SMI Scrubber

mverick

Nope,
Not at all.

Heat from the metal of the scrubber. Transfers 2 ways. One to the air and 2 to the scrubber material. Which one is a more efficient energy transfer? The one back to the Scrubber material is solid to solid. Much more energy efficient.

The Scrubbing process makes heat. Always, So storing heat to transfer back to the process when it needs it. Deep,Cold. Is a good thing. Shallow and warm is where you start and where you'll put the heat into the metal of the scrubber. Not all dives are this way. But, you'll be storing the heat in the metal at the begining of the dive no matter what. Not pulling away at the end of the dive.

HYRAX,
If you read all my posts. You know I'm talking about the PRISM. NOT the Meg. The Ready's stated the reason for plastics in the scrubber itself was for themal. I didn't state that. I'm trying to figure out how that Plastic is a Good or More effiecient reason. From all aspects. It isn't.

Yep, the radiator is a Ridiculous comparison. And they know it. The Metal plated scrubber isn't built anything like a radiator. That's my reason. It's a Plate, Not a finned, tubed heat exchanger.

Sorry Andy, but you are completely not getting the point.

You aren't going to loose a lot of heat to the air from the metal scrubber plate. I'm still talking about the Prism. The Plastic bucket doesn't transfer much heat or absorb it quickly from the air. So, the metal scrubber plate will store heat. Just like the plastic of the scrubber. There is just more Thermal mass for the metal and it can store more heat.

Why is it. I've been talking about the prism. And you all keep going back to the Meg design?

I use Prism words and Prism divers get confused.

REMEMBER, I'M TALKING ABOUT A PRISM.

silent running

Yes mverick, I am confused. What is this about the Prism having a metal plate? "You aren't going to loose a lot of heat to the air from the metal scrubber plate. I'm still talking about the Prism." No comprende on this...

Back to the other point, whatever the efficiency of the energy transfer from from warm sorb to metal, it's still not much if any advantage when the other side of the perf metal is next to gas which sits next to a cold metal can with cold seawater on the other side. Do you really think that being less than .5 inches away from a metal surface that's 40+ degrees cooler is not going to take away some of that "stored" heat? Try keeping your dinner warm in a metal pot .5 inches from a window with a 40 degree temp differential. Does that seem like a good place to do that? And that's with air. Seawater is many times denser than air and has much greater capacity to absorb heat, continually absorbing up any heat it can. Why do you think that "stored" heat in the perf metal is only going to be affected by the heat coming from the sorb? Metal doesn't just absorb heat, it also radiates it in any direction which is even slightly cooler that it is. And on the Meg, this benefit will be less and less as you get further in and the reaction moves away from the outside perf metal, which will become more and more cool as the reaction moves away from the perf metal. And then the transfer of heat from the perf metal to the gas to the cold can will become even greater.-Andy

mverick

So, now what your saying is your prism has a Metal bucket...

What part of. "I'm Talking About a Prism". Isn't coming through????

IF you re read the Ready's post on his Prism scrubber. It went like this.

""""""

1. Plastic is the material of choice for SMI because it has lower thermal conductivity than stainless steel and aluminum, i.e. does not dissipate heat quickly. Maintaining a higher temperature is more efficient for your chemical reaction, which contributes to better duration.

""""""

I stated that doesn't make sense. A metal plate in a Prism would transfer heat back to the Sorb material. Better then a Plastic mesh.

I've repeated this multiple time. Show me a way that doesn't work.

THE PRISM
has a Plastic bucket. And believe it or not. In 65f water. That bucket will be 65F. It will release heat to the water also. If you want to insulate it. You would have a double walled bucket. Plastic then air then Plastic.

Transfering heat to a Plastic bucket through the airspace from the scrubbers outside surface isn't going to amount to didly. It's inefficient. Air is an Insulator. Better then plastic. If you look at your house insulation. It is filled with what? Air. It isn't the fiberglass that insulates in expanded fiberglass insulation. It is the air. In foam insulation. It is the Air that is the insulator. Not the plastic of the foam material.

You keep trying to make this a Prism/Meg debate. I ain't saying anything about the Meg. You keep talking about the Meg. All I'm saying is that post of a reason for why it's plastic. Doesn't hold water. The other reasons, maybe yes. That reason. Nope.

And, I do think the Prism scrubber is the best out there. BUT, I also see there is room for better. Putting a Metal plate outside the scrubber. Looks to be a Better design. The Thermal reasoning behind it, shows there to be a good chance at increasing efficency and duration.

Are you just trying to be difficult?

Or, are you trying to have a discussion on how to better a scrubber design? That's what I'm trying to do.

I do realize the better efficiency through and in to out design. Think it's more efficient. Without question. BUT, I don't like the ease of being able to flood the center section of the scrubber. It isn't worth Risking Murphys Law to me.

What it looks like. Is the Newly designed scrubber for the Meg would actually extend duration in the Prism. Just like I said before the new scrubber that it looked like the Prism scrubber would extend duration in a Meg.

How it's going to work in a Meg. I don't know.

silent running

mverick, I keep mentioning the Meg because it has a perf metal scrubber, not to bash. If you think you've been perfectly clear, then I'm living proof you have not. Why would I try to be difficult in print? It's way too time consuming and this subject is difficult enough as it is...

And you've stated that you think the Prism is the best scrubber out there, how do you think this came to be? By guessing? It's because of a bunch of different little details together, like flow direction, scrubber canister material, bucket material, proportions, etc... all chosen after a lot of testing... by an engineer. And one of the things that was found out was that insulation and heat conductivity were very important to maintaining an optimal scrubber reaction. Why aren't there any winter coats made out of metal? Because you want to slow down the transfer of heat as much as possible-there is no holding of heat without also losing heat. Yes air is the best insulator, but it's not solid, so we must chose a solid for our structural materials, one that will transfer heat as slowly as possible. Why then would we choose a material that heats up easily and radiates it just as easily?

I never said there wasn't room for improvement, and said as much in response to Joe R. when he tried to clarify your point about a metal scrubber. However, I remain unconvinced about the merits of metal in scrubbers. A really good test will tell all, but currently there's a scarcity of them, or at least of posted test results... except for SMI. -Andy

hyrax

mverick

Ok, I went back and reread just your posts. You state in your first post just what you are talking about and yes, you are most likely correct. I would not expect to make much difference, just on the inside edge and outside edge of the scrubber where you really need it. So if someone built a metal scrubber for the prism it should be better. I think the meg keeps coming up because it is the only rebreather to compare it to.

mverick

If SMI did all the testing you claim. And release it. Where is the proof of the Plastic better then the metal?

I'm sure they've read this post.

silent running

mverick, you know as well as I do that all manufacturers do lots of in-house tests and that writing all of them up would take time and effort that could be spent getting product out the door... The better question is why don't other manufacturers have as much detailed 3rd party tests up on their sites as SMI? Not, "Why don't SMI have more test data up?" They already have more info up than anyone else. That's the testing I was talking about.

Pete has lots of direct experience testing other CCRs like the MKs, experience from his work with the USN(who tested lots of CCRs)and from working for other manufacturers. So when he tells me about an inhouse test he did, he always gives me supporting info from other sources. I can't think of many people in the business with his level of experience/knowledge, which is a big reason why I bought his unit. I'm not expecting you to take my or his word for it from some inhouse test he did. I was/am prepared to argue the point of metal vs. plastic on the physics alone, however clumsily I may do it.

As a matter of fact, just yesterday, while talking to Pete he mentioned that they did try an all metal scrubber in the Prism at one point. He also mentioned that for the metal scrubber to actually reflect any heat back-like the directional, one-sided aluminized space blanket-it would have to be polished to a shine. Of course when they did polish the inside of the scrubber, the tightly packed sorb abraided the shine away after several fills and the effect was not achieved. Not sure which metal, aly or ss. I will try to get more details out of him soon. -Andy

Steve

The space blanket I have in my outdoor survival kit isn't directional. It isn't even that shiny. It works by trapping radiant heat, reducing convective and evaporative heat loss. They work well in wet windy places. They work best when wrapped tightly for good reason.

This is the same issue with scrubbers, the metal, plastic, wood if you like will absorb some of the heat energy from the scrubbing process. It will then loose some of this heat through conduction and convection. It isn't directional.

Was he at all serious when discussing radiated energy?

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silent running

Umm yeah, I think so. It was a test he did a long time ago and he mentioned it quickly. I think the jist was that in order to focus the heat most effectively in a particular direction, the best way would be use a shiny or polished surface. It seems to work well enough with lasers. I guess another example of this principle at work is the lining of a thermos having a mirror like shine, very thin and then a large-ish airspace, then an outer case, usually made of plastic.

My space blaket was directional and reasonably shiny, as shiny as aluminizied fabric can be, there was definitely an in and an out side. Are you saying that both sides were the same on yours?

I have been saying all along that absorbed heat loss is not directional in nature, to the great protestations of others. -Andy

Steve

Looking at the bag for the survival blanket it is 'metalised polyester' and both sides look the same.

A Thermos or vacuum flask works due to the vacuum being really good at being an insulator. Bugger all there to conduct heat. I remember the old glass inner ones you mention. Mine are all stainless steel.

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WARNING: I contain occasional coarse language, extreme sexual references, nudity, and adult themes, which may offend some people - Usually churchy types.