Air moving apparatus and method of optimizing performance thereof

An air moving apparatus for generating cooling air flow in an enclosure including heat generating components, the air moving apparatus having a preferred operating area of output pressures and corresponding air flows and comprising:

• a fan housing;
• a fan having a rotatable hub and plurality of blades mounted to the hub for rotation about an axis of rotation to provide pressurized airflow out from the housing in the enclosure;
• an annular wall of the housing extending about tip end portions of the blades and generally directing airflow out from the housing in an axial direction along the fan rotary axis, there being a pressure differential between higher pressures at the tip end portions of the blades and the fan hub;
• and
• through openings in the annular wall having a predetermined area relative to that of the annular wall to minimize said pressure differential for increasing maximum pressure by a predetermined amount and minimizing loss of airflow at low pressures in the preferred operating area of the fan, wherein the fan blades rotate in a plane of rotation, the fan rotary axis extends normal to the plane of rotation, and the through openings are sized to include a major dimension that extends transverse to the plane of rotation.

In a fan having a plurality of blades that rotate in a housing about an axis of rotation, the housing having an annular wall about the blades, the fan comprising:

• slot openings in the annular wall extending axially generally parallel to the fan rotary axis and sized to provide a desired differential in maximum pressure over that provided by a conventional fan having an unslotted annular wall,
• the slots having an axial length substantially equal to that of the annular wall,
• the slots having a Reynolds number not too exceed a predetermined critical Reynolds number;
• a pressure coefficient for the maximum pressure differential having a predetermined relationship with the number of slots multiplied by the Reynolds number so that the number of slots can be determined to avoid exceeding the critical Reynolds number;
• and
• a width of the slots having a predetermined relationship with the Reynolds number to allow the slot width to be predetermined to achieve the desired maximum pressure differential.

A method of optimizing the performance of an axial flow fan having an efficient operating range thereof, the method comprising:

• providing a fan housing having an annular wall extending about a predetermined number of blades of the fan with pressure equalizing slot openings in the wall spaced from each other in a circumferential direction thereabout;
• selecting one of a plurality of predetermined numbers of slot openings for obtaining a desired maximum pressure in the efficient operating range of the fan, the selected one of the plurality of predetermined slot numbers rendering a Reynolds number for the slots that is less than a predetermined critical Reynolds number;
• deriving a predetermined width in the circumferential direction for the slots based on the rendered Reynolds number, wherein the one of the plurality of predetermined numbers of slots is selected by deriving an initial minimum number of slots and calculating a first Reynolds number therewith, comparing the calculated first Reynolds number to the critical Reynolds number, and, if the calculated Reynolds number is greater, deriving a second higher number of slots having a predetermined relationship with the initially derived minimum number of slots and calculating a second Reynolds number therewith, comparing the calculated second Reynolds to the critical Reynolds number, and repeating the deriving of slot numbers, calculating of Reynolds numbers, and comparing to the critical Reynolds number until a Reynolds number is calculated that is less than the critical Reynolds number to determine the number of slots that will be used to provide the desired maximum pressure, and wherein the initial minimum number of slots, is derived by subtracting (1) one from the predetermined number of fan blades, b, and the higher numbers of slots are calculated by multiplying (b−1) by successive numbers greater than (1) one until the Reynolds number is below the critical Reynolds number;
• sizing the slots in the annular wall so that the slots extend axially along their length for the full axial distance of the wall;
• deriving a pressure coefficient based on the desired maximum pressure increase;
• and
• deriving a number corresponding to the number of slots multiplied by a Reynolds number based on a predetermined relationship with the pressure coefficient to allow the slot number to be varied until said rendered Reynolds number below the critical Reynolds number is achieved keeping the derived number constant to maintain the derived pressure coefficient the same for obtaining the desired maximum pressure increase.