Fluid moving device and associated method

A fluid moving device (100) includes a rotatable assembly (101), and a plurality of fan blades (102-04) disposed circumferentially around and extending outward from rotatable assembly (101), at least one of plurality of fan blades (102-04) includes shape memory alloy. The fan blade which includes shape memory alloy transforms into a predetermined shape memory state when the fan blade experiences a predetermined temperature which may be as a result of a predetermined temperature of surrounding fluid passing over fan blades (102-04) when rotation of rotatable assembly (101) is at a given speed. The shape memory state increases or decreases volume flow of surrounding fluid when rotatable assembly (101) is rotating at substantially a constant speed. The speed is substantially constant which limits noise generated from fluid moving (100) device while volume flow rate of the fluid moving device is being changed.

FIELD OF THE INVENTION 
The present invention relates to a fluid moving device, and more 
particularly, to an air moving device. 
BACKGROUND OF THE INVENTION 
Acoustic noise generated from an air moving device, such as a fan assembly, 
is problematic in many air cooling applications. As the surrounding air 
temperature rises, the acoustic noise is increased due to an increase in 
rotation speed of a rotating assembly in the air moving device. The 
rotating assembly very often is coupled to a number of fan blades with fix 
airfoil shape. The rotation speed and airfoil shape of the fan blades 
determine the volume flow rate of the fluid moving device. Volume flow 
rate of the device is controlled by controlling the rotation speed to 
maintain a constant air temperature. The rotation speed is increased or 
decreased in response to, respectively, a rise or drop in air temperature. 
Such a control mechanism very often requires a control circuitry which 
consists of resistors, capacitors, or other types of electronic components 
which adds to the manufacturing cost and increases power consumption of 
the fluid moving device. 
Therefore, it is highly beneficial to have a fluid moving device which 
provides low noise operation, and controls its volume flow rate with no or 
minimal control circuitry.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
According to an embodiment of the invention, a fluid moving device includes 
a rotatable assembly, and a plurality of fan blades disposed 
circumferentially around and extending outward from the rotatable 
assembly, wherein at least one of the plurality of fan blades includes a 
shape memory alloy. The term shape memory alloy is applied to a group of 
metallic materials that demonstrate the ability to return to some 
previously defined shape or size when subjected to an appropriate thermal 
procedure. In a two way shape memory alloy, the alloy transforms its shape 
or size at a predetermined transform temperature level, and returns to the 
initial shape or size when the temperature is returned to the initial 
temperature level. A few of such known alloys are nickel-titanium, copper 
zinc aluminum, and copper aluminum nickel alloys. 
Referring to FIG. 1, a fluid moving device 100 which includes a rotatable 
assembly 101 coupled with fan blades 102-04 is shown. Rotatable assembly 
101 may be one of a shaft and a hub. At least one of fan blades 102-104 
that has the shape memory alloy transforms into a predetermined shape 
memory state when the fan blade experiences a predetermined transform 
temperature. Fluid moving device 100 may be mounted on an actuating device 
such a motor, (not shown), for rotating rotatable assembly 101 to cause 
flow of the surrounding fluid. When rotation of the rotatable assembly at 
a given speed causes surrounding fluid to flow, the surrounding fluid 
passing over the fan blades at substantially a predetermined transform 
temperature causes the fan blade to transform into substantially a 
predetermined shape memory state. When the fan blade has the predetermined 
shape memory state, it increases or decreases volume flow of surrounding 
fluid. The change in volume flow of surrounding fluid affects the 
temperature of the fluid. 
Referring to FIG. 2, for example, if the fluid temperature rises to a 
predetermined transform temperature level, a fan blade with shape memory 
alloy changes its initial airfoil shape state 201 to a new airfoil shape 
state 202. The fan blade with airfoil shape state 202 has a higher fluid 
moving capacity than the fan blade with airfoil shape state 201, which 
results in an increase in volume flow rate while the fan is in rotation 
for a constant rotation rate. The increase in the fluid flow causes the 
surrounding fluid to return to a temperature below the transform 
temperature level, and consequently causing the fan blade to return to the 
initial airfoil shape state 201. When the fan blade changes its airfoil 
shape from state 202 to 201, it results in a decrease in volume flow rate. 
The fluid temperature, thus, is controlled by the changes in the airfoil 
shape of the fan blade caused by the fluid temperature. According to one 
benefit of the invention, a need for changing the rotation speed to 
control fluid temperature is eliminated. The rotation of the rotatable 
assembly is maintained substantially at the given speed, thereby, any 
noise generated from the rotation is kept at a constant level. 
Electronic components very often generate heat while in operation. Such 
components must be cooled in order to maintain their optimum operating 
conditions. An air cooling device is normally mounted in an area close to 
the electronic components to cool off the components by moving the air 
that surrounds the components. According to the prior art, to lower the 
air temperature as the air temperature rises, the fan rotation speed is 
increased to increase the air flow rate. The increase in air flow rate 
results in lowering the surrounding air temperature. An increase in the 
rotation speed of the fan also increases the acoustic noise, and power 
consumption of the fan motor which also is a heat source. The acoustic 
noise and power consumption problems are both solved according to one or 
more embodiments of the present invention by eliminating any need to 
increase rotation speed while maintaining a control over the surrounding 
fluid temperature. 
Referring to FIG. 3, in another embodiment of the invention, a fluid moving 
device, such as fluid moving device 100, includes a rotatable assembly, 
such as rotatable assembly 101, and a plurality of fan blades disposed 
circumferentially around and extending outward from the rotatable 
assembly, wherein at least one of the plurality of fan blades, such as fan 
blades 301 or 303, includes a tail piece, such as 302 or 304, coupled at a 
proximity of a trailing edge of the fan blade, wherein the tail piece 
includes a shape memory alloy. The fan blades 301 or 303 may be formed 
from plastic, wood, or metallic materials. The tail piece 302 or 304 is 
made of one of the memory shape alloys. 
Referring to FIG. 4, details of fan blade 301 with a tail piece 302 in two 
coupling positions are shown. An angle 403 of tail piece 302 with respect 
to an angle of airfoil 404 of fan blade 301 at a trailing edge is changed 
to substantially a predetermined memory angle when tail piece 302 
experiences a predetermined temperature. The predetermined memory angle 
changes overall camber of fan blade 301. The change in temperature may be 
as a result of rotation of rotatable assembly 101 in the fluid moving 
device at a given speed which causes the surrounding fluid to flow over 
fan blade 301 and tail piece 302. The predetermined memory angle changes 
the overall camber of fan blade 301 which results in an increase or 
decrease in volume flow of the surrounding fluid. The change in volume 
flow rate is accomplished while the rotation of the rotatable assembly is 
substantially maintained at a constant speed. 
According to an embodiment of the invention, a method of controlling volume 
flow rate of a fluid moving device that includes a rotatable assembly and 
a plurality of fan blades coupled to the rotatable assembly, at least one 
of the plurality of fan blades having a trailing edge, includes coupling a 
tail to the fan blade at the trailing edge, wherein the tail includes a 
shape memory alloy, and rotating the rotatable assembly at a constant 
speed. At a predetermined temperature of surrounding fluid as passing over 
the fan blades, the volume flow rate of the fluid moving device changes 
according to the tail responding to the predetermined temperature which 
causes a change in an overall camber of the fan blade. 
According to another embodiment of the invention, a method of limiting 
noise generated from a fluid moving device while changing volume flow rate 
of the fluid moving device that includes a rotatable assembly and a 
plurality of fan blades coupled to the rotatable assembly, at least one of 
the plurality of fan blades having a trailing edge, includes coupling a 
tail to the trailing edge, wherein the tail includes a shape memory alloy, 
and rotating the rotatable assembly at a constant speed. At a 
predetermined temperature of surrounding fluid as passing over the fan 
blades, the volume flow rate of the fluid moving device changes according 
to the tail responding to the predetermined temperature which causes a 
change in an overall camber of the fan blade. Any noise generated by the 
fluid moving device, thus, is limited since the rotation speed of the 
rotating assembly is maintained at a constant speed. 
Power consumption and the generated acoustic noise from a fluid moving 
device play important factors into market desirability and performance 
optimization of many electronic products, such as personal computers, 
wireless communication products, compact cellular base stations, and 
alike. For example, a compact cellular base station may be mounted at a 
site which is in close proximity of people who can hear any fan noise 
generated from the fan that is used to remove the heat generated by the 
power amplifier in the base station. To limit annoyance of the fan noise, 
a low noise fan is highly desirable. Moreover, in case of power outage, 
the base station may run on reserve battery power which requires efficient 
use of power. In such situation, the power consumption of the cooling fan 
may constitute a large power drain. The present invention provides an 
efficient apparatus and method for moving air to remove heat in cellular 
base stations while conserving power consumption by eliminating additional 
control circuitry and running the fan at a constant speed, and reducing 
fan noise in noise sensitive sites. The expected temperature range of such 
an application is between 0 to 100 degree Celsius. Shape memory alloys 
that can be used at such a temertaure range are readily obtainable. 
While the invention has been particularly shown and described with 
reference to a particular embodiment, it will be understood by those 
skilled in the art that various changes in form and details may be made 
therein without departing from the spirit and scope of the invention. The 
corresponding structures, materials, acts and equivalents of all means or 
step plus function elements in the claims below are intended to include 
any structure, material, or acts for performing the functions in 
combination with other claimed elements as specifically claimed.