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Sodium filled valves

Sodium filled valves

(OP)
Hi all!

Sodium melts at 98 ° C and boil / vaporize at 882 ° C.

1. Why is it precisely sodium they use into the valves, for example cars?
2. Why doesn't they explode from the increased pressure inside the sodium-filled valves?
3. Is there an increased pressure inside the valves when the sodium melts/boil/evaporates? 4. If not, why?
5. Are there any similar material you can use inside the valves if you want the media to boil / vaporize at 100 ° C? Solid or liquid?
6. Are there any similar material you can use inside the valves if you want the media to boil / vaporize at 120 ° C? Solid or liquid?

Is there any good Internet links I can take a look on?

Regards,
Gerre

RE: Sodium filled valves

For high power density engines the exhaust valves have hollow stems and they are partially filled with sodium and then inert gas and sealed. Often these valves have Ni alloy heads that are very thin mated to high alloy steel stems.
You need something with a fairly low melting point and high heat capacity. It also needs to be chemically stable not reacting with steels or breaking down over time.
The sodium cannot vaporize because the internal pressure is too high, or if it does vaporize it will condense in the cooler stem of the valve.
The function is that the sodium melts and then splashes inside the valve, in some cases some also vaporizes and this condenses in the stem. This greatly accelerates heat dissipation from the head of the valve (hottest section) to the stem where heat can be removed through conduction to the guides and by engine oil.
In the past other things have been used. This technology was well known in aircraft engines in the 1940's, and greatly expanded in WWII. There have been some use of salts for this, but corrosion and stability are limiting factors.
http://www.newcomen.com/wp-content/uploads/2012/12...

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P.E. Metallurgy, Plymouth Tube

RE: Sodium filled valves

(OP)
Why is it an inert gas inside the spindle of the valve?

Regards
Gerre

RE: Sodium filled valves

Since you need the pure sodium metal to stay as pure sodium metal, you don't want it to react with the different elements in the air (assuming you would try to use air instead of an inert gas to fill the space). The inert gas will not pollute the sodium metal as it changes phases by reacting with the sodium and forming other compounds that could hinder the performance of the valves.

RE: Sodium filled valves

I would surmise that the void space in the valve stem is a vacuum rather than filled with inert gas. This is a heat pipe application and any gas would severely reduce heat transfer.

RE: Sodium filled valves

It is a matter of practicality. If oxygen was present you could start getting reactions with the metal of the valve.
Due to the motion they don't strictly operate like a heat pipe, there is a lot of mass transport as well.
These often have very thin Ni alloy heads welded to stainless stems.
The head temps will be 200-500F lower than with solid valves.

There is also a huge body of work on liquid Na cooled reactors, the fast flux breeder reactor was Na cooled.
Today molten salt is used as a heat transfer medium in thermal solar power plants. Handling it is a bear.

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P.E. Metallurgy, Plymouth Tube

RE: Sodium filled valves

(OP)
I need to know the function of "sodium filled valves". Rather, the chemistry behind "sodium cooled valves". Sodium in an exhaust valve melts at a certain temperature and then "bounce up and down" when the exhaust valve opens and closes (is it fluid or gas now?) and thus dissipated heat from the combustion chamber through the valve guides and up to the cam shaft etc. Condenses the heated sodium liquid when it has to travel up to cool and drain inside the valve again? The phase transition from liquid to gas absorbs a lot of heat. Is it gas and not liquid substance now?
Why does not the valve explode when sodium + vacuum, (or it is sodium + inert gas) is heated in a closed system? For example an exhaust valve, which 60% is filled with sodium? I assume that it is in solid form and then begins to melt at 100°C. Is 60% solid sodium as much as 60% liquid sodium, i.e. no volume change inside the valve? Why will it work with sodium and vacuum, or sodium + inert gas, if it now is sodium and gas?
I have plans to make a similar solution. My valve construction would use a sodium-like substance, but in my mechanical design would sodium boiling and vaporizing at about 100 ° C with a good heat dissipation system and without exploding.

Regards
Gerre

RE: Sodium filled valves

Look at the ref in my first post.
I am not sure that much Na vaporizes.
Lets assume that the valve stem is 0.300" OD with 0.065" wall and that it is made from a high strength SS or Ni alloy (use 120ksi UTS)
The burst strength of the stem is OVER 50,000 psi, what is the boiling point of Na at elevated pressure?

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P.E. Metallurgy, Plymouth Tube

RE: Sodium filled valves

"need to know"?
Think about the velocity of the valve in service, and the accelerations it undergoes.
- obviously, that depends on the engine rpm, the cam profile, valvetrain geometry, etc.
That should offer some insight on the forces on the sodium, and how it might move around when the valve warms up enough to melt it.
Oh, yes - think!
Do you realize that sodium is reactive in air?

Jay Maechtlen
http://www.laserpubs.com/techcomm

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