designing a diver powered etCO2 for rebreathers

[crewiscool]

I am a retired computer and electrical engineer who now runs a small machine shop as a retirement gig. To make a long story very short. I think I have a valid design for etCO2 monitoring and I am looking for input from someone with more knowledge on side-sampling etCO2 systems and the fluid dynamics and environmental conditions of rebreather loops than I have. Hopefully even the ability to model some configurations.

I saw a talk a few months ago given by Dr. Mitchell where he - in passing - mentioned that side-sampling would work but the energy to power the pump needed to consistently pull from the loop was a barrier to commercialization. To solve this problem I propose introducing a venturi nozzle on the loop and a negative pressure reservoir, check value and mass flow nozzle to the side-sampling sensors to act as the "pump". I know that this will work - I have leveraged this type of mechanism before. The technical component I don't know is if you can design a venturi with enough vacuum/cfm without an unacceptable increase in the WOB. I also don't know if can be built to work cost effectively.

Any constructive input would be welcome. Please contact me if you are interested in helping evaluate this idea. Note, I plan to release any findings or functional design into the public domain so this is not a money making endeavor.

I have attached a little diagram to aid in understanding the system.

Thanks for any help.

 

[Mobulai]

I am a retired computer and electrical engineer who now runs a small machine shop as a retirement gig. To make a long story very short. I think I have a valid design for etCO2 monitoring and I am looking for input from someone with more knowledge on side-sampling etCO2 systems and the fluid dynamics and environmental conditions of rebreather loops than I have. Hopefully even the ability to model some configurations.

I saw a talk a few months ago given by Dr. Mitchell where he - in passing - mentioned that side-sampling would work but the energy to power the pump needed to consistently pull from the loop was a barrier to commercialization. To solve this problem I propose introducing a venturi nozzle on the loop and a negative pressure reservoir, check value and mass flow nozzle to the side-sampling sensors to act as the "pump". I know that this will work - I have leveraged this type of mechanism before. The technical component I don't know is if you can design a venturi with enough vacuum/cfm without an unacceptable increase in the WOB. I also don't know if can be built to work cost effectively.

Any constructive input would be welcome. Please contact me if you are interested in helping evaluate this idea. Note, I plan to release any findings or functional design into the public domain so this is not a money making endeavor.

I have attached a little diagram to aid in understanding the system.

Thanks for any help.

I’m very interested in that — I’ll reach out over DM

 

[inquis]

I think another barrier is the 100% humidity.

 

[crewiscool]

I think another barrier is the 100% humidity.

My understanding is the side sampling obviates this problem.

 

[Mobulai]

My understanding is the side sampling obviates this problem.

I don’t fully get how it would, but maybe the low pressure reservoir could carry (for eg) silica gel beads to suck up the humidity

I’m extremely unfamiliar with co2 sensors specifics, so I can’t say it that basically “voids the samples”

 

[CG43]

How much power do you want to gain from the diver's breath work?
For OC, EN 250 requires a maximum WOB of 3 joules/litre.
If the diver breathes 25 liters/min., that's just 1.25 watts.
So you can gain max about 0.5 watts from the WOB.

The power you need to push your measuring volume through the CO2 sensor is also low with :
Power = Pressure * Volumen/sec.
The problem of pumping a small volume flow against a very low pressure through a CO2 sensor
should be easy to solve with a small, cheap dosing pump.

What does the CO2 sensor need?
A constant volume flow , or constant mass flow , or simply a measuring volume
that has to be replaced regularly ?

 

[runsongas]

or just commercialize the NASA sensor once MWCNT become more commercially available

Solid State Carbon Dioxide (CO2) Sensor | T2 Portal

technology.nasa.gov

 

[rjack321]

I am a retired computer and electrical engineer who now runs a small machine shop as a retirement gig. To make a long story very short. I think I have a valid design for etCO2 monitoring and I am looking for input from someone with more knowledge on side-sampling etCO2 systems and the fluid dynamics and environmental conditions of rebreather loops than I have. Hopefully even the ability to model some configurations.

I saw a talk a few months ago given by Dr. Mitchell where he - in passing - mentioned that side-sampling would work but the energy to power the pump needed to consistently pull from the loop was a barrier to commercialization. To solve this problem I propose introducing a venturi nozzle on the loop and a negative pressure reservoir, check value and mass flow nozzle to the side-sampling sensors to act as the "pump". I know that this will work - I have leveraged this type of mechanism before. The technical component I don't know is if you can design a venturi with enough vacuum/cfm without an unacceptable increase in the WOB. I also don't know if can be built to work cost effectively.

Any constructive input would be welcome. Please contact me if you are interested in helping evaluate this idea. Note, I plan to release any findings or functional design into the public domain so this is not a money making endeavor.

I have attached a little diagram to aid in understanding the system.

Thanks for any help.

I'm not fluid dynamics engineer but most sensors expect 2L/min flow. Normal relaxed tidal volume is 500mL. Normal respirations = 16. That's 8L/min. Back of the envelope math, you need 25% of that across that sensor face. So this is WAY more than a diver powered side loop.

 

[crewiscool]

I'm not fluid dynamics engineer but most sensors expect 2L/min flow. Normal relaxed tidal volume is 500mL. Normal respirations = 16. That's 8L/min. Back of the envelope math, you need 25% of that across that sensor face. So this is WAY more than a diver powered side loop.

Most medical side-sampling etCO2 sensors only need 30-60mL/min from my research. so you would only need about 6% efficiency. You could also pause the sampling if your if the revoir gets below a certain pressure. I also think your normal respiration numbers are a bit low for scuba diving. How many people do you know with an RMV of 8L/.28cuft/min?

 

[Duke Dive Medicine]

I think another barrier is the 100% humidity.

We use end tidal CO2 monitors in health care to confirm endotracheal tube placement and monitor respiratory status. I'm not an engineer by any stretch but if humidity were a factor then that may have been solved for.