What a centrifugal fan does differently
A centrifugal (radial) fan pulls air in parallel to its shaft and throws it out at 90° through a scroll-shaped housing, rather than pushing air straight through like an axial fan. That change in direction is what lets a centrifugal fan build significantly more static pressure for a given size — the reason it gets specified whenever air has to travel through ducting, a filter bank, or a restrictive enclosure rather than blow across open space.
Within "centrifugal," equipment cooling catalogues typically split further into true centrifugal blowers, tangential (cross-flow) fans, and general-purpose blowers. Tangential units produce a long, even curtain of airflow along their length — common in space heaters, laser printers and thin enclosures — where a true centrifugal unit concentrates its output through a single round or rectangular outlet.
The two specs that actually decide sizing
Air flow (m³/h, m³/min or CFM) is the number most people search for first, but a fan's flow rating is only true at zero back-pressure — free air with nothing in the way. The moment that air has to pass a filter, travel down ducting, or exit through vents, the real flow drops, and how much it drops depends on the fan's static pressure rating (measured in Pa) plotted against your system's actual resistance.
In practice: estimate the heat load you need to remove and the temperature rise your enclosure or space can tolerate to get a required air-flow figure, then check that figure against the fan's air-flow curve at the pressure your ducting/filter/enclosure will actually present — not the unrestricted, headline number on the datasheet.
AC or DC — and what else to confirm before ordering
Supply type is fixed by the motor design and can't be adapted after the fact. DC fans (commonly 6–48V in equipment-cooling applications) suit panel and electronics cooling powered from a control circuit; AC fans (115V/230V is standard) suit mains-powered ventilation. Confirming this — along with IP rating for any exposure to dust, moisture or washdown, and a noise-level figure if the fan runs in an occupied space — up front avoids the most common reason a fan order gets returned.