Tomiya Sasaki

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>>

Air Resistance Coefficients for Perforated Plates in Free Convection

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.

Cooling performances for fins under an obstacle.

The effect of a cubic obstacle above small rectangular fins on the natural air cooling performances was experimentally investigated, varying the clearance between the fin tip and the obstacles, the fin height and the fin interspacing parametrically. The heat dissipation capability of a fin was diminished under the critical clearance which was not significantly affcted by the fin height and the fin interspacing. Through the flow visualization, natural convection flow pattern was not altered by the clearance, the fin height and the fin interspacing. It was found that the correlations of the fin cooling performances and the clearance were not reversed by altering the fin height.

On the cooling of natural-air-cooled electronic equipment casings (Proposal of a practical formula for thermal design)

This paper presents a simple formula for thermal designing of natural-air-cooled electronic equipment casings with standard arrangement for circuit boards and power supplies. The formula meets the requirements as a practical formula, since it represents the air-cooling system in its simplified form with due regard to such factors as the stack effects, air Flow resistance, natural convective transfer and so on. The formula was applied to predict temperature rise for two practically used electronic equipment cabinets with standard arrangements and a modeling case. The predicted temperature rise values, obtained through the formula, caused very slight errors, with only 10 percent in the actual values based upon experiment results.

Flow Visualization in X-Ray CT Gantry

We have developed a high power and high speed X-ray CT helical scanner, whose rotational speed is 120rpm. Heat dissipation of the machine is about 2.5 times more than that of previous machine, hence thermal design is becoming very important item in design. Three-dimensional thermo-fluid analysis and flow visualization experiment were performed in order to understand temperature and flow field in the gantry. The results of three-dimensional thermo-fluid analysis and flow visualization led some understanding to be applied in thermal design, and served an important role as thermal design tools.

Application of the thermal network method to the transient thermal analysis of multichip modules

In recent years, there has been a growing demand to have smaller and lighter electronic circuits with greater complexity, multifunctionality and reliability. High-density multichip packaging technology has been used to meet these requirements. The higher the density scale is, the larger the power dissipation per unit area becomes. Therefore, in thermal design process it has become very important to carry out the thermal analysis. However, the heat transport model in multichip modules is 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.

Flow Visualization of a Heat Exchanger Using Water Surface Particle Tracing Technique (A Mixture of Water, White Water Paint and Surface Active Agent was Used as Tracer)

In order to understand the internal flow pattern of a heat exchanger, new method flow visualization is developed using water paint instead of the aluminum powder or saw dust in conventional way. A mixture of water and white water paint adding a little amount of surface active agent is adopted to obtain the internal flow pattern of heat exchanger without sticking of tracer to the model surface. The mixture liquid having weight ratio of water, white water paint and surface active agent 4:1:1/2000 shows the best condition for visualization. Using this tracer, it is possible to trace the time-line and the streak-line around the model clearly. Various kinds of fin arrangement of the exchanger are tested.

Flow Visualization of Heat Exchanger's Fins

Recent advancement of technology.need the compactness of heat exchanger to be used in the air conditioner without lowering its overall performance. It is well known that the performance of heat exchanger can be improved by introducing slits on the fin. However, the important problem here, is to choose the best possible slit pattern. In order to study the above mentioned problem, in the present work, experiment is carried out by using 10 times enlarged model fins of heat exchanger for flow visualization.Results indicate fully developed laminar flow pattern in the case of flat parallel plate. In the case of alternative arrangement of the slits, it is observed that the flow is symmetrical downstream the second stage of alternative slit pattern. Comparison of the experimental flow pattern with the calculated heat transfer coefficient lead to the understanding that downstream the second stage, if slits are arranged in such a way that the flow interact with the slits in the portion where the flow velocity is high, it is possible to increase the heat transfer coefficient.

Evaluation of Heat Transfer Coefficient for Heat Exchanger's Fins Using a Scannning Infrared Camera

The improvement and compactness of heat exchangers need the technique for fins heat transfer promotion. Several ideas have been created, for example, setting slits on fins etc.. However, it is impossible that prototypes for all the ideas are produced, and their performance are estimated.Therefore, we considered the heat transfer characteristics for one fin. In order to investigate them, the surface temperature of the fin, which was heated uniformly by direct current, was measured using a scanning infrared camera. And the heat transfer coefficient was calculated.It is significant to change the visualization data to the heat transfer coefficient, which is quantitative value, in this study.

FLOW VISUALIZATION IN AN ELECTRONIC-EQUIPMENT CASE

In order to conduct an effective computer simulation for the thermal design, flow visualization was performed. A transparent model, incorporated with boxes which could be supplied a specific heat flux, was used. The mist method by liquid paraffin was adopted for air flow visualization, and the thermo graphic method was used for temperature distribution measurments. By the comparison of analysis and experimental results, the simulation method and boundary condition were examined.