SMI Scrubber

**Steve** · 25th August 2006, 15:37

Quote: (Originally Posted by Shas)

Radiators for automobiles are metal because heat is dissipated fairly efficiently from the water through the copper/aluminium to the air passing through it. The use of a metal material for the scrubber housing is mechanically superior to plastic, but metal, being an excellent conductor, is not good for an absorbent container. Radial flow would be more of an issue because the large surface area of metal acts as a radiator. For divers it is best to keep as much of the heat in the scrubber not let the metal conduct it away.
Effectively the absorbent is your heat supply like a human body, trying to keep warm. If you go out on a cold day wrapped in metal jacket its not going to be pleasant keeping you body core warm especially if its windy. A metal canister is a heat sink, not what you want to keep your scrubber happy. :-)

Also the fabricated metal canister is not optimal as the number of holes or open surface area to closed is not good for pressure drop at higher RMV's not to mention the extra metal to absorb the heat.

Pete

Hi Pete,

What is the mesh to open space ratio of the plastic mesh you use?

Have you ever used a 'space blanket'?

I will be sure to let you know the loop temperatures I measure with your scrubber and the 2 Meg ones.

paulraymaekers · 25th August 2006, 15:44

Quote: (Originally Posted by Shas)

Radiators for automobiles are metal because heat is dissipated fairly efficiently from the water through the copper/aluminium to the air passing through it. The use of a metal material for the scrubber housing is mechanically superior to plastic, but metal, being an excellent conductor, is not good for an absorbent container. Radial flow would be more of an issue because the large surface area of metal acts as a radiator. For divers it is best to keep as much of the heat in the scrubber not let the metal conduct it away.
Effectively the absorbent is your heat supply like a human body, trying to keep warm. If you go out on a cold day wrapped in metal jacket its not going to be pleasant keeping you body core warm especially if its windy. A metal canister is a heat sink, not what you want to keep your scrubber happy. :-)

Also the fabricated metal canister is not optimal as the number of holes or open surface area to closed is not good for pressure drop at higher RMV's not to mention the extra metal to absorb the heat.

Pete

pete, I don't think the comparison between radiator and cannister is correct

in radiator you have two flows (gas or liquid) at different temperature that want to come in 'equilibrium'

in the scrubber, the same gas that travels trough the sorb travels trough the metal perforation , and once at the same temperature (very fast) there is no temperature-drop due to this metal shield.

if the metal would be the outside of the scrubber, and in contact with the cold water, that would be a different issue. the only thing that counts is that the outside of the cannister/scrubber that is in contact with the cold water, is made in an isolated material

regards
paul

conc pressure-drop over the perforation: you will never be able to mesure it, compared to the pressure drop in the rest of the system :-) (completely neglectable)

silent running · 25th August 2006, 18:14

Quote: (Originally Posted by paulraymaekers)

pete, I don't think the comparison between radiator and cannister is correct

in radiator you have two flows (gas or liquid) at different temperature that want to come in 'equilibrium'

in the scrubber, the same gas that travels trough the sorb travels trough the metal perforation , and once at the same temperature (very fast) there is no temperature-drop due to this metal shield.

regards
paul

conc pressure-drop over the perforation: you will never be able to mesure it, compared to the pressure drop in the rest of the system :-) (completely neglectable)

Hi all. That's actually Sharon Ready posting...

Paul, don't you think the perf metal wants to come to equalibrium with the cooler jacket of air surrounding it? The metal in the scrubber doesn't just "radiate" 1 way, especially when the scrubber is just starting up and the reaction front on the out to in Meg is on the outside of the scrubber circumference and nearest to the water... -Andy

silent running · 25th August 2006, 18:17

[quote=Steve]Hi Pete,What is the mesh to open space ratio of the plastic mesh you use?/QUOTE]

Good question Steve, I want to know this too... -Andy

***jradomski*** · 25th August 2006, 19:10

Quote: (Originally Posted by silent running)

Hi all. That's actually Sharon Ready posting...

Paul, don't you think the perf metal wants to come to equalibrium with the cooler jacket of air surrounding it? The metal in the scrubber doesn't just "radiate" 1 way, especially when the scrubber is just starting up and the reaction front on the out to in Meg is on the outside of the scrubber circumference and nearest to the water... -Andy

primarily heat transfer is going to be at the physical contact point, whether it is to or from the material.. the air gap is a fairly good isulator and the delta temperture in this gap is going to be small compared the scrubber to metal or the bucket to water. To do cooling/heating on a large scale with air you need alot of surface area, thats why things like condensrs and radiators have lots of fins.. they need to increase the air/surface contact area, and ideally force a flow contunualy across this increased area.. The high energey transfer is also at the physical contact point (liguid to tubing to fins), with the fins being an inefficient transfer point.

energy transfer by conducton is aways higher that by convection..

***schford*** · 25th August 2006, 19:59

Quote: (Originally Posted by silent running)

Hi all. That's actually Sharon Ready posting...

I guess signing it Pete made us think it was Pete posting

silent running · 25th August 2006, 20:23

Quote: (Originally Posted by schford)

I guess signing it Pete made us think it was Pete posting

Yeah true, sometimes she posts something for him that's effectively a quote, so it's hard to tell...

silent running · 25th August 2006, 20:30

Quote: (Originally Posted by jradomski)

primarily heat transfer is going to be at the physical contact point, whether it is to or from the material.. the air gap is a fairly good isulator and the delta temperture in this gap is going to be small compared the scrubber to metal or the bucket to water. To do cooling/heating on a large scale with air you need alot of surface area, thats why things like condensrs and radiators have lots of fins.. they need to increase the air/surface contact area, and ideally force a flow contunualy across this increased area.. The high energey transfer is also at the physical contact point (liguid to tubing to fins), with the fins being an inefficient transfer point.

energy transfer by conducton is aways higher that by convection..

Yes Joe, physical conductance would always be more than transfering to gas, but that's what radiators do-transfer heat from metal to the air around it. And a radiator is not usually transfering it's heat into a gas jacket which is continually being exchanged and is less than .5 inches next to a solid which is .25 inches away from cold sea water... -Andy

paulraymaekers · 25th August 2006, 21:17

Quote: (Originally Posted by silent running)

Hi all. That's actually Sharon Ready posting...

Paul, don't you think the perf metal wants to come to equalibrium with the cooler jacket of air surrounding it? The metal in the scrubber doesn't just "radiate" 1 way, especially when the scrubber is just starting up and the reaction front on the out to in Meg is on the outside of the scrubber circumference and nearest to the water... -Andy

andy, it does not make any diff: the mesh is in the flow of one gas at a specific temperature: this mesh quickly comes to that temp and that's it, there can not be any heat loss, because there is no second medium, gas or liquid, that can take over the heat
so metal or plastic mesh, it's all the same :-)

only heat capacity, not conductance, has to do with the time it takes, but it is of no importance, really neglectable
regards
paul

RonMicjan · 25th August 2006, 21:58

in my meg the loop temp is usually 10-20 degrees warmer than the ambient water temp (farienheit), the 120 deg was a ways off. : )

In 46 degree water, our usual home turf temp, the loop runs about 55-60, this depends on work load, current too. (do you get cooler when the current is running by you? your can does too) In warmer climates the loop runs about 5-10 warmer. the highest I have ever seen was 95 in cayman. In a section of the CUMA CF Navy rebreather manual, they suggest that for warm water that the diver reverse the flow of the loop to cool the loop temp, but this is an SCR that works on different principles of the MEG or PRISM, unless the manufacturer recommends swapping flow direction, I wouldnt do that.

Someone suggested that having a metal scrubber in contact with the ambient water was a bad thing, neither the meg or prism do this, so its rather a moot point.

25th August 2006, 15:37	#41 (permalink)
Steve Ladies bring a plate Current Rebreather/s: Megalodon Home Build Other Rebreather/s: Not Bought Yet Inspiration Classic Sport Kiss Classic Kiss MK 15.X Home Build Join Date: Feb 2005 Location: Perth - Australia Posts: 1,117	Re: SMI Scrubber Quote: (Originally Posted by Shas) Radiators for automobiles are metal because heat is dissipated fairly efficiently from the water through the copper/aluminium to the air passing through it. The use of a metal material for the scrubber housing is mechanically superior to plastic, but metal, being an excellent conductor, is not good for an absorbent container. Radial flow would be more of an issue because the large surface area of metal acts as a radiator. For divers it is best to keep as much of the heat in the scrubber not let the metal conduct it away. Effectively the absorbent is your heat supply like a human body, trying to keep warm. If you go out on a cold day wrapped in metal jacket its not going to be pleasant keeping you body core warm especially if its windy. A metal canister is a heat sink, not what you want to keep your scrubber happy. :-) Also the fabricated metal canister is not optimal as the number of holes or open surface area to closed is not good for pressure drop at higher RMV's not to mention the extra metal to absorb the heat. Pete Hi Pete, What is the mesh to open space ratio of the plastic mesh you use? Have you ever used a 'space blanket'? I will be sure to let you know the loop temperatures I measure with your scrubber and the 2 Meg ones. __________________ WARNING: I contain occasional coarse language, extreme sexual references, nudity, and adult themes, which may offend some people - Usually churchy types. Last edited by Steve : 25th August 2006 at 15:45.
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25th August 2006, 15:44	#42 (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: 1,494	Re: SMI Scrubber Quote: (Originally Posted by Shas) Radiators for automobiles are metal because heat is dissipated fairly efficiently from the water through the copper/aluminium to the air passing through it. The use of a metal material for the scrubber housing is mechanically superior to plastic, but metal, being an excellent conductor, is not good for an absorbent container. Radial flow would be more of an issue because the large surface area of metal acts as a radiator. For divers it is best to keep as much of the heat in the scrubber not let the metal conduct it away. Effectively the absorbent is your heat supply like a human body, trying to keep warm. If you go out on a cold day wrapped in metal jacket its not going to be pleasant keeping you body core warm especially if its windy. A metal canister is a heat sink, not what you want to keep your scrubber happy. :-) Also the fabricated metal canister is not optimal as the number of holes or open surface area to closed is not good for pressure drop at higher RMV's not to mention the extra metal to absorb the heat. Pete pete, I don't think the comparison between radiator and cannister is correct in radiator you have two flows (gas or liquid) at different temperature that want to come in 'equilibrium' in the scrubber, the same gas that travels trough the sorb travels trough the metal perforation , and once at the same temperature (very fast) there is no temperature-drop due to this metal shield. if the metal would be the outside of the scrubber, and in contact with the cold water, that would be a different issue. the only thing that counts is that the outside of the cannister/scrubber that is in contact with the cold water, is made in an isolated material regards paul conc pressure-drop over the perforation: you will never be able to mesure it, compared to the pressure drop in the rest of the system :-) (completely neglectable) __________________ www.rEvo-rebreathers.com .... the earth is flat, Elvis is alive, and radial scrubbers give longer dwell time than axials... Last edited by paulraymaekers : 25th August 2006 at 16:11.
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25th August 2006, 18:14	#43 (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: 1,832	Re: SMI Scrubber Quote: (Originally Posted by paulraymaekers) pete, I don't think the comparison between radiator and cannister is correct in radiator you have two flows (gas or liquid) at different temperature that want to come in 'equilibrium' in the scrubber, the same gas that travels trough the sorb travels trough the metal perforation , and once at the same temperature (very fast) there is no temperature-drop due to this metal shield. regards paul conc pressure-drop over the perforation: you will never be able to mesure it, compared to the pressure drop in the rest of the system :-) (completely neglectable) Hi all. That's actually Sharon Ready posting... Paul, don't you think the perf metal wants to come to equalibrium with the cooler jacket of air surrounding it? The metal in the scrubber doesn't just "radiate" 1 way, especially when the scrubber is just starting up and the reaction front on the out to in Meg is on the outside of the scrubber circumference and nearest to the water... -Andy Last edited by silent running : 25th August 2006 at 18:16.
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25th August 2006, 18:17	#44 (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: 1,832	Re: SMI Scrubber [quote=Steve]Hi Pete,What is the mesh to open space ratio of the plastic mesh you use?/QUOTE] Good question Steve, I want to know this too... -Andy
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25th August 2006, 19:10	#45 (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: 3,001	Re: SMI Scrubber Quote: (Originally Posted by silent running) Hi all. That's actually Sharon Ready posting... Paul, don't you think the perf metal wants to come to equalibrium with the cooler jacket of air surrounding it? The metal in the scrubber doesn't just "radiate" 1 way, especially when the scrubber is just starting up and the reaction front on the out to in Meg is on the outside of the scrubber circumference and nearest to the water... -Andy primarily heat transfer is going to be at the physical contact point, whether it is to or from the material.. the air gap is a fairly good isulator and the delta temperture in this gap is going to be small compared the scrubber to metal or the bucket to water. To do cooling/heating on a large scale with air you need alot of surface area, thats why things like condensrs and radiators have lots of fins.. they need to increase the air/surface contact area, and ideally force a flow contunualy across this increased area.. The high energey transfer is also at the physical contact point (liguid to tubing to fins), with the fins being an inefficient transfer point. energy transfer by conducton is aways higher that by convection.. __________________ 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, 19:59	#46 (permalink)
*schford* Despotic Overlord Current Rebreather/s: Megalodon Sport Kiss Other Rebreather/s: Join Date: Jan 2005 Location: London, UK Posts: 3,559	Re: SMI Scrubber Quote: (Originally Posted by silent running) Hi all. That's actually Sharon Ready posting... I guess signing it Pete made us think it was Pete posting __________________ 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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25th August 2006, 20:23	#47 (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: 1,832	Re: SMI Scrubber Quote: (Originally Posted by schford) I guess signing it Pete made us think it was Pete posting Yeah true, sometimes she posts something for him that's effectively a quote, so it's hard to tell...
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25th August 2006, 20:30	#48 (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: 1,832	Re: SMI Scrubber Quote: (Originally Posted by jradomski) primarily heat transfer is going to be at the physical contact point, whether it is to or from the material.. the air gap is a fairly good isulator and the delta temperture in this gap is going to be small compared the scrubber to metal or the bucket to water. To do cooling/heating on a large scale with air you need alot of surface area, thats why things like condensrs and radiators have lots of fins.. they need to increase the air/surface contact area, and ideally force a flow contunualy across this increased area.. The high energey transfer is also at the physical contact point (liguid to tubing to fins), with the fins being an inefficient transfer point. energy transfer by conducton is aways higher that by convection.. Yes Joe, physical conductance would always be more than transfering to gas, but that's what radiators do-transfer heat from metal to the air around it. And a radiator is not usually transfering it's heat into a gas jacket which is continually being exchanged and is less than .5 inches next to a solid which is .25 inches away from cold sea water... -Andy
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25th August 2006, 21:17	#49 (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: 1,494	Re: SMI Scrubber Quote: (Originally Posted by silent running) Hi all. That's actually Sharon Ready posting... Paul, don't you think the perf metal wants to come to equalibrium with the cooler jacket of air surrounding it? The metal in the scrubber doesn't just "radiate" 1 way, especially when the scrubber is just starting up and the reaction front on the out to in Meg is on the outside of the scrubber circumference and nearest to the water... -Andy andy, it does not make any diff: the mesh is in the flow of one gas at a specific temperature: this mesh quickly comes to that temp and that's it, there can not be any heat loss, because there is no second medium, gas or liquid, that can take over the heat so metal or plastic mesh, it's all the same :-) only heat capacity, not conductance, has to do with the time it takes, but it is of no importance, really neglectable regards 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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25th August 2006, 21:58	#50 (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: 1,100	Re: SMI Scrubber in my meg the loop temp is usually 10-20 degrees warmer than the ambient water temp (farienheit), the 120 deg was a ways off. : ) In 46 degree water, our usual home turf temp, the loop runs about 55-60, this depends on work load, current too. (do you get cooler when the current is running by you? your can does too) In warmer climates the loop runs about 5-10 warmer. the highest I have ever seen was 95 in cayman. In a section of the CUMA CF Navy rebreather manual, they suggest that for warm water that the diver reverse the flow of the loop to cool the loop temp, but this is an SCR that works on different principles of the MEG or PRISM, unless the manufacturer recommends swapping flow direction, I wouldnt do that. Someone suggested that having a metal scrubber in contact with the ambient water was a bad thing, neither the meg or prism do this, so its rather a moot point. __________________ 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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