Big gas bottles

[backpurge]

oh right, ill check my flow rate next time it happens i usually have it set around the 7-9lpm mark, how could the reg malfunction what should i check for? as far as i know its a propper argon/co2 bottle reg.

i just thought thats what happened, my big red propane cylinder does it also in certain conditions, also when refilling re-fillable lighters the fuel gets cold and starts to freeze.

You need to check what is coming out of the torch rather than what the clocks say, they are notoriously innaccurate and deteriorate with age (only given a life of 5 years by manufacturers)

Its a totally diferrent thing with propane/CO2/lighter fuel etc as this is stored as a liquid.

 

[superls]

oh right ill have to investigate a little, cheers.

 

[Omniata]

The other thing with cryogenic cylinders the coils of pipe you see also function like a fridge/freezer... When the liquid starts to warm up it is driven through the radiator system to cool it again...

They try to do this to maintain the pressure to reduce venting from the blow off valve...
And to save them having to keep coming and filling it and you venting to the atmosphere...

It tends to be more economical the more you buy and they help out a bit more as they want to keep the contracts...

 

[backpurge]

The other thing with cryogenic cylinders the coils of pipe you see also function like a fridge/freezer... When the liquid starts to warm up it is driven through the radiator system to cool it again...

They try to do this to maintain the pressure to reduce venting from the blow off valve...
And to save them having to keep coming and filling it and you venting to the atmosphere...

It tends to be more economical the more you buy and they help out a bit more as they want to keep the contracts...

So you're saying once the liquid has been drawn off of the vessel and is in the vapourising coils and has started to vapourise it is then somehow cooled back down again and re circulated back into the vessel

 

[Omniata]

From previous experience not all are vapourising coils...
Some are just there to act like radiators...

This is going back about 5 years or so when I knew a few techy peeps from a local company that had a liquid Helium cryotank outside...
I asked if the tubes were a radiator to help keep it liquid, they told me some are for the gas to go through when they use it, some help to release excess heat to stop it over pressurising and keep it liquid like in a fridge...


There are flow dynamics for cryogenic liquids but it's a bit over complicated for my liking
Liquid helium has some bizarre characteristics too:

Super fulid

 

[Robotstar5]

Hi Folks, thanks for all the interest, even though I have to read the "meter" every monday I can't remember the pressures in each, one is about 15 barg and the other about 18 barg.Post mix pressure is 60 psig. I do know there are various valves to select gas or liquid draw off as we had to get the engineer out when a tanker driver opened the wrong valves and it went into loop until the safety valves blew!

 

[thinfourth]

Okay i know not much about liquid argon but i do know lots and lots about liquid nitrogen and liquid methane. 2 years working with bulk liquid nitrogen tanks and 5 years working on LNG carriers

Now forget the temps and think of heat and pressure. Next forget about liquid gases as most folk aren't familiar with them instead think of water as most folk know about this stuff.

At atmospheric pressure (1 bar absolute 0bar gauge) water boils at 100C. Go below atmospheric pressure it boils below 100C and go above and it boils at more then 100C. We all know this.

To increase the temperature of water we must add heat. And for every 1C rise in temp needs exactly the same amount of heat. so it takes the same amount of energy to go from 5C to 10C as it does to go from 85C to 90C.

What less folk know about is a thing called latent heat of vaporization which means to take water from 100C to steam at 100C needs lots of energy.

Now imagine you had a container of water and you add the same amount of energy per minute and you measure the temp every minute. The temp will go up by the same amount every minute until you reach 100C where the temp will stick as you vapourise the water to steam then once you have got everything to steam the temp will then rise again.

So to turn any liquid into a gas needs energy in the form of heat.

Now if you take a container of water at 150C and 60bar the water will be liquid and not boiling but as soon as you dump the pressure to atmosphere the water will flash off to steam but doing this it will drop its temperature very quickly as it needs the heat energy to vaporise. Exactly the same happens with propane you will see a frost line on a heavily used propane tank where the liquid it drawing heat from the atmosphere.

Pressure and temperature are hugely linked

So far all stuff we know

Now with cryogenic liquids they are held in sure insulated tanks. These tanks have a bottom outlet and a top outlet. The bottom one takes out liquid the top one takes out gas. The liquid is just at the boiling point. So if you drop the pressure slightly some gas boils off by taking heat from the environment which in the case of a cryo tank is the inner tank so dropping its temp to below the boiling point.

Now when you use product out of the bottom of the tank you drop the pressure of the whole tank and a bit boils off taking out a bit of heat. And providing you keep taking stuff out the bottom your tank will stay cold.

But if you don't take stuff off the gas outlet comes into play where safety valve is. This will lift at 18bar and dump gas to atmosphere but it won't reseat until 17.5bar roughly which gives the temp drop needed to cool the liquid.



Now the "radiators" you see on these tanks aren't for cooling the gas as this is utterly impossible for the atmosphere at 15C to make something which is -196C colder.

They are vapourisers which turn the liquid into a gas for use and if you are using too much liquid the tank pressure drops too low to push the liquid into your system. So you vapourise some liquid into gas which you return to the tank to increase the tank pressure.


It is all basic schoolboy physics no magic whatsoever. If you understand how a fridge works then cryo tanks are easy

 

[gavuk]

nicely written