Pressure Reading

Which school do you attend?

What a nice homework question! But I am afraid I think you need more input.

Do you know what is missing?

This should be interesting.

Yes, we can answer a question with a question!

Its FunFriday isnt it?

celcious????

What's that?

Not enough information...............................................................

Do your own homework!

Sorry Guru,

"Celsius" not "celcious". Please pardon my typo.

Regards,

Dear friend,

Your Question is NOT clear.

Water will change to vapour/steam, at 100 Deg.C, as it is the Boiling Point of Water, at Atmospheric Pressure.

How long you heat is not mentioned. At 100 degree C, the pressure build up depends upon the quantum of heat supplied, once the water is fully evaporated, then the wet/saturated steam will go to super heated zone.

DHAYANANDHAN.S

Dear Mr. Dayanathan,

Thank you for your sensible comment.

Please correct me if I am wrong; My statement was that the temperature of the content was brought to 100 degree C; not more than 100. Agree that water boils at 100 degree C at 760 mm of Hg. The instant the water starts boiling, the pressure inside the air-tight vessel will be slightly over 760 torr and therefore the water will stop boiling unless the temperature is raised above 100 degree C, in which case water becomes super heated.

Remember that I stated that the temperature was brought to 100C. Since the vessel is air tight, the water will not boil. The vapor pressure will climb to a dangerous level only if the you kept on heating and the temperature water kept on rising. In our case this is not true.

I should have given some wall thickness and material of the vessel beyond that I do not think that any thing else was necessary for this hypothetical question.

To all other friends who posted a comment; thanks; but please do not assume that this is a home work. Obviously, you know nothing; I suggest that you either go go back to school.

Regards;

If the temperature is 100degC and the water had all boiled to steam in the superheat region, then the pressure would be less than 760mmHg absolute, and therefore the volume would be greater than 2000ml. At least, that's what these Steam Tables say. So superheating is a red herring.

So in the vessel there will be air, steam and water. As it is a closed vessel, the pressure will be higher than 760mmHg absolute because of the undisplaced air being present. So at 100degC, there will still be quite a lot of water still present in the vessel.

<...pressure will climb to a dangerous level...>

Dangerous is a very troublesome word. To illustrate: is 5psig "dangerous"? The answer is "yes, if it is propelling a manhole cover towards you" - the School of Hard Knocks teaches one that. Much process plant operates at pressures far higher than 760mmHg absolute in complete safety.

<...closed vessel...>

The numpty that doesn't select the correct vessel wall thickness and doesn't select a pressure relief valve for it, is more dangerous, frankly.

OP has not stated that the vessel contains air. He/she only stated that it is half filled with water - other half is not specified. The answer to his problem will, of course, depend on whether the air was evacuated before he starts heating the vessel.

Dear Guru,

I respectfully disagree with you. For argument sake, let us say that the container was sealed at normal temperature and pressure. The instant the contents start heating up, even by fraction of a degree, the pressure inside the vessel will start to rise. The pressure will continue rising until the given 100 degree C is reached and at this point the temperature is maintained at the same level, causing no further rise in pressure inside the vessel. Even if this pressure is only a few torr above 760 mm of Hg, which is the boiling point of water, molecules of water will not be able to escape from the body of water. In other words, water will not boil no matter how high you increased the temperature (Provided the temperature is below the critical temperature of water, about 647 Kelvin). The pressure will keep on rising to a point where it may rupture the vessel. Depending on the strength of material of the vessel, this could be thousands of torr. Upon rupture, the water which was at a supper heated state, will go into spontaneous boiling resulting in release of super heated steam.

In essence, what I was trying to say is water will not boil in the closed container.

You might find the answer here http://www.spiraxsarco.com

Steam Engineering Tutorials

If the school at which the Physics Teacher can be made known, there are those in the Local Authority that can remove that individual from post on the grounds of serious under-performance. Please advise.

There is no pressure reading unless there is a cat there to look at the gauge.
Del

The volume - 1000ml - that's a red herring, right?

And who on earth would close off a vessel with boiling water in it? At the very least it should have a pressure relief valve and ideally it should have a steam trap so that all the non-condensibles can come out.

Dear Mr.PWSlack,

You are right. But, I suggest, that this question to be seen or taken as hypothetical case, as I did, and in practise, nobody will do.

DHAYANANDHAN.S

<...Dear Mr...>

How abstruse.

Bursting pressure of containment vessel....?

What - no piccie this time?

I don't see how the water will affect the pressure unless additional heat is applied after reaching 100 C. However, the 1 liter of air will also be heated and that will increase the pressure. As the starting temperature and pressure are unknown, I can't tell you the final pressure. 'bout fifty years ago, I knew about STP, Boyles Law and Charles law. Using those, you can figure out the rest.

Well I think you get to point with what is missing in this question. OP must have realised something in the later posts as he made an assumption of normal pressure and temperature. I guess he is on a mission to get some numbers now!

I'm still working on the celcious"