Takafumi Nakahama

Cooling airflow in unidirectional ventilated open-type motor for electric vehicles

In this paper, the cooling airflow in a unidirectional ventilated open-type motor for electric vehicles (EV) was studied. Numerical fluid analysis was performed on the airflow in the motor through a ventilation path outside the stator iron core inside the frame. It is confirmed that there was a flow separation where air did not flow along the path surfaces. This was observed in a flow visualization experiment using water instead of air. We propose a new structure to prevent air separation and confirm its effectiveness by a visualization experiment. It is also shown that another structure with paths both inside and outside the stator iron core in the frame improves the motors cooling performance. These structures are effective for EV motor downsizing

Influence on Cooling Performance of Jet Impingement Heat Sink Structures

We studied a jet impingement heat sink for cooling modular power semiconductor devices. The purpose of the study was to investigate the influences on cooling performance of simplified structures of the heat sinks that suppresses the jet velocity to avoid pitting corrosion or erosion of the impingement wall. The influence on the cooling performance of partition plates used to prevent mutual interference between jets from circular nozzles was verified. We confirmed the influence on the cooling performance of the wall shape of the header and the influence of the distance from the nozzle to the wall (jet height) in the case of small ratio of the jet height to the nozzle diameter. We verified the influence on the cooling performance of the relation between the directions of the array of multiple jets and the direction of the exhaust flow. Flow visualization was performed using a mock-up model of a jet impingement heat sink. From the visualization, we found the reason on the influence of the relation between those directions. As a result, we found that the structure of the heat sink was able to be simplified maintaining the cooling performance of the conventional heat sink.

Reactor Size Reduction by Slot Jet Cooling

We studied reactor size reduction by applying a slot jet cooling method. In power electronics products such as large power conversion equipments for industry applications (conversion equipments), reactors take up a large proportion of the volume and weight, and miniaturization of reactors is an important issue in reducing the size of conversion equipments. Reactors cooled by forced air convection are generally almost the same size as those cooled by natural air convection. We applied a slot jet cooling method to make cooling air flowing out from two or more slots impinge on the reactor surface at high speed. There have been many reports concerning jets from single slots or two or more slots distributed in parallel. However, many of the details of mutual interference and the exhaust flow along the direction of the slot after jet impingement on a surface remain unknown. Therefore, these basic findings were experimentally verified, and an optimum slot jet giving the greatest improvement in cooling performance, while taking account of exhaust flow, was found. By applying this slot jet cooling, the mass was reduced by about half compared with a conventional reactor.