Yasushi Nishino

Modeling of a 3-Dimensional Conjugate Heat Transfer on the Channel-Composite-Wall for Electronics Cooling

We report the modeling of a novel approach to passive heat transfer from electronic equipment through an enclosure wall with built-in vertical channels. This passive cooling method is based on the different temperature requirements between the enclosure surface and the internal heat-generating devices. This approach takes advantage of natural convection, known as the chimney effect, resulting from higher temperatures in vertically oriented channels. In addition to channel convection, the skin surface exposed to the environment dissipates the heat passively by both natural convection and radiation. The configuration of the wall and channels, termed a Channel-Composite-Wall (CCW), creates a novel form of passive cooling that we have analyzed and modeled. The inner side of the CCW is assumed to be uniformly heated. The three-dimensional flow regime is observed by means of PIV (particle image velocimetry) experiments and numerical studies. The unique velocity profile inside each channel is observed and can be regarded as similar to the flow in the differently heated parallel plates. The channel flow is modeled by breaking the channel down into two sections plus the exposed skin wall. Based on these observations, the relationship between the internal flow field and external convective flow can be considered to be handled separately. The thermal characteristic is also studied based on the correlations. The thermal conductivity and thickness of the solid partition of channels are found to be significant contributors to performance. The analytic model of the CCW was verified by numerical calculations and experiments. The model reasonably closely expresses the characteristics of this comprehensive conjugate heat transfer. The model can thus be used for the development of passively cooled electronics enclosure.Copyright

Experimental Validation of Channeled Wall Passive Cooling Enhancement

Passive cooling enhancement with least additional mass of the material on the external wall can be a method for least energy thermal management for the consumer electronics. Previously, the channeled wall enhancement was found to have potentially four fold performance compare to the single wall in the analysis work, in which the enhancement factor with optimum shape with appropriate thermal conductivity of the material was presented. This method is assumed promising to help the energy efficient and quieter thermal design without sacrificing the valuable flat cosmetic surface of equipment. In this paper, flow regime in a channel composite wall is observed experimentally with PIV method as well as thermal resistance of the wall is observed in the same apparatus. These observation results are discussed with numerical analysis. The discussion is summarized with cooling enhancement factor based on the allowable temperature with comparing to the single wall. The result provides the strong evidence for the optimization on proposed analytic models.Copyright

Comparison Between PIV Results and CFD Simulations of Air Flows in a Thin Electronics Casing Model

The aim of this study was to acquire benchmark test data for simulating computational fluid dynamics in thin electronic equipment. Flow in the model of thin electronic equipment was measured by using particle image velocimetry PIV). Dummy components were placed in the model and their configurations altered. The temperature rise of a heat source in the model was also measured and the cooling performance examined. The PIV measurement results revealed the changes in flow with changes in the configuration of the components. Comparison of the experimental results with numerical results showed good agreement in terms of the overall velocity field.Copyright

Comparison between experimental results and CFD simulations for air flows in a thin electronics casing model

This study has been conducted by aiming at acquisition of benchmark test data for CFD simulations for thin electronic equipment. Flow in the model of a thin electronic equipment was measured using a PIV. Dummy components were placed in the model and those configurations were altered. The temperature rise of a heat source in the model was also measured and the cooling performance was examined. PIV measurement results clarified the change of flow depending on the configuration. The comparison of experimental results with numerical results shows a good agreement when seeing in the overall velocity field.

Optimization of Natural Air Cooling in a Vertical Channel of Electronic Equipment

The natural convection cooling capability in a compact item of electronic equipment was investigated quantitatively by experiment and numerical simulation with a simple channel model. The optimization of the channel sizes, especially the clearance between heated walls, was discussed. The channel model, which consists of a vertical duct of rectangular section, was applied as the experimental model of electronic equipment in this study. The channel model consists of two heated copper walls and two transparent acrylic walls. The clearance between the copper walls of the channel was varied from 5 mm to 15 mm. Temperature measurement on the copper wall surfaces and velocity measurement of natural air flow in the channel by using a particle image velocimetry (PIV) were conducted for a few clearances of the channel. Numerical simulation was also carried out, with a model following the experimental setup, for more detailed discussion of various clearances of the channel. The relationship between the clearance and the temperature rise of the walls or velocity profile was investigated. The correlation between the Rayleigh number and the Nusselt number was obtained from measured temperature. The natural cooling capability and the velocity profiles depend on the clearance between the copper walls. When the wall clearances are more than 15 mm, the cooling is not enhanced. On the other hand, in the case that the clearance becomes less than 7 mm, the cooling capability becomes significantly lower. Consequently, it is clarified that the clearance from 8 mm to 10 mm is the best size for natural cooling from the view point of the space and the capability.Copyright

Experimental study on cooling air flow in a thin electronics casing model

This study has been conducted by aiming at acquisition of benchmark test data for CFD simulations for thin electronic equipment. Flow in the model of a thin electronic equipment was measured using a PIV. Dummy components were placed in the model and those configurations were altered. The temperature rise of a heat source in the model was also measured and the cooling performance was examined. PIV measurement results clarified the change of flow depending on the configuration. The comparison of experimental results with numerical results shows a reasonable agreement.

Effects of Clearance Between Heating Walls on Natural Cooling in a Channel Model of Electronic Equipment

Making electronic products smaller in size requires air passages in the products to be narrow. For effective thermal management with natural convection, the relationship between cooling performance and a space for the air passages must be clarified. In this study, the natural cooling capacity and flow field in relatively small electronic equipment have been investigated. A channel model was used as an experimental model of electronic equipments. The channel model has two vertical copper walls modeling the printed circuit boards and two transparent walls modeling the casing walls. The walls constitute a vertical channel with the height of 120mm, the depth of 56mm, and the variable width. The width of the channel is called “a wall clearance” here and it is varied from 5mm to 15mm. The copper walls were heated using electric heaters. Temperatures in the model were measured with thermo-couples. In addition, velocity distributions in the channel were quantitatively measured using a particle image velocimetry (PIV). The natural cooling capacity was obtained as functions of the wall clearance and heating power. Temperature rise of the heated wall showed small differences with the clearances of 10 mm and 15mm. However, when the clearance was decreased to 5mm, temperature rise increased. The relationship between Nusselt number and Rayleigh number obtained in this study agrees with those obtained for the parallel plates without side walls. The results of the velocity measurement revealed that the velocity showed a 33% decrease when the wall clearance decreased from 10mm to 5mm. On the other hand, the maximum velocity in the channel showed a 10% increase when the clearance decreased from 15mm to 10mm. The changes in the velocity profiles depending on the heating conditions are clarified.Copyright