A rack and system for cooling computing devices such as in a data center is disclosed. In one embodiment, the rack supports a plurality of computing devices and comprises a plurality of planar annular sector or trapezoidal shelves, each having one or more positions for holding computing devices. A number of vertical supports may hold the shelves in a vertically spaced arrangement, and an air barrier may be affixed to the rack and have openings that permit exhaust air to flow from the computing devices through the air barrier into a hot aisle. The rack may be configured to be connected to other similar racks to form a vertical annular cylinder, which may be tapered, and the computing devices may be installed to discharge exhaust at an angle relative to a centerline of the vertical annular cylinder to improve airflow.