Centrifugal blower system and fuel cell incorporating same

A centrifugal blower system comprising: (a) a series of blower units, each blower unit in the series comprising a casing having an axial inlet and a radial outlet, an impeller disposed within the casing for drawing a gaseous medium at a first pressure into the inlet and expelling gaseous medium at a second higher pressure through the outlet and a motor for driving the impeller; and, (b) a duct connecting the outlet of at least one blower unit in the series with the in-let of at least one other blower unit in the series, (c1) the interior walls of duct (b) configured to be substantially parallel to the trajectory of the gaseous medium expelled from the outlet of a blower unit to which the duct (b) is connected, and (c2) a gas stream housing for receiving the gas stream from the outlet of a successive blower unit in the series, the walls of the gas stream housing being configured to be substantially parallel to the trajectory of the gaseous medium expelled from the outlet.