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Old Mar 29th 2019, 12:53 AM   #1
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N2 Heater

Hello everyone, this is my first post. I hope I am in the correct spot. I am 13 years old and trying to design a N2 heater for my dad, so he can use it on his race car. I'll explain

My dad uses Nitrogen to inflate his tires before a race. The perfect pressure is about 25-28 psi for optimal grip. However, The tires are cold at the start, so to allow for expansion he sets them at 15psi. They normally take about 25 laps to heat up and get to max temp of about 230f.

I suggested using hot nitrogen at the start of the race to give him an advantage because it will take less laps to heat up and give him a better grip advantage over the other racers. (tire warmers are now allowed like they use in nascar, but no rules about using hot n2)

I am designing a cylindrical case with a electric heating element that will allow me to preheat the n2. I am trying to decide how many watts of power I will need to preheat the flow. I know the volume of the tire, (and flow) but I am having a hard time figuring out the temp change of the n2 once it goes through the heater. in the supply cylinder, its about 2000psi. It will drop to 30psi, and I know this will lose alot of heat. can someone point me in the right direction how to figure this out. Thanks
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Old Mar 30th 2019, 03:48 AM   #2
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I've been thinking about this and the theoretical answer is the <Ideal Gas Law>
However I can see that defining all the terms in your practical problem would be difficult.
Would it be possible to directly measure the temperature of the gas entering the tire?

Given this you can work out the energy required to raise the temperature the required amount.
The <molar heat capacity> of Nitrogen is 29.124 J/(molK)
which means that it requires 29.124 <Joule> to raise 1 mole of Nitrogen by one Kelvin

One <Kelvin> is essentially the same as 1 Celsius (or 1 degree centigrade).
(Kelvin, Celsius and centigrade differ only in where they are defined to be zero,
0 K is equivalent to −273.15 C {−459.67 F})

A <mole> is a defined (very big) number of nitrogen molecules (602,214,076,000,000,000,000,000 molecules)
one mole of nitrogen has a mass of 14 grams.

at 1 Bar (14.5 psi) 1 liter of nitrogen has a mass of 1.25 g.

1 watt is 1 joule per second.

So from your flow rate you should be able to work out, theoretically, how many watts you will need to raise the temperature by the required amount.

However, in practice you will have inefficiencies, so you will need more than this.

In the end you may find that trial and error will be your best bet!

Note that where I have <> there are links to relevant Wikipedia pages.
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Last edited by Woody; Apr 5th 2019 at 11:16 AM.
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Old Mar 30th 2019, 07:10 AM   #3
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Here's another idea ....

Fill the tire with air and a small amount of hydrogen . At the start of the race a small electrical spark inside each tire ignites the mixture instantly raising the temp and pressure .

By experiment it should be possible to determine the right % of hydrogen , and the correct start pressure , to get the final temp and pressure require ....

Whichever way you do it there is still the problem of the cool tire reducing the temp of trapped gas by conduction.
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Old Mar 30th 2019, 07:24 AM   #4
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Originally Posted by Jaek View Post
I am designing a cylindrical case with a electric heating element that will allow me to preheat the n2. I am trying to decide how many watts of power I will need to preheat the flow. I know the volume of the tire, (and flow) but I am having a hard time figuring out the temp change of the n2 once it goes through the heater. in the supply cylinder, its about 2000psi. It will drop to 30psi, and I know this will lose alot of heat. can someone point me in the right direction how to figure this out. Thanks
You really don't need to know the exact amount of watts , it can only be done by experiment ...

I would take the heating coil out of a hot air gun or similar and vary the amount of power you feed it with a high power mains dimmer ...

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Old Mar 30th 2019, 08:57 AM   #5
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Burning hydrogen has many disadvantages .... awkward and difficult to measure ... it burns to water vapor which will condense and cool the gas...

Here is the ultimate solution .... bore a hole through the wheel into the tire airspace , thread the hole . The bolt which will be screwed into this hole has a tip containing a mixture of charcoal and potassium nitrate with an ignition hot wire..

At race start the pellet is ignited electrically raising the tire pressure and temperature by the release of hot carbon dioxide ..

The threaded bolt with pellet and igniter would be cheap to make , always the same size . The idea could catch on . Start your own company , you could be a millionaire before you leave school !
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Old Mar 31st 2019, 05:50 AM   #6
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Safety First

Some of Oz's ideas seem a little dangerous for a 13 year old...

The hot air gun idea could work, but be careful.
Ideally if your Dad is good at engineering and electrical work get him to help.
If not, I am sure that among his racing buddies he will know someone with the appropriate expertise to advise you on how to do this without hurting yourself.
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