초록 ▼

A fan is provided for use with a casing having a bellmouth and a conduit portion. The fan has a hub, a number of blades extending from the hub, and a shroud. In cooperation with the casing and the conduit portion surrounding the shroud, the shroud has means for generating a separation bubble effecti

A fan is provided for use with a casing having a bellmouth and a conduit portion. The fan has a hub, a number of blades extending from the hub, and a shroud. In cooperation with the casing and the conduit portion surrounding the shroud, the shroud has means for generating a separation bubble effective to limit a recirculation flow.

대표청구항 ▼

What is claimed is: 1. A fan comprising: a hub; a plurality of blades extending from the hub; and a shroud unitarily formed with the blades and having: a first rim; a second rim; inboard and outboard surfaces extending between the first and second rims, wherein: along a portion of the shroud prox

What is claimed is: 1. A fan comprising: a hub; a plurality of blades extending from the hub; and a shroud unitarily formed with the blades and having: a first rim; a second rim; inboard and outboard surfaces extending between the first and second rims, wherein: along a portion of the shroud proximate the second rim, the outboard surface is radially inwardly convergent toward the second rim along a longitudinal span effective to generate a separation bubble to limit a recirculation flow. 2. The fan of claim 1 wherein: the longitudinal span is at least 3 mm. 3. The fan of claim 1 wherein: the first rim has a first diameter; and the second rim has a second diameter greater than the first diameter. 4. First and second fans of claim 3 stacked with the first rim of the first fan received concentrically within portion of the shroud of the second fan. 5. The fan of claim 1 in combination with a casing including: a first portion having a first rim having a third diameter, less than the first diameter; and a second portion, at least partially surrounding the shroud. 6. The combination of claim 5 wherein: the first portion is a bellmouth of essentially outward longitudinal concavity; and the second portion is a stack, extending beyond the bellmouth. 7. The combination of claim 6 wherein: the shroud first rim faces upward; and the stack has a distal end beyond the shroud first rim. 8. The combination of claim 5 wherein: the casing first portion is partially within the shroud. 9. The fan of claim 1 wherein a cross-sectional median of a portion of the shroud proximate the second rim is radially inwardly convergent toward the second rim along a longitudinal span of at least 3 mm. 10. The fan of claim 1 wherein the hub is unitarily formed with the blades and the shroud. 11. The fan of claim 1 wherein the hub is formed as an open cup having a sidewall and a base. 12. The fan of claim 11 wherein the hub further comprises: a central boss for engaging a shaft mounting insert; and a plurality of substantially radially-extending ribs extending from the boss to the sidewall and along the base and having rims. 13. The fan of claim 12 wherein: for each of the blades, there is a single associated one of the ribs aligned with a root such blade. 14. The fan of claim 12 wherein the hub further comprises: for each of the ribs, a longitudinally and transversely-extending post formed in an outboard portion of the associated rib. 15. The fan of claim 14 wherein: each post has a cross section characterized by a flat central web and first and second terminal protuberances; inboard of the associated post, each of the substantially radially-extending rib rims generally increases in longitudinal position from inboard to outboard; and outboard of the associated post, each of the substantially radially-extending rib rims is of generally constant longitudinal position from inboard to outboard. 16. The fan of claim 1 further comprising a polymeric cover secured at an open end of the hub. 17. The fan of claim 1 in combination with an electric motor driving the fan. 18. A fan system having: a motor, a fan according to claim 1 driven by the motor; and a casing having a conduit at least partially surrounding the shroud. 19. The fan system of claim 18 wherein: the casing has a distal rim downstream of a downstream rim of the shroud. 20. The fan system of claim 18 wherein: the shroud inboard and outboard surfaces are dimensioned effective to permit a plurality of identical fans to be stacked in a partially nested configuration when off-motor.