US20030123988A1 - Fan blades - Google Patents

Abstract

A set of fan blades comprises a plurality of blades evenly distributed around a hub case, wherein each of the blades has an outer edge from which a projection extends away at an angle.

Description

BACKGROUND OF THE INVENTION
• 1. Field of the Invention [0001]
• The present invention relates to a set of fan blades, particularly to a set of fan blades delivering increased air pressure at reduced noise for better usability. [0002]
• 2. Description of Related Art [0003]
• Producing fans is done with the object of high effectiveness at low noise. Crucial for this object is the design of fan blades, which accordingly is done with great care. [0004]
• As shown in FIGS. 5 and 6, a fan has [0005] blades 10 moving through air 20. At a front edge 11 of each of the blades 10, air 20 splits into an upper stream 21 and a lower stream 22, which are combined again at a rear edge 12 of the blade 10. Since the way from the front edge 11 to a rear edge 12 is longer for the upper stream 11 than for the lower stream 22, the upper stream 11 flows faster than the lower stream 22, according to Bernoulli's law generating under pressure on the upper side of the fan blade 10 and consequently a dynamic lift.
• When the upper and [0006] lower streams 21, 22 reunite at the rear edge 12, different velocities thereof cause a mutual influence, with vortices developing. If each of the fan blades 10 had an unlimited length and an unlimited area, there would be no path from a region of relatively high pressure to a region of relatively low pressure, and direct flow of the upper and lower streams 21, 22 from the front edge 11 to the rear edge 12 would result. Since, however, both the length and the area of each of the blades 10 are limited, the lower stream 22 flows upward to a region of relatively low pressure. Then, as shown in FIG. 6, vortices 23 are generated at outer edges 13. This leads to an increased resistance against the movement of the blades 10 and to a reduced dynamic lift so that the fan works less effective at higher noise.
SUMMARY OF THE INVENTION
• It is the main object of the present invention to provide a set of fan blades having outer edges with projections, which prevent vortices from developing for more effective operation at lower noise. [0007]
• The present invention can be more fully understood by reference to the following description and accompanying drawings.[0008]
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a perspective view of the set of fan blades of the present invention. [0009]
• FIG. 2 is a top view of the set of fan blades of the present invention. [0010]
• FIG. 3 is a sectional view along line [0011] 3-3 of FIG. 2.
• FIG. 4 is diagram illustrating experimental data with regard to static pressure with respect to airflow rate for the present invention and two conventional fan blades respectively. [0012]
• FIG. 5 is a schematic illustration of air currents around a conventional fan blade. [0013]
• FIG. 6 is a perspective schematic illustration of vortices at a conventional set of fan blades.[0014]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
• As shown in FIGS. [0015] 1 to 3, the present invention is a set of fan blades 30 comprising a plurality of blades 32 evenly distributed around a hub case 31. Each of the blades 32 has an outer edge 321 from which a projection 322 extends away at an angle θ. Since the projection 322 points upward, no vortices are generated at the outer edge 321 so that more effective operation at a lower noise is achieved.
• The effect of the present invention has been verified in experiments, the results of which are shown in the following table and the chart shown in FIG. 4. Therein, the present invention is compared with two conventional designs. At the same rotational speed, the present invention attains higher static pressure and higher airflow rate while noise is lower. [0016]

  	Rotational	Static	Airflow
  	speed	pressure	rate	Noise
  	(rpm)	(mm-H2O)	(CFM)	(dBA)

  Present invention	3800	4.0125	32.9525	36.2
  Conventional 1	3800	3.6525	31.9	37.4
  Conventional 2	3800	3.241	23.1709	37.0

• As the above explanation shows, the present invention achieves the object of lower noise and more effective operation for better dissipation of heat. [0017]
• While the invention has been described with reference to a preferred embodiment thereof, it is to be understood that modifications or variations may be easily made without departing from the spirit of this invention which is defined by the appended claim. [0018]

Claims (1)

1. A set of fan blades, comprising a plurality of blades evenly distributed around a hub case, wherein each of the blades has an outer edge from which a projection extends away at an angle.

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