Takashi Fukue

Evaluation of cooling performance of a piezoelectric micro blower in narrow flow passage

This paper describes a cooling performance of a novel miniature piezoelectric micro blower. We especially focus on an investigation whether the piezoelectric micro blower is available for a novel cooling method of high-density packaging electronic equipment or not. In order to investigate the effectiveness of the piezoelectric micro blower, an understanding of the blower performance (P - Q curve) becomes important. Especially, the effects of narrow flow passages and components around the blower on the P - Q curve should be investigated in order to apply the blower to high-density packaging electronic equipment. In addition, because of the miniature structure of the piezoelectric micro blower, a supply flow rate of the blower becomes relatively small. Therefore, an estimation of a net cooling performance of the piezoelectric micro blower should be investigated. In this paper, we evaluated a cooling performance of the piezoelectric micro blower. We firstly evaluated the P - Q curve of the piezoelectric micro blower. Especially the effects of the electrical components mounted near the blower on the P - Q curve. It is found that the performance characteristic of the proposed blower is almost not changed regardless of the existence of the components near the blower. In addition, we secondly investigated the cooling performance of the proposed blower in a narrow flow passage with finned heat sinks experimentally. Through the investigations, we evaluated the effectiveness of the piezoelectric micro blower as the cooling method of high-density packaging electronic equipment.

Relationships Between Supply Flow Rate of Small Cooling Fans and Pressure Drop Characteristics in Electronic Enclosure

This study describes a prediction method of a supply flow rate of axial cooling fans mounted in high-density packaging electronic equipment. The performance of an air-cooling fan is defined by its P – Q (pressure difference – flow rate) curve. Generally the operating point of a fan, which is the operating pressure and the flow rate in equipment, is the point of intersection of a P – Q curve and a flow resistance curve. Recently, some researchers reported that catalogue P – Q curves have not necessarily been able to predict a correct supply flow rate in thermal design of high-density packaging equipment. Our study aims to improve prediction accuracy of the supply flow rate. In this report, a relationship between the P – Q curve and a pressure drop characteristic in a fan-mounted enclosure was investigated. A test enclosure which includes an obstruction was mounted in front of a test fan and the supply flow rate of the fan was measured while changing the obstruction. Additionally the flow resistance curves in the test enclosure were measured and the relationship among the supply flow rate, the P – Q curve and the flow resistance curve was investigated. It is found that the correct supply flow rate can be obtained by using the flow resistance from the enclosure inlet through the fan outlet and the revised P – Q curve which is made compensation for the pressure drop at the inlet and the outlet of the fan.Copyright

Measurement of Performance Characteristics of a Piezoelectric Micro Blower

This study conducts a measurement system of a performance of a piezoelectric micro blower. Electronic equipments such as laptop computers and cellular phones become smaller and thinner while their functions become more complex. As a result, a lot of components are mounted in an electronic enclosure and flow passages for the cooling air become narrow. This causes significant pressure drop and general cooling fans cannot supply enough cooling air. To improve cooling performance in small electronic equipment, a new air supply system which combines smaller and thinner size with a high pressure performance characteristic is needed. We focused on a novel piezoelectric micro blower. This blower can supply the airflow with high static pressure using the vibration of the piezoelectric element. This may produce a forced convection cooling with low electric power regardless of the size of electronic equipment and packaging density of electrical devices. However, to predict accurate cooling performance of the piezoelectric micro blower in thermal design, we have to obtain a correct supply flow rate of the blower because the cooling performance of forced convection is significantly dependent on the supply flow rate. Generally, an operating point of the blower, which is the operating pressure and the flow rate in electronic equipment, is the point of intersection of performance characteristic curve, which is the relationship between the blower’s pressure rise and the supply flow rate, and flow resistance curve in equipment. Therefore the measurement of the performance characteristic curve is most important.We tried to develop the measurement system of the performance characteristic curve of the piezoelectric micro blower with high accuracy. We succeeded to measure the relationship between the supply flow rate and the static pressure rise of the micro blower. Moreover, in order to clarify whether the micro blower is available for a cooling method of high-density packaging electronic equipment or not, we tried to investigate the effects of the obstruction, which is mounted in front of the blower, on the performance characteristic. Then, we confirmed whether the performance of the blower is changed by the components mounted near the blower or not.Copyright

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.

Effects of obstruction in front of a piezoelectric micro blower on performance characteristics

This study describes a performance characteristic of a piezoelectric micro blower which may be available for a novel cooling technology of portable electronic equipment. We especially focus on the investigation whether the micro blower is available for a cooling method of high-density packaging electronic equipment or not. In this paper, the effect of the obstruction, which simulates the electrical components and is mounted very near the blower, on the P-Q characteristic was investigated. Especially we tried to measure the performance characteristic of the micro blower when the obstruction was mounted in front of the blower. From the experiment, it is found that the performance characteristic of the proposed micro blower is almost not changed regardless of the existence of the obstruction in front of the blower. There is a possibility that this novel blower can achieve a high cooling performance regardless of a packaging density of electronic components in electronic equipment.

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.

Basic Study on Transient Temperature Response of Papers in a Thermal Transfer Printer

This study describes temperature response of papers in a thermal transfer printer. Thermal transfer printer produces an image by heating heat sensitive papers using a thermal head. The print quality of the thermal printing is highly dependent on a temperature response of the paper.Our research targets to develop a control technique of temperature of the printing paper to improve the print quality of the thermal transfer printer. In this report, our special attention is paid to investigate the temperature response of a paper when the heat is applied by the thermal head. The temperature transient in the paper is measured while changing the type of the paper. Moreover, in order to investigate a relationship between thermophysical properties of papers and the temperature response, the thermophysical properties are measured. A thermal network analysis is additionally performed and the effects of a contact resistance between the paper and the thermal head are also investigated. It is found that transient temperature response of the printing paper is strongly dependent on a type of the printing paper and the level of an input heat. A change of the temperature response is caused by the difference of thermophysical properties of the paper and a variation of a contact resistance between the paper and the thermal head.Copyright

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.

Basic investigation of cooling performance at upstream side of bend to develop 1-dimensional thermal design scheme

This study describes a cooling performance in a rectangular bend that a sudden contraction or a sudden expansion simultaneously occurs. This flow pattern can be found in high-density packaging electronic equipment such as laptop or desktop computers. In order to predict cooling performance in electronic equipment using rapid thermal design scheme such as a thermal resistance network analysis, a prediction of heat transfer coefficient cannot be done easily by using conventional formulas for calculating the performance in simple ducts. This paper especially investigated the heat transfer in the upstream side of the bend in the rectangular duct with the sudden contraction or the sudden expansion through the CFD analysis. We found that the cooling performance was dependent on the cross-sectional area ratio of the bend significantly.