A relation between flow, noise, and system impedance for notebook computers.

Performance of notebook computers is strongly limited by the ability to reject heat from the system. In a typical mainstream design, the airflow driven by the internal fan is responsible for about 80% of the maximum cooling capability, and this airflow impacts all the internal components (CPU, memory, radios, etc.) as well as the top and bottom skin temperatures. Fan flow, in turn, is limited by acoustics. It has been shown that the fan installation conditions inside a notebook computer have an adverse effect on both flow rate and noise. The market trend is toward thinner systems, which generally have a higher system impedance. As impedance increases, system airflow must decrease to maintain a fixed acoustic limit, holding all other variables constant. In order to demonstrate the effect of impedance, this paper describes a simple, two parameter model relating the flow rate in a notebook computer at a given operator position sound pressure level to the impedance index of the system. This relation is shown ...