A semi-empirical approach to the thermal design of electronic equipment is presented. Although recent progress in computer technology has enabled a complex analysis to be done, it is difficult to carry out numerical studies for practical electronic equipment cabinets, which have extremely complicated boundary conditions due to the various sized components mounted in the cabinets. It has thus become important to establish an analytical model in order to apply computer simulation to the thermal design of electronic equipment. This paper reports on the semiempirical approach based on a lumped model, and experimental data of the flow resistance coefficient and heat transfer coefficient. A simulation was carried out for a photocopy machine model by using a personal computer. The proposed method is confirmed to be capable of serving thermal designers satisfactorily.

Application of a semi-empirical approach to the thermal design of electronic equipment

A semi-empirical approach to the thermal design of electronic equipment is presented. Although recent progress in computer technology has enabled a complex analysis to be made, it is difficult to carry out numerical studies for practical electronic equipment cabinets, which have extremely complicated boundary conditions due to the various sized components mounted in the cabinets. It has thus become important to establish an analytical model in order to apply computer simulation to the thermal design of electronic equipment. This paper reports the semi-empirical approach based on a lumped model, and experimental data on the flow resistance coefficient and heat transfer coefficient. A simulation was carried out for a photocopy machine model by using a personal computer. The proposed method is confirmed to be capable of serving thermal designers satisfactorily.

Numerical studies have been implemented to examine an effective computer simulation method of thermal design for electronic equipment. The proposed approach is a simple analysis using a lumped model which includes experimental values such as the fluid resistance coefficient and heat transfer coefficients. The proposed approach was applied to the design of a laptop computer using a personal computer. >

Thermal design of a laptop computer by a personal computer

As the power dissipation density of electronic equipment has continued to increase, it has become necessary to consider the cooling design of electronic equipment in order to develop suitable cooling techniques. Almost all electronic equipment is cooled by air convection. Of the various cooling systems available, natural air cooling is often used for applications for which high reliability is essential, such as telecommunications. The main advantage of natural convection is that no fan or blower is required, because air movement is generated by density differences in the presence of gravity. The optimum thermal design of electronic devices cooled by natural convection depends on an accurate choice of geometrical configuration and the best distribution of heat sources to promote the flow rate that minimizes temperature rises inside the casings. Although the literature covers natural convection heat transfer in simple geometries, few experiments relate to enclosures such as those used in electronic equipment, in which heat transfer and fluid flow are generally complicated and three dimensional, making experimental modeling necessary. Guglielmini et al. (1988) reported on the natural air cooling of electronic boards in ventilated enclosures. Misale (1993) reported the influence of vent geometry on the natural air cooling of vertical circuit boards packed within a ventilated enclosure. Lin and Armfield (2001) studied natural convection cooling of rectangular and cylindrical containers. Ishizuka et al. (1986) and Ishizuka (1998) presented a simplified set of equations derived from data on natural air cooling of electronic equipment casings and showed its validity. However, there is insufficient information regading thermal design of practical electronic equipment. For example, the simplified set of equations was based on a ventilation model like a chimney with a heater at the base and an outlet vent on the top, yet in practical electronic equipment, the outlet vent is located at the upper part of the side walls, and the duct is not circular. Therefore, here, we studied the effect of the distance between the outlet vent location and the heat source on the cooling capability of natural-air-cooled electronic equipment casings.

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Design of Electronic Equipment Casings for Natural Air Cooling: Effects of Height and Size of Outlet Vent on Flow Resistance

In recent years, the increasing demand of compactness and high-speed performance of electronic equipment had led to an increasing trend of power dissipation density. Therefore, suitable cooling techniques to the thermal designing of electronic equipment need to be developed. Several research reports on electronic equipment cooling are available in the literature sources [1-5]. In these studies it can be observed that air-cooling is getting one of the important cooling techniques, since most of the electronic equipment are cooled by air convection. Although fan cooling is most widely used in the air cooling techniques, the noise generated by the fan is publicly criticized. As a result, cooling on the basis of natural convection is one of the attractive approaches. However, only limited data on natural convection, which can be used in the practical design of electronic equipment, are available. Noronha [6] studied the effect of the component locations in cabinets to achieve maximum natural cooling efficiency. Guglielmini et al [7] have reported on the natural air cooling of electronic cards in ventilated enclosures. Ishizuka et al. [8] proposed an approach using a simplified set of equations which represent the cooling capability through a natural air-cooled electronic equipment casings. However, detailed discussions on derivation of the set of equations were not made in that paper. Therefore, in the present work, an attempt has been made to study the effects of the outlet vent area and power dissipation unit location on the natural air-cooled electronic equipment casings.

A thermal design approach for natural air cooled electronic equipment casings

With the recent rapid increase in close packaging density, and higher power for electronic equipment, the cooling design involved in casings which enclose them has become more important. For the electronic equipment cooling design, data on flow path resistance in the casing are needed. The most significant factors in the flow resistance are considered to be vent perforations. However, all the resistance data for perforated plates were obtained for forced convective flows (higher Reynolds numbers), as reported by Collar (1939), Macphail (1939), and Taylor (1949). Smith and Van Winkle (1957) studied discharge coefficients through perforated plates at a wide Reynolds number range of 2,000 to 20,000, and Kolodzie and Van Winkle (1958) also made a study at a 400 to 3,000 Reynolds number range. Their work was limited to a lower porosity coefficient range of 0.023 to 0.158. However, resistance data in air free convection paths have not been reported. Therefore, the measuring system for determining the resistance values for perforated plates in an air free convection path was designed. This note describes the measuring system and resistance values for perforated plates obtained by using the system.

Y. Miyazaki

Papers

Air Resistance Coefficients for Perforated Plates in Free Convection