Blower / vac tools with improved fan blade noise
Blower/vacuum tools having reduced fan blade noise are provided. A blower/vacuum tool includes a main body extending between a first end and a second end defining an airflow conduit therethrough; and a fan assembly. The fan assembly includes an axial fan having a number of fan blades (n b ), and a motor rotatably connected to the fan. In some embodiments, when ng is in a range from 17-45, the axial fan has a Blade Solidity in a range from 0.0464n b ≤Blade Solidity≤0.089n b calculated by the equation Blade Solidity=c/s where c is the length of the chord line of the fan blades, s=2πr m /n b , and r m is the mean radius of the fan blades. In some embodiments, when the motor operates at a speed of between 21000-38000 rotations per minute (RPM), blade pass frequency (BPF) of the fan assembly as defined by the equation B P F = ( R P M 6 0 ) * ( # of blades ) is greater than 6 KHz.
1 . A blower tool comprising:
a main body defining an airflow conduit therethrough, the main body extending between a first end and a second end; and
a fan assembly disposed between the first end and the second end, the fan assembly comprising an axial fan having a plurality of fan blades, and a motor rotatably connected to the fan;
wherein when the motor operates at a rotational speed of between 21000-38000 rotations per minute (RPM), the fan assembly has a dimensionless flow coefficient Φ in a range from about 0.3 to 0.5 as calculated by an equation
Φ
=
q
/
(
A
)
ω
R
where q represents flow (m 3 /s), A represents cross sectional area at the axial fan (m 2 ), ω represents speed (rad/s) and R represents fan tip radius (m) measured at a blade tip.
2 . The blower tool of claim 1 , wherein the plurality of fan blades comprises from 17 to 45 fan blades.
3 . The blower tool of claim 1 , wherein the axial fan comprises a hub and the plurality of fan blades extend from the hub at a root of each respective fan blade.
4 . The blower tool of claim 3 , wherein each of the plurality of fan blades terminates at a tip of each respective fan blade, the axial fan further comprising an outer ring in contact with the tip of each respective fan blade.
5 . The blower tool of claim 4 , wherein the outer ring rotates with rotation of the axial fan.
6 . The blower tool of claim 4 , wherein the outer ring comprises an inner diameter, wherein the inner diameter of the outer ring is generally equal to an inner diameter of the first end and/or an inner diameter of the second end.
7 . The blower tool of claim 4 , wherein a longitudinal axis extends through a center point of the first end of the main body, a center point of the outer ring, and a center point of the second end of the main body.
8 . The blower tool of claim 1 , further comprising an inlet muffler disposed at the first end of the main body, the inlet muffler including a liner comprising noise-absorbing material configured to absorb noise in a frequency range of 2-6 KHz.
9 . The blower tool of claim 8 , wherein the noise-absorbing material comprises foam.
10 . The blower tool of claim 1 , wherein when the motor operates at the rotational speed of between 21000-38000 rotations per minute (RPM), blade pass frequency (BPF) of the fan assembly as defined by the equation
BPF
=
(
RPM
60
)
*
(
#
of
blades
)
is greater than about 6 KHz.