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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: mooseboi4444 on July 29, 2020, 04:48:13 AM

Title: Does heat affect the distribution of gases in an enclosed space?
Post by: mooseboi4444 on July 29, 2020, 04:48:13 AM
I have built an enclosed space 2.4x2.4x2metres to use for doing epoxy work. While the particular brand I am using is touted as no fumes, I still find myself getting a migraine in the enclosed space implying there is something in the product/or perhaps unburnt butane from the torch which is giving me the headache.

Anyway, the purpose of building the room was to give me a stable temperature to use the epoxy. I use a single 1250watt fan-free convection heater as the temperature controller. So I understand that the nature of gases is to evenly distribute themselves in a space...

(1)but when temperature is concerned, does this cause a variance in the distribution of gases as the fume particles heat up and rise also? Or do they stay evenly distributed regardless of temperature?

I am ultimately trying to figure out the best placement to put the exhaust fan on the 2metre high wall.

(2)Should it be up at the ceiling where the most heat is, or down at the foot of the wall? The goal is maximum heat retention, and maximum fume extraction.

(3)is the temperature variance between the height in such a small space negligible that I am over thinking this design and the exhaust fan would be effective positioned anywhere

(4)how would the internal temperature/fumes of the room be affected if the extraction fan was reversed and was blowing in cold fresh air from the outside? would it be better to have the fan blowing fresh air in or sucking air out?

I am curious to know your responses to the four questions above. Thank you
Title: Re: Does heat affect the distribution of gases in an enclosed space?
Post by: MNIO on July 29, 2020, 03:53:49 PM
Sounds like you're painting a jail cell and warming it with a ceramic heater. IF UNDISTURBED, the vapor may settle so that the denser gases are at the bottom of the cell and lighter gases at the top.  However, any movements (such as you moving through the room) will stir it all up again.  AND temperature variations will cause air movement and stir things up also.  So I don't believe any layering effect is the problem here.

You state you're using a odor free epoxy resin.  I have no idea what chemicals are in your particular brand but many of those odor free ones use mineral / vegetable oils, small amounts of petroleum distillates and pigments.  And if you're using a a hardener, they might contain amines, phenols and formaldehyde (the latter is notorious for causing headaches, vomiting, irritation of throat, nose, etc).  I doubt the pigments are the root cause of your headaches but any of the rest of the chemicals are fair game.  Can you elaborate on brand?  and what's this about butane?

As to ventilation, the general idea is you want to bring in fresh air where you breathe and vent air away from where you breathe.  If you're standing up and painting the floor with a roller, an inlet vent on the wall or ceiling and an exhaust fan on the floor might be best.  But of course, you want to paint your entire cell right?  Not just the floor.  So another consideration is air turnover rate. 

Although to properly design a ventilation system requires knowledge of the chemicals in the vapor phase, as a rough estimate you could use the standard 15-30 turnovers per hr (CPH) for noxious fumes.  Let's go with 30 for the moment.

you can estimate Q (cubic feet / min.. cfm) required by this equation.
  Q = CPH * V / 60 = 30 * (2.4*2.4*2.0 m^3)*(3.2ft/m)^3/60 = 230 cfm

Most of the common bathroom exhaust fans are about 1/4 to 1/2 of that capacity so, you could try 2 bathroom exhaust fans placed on either side of your cell near the floor with an inlet near the ceiling or 1 high capacity fan near the floor.  I suspect that will help tremendously.

as to the temperature effects bringing in cold air... Your major concern right now is ventilation.  You don't want to harm yourself right?  IF after correcting this the temperature is too cold, add another space heater.   

Title: Re: Does heat affect the distribution of gases in an enclosed space?
Post by: Enthalpy on July 30, 2020, 04:35:22 PM
What is this butane torch?

DANGER you may be at risk from >>>>> CARBON MONOXIDE <<<<<