In the diagram above is the type of axial fan, soft bodied bubble generator we are proposing to use on the x-tent. Being a mobile unit, the b’gens and pumps will most likely be powered by PV. It is essential in this case, that these electrical systems are as efficient as we can make them so as to keep the PV system a reasonable size.
Bubble generators used in Solaroof buildings are not high pressure devises. About 1" water gauge of pressure is adequate for a small building like the x-tent, where the bubble flow path is curved with no corners or u-bends which will increase the pressure needed to push the bubbles through a cavity.
There are many things that can be varied to optimise the efficiency of a b’gen:-
1. Fan blade type
For the x-tent project and other low pressure systems, a vaneaxial fan might possibly the most efficient fan choice.
2. Fan speed and size
Generally speaking, one can be paid off against the other to generate the same air flow. As electric motors tend to be more efficient when running at high speed at low torque, a smaller fan size running at a higher speed, would prove more efficient.
3. Bubble Screen size
The larger the screen aperture for the bubble outlet the greater the pressure and the lower the air speed of the air going into making the bubbles. If we have a smaller screen aperture our air will have greater velocity at lower pressure. Once the ideal fan and motor are selected, maybe adjusting the screen size will enable us to fine tune our b’gen performance.
4. Screen Material
Thicker material will create more resistance, slowing bubble generation. 5mm open cell pond filter has been used with good results.
For the x-tent a 24v dc motor will enable the use of PV supply and will make for a safer unit.
Unsuitable Fans Motors
This is the first fan i used in my solarbubblebuild project in my back yard. I brought it from ebay for £44, which was a good price. This is a centrifugal type fan, which generally speaking provide good amounts of pressure. The motor is 525watts and i estimate it turns out about a 1000cfm. The problem with this fan is that the motor is not drip proof.
Bubble Generator/Destroyer will Get Wet
Because the fan is used to consume old bubbles in a bubble regeneration cycle, it is exposed to wet and soapy conditions. I overlooked this important aspect of the Solaroof system when building my first b'gen. In some respects I feel the name 'bubble generator' is a little misleading and would more acurately be described as a 'bubble generator/destroyer'.
In the UK electric motors are normally given an IP number which indicates the level of 'Ingress Protection', form dust, water chemicals ect. The higher the number the more protected. Because soap reduces the surface tension in water it will increase moisture penetration into seals. Thus for safe and trouble free operation a motor with a IP value of 65 or over is desirable.