A vacuum cleaner works by creating airflow
through the machine. The air enters through a nozzle held close to the
floor
and passes through filters to extract the dust and dirt that is drawn
in by the airflow. Clean air is then exhausted back into the room.
Figure 1. Guidance blades were added to the upper side of a motor
diffuser plate to help re-direct airflow, passing it
past the diffuser plate (left). Johnson Electric says
by doing so, the airflow became more fluid and losses
were diminished. |
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Generally, the greater the airflow, the greater the vacuum created at
the nozzle (depending on nozzle size) and, consequently, the greater
the prospect
of removing more dirt and dust. The company says it would have been easy
to use a more powerful motor with a bigger fan, but this would have led
to increases in product size, weight, power consumption, noise, and cost—product
aspects consumers do not want in their vacuum cleaners.
The
Key Aspect
According to Johnson
Electric, air, like any other fluid material, can
be made to flow from one point to another by creating a pressure differential
between those points and by being channeled to follow a particular route.
The motor drives the fan at a specific power output and converts the mechanical
energy from the moving rotor to the mechanical energy of the moving air.
Unfortunately, as air is pulled into the fan and expelled from
its perimeter, losses occur. Every time the air passes through a channel
or is made to
change direction, there is resistance to the air movement and power losses
occur. In search of a solution, Johnson Electric undertook a study focused
on reducing the losses, thereby increasing the air output power without
increasing the input power to the motor.
Simulation Experimentation
The company utilized a computer simulation software program to review the
product’s air performance by developing a program for inputting all
of the known parameters of dimensions, material, and airflow chamber shapes.
Figure 2. Modifications were made to the blade angles and dimensions
of the impeller to help improve airflow and force.
The design changes helped to increase the performance
of a customer’s vacuum cleaner. |
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The company says the greatest attention was paid to the motor/fan itself,
comprising the impeller (fan) and the diffuser plate, which captures
the air thrown out by the impeller and re-directs that airflow to where
it
is needed. According to Johnson Electric, this particular system is known
as a “flow-through” system because the air is directed through
the motor to cool down the heat in the motor generated by internal motor
losses. The simulation demonstrated that there was excessive turbulence
around the perimeter of the impeller from which the air was forced outwards
by the centrifugal forces of rotation. The company found that this turbulence
was diminishing the useful flow of air.
To reduce the turbulence, guidance blades were added to the upper side
of the diffuser plate. The blades were designed to re-direct airflow downward
from the tangential direction given to it by the impeller, permitting the
air to pass below the diffuser plate. By having a multiplicity of blades,
the exiting air is now re-directed almost immediately, avoiding collision
and turbulence with other channels of air exiting from neighboring impeller
sections. According to the company, airflow now becomes more fluid and
losses are diminished (see Figure 1).
Figure 3. Using a software program, Johnson Electric analyzed
the motor’s air pressure at the inlet of the
impeller. After design changes were made, an increase
in the amount of negative pressure and airflow was
evident. |
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The performance of the impeller itself was also reviewed. Since the air
enters into the eye of the impeller and passes through the impeller to
be centrifuged out from the periphery, the impeller is part of the total
airflow path while also providing the pressure differential to create the
airflow. This type of centrifugal impeller has been in use for many decades,
and it was agreed that the number of blades selected and the shape of the
cover that shrouds the impeller needed to be optimized. The company said
it also felt there was room to optimize the angles of the blades and the
orifice sizes.
Figure 2 shows how the modifications to the blade angles and dimensions
were made. Using the software, the company predicted a change in the air
pressure at the inlet of the impeller. As shown in Figures 2 and 3, there
was a substantial increase in negative pressure, or vacuum, and a valuable
increase in airflow volume.
Confirming the Results
Johnson Electric made tooling changes to produce a new impeller and diffuser
plate according to the suggested design, and a series of tests were performed
to validate both the new impeller and diffuser plate. Tables 1 and 2 illustrate
the improvement in performance for both the new diffuser and the new impeller.
An inlet orifice diameter of 0.75 in is used in both cases. Both tests
confirmed the airflow rate improved due to the design modifications to
the diffuser and impeller.
| |
Model
|
Vacuum |
Performance |
Old
|
297.9
mm H2O |
Initial |
Modified
|
329.6
mm H2O |
Plus
10.6 percent |
Table
1. Diffuser Performance
|
Model
|
Vacuum |
Performance |
Old
|
293
mm H2O |
Initial |
Modified
|
322.4
mm H2O |
Plus
9.8 percent |
Table
2. Impeller Performance
|
|
|
Conclusion
Vacuum cleaner motors have to be designed with their application in mind
and with thought given to how the vacuum cleaner manufacturer will mount
and employ the motor within its cleaner. This requirement does not allow
the motor designer to make drastic modifications to the motor but, nevertheless,
it is possible and advantageous to make a series of incremental improvements
in vacuum cleaner airflow efficiency by fine-tuning the impeller and diffuser
designs within the motor.
This
information is provided by Roger Baines for Johnson Electric.
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