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brushless dc (bldc) fans have become the most popular mode of electronics cooling in recent years. they impart kinetic energy to a localized air mass and increase the fluid velocity, which in turns increases the convectional coefficient, h, and increases the amount of heat removed. the fluid velocity is directly proportional to h through the reynolds and nusselt number equations. the proliferation of compact and cheap dc power supplies has relegated ac fans to the fringes of the cooling industry.

compared to brushed dc motors, bldc motors have various advantages, such as having easier speed control, which therefore allows better optimization of fan speed, efficiency,and acoustic performance. brushless motors also do not have any mechanical brush contacts with the commutator, which reduces the motor temperature and increases the bearing life, and consequently the overall fan life.

due to it's larger popularity in the sanyo denki product lineup, this document will mainly with axial fans. axial fans are defined as an air-moving device where the airflow is in a direction parallel to the axis of the impeller. the air exiting the fan is imparted with energy from the rotating blades that increases the total pressure and velocity of the flow.