Yuichi Funawatashi

Application of Thermal Network Model to Transient Thermal Analysis of Power Electronic Package Substrate

In recent years, there is a growing demand to have smaller and lighter electronic circuits which have greater complexity, multifunctionality, and reliability. High-density multichip packaging technology has been used in order to meet these requirements. The higher the density scale is, the larger the power dissipation per unit area becomes. Therefore, in the designing process, it has become very important to carry out the thermal analysis. However, the heat transport model in multichip modules is very complex, and its treatment is tedious and time consuming. This paper describes an application of the thermal network method to the transient thermal analysis of multichip modules and proposes a simple model for the thermal analysis of multichip modules as a preliminary thermal design tool. On the basis of the result of transient thermal analysis, the validity of the thermal network method and the simple thermal analysis model is confirmed.

Chimney effect on natural air cooling of electronic equipment under inclination

Natural air-cooling needs neither a fan nor a blower. However, cooling capability of natural air-cooling is low, so the improvement of its capability is indispensable. In this study, the system box is inclined for the purpose to raise the capability of natural air-cooling, and the increase in natural circulation flux in the box is quantitatively proven by experiments. The case studies used three models of notebook PC that have two kinds of heat sources. The box was inclined 0 to 90 degrees up from the horizontal plane. The influence by the box inclination, the box dimensions, and the heating element size was investigated. Moreover, the experimental data were reduced to a Nusselt number — Rayleigh number correlation that does not include explicitly the box dimensions, the heat source size, and the inclination angle.

Natural convection heat transfer between concentric rectangular parallelepipeds

Natural convection heat transfer between concentric rectangular parallelpipeds was studied numerically for low Rayleigh numbers Ra(≦ 3500) with aspect ratios of the inner parallelepiped of 2.0, 4.0, 6.0, and 8.0. It has been found that the flow patterns for the higher Rayleigh numbers in the space over the inner parallelpiped are ring or rectangular rolls. The number of rolls increases with the aspect ratio. The flow pattern in the side space is an oblong circulation, which extends into the bottom space. The local Nusselt number distribution on the top surface of the inner parallelpiped has peaks at the stagnation points. The relation between the Nusselt and Rayleigh numbers on the top surface is similar to that of the Rayleigh–Benard convection obtained by Silveston (Chandrasekhar S.Hydrodynamic and Hydromagnetic Stability, 1961, p 68, Oxford University Press), while on the side and bottom surfaces the Nusselt number increases proportionately with the power of the Rayleigh number.

Natural convection heat transfer between horizontal concentric rectangular pipes

Natural convection heat transfer between concentric rectangular pipes was studied numerically. It has been found that rolls of even numbers form in the region on the top surface of the inner pipe. The number of rolls depends on both the Rayleigh number and the aspect ratio. An oblong circulation of flow forms in the region between the side surface of the inner pipe and the surface of the outer pipe. The aspect ratio does not have much effect on the average Nusselt number at the side surface of the inner pipe. The relation between the Nusselt and Rayleigh numbers at the top surface resembles that of the Rayleigh-Benard convection obtained by Silveston (Chandrasekhar, S. 1961. Hydrodynamic and Hydromagnetic Stability, Oxford University Press, 68). The average Nusselt number at the bottom surface of the inner pipe decreases with increasing aspect ratio because the region where heat transfer is affected significantly by convection is limited.