Hidemi Shirakawa

Basic study on cooling performance of pulsating airflow around components mounted in high-density packaging electronic equipment (effects of shapes of components on cooling performance)

This study describes a cooling performance of pulsating airflow around an obstruction mounted in a rectangular duct which simulates high-density packaging electronic equipment. Several researchers have reported the possibility of the heat transfer enhancement by pulsating flow. Our study is trying to apply pulsating flow to the heat transfer enhancement method in electronic equipment. In this report, the cooling performance of the pulsating airflow around the cylinder type obstruction and the square prism type obstruction individually. The obstructions simulate components in electronic equipment. It was found that the cooling performance of the obstructions by using pulsating airflow can be observed regardless of the shape of the obstruction.

Possibility of enhancement of cooling performance on heating surface by using intermittent jet flow

This study describes a possibility of an improvement of cooling performance on the surface of heating elements by using an intermittent jet flow like a geyser in nature. An impinging jet flow is widely used for electronics cooling such as CPU coolers and advanced mini-channel devices because the high heat transfer performance can be generally obtained. Due to a miniaturization of electronic equipment, an improvement of cooling performance of cooling devices is strongly needed in order to eject higher heat flux while miniaturizing the dimensions of the cooling devices. We focus on an intermitted jet flow like a geyser in nature. In this study, we investigated the possibility of the heat transfer enhancement on heating surface, which simulates the surface on the cooling channel or the electrical chips, by using the intermittent impinging jet. By controlling the supply flow rate of the jet periodically, the development of the boundary layer on the cooling surface may be inhibited and the net heat transfer performance may be improved. The cooling performance of the intermittent impinging jet on the surface was evaluated experimentally while changing the pattern of the time variation of the supply flow rate. Through the experiment, we clarified the possibility of improving the cooling performance of the impinging jet by controlling the flow rate intermittently.

Effects of Clearance around Square Pillar in Rectangular Enclosure on Cooling Performance of Pulsating Airflow

This study focuses on a development of heat transfer enhancement techniques using pulsating flow for thermal equipment such as electronic equipment and heat exchangers. In this report, the heat transfer performance of the pulsating airflow around the heating pillar mounted in the rectangular enclosure was investigated experimentally while changing the size of the clearance between the enclosure wall and the pillar. The pillar simulates the components mounted in thermal equipment such as fins and electrical components. The rectangular enclosure simulates an enclosure of electronic equipment and heat exchangers. The shape of the cross section of the pillar was square having sides 30 mm. The dimension of the width of the enclosure was changed from 50 mm to 80 mm. It was found that the heat transfer performance of the pulsating airflow became higher than that of the steady flow regardless of the dimension of the clearance. The heat transfer enhancement around heating components by the pulsating flow can be available regardless of the clearance around the components.

Improvement of cooling performance of impinging air by intermittent flow control : Relationship between nozzle diameter and cooling performance

This study describes a possibility of an improvement of cooling performance of electrical components by using an intermittent jet flow like a geyser in nature. In this report, a relationship between cooling performance of intermittent jet on the heating surface and the nozzle diameter was investigated through the experiment. Through the experiment, it was found that the level of the improvement of the cooling performance by the intermittent impingement jet was dependent on the nozzle diameter. However, when the diameter was smaller than 5 mm, the cooling performance was almost the same as that of the steady impingement jet regardless of the decrease of the time-averaged supply flow rate.

CFD-based basic investigation on heat transfer characteristics of pulsating flow in narrow cooling passages

This paper describes a basic heat transfer characteristic of pulsating flow in narrow cooling channel which can be observed in high-density packaging electronic equipment or miniature water cooling channel. There is a strong demand of miniaturization of cooling devices in order to decrease the dimensions of electronic equipment. However, due to the high pressure resistance in the miniature cooling devices, the supply flow rate of the working fluids is generally inhibited and the net cooling performance may become small unless a special miniature pump which has extremely high pressure characteristic is used. Therefore, an innovative idea of cooling technique for miniature electronic equipment should be investigated. Our research focuses on a pulsating flow likes a blood flow in our body. Through our previous studies, we reported that the cooling performance of the heating elements was enhanced by controlling the supply airflow rate periodically. By generating the pulsating airflow, the time-averaged supply flow rate of the cooling air becomes smaller than that of the steady airflow. However, the pulsating airflow can achieve almost the same cooling performance as the steady airflow. Through these backgrounds, in this report, we tried to apply the pulsating flow to the miniature ducts like flow passages in water coolers. We investigated a possibility of heat transfer enhancement in the miniature cooling channel by using the flow pulsation while decreasing the time-averaged supply flow rate of the working fluid in order to inhibit the power consumption of the fluid machineries. The investigation was proposed by the 3D-CFD (computational fluid dynamics) analysis. Through the research, we obtained basic information about the pulsating flow in the miniature flow passage.