le, and N was done. A finite volume scheme has been used to predict the flow, temperature, and concentration distributions at any space from a heat cylinder buried into a fluid-saturated porous medium for a bipolar coordinates system. Examples presented show that the differences in the flow distribution caused not only when Rayleigh number range is considered but also when Lewis number range is considered. Further, increase in the Rayleigh number has a significant influence in the flow distribution when the concentration distribution is considered. Steady natural convection heat transfer by double diffusion from a heated cylinder buried in a saturated porous medium is studied numerically using the finite volume method. To model fluid flow inside the porous medium, the Darcy equation is used. Numerical results are obtained in the form of streamlines, isotherms, and isoconcentrations. The Rayleigh number values range from 0 to 1000, the Lewis number values range from 0 to 100, and the buoyancy ratio number is equal to zero. Calculated values of average heat transfer rates agree reasonably well with values reported in the literature.

Feasibility study of chromium electroplating process in stamping tooling

Due to the great need for reducing production costs, productivity increasing quality improvement of products, the study had its start drafting surface treatment of dies process development, where the first step was a market study looking for the treatment types and their applications. These treatments are intended to stabilize the production process so that there are no variations on the production and increasing the useful life of dies and their appropriate tools. It was determined through analysis, that the parts had problems in dies drawing which influenced on productivity, quality and cost. It had been realized that those parts had similar problems and the treatments could generally minimize such problems. The following step was to apply the treatment of dies and tools, and then realized that the results achieved certain goals, managing to stabilize the stamping process of those parts.

Computational simulation of frequency inverter ramps applied to an electric vehicle

This work aims to represent acceleration/deceleration ramps generator and a voltage/frequency control through a SCICOS block diagram for evaluation of values commonly used with electric vehicles. It was opted for the representation of functional block diagrams for implementing the models, and was adopted the free software SCILAB/SCICOS to design and to simulate the representations proposed. Also measurements from electric vehicle coupled to frequency inverter were done and compared to values obtained with simulations. The diagrams for the functions of acceleration/deceleration ramps and of V/f control was implemented, being fundamentals characteristics to simulate the operation of a frequency inverter for driving induction motors. Although the analysis was limited to these characteristics, in view of a variety of functions available on the inverter, the models were presented satisfactory to the representation of the basic characteristics of an inverter in the scalar configuration. n n xa0 n n Key words:xa0Acceleration/deceleration ramps, electric vehicle type mini-baja, voltage/frequency control.