Algae Scrubber Basics

[acroman]

cuts the temp in half as felt by hand.

That's the key word.

Unless it is thermally conductive paint, it acts as an insulator. Check with a sensitive thermometer.

 

[herring_fish]

1+ There you go.

 

[BeanAnimal]

Yes it does Makes a big difference spraying a thin coat of satin black on it; cuts the temp in half as felt by hand. And this is before being in contact with water.

Delta T does not play a part; it's radiation, not conduction. And it's not insulated on the top; just the sides and bottom.

Plus, it's working on multiple units

Your position contradicts known physics and the established performance (science) of heatsinks. Respectfully, you can't just toss out a scientific term, a misapplied definition and a personal observation and succefully contradict the laws of the universe... I am not looking for a personal fight here, but rather simply trying to ensure that we don't mangle the laws of the universe in order to promote a product or idea.

Is your heatsink capable of moving enough heat to serve the purpose? Maybe, but it is not because you painted it flat black.

black-body radiation - Anything in the universe that has a temperature over absolute zero RADIATES energy (in the form of photons). That is, everything in our known world is a black-body radiator in the context that you used the term. I am not painted black, but can be thought of as a black body radiator, as can your raw aluminum heat sink or your left eyeball or your cold beer can or an iceberg.

Stefan's Law (Stefan/Boltzmann equation) - Defines the quantity of black-body energy radiated from an object (our heatsink in this case). The law relates the emissive power to the area... It says that a body radiates energy at a rate proportional to the 4th power of its absolute temperature times its area....

Notice the 10<SUP>-8 </SUP>, that constant is very tiny... so either your heatsink must be VERY hot AND the surroundings very COLD (delta T) or the heatsink must be the size of a battleship if it is COLD (low emissive power).

Black Paint - The COLOR of the paint being BLACK has nothing to do with black-body (see the tiny constant we are multiplying by). From an emissive standpoint, the paint color is not really relevant. What is relevant about it with regard to emissivity? Its chemical composition, but even that matters little for our given use scenario (temperature and size). I ask again, is your heat sink aglow?

Again, MOST of the energy loss of the heatsink is due to contact (CONDUCTION) between the molecules in the air and the molecules at the surface of the heatsink. Lets say 85% to the 15% emissive (radiation) transfer at the temperatures we are working with. If we add a layer of paint that increases emissivity by 20% but reduces conduction by 10% we are going in the wrong direction....

All that said, raw aluminum is not ideal at either conduction or radiation, so anodizing (or painting) the surface may help in both departments (color does not matter) and will also serve to protect the aluminum. If it is paint, the conductive properties of the paint are more important then the emissive properties (see law governing black-body transfer above). A finned or rippled surface will be better than a smooth surface, etc. Our major (only) concern is conductivity, be it driven by passive or active (fan or convective) air movement.

 

[herring_fish]

One day I was getting ready to barbeque some steaks. I had build a charcoal fire and now it was just about ready. There was a deep, even red glow coming up from the bottom and I had a thought.

How do those guys walk across burning hot coals? Much to the chagrin of my friends, I thrust my hand over the coals and timidly touched the bed with a couple of fingers before retracting them quickly. My friends were stunned and asked what possessed me to do that.

I simply said Hmmm and began to extend my arm again. They tried to stop me but it was too late. I placed my outstretched hand on the hot coals for about 3 seconds and then quickly pulled it back.

They look with amazement as I nonchalantly wiped the ash that suck to my hand which belied the fact that there were a few hot spots that were too hot to handle.

Yes, the coals on the bottom glowed red hot and would have scorched my skin on contact. The gray white ash was an insulator and the stuff at the contact point was relatively cool, "as felt by hand."

Aside from actual contact, without the insulating properties of the ash, the radiant heat would have not have allowed me to bring my hand within an inch of the coals without injury.

Heat will go through ash or paint, regardless of whether it is black or grayish white but it will impede heat transfer to the air unless it is more conductive than aluminum, which is normally not the case.

 

[salty joe]

Hey and a favorite campfire trick of mine is to snatch up a meaty red hot ember with my bare fingers and roll it in my hand. First someone has to not believe I can hold an ember without getting burned.
Back to scrubbing, what do you say?

 

[SantaMonica]

Is your heatsink capable of moving enough heat to serve the purpose?

Yep, the LEDs cool way off after the paint. Try it

 

[Floyd R Turbo]

Is your heatsink capable of moving enough heat to serve the purpose? Maybe, but it is not because you painted it flat black

:headwalls:

Yep, the LEDs cool way off after the paint. Try it

...is it just me, or does this statement just prove the point that Bean made? If I'm understanding this correctly, the paint is not causing the heat to dissipate faster, it is the opposite, the heat is being trapped (in the aluminum) by the paint. The paint is acting as an insulator, resulting in the LEDs getting hotter. The heat sink will feel cooler, but that's because the heat cannot transmit through the paint. The heat is dissipating elsewhere

 

[acroman]

:headwalls:



...is it just me, or does this statement just prove the point that Bean made? If I'm understanding this correctly, the paint is not causing the heat to dissipate faster, it is the opposite, the heat is being trapped (in the aluminum) by the paint. The paint is acting as an insulator, resulting in the LEDs getting hotter. The heat sink will feel cooler, but that's because the heat cannot transmit through the paint. The heat is dissipating elsewhere

This is 100% correct.... due to the laws of thermodynamics

 

[JustinGr]

They make a heat dissipating paint and they make a ceramic paint that helps conduct heat way. Regular paint will eventually flake off.

 

[SantaMonica]

How to build a floating surface scrubber...

 

[ganjero]

How to build a floating surface scrubber...

Looks promising, thanks.

Do you have pictures of an actual unit running?

Are this type of scrubber as efficient as scrubbers having water circulation through the scrubber?

 

[_shorty_]

How to build a floating surface scrubber...

Thanks for sharing.

I noticed the same thing you probably did in running a UAS. That the growth at the surface of the water grew much longer and faster than the rest of the screen. At least in my experience (where the screen was in sump, vertical, and went up just past the surface of the water level)

So, I am interested see results of people trying this.

 

[SantaMonica]

This is actually the same UAS scrubber as "water circulation through the scrubber". It is just 2" deep. After a few cleanings, the growth attaches to the texture on the bottom too.

First harvest video:
http://youtu.be/Zjx4WA-oej0

 

[FishysPlace]

I found this thread about a week ago and am ready to DIY my own ATS. My question is how much screen do I need? I was thinking 10"x10" with some CFL lighting. Ideally I would like to use my siphoned drain for the supply rather then using a tee on my return pump. I was thinking I could re-work my drain pipe so it runs across the width of my sump, 12", have a 1/8" slot running across it with the screen suspended down into the sump. I could make a drawing later if it would help. Thanks for your information!

 

[Floyd R Turbo]

See the posts in my signature below, how much do you feed?

 

[JustinGr]

I have a 14x8 screen that will be lit from one side, I am using an AI SOL Blue on it. I would like to know what happens, and right now, it's 5 inches over the water and at 100% all 3 channels of light. I'll play with the color and intensity over the next few weeks to see what happens, unless someone has already tried this and I would love your data.

Thanks

 

[Floyd R Turbo]

I would not think the SOL blue would work as well as deep red. Wrong primary spectrum, but let us know how it does.

 

[JustinGr]

I'll give it a whirl. It's just an experiment, I have several of these thing. The AI Blue offers the following color spectrum

,

so I'll see what happens.

 

[_shorty_]

your test could be helpful to answer some of the questions posted before about the blue vs red spectrums, specifically in regards to that comment of how blue is typically used for growth vs the red spectrum for flowering of plants.

Your blues are very high intensity in the blue spectrum utilized in photosynthesis. So it'll be interesting to hear about your results. So keep us posted.

 

[Floyd R Turbo]

All hydroponics people and horticulture people I have spoken with have confirmed the need for primarily red and deep red ends of the spectrum. This is why you see so many fixtures with the 6:1 red:blue ratio or higher being sold as grow lights.

There are spectra that are better for flowering or budding that are more of a broad mixture of spectra, generally much more white and blue, but we are not flowering or budding.