Optional Mini Air Cooling Fan like common sense

In the purchase of "Mini Air Cooling Fan" when general information necessary to understand the following:
★ fan size.
★ OK "Mini Air Cooling Fan" is DC or AC.
★ value of the supply voltage of the fan. For example: AC 220V, 110V, 380V. DC 5V, 12V, 24V, 36V, 48V.
★ fan bearings form, balls or oil.
★ "Mini Air Cooling Fan" of wind speed. For example, the number of cubic meters, or the number of cubic feet per minute per minute.
★ pressure value.