Does nitrogen expand when heat is applied?
Back in the days of new construction when we would install a new system in a house, furnace,a/c, duct work, and gas pipe. I would charge the gas pipe with 20#'s of air for the pressure test. And let it set overnight for the inspector to see it was air tight. If it was a 70 degree day when I filled it with air then the outdoor temperature dropped to 45 degree's. When the mech inspector checked the pressure gauge it would be at about 17#'s, not 20#'s. The temperature affected the final reading. Will the same thing happen when using nitrogen?
I filled a lineset with 150# of nitrogen after fixing a couple leaks I found. Last service call of a very long 12 hour day. I'm going back tomorrow after 4 days because the customer was leaving town that night. There is going to be a 35degree temperature difference from the time I put the nitrogen in the lineset. Will there be a different affect with the nitrogen because of no moisture in nitrogen? Does temperature make nitrogen expand and contract like CO2 ?
ALL gases expand and contract as their heat content varies.
The rate of expansion or contraction per degree change is what will matter in your case.
Building Physics Rule #1: Hot flows to cold.
Building Physics Rule #2: Higher air pressure moves toward lower air pressure
Building Physics Rule #3: Higher moisture concentration moves toward lower moisture concentration.
ALL gasses are subject to that phenomenon. In fact, by taking careful measurements, you can predict the actual pressure after a temperature change.
Nitrogen is a colorless, odorless, tasteless, diatomic and generally inert gas at standard temperature and pressure. At atmospheric pressure, nitrogen is liquid between 63 K and 77 K. Liquids colder than this are considerably more expensive to make than liquid nitrogen is.
For all intensive purposes you do not need to worry about the minute amount nitrogen will expand with heat.
Do not take my word for it Google Nitrogen and read the results. There are many interesting facts about this marvelous gas.....
How about you google the ideal gas laws and understand how they relate before you start giving inaccurate information.
Originally Posted by trouble time
Thank You All for your input, Kimosobee
Here's Marc O'Brien's Nitrogen Pressure Change Calculator:
Nitrogen is subject to change in pressure when there is a change in temp. However, any change in temp that may be experianced at a single location here on Earth, will not effect the pressure enough to worry about. Now if there is any refrigerant or oil (which tends to hold refrigerant) present where you're doing a pressure test, you should put a vacuum pump on for a little while before adding nitrogen. I wouldn't waste time trying to predict the exact pressue change versus temp change unless you like to do math for the fun of it.
Using the posted pressure change calculator, I calculated what would have happened if I had pressurized a system to 200# yesterday at the high temperature of 80 degrees and read that pressure today at 50 degrees.
Originally Posted by ChrisTechMech
The change in pressure was 12#
Not an insignificant change.
As I said before, please learn and understand the ideal gas laws before spouting inaccurate information.
Icemeister,Thanks. This is exactly what I was looking for, ChrisTechMech as a matter of fact I do like to do math.I had planned on doing a deep vacuum when I returned to the job. I was just curious . Thanks for your response also. I believe you guys answered my question!
INERT, INERT, INERT......
Originally Posted by jpsmith1cm
Do not sweat the little things. I explained that the differences were small.
That is accurate information!
Never give up; Never surrender!
Installed an oil furnace with a DX coil filled with nitrogen with rubber plugs to keep the nitrogen in until ready for piping. It was cold, so we fired up the furnace before we brazed in the lineset to the coil. After about ten minutes of furnace operation, I hear a loud pop and something whizes past my head and bounces off of the wall. It was the large rubber plug keeping the nitrogen in the coil that blew out from the pressure from heating the nitrogen in the coil.
Originally Posted by trouble time
I don't think being "INERT" kept that nitrogen from expanding enough to scare the bejezzes out of me.
Government is a disease...
...masquerading as its own cure
Ecclesiastes 10:2 NIV
No gases are truly ideal, but nitrogen is close to ideal at atmospheric pressure and near room temperature.
Ideal gas law is: PV=nRT
For real gases, it is: PV=ZnRT, where Z is the compressibility factor
For nitrogen at 1.013 bar, 59 F, the compressibility factor is 0.9997 (so really close to ideal)
I'm not sure if that nitrogen calculator accounts for compressibility or not (probably not). If it did, it would need to have tables in there to look up Z (which depends on both pressure and temperature).
Whether or not it is considered inert (which only means whether is reacts easily) gas nothing to do with this question. Nitrogen isn't really an inert gas, but it is close to being inert and is much cheaper and more abundant than the true Noble (inert) gases (such as helium, neon, argon, etc.).
You could use that calculator to estimate what changes might be due to temperature changes. If the change is still near where is could be from changing temperatures or might be a really small leak, one option would be to come back say a day later. If it is a leak, the pressure will have fallen even more. If it was due to temperature, it may be the same pressure (if the temp is about the same) or the pressure may go up a bit if it is warmer.
What also matters is the average temperature for this calc. Since I assume that most of the lineset (and evap coil) is inside and is within normally heated/cooled space, so this volume is not going to see much temperature change. If the outdoor unit was empty and you had filled it too with nitro for this test, then you have that whole volume (compressor, condensing coils, etc.) that will be exposed to temperature swings. If the lineset/air handler is in the attic, then those will see even larger temperature swings.