New Fluid air

 

The Stall Resistant Jetfan

The following video demonstrates Jetfan’s efficiency over a conventional axial flow fan. The Jetfan (grey one on the left) and the conventional fan both have the same diameter and are belt driven from a singular central motor running at the same RPM. A ping-pong ball has been placed inside the bore that connects the two fans, to function as a piston to gauge which fan produces the greater pressure. As the video clearly demonstrates, the pressure created by the Jetfan easily overcomes the opposing pressure from the conventional axial fan and forces the ping-pong ball to the right. This performance advantage over axial fans also applies at different fan diameters.

ping-pong

 
Back view. One motor drives same size fans
at the same RPM.
Ping-Pong Ball Pressure comparison

 

 

 

 

 

 

 

 

Queensland University of Technology report conclusions

jetfan-man-head
Nylon Jetfan
Glass filled Nylon Jetfan

‘This series of performance tests has demonstrated the advantages of the Jetfan compared to other small fans. The ability of the Jetfan to be operated over a large speed range without the presence of the stall region characteristic of axial fans gives the Jetfan a superior volume rate over a wide range of static pressure requirements.

Where the static pressure requirements fall within the stall region of an axial flow fan, the ability of the Jetfan to be operated at higher speeds without the decrease in volume flow rate associated with stalling, allows the possibility of using a single fan for a larger range of static pressure and flow rate requirements than would be possible with a conventional axial flow fan.’

Recirculation

Conventional fans generally are prone to recirculation which is where the air drawn into the fan reverses direction. It is caused by downstream resistance and blade divergence. In the ping pong ball video the axial fan is suffering re-circulation while the Jetfan is not.

For centrifugal fans, because the distance between the blade trailing edges is relatively large and the blades diverge, the increased pressure air migrates across the blade passageway to the lower pressure area found along the adjacent blade. This is turbulence. In some cases the fluid reverses direction and leaves where it entered; it recirculates.

How the Jetfan geometry differs

 

flow-jetfan

converge-blades

Flow direction through Jetfan

The Jetfan. A is a greater distance than B

Instead of diverging as with conventional fans, the Jetfan blades converge. The trailing edges are much closer together than those of an axial, mixed flow or centrifugal fan. There is a reduction in cross sectional area of the passageways between the blade trailing edges compared to between the leading edges.

This greatly reduces recirculation and in combination with the high solidity and mixed flow geometry, results in a stall free fan of high efficiency. (High solidity means you cannot see between the fan blades facing directly on).

Conventional fans

All conventional fans accelerate the fluid off the blades to an increased speed. (Impart higher kinetic energy). The fluid is immediately slowed by many foil like stationary blades called stators or otherwise is flung (not forced) into a diffuser which has a progressively increasing cross sectional area which enforces a slowing of the air. The fan and diffuser as a stage or fan and stators as a stage is the only way conventional fans can develop the static pressure necessary to be utilized in appliances and larger systems such as Heating, Ventilation and Air Conditioning (HVAC).

Conventional axial flow fans stall readily thus reducing flow and increasing noise. See stall explained in The Coanda Effect and Lift.pdf(section 2.1)

Jetfan does not employ a diffuser

The fluid discharge from the Jetfan blade apertures is at the maximum pressure it is capable of producing so no diffuser or stator blades are required that are common to all other fan types and which are essential to enable conventional fans to achieve a reasonable efficiency.

Noise (Sound Pressure Levels)

When the fluid flung from the blades of a conventional fan encounters the downstream stators or the “cutwater”, entry to the diffuser, (sometimes termed a volute), noise is generated due to “wake collisions”. Noise generating wake collisions do not occur with the Jetfan as it does not employ stators or a diffuser.

That is why in the examples of appliances given in the Jetfan appliance page all performance figures show reduced noise. (reduced Sound Pressure Levels)


Why the Jetfan is unique

The unique mix of blade convergence, high solidity and mixed flow geometry of the Jetfan gives a higher efficiency than other fan types of comparable size (less electricity consumed) and importantly gives a higher “static efficiency”, a feature important to fan and appliance manufacturers because most appliances contain internal structures that obstruct flow which produces back pressure resulting in recirculation.

Conventional axial flow fans do not produce enough pressure for most appliances so flow is reduced. Centrifugal fans produce enough pressure but must employ diffusers and so are much larger with an inherently lower flowrate and they discharge in an impractical direction for most appliances. They are also much more expensive. The breakthrough has been to now have a stall free fan at the low manufacturing cost of an axial fan.

Notes For Engineers

A New Fluid Test Rig below does not incorporate the usual diffusing section immediately after the fan. There are also no stators after the fan. The static pressure offtake is placed before the flow straightening tubes.

 

Test Rig – Testing Procedures comply with ; AS 2360 (Aust), BS 1042 (UK), ISO 5167 (International) standards.
Performance graphs (see example below) therefore reveal the true performance of the impeller itself and not of the whole fan/diffuser/straightening tubes/test pipe system. Engineers will see the significance of this.

test-rig-small

jetfan-graph

The performance table above is of a 128mm (5”) diameter Jetfan. The efficiency is much higher than can be attained by any conventional fan of the same size not employing stators or a diffuser.

Jetfan; a high pressure fan

Many appliance manufacturers purchase fans based on a manufacturers performance graph not knowing the graph is not of the fan alone but of the fan/diffuser/straightening tubes/test pipe system and is not a real world situation. (It is hard to squeeze a 20ft long pipe into a hairdryer to get the manufacturers advertised result!).

Many appliances employ axial flow fans. An axial flow fan manufacturer’s performance graph usually indicates a higher free discharge flowrate than that of a Jetfan graph. However that is a superficial view. The conventional axial flow fan cannot develop sufficient pressure to efficiently overcome the system resistance in most appliances. A Jetfan installed in the same appliance overcomes the resistance and the result is up to 30% more flow through the appliance (with lower “noise”).

That is why the Jetfan gives a higher pressure and flow and lower noise in most small and large appliances and for many industrial applications listed below.

Jetfan Applications:

  • Vacuum cleaners
  • Professional and domestic hairdryers.
  • Wall mounted hairdryers for hotels.
  • Cooling fans for electric motors.
  • Computer cooling.
  • Garden blower/vacs.
  • Toilet handryers.
  • Superior for HVAC applications.
  • Window mounted ventilators.
  • Automotive ventilation.
 

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