SMI Scrubber

webslave · 24th August 2006, 22:04

Quote: (Originally Posted by mverick)

Ok,
Saying thermal conductivity of the scrubber is a reason for it being plastic? I understand a little. But, if it's metal. Won't it come to temp and stay there? You're already loosing heat through the bucket. All the time. So, loosing heat to metal of a scrubber and then holding it there might be a good thing. That Thermal Mass thing. Also, when you want to hold the temp there. The metal would hold more heat to release to the scrubber material? If the ends of the scrubber are plastic and the mesh is metal. No direct transfer of heat to the bucket. Or, not much.

Seems some terms are being mixed-up and/or misunderstood. Here's a very basic review for those of us who are neither physicists nor engineers:
Thermal Conductivity,
http://encyclopedia.thefreedictionar...l+conductivity

and Thermal Mass.
http://encyclopedia.thefreedictionary.com/Thermal+mass

The simplified definition of a thermal insulator is the opposite of a thermal conductor. Thermal insulators are used to minimize a change in temperature, like a down jacket minimizes the gradient between you and cold weather (keeps body heat in and cold out), or the air in a scrubber housing or bucket, air insulates the scrubber from the housing or bucket exposed to the water.

***schford*** · 24th August 2006, 22:32

Thanks for this great article and discussion - I am learning loads!

mverick · 24th August 2006, 23:51

Not mis understood. Anything can be a Thermal Insulator. Some just aren't good at it. You can use Steel as a Thermal Insulator. But, it would be a waste of time. Since it conducts heat so well. So, it would be stupid to use. Now, steel works as the housing of the scrubber if you have Air in the bucket to insulate it. Because, transfering heat from the steel to air doesn't work near as well as from the bucket to the surrounding water. Air/Air intercoolers need huge area. While Water/Air intercoolers can be relatively small.

If you have a Scrubber in a steel cage as it is. And the Steel is heated, it has to have something to conduct the heat to. Well, in the case of the scrubber it is only air. Top and bottom are still plastics. So conductivity through those isn't much. If the Steel was touchin a Steel bucket. Great conductivity. But, it isn't touching a metal bucket. Or a Plastic bucket. It only touches the Base and cap of the scrubber. Which are good thermal insulators. So only heat loss is to the air. Which isn't that great at stealing heat. The steel isn't built like a radiator. It's a flat punched plate.

Ok, so once you heat the steel up. It will hold the heat. It will only absorb so much. The plastic scrubber is going to heat up. Insulator it might be. But after 8 hours in heat. It's going to heat up. Probably within the first hour. Steel will heat up within the first 15min. You aren't going to have huge heat loss in the scrubber no matter what you do.

Run the plastic scruber out to in and it will be as efficient as the steel scubber is out to in.

I'm just saying I don't see the reason for the plastic for thermal reasons. As long as both are in to out. You are going to hold heat. In fact, an outside plate holding heat to transfer back to the scrubber material would seem to work better then plastic. Since it's part of the thermal mass of the scrubber. Conducting heat back to the scrubber material if it cools. Like between breaths. Since the outside is where your last bit of scrubber will be. The metal would be like a heat battery. Holding it and transfering it back to the scrubber material should it cool.

Chemical Engineering. So, I did take Thermo Dynamics. Plus worked with lots of exotic metals. None that have much to do with this though. Plastics are great. But we had problems with them because of heat.

But, I've been mistaken before. LOL..

Having the metal in the scrubber just seems more logical to hold heat for when you need it at the end. Where the plastic of the scrubber won't conduct heat it's saved back to the scrubber material because of it's better qualities as a thermal insulator. Once it heats up. It will hold it's heat. While the metal cage would transmit it back to the scrubber material. Conductivity to 2 solids would be pretty good.

Quote: (Originally Posted by webslave)

Seems some terms are being mixed-up and/or misunderstood. Here's a very basic review for those of us who are neither physicists nor engineers:
Thermal Conductivity,
http://encyclopedia.thefreedictionar...l+conductivity

and Thermal Mass.
http://encyclopedia.thefreedictionary.com/Thermal+mass

The simplified definition of a thermal insulator is the opposite of a thermal conductor. Thermal insulators are used to minimize a change in temperature, like a down jacket minimizes the gradient between you and cold weather (keeps body heat in and cold out), or the air in a scrubber housing or bucket, air insulates the scrubber from the housing or bucket exposed to the water.

mverick · 25th August 2006, 00:16

One thing, I don't know if it's working. I'm not trying to include the Meg to Prism debate. I'm just trying to see the reason for Plastic scrubber over Metal plate.

I already understand the In to out. I believe it is more efficient. What I'm trying to see is why the plastic. They stated for thermal reasons. And that I'm not seeing. They stated other reasons. But for thermal reasons is what I'm trying to justify.

I also think flooding on a in to out is a bad thing. So, I don't want to go there.

All, about the Meg I wanna say since you asked.
I didn't like the drain. Failure point. Remember the plenum is insulated by a Oring. between the lid and the sensor housing. It's insulated pretty well.

Everything in the airpath is going to be thermal mass. Your scrubber bed. Your Metal or plastic of the scrubber. So, like I said I'm not talking the bucket materials or anything else. Just scrubber efficiency.

If you can hold some extra heat in the scrubber itself near the outside. Wouldn't this be a good thing for when the effective scrubber material near the end starts to fall off. Since the metal plate can transfer heat back into the scrubber bed? Which means, it would be better to build the outside out of Metal then Plastic. You don't want the metal touching anything other then the scrubber material that it could conduct heat away to. Air is the only thing and it's not an efficient transfer. So, the metal has 4 paths to conduct heat too.
1 top plate. Made of plastic is a good insulator.
2 Bottom plate. Made of plastic it's also a good insulator.
3 air. Will transfer some heat but it's a air to solid and not that good of a transfer.
4. Back to the scrubber material. It's solid to solid. So a good path to transfer back to. Putting the heat back to the scrubber material like we all seem to think is the best thing.

Now on the plastic. As the scrubber heats up and the heat front moves towards the outside. It still puts heat into the Air passing through. Also, to the plastic of the scrubber. But without a lot of thermal mass. It doesn't take much heat. And also, because of insulating properties. Takes a lot of time to transfer heat. So, heat that builds in the scrubber doesn't transfer to the plastic quickly. But, all the heat in the scrubber still has to go somewhere. Or it would get to hot to breath. So, you loose it once it hits the bucket. If the outer part of the scrubber itself was metal. It would hold some heat there. Not letting it take out as much moisture when hitting the bucket. But your keeping heat in the scrubber itself. Like a heat battery.

Quote: (Originally Posted by silent running)

mverick, my undersanding of thermodynamics, very limited as it is, is that it's not just the temp differential and conductivity that are taken itnto account, it's also the density and mass of the things transfering the heat. The CCR loop gas is much less dense and there's much less of it than the water surounding it, which would constantly draw the heat away from the loop. The plastic makes this happen more slowly in colder water. And an in to out flow further minimizes this.

As for condesation, the Meg sensors are mounted in the plenum, which directly contacts the outside/water, right? And the first point of condensation is here, right? I think I'd rather have my first point of condensation occur on the scrubber wall-in to out-before it hits the sensors, ala Prism. It sounds like the 1 way drain in the older Megs might have been a good idea, although less simple than a moisture pad... -Andy

***jradomski*** · 25th August 2006, 00:21

Quote: (Originally Posted by mverick)

One thing, I don't know if it's working. I'm not trying to include the Meg to Prism debate. I'm just trying to see the reason for Plastic scrubber over Metal plate.

I already understand the In to out. I believe it is more efficient. What I'm trying to see is why the plastic. They stated for thermal reasons. And that I'm not seeing. They stated other reasons. But for thermal reasons is what I'm trying to justify.

I also think flooding on a in to out is a bad thing. So, I don't want to go there.

All, about the Meg I wanna say since you asked.
I didn't like the drain. Failure point. Remember the plenum is insulated by a Oring. between the lid and the sensor housing. It's insulated pretty well.

Everything in the airpath is going to be thermal mass. Your scrubber bed. Your Metal or plastic of the scrubber. So, like I said I'm not talking the bucket materials or anything else. Just scrubber efficiency.

If you can hold some extra heat in the scrubber itself near the outside. Wouldn't this be a good thing for when the effective scrubber material near the end starts to fall off. Since the metal plate can transfer heat back into the scrubber bed? Which means, it would be better to build the outside out of Metal then Plastic. You don't want the metal touching anything other then the scrubber material that it could conduct heat away to. Air is the only thing and it's not an efficient transfer. So, the metal has 4 paths to conduct heat too.
1 top plate. Made of plastic is a good insulator.
2 Bottom plate. Made of plastic it's also a good insulator.
3 air. Will transfer some heat but it's a air to solid and not that good of a transfer.
4. Back to the scrubber material. It's solid to solid. So a good path to transfer back to. Putting the heat back to the scrubber material like we all seem to think is the best thing.

Now on the plastic. As the scrubber heats up and the heat front moves towards the outside. It still puts heat into the Air passing through. Also, to the plastic of the scrubber. But without a lot of thermal mass. It doesn't take much heat. And also, because of insulating properties. Takes a lot of time to transfer heat. So, heat that builds in the scrubber doesn't transfer to the plastic quickly. But, all the heat in the scrubber still has to go somewhere. Or it would get to hot to breath. So, you loose it once it hits the bucket. If the outer part of the scrubber itself was metal. It would hold some heat there. Not letting it take out as much moisture when hitting the bucket. But your keeping heat in the scrubber itself. Like a heat battery.

good analysis..

unfortunately your msgs bring back nightmares.. Thermo 1 and 2 were the two classes I dreaded attending..

RonMicjan · 25th August 2006, 00:22

Quote: (Originally Posted by silent running)

As for condesation, the Meg sensors are mounted in the plenum, which directly contacts the outside/water, right? And the first point of condensation is here, right? I think I'd rather have my first point of condensation occur on the scrubber wall-in to out-before it hits the sensors, ala Prism. It sounds like the 1 way drain in the older Megs might have been a good idea, although less simple than a moisture pad... -Andy

this is incorrect, the sensors are mounted in the sensor carriage, it is mounted to 4 pins that are screwed into the head. The sensor carriage is seperated from the head with an o ring, which further insulates it from the head, which is exposed to ambient water. There is condensation in the area of the sensor carriage, but from what I have seen, much less than say an Inspio, but there is usually lots of condensation in the bottom of the plenum. (again the plenum on a meg is the can, or bucket as yall prism divers call it), the first real point of condensation is the aluminum plenum, which always has drops on it after a dive, as well as in the bottom moisture pads.

there is a moisture pad in the sensor carriage, made of chamois material that gets moist after the dive, and after several hours can be wrung out. The one way valve in the sensor carriage was removed when ISC realised that most divers were not checking its function properly, even though its on the pre dive checklist. When units would come in for servicing, most every one would fail the one way valve check due to crud collecting in the flapper. It also was realised that it wasnt doing anything that the chamois couldnt.

silent running · 25th August 2006, 00:53

Quote: (Originally Posted by RonMicjan)

this is incorrect, the sensors are mounted in the sensor carriage, it is mounted to 4 pins that are screwed into the head. The sensor carriage is seperated from the head with an o ring, which further insulates it from the head, which is exposed to ambient water. There is condensation in the area of the sensor carriage, but from what I have seen, much less than say an Inspio, but there is usually lots of condensation in the bottom of the plenum. (again the plenum on a meg is the can, or bucket as yall prism divers call it), the first real point of condensation is the aluminum plenum, which always has drops on it after a dive, as well as in the bottom moisture pads.

there is a moisture pad in the sensor carriage, made of chamois material that gets moist after the dive, and after several hours can be wrung out. The one way valve in the sensor carriage was removed when ISC realised that most divers were not checking its function properly, even though its on the pre dive checklist. When units would come in for servicing, most every one would fail the one way valve check due to crud collecting in the flapper. It also was realised that it wasnt doing anything that the chamois couldnt.

Hi Ron, thanks for the clarification. I'd still rather have as much of the condensate on the scrubber housing/plenum/bucket wall as possible, away from the sensor, wiring harness, and connectors.

I think it would be interesting to compare how much condensate/water is generated from both flow directions of a radial under the same conditions. I'd guess that a scrubber that is working most efficeintly would generate more condensate. Does that make sense? -Andy

mverick · 25th August 2006, 01:04

Quote: (Originally Posted by jradomski)

good analysis..

unfortunately your msgs bring back nightmares.. Thermo 1 and 2 were the two classes I dreaded attending..

I kinda liked Thermo... LOL

But, I'm weird...

silent running · 25th August 2006, 01:20

Quote: (Originally Posted by mverick)

One thing, I don't know if it's working. I'm not trying to include the Meg to Prism debate. I'm just trying to see the reason for Plastic scrubber over Metal plate.

I already understand the In to out. I believe it is more efficient. What I'm trying to see is why the plastic. They stated for thermal reasons. And that I'm not seeing. They stated other reasons. But for thermal reasons is what I'm trying to justify.

I also think flooding on a in to out is a bad thing. So, I don't want to go there.

All, about the Meg I wanna say since you asked.
I didn't like the drain. Failure point. Remember the plenum is insulated by a Oring. between the lid and the sensor housing. It's insulated pretty well.

Everything in the airpath is going to be thermal mass. Your scrubber bed. Your Metal or plastic of the scrubber. So, like I said I'm not talking the bucket materials or anything else. Just scrubber efficiency.

If you can hold some extra heat in the scrubber itself near the outside. Wouldn't this be a good thing for when the effective scrubber material near the end starts to fall off. Since the metal plate can transfer heat back into the scrubber bed? Which means, it would be better to build the outside out of Metal then Plastic. You don't want the metal touching anything other then the scrubber material that it could conduct heat away to. Air is the only thing and it's not an efficient transfer. So, the metal has 4 paths to conduct heat too.
1 top plate. Made of plastic is a good insulator.
2 Bottom plate. Made of plastic it's also a good insulator.
3 air. Will transfer some heat but it's a air to solid and not that good of a transfer.
4. Back to the scrubber material. It's solid to solid. So a good path to transfer back to. Putting the heat back to the scrubber material like we all seem to think is the best thing.

Now on the plastic. As the scrubber heats up and the heat front moves towards the outside. It still puts heat into the Air passing through. Also, to the plastic of the scrubber. But without a lot of thermal mass. It doesn't take much heat. And also, because of insulating properties. Takes a lot of time to transfer heat. So, heat that builds in the scrubber doesn't transfer to the plastic quickly. But, all the heat in the scrubber still has to go somewhere. Or it would get to hot to breath. So, you loose it once it hits the bucket. If the outer part of the scrubber itself was metal. It would hold some heat there. Not letting it take out as much moisture when hitting the bucket. But your keeping heat in the scrubber itself. Like a heat battery.

mverick, I think the problem with this analysis is that the very thing you think is an advantage-metal heat conductivity-is actually a disadvantage when you are trying to slow down the transmission of heat from say a 100F loop to 65F water. You want a barrier material between the water and gas with less heat conductivity + an air insulator. Plastic has much less=slower heat conductivity than metal. If you were to put a Prism scrubber bucket in the fire it would probaly start to melt before it burned you. I'm reasonably sure a Meg plenum put to the same fire would heat up rapidly and burn you good in short order.

In a radial design, air would be the best insulator btw the scrubber and the bucket and plastic the lowest heat conducting actual solid barrier btw the 2 temp extremes. -Andy

silent running · 25th August 2006, 01:36

Quote: (Originally Posted by mverick)

One thing, I don't know if it's working. I'm not trying to include the Meg to Prism debate. I'm just trying to see the reason for Plastic scrubber over Metal plate.

I also think flooding on a in to out is a bad thing. So, I don't want to go there.

Also mverick, the Prism is very unlikely to flood through the center tube for the reasons I mentioned on the Meg radial thread. I think the chance is next to nil. And I don't think there's any bashing going on, just people hashing things out... -Andy

24th August 2006, 22:04	#11 (permalink)
webslave New Member Current Rebreather/s: Other CCR Other Rebreather/s: Other CCR Join Date: Feb 2005 Location: Confusion Posts: 14	Re: SMI Scrubber Quote: (Originally Posted by mverick) Ok, Saying thermal conductivity of the scrubber is a reason for it being plastic? I understand a little. But, if it's metal. Won't it come to temp and stay there? You're already loosing heat through the bucket. All the time. So, loosing heat to metal of a scrubber and then holding it there might be a good thing. That Thermal Mass thing. Also, when you want to hold the temp there. The metal would hold more heat to release to the scrubber material? If the ends of the scrubber are plastic and the mesh is metal. No direct transfer of heat to the bucket. Or, not much. Seems some terms are being mixed-up and/or misunderstood. Here's a very basic review for those of us who are neither physicists nor engineers: Thermal Conductivity, http://encyclopedia.thefreedictionar...l+conductivity and Thermal Mass. http://encyclopedia.thefreedictionary.com/Thermal+mass The simplified definition of a thermal insulator is the opposite of a thermal conductor. Thermal insulators are used to minimize a change in temperature, like a down jacket minimizes the gradient between you and cold weather (keeps body heat in and cold out), or the air in a scrubber housing or bucket, air insulates the scrubber from the housing or bucket exposed to the water.
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24th August 2006, 22:32	#12 (permalink)
*schford* Despotic Overlord Current Rebreather/s: Megalodon Sport Kiss Other Rebreather/s: Join Date: Jan 2005 Location: London, UK Posts: 3,673	Re: SMI Scrubber Thanks for this great article and discussion - I am learning loads! __________________ Bailout and Kit Management account for Murphy's Law The only bad question is one you did not ask and later wish you had. Use of Rebreather World is subject to the Rebreather World Terms & Conditions of Use
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24th August 2006, 23:51	#13 (permalink)
mverick ScubaPimp Current Rebreather/s: Megalodon Other CCR Home Build Other Rebreather/s: Other CCR Home Build Join Date: Aug 2005 Posts: 510	Re: SMI Scrubber Not mis understood. Anything can be a Thermal Insulator. Some just aren't good at it. You can use Steel as a Thermal Insulator. But, it would be a waste of time. Since it conducts heat so well. So, it would be stupid to use. Now, steel works as the housing of the scrubber if you have Air in the bucket to insulate it. Because, transfering heat from the steel to air doesn't work near as well as from the bucket to the surrounding water. Air/Air intercoolers need huge area. While Water/Air intercoolers can be relatively small. If you have a Scrubber in a steel cage as it is. And the Steel is heated, it has to have something to conduct the heat to. Well, in the case of the scrubber it is only air. Top and bottom are still plastics. So conductivity through those isn't much. If the Steel was touchin a Steel bucket. Great conductivity. But, it isn't touching a metal bucket. Or a Plastic bucket. It only touches the Base and cap of the scrubber. Which are good thermal insulators. So only heat loss is to the air. Which isn't that great at stealing heat. The steel isn't built like a radiator. It's a flat punched plate. Ok, so once you heat the steel up. It will hold the heat. It will only absorb so much. The plastic scrubber is going to heat up. Insulator it might be. But after 8 hours in heat. It's going to heat up. Probably within the first hour. Steel will heat up within the first 15min. You aren't going to have huge heat loss in the scrubber no matter what you do. Run the plastic scruber out to in and it will be as efficient as the steel scubber is out to in. I'm just saying I don't see the reason for the plastic for thermal reasons. As long as both are in to out. You are going to hold heat. In fact, an outside plate holding heat to transfer back to the scrubber material would seem to work better then plastic. Since it's part of the thermal mass of the scrubber. Conducting heat back to the scrubber material if it cools. Like between breaths. Since the outside is where your last bit of scrubber will be. The metal would be like a heat battery. Holding it and transfering it back to the scrubber material should it cool. Chemical Engineering. So, I did take Thermo Dynamics. Plus worked with lots of exotic metals. None that have much to do with this though. Plastics are great. But we had problems with them because of heat. But, I've been mistaken before. LOL.. Having the metal in the scrubber just seems more logical to hold heat for when you need it at the end. Where the plastic of the scrubber won't conduct heat it's saved back to the scrubber material because of it's better qualities as a thermal insulator. Once it heats up. It will hold it's heat. While the metal cage would transmit it back to the scrubber material. Conductivity to 2 solids would be pretty good. Quote: (Originally Posted by webslave) Seems some terms are being mixed-up and/or misunderstood. Here's a very basic review for those of us who are neither physicists nor engineers: Thermal Conductivity, http://encyclopedia.thefreedictionar...l+conductivity and Thermal Mass. http://encyclopedia.thefreedictionary.com/Thermal+mass The simplified definition of a thermal insulator is the opposite of a thermal conductor. Thermal insulators are used to minimize a change in temperature, like a down jacket minimizes the gradient between you and cold weather (keeps body heat in and cold out), or the air in a scrubber housing or bucket, air insulates the scrubber from the housing or bucket exposed to the water.
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25th August 2006, 00:16	#14 (permalink)
mverick ScubaPimp Current Rebreather/s: Megalodon Other CCR Home Build Other Rebreather/s: Other CCR Home Build Join Date: Aug 2005 Posts: 510	Re: SMI Scrubber One thing, I don't know if it's working. I'm not trying to include the Meg to Prism debate. I'm just trying to see the reason for Plastic scrubber over Metal plate. I already understand the In to out. I believe it is more efficient. What I'm trying to see is why the plastic. They stated for thermal reasons. And that I'm not seeing. They stated other reasons. But for thermal reasons is what I'm trying to justify. I also think flooding on a in to out is a bad thing. So, I don't want to go there. All, about the Meg I wanna say since you asked. I didn't like the drain. Failure point. Remember the plenum is insulated by a Oring. between the lid and the sensor housing. It's insulated pretty well. Everything in the airpath is going to be thermal mass. Your scrubber bed. Your Metal or plastic of the scrubber. So, like I said I'm not talking the bucket materials or anything else. Just scrubber efficiency. If you can hold some extra heat in the scrubber itself near the outside. Wouldn't this be a good thing for when the effective scrubber material near the end starts to fall off. Since the metal plate can transfer heat back into the scrubber bed? Which means, it would be better to build the outside out of Metal then Plastic. You don't want the metal touching anything other then the scrubber material that it could conduct heat away to. Air is the only thing and it's not an efficient transfer. So, the metal has 4 paths to conduct heat too. 1 top plate. Made of plastic is a good insulator. 2 Bottom plate. Made of plastic it's also a good insulator. 3 air. Will transfer some heat but it's a air to solid and not that good of a transfer. 4. Back to the scrubber material. It's solid to solid. So a good path to transfer back to. Putting the heat back to the scrubber material like we all seem to think is the best thing. Now on the plastic. As the scrubber heats up and the heat front moves towards the outside. It still puts heat into the Air passing through. Also, to the plastic of the scrubber. But without a lot of thermal mass. It doesn't take much heat. And also, because of insulating properties. Takes a lot of time to transfer heat. So, heat that builds in the scrubber doesn't transfer to the plastic quickly. But, all the heat in the scrubber still has to go somewhere. Or it would get to hot to breath. So, you loose it once it hits the bucket. If the outer part of the scrubber itself was metal. It would hold some heat there. Not letting it take out as much moisture when hitting the bucket. But your keeping heat in the scrubber itself. Like a heat battery. Quote: (Originally Posted by silent running) mverick, my undersanding of thermodynamics, very limited as it is, is that it's not just the temp differential and conductivity that are taken itnto account, it's also the density and mass of the things transfering the heat. The CCR loop gas is much less dense and there's much less of it than the water surounding it, which would constantly draw the heat away from the loop. The plastic makes this happen more slowly in colder water. And an in to out flow further minimizes this. As for condesation, the Meg sensors are mounted in the plenum, which directly contacts the outside/water, right? And the first point of condensation is here, right? I think I'd rather have my first point of condensation occur on the scrubber wall-in to out-before it hits the sensors, ala Prism. It sounds like the 1 way drain in the older Megs might have been a good idea, although less simple than a moisture pad... -Andy
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25th August 2006, 00:21	#15 (permalink)
*jradomski* Moderator Current Rebreather/s: Inspiration Classic Sport Kiss Optima rEvo Other CCR Home Build Other Rebreather/s: Inspiration Vision Evolution Megalodon Classic Kiss rEvo Other CCR Home Build Join Date: Mar 2005 Location: "Da" Bronx Posts: 2,885	Re: SMI Scrubber Quote: (Originally Posted by mverick) One thing, I don't know if it's working. I'm not trying to include the Meg to Prism debate. I'm just trying to see the reason for Plastic scrubber over Metal plate. I already understand the In to out. I believe it is more efficient. What I'm trying to see is why the plastic. They stated for thermal reasons. And that I'm not seeing. They stated other reasons. But for thermal reasons is what I'm trying to justify. I also think flooding on a in to out is a bad thing. So, I don't want to go there. All, about the Meg I wanna say since you asked. I didn't like the drain. Failure point. Remember the plenum is insulated by a Oring. between the lid and the sensor housing. It's insulated pretty well. Everything in the airpath is going to be thermal mass. Your scrubber bed. Your Metal or plastic of the scrubber. So, like I said I'm not talking the bucket materials or anything else. Just scrubber efficiency. If you can hold some extra heat in the scrubber itself near the outside. Wouldn't this be a good thing for when the effective scrubber material near the end starts to fall off. Since the metal plate can transfer heat back into the scrubber bed? Which means, it would be better to build the outside out of Metal then Plastic. You don't want the metal touching anything other then the scrubber material that it could conduct heat away to. Air is the only thing and it's not an efficient transfer. So, the metal has 4 paths to conduct heat too. 1 top plate. Made of plastic is a good insulator. 2 Bottom plate. Made of plastic it's also a good insulator. 3 air. Will transfer some heat but it's a air to solid and not that good of a transfer. 4. Back to the scrubber material. It's solid to solid. So a good path to transfer back to. Putting the heat back to the scrubber material like we all seem to think is the best thing. Now on the plastic. As the scrubber heats up and the heat front moves towards the outside. It still puts heat into the Air passing through. Also, to the plastic of the scrubber. But without a lot of thermal mass. It doesn't take much heat. And also, because of insulating properties. Takes a lot of time to transfer heat. So, heat that builds in the scrubber doesn't transfer to the plastic quickly. But, all the heat in the scrubber still has to go somewhere. Or it would get to hot to breath. So, you loose it once it hits the bucket. If the outer part of the scrubber itself was metal. It would hold some heat there. Not letting it take out as much moisture when hitting the bucket. But your keeping heat in the scrubber itself. Like a heat battery. good analysis.. unfortunately your msgs bring back nightmares.. Thermo 1 and 2 were the two classes I dreaded attending.. __________________ Joe Radomski CCR Trimix Instructor Trainer ANDI Instructor Trainer Director #10 All posts are personal opinions and DO NOT reflect any affiliated agency unless specifically stated.
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25th August 2006, 00:22	#16 (permalink)
RonMicjan Cap Ron scourge of the NW Current Rebreather/s: Megalodon Dolphin Home Build Other Rebreather/s: Sport Kiss Classic Kiss Dolphin Home Build Join Date: Feb 2005 Location: Cape Disapointment, The Graveyard of the Pacific Posts: 1,082	Re: SMI Scrubber Quote: (Originally Posted by silent running) As for condesation, the Meg sensors are mounted in the plenum, which directly contacts the outside/water, right? And the first point of condensation is here, right? I think I'd rather have my first point of condensation occur on the scrubber wall-in to out-before it hits the sensors, ala Prism. It sounds like the 1 way drain in the older Megs might have been a good idea, although less simple than a moisture pad... -Andy this is incorrect, the sensors are mounted in the sensor carriage, it is mounted to 4 pins that are screwed into the head. The sensor carriage is seperated from the head with an o ring, which further insulates it from the head, which is exposed to ambient water. There is condensation in the area of the sensor carriage, but from what I have seen, much less than say an Inspio, but there is usually lots of condensation in the bottom of the plenum. (again the plenum on a meg is the can, or bucket as yall prism divers call it), the first real point of condensation is the aluminum plenum, which always has drops on it after a dive, as well as in the bottom moisture pads. there is a moisture pad in the sensor carriage, made of chamois material that gets moist after the dive, and after several hours can be wrung out. The one way valve in the sensor carriage was removed when ISC realised that most divers were not checking its function properly, even though its on the pre dive checklist. When units would come in for servicing, most every one would fail the one way valve check due to crud collecting in the flapper. It also was realised that it wasnt doing anything that the chamois couldnt. __________________ Ron "Life is pain princess, anyone who tells you different, is selling something", The Dread Pirate Wesley. www.tmishop.com Diving bits etc.
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25th August 2006, 00:53	#17 (permalink)
silent running Mature mouth breather Current Rebreather/s: Prism Topaz Other Rebreather/s: Join Date: Jun 2005 Location: U.S.A. Brooklyn, New York Posts: 1,813	Re: SMI Scrubber Quote: (Originally Posted by RonMicjan) this is incorrect, the sensors are mounted in the sensor carriage, it is mounted to 4 pins that are screwed into the head. The sensor carriage is seperated from the head with an o ring, which further insulates it from the head, which is exposed to ambient water. There is condensation in the area of the sensor carriage, but from what I have seen, much less than say an Inspio, but there is usually lots of condensation in the bottom of the plenum. (again the plenum on a meg is the can, or bucket as yall prism divers call it), the first real point of condensation is the aluminum plenum, which always has drops on it after a dive, as well as in the bottom moisture pads. there is a moisture pad in the sensor carriage, made of chamois material that gets moist after the dive, and after several hours can be wrung out. The one way valve in the sensor carriage was removed when ISC realised that most divers were not checking its function properly, even though its on the pre dive checklist. When units would come in for servicing, most every one would fail the one way valve check due to crud collecting in the flapper. It also was realised that it wasnt doing anything that the chamois couldnt. Hi Ron, thanks for the clarification. I'd still rather have as much of the condensate on the scrubber housing/plenum/bucket wall as possible, away from the sensor, wiring harness, and connectors. I think it would be interesting to compare how much condensate/water is generated from both flow directions of a radial under the same conditions. I'd guess that a scrubber that is working most efficeintly would generate more condensate. Does that make sense? -Andy
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25th August 2006, 01:04	#18 (permalink)
mverick ScubaPimp Current Rebreather/s: Megalodon Other CCR Home Build Other Rebreather/s: Other CCR Home Build Join Date: Aug 2005 Posts: 510	Re: SMI Scrubber Quote: (Originally Posted by jradomski) good analysis.. unfortunately your msgs bring back nightmares.. Thermo 1 and 2 were the two classes I dreaded attending.. I kinda liked Thermo... LOL But, I'm weird...
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25th August 2006, 01:20	#19 (permalink)
silent running Mature mouth breather Current Rebreather/s: Prism Topaz Other Rebreather/s: Join Date: Jun 2005 Location: U.S.A. Brooklyn, New York Posts: 1,813	Re: SMI Scrubber Quote: (Originally Posted by mverick) One thing, I don't know if it's working. I'm not trying to include the Meg to Prism debate. I'm just trying to see the reason for Plastic scrubber over Metal plate. I already understand the In to out. I believe it is more efficient. What I'm trying to see is why the plastic. They stated for thermal reasons. And that I'm not seeing. They stated other reasons. But for thermal reasons is what I'm trying to justify. I also think flooding on a in to out is a bad thing. So, I don't want to go there. All, about the Meg I wanna say since you asked. I didn't like the drain. Failure point. Remember the plenum is insulated by a Oring. between the lid and the sensor housing. It's insulated pretty well. Everything in the airpath is going to be thermal mass. Your scrubber bed. Your Metal or plastic of the scrubber. So, like I said I'm not talking the bucket materials or anything else. Just scrubber efficiency. If you can hold some extra heat in the scrubber itself near the outside. Wouldn't this be a good thing for when the effective scrubber material near the end starts to fall off. Since the metal plate can transfer heat back into the scrubber bed? Which means, it would be better to build the outside out of Metal then Plastic. You don't want the metal touching anything other then the scrubber material that it could conduct heat away to. Air is the only thing and it's not an efficient transfer. So, the metal has 4 paths to conduct heat too. 1 top plate. Made of plastic is a good insulator. 2 Bottom plate. Made of plastic it's also a good insulator. 3 air. Will transfer some heat but it's a air to solid and not that good of a transfer. 4. Back to the scrubber material. It's solid to solid. So a good path to transfer back to. Putting the heat back to the scrubber material like we all seem to think is the best thing. Now on the plastic. As the scrubber heats up and the heat front moves towards the outside. It still puts heat into the Air passing through. Also, to the plastic of the scrubber. But without a lot of thermal mass. It doesn't take much heat. And also, because of insulating properties. Takes a lot of time to transfer heat. So, heat that builds in the scrubber doesn't transfer to the plastic quickly. But, all the heat in the scrubber still has to go somewhere. Or it would get to hot to breath. So, you loose it once it hits the bucket. If the outer part of the scrubber itself was metal. It would hold some heat there. Not letting it take out as much moisture when hitting the bucket. But your keeping heat in the scrubber itself. Like a heat battery. mverick, I think the problem with this analysis is that the very thing you think is an advantage-metal heat conductivity-is actually a disadvantage when you are trying to slow down the transmission of heat from say a 100F loop to 65F water. You want a barrier material between the water and gas with less heat conductivity + an air insulator. Plastic has much less=slower heat conductivity than metal. If you were to put a Prism scrubber bucket in the fire it would probaly start to melt before it burned you. I'm reasonably sure a Meg plenum put to the same fire would heat up rapidly and burn you good in short order. In a radial design, air would be the best insulator btw the scrubber and the bucket and plastic the lowest heat conducting actual solid barrier btw the 2 temp extremes. -Andy
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25th August 2006, 01:36	#20 (permalink)
silent running Mature mouth breather Current Rebreather/s: Prism Topaz Other Rebreather/s: Join Date: Jun 2005 Location: U.S.A. Brooklyn, New York Posts: 1,813	Re: SMI Scrubber Quote: (Originally Posted by mverick) One thing, I don't know if it's working. I'm not trying to include the Meg to Prism debate. I'm just trying to see the reason for Plastic scrubber over Metal plate. I also think flooding on a in to out is a bad thing. So, I don't want to go there. Also mverick, the Prism is very unlikely to flood through the center tube for the reasons I mentioned on the Meg radial thread. I think the chance is next to nil. And I don't think there's any bashing going on, just people hashing things out... -Andy
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