Hello,
Have been searching the web for quite some time but to no avail. Recently ran into your forum and thought to run it by the people here. Have formal machine design education but next to none concerning electric except for basic equations.. The mechanical aspects are fairly worked out and i only need help/suggestions concerning heating a plate thru which cold air flows on it's course to the face mask.This plate is designated as number "3" in the drawing. Not sure rather to simply thread nichrome coated wire thru said plate #3 or attach a power resister of which i have no idea how to do. mask has a one way outlet valve

At present i have
1. temperature controller.
2.sensor to warn me when my battery falls below a certain voltage.
3.5000mAh 11.1 volts battery-rechargeable Lipo Pack
and of course a multimeter
I can machine aluminum.
The entire project is of aluminum. inside mask temperature should be 60-75f which i think to control with the temp troller regardless of any normal outside temperature differentiation?
Thanx for any time, suggestions or critique

ps links could be given to the components but not sure rather it would be appropriate here.

 

Heating air requires energy, and the amount needed per unit time (heater power) is directly proportional to the mass flow rate of the air and the temperature change needed. You haven't mentioned these critical parameters.

 

A link to your temperature controller will come in handy later on.

 

Heating air requires energy, and the amount needed per unit time (heater power) is directly proportional to the mass flow rate of the air and the temperature change needed. You haven't mentioned these critical parameters.

Thanx wayneh.
Did not know these variables would come into play as i was just hoping for a round about idea. Not asking anyone to go into it that kind of deep.
These are the only numbers i can come up with regarding volume of air flow across the plate over time. I have to go by my copd testing (pulmonary function test) as i have copd and these are the results of that test. But they are at max.??? I think to take 70% of these values?

MY LUNG capacities
PEF
Peak expiratory flow; the highest forced expiratory flow (L/second) litters per second)=4.10
TLC
Total lung capacity; the total volume of air in the lungs at full inhalation=5.70 liters

Temperature differentiation.. max. outside temperature that i would go out in circa 27 degrees.
i wish to keep 60-75 degrees inside the mask.
Do i also need aluminum transmissive factors?

I don't expect for anyone to go thru any heavy calculations on my behalf. A rough estimate and a feasible heating method to put me in the ball park and the rest i could get by testing and keeping notes as outside temperature and varying resistance across the plate changes.yes?
I am happy that anyone even answers.

 

A link to your temperature controller will come in handy later on.

ronv,
thanx for reading. anything you guys need just ask and i will get it to you.
I just did not want to load this request with outside links as if taking for granted anyone would respond. Also in some forums it is frowned upon.

ps my components came in today and i am rather excited. To not be locked in the house all winter because of these d_ _ _ lungs!!

 

I calculate 70 to 100 watts to change 16 liters per minute from 27F to 60F/75F.

 

I would consider adding a heat exchanger to the system so that exhaled air (at ~90F ?) pre-heats incoming air. That would significantly reduce the power requirements.

 

Thanks for the details, jarity. I know you said "mask" but I wasn't sure this had anything to do with a facial mask for copd.

Inline heating - for instance in a flexible tube - is a big challenge in my opinion. It would be easier if we didn't have any concern about pressure drop across a heat exchanger (like pulling air over aluminum fins), but you certainly don't want to sense any restriction of air flow, like having to suck through a straw.

Instead I'm picturing a large heat exchange "chamber", something that has a fair amount of thermal mass and provides more contact time with the incoming air than would be possible with the hose alone. Same concept as the water heater in your house. I'd say you could pull the air through warm water, but that would be like sucking on a bong. Or so I've heard.

Using a thermal reserve would make it much easier to hold a constant temperature, and there would be far less risk of failure of the control system.

 

I calculate 70 to 100 watts to change 16 liters per minute from 27F to 60F/75F.

Hmmm, I get a smaller number:

Flow of cold air: 16L/min (moderate exercise could take this to 50)
∆T = 25°C
heat capacity of air: ~0.00121 joule/cc/°C 1J = 1 W•sec

0.00121W•sec/cc/°C*16000cc/min*25°C*1min/60sec = 8W

The volumetric heat capacity of course changes as the air expands due to warming, but that small error doesn't explain the discrepancy. Frankly your number seems more plausible but I don't see an error in my calc.

 

Raising the air temperature that far is definitely going to require some humidification, and, as someone who's worn a gas mask once or twice, you don't want anything restricting airflow. Anything you can call a "tube" wont work.

If you really want to do this you need to implement positive pressure and humidification.

 

Thanks for the details, jarity. I know you said "mask" but I wasn't sure this had anything to do with a facial mask for copd.

Inline heating - for instance in a flexible tube - is a big challenge in my opinion. It would be easier if we didn't have any concern about pressure drop across a heat exchanger (like pulling air over aluminum fins), but you certainly don't want to sense any restriction of air flow, like having to suck through a straw.

Instead I'm picturing a large heat exchange "chamber", something that has a fair amount of thermal mass and provides more contact time with the incoming air than would be possible with the hose alone. Same concept as the water heater in your house. I'd say you could pull the air through warm water, but that would be like sucking on a bong. Or so I've heard.

Using a thermal reserve would make it much easier to hold a constant temperature, and there would be far less risk of failure of the control system.

----------------------------------
wayneh,
As i am understanding this it seems as if the air will not be in the chamber long enough to significantly raise the temperature.
1. I could add the number of heating plates along the axis of the 2" aluminum pipe.
2. Eliminate the plates and coil a length of coated nichrome wire arount the pipe itself. That would increase the thermal mass significantly.
3. Increase the temperature of the plate which would require a much "larger" battery.
I only hope the larger wattage calculation is off!!! Being that i calculated the ordered battery to give me 40 watts for 1 hour it's inefficiency taken into account.
Again,Thanx for your time.
Attached is the mask itself and the components ordered.

 

Why do you need to preheat your breathing air?
Do you have some sort of respiratory health/illness issue?

Where I live I regularly spend whole days outside in the winter at ambient temps of -20 to -30f without problems breathing the air at that temp regardless of if I am at rest or working hard and breathing hard.

 

I would consider adding a heat exchanger to the system so that exhaled air (at ~90F ?) pre-heats incoming air. That would significantly reduce the power requirements.

Alec,
I have indeed tried these masks. Your exhaled breath heats the incoming air via a heat exchanger. I had to send them back. You have to breath out of your mouth to heat the exchanger. You can breath out of your nose if you wish but then there is no heat given to exchange. Again too the increase in temperature is minimal. When i first ran across them i thought,"this is the answer to my prayers!" Also They are quite claustrophobic and drag on your breathing with the least bit of effort.

 

Why do you need to preheat your breathing air?
Do you have some sort of respiratory health/illness issue?.

Love it, one of the dumbest questions I've seen in ages. Try reading the thread again.

 

You must have pretty high standards for what constitutes a dumb question then!

There are no dumb questions. There are only dumb people with questions.

 

Love it, one of the dumbest questions I've seen in ages. Try reading the thread again.

I can't see why it was a dumb question (nor, even if it was why there was a need to be insulting). Having re-read the thread myself I still can't see a clear reason for needing to heat the air. The human body is in fact remarkably well adapted to breathing very cold air and face masks are normally used to protect the skin on the face from frostbite as much as to increase the temperature of the air taken in.

 

I see. His second post mentions he has COPD. I didn't catch that during the first read with my wife talking to me at the same time.

Personally if it was me I would just wear a proper winter face mask or scarf to cover my mouth. Both air preheat and moisture are rather well controlled and recycled that way.

At worse I would look into designing a simple heat exchanger that draws fresh air in through a sort of body to air heat exchanger vest. Draw the cool air in from around the waist through a thin vest that goes against the body and use your own body heat to preheat the air.

From there a simple double flap type breathing mask to let fresh air being fed from the vest supply go in and let the air being breathed out get vented from the mask. That way all air flow only goes one way.

At most a small fan could be added to keep the supply air in the vest at a slight positive pressure while greatly reducing the overall power requirements needed.

 

sorry that this discussion went this way
Just so everyone understands...One of the things that can happen when you have copd is that the "smooth muscles" coiled around the airways can constrict and cause an exacerbation. I have to fight for air. It can be quite scary An emergency issue. Different things can trigger this event in different people. One of mine is temperature. Anything 45 degrees and below (after 15-20 minutes and i am in trouble. Which makes me a prisoner in winter. So am trying to develop a mask for myself and was hoping for a little help. Certainly not cause a conflict here.

 

Tcmtech's heat-exchanger vest looks good. That could provide a large area for heat exchange hence rapid air warming and, more importantly, low flow resistance. The vest could also be constructed to act as a bellows to assist breathing in an emergency.
Murphy's Law applies, of course, so there would also be body cooling. That could be overcome by a supplementary electrical heat source.

 

Hmmm, I get a smaller number:

Frankly your number seems more plausible but I don't see an error in my calc.

From air conditioning: BTU = 1.08 CFM dt
From some TV show: "Doctor, I count 16 respirations per minute."
From sitting here breathing: I think that's about a liter at rest.
From Google: 16 liters per minute = .565 cubic feet per minute
Definition of a B.T.U.: 1 Watt hour = 3.412 BTU
dt = 60F-27F or 75F-27F = 33F to 48F

calculate, calculate, calculate...

BTU = 1.08 .565 CFM 33dt
P = 1.08 .565 33 / 3.412
P = 5.9 watts absolute minimum

Seems I shot myself in the foot.
Now my math is open for inspection. Please inspect if you care to, and be invited to correct me.