Yeah, I've been using canisters, and they're expensive and a chore (and because of that, it encourages me to give the plants much less than would be ideal).

The basic process is potassium carbonate/bicarbonate swing absorption. Potassium carbonate absorbs CO2 (and H2O) from the air at low temperatures , forming bicarbonate, but the bicarbonate emits CO2 (and H2O) at high temperatures. So the system has two modes: one, a powerful radial blower blows air through a pumice bed packed with potassium carbonate so that it absorbs CO2 (more specifically, it first absorbs H2O, and then CO2); and in the other, the fan is shut off and a PTC heater turns on to heat the pumice bed.

I'm trying to make the whole system as passive as possible. Since the fan is so powerful (you have to move a LOT of air to capture CO2), it's designed to blow dampers shut or open that control its path, while a different path opens up when the fan is not on. The PTC heater being on will automatically force the fan off. I've also set up (cross my fingers whether it works...) a weight-based system to control fan/heater switching. The core is PPS-CF (super heat tolerant) and mounted on springs, so it should move downward as it absorbs more moisture and CO2, and when it's full, it should force the fan off (even if my greenhouse controller hasn't requested CO2, aka triggered the PTC heater). And when the PTC heater is on, it rises from losing H2O and CO2 mass, and if it rises too much, that triggers a switch to force the fan off.

I'm also perhaps overcomplicating it and making a rod for my own back, in that I've designed it so that both modes have the air travel through a system of (also 3d printed) heat exchangers (in general, heat exchangers working with air have no issue with being made of plastic, because the heat flow from the air to the wall is slower than heat transfer across the wall). So these are big and made of multiple parts, in order to not slow down the airflow from the blower too much. But the idea is that the CO2+H2O flowing outwards cools and deposits H2O in the exchanger (then a secondary heat exchanger re-heats it to drive the convection force), while in capture mode, the incoming air can use that H2O instead of having to rely just on atmospheric H2O (which is viable, but does impose a capture delay). And of course, it helps maintain a warmer temperature inside the core on very cold days that might slow down the reaction (it's designed to be able to be mounted outside; the bulk of it will be printed in ASA).

Right now I'm in that annoying phase of prototyping where you print chunks of parts out, see if they actually print right ("whoops, there are supports in this area, but I CAN'T REACH THAT!"), actually fit together right (for example, dampers not jamming in their paths), the non-printed parts actually fit (I keep screwing up the mount for the blower, lol), that sort of stuff.

Dunno, but it's a fun project, and hopefully it will work :) Then the question for me (if it actually works well) will be, just release the plans open source, or actually manufacture them (and if so, continue 3d printing, or switch to injection moulding - though that would take redesign!). Because I've not found anything else like it on the market. There are some greenhouse CO2 capture systems out there, but they're gigantic and super-expensive, with even the monthly service contracts being in the hundreds of dollars. This - because it relies on the super stable potassium carbonate/bicarbonate swing absorption cycle (even though it's not the most efficient) - should last basically forever with minimal maintenance (though it is designed for maintenance - for example, I've designed it so that the switch set points that determine when the core is fully saturated vs. fully unsaturated, can be adjusted with a screwdriver)

I do think your "you can't print horizontal holes" in PETG thing is pretty hilarious, BTW, because it's an open admission that you're terrible at understanding how to set print parameters ;)

I don't plan to link anything with my name to you, so you can believe whatever you want, though if you'd like I'll 3d print something with your name on it, with horizontal holes, in PETG and post it online for you. And yes, I have a BA in Horticulture (subfield: greenhouse cultivation) from Fjölbrautaskóli Su[th]urlands (originally Landbúna[th]arháskólinn, in Hveragerði), along with a BS in CS - again, I don't plan to link anything with my name on it, so you're free to believe whatever you want, if it shocks you that people have more than one field. Just like you're free to believe whatever nonsense you want about forests.

https://carbonneutral.com.au/carbon-jargon-how-trees-capture-and-store-carbon/

Age also has an influence when thinking about collective communities of trees rather than individuals. Younger forests typically grow faster and absorb more carbon overall because trees can be crowded together when they’re small.

When forests consist of middle-aged trees, they also capture and store relatively high amounts of carbon, because middle-aged trees sequester more carbon than younger trees, and if any trees die, they are replaced by younger trees that grow more quickly.

Old-growth forests have a less fluctuating carbon cycle. There are usually fewer trees in an old-growth forest, and the large old trees dominate by blocking out light for younger trees.

https://www.stateforesters.org/wp-content/uploads/2022/03/NCASI22_Forest_Carbon_YoungVsOld_print.pdf

Forests of different ages play different roles in removing carbon from the atmosphere and storing it in wood. Old forests
have accumulated more carbon than younger forests; however, young forests grow rapidly, removing much more CO2
each year from the atmosphere than an older forest covering the same area. Managing forests to avoid large emissions
from the loss of old trees while rapidly removing CO2 from the atmosphere through young forest growth can provide both
storage and sequestration benefi ts

https://www.frontiersin.org/journals/forests-and-global-change/articles/10.3389/ffgc.2025.1702442/full

During the initial years of stand development, either after a new establishment or a stand from regeneration after disturbance, the losses due to RA (autotrophic root respiration) and RH (soil organic matter decomposition) exceed the carbon sequestration resulting in forest ecosystems typically functioning as net carbon emission sources. The duration of this phase varies based on growth rates, site conditions, climate variables, and post-disturbance effects. Rapidly growing forests then transition to carbon sinks within approximately 10-20 years as increasing leaf area and biomass accumulation enhance carbon uptake and eventually surpasses carbon losses from respiration and decomposition. NEP reaches its maximum at an intermediate stand age, after which age-related declines in net primary production (NPP) occur due to reduced nutrient availability, increased mortality (Ryan, 1991; Hartmann and Trumbore, 2016), changes in stomatal conductance, and decreases in photosynthetic efficiency, which shift the balance between carbon uptake and respiratory losses (Bond-Lamberty et al., 2004; Gower et al., 1996; Tang et al., 2014), so that old-growth forests frequently function as a minor carbon sink, or remain carbon neutral, or even become a net emissions source, depending on various factors such as climate, disturbance history, and species composition (Chang et al., 2020; He et al., 2012).

The traditional view is that old-growth forests are roughly carbon neutral - that new growth happens roughly at the same rate as decay. This is not entirely accurate (esp. e.g. in boggy areas or other long-term-accumulation-prone habitats), but by and large, yes, old-growth forests are primarily neutral. Carbon-bearing matter grows, dies, and decays. Certain types of compounds decay faster than others - for example, lignin is humus-forming, and humus is very decay resistant, but is not immune to decay, and is lost over time from the soil. It requires anoxia or mineral binding to protect over geological timeframes. In general, the rates of this, if present at all, are orders of magnitude lower than than the influxes from photosynthesis and loss to decay.

To be clear, this is not that individual trees store less carbon as they age - just the opposite, rates continue to grow as a trees get older. But every tree is fated to die, and when it does, it overwhelmingly rots. Mature forests are in balance. It is forests that are not in balance - e.g. young forests, say 20-40 years old - that are massive at net removing CO2 from the atmosphere, because growth is fast but decay is slow (because not much has yet died).

TL/DR:
* Clearcut forest: terrible emission source. Lots of decay going on / soil carbon loss, even if immediately replanted. Takes a decade or more to go back to net sequestration
* Young growing forest: peaking at 20-40 years, massively net sequestering. Lots of new growth, comparatively little decay.
* Old growth forest: roughly in balance between growth and decay. Stores lots of carbon, but does not net sequester much, if any, carbon.

I hope that helps.

Literally just look at the spec sheets from Bambu above you:

Max bridging length: 30mm vs. 30mm (tie)

You've never printed anything with a horizontal hole?

All the time? Low overhang speeds + fan with overhang. Not tricky.

So what? Your average colored PLA has additives in it anyway.

Not remotely the same. Black is carbon black. Basically soot. Tiny amounts. White is titanium dioxide (like in sunscreen - just a mineral). Blues and greens, generally like 1% or so copper phthalocyanines (very stable, sort of like humus, *very* slowly give off copper (an essential micronutrient) as they break down over hundreds of years). Name a colour that you think is bad as "a double digit percentage of the entire volume of the plastic turning into PU / acrylic microplastics". When you have that much persistent additive, you don't want the plastic breaking down - if not recycled, then you want it incinerated.

It reduces it, it doesn't eliminate it. Try actually printing some PLA+.

Yes, I've totally never printed PLA+ before *eyeroll*.

Bambu PETG Basic vs. Bambu PLA Tough:

Max overhang angle: 70C vs. 55C (PETG wins)
Max bridging length: 30mm vs. 30mm (Tie)
Melting point: 225C vs. 151C (PETG wins)
Glass transition temperature: 68C vs. 61C (PETG wins)
Heat deflection temperature 1.8MPa: 65C vs. 58C (PETG wins)
Heat deflection temperature 0.4MPa: 69C vs. 61C (PETG wins)
Young's Modulus (XY): 1460MPa vs. 1860MPa (depends on whether you want high or low, as per the application; the Tough PLA is somewhat stiffer than PETG, though not as much as regular PLA)
Young's Modulus (Z): 1120MPa vs. 1920 MPa (same story)
Tensile strength (XY): 48MPa vs. 34.9 MPa (PETG wins solidly)
Tensile strength (Z): 39MPa vs. 20.9 MPa (PETG wins even more because PLA has *worse* layer adhesion)
(Skip bending modulus and bending strength, as they're derived parameters)
Impact strength (XY): 52.7 kJ/m2 vs. 80.6 kJ/m2 (Finally, something the PLA wins on!)
Impact strength (Z): 13.6 kJ/m2 vs. 25.9 kJ/m2 (Same)
Flammability: Flammable and self-extinguishing vs. just flammable (PETG wins)
Cost: Depends on the store, but Bambu's base price is cheaper (and I buy filament wholesale, and there's a pretty stark difference in price, with PETG at the factory door in China being under $4/kg, and even plain PLA being over 5$/kg)

So I have no idea why so many people are stuck on PLA.

I can understand arguments against ABS, ASA, PC, PA, etc. They're more difficult to print, need enclosed chambers, etc. But that doesn't apply to PETG; it's super-easy to print (IMHO, easier than PLA). And basically any modern printer can handle it. And it's cheaper. So I simply do not understand the people still sticking with PLA so much (beyond a desire to be more environmentally conscious, or wanting a very specific product that doesn't have a PETG equivalent).

I've never experienced any sort of "sagging" with PETG, and honestly don't even know what you mean by that (and I generally print very hot). Do you mean printing overhangs without support? That's not great with anything. Do you mean elephant foot? Never experienced it. I make primarily functional parts, not decor, so dimensional accuracy is key; zero problems. And concerning sagging, let me tell you, PLA *really* sags if it sits in the hot sun long enough...

To get PLA to be "tough" (impact resistant) on the order of PETG you have to load it up with PU microplastics, which makes it worse for the environment than PETG so you lose that advantage. And it gets rid of its stiffness, which is the main thing PLA had mechanically on PETG. You basically make PLA be "not as crap" by making it... have increasingly low fractions of PLA, and higher fractions of "other stuff".

The criticism that many people still use PLA even when there's far better options available is an argument not exactly responded to with "X community overwhelmingly uses it". Yes, and for them too there are far better options available. Unless you like your guns melting in a hot car, being brittle (or being loaded with PU), not entirely water stable, etc etc.

And if we're doing the "X community overwhelmingly uses" argument, let me point to where things are made for critical function, not for fun: the war in Ukraine. Both Ukraine and Russia extensively use 3d printed parts. And almost none of them are PLA - it's overwhelmingly PETG.

It's just a hobby (and content for his channel). Everyone has their own :) Right now I'm working on a CO2 capture system to take atmospheric CO2 and pump it into my greenhouse.

I imagine a standard thickness is probably something like 9.5mm.

It's not all resin printing, he only used resin printing for one part in the video. Most was FDM printing. Though I did find it strange that he was using PLA. If it's parts facing repeated impact, you think he'd at least go with PETG, if not something like ABS/ASA or a nylon. I really don't get why so many people are so averse to non-PLA polymers. I guess PLA is more "eco-friendly"**, and yeah, there's a ton of PLA options out there, but that's mainly just because people are buying so much PLA.

** I'm actually thinking about switching some of my prototyping back to PLA, even though it costs more than PETG, because I can break down my PLA waste in sodium hydroxide at home. But I almost never make production parts in PLA unless that's the only practical option (for example, a given type of material only being available in PLA). Who wants parts that break if you look at them wrong, or melt in a hot car?

By "quite a large scale" you mean 1.3m long. He certainly could have made it longer than that. Honestly, I mainly think he just wanted an excuse to do more 3d printing and electronics work ;)

As per the principle in this article, that would make it worse if applied to the Reynolds regime in question. This is not about "general roughness", but specifically shaped roughness. In particular, a very sparse roughness on an otherwise smooth surface.

Sanding a hull is dealing with entirely different things. Sanding in general first off gets rid of microprotrusions and broader undulations. There is no question that this helps. The question to whether to polish to a matte or smooth surface is less obvious. Matte probably is better in general, as it helps make the surface more hydrophilic (there is also argued to be some potential to be making something like "riblets", although in practice you're unlikely to get the geometry right (true riblets are extremely thin walled).

This comment section is jam packed full of people mentioning the same misconceived and inapplicable thing, over and over. A thing that was actually discussed in the article, which they did not read.

How deep are the grooves?

A phrase to be heard either uttered on Slashdot in 2026, or at Woodstock ;)

But to be clear, the answer (assuming you're talking about sharkskin / riblets): a few dozen microns tall and a few dozen microns apart, with the individual riblets being very narrow, just a couple microns.

Hi, someone who regularly does CFD simulations in OpenFOAM here. It is a fundamental principle. I hope that helps.