Centrifugal fan

1. A fan comprising:

a fan housing located on an axis, and having axially front and rear sections that together define a chamber;

an inlet in the front section through which air can enter the chamber;

an impeller in the chamber configured to rotate about the axis to drive the air radially outward; and

a trough-shaped channel in the rear section, extending circumferentially about the axis from a first end of the channel to a second end of the channel, configured to channel the air away from the first end circumferentially toward the second end;

the channel having a radially extending width and an axially extending depth, the depth increasing from the first end toward the second end such that, over a 90° range, an increase in the depth is greater than twice an increase in the width.

2. The fan of claim 1 wherein the channel width increases over the 90° range.

3. The fan of claim 1 wherein the 90° range extends from a first location in the channel located 90° from the first end, to a second location in the channel located 180° from first end.

4. The fan of claim 1 wherein, at a location in the channel diametrically opposite the first end, the channel depth is greater than the channel width.

5. The fan of claim 1 wherein the rear housing section has a surface bordering the channel that extends, at a location in the channel diametrically opposite the first end, linearly rearward along a distance of greater than 65% of the channel depth.

6. The fan of claim 1 wherein the channel depth increases approximately linearly with circumferential distance over the 90° range.

7. The fan of claim 1 wherein the channel width increases by less than 30% over the 90° range.

8. A fan comprising:

a fan housing located on an axis, and having axially front and rear sections that together define a chamber;

an inlet in the front section through which air can enter the chamber;

an impeller in the chamber configured to rotate about the axis to drive the air radially outward; and

a trough-shaped channel in the rear section, extending circumferentially about the axis from a first end of the channel to a second end of the channel, configured to channel the air away from the first end circumferentially toward the second end and having, at a reference location in the channel diametrically opposite the first end, a depth greater than the width of the channel.

9. The fan of claim 8 wherein at another reference location, 270° from the first end toward the second end, the channel depth is greater than 1.5 times the channel width.

10. A fan comprising:

a fan housing located on an axis, and having axially front and rear sections that together define a chamber;

an inlet in the front section through which air can enter the chamber;

an impeller in the chamber configured to rotate about the axis to drive the air radially outward; and

a trough-shaped channel in the rear section, extending circumferentially about the axis from a first end of the channel to a second end of the channel, configured to channel the air away from the first end circumferentially toward the second end, in which, at a reference location in the channel diametrically opposite the first end, a surface of the rear housing section, bordering the channel, extends linearly rearward along a distance of greater than 65% of the channel depth.

11. The fan of claim 10 wherein at another reference location, 270° from the first end, the surface extends linearly rearward along a distance of greater than 80% of the depth of the channel.

12. A fan comprising:

a fan housing located on an axis, and having axially front and rear sections that together define a chamber;

an inlet in the front section through which air can enter the chamber;

an impeller in the chamber configured to rotate about the axis to drive the air entering the chamber radially outward; and

a trough-shaped channel in the rear section, extending circumferentially about the axis from a first end of the channel to a second end of the channel, configured to channel the air away from the first end circumferentially toward the second end, and having a width that increases by less than 10% over a 90° range along the channel extending from a location 90° from the first end to a location 180° from the first end.

13. The fan of claim 12 wherein the distance between the channel and axis is uniform about the axis.

14. A fan comprising:

a fan housing located on an axis, and having axially front and rear sections that together define a chamber;

an inlet in the front section through which air can enter the chamber;

an impeller in the chamber configured to rotate about the axis to drive the air entering the chamber radially outward; and

a trough-shaped channel in the rear section, extending circumferentially about the axis from a first end of the channel to a second end of the channel, configured to channel the air away from the first end circumferentially to the second end; and

an outlet channel extending rearward from the second end to redirect the air to flow axially away from the collection channel;

wherein the impeller includes a backplate with a radially outer periphery and blades extending forward from the backplate, and the outlet channel is closer to the axis than is the periphery of the backplate.

15. A fan comprising:

a fan housing located on an axis, and having axially front and rear sections that together define a chamber;

an inlet in the front section through which air can enter the chamber;

an impeller in the chamber configured to rotate about the axis to drive the air entering the chamber radially outward; and

a trough-shaped channel in the rear section, extending circumferentially about the axis from a first end of the channel to a second end of the channel, configured to channel the air away from the first end circumferentially to the second end; and

an outlet channel extending rearward from the second end to redirect the air to flow axially away from the collection channel;

wherein the outlet channel has a laterally extending width that is smaller than its axially extending length.

16. A fan comprising:

a fan housing located on an axis, and having axially front and rear sections that together define a chamber;

an inlet in the front section through which air can enter the chamber;

an impeller in the chamber configured to rotate about the axis to drive the air entering the chamber radially outward; and

a trough-shaped channel in the rear section, extending circumferentially about the axis from a first end of the channel to a second end of the channel, configured to channel the air away from the first end circumferentially to the second end; and

an outlet channel extending rearward from the second end to redirect the air to flow axially away from the collection channel;

wherein the outlet channel has a laterally extending width that is greater than its radially extending height.

17. A fan comprising:

a fan housing located on an axis, and having axially front and rear sections that together define a chamber;

an inlet in the front section through which air can enter the chamber;

an impeller in the chamber configured to rotate about the axis to drive the air entering the chamber radially outward; and

a trough-shaped channel in the rear section, extending circumferentially about the axis from a first end of the channel to a second end of the channel, configured to channel the air away from the first end circumferentially to the second end; and

an outlet channel extending rearward from the second end to redirect the air to flow axially away from the collection channel;

wherein the outlet channel is defined by an outlet tube that is part of the fan housing and rigidly fixed with respect to the front and rear housing sections.