Superheating Water

Have you considered in your computation with how much the bottle will expand? If so which material is it from?

How thick is the bottle wall?

If you write about temperature generated pressure it CANNOT be computed if the thermal and pressure expansions are not considered.

Yes, although it is a learning experience.

Is there a specific formula for calculating this?

I was considering using a continuous flow through the system so it would seem that having any "air" in the system would be near impossible as it would be driven out over time.

use the thermal expansion rate to see how the water expands and the compressibility to see how pressure contracts it.

You changed the question, you said continious flow now. In any case, you'll need a thermal expansion or relief valve to compensate. If you heat the water to 100 C, it will not boil if the pressure is over 1 atm. If you rasie the temp, you will need to keep pressure on the system. Look up saturated steam tables for the relationship.

Well, it's a force balance between the volumetric expansion of the liquid water and the volumetric expansion and strength of the material containing it.

The properties of ice/water/steam systems are well-studied, well-documented and widely published in Steam Tables. Mayhew & Rogers is a good source. Here is a basic one for general use.

Hi PWSlack,

Synthetic quartz and other gems of a high quality are regularily grown in a proccess called the "Hydrothermal method". At elevated temperatures water will disolve most elements, to grow quartz the water is at 700c and at 3,000 bar, such conditions are very similar to those odtained in the Earths lower crust. All this takes place in what is known as an Autoclave, a vessel of of cobalt containing stainless steel, this vessel is usually about 15" dia whose walls are 4" thick! The inside of these walls has a liner made of Platinum, this is to ensure freedom from contaminants such as iron.

So before anyone starts to heat water in a closed container, they should contact a company that produses Autoclaves, and explain to them what temperatures they will be operated at!

Spencer.

Hi Scapolie,

your numbers are a bit exaggerated: conditions for quartz growing are 530°C and 350 bar. This is pretty hot and not too easy to design in a big pressure vessel.

Above this temperature the quartz is crystallising in true hexagonal mode, so no longer useful as crystal oscillators and filters, and not useful as precious stones as all these hexagonal ones are white-opaque because recrystallised at cooling.

Dissolution is in the bottom of the container, crystal growth up in the region of the bolted "hat".

The biggest I saw had 4m diameter and more than 10m in height!!!

These did only some preproduction runs and then were dismantled and scrapped as the mother company in Japan decided to build 5m diameter vessels.

They had big problems with production for 6 months, upgrading is sometimes very difficult.

RHABE

Thank you. I am checking them out now. I had some difficulty finding the necessary charts. Probably because I didn't know what I was searching for.

Thanks. I posted the question in the simplest form possible at first as I like to know what I'm dealing with. The continuous flow is something I'd like to implement but this would not take away from the idea of a closed system without gas.

I will look up thermal expansion in the meantime.

I hope this is just a thought experiment here. If you tried to do this, you could very well end up killing yourself.

yes i agree there! should your container break all the liquid will vaporise instantly. This is what happens when blocked domestic water heaters explode and they can go through several floors and blow apart buildings simply by the sheer amount of steam produced

It sounds to me like you want a closed loop system at 100-C. That means that the entire system would be at much the same pressure with a circulating pump of some sort. In this type of system you could employ an accumulator or a series of them to absorb/regulate the pressure. It would still have to have a safety relief valve to protect the system from over pressurization.

Thanks for all the replies guys. It does indeed look like attempting to exclude gas from the vessel would be disastrous as the pressure increases dramatically even with small changes in temperature.

I've looked around at various thermal expansion tables and found that the volume of water increases nearly 150% at 300C from its volume at room temperature so I would need sufficient gas to leave room for expansion.

I suppose one way to accomplish this would be to inject gas into the system as water is being injected. Another would be to use a piston with a volume of gas on the other side. This would exclude gas from the water itself.

And as to the dangers. I am acutely aware of the dangers involved and am going to spend as long as necessary learning everything I need to know to make this before attempting to make it. My main field of interest is electronics and computers and although I've always been interested in chemistry, I am just now getting serious about it.

This project is aimed at designing a system for superheating water to break an oil molecule into glycerol and fatty acids without the need for a catalyst. I have seen the research and have a couple of different methods to try. The supercritical water method is the second (backup) approach if the primary approach proves to not work.

You don't need room for expansion at all. You just need a very strong reaction vessel. Superheated water is used as a heat transfer medium in so-called "Hot Water" nuclear reactors. Superheated water pumped from the reactor to a heat exchanger produces steam that drives the turbines that spin the generators.

Under sufficient pressure, water will remain a liquid up to the Critical Point.

http://en.wikipedia.org/wiki/Critical_point_(thermodynamics)

So long as your reaction will proceed at or below 374^o Celsius, all is well. Be careful. That's Hot!

Hi bubbapebi,

above the critical point (temperature and pressure above) there is no longer any difference between liquid and gaseous.

It looks like water, it has lower density it is quite viscous ...

There are natural areas of supercritical water deep in trhe oceans near the black smokers.

Any modern power plant (coal, oil, gas) operate the boiler above critical conditions but only some of the nuclears.

RHABE

At one point, you talk about wanting superheated water (which means vapor above its dewpoint at the existing pressure). At another point, you talk about wanting liquid water. Later you mention supercritical water (which means gas phase water above both its critical pressure and temperature, possibly more dense than it exists as a liquid at its bubblepoint at a lower pressure and Temp).

All are attainable, but you have to design you system to obtain what you want. The designs are definitely not the same, both as a process and mechanically.

If you want a liquid full system until you reach the critical point or the systems maximum rated pressure at operating temp, fill it with water at a low temp and put a completely reliable relief system on it at the MAWP of the equipment (be sure to protect every component). Obviously if you need to make up water while at pressure, you will need a source higher than your system pressure.

Yes, I was researching supercritical water and mistyped that in my post. The water will be kept below the supercritical temperature. I do want to maintain it in a liquid state.

There was an article in Chemical Engineering (May 1989) - 'Safer Relief Valve Sizing', which deals with this sort of problem of locked in pressure and heating. I belong to a mechanical seal company and we can have a similar problem. A dual pressurised seal system consists of a closed loop of piping with a source of heat in the loop (the heat generated by the seals) and if you did not allow for any expansion you would generate extremely high pressures. One answer is to put an accumulator in the circuit to absorb the expansion of the liquid.

The above article gives a simple formula to calculate the locked in pressure (neglecting expansion of the container).

P2-P1 = A(T2-T1)/B

P2-P1 = Pressure Increase

T2-T1 - Temperature Increase

A = Cubical Expansion Coefficient (Say 1.15E-4 /ºF for water)

B = Isothermal Compressibility Cefficient (Say 3.15E-6 /psia for water)

So according to this formula, heating a locked in volume of water from 60ºF to 212ºF, would give a pressure increase of 5549 psi!

Again the same problem: if only the fluid is taken into consideration the results are not correct. The "bottle" expansion and compliance MUST be as well considered especially when temperature changes lead to high pressure variations.

In fact the pressures can be less important than computed according to such relationships.

You should be looking at heat pipe technology. Water heatpipes have been operated

at temperatures well above 300 degrees, however, water is not compatible with

stainless steel (hydrogen gas generation). Water can be used with carbon steel with

proper cleaning and preparation. Pressures will be high. rlphaywards@hotmail.com

have a continuous flow of water in a closed container? neat trick how do you propse to do it, i am intrigued by seeing any example of how that can be done./ having the s.s. heated up at a temp equaling the water requires even more knowledge of the way you intend to stop the expansion of the ater inside the pipe from causing it to burst. you may have found a cheap replacement for shrapnel.

'da ber

Been really busy with "the other method" of production and didn't have a lot of time to reply to all of your comments until now.

I am very glad I posted on these forums. I'll have to get an account here :)

I appreciate you all taking the time to answer this even though it may seem dangerous. I realize the danger and would never attempt something like this without thoroughly understanding the entire process, and its dangers.

This of course means it will probably take a while as I like to be thorough.

Any thoughts on how to maintain a continuous flow through a system like this? I was thinking something on the order of a pump that created the high pressure and a flow regulator and heat exchanger on the output end.

going back to the original question:you could heat water without any saved space for vapor until 374C :you could see that, i mean the theorical question when you study the Van der waals equations.Specifical charts or tables for water were made because the great numbers of engines in the past or so actual electricity generators.Looking those tables you could see as much the pressure could be increased by the increased temperature or calculate using those formulas the relationship between critical pressure and critical temperature (374C).Will take, may be 539 cal for each gram of vapor you produce in lower pressure so you are wright when you think much free space will take a lot of your energy:on this is based the pressure vessels for cocking food.Material resistance ,etc.is a different matter to the original question.

Hi,

the flow in the quartz crystallisation that I mentioned above is maintained by temperature difference and gravity only.

RHABE