Hideo Uzuhashi

Microcomputer Control for Sensorless Brushless Motor

The microcomputer control of a brushless motor without a shaft position sensor is studied. A method which permits the determination of the permanent magnet rotor position by the back electromotive force (EMF) induced in the stator windings and the starting technique which uses the motor as a synchronous motor at standstill are explained. The motor voltage is chopped by commutator transistors to change the motor speed. The control system consists of a 4-b single-chip microcomputer and two quad-comparators.

Experimental study on heat transfer from parallel louvered fins by laser holographic interferometry

Abstract The objectives of this paper are to study experimentally the details of the heat transfer process in louver arrays and to propose the geometrical arrangement of louvers that would be most effective in improving the performance of heat exchangers. That goal is approached via the following steps. In the first step, the temperature field around louvers is visualized, employing the simple flat-louver model made of a thin bakelite plate and thin nichrome foil heaters, and at the same time the heat transfer coefficient on the louvers is measured. The isotherms are visualized by means of laser holographic interferometry. The isotherms for various louver arrangements were obtained; the thermal boundary layer and the wake generated by an upstream louver extending toward the downstream louvers were observed. It is found that the heat transfer coefficient on the downstream louver is sensitive to the behavior of those boundary layers and wakes. In the second step, the arrangement of louvers is examined with the purpose of enhancing heat transfer. A displacement of a downstream louver out of the influence of the heated air wake from the preceding upstream louver is proposed on the basis of both the observation of isotherms and the measurement of heat transfer coefficients in staggered louver arrays. The experimental results indicate that the performance of heat exchangers may be improved by rearranging the louvers with a small-magnitude displacement.