I'm no expert on COPD but I'd have thought that you would need to ensure that any benefit from heating the incoming air wasn't at the expense of either reducing the volume you have available (through too much pressure drop) or lower the available oxygen (my mixing incoming and outgoing air).
Tcmtech's solution would have the benefit of reducing the amount of heat loss to the environment that you'd have if you were heating in the mask, but unless it was a semi rigid vest I'd be worried about the potential for it collapsing and hence restricting airflow. If you went for a simple flexible tube inside your clothing you would avoid this risk and you could add a simple heating filament along the axis of the tube in the upper part. You'd probably still need a fan to compensate for the pressure drop.

 

[Edit] Got interrupted whilst typing this so took an age to complete - ignore most of it becuase it has already been said above [/Edit]


Would it be possible to have a relatively large canister worn close to the skin (say on your back under your outer clothes, may be something like an aluminium hot water bottle) that you draw the air through so that your body heat warms it. The container needs to be reasonably large to give the air sufficient residence time to heat up. You could supplement the heating electrically.

Someone else calculated a requirement for 100W, not disputing their figures because I haven't done any calcs but my Hot Air rework gun is rated at 90W and that raises the temp of a reasonable air flow by 300C easily so my hunch is that you would get away with less - but I guess it would still mean a large battery.

 

Someone else calculated a requirement for 100W,

That was me. See post #20 for a retraction.

 

[responding to #12 in #20]
Nah, your 6W is plenty close to my 8W. If the OP designs for the capability to drive 10W into the delivered air, that should allow for a little safety headroom.

The challenge is, how to drive a regulated 0-10W into the air without appreciable pressure drop.

Drawing heat from the body is not viable, in my opinion. I would not want 5-10W being sucked out of me if I'm sitting quietly and not exercising. Reminds me of sitting on an aluminum stadium bleacher. Not comfy. We've got a battery - use it.

I like the idea of a fan assist to generate a bit of positive pressure. The computer industry has produced some really quiet and efficient fans.

 

Supplemented body heat or not, large area, low flow rate has to be the way to go. A stack of aluminium plates in a box with trace heating wire attached may do it - at 20W/m you would need 0.5m of trace heating e.g. a box with 5 50x100mm plates 6mm apart?

 

Just to brainstorm a bit: I wonder if you could use a standard CPU cooler (large heatsink plus fan) attached to a peltier. These are easily obtained off the shelf components and wouldn't require much custom fabrication.

All incoming air would pass thru the fan and across the sink. Temperature near the mask (after mixing, passing thru colder tubes, whatever) would control current to the peltier. I'm thinking the heat sink alone might have enough thermal mass to smooth things out a bit, but a micro controller might be needed to provide PID control.

 

I think it's a shame if the heat from exhaled air goes to waste. With a 100% efficient heat exchanger (dream on!), air in at 27'F and air out at 87'F = pre-warmed air at 57'F.

 

I agree. A tall fin CPU sink is a good option. I also found a fully formed, fan fed, 4" by 4" heat exchanger in a "ceramic" room heater with 5 resistance sections from 300 ohms to 2200 ohms per section. Probably not right for this job because it was designed for 120 VAC RMS, but it illustrates the possibility of finding what you need in your junque pile.

 

If we're just looking at 10W a couple of 5W power resistors in parallel would do it. If the battery is 12V then 15R would be about right (if I've not screwed up my calculation).

Not sure if you'd need a heat sink or if the airflow would be sufficient itself

 

[responding to #12 in #20]

Drawing heat from the body is not viable, in my opinion. I would not want 5-10W being sucked out of me if I'm sitting quietly and not exercising. Reminds me of sitting on an aluminum stadium bleacher. Not comfy.

I believe the body produces about 90W at rest so depending on how much heat is being lost through clothing and breathing, 10W into the "lung preheat" doesn't seem unreasonable. This energy has to be "lost" somewhere otherwise the body will overheat.

 

I was unclear. What I was addressing was using the body to help warm incoming cold air. That pulls heat from the body and should be avoided.

Reclaiming exhaust heat is fine, since it is totally lost otherwise. (Although "who cares?" comes to mind. The cost of supplying battery energy is not a significant design concern.)

 

I keep thinking of a mask that looks akin to this:

http://4.bp.blogspot.com/-9o4YRxyjl...metheus+space+jockey+engineer+pilot2+pics.jpg

With the long snout going down into a vest.

 

I was unclear. What I was addressing was using the body to help warm incoming cold air. That pulls heat from the body and should be avoided.

The way I am looking at it is that if its cold enough outside to need such a device you are already going to be, or at least should be, wearing more than enough clothing so that keeping warm should not be a problem.

The thing is being alive is a very exothermic reaction and we need to have a way to keep cool otherwise we can literally overheat to the point of it being fatal.

Believe me as from my own personal experience if I am dressed well enough I have trouble staying cool not warm even when its -30F and blowing hard and I am doing very little physical exertion.

BTW I used to have similar breathing problems when I was young. If the air was too cold it would cause a sort of asthma attack for me as well. Even today if I don't condition myself to working and breathing hard in cold weather I can trigger an attack although I do not use it for an excuse to not go outside when it cold. In fat I take it as a good reason that I have to go out and keep my tolerances up to it.

 

I don't live in a cold place now, but I remember vividly the first breath of 20 F air when leaving the house. It hurts! You have to take small breaths until your body adjusts. It takes less than a minute for a perfectly normal person to go through that process. I have no clue how difficult it is if your lungs are not, "normal".

 

For me it takes about 10 minutes to get comfortable the first day it gets real cold.

After that the being able to breath hard while exerting myself can take a good day or two with numerous events of my lungs tightening up and having trouble taking a deep breath until then. I know what the feeling is when its starting so I adjust my exertion until the feeling goes away.

Still I find it is a physical reaction that I can work at to condition myself to keep from triggering.

The odd thing is once I get to that point I find the cold air very refreshing and rather enjoyable to breath! Being more dense and dry than warm air you get more oxygen in each breath and for me that feels really good!

 

I run ~5 miles every day at any temperature between -20° to +80°F. Because of this conditioning, I never suffer EIA (exercise induced asthma) anymore. I adjust to each season as it unfolds. I recall having EIA very badly when I was a sedentary college student and would go for a run on beautiful winter day.