Thiago Antonini Alves

Convective cooling of three discrete heat sources in channel flow

A numerical investigation was performed to evaluate distinct convective heat transfer coefficients for three discrete strip heat sources flush mounted to a wall of a parallel plates channel. Uniform heat flux was considered along each heat source, but the remaining channel surfaces were assumed adiabatic. A laminar airflow with constant properties was forced into the channel considering either developed flow or a uniform velocity at the channel entrance. The conservation equations were solved using the finite volumes method together with the SIMPLE algorithm. The convective coefficients were evaluated considering three possibilities for the reference temperature. The first was the fluid entrance temperature into the channel, the second was the flow mixed mean temperature just upstream any heat source, and the third option employed the adiabatic wall temperature concept. It is shown that the last alternative gives rise to an invariant descriptor, the adiabatic heat transfer coefficient, which depends solely on the flow and the geometry. This is very convenient for the thermal analysis of electronic equipment, where the components’ heating is discrete and can be highly non-uniform.

Conjugate Cooling of a Discrete Heater in Laminar Channel Flow

Electronic components are usually assembled on printed circuit boards cooled by forced airflow. When the spacing between the boards is small, there is no room to employ a heat sink on critical components. Under these conditions, the components’ thermal control may depend on the conductive path from the heater to the board in addition to the direct convective heat transfer to the airflow.The conjugate forced convection-conduction heat transfer from a two-dimensional strip heater flush mounted to a finite thickness wall of a parallel plates channel cooled by a laminar airflow was investigated numerically. A uniform heat flux was generated along the strip heater surface. Under steady state conditions, a fraction of the heat generation was transferred by direct convection to the airflow in the channel and the remaining fraction was transferred by conduction to the channel wall. The lower surface of the channel wall was adiabatic, so that the heat conducted from the heater to the plate eventually returned to the airflow. A portion of it returned upstream of the heater, preheating the airflow before it reached the heater surface. Due to this, it was convenient to treat the direct convection from the heater surface to the airflow by the adiabatic heat transfer coefficient. The flow was developed from the channel entrance, with constant properties.The conjugate problem was solved numerically within a single solution domain comprising both the airflow region and the solid wall of the channel. The results were obtained for the channel flow Reynolds number ranging from about 600 to 1900, corresponding to average airflow velocities from 0.5 m/s to 1.5 m/s. The effects of the solid wall to air thermal conductivities ratio were investigated in the range from 10 to 80, typical of circuit board materials. The wall thickness influence was verified from 1 mm to 5 mm. The results indicated that within these ranges, the conductive substrate wall provided a substantial enhancement of the heat transfer from the heater, accomplished by an increase of its average adiabatic surface temperature.

Experimental Study of a Cu-Mo Alloy Vapor Chamber

In this research, the thermal behavior of a vapor chamber embedded in the base of a heat sink was experimentally analyzed considering the influence of the heat source position. The vapor chamber was produced by a copper and molybdenum alloy with length of 240 mm, width of 54 mm, thickness of 3 mm, and capillary structures composed by copper screen meshes. The working fluid used was de-ionized water. The pure aluminum heat sink was cooled by air forced convection and the evaporator vapor chamber was heated using an electrical resistor simulating integrated circuit power dissipation. The experimental tests were done in a suction type wind tunnel with open return for a heat load varying from 20 to 80 W, for an airflow velocity varying from 1 to 4 m/s, and for three different heat source positions. The experimental results showed that, independently of the heat source position, the considered vapor chamber worked successfully, maintaining low operating temperature.

ESCOAMENTO LAMINAR EM DUTOS DE SETOR CIRCULAR

The fluid flow inside ducts is of great importance in engineering, because it is present in most domestic, commercial, and industrial application equipments. In this work was presented a hybrid analytical-numerical solution to hydrodynamic problem of fully developed laminar flow inside circular sector ducts. In order to facilitate the analytical treatment and the application of the boundary conditions, a Conformal Transform was used. Thereafter, the Generalized Integral Transform Technique was applied on the momentum equation to obtain the velocity field. Numerical results were obtained for quantities of practical interest, such as maximum and minimum velocity, Fanning friction factor, Poiseuille number, Hagenbach factor, and hydrodynamic entry length. The results were compared, as much as possible, with the parameter values available in the literature and they presented a great agreement, with a difference less than 1.5%. Keywords: Integral Transform, Conformal Transform, Laminar Flow, Newtonian Fluid, Circular Sector.

Unorganized machines to predict hospital admissions for respiratory diseases

The impact of air pollution on human health is widely studied, especially at large cities in the world. The most used methodologies to access this impact are based on statistical regressions, such as Generalized Linear Models. A few researchers use neural networks. In this context, the present work intend to predict the number of hospital admissions for respiratory diseases in Campinas city, São Paulo State, Brazil, related to the concentration of particulate matter less than 10 µm in aerodynamic diameter (PM10) using neural networks. The used data set comprises daily measures of average temperature, relative humidity and PM10 concentration scattered in the air during 2007 to 2009. To do so, it is proposed the use of two neural networks architectures known as unorganized machines: the echo state networks and the extreme learning machines. The obtained computational results were compared to the performance of the multilayer perceptron. In general, it may be concluded that the proposed neural networks showed to be more relevant to solve problems of health risks, contributing to a better understanding of the applicability of these networks.

Laminar Flow of Newtonian Fluids in Concentric Annular Ducts

In this work it was presented a hybrid analytical-numerical solution to hydrodynamic problem of fully developed laminar flow of Newtonian fluids in concentric annular ducts employing the Generalized Integral Transform Technique (GITT). In order to facilitate the analytical treatment and the application of the boundary conditions, a Conformal Transform was used to change the domain into a more suitable coordinate system. Thereafter, the GITT was applied on the momentum equation to obtain the velocity field. The numerical results were obtained for fluid dynamic parameters of interest, such as: maximum and minimum velocities, Fanning friction factor, Poiseuille number, Hagenbach factor and the fluid dynamic entry length. These results were compared, as much as possible, with the parameter values available in the literature and they presented an excellent agreement.