R. D. M. Carvalho

Bio: R. D. M. Carvalho is an academic researcher from State University of Campinas. The author has contributed to research in topics: Electronic circuit & Thermal resistance. The author has an hindex of 1, co-authored 1 publications receiving 4 citations.

Heat Transfer Analysis of Digital Transmission Equipment with Horizontally Arranged Printed Circuit Boards

Abstract: Printed circuit boards (PCBs) may be arranged horizontally in many situations, as for example in some digital transmission equipment being used in Brazil Such pieces of equipment, known as slim racks, have a high aspect ratio (height/width) and are assembled side by side and back to back The present work deals with the steady-state thermal dissipation in the so-called thermal unit of the slim rack made of the PCB, the magnetic shield above it and the bounding walls constituting an enclosure The heat transfer in each thermal unit was investigated by assuming isothermal enclosure surfaces with uniform radiosities Once the thermal paths are identified, an electric circuit analogy is employed to obtain the overall thermal resistance network Most of the thermal resistances are temperature-dependent, so the associated nonlinear algebraic equations can be solved only by an iterative method An experimental investigation was carried out in a module of the slim rack with simplified boundary conditions in orde

Combined Conduction, Natural Convection, and Radiation Heat Transfer in an Electronic Chassis

Abstract: A numerical study of the combined heat transfer by conduction, natural convection, and radiation in a sealed electronic package is reported. The goal of the study is to investigate the importance of the various heat transfer modes, the effectiveness of different heat transfer paths, and the impact of a number of design changes on the overall thermal performance of a typical electronic package. The package consists of an enclosure containing three printed circuit boards on which are mounted various heat-generating electronic components. Heat transfer processes at both small (i.e., inside a component) and large (i.e., the package) scales as well as all heat transfer modes are included simultaneously in the numerical model. Both one and twodimensional radiation is considered. Results are presented in terms of streamline and isotherm plots and average temperatures and heat transfer rates. Overall, the numerical data show favorable agreement with available empirical data. One sig­ nificant conclusion is that natural convection inside the enclosure has only a minor effect on the heat transfer in the present system.

Analysis of Entropy Generation Minimization during Natural Convection in Trapezoidal Enclosures of Various Angles with Linearly Heated Side Wall(s)

Abstract: Entropy generation during natural convection in trapezoidal enclosures with various inclination angles (φ), φ = 45°, 60°, and 90° for uniformly heated bottom wall and insulated top wall with linearly heated side walls (case 1) or linearly heated left wall with cold right wall (case 2) have been investigated numerically using penalty finite element method. Parametric studies for the wide range of Rayleigh numbers (Ra = 103–105) and Prandtl numbers (Pr = 0.015–1000) have been performed. Symmetry in flow pattern is observed for case 1. During the conduction regime at low Ra (Ra = 103), the entropy generation in the cavity is dominated by heat transfer irreversibility for all Pr. The strength of fluid flow increases with Ra and that leads to an increase in thermal energy transport due to enhanced convection at Ra = 105. Consequently, the entropy generation due to heat transfer (Sθ) and fluid friction (Sψ) also increases with Ra for all Pr. The comparison of magnitudes of Sθ and Sψ indicates that maximum entro...

Minimization of entropy generation due to MHD double diffusive mixed convection in a lid driven trapezoidal cavity with various aspect ratios

Abstract: Entropy generation minimization has significant importance in fluid flow, heat and mass transfer in an enclosure to get the maximum efficiency of a system and to reduce the loss of energy. In the present study, the analysis of mixed convection fluid flow, heat and mass transfer with heat line and mass line concept and entropy generation due to the effects of fluid flow, heat flow, mass flow and magnetic field in a trapezoidal enclosure with linearly heated and diffusive left wall, uniformly heated and diffusive lower wall, cold and nondiffusive right wall, adiabatic and zero diffusion gradient top wall have been reported. Parametric studies for the wide range of Prandtl number (Pr = 0.7 for air cooling system and Pr = 1000 for the engines filled with olive or engine oils), Rayleigh number (Ra = 103–105), aspect ratio (A = 0.5–1.5) and inclination angle of the cavity (ϕ = 45°–90°) have been performed, which help to construct the perfect shape of cavity in many engineering and physical applications so that the entropy is minimum to get the maximum efficiency of any system. The finite-difference approximation has been used to find out the numerical solutions. Biconjugate Gradient Stabilized (BiCGStab) method is used to solve the discretized nonhomogeneous system of linear equations.