Need to cool air for experiment

[pixmanvegas]

I am going to be conducting an experiment in which I need to cool approximately 55 liters of air per minute to as close to -40C as possible. If I can't hit that target, as cold short of that as possible.

The air needs to be breathable.

If the solution is not pre-cooled or compressed air, I will be starting from an ambient temp of around 20C (standard room temp)

Does anyone have any suggestions on a low budget way, or for that matter ANY way, to accomplish this?

The solution needs to be portable enough to take to an office building to deploy with a quick set up time. This will be a 3 or 4 event experiment.

Edited September 13, 2016 by pixmanvegas

[Strange]

Typing this into Wolfram Alpha:

 

55 litres * 1.3 (kg/m^3) * 60 * 1 (kJ/(kg K)) * 75K / 60 seconds

 

Tells us that you need to remove about 322 kJ from the air per minute (over 5kW). This doesn't sound to me like something that can be done cheaply or easily (or quietly!).

 

(I am guess the future of 1.3 for the density of air at a sort of midpoint of the temperature range; it change quite rapidly here so the calculation won't be that accurate.)

http://www.wolframalpha.com/input/?i=55+litres+*+1.3+(kg%2Fm%5E3)++*+60+*+1+(kJ%2F(kg+K))+*+75K

Edited September 15, 2016 by Strange

[michel123456]

I am going to be conducting an experiment in which I need to cool approximately 55 liters of air per minute to as close to -40C as possible. If I can't hit that target, as cold short of that as possible.

The air needs to be breathable.

If the solution is not pre-cooled or compressed air, I will be starting from an ambient temp of around 20C (standard room temp)

Does anyone have any suggestions on a low budget way, or for that matter ANY way, to accomplish this?

The solution needs to be portable enough to take to an office building to deploy with a quick set up time. This will be a 3 or 4 event experiment.

Please give some more information.

Will the experiment be conducted in an open room (as a presentation for students where the students will freeze too), or in some kind of closed chamber?

The -40c seems to me difficult to reach with conventional coolers. I guess you'll need some chemical thing.

[pixmanvegas]

Strange, Thank you. We will look into that...

Michel,

the only person in the room who needs to receive the cool air is the single human subject. Air delivered through a hose attached to a mask. no one else should be affected. The experiment will be performed in an office/room. We can probably exhaust the waste heat through the return vent of the building A/C. We would need to avoid excessive noise though.

[michel123456]

Strange, Thank you. We will look into that...

Michel,

the only person in the room who needs to receive the cool air is the single human subject. Air delivered through a hose attached to a mask. no one else should be affected. The experiment will be performed in an office/room. We can probably exhaust the waste heat through the return vent of the building A/C. We would need to avoid excessive noise though.

The noise produced by the human screaming?

I don't know if it safe to make him inhale air at minus 40 celsius.

[Klaynos]

A quick Google strongly suggests this is a very bad idea. Why are you trying to do it?

[Strange]

the only person in the room who needs to receive the cool air is the single human subject. Air delivered through a hose attached to a mask. no one else should be affected.

 

 

Well, at least you have made it easy for the police to track you down, by posting here.

[pixmanvegas]

The noise produced by the human screaming?

I don't know if it safe to make him inhale air at minus 40 celsius.

Yeah, sounds pretty horrible. Here's the thing.

It's the equivalent of being outside at -40C (or F for that matter) and there is no danger at all to human damage. Studies have been done to determine the effects of cold air on the human lung. The body warms it as it goes down the throat. There was a military study of cold air exposure down to -70F in the arctic that found no negative effects. Although there were a few anecdotal cases added of slight frostbite in the lungs after the study concluded.

The pain or discomfort one feels when outside breathing very cold air is not caused by the cold but by dehydration of the membranes of the nasal passages and throat.

So..

We don't anticipate any screaming or actual damage.

Now back to the question. How to cool the air?

Anyone? Anyone....

Thanks

A quick Google strongly suggests this is a very bad idea. Why are you trying to do it?

Please site your sources. Here's a couple of studies of my sources that indicate there should be no problem...

This one was performed at our target temp...(-40 degrees C, dry)

Cold air inhalation and esophageal temperature in exercising humans. - PubMed - NCBI

http://www.ncbi.nlm.nih.gov/pubmed/7453516

This one at -35C

Physiological effects of cold air inhalation during exercise. - PubMed - NCBI

http://www.ncbi.nlm.nih.gov/pubmed/7417121

Our reasons are different, hence the new experiment, but it's not unprecedented or dangerous.

Thank you for your concern.

Edited September 15, 2016 by pixmanvegas

[Endy0816]

You might look at cooling scuba tanks. Dry ice has the portability and lower upfront cost you are after. Pressure reduction as the air leaves the tank will lower the temperature as well.

 

Really need to consult someone local though. Potential for safety issues and mechanical trouble.

Edited September 15, 2016 by Endy0816

[pixmanvegas]

You might look at cooling scuba tanks. Dry ice has the portability and lower upfront cost you are after. Pressure reduction as the air leaves the tank will lower the temperature as well.

 

Really need to consult someone local though. Potential for safety issues and mechanical trouble.

Do you mean there are "cooling scuba tanks" as in there are scuba tanks that work to cool air. or I should look into making scuba tanks cold? I will check with a local scuba expert. this is a good idea. I like the idea of using dry ice to cool the air inline on the way to the regulator. Good thought.

I found a commercial "vortex valve" that will cool compressed air with a 50 degree drop in temperature. That gets us part of the way.

Edit: I can word that better...

I found a commercial "vortex valve" that will create a 50 degree drop in temperature.

Edited September 15, 2016 by pixmanvegas

[Endy0816]

 

or I should look into making scuba tanks cold? I will check with a local scuba expert. this is a good idea. I like the idea of using dry ice to cool the air inline on the way to the regulator. Good thought.

 

This. Definitely checking with someone local first.

[Klaynos]

Yeah, sounds pretty horrible. Here's the thing.

It's the equivalent of being outside at -40C (or F for that matter) and there is no danger at all to human damage. Studies have been done to determine the effects of cold air on the human lung. The body warms it as it goes down the throat. There was a military study of cold air exposure down to -70F in the arctic that found no negative effects. Although there were a few anecdotal cases added of slight frostbite in the lungs after the study concluded.

The pain or discomfort one feels when outside breathing very cold air is not caused by the cold but by dehydration of the membranes of the nasal passages and throat.

So..

We don't anticipate any screaming or actual damage.

Now back to the question. How to cool the air?

Anyone? Anyone....

Thanks

 

Please site your sources. Here's a couple of studies of my sources that indicate there should be no problem...

This one was performed at our target temp...(-40 degrees C, dry)

Cold air inhalation and esophageal temperature in exercising humans. - PubMed - NCBI

http://www.ncbi.nlm.nih.gov/pubmed/7453516

This one at -35C

Physiological effects of cold air inhalation during exercise. - PubMed - NCBI

http://www.ncbi.nlm.nih.gov/pubmed/7417121

Our reasons are different, hence the new experiment, but it's not unprecedented or dangerous.

Thank you for your concern.

 

That's more thorough than I was. Most of what I read was about increased occurrences of things like asthma with quite long term exposures.

 

 

My thoughts would be to investigate mixing nitrogen evaporated from liquid nitrogen. With oxygen and co2 from tanks and ambient air to adjust them temp. Not easy to build or control though.

 

I'm sure I've seen footage of a quite large enclosure (on top gear so large enough to fit a car) that could get down to -30 deg C I think. Might be worth finding out where it is and contacting them to see how they do it.

[Sensei]

Typing this into Wolfram Alpha:

 

55 litres * 1.3 (kg/m^3) * 60 * 1 (kJ/(kg K)) * 75K / 60 seconds

 

Tells us that you need to remove about 322 kJ from the air per minute (over 5kW). This doesn't sound to me like something that can be done cheaply or easily (or quietly!).

 

(I am guess the future of 1.3 for the density of air at a sort of midpoint of the temperature range; it change quite rapidly here so the calculation won't be that accurate.)

 

http://www.wolframalpha.com/input/?i=55+litres+*+1.3+(kg%2Fm%5E3)++*+60+*+1+(kJ%2F(kg+K))+*+75K

Are you sure your calculations?

I assume 60 (on the left) is difference between +20 C and -40 C,

then what is 75K on the right?

 

322 kJ is enough energy to increase temperature of 1000 g (~ 55.5 mol) of water for 77 C.

55 L of air has just 0.04464 mol * 55 = ~ 2.4552 mol.

Edited September 18, 2016 by Sensei

[Strange]

Are you sure your calculations?

 

 

No.

 

It was volume (55) * density (1.3) * one minute (60) * specific heat (1) * temp change = total energy required / 60 = power

 

(I know multiplying the volume by 60 (seconds) and then dividing by 60 is redundant, but that's just because of the steps I took to get the final result.)

[Sensei]

Maybe I am reading it incorrectly?

Is it 55 L (box with 38 cm x 38 cm x 38 cm) per minute = 0.9167 L per second.. ?

or

Is it 55 L per second for minute.. ? 3300 L total per minute.. ?

Still not understanding why you multiplied by 60 (if 75K is delta between +25C and -50C, OP wanted +20 C -> -40C).

 

It was volume (55) * density (1.3) * one minute (60) * specific heat (1) * temp change = total energy required / 60 = power

 

(I know multiplying the volume by 60 (seconds) and then dividing by 60 is redundant, but that's just because of the steps I took to get the final result.)

 

Wouldn't that cancels units s/s.. giving result in J or kJ? Power should be in W.

[Strange]

Maybe I am reading it incorrectly?

Is it 55 L (box with 38 cm x 38 cm x 38 cm) per minute = 0.9167 L per second.. ?

or

Is it 55 L per second for minute.. ? 3300 L total per minute.. ?

 

You are right. It is 55 litres per minute, so I am out by a factor of 60.

 

 

if 75K is delta between +25C and -50C, OP wanted +20 C -> -40C

 

You are, again, right. I misread the 55 as the temperate.

 

Thanks for checking.

 

 

Wouldn't that cancels units s/s.. giving result in J or kJ? Power should be in W.

 

No, because one was a dimensionless scaling factor (an unnecessary dimensionless scaling factor).

 

 

So: 55 litres * 1.3 (kg/m^3) * 1 (kJ/(kg K)) * 60K / 60 seconds = 7W, which is much more reasonable.

http://www.wolframalpha.com/input/?i=55+litres+*+1.3+(kg%2Fm%5E3)++*+1+(kJ%2F(kg+K))+*+60K+%2F+60+seconds

Does that seem right?

[pixmanvegas]

Thanks for continuing to discuss this, people!

I am paying attention.

55 lpm is the volume of air needed to breathe for an adult male under stressful activity (approximate). We need him to be able to breathe air at the target temp while performing a standard cardiopulmonary stress test. Does that help with the calculations?

[Sensei]

Not 7 W but 71.5 W is needed, according to Wolfram website.

If I were you, I would check if peltier coolers in grid would solve it.

They have efficiency 10-15%. So to have 72 W, you need grid with 720 W (I guess).

See this model TEC1-12706. It's 92 W 12 V.

https://www.amazon.com/TEC1-12706-Thermoelectric-Peltier-Cooler-Volt/dp/B002UQQ3Q2

(I am using TEC1-12705)

Buy 10 units for 170 usd, plus fans, plus heat sinks, on either cool and hot side (silicon/thermal conductive paste).

And connected them to powerful power supply (1 kW+ 12 V).

 

After experiment you can use them to make Cloud Chamber

 

[Strange]

Not 7 W but 71.5 W is needed, according to Wolfram website.

 

 

Doh.

[Handy andy]

I am going to be conducting an experiment in which I need to cool approximately 55 liters of air per minute to as close to -40C as possible. If I can't hit that target, as cold short of that as possible.

The air needs to be breathable.

If the solution is not pre-cooled or compressed air, I will be starting from an ambient temp of around 20C (standard room temp)

Does anyone have any suggestions on a low budget way, or for that matter ANY way, to accomplish this?

The solution needs to be portable enough to take to an office building to deploy with a quick set up time. This will be a 3 or 4 event experiment.

 

Are you sure you want to breathe air at -40C, it will give your nasal passages frost bite.

[EdEarl]

Dry ice sublimates at about -78C, and it is inexpensive. You will need a heat exchanger; perhaps several pieces of 1/2 in electrical conduit made of metal.

[John Cuthber]

I rather hope not, but it may be no coincidence that the OP hasn't posted since he asked about this some months ago.