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
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
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
Regards
Gerre
RE: Sodium filled valves
RE: Sodium filled valves
RE: Sodium filled valves
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
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
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
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