Stelth Principle

Stelth Principle

pump case

Conventional centrifugal water pumps accelerate water via an impeller which flings it into nearby geometrically expanding passages that slow it, thereby raising its static pressure which in turn overcomes the resistance of the system including filters etc.

New Fluid Technology Pty Ltd`s "SUPA STELTH" pump works entirely differently to conventional pumps. The water is accelerated via a unique high efficiency, patented impeller. However by far the main feature of the SUPA STELTH pump is the internal shape of the pump casing itself.

Conventional diffusers are the major source of pump noise but are not employed in the STELTH.

Below; another version of the STELTH pump: shorter, more efficient and easy to manufacture.


The pump casing has the internal geometry of a hat box. The impeller tangentially flings the water into the casing generating a high rpm vortex. Isaac Newton described how a rotating parallel sided bucket induced water to spin up to the rpm of the bucket.

Due to its weight and viscosity, the water becomes a "Solid Body" vortex.

In a solid body vortex all the water molecules line up like wheel spokes as well as in the axial direction i.e. there is no shear between the molecules. This is different to a bag-less vac vortex. A solid body vortex cannot form if there is a small divergence of the bucket walls or a small slope to the bucket bottom.

drum casingWe also add a large diameter drum (spigot) integral to the impeller which entrains and spins the water. i e, internal rotating structures can generate the solid body vortex as efficiently as the rotating bucket walls of Newtons experiment. You could think of the drum or spigot as an "axle" to which the "Solid Body Vortex" or "wheel of water" then attaches and spins around with.

The STELTH develops its pressure by centrifugal force at the solid body vortex periphery only millimetres inside the casing wall.

The result is a higher efficiency than conventional centrifugal water pumps.

This is because the water undergoes less momentum and direction changes than with conventional water pumps.

THE LOW SPEED TREND

Pool pumps are one of the most energy hungry appliances.

California legislation requires at least 2 speeds for pumps and soon multiple speed pool pumps will be universally required—why?

Australia also requires energy stars and noise levels on all pool pumps from 2011.

LOW SPEED INCREASES EFFICIENCY AND REDUCES NOISE

Within the pool industry worldwide the trend is to lower RPM for pool filtration.

The reason is that as the water speed reduces through the filter and the overall system, the energy requirements (electricity) reduces by the cube. That means that if the water speed is halved the electricity required reduces a massive eight times.

Of course the time to do the filtering increases significantly but the overall result is reduced power consumption and greatly reduced noise.

THIS IS ONLY OK FOR CONVENTIONAL PUMPS BUT GREAT FOR THE SUPA STELTH CONCEPT.

For pool filtration efficiency is expressed as "wire to water".

The volts into the motor are multiplied by the amps to derive electrical watts.

Water flow at a particular point on the performance chart is multiplied by the pressure at the same point. The result is called watts of water power. That is then divided by the electrical watts to arrive at "wire to water" efficiency.

Conventional pumps employ diffusers which the impeller flings the water into. The water speed must be very high (high kinetic energy). The diffusers then enforce a slowing of the water which transforms the high kinetic energy into static pressure.

With the conventional pump the highest kinetic energy is found at the impeller periphery which may be 128 millimetres diameter for example.

THE SIGNIFICANT STELTH DIFFERENCE

With the STELTH the highest kinetic energy is found further out inside the pump casing wall (which may be 200 millimetres diameter) because the "solid body rotation" has caused the water molecules to line up like spokes (on a wheel) with no shearing action occurring between them.

So the conventional pump and the STELTH may have the same impeller diameter rotating at the same rpm but the highest water speed in the conventional pump may be 19 meters per second found at the impeller periphery but with the STELTH the water speed may also be 19 meters per second at the impeller periphery but simultaneously can be 24 meters per second further out closer to the pump casing wall.

The STELTH pump then is actually a centrifuge working in the same way that a milk and cream separator works. The higher density watery milk goes to the outside and the lighter cream migrates towards the centre.

Water going that fast (approximately 45 revolutions per second at full flow, giving a speed of about 24 meters per second) cannot go out the pump outlet that fast.

The downstream filter and system impose a resistance and so the water may enter the outlet pipe at only 2 meters per second at pool filtration flow requirements.

Because we cannot have our cake and eat it too, nature organizes the fluid dynamics near the inside of the pump casing. The total energy within the water there cannot change. We cannot have high kinetic energy AND also high static pressure found in the water if the sum of the two would exceed the total possible.

The centrifugal force increases the static pressure closer to the inside wall. That static pressure can only be high if the water has slowed very significantly. That could be inconsistent with the "solid body vortex" but what happens is a slow moving layer of water hugs the entire circumference of the inside of the pump circular casing and is moving at the same speed as the outlet water speed.

That means there is a transition zone a very short distance from the inside wall where there IS shear between the molecules.

EXPERIMENTAL RESULTS

Free floating paddles (telltales) are placed in the rotating water vortex and a stroboscope is employed to determine the rpm of the water at any distance from the axis of rotation. (A transparent pump casing is used). It is found that the water molecules do in fact line up in the radial and in the axial direction according to the vortex theory of solid body rotation.

When some of the water is leaving the pump casing at 2 meters per second the water speed (only millimetres from the wall) may still be in EXCESS of 20 meters per second!!

That very thin transition and shear area is spread right round the 360 degrees and so a kind of diffusion takes place.

Consequentially the outlet water speed reduction from say 20 meters a second to 2 meters a second does not have to happen abruptly over the short distance of the rectangular outlet which may be only 20 millimetres across.

This slower moving water layer (just millimetres thick) functions as a supporting "bush" for the much faster water in the vortex.

LOW SPEED ADVANTAGE

Because the conventional water pump diffusers require high speed (high kinetic energy) water to be flung into them, when the rpm and consequently the water speed is reduced, the dynamic pressure reduces according to the inverse square law. That means that if water speed flung off the impeller is halved the kinetic energy is reduced 4 times. If water speed there reduces 3 times the kinetic energy is reduced 9 times.

This does not apply to the STELTH. It has no diffusers and because of the "solid body rotation" its internal water speed is higher than that in a conventional pump.

The result is much higher "wire to water" efficiency than conventional pumps at the lower speeds that are the worldwide pool industry trend right now.

There are other industries that can now take advantage of the low speed efficiency of the SUPA-STELTH pump.

NOISE REDUCTION

The noise in a conventional pump is from the water wake collisions with the diffuser inlets or the water interaction with the "cutwater" if a single diffuser, termed a volute, is used.

The STELTH uses no diffusers or volute and so the noise is reduced to usually several times less than conventional pumps.

MANUFACTURING

The STELTH pump is extremely easy and inexpensive to manufacture. By eliminating the diffuser (or volute & cutwater) is a significant saving

The pump casing itself is a simple "hat box" shape and the outlet moulding tool simply engages and disengages from the outside making for uncomplicated manufacturing.

All moulding tools and materials are STOCK standard.

By introducing internal "snap-inserts" of varying thickness into our SS "Wet-end" allows any  motor to effectivley vary its HP rating. This means for example a 2hp pump can reduce its internal dimensions thus unloading the motor in steps (depending on the insert) down to say 1hp. There are warehousing savings of not having to stock several different pump sizes. A series of colour coded "snap-inserts" and impellers that can be matched together and  retrofitted by the customer or at point of manufacture (depending on the pump application) is unique.