Meg Radial Scrubber Test report

silent running · 22nd August 2006, 20:59

Hello all, a couple of things. There is a post coming on scrubber dynamics from SMI, so things will at least be stated clearly. For the time being, if you have not done so yet, take a look at the news and testing section on the SMI website. There is much more info there on scrubber perfromance, from 3rd parties even, than any other manufacturer.

But until then, a few things to chew on:

-If you belive that the expanding larger cross sectional area of the scrubber that results from an in to out radial design is going to give you the most efficiency, then the reverse would not. If you don't believe this, then the point is moot. Similarly, if you actually believe that scrubber design has nothing to do with shape or direction and only comes down to 1lb=1hr, then you must not believe that one could get 11 hrs out of a 8-12 filled 6lb Prism radial scrubber. This in spite of the fact that there are multiple living proofs-including me-that it's true.

-Joe may be right about the greater flood tolerance of out to in-I'm far from convinced-but I'm more concerned with the unit functioning optimaly in everyday situations, which I think trumps an emergency situation.

-It seems to me that out to in will cause a faster breakthrough and a soggy inside of the scrubber. Why? Because if the available surface area is decreasing as you get to the inside, then there is less sorb and less resevoir gas volume btw you and breakthrough than in the other direction. If, as Ron suggests, the outlet temp for an out to in scrubber is higher than other way around, due to it's being further away from the water, all that condensate will now be formed on the surface of the inner tube, which can't be good for scrubber efficiency or WOB. I don't think that whatever outlet temp difference there is between the 2 designs is enough to overcome the significant decrease in available crossectional area as we near breakthrough.

-Furthermore on the subject of temp. is the choice of materials for the scrubber housing. SMI chose plastic for the scrubber housing for many reasons, but 1 more than any other. The better insulating qualities of plastic. Apparently in temps colder than 65 F, an aly housing will actually start to cool the gas. So it may make sense to reverse the flow from out to in if you've decided that you must have a metal scrubber housing. Me, I'd rather have my condesate form on the outside of the scrubber, on the scrubber housing wall and be drawing a breath from the larger volume around the scrubber, not the narrow, soggy tube at the center of the radial. Drawing from this larger volume around the outside of the scrubber will, I believe, give the lowest possible WOB. Any wet, spent sorb will clump around the center tube as the front moves out, which will also help WOB. Oh, and I'd still bet that you'd get better duration from a reaction front which is increasing in size, rather than decreasing. All those compromises just to have a metal housing?

I have plenty of laughs, sometimes from my own spubidity and I have not drank any koolaid. I do not trust anybody so much and I believe what makes sense to me until I find out otherwise, which is called learning and it's why I spend so much time on this forum-trying to learn. -Andy

silent running · 22nd August 2006, 22:21

Quote: (Originally Posted by paulraymaekers)

I promised myself not to get dragged into this again.....

You're 100% right!!, and you don't need a high IQ to see this

simply put: if you neglect possible temperature effects (isolation, cooling down gas on walls etc)(and only because of that, worse sorb use), there is no difference at all between in-out and out-in, between radial and axial, donut and whatever,

all that counts then is the amount of sorb you have in your system, that there is no channeling (equal use of the sorb) and that the gas goes trough the whole scrubber-bed (uniformal scrubber, not like the SK)

paul

Hi Paul, I think I finally see why you and I keep going round and round. You are speaking theoreticaly about scrubber volumes, without any other factors. But scrubbers don't function independant of temp/insulation and distribution/amount of moisture/condensate. In fact, I don't see how a scrubber can "function" at all in theorectical terms. So when you introduce temperature, then of course all these variables, like shape, gas flow direction, insulation factors, will all contribute in some direction to it's efficeincy. I guess I was taking for granted that there was an ambient temperature. Temp is not a "possible" factor in scrubber performance, it's one of 2 main factors along with moisture content. Maybe I'm still misunderstanding you? -Andy

paulraymaekers · 22nd August 2006, 22:38

andy, I do know that temperature is very important in scrubber-behaviour. But if you read my posts, you'll read always this: I mainly talk about the mith conc dwell-time

I simply state that dwell-time is only depending on volume and gas-speed, and nothing else. point.

shurely not dependant on temperature.. :-)

it CAN be dependant on un-even packing or channeling, but normally in comparing scrubbers, we suppose uniform sorb volume

regards
paul

silent running · 22nd August 2006, 22:44

Quote: (Originally Posted by jradomski)

Andy,

All test data I have ever heard about, only supports In to Out increases duration.. Home much it increases it really depends on the cannister and how insulated it is.. What it helps is the scrubber when it is near the end of life, since temperature determines how active a chemical reaction is (overal efficiency, remember no scrubber for our use uses all the available chemical).. If dwell time were long enough it wouldn't make ANY difference

As to WOB, if you get a wet scrubber out to in will breath easier (since it can usually be trapped away from the scrubber) and will allow use with much more water in the cannister..

Hi Joe, you are right to keep pointing out the temp/efficiency connection. The scrubber which has the best insulation will have a big advantage over any other, to start with. If you have the best insulation and you then add in all the other factors I mentioned, they will all then contribute some to increased efficiency. From what I can gather at this point, the scrubber housing material and the amount of insulating airspace around the scrubber-radial-may be the most significant factor in the efficeincy of the overall design. I was told in my tmix CCR Prism class to knock off 30 minutes from the manufacturers 6hr recomendation in cold water while using HE, that's only 12%.
Anybody have other manufacturters recomendations for scrubber duration using HE? -Andy

paulraymaekers · 22nd August 2006, 22:49

from what I heard (I think US navy tests), the depth-related decrease of scrubber efficiency, is much LESS with He then with air as dil

paul

silent running · 22nd August 2006, 22:49

Quote: (Originally Posted by paulraymaekers)

andy, I do know that temperature is very important in scrubber-behaviour. But if you read my posts, you'll read always this: i mainly talk about the mith conc dwell-time

I simply state that dwell-time in only depending on volume and gas-speed, and nothing else. point.

shurely not dependant on temperature.. :-)

it CAN be dependant on un-even packing or channeling, but normally in comparing scrubbers, we suppose uniform sorb volume

regards
paul

Ah yes, dwell time, didn't mean to imply you didn't understand the temp factor. We will probably have to disagree about whether or not dwell time is affected by the shape of the scrubber until there's more testing/info available... -Andy

RonMicjan · 22nd August 2006, 22:56

Quote: (Originally Posted by silent running)

-It seems to me that out to in will cause a faster breakthrough and a soggy inside of the scrubber. Why? Because if the available surface area is decreasing as you get to the inside, then there is less sorb and less resevoir gas volume btw you and breakthrough than in the other direction. If, as Ron suggests, the outlet temp for an out to in scrubber is higher than other way around, due to it's being further away from the water, all that condensate will now be formed on the surface of the inner tube, which can't be good for scrubber efficiency or WOB. I don't think that whatever outlet temp difference there is between the 2 designs is enough to overcome the significant decrease in available crossectional area as we near breakthrough.

Hey Andy, thanks for joining the discussion.

on the condensation issue, you will not get condensation at the center of the tube no matter what its material compostion, the reason this is pertains to how condensation works. even in 100% humidity enviroments you will not encounter condensation until the moist gas hits a surface that has a lower temperature than the gas, with the tube being at the center of the hot part, its temp is the same as the surrounding material, the condensation will happen on the surfaces that border the water/air boundary, as the water will always be cooler than the loop gas. Relative Humidity is exressed as a percentage because the amount of water that air can hold is dependent on the temperature of the air, warmer air will hold more moisture than cold. The relative part of RH means relative to the ambient temperature. So if gas with 100% humidity at temperature X hits a surface with temperature of <X the gas must relenquish some of its humidity, which happens as droplets of water condensing on the surface. There is also a condition known as supersaturation, but that is a weather phenomenon, not a diving one.

dew point is a factor in all this also, what dew point is is the temperature at which condensation happens. say you have a mass of air at 72 degrees F with a relative humidity of 50%, the dew point is the temperature at which that air mass will reach 100% humidity, the amount of water in the air mass has not changed, just the ability of the air to HOLD that same amount has changed due to the decreased temperature. dew point is always either equal to or less than ambient. if the dew point and temperature are equal, this usually means condensation is happening, rain, snow, or dew. this the reason that we have dew in the evening, as the air and ground temperature decrease at the end of a day, the air dumps its moisture on the closest cool surface.

Unless the center tube extends outside of the insulation properties of the housing its in, there will be no (or very little) condensation. metal in itself does not warm or cool anything, it is a terrible insulator true, and it transmits energy in heat form through its length quite readily. The Meg with its aluminum plenum is not a good insulator of the gas, however with the out to in design, the warmest gas comes up through the inhale hose to the diver, gets warmed again by the diver, then heads out to the outside of the scrubber where it contacts the aluminum plenum, dropping its moisture, which drains to the bottom of the can and gets absorbed by the moisture pads there. The other place water condences is at the plastic sensor carriage, which is in close contact to the head, which is in close contact with the ambient water. the heat energy developed by the exothermic action of the scrubber is constantly flowing out into the water through the plenum and the head. the sensor carriage is also somewhat insulated by the Oring that seats to the head, so it is not in direct contact with the head, also helping with the heat transfer issue. There will be some condensate in the sensor carriage, but that is what the moisture pad there is for, to collect it and keep it off the sensor faces.

The meg with apecs has temperature sensors in the handset as well as the loop, the diver will usually see a 5-15 degree difference between the ambient water and the loop temp. I never find moisture in the center of the scrubber tube, just in the bottom of the can and in the pad in the sensor carriage and on the surrounding plastic in the carriage.

more info on moisture, condensation and dewpoint can be found here.
http://www.ace.mmu.ac.uk/eae/Weather...densation.html

sorry for the bandwidth, hope this helps out enough to make it worth typing.

silent running · 22nd August 2006, 23:21

Quote: (Originally Posted by RonMicjan)

Hey Andy, thanks for joining the discussion.

on the condensation issue, you will not get condensation at the center of the tube no matter what its material compostion, the reason this is pertains to how condensation works. even in 100% humidity enviroments you will not encounter condensation until the moist gas hits a surface that has a lower temperature than the gas, with the tube being at the center of the hot part, its temp is the same as the surrounding material, the condensation will happen on the surfaces that border the water/air boundary, as the water will always be cooler than the loop gas. Relative Humidity is exressed as a percentage because the amount of water that air can hold is dependent on the temperature of the air, warmer air will hold more moisture than cold. The relative part of RH means relative to the ambient temperature. So if gas with 100% humidity at temperature X hits a surface with temperature of <X the gas must relenquish some of its humidity, which happens as droplets of water condensing on the surface. There is also a condition known as supersaturation, but that is a weather phenomenon, not a diving one.

dew point is a factor in all this also, what dew point is is the temperature at which condensation happens. say you have a mass of air at 72 degrees F with a relative humidity of 50%, the dew point is the temperature at which that air mass will reach 100% humidity, the amount of water in the air mass has not changed, just the ability of the air to HOLD that same amount has changed due to the decreased temperature. dew point is always either equal to or less than ambient. if the dew point and temperature are equal, this usually means condensation is happening, rain, snow, or dew. this the reason that we have dew in the evening, as the air and ground temperature decrease at the end of a day, the air dumps its moisture on the closest cool surface.

Unless the center tube extends outside of the insulation properties of the housing its in, there will be no (or very little) condensation. metal in itself does not warm or cool anything, it is a terrible insulator true, and it transmits energy in heat form through its length quite readily. The Meg with its aluminum plenum is not a good insulator of the gas, however with the out to in design, the warmest gas comes up through the inhale hose to the diver, gets warmed again by the diver, then heads out to the outside of the scrubber where it contacts the aluminum plenum, dropping its moisture, which drains to the bottom of the can and gets absorbed by the moisture pads there. The other place water condences is at the plastic sensor carriage, which is in close contact to the head, which is in close contact with the ambient water. the heat energy developed by the exothermic action of the scrubber is constantly flowing out into the water through the plenum and the head. the sensor carriage is also somewhat insulated by the Oring that seats to the head, so it is not in direct contact with the head, also helping with the heat transfer issue. There will be some condensate in the sensor carriage, but that is what the moisture pad there is for, to collect it and keep it off the sensor faces.

The meg with apecs has temperature sensors in the handset as well as the loop, the diver will usually see a 5-15 degree difference between the ambient water and the loop temp. I never find moisture in the center of the scrubber tube, just in the bottom of the can and in the pad in the sensor carriage and on the surrounding plastic in the carriage.

more info on moisture, condensation and dewpoint can be found here.
http://www.ace.mmu.ac.uk/eae/Weather...densation.html

sorry for the bandwidth, hope this helps out enough to make it worth typing.

Hi Ron, thanks for the detailed explanation of condensation. I think I understand. So you don't find any moisture in the inner tube, even though moisture is released as part of the scrubber reaction? Isn't there a 1 way drain in the bottom of the Meg scrubber? Also, wouldn't the 100% humid air be denser with all that post scrubber humidity traveling up the tube to the plenum before it condenses? Still seems like an advantage to have the moisture condense on the outside of the scrubber housing-in to out-before it's inhaled and drawn up to the sensors, sensors stay more dry and the gas is lighter with less humidity in it as it's inhaled, maybe less WOB.

Also, it still seems to me that breakthrough would be quicker with out to in. -Andy

***schford*** · 23rd August 2006, 09:51

Quote: (Originally Posted by silent running)

Similarly, if you actually believe that scrubber design has nothing to do with shape or direction and only comes down to 1lb=1hr, then you must not believe that one could get 11 hrs out of a 8-12 filled 6lb Prism radial scrubber. This in spite of the fact that there are multiple living proofs-including me-that it's true.

To be honest I truly believe that the single biggest factor (subject to the gas flow ensuring all the sorb is used) is amount of scrubber material.

11 Hours out of 6 pounds - sure no probs just liked Cedric did umpteen hours on his axial scrubber...and I know people who have done 9 hours plus on their inspiration visions poodling round in the red sea - or hanging motionless with no CO2 production on a shot line at shallow depths waiting for deco to clear.

But none of them would hit those figures with CE testing - you just can not throw around use figures and have them mean anything without us knowing what the temp was, depth was and how much CO2 was producded.

I truly would like to get every unit fill em with the same scrubber material and whack em in a breathing machine at oh say 40m or 5 ata and see when break through occured - I bet that the single biggest factor would be amount of sorb in there....

Padowan · 23rd August 2006, 12:18

I would have thought that another consideration is dive profile. If you think about a typical dive profile, you spend the first part deep, then get shallower and spend a long time with little exertion shallow. If you match this against the scrubber performance over time, then perhaps this defines whether in-out or out-in is better.

By running out-in makes more sense based on this premise, as the higher gas density would result in a thinner reaction front if the start of the dive is operating on the outside portion of the stack. As I get shallower, and the reaction front thins out due to decreasing gas density then operating within the inner sections of the radial is more appropriate.

22nd August 2006, 20:59	#61 (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: 1,873	Re: Meg Radial Scrubber Test report Hello all, a couple of things. There is a post coming on scrubber dynamics from SMI, so things will at least be stated clearly. For the time being, if you have not done so yet, take a look at the news and testing section on the SMI website. There is much more info there on scrubber perfromance, from 3rd parties even, than any other manufacturer. But until then, a few things to chew on: -If you belive that the expanding larger cross sectional area of the scrubber that results from an in to out radial design is going to give you the most efficiency, then the reverse would not. If you don't believe this, then the point is moot. Similarly, if you actually believe that scrubber design has nothing to do with shape or direction and only comes down to 1lb=1hr, then you must not believe that one could get 11 hrs out of a 8-12 filled 6lb Prism radial scrubber. This in spite of the fact that there are multiple living proofs-including me-that it's true. -Joe may be right about the greater flood tolerance of out to in-I'm far from convinced-but I'm more concerned with the unit functioning optimaly in everyday situations, which I think trumps an emergency situation. -It seems to me that out to in will cause a faster breakthrough and a soggy inside of the scrubber. Why? Because if the available surface area is decreasing as you get to the inside, then there is less sorb and less resevoir gas volume btw you and breakthrough than in the other direction. If, as Ron suggests, the outlet temp for an out to in scrubber is higher than other way around, due to it's being further away from the water, all that condensate will now be formed on the surface of the inner tube, which can't be good for scrubber efficiency or WOB. I don't think that whatever outlet temp difference there is between the 2 designs is enough to overcome the significant decrease in available crossectional area as we near breakthrough. -Furthermore on the subject of temp. is the choice of materials for the scrubber housing. SMI chose plastic for the scrubber housing for many reasons, but 1 more than any other. The better insulating qualities of plastic. Apparently in temps colder than 65 F, an aly housing will actually start to cool the gas. So it may make sense to reverse the flow from out to in if you've decided that you must have a metal scrubber housing. Me, I'd rather have my condesate form on the outside of the scrubber, on the scrubber housing wall and be drawing a breath from the larger volume around the scrubber, not the narrow, soggy tube at the center of the radial. Drawing from this larger volume around the outside of the scrubber will, I believe, give the lowest possible WOB. Any wet, spent sorb will clump around the center tube as the front moves out, which will also help WOB. Oh, and I'd still bet that you'd get better duration from a reaction front which is increasing in size, rather than decreasing. All those compromises just to have a metal housing? I have plenty of laughs, sometimes from my own spubidity and I have not drank any koolaid. I do not trust anybody so much and I believe what makes sense to me until I find out otherwise, which is called learning and it's why I spend so much time on this forum-trying to learn. -Andy Last edited by silent running : 22nd August 2006 at 21:03.
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22nd August 2006, 22:21	#62 (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: 1,873	Re: Meg Radial Scrubber Test report Quote: (Originally Posted by paulraymaekers) I promised myself not to get dragged into this again..... You're 100% right!!, and you don't need a high IQ to see this simply put: if you neglect possible temperature effects (isolation, cooling down gas on walls etc)(and only because of that, worse sorb use), there is no difference at all between in-out and out-in, between radial and axial, donut and whatever, all that counts then is the amount of sorb you have in your system, that there is no channeling (equal use of the sorb) and that the gas goes trough the whole scrubber-bed (uniformal scrubber, not like the SK) paul Hi Paul, I think I finally see why you and I keep going round and round. You are speaking theoreticaly about scrubber volumes, without any other factors. But scrubbers don't function independant of temp/insulation and distribution/amount of moisture/condensate. In fact, I don't see how a scrubber can "function" at all in theorectical terms. So when you introduce temperature, then of course all these variables, like shape, gas flow direction, insulation factors, will all contribute in some direction to it's efficeincy. I guess I was taking for granted that there was an ambient temperature. Temp is not a "possible" factor in scrubber performance, it's one of 2 main factors along with moisture content. Maybe I'm still misunderstanding you? -Andy
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22nd August 2006, 22:38	#63 (permalink)
paulraymaekers rEvo's daddy Current Rebreather/s: rEvo Other CCR Home Build Other Rebreather/s: rEvo Other CCR Home Build Join Date: May 2005 Location: belgium Posts: 1,638	Re: Meg Radial Scrubber Test report andy, I do know that temperature is very important in scrubber-behaviour. But if you read my posts, you'll read always this: I mainly talk about the mith conc dwell-time I simply state that dwell-time is only depending on volume and gas-speed, and nothing else. point. shurely not dependant on temperature.. :-) it CAN be dependant on un-even packing or channeling, but normally in comparing scrubbers, we suppose uniform sorb volume regards paul __________________ www.rEvo-rebreathers.com .... the earth is flat, Elvis is alive, and radial scrubbers give longer dwell time than axials... Last edited by paulraymaekers : 22nd August 2006 at 22:51.
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22nd August 2006, 22:44	#64 (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: 1,873	Re: Meg Radial Scrubber Test report Quote: (Originally Posted by jradomski) Andy, All test data I have ever heard about, only supports In to Out increases duration.. Home much it increases it really depends on the cannister and how insulated it is.. What it helps is the scrubber when it is near the end of life, since temperature determines how active a chemical reaction is (overal efficiency, remember no scrubber for our use uses all the available chemical).. If dwell time were long enough it wouldn't make ANY difference As to WOB, if you get a wet scrubber out to in will breath easier (since it can usually be trapped away from the scrubber) and will allow use with much more water in the cannister.. Hi Joe, you are right to keep pointing out the temp/efficiency connection. The scrubber which has the best insulation will have a big advantage over any other, to start with. If you have the best insulation and you then add in all the other factors I mentioned, they will all then contribute some to increased efficiency. From what I can gather at this point, the scrubber housing material and the amount of insulating airspace around the scrubber-radial-may be the most significant factor in the efficeincy of the overall design. I was told in my tmix CCR Prism class to knock off 30 minutes from the manufacturers 6hr recomendation in cold water while using HE, that's only 12%. Anybody have other manufacturters recomendations for scrubber duration using HE? -Andy
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22nd August 2006, 22:49	#65 (permalink)
paulraymaekers rEvo's daddy Current Rebreather/s: rEvo Other CCR Home Build Other Rebreather/s: rEvo Other CCR Home Build Join Date: May 2005 Location: belgium Posts: 1,638	Re: Meg Radial Scrubber Test report from what I heard (I think US navy tests), the depth-related decrease of scrubber efficiency, is much LESS with He then with air as dil paul __________________ www.rEvo-rebreathers.com .... the earth is flat, Elvis is alive, and radial scrubbers give longer dwell time than axials...
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22nd August 2006, 22:49	#66 (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: 1,873	Re: Meg Radial Scrubber Test report Quote: (Originally Posted by paulraymaekers) andy, I do know that temperature is very important in scrubber-behaviour. But if you read my posts, you'll read always this: i mainly talk about the mith conc dwell-time I simply state that dwell-time in only depending on volume and gas-speed, and nothing else. point. shurely not dependant on temperature.. :-) it CAN be dependant on un-even packing or channeling, but normally in comparing scrubbers, we suppose uniform sorb volume regards paul Ah yes, dwell time, didn't mean to imply you didn't understand the temp factor. We will probably have to disagree about whether or not dwell time is affected by the shape of the scrubber until there's more testing/info available... -Andy Last edited by silent running : 22nd August 2006 at 22:52.
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22nd August 2006, 22:56	#67 (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: 1,120	Re: Meg Radial Scrubber Test report Quote: (Originally Posted by silent running) -It seems to me that out to in will cause a faster breakthrough and a soggy inside of the scrubber. Why? Because if the available surface area is decreasing as you get to the inside, then there is less sorb and less resevoir gas volume btw you and breakthrough than in the other direction. If, as Ron suggests, the outlet temp for an out to in scrubber is higher than other way around, due to it's being further away from the water, all that condensate will now be formed on the surface of the inner tube, which can't be good for scrubber efficiency or WOB. I don't think that whatever outlet temp difference there is between the 2 designs is enough to overcome the significant decrease in available crossectional area as we near breakthrough. Hey Andy, thanks for joining the discussion. on the condensation issue, you will not get condensation at the center of the tube no matter what its material compostion, the reason this is pertains to how condensation works. even in 100% humidity enviroments you will not encounter condensation until the moist gas hits a surface that has a lower temperature than the gas, with the tube being at the center of the hot part, its temp is the same as the surrounding material, the condensation will happen on the surfaces that border the water/air boundary, as the water will always be cooler than the loop gas. Relative Humidity is exressed as a percentage because the amount of water that air can hold is dependent on the temperature of the air, warmer air will hold more moisture than cold. The relative part of RH means relative to the ambient temperature. So if gas with 100% humidity at temperature X hits a surface with temperature of <X the gas must relenquish some of its humidity, which happens as droplets of water condensing on the surface. There is also a condition known as supersaturation, but that is a weather phenomenon, not a diving one. dew point is a factor in all this also, what dew point is is the temperature at which condensation happens. say you have a mass of air at 72 degrees F with a relative humidity of 50%, the dew point is the temperature at which that air mass will reach 100% humidity, the amount of water in the air mass has not changed, just the ability of the air to HOLD that same amount has changed due to the decreased temperature. dew point is always either equal to or less than ambient. if the dew point and temperature are equal, this usually means condensation is happening, rain, snow, or dew. this the reason that we have dew in the evening, as the air and ground temperature decrease at the end of a day, the air dumps its moisture on the closest cool surface. Unless the center tube extends outside of the insulation properties of the housing its in, there will be no (or very little) condensation. metal in itself does not warm or cool anything, it is a terrible insulator true, and it transmits energy in heat form through its length quite readily. The Meg with its aluminum plenum is not a good insulator of the gas, however with the out to in design, the warmest gas comes up through the inhale hose to the diver, gets warmed again by the diver, then heads out to the outside of the scrubber where it contacts the aluminum plenum, dropping its moisture, which drains to the bottom of the can and gets absorbed by the moisture pads there. The other place water condences is at the plastic sensor carriage, which is in close contact to the head, which is in close contact with the ambient water. the heat energy developed by the exothermic action of the scrubber is constantly flowing out into the water through the plenum and the head. the sensor carriage is also somewhat insulated by the Oring that seats to the head, so it is not in direct contact with the head, also helping with the heat transfer issue. There will be some condensate in the sensor carriage, but that is what the moisture pad there is for, to collect it and keep it off the sensor faces. The meg with apecs has temperature sensors in the handset as well as the loop, the diver will usually see a 5-15 degree difference between the ambient water and the loop temp. I never find moisture in the center of the scrubber tube, just in the bottom of the can and in the pad in the sensor carriage and on the surrounding plastic in the carriage. more info on moisture, condensation and dewpoint can be found here. http://www.ace.mmu.ac.uk/eae/Weather...densation.html sorry for the bandwidth, hope this helps out enough to make it worth typing. __________________ Marine rescue, towing and salvage. Interfering with natural selection since 1983. www.tmishop.com Diving bits etc. www.seatowpdx.com The Summer Job
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22nd August 2006, 23:21	#68 (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: 1,873	Re: Meg Radial Scrubber Test report Quote: (Originally Posted by RonMicjan) Hey Andy, thanks for joining the discussion. on the condensation issue, you will not get condensation at the center of the tube no matter what its material compostion, the reason this is pertains to how condensation works. even in 100% humidity enviroments you will not encounter condensation until the moist gas hits a surface that has a lower temperature than the gas, with the tube being at the center of the hot part, its temp is the same as the surrounding material, the condensation will happen on the surfaces that border the water/air boundary, as the water will always be cooler than the loop gas. Relative Humidity is exressed as a percentage because the amount of water that air can hold is dependent on the temperature of the air, warmer air will hold more moisture than cold. The relative part of RH means relative to the ambient temperature. So if gas with 100% humidity at temperature X hits a surface with temperature of <X the gas must relenquish some of its humidity, which happens as droplets of water condensing on the surface. There is also a condition known as supersaturation, but that is a weather phenomenon, not a diving one. dew point is a factor in all this also, what dew point is is the temperature at which condensation happens. say you have a mass of air at 72 degrees F with a relative humidity of 50%, the dew point is the temperature at which that air mass will reach 100% humidity, the amount of water in the air mass has not changed, just the ability of the air to HOLD that same amount has changed due to the decreased temperature. dew point is always either equal to or less than ambient. if the dew point and temperature are equal, this usually means condensation is happening, rain, snow, or dew. this the reason that we have dew in the evening, as the air and ground temperature decrease at the end of a day, the air dumps its moisture on the closest cool surface. Unless the center tube extends outside of the insulation properties of the housing its in, there will be no (or very little) condensation. metal in itself does not warm or cool anything, it is a terrible insulator true, and it transmits energy in heat form through its length quite readily. The Meg with its aluminum plenum is not a good insulator of the gas, however with the out to in design, the warmest gas comes up through the inhale hose to the diver, gets warmed again by the diver, then heads out to the outside of the scrubber where it contacts the aluminum plenum, dropping its moisture, which drains to the bottom of the can and gets absorbed by the moisture pads there. The other place water condences is at the plastic sensor carriage, which is in close contact to the head, which is in close contact with the ambient water. the heat energy developed by the exothermic action of the scrubber is constantly flowing out into the water through the plenum and the head. the sensor carriage is also somewhat insulated by the Oring that seats to the head, so it is not in direct contact with the head, also helping with the heat transfer issue. There will be some condensate in the sensor carriage, but that is what the moisture pad there is for, to collect it and keep it off the sensor faces. The meg with apecs has temperature sensors in the handset as well as the loop, the diver will usually see a 5-15 degree difference between the ambient water and the loop temp. I never find moisture in the center of the scrubber tube, just in the bottom of the can and in the pad in the sensor carriage and on the surrounding plastic in the carriage. more info on moisture, condensation and dewpoint can be found here. http://www.ace.mmu.ac.uk/eae/Weather...densation.html sorry for the bandwidth, hope this helps out enough to make it worth typing. Hi Ron, thanks for the detailed explanation of condensation. I think I understand. So you don't find any moisture in the inner tube, even though moisture is released as part of the scrubber reaction? Isn't there a 1 way drain in the bottom of the Meg scrubber? Also, wouldn't the 100% humid air be denser with all that post scrubber humidity traveling up the tube to the plenum before it condenses? Still seems like an advantage to have the moisture condense on the outside of the scrubber housing-in to out-before it's inhaled and drawn up to the sensors, sensors stay more dry and the gas is lighter with less humidity in it as it's inhaled, maybe less WOB. Also, it still seems to me that breakthrough would be quicker with out to in. -Andy
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23rd August 2006, 09:51	#69 (permalink)
*schford* RBW Founder Current Rebreather/s: Megalodon Sport Kiss Other Rebreather/s: Join Date: Jan 2005 Location: UK Posts: 3,564	Re: Meg Radial Scrubber Test report Quote: (Originally Posted by silent running) Similarly, if you actually believe that scrubber design has nothing to do with shape or direction and only comes down to 1lb=1hr, then you must not believe that one could get 11 hrs out of a 8-12 filled 6lb Prism radial scrubber. This in spite of the fact that there are multiple living proofs-including me-that it's true. To be honest I truly believe that the single biggest factor (subject to the gas flow ensuring all the sorb is used) is amount of scrubber material. 11 Hours out of 6 pounds - sure no probs just liked Cedric did umpteen hours on his axial scrubber...and I know people who have done 9 hours plus on their inspiration visions poodling round in the red sea - or hanging motionless with no CO2 production on a shot line at shallow depths waiting for deco to clear. But none of them would hit those figures with CE testing - you just can not throw around use figures and have them mean anything without us knowing what the temp was, depth was and how much CO2 was producded. I truly would like to get every unit fill em with the same scrubber material and whack em in a breathing machine at oh say 40m or 5 ata and see when break through occured - I bet that the single biggest factor would be amount of sorb in there.... __________________ 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 RBW is subject to the Rebreather World Terms & Conditions of Use
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23rd August 2006, 12:18	#70 (permalink)
Padowan RBW Member Current Rebreather/s: Inspiration Classic Other Rebreather/s: Join Date: Feb 2005 Location: Exeter, UK. Posts: 526	Re: Meg Radial Scrubber Test report I would have thought that another consideration is dive profile. If you think about a typical dive profile, you spend the first part deep, then get shallower and spend a long time with little exertion shallow. If you match this against the scrubber performance over time, then perhaps this defines whether in-out or out-in is better. By running out-in makes more sense based on this premise, as the higher gas density would result in a thinner reaction front if the start of the dive is operating on the outside portion of the stack. As I get shallower, and the reaction front thins out due to decreasing gas density then operating within the inner sections of the radial is more appropriate. __________________ Padowan The future's bright, the future's Yellow .....for now padowan.net - Latest Video: Scapa Flow Rebreather Diving
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