Characterization of airflow impedance in two types of telecommunications chassis

The airflow impedance curve for two common configurations used in telecommunications chassis were measured and examined in non-dimensional coordinates, such that data obtained at sea level may be scaled to increased altitudes. The results show that the non-dimensional airflow impedance curves for both chassis configurations predict minimal changes in air velocity with increased altitude for most of the Reynolds number ranges studied. However, for one chassis configuration studied, a slight decrease in air velocity is predicted with increased altitude. Because a nonconservative component temperature predictions at high altitude will result if constant air velocity is assumed, the decrease in air velocity should be accounted for if there are critical electronic components operating near their maximum temperatures. Reliable operation of electronic components in telecommunications equipment up to 4000 m (13,000 ft.) is a requirement of the Network Equipment and Building Standard (NEBS).