Masaru Ishizuka

Development of prediction technique for cooling performance of finned heat sink in uniform flow

Numerical simulation was carried out on the flow and the temperature fields around a plate fin array subjected to a uniform flow, varying the ratio of fin length L to the half-pitch of fins s. As Re/sub 0/s/L decreased, the flow approaching the fin array had a tendency to bypass it and thus the average flow velocity through fins U/sub f/ became lower, where Re/sub 0/ is the Reynolds number defined by uniform flow velocity and s. It was also found that frictional resistance and heat transfer of the fins showed excellent agreement with those for the developing flow between parallel plates with uniform inlet flow velocity equal to U/sub f/. A prediction technique for the cooling performance of the array was developed in which U/sub f/ was estimated under the condition of constant pressure distribution at its downstream edge. The present technique can predict the heat transfer of the fin array with an error level below 30% under practical conditions of electronics design, although it underestimates U/sub f/ in the region of small Re/sub 0/s/L.

Cooling performance of plate fins for multichip modules

Numerical and experimental studies were carried out to evaluate the air cooling characteristics of plate fins for MCMs (multichip modules) with and without some spanwise space around the plate fins. The flow field in-between the plate fins can be assumed to be similar to that of a parallel plate duct, and hence two dimensional laminar flow analyses using the finite volume method were performed. Calculations were carried out for Res (S/L)=1 to 200 and S/t (plate spacing to plate thickness ratio)=3, 4 and 7. Some empirical equations for the Nusselt number and friction factor based on the numerical results are proposed. Considering the fin efficiency calculated from the conventional conduction fin model, the thermal resistance of the plate fins with no space around the fins could be estimated easily on the basis of the above-mentioned equations. Comparisons with experimental results show that this method is valid for H/S (fin height to plate spacing ratio)/spl ges/7. In the case of H/S=4, the thermal resistance is overestimated by this method. Furthermore, nodal network analyses were carried out to estimate the thermal resistance of the plate fin including some spanwise space by specifying the cooling characteristics of the plate fin with no space around the fin. The good agreement between the predicted results and corresponding experimental data shows that this relatively simple nodal network method is quite useful to estimate the thermal resistance of plate fills including some spanwise space.<<ETX>>

An Application of the Thermal Network Method to the Thermal Analysis of Multichip Packages (Proposal of a Simple Thermal Analysis Model)

In recent years, electronic circuits have been required to be smaller and lighter and to have greater complexity, more multifunctions and higher reliability. High-density multichip packaging technology has been used in order to meet these requirements. The higher the density scale, the larger the power dissipation per unit area will become. Therefore, thermal analysis becomes one of the most important design factors. However, the multichip package heat transport mode is very complex and its treatment is tedious and time consuming. This paper describes an application of the thermal network method and proposes a simple thermal analysis model for the thermal analysis of multichip packages as a preliminary thermal design tool. As a result, the validity of the thermal network method and the simple thermal analysis model can be confirmed.

Thermal analysis of notebook personal computer

This paper describes a thermal analysis of a notebook personal computer (PC). A numerical analysis was carried out for the whole domain of the PC, excluding display portion. The numerical model includes Si chips, packages, printed circuit boards (PCBs), casing, etc. In the design of a notebook PC, dead space is kept to a minimum, so the characteristic length for Rayleigh number, which represents the property of the heat transfer between components inside the cabinet is lower than its critical value, and natural convection does not occur inside the PC. Hence, thermal analysis can be performed by heat conduction analysis. To reduce computational load, thermal analysis was divided in two stages and calculation was performed on an EWS. Measured and calculated temperature rise of the electronic parts showed good agreement. This led to the conclusion that the present thermal analysis method can be a useful tool for the design of notebook PCs.

Thermal design of a laptop computer by a personal computer

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.<<ETX>>

Thermal studies on finned LSI packages using forced convection

The authors describe extensive computer-based analytical and experimental studies on finned LSI packages, utilizing a cavity-down-type QFP348pin (quad flat pack 348pin) package, in order to develop a simulation method for a high-thermal-performance package and its heat sink. The numerical analysis was accomplished for a conjugate problem, which encompassed flow and heat transfer in the cooling air stream and heat conduction in the package and the heat sink. Experiments were conducted to measure the temperature rise at the junction, the package surface, and the fin, using several kinds of omnidirectional heat sink fins in a wind tunnel. The applicability of the model used for the simulation and the computational scheme were verified by comparing the experimental results with those obtained on the basis of the model. These comparisons lead to the conclusion that the proposed numerical method of predicting the thermal resistance of finned LSI packages will be satisfactory for thermal designers. >

Natural convection air cooling characteristics of plate fins in a ventilated electronic cabinet

This work aims to evaluate natural convection air cooling characteristics of compact vertical rectangular plate fin arrays in a ventilated electronic cabinet. The work focuses on plate fin arrays applicable to notebook personal computers and engineering workstations. 3D laminar flow analyses using the finite volume method were performed in order to evaluate the natural air cooling characteristics of vertical rectangular plate fin arrays located in a ventilated electronic cabinet with cooling air inlet and exit. The governing equations are the continuity, momentum, and energy equations with buoyancy term using Boussinesq approximation. The equations were solved using the SIMPLE scheme. Calculations were carried out for plate spacing S=3, 4, 5 mm, fin height H=20, 30, 40 mm, cooling air inlet and exit height B=2.5, 5, 10 mm, and fin length L=10 mm. Numerical results indicated that the average heat transfer coefficient of the fin increases with increase in both the plate spacing S and the cooling air inlet and exit height B, and that the average heat transfer coefficient of the fin base is about one order of magnitude less than that of the fin surface. Results also showed that in the case where the fin length is equal to the air inlet height, the average fin heat transfer coefficient is almost equal to that of natural convection in a vertical rectangular channel. Additionally, based on numerical results, some empirical equations for the average Nusselt number of vertical rectangular plate fin arrays located in a ventilated electronic cabinet with cooling air inlet and exit are proposed as a function of Ra/sub s/.

Thermal Analysis of a New High Density Package Cooling Technology Using Low Melting Point Alloys

This paper describes one of the new package cooling technology concepts using a phase changing material (PCM) which would help develop high density packaging. A low cost alloy, composed of Bi/Pb/Sn/In whose melting point is 57°C, was used as the PCM. Thermal experiments using the abovementioned alloy had been studied by the authors.1) It was confirmed that the substrate back surface temperature could be fixed at the PCMs melting temperature for several minutes by thermal absorption, while the PCM phase changed from its original solid state into the liquid state. Also, in the present work, it has been confirmed that thermal network method is practically useful using a personal computer for the thermal design of a package with a PCM.

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

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.

Thermal Resistance Measurement and Thermal Network Analysis of Printed Circuit Board With Thermal Vias

Thermal vias are widely used to reduce thermal resistance of a printed circuit board (PCB). However, fine via structure becomes an obstacle to computational fluid dynamics (CFD) simulation because fine structure requires a huge number of meshes. Therefore, an efficient modeling method of thermal via structure is needed to reduce computational time. In this paper, an effect of thermal vias on reduction of thermal resistance was experimentally and numerically investigated to gather fundamental data for thermal management of electronics. We used printed circuit board models with some kind of arrangements of thermal vias. Board materials and copper dissipating pad patterns were explored as experimental parameters. Copper pipes (unfilled vias) or rods (filled vias), the diameter of which was 1.5, 3.0 and 5.0 mm, were used as thermal via. Three materials (Glass epoxy, Stainless, and Polycarbonate), thermal conductivity of which were different, were used as board materials. The experimental results showed that area of heat dissipating copper pad patterns and board materials have strong effect on the temperature rise of the heat source. On the other hand, the number of thermal vias and via shapes have no effect on the heat source temperature. Then we performed thermal network analysis to evaluate the experimental results. From the results of the thermal network analysis, it was confirmed that an effect of thermal via is saturated at certain ratio of via area.Copyright