Pressure Cooker - What Happens Inside

https://www.youtube.com/watch?v=dA369GWrVRo

Clearly you can't make pressure cookers stupid proof. I watched in disbelief as the moron tried to release the interlock pressure mechanism. Damn lucky he didn't end up with more then first/second degree burns on just his feet.

Some pressure cookers won't unlock until the pressure is at a safe level....clearly he pushed this one near its limit....hard to believe there are people like this running around, you have to wonder how they have managed to survive....

Sounds like another couple of brain dead morons are looking for the "Darwin" award.

A) It depends on if/when one distinguishes "evaporating" from "boiling"; in the range from 100dC to whenever the weights lift, it won't be a "rolling" boil, but you might call it a "slow" boil.

B) When the weights lift, there will be more of a "rolling" boil until the water is gone.

C) The heat of evaporation of water is about 970 Btu/lb. The burner will have a Btu/h or equivalent rating, some of which is wasted into the air around the pressure cooker, but maybe 60% goes into the cooker. Simple arithmetic takes care of the rest.

At 200kPa (absolute) temperature of saturated steam = 120.24°C. Steam tables in link below.

http://www.spiraxsarco.com/Resources/Pages/Steam-Tables/saturated-steam.aspx

Dear Codemaster,

just for your clarification, absolute temperature ( Kelvin) is not the same as Celsius / Centigrade

273 degrees Kelvin = 0 or 25 degreesC , forget which

I know, it's the 200 kPa that's absolute, not the temperature! On temperature, if you say K it's automatically absolute, if you say C you know it's not.

BTW 273K = 0 degC.

never mind

!st We need to look at a saucepan or or open clear water and observe changes happening as the heat rises as it temperature rises nucluoids form on the bottom in the form of bubbles rising to the top of water increasing in size and violence as we approach boiling Flash point. This point air, oxygen,and other gasses are driven off at sea level of 100 c at the rate of heat supplied. Now if we were to look through a window into a pressure Vessel say a large steam boiler of 450 Kpa. we would see level would be quite still with some slight level movement with a large mass of very small bubbles rising and this movement according to steam demand or steam let off. This is a simple explanation of what will be happening inside your pressure cooker.NB Do not release the lid while there is pressure inside the vessel as you may get severe burns.

You need to tell that to others than Codemaster. A correct description was given in post 2, with slight variations given in later posts.

He got it from the tables, since we are not using quite everyday kelvin scale, steam tables are tabulated in Celcius for covenience.

I can't agree with that. Why does water boil at 100°C at 100kPa? If atmospheric pressure happened to be 200kPa instead of 100, do you think water in an open vessel would not boil?

There is a lot of freedom in your 100KPa, 100 deg celcius, but try doing it in a close fixed vessel.

Carbon dioxide in a transparent bottle does not boil away when the bottle is closed how you may heat it, until the bottle burst.

As what rixter below said is true. Take note that increasing temperature will also increase pressure, so there is no way vapor pressure vould be achieve. Try resolving this in the P-v-T diagram of water, with constant v, you will see that theres no way to boil water not unless depressurize or open the vessel.

But it's not in a closed bottle (or vessel). The pressure is limited to 200kPa by the relief valve. The liquid then boils. I'm not sure you understand basic physics.

OK you win, I can't be bothered to argue any more ��

Not a basic physics, it's thermodynamics of the BS in Mechanical Engineering course.

Thermodynamics is a branch of physics.

Everything is a branch of physics. Simply ask Dr Steven Hawking.......

Maybe, but only a few subjects are taught as part of a physics course. And Professor Hawking, please

I do not know with you CM, how would this connect to the post you replied. Your answer is quite off the course. By logic in philosophy "not basic physics" does not mean it is not a branch of physics. I guess your both compatible buddy with Andy.

Dead right we are Buddies, we both understand that EVERYTHING is physics, I might say with different "Branches", but some purists may even find that too "confining"! I have no problem either way.....

For those who know nothing, belief is tiny! Also those who believe narrowly, have even less dream power. Then there are those who kill others dreams by pissing in the water. I say we raid whatever stupid village these village idiots come from, and make them work at plowing the fields as stupid beasts of burden. Sounds rather not PC of me to say that, almost National Socialist, therefore I must already suppress my own thoughts. In another era, we would have been the ones on the long boats.

Riddle me this: Why do the refer to pressure boilers as boilers then if no boiling is taking place? Are you quite completely daft? What courses did you skip in junior high school physics class?

Misnomer, may be isochoric term came lately and people or folks usually compared it more like a kettle.

The simple answer:

We are cooking some artichokes in our pressure cooker, and I simply put my ear near the bottom of the cooker.

I can clearly hear it boiling.

No theory or math required!

Why did you post off topic????

Its On Topic!!

Oops!

I just replied to post 6, and didn't notice that it was marked OT, so the reply was automatically marked the same.

Easily done.....sadly.

I almost did the same with your post!!

A liquid boils when the vapor pressure exceeds the external pressure. At about 120 C the pressure will be 200 kpa, the safety valve will release vapor to the atmosphere, and the water will boil until it boils away. How long this takes depends on how much heat energy can be supplied by your stove, which is not only a function of temperature but also other factors such as heat conductivity.

a) It starts to boil at the boiling temperature consistent with the ambient pressure. Because of the pressure regulator the pressure starts to increase. Since there is air inside the water temperature is less than the equilibrium temperature if only water and its vapor filled the space.

b) However, the water continues to boil and when the pressure reaches the set value it releases air and steam initially. Fairly quickly tall the air gets eliminated and the water boils at the temperature consistent with the sum of the ambient and set regulator pressure.

c) About 1.5 litres of water evaporate/ hr/KWHr (delivered to the cooker). Not all the wattage of the heat source gets delivered to the cooker. Also about 300 Watts is lost from the cooker surface to the ambient as combined radiation and conduction losses.

Can't you read a set of Steam Tables, then, Mildred?

a) with water inside the pressure cooker before reaching 2 x100kPa =200kPa, does it boil inside? ANSWER: Generally speaking it will boil until pressure is reached determined by safety valve then it will stop momentarily until the valve releases vapor then that vapor should be replaced and the cycle resumes. I will use PSI and degrees F. For approximately every lb, pressure the valve is set at the boiling point goes up 3 degree F. Pressure is evident as the container is closed.

b) upon reaching 200kPa and gas is exhausted outside, what happens inside, does it also boil? ANSWER: There may be a flash of boiling as gas (steam) is released only to settle down as the pressure is again building.

c) If I am hanging out with friends on my living room watching UFC or boxing and left the pressure cooker lit, how long before all the water is emptied? ANSWER: This all depends on how much heat is applied and how often the safety valves releases steam ( water) as the gas is released water inside drops in volume. Sooner or later you will loose all water. At this point the chicken broth becomes a burnt offering.

Similar example is suppose you are climbing a mountain and at 6000 feet decide to cook some potatoes. In this case the water will boil at a lower temperature and the potatoes will take longer to boil than at sea level. Reason is same as the lid on the pot the air pressure at sea level acts like a lid and the lid is lighter at higher altitude. Conversely if yo want a liquid to boil at a lower temperature you can apply negative pressure and the liquid or gas for that matter will boil sooner. This happens a lot on hydraulic systems when there is negative pressure before a pump and the result is cavatation from released gas and subsequent pump damage.

Dear Mr.Kulas,

Answers for your questions in the same seriatim is:

1. No. The water will not boil before it reaches temperature corresponding to the Saturation Temp. at 200 kPa. But there will be circulation of water with in the cooker. The reason is the water at the bottom will be relatively at higher temp. than at the top , which creates a density differenc and this density difference creates circulation. See the Steam Table for Density Difference.

2. Once the gas is exhausted the pressure inside the cooker falls and flash it in to vapour till it reaches an equilibrium, and vapour will accumulate and the pressure slowly builds up After gaining heat it will start boiling.

3. The 3rd question is related to Time - how long it will take to empty the water. It depends upon the rate of Heat added to the water and the quantity of water available inside the cooker. At 200 kPa, the Saturation Temp. is 122 Deg.C and the Latent Heat at this Temp. is 2201 KJ/Kg. or 528.80 KCal/Kg.

So, the water will be exhausted after absorbing a LATENT HEAT of (Weight of Water) x 2201 K.Joules (or) (Weight of Water) x 528.80 K.cal. of Heat, since the water will be transformed in to vapour/steam only by Laten heat.

Since the heat required is estimated, the time required will be calculated once the heat released to the cooker. Lesser the Heat added will need more time and viseversa.

All these working is simple Mathematics.

DHAYANANDHAN.S

Do the bubbles of vapour that constitute boiling occur when heat is applied to the bottom of the liquid and vapour pressure equilibrates somewhere above the surface of the liquid at 200 kPa ?
I would bet yes, with smaller bubbles than at atmospheric pressure.
To relolve this contentious issue...
a) get a glass vessel that's supposed to be able to take the pressure and watch behind a sheet of Plexiglass
b) put an optical emitter / detector that can take the temperature in the vessel and look for index of refraction disruption signal
Unbelievable how muddled this thread got

There's nothing contentious about it. It's just that some posters understand the science behind it but some don't.

Speaking of which to where you belong?

You should make use of public humiliation sometimes to learn, you are speaking a lot of confidence and expertise around here.

The witty ones, don't need much words to figure it out what is happening on the diagram pertaining to the process in the pressure cooker.

Assuming pressure cooker's volume is 10L, then inside specific volume given 2 L(1.922kg) water is about 0.005 m3/kg and it is fixed there as long as the vessel remains close.

"If a picture paints a thousand words, but why can't I paint you?"

Here is the solution of your problem Kulas, solved.

Question, is evaporation means boiling? How do you mean by flash evaporation and expansion?

I never knew it happened quite like that in Geysers, but once I had read it, its simply obvious!!!

Thanks.

"In my pressure cooker (which we use every few days), there is a short period just after the seals close and before the weight begins to lift, when it could be considered isochoric."

Well, okay... but some of us have a different pressure cooker.

http://www.leaderjar.com/gowith_images/ball_pressure_cooker_cookbook_cover.jpg

This is a cookbook with an image of my old Ball Brothers canner. There is a gauge, a fuse, a manual vent, and an adjustable pop-off PRV. There is no weight, and as long as the source heat is properly balanced with the PRV setting there is no steam escape in operation.

Yep! That is quite similar to the one my mother used 60 or so years ago. Obviously there are a lot of details that I don't remember well from that long ago!

That would be quite a tedious job, to set the heat precisely enough to achieve and maintain the correct pressure without any steam escaping. I seriously doubt if many people would be that careful.

I have personally used several pressure cookers, of several different types, with weights and with other pressure regulation systems, and have observed even more being used (including industrial versions), but I don't recall having seen one that didn't have steam escaping once up to temperature.

If there is a pressure cooker that can easily be operated without steam release, then I'd have to concede the isochoric concept. Of course then the answer to how long it could be left on would be: infinitely.

I have several and all instructions state to let the pressure valve rock gently to prevent excessive water loss. I really like my pressure cookers saves time and energy and preserves the flavor.. any one ready for some great beef tongue.

I have had my share of pressure cookers, being taught how to use one by my Mother in the 50's.

All the ones I have used were used on stove tops and you had to balance the energy input to maintain the pressure with a little bit of steam loss. All of them.

The steam loss has a further use, you can sometimes smell when some foods are actually fully cooked as well.....but not always....

There are pressure cookers, sold on TV, that have the heating element integrated and a micro controller as well. I have never had one myself but I can well imagine that temperature and pressure are controlled far more exactly, maybe without steam loss....

Has anyone here used one of those? Do they let the steam out when running?

My daughter in law has one and thinks it is the greatest.. Likes it over the slow cooker of which I really like. Each has a different approach to cooking and both have their place.

BUT DOES IT HISS?

Along that line, has anyone tried Wolfgang Puck's Pressure Oven?

Hmm.., how about 10 microsecond time elapse? Would it not applicable to treat as an isochoric? Well, personally, depends on perpective. Noudge79 have some points in that sense.

Now it gets interesting, what condition that bubbles form on boiling in a close vessel? You said water boils even compressed. Could you elaborate how is boiling or vapor bubbles rise on a close and pressurized vessel?

You're dead right on your example of flash evaporation on a flask. How would that differ in anology in a pressure cooker then? Obviously its in a vacuum, pressure cookers compressed the liquid. The flask behaves like a heat pipe. No missed thought about it, boiling is not favored in a compressed liquid. Compression of a medium in thermodynamics means 3 things 1) increase in pressure in constant volume 2) decrease in volume in constant pressure 3) both happens instanteneously, increase in pressure and decrease in volume to the point of incompressible state. Expansion of a medium means also 3 things(needless to write- the opposite of compression) Now, back in the pressure cooker, does boiling happens? You and others decide from above figure and cognitive definition. I enjoy the off topic by the way, dont need blings to sharpen my arrow- as usual "aim small, miss small"

To my way of thinking, even negative results are educational.

Me and my beef tongue will go away now.

I'll try to answer 78 and 81 together:

"1) increase in pressure in constant volume 2) decrease in volume in constant pressure 3) both happens instanteneously (sic),"

I'll agree with 1) and 2), as long as there is an OR included. The two processes are mutually exclusive.

As to 3), virtually NOTHING happens instantaneously. and this process certainly does not.

The pressure inside a vessel is the result of the sum of the forces exerted by atoms and molecules impinging on and bouncing off the surface. In the case of liquids, these collisions are the result of vibratory motion, while in the case of gases (vapors), they are the result of vector changes in trajectory. An increase in pressure at one point in the vessel can only affect a different point inside the same vessel after either: 1) an atom or molecule travels from point A to point B, or 2) an atom or molecule from point A bumps its neighbor, which in turn bumps it neighbor, etc. until an atom or molecule bumps the surface at point B. Either of these processes results in pressure travel at the speed of sound in that medium at those conditions. This is fast, but not instantaneous.

How can bubbles form at the bottom of the liquid in a closed container? Temperature is essentially a measure of the energy of motion of atoms & molecules; higher temperature means more rapid motion, vibratory in the case of solids and liquids, and trajectory/translational in the case of vapors/gasses. In a normal pressure cooker, the heat is applied almost exclusively to the bottom surface, so the temperature at the bottom surface is higher than at other points in the vessel. This higher temperature imparts greater velocities to the molecules in contact with the bottom. This means that in essence, the pressure is greater at the bottom surface than anywhere else, because the atoms/molecules at the bottom have greater velocities. This is in addition to the pressure due to the vapor and the weight of the liquid. if the temperature at the bottom is sufficiently higher than the temperature of the main liquid, then some of these molecules have sufficiently high velocities to escape the liquid state and become vapor, forming a bubble, aka boiling.

Since you mention heat pipes, there is no law saying the liquid can't boil in a heat pipe. If ordinary evaporation can't extract sufficient heat from the hot end of a heat pipe to keep that end below the boiling point of that fluid at that pressure, then the liquid will boil. If condensation at the cool end of the heat pipe can't keep the vapor pressure low enough, then the heat pipe may explode! I know that browsing GoogleEarth makes my microprocessor work hard, but the fans come on, so I can't hear whether the liquid in the heat pipe is boiling or not...

You see this plot, its a thermodynamic curve. See figure (c)

EXPANSION means

1) Decrease in Pressure at a constant volume (drawing a vertical line parallel to pressure from higher to lower)

2) Increase in volume at a constant pressure(drawing a horizontal line from lower to higher volume(specific).

3) See the isotherm at figure (c) when temperature T is greater than Tc- Critical temperature in equation PV=constant for an isotherm but for an adiabatic process PVⁿ = constant; n>1 ---WHERE EXPANSION IS BOTH LOSS OF PRESSURE AND GAINING VOLUME. -this is what i mean.

Work =∫P dv =∫ Vⁿ/const * dv

The needless to say the opposite of this is COMPRESSION.

As in this case, static head wont affect much the vessel pressure.

Remember that a 1 meter static head could only influence as much as 9.8KPa. It's pretty small when actual is just - 0.1 or less of 1 meter.

The vessel will have a uniform pressure.

May be it's your professor's fault not to encounter such.

Big respect though to all senior citizen. I am just about half the age you got.

Staying Alive, More Power!!!

I've been familiar with these diagrams for well over 50 years!

Notice that your "3)" is referring to water "...when temperature T is greater than Tc..."

The critical temperature for water is 374°C, and the critical pressure is 218 atmospheres. We have been talking about 2 atmospheres pressure.

...and we certainly are NOT talking about an adiabatic process, so ". -this is what i mean." has absolutely nothing to do with household (or industrial) pressure cookers.

You give me the impression of one who studied the theory, but never did the actual experiments, similar to the worthless engineer who has the degree and the title, but has never actually built anything.

Well, if that is your side of the story. I believe I could be of any help.

Take care.

It is, if you notice on your previous post you said that expansion and compression are exclusive on to constant pressure and constant volume only. You see that if you follow isotherm above critical temperature Pressure and volume varies respectively according to equation PV= const. Get it now?

I'm afraid you are the one who doesn't "get it"!

In your first two words, ("It is") you appear to agree that supercritical is irrelevant, then in your second sentence you go back to talking about properties above the critical point.

The rest of your first sentence: "you said that expansion and compression are exclusive on to constant pressure and constant volume only." This phrase is so poorly worded that it is meaningless.

I quote from that post:

"1) increase in pressure in constant volume 2) decrease in volume in constant pressure 3) both happens instanteneously (sic)," [a quote from your previous post]

I'll agree with 1) and 2), as long as there is an OR included. The two processes are mutually exclusive."

What I effectively said was that you can't have 1) constant volume and 2) decrease in volume, at the same time. Those two processes are indeed mutually exclusive.

The gas law PV=const is just what the name implies: an equation relating to gasses. Above the critical point. it is no longer a gas, so that equation no longer applies!

...and PV=const. is only correct for a fixed quantity of gas. Here, where gas is continually escaping, the equation must be PV=nRT, where n is continually decreasing.

Finally, even if we only consider your preferred isochoric pressure cooker, it is still perfectly possible for boiling to occur continuously at the bottom surface. Water vapor is continuously condensing on the top and sides of the pressure cooker and flowing back down to join the rest of the liquid. The vapor thus condensed removes molecules from the vapor region, lowering the pressure, so more liquid boils to vapor at the bottom to replace the molecules lost to condensation and maintain the pressure.

In case it wasn't obvious before, ordinary evaporation is a rather gentle and silent process. Boiling is a much more violent process that is usually quite audible. Forget your theory, and just listen! you can hear the boiling occurring!

Maybe he's just deaf, and can't hear the boiling. Once again, post 2 explains correctly, including some semantics between evaporating and boiling, which is just a matter of degree.

I agree!

A valid possible explanation. Thanks.

Does deaf matters really in an ocular forum?

Also, how can you determine that there is boiling from the hissing sound.--This needs proof.

Have you ever done a single experiment in your life? Do a few now!

On second thought, please have a qualified and experienced supervisor while you experiment; this could be dangerous.

Actually, the hissing sound is from the escaping gasses. The boiling produces something more resembling a gurgling sound. As I indicated, I had to get my ear near the bottom of the vessel in order to hear the boiling. A stethoscope might help, but I didn't want to risk damaging it.

You still do not understand the question I made!

Nothing new there!!

Noudge79: Ever heard of ocular-intrarectumitis? What about aural-noncopral dysfunction? Could it be that you suffer from one or both of these maladies?

English is not my native tongue.

PV=const; const = mR'T=nRT

Would you agree that pure substances undergoes 3 phases? If yes, water is a pure substance, at higher pressure and temperature than critical point, Isotherm behave to approach PV=const - this equation is applicable to pure substance at gas state higher that critical point.

Also, the equation is not limited only to a close system but also to an open system in a steady state steady flow process.

A what? "forget your theory" -it's not mine - it sounds so idiotic to follow yours-this does mean i will have to throw the works of the steam era?

Well, your written English is good enough that I did not suspect it to be your second (or other) language. Congratulations!

Yes, I agree that pure substances can be found in 3 different phases, and that water is such a substance. Of course those phases are solid, liquid, and gas (or vapor).

Perhaps our disagreement originates in those last two terms. According to my textbooks (from 50 years ago), a substance is only considered to be a gas if it is above its critical temperature; below the critical temperature, it is considered a vapor. The equation PV=const is known (at least here in the USA) as Boyle's Law, or the Ideal Gas Law, but it is also very useful for vapors, as in the case of water.

The critical temperature for water is 384°C, while the temperature in a standard pressure cooker is only roughly 120°C, so the water is NOT a gas, but rather a vapor.

You keep referring to "a gas state higher that [than] critical point." , but ALL standard pressure cookers operate very far below the critical point pressure and temperature of water, not above it.

No, you do not need to throw away the works of the steam era, you only need to realize that all of the data regarding commercial steam engines of any kind, reciprocating or turbine or other, is dealing with vapors, not gasses. If you can find a steam engine that operates above 384°C please send me a link!

Once again, theory is wonderful, IFF (when written with two F's, this is meant to be interpreted as "If and only if") it can predict that which is observed in actual experiments. I place a very high value on experiments, which can either verify or reject theories. If you don't have an actual pressure cooker, find someone who does, and borrow it. Then put some water in it, apply heat, and observe! In this case, observe might include vision, hearing, watching one or more thermometers, and ideally, a pressure gauge. The best observations would include looking inside, so check out that earlier link to a glass lid. ...and of course the experiment must be repeated several times under different conditions. In this case that pretty much means different heat input levels, unless you have the luxury of being able to perform the same experiment at widely different altitudes.

Once you have observed the conditions under which a standard pressure cooker operates, come back and tell me what you found!

Your posts are really interesting and despite a complete lack of knowledge on my part, still very understandable. Your teaching experience I presume?

You said:-

If you can find a steam engine that operates above 384°C please send me a link!

You are totally right for most steam boiler designs/applications that the temperatures in use are quite low (pressure cookers of course even lower!), but I was able to find an article that describes a particular boiler type that not only had much higher (very dangerous?) temperatures and pressures, but might interest you personally, here:-

http://en.wikipedia.org/wiki/Boiler

This was found a little over halfway down, just before the paragraph titled "5.1 Supercritical steam generator":-

The temperature in this area is typically between 1,300 and 1,600 °C (2,372 and 2,912 °F).

In that paragraph mentioned, I found this:-

In contrast to a "subcritical boiler", a supercritical steam generator operates at such a high pressure (over 3,200 psi or 22 MPa) that the physical turbulence that characterizes boiling ceases to occur; the fluid is neither liquid nor gas but a super-critical fluid. There is no generation of steam bubbles within the water, because the pressure is above the critical pressure point at which steam bubbles can form.

Might this be the data that is misleading the great "Noudge"?

Mixing up "subcritical" and "supercritical" Boilers? They both appear to me as a novice to be almost following completely different "laws" to do with steam generation....almost!

I know that all of this has absolutely nothing to do with pressure cookers at all, but I still found it very interesting....I hope that it is of use to you further....

A supercritical steam Pressure Cooker, would cook so rapidly, that a lot of time might be saved!!

Have a great day and keep posting!!

Thank you! Yes, I think 32 years of teaching physics was helpful. When you explain something to others over and over using your own words (not just quoting someone else) each time you do it, you understand it better yourself. I still remember the first year I taught first-year engineering physics: I just finished explaining some concept, and made a small pause, thinking to myself: "Wow! That makes sense!". I had not truly understood the concept until I put it in my own words; then I did.

Thanks for the link! I was not aware of supercritical steam turbines. Most of my normal work is for jet engines, which operate at similar temperatures, but at only a few hundred psi. I sure as heck would not want to work or live near anything that operates at that kind of pressure-temperature combination!

"A supercritical steam Pressure Cooker, would cook so rapidly, that a lot of time might be saved!!"

HA! Any food you put in there would be mush long before it got up to T/P. Then you'd have to let it cool before it was safe to open... There went the time savings.

Thanks, and a great day to you too!

Obviously, any fluid above the critical point of temperature and pressure, there is no distinguishing the fluid as two separate phases, it all exists as either colder or hotter parts of the phase, more or less pressure, and more or less density (specific volume).

Hence the beauty of super-critical carbon dioxide as a working fluid in the closed Brayton Cycle - there is no condensate to form, and no quantity of energy below the condensation line (on the T-S diagram) to expel from the "system". This cycle lends itself to (1) smaller size owing to the high density of the working fluid in both the hot and the cold halves, and (2) high mass throughput achievable, and (3) higher working efficiency due to not having to condense and re-evaporate a liquid phase. No phase transition to deal with at all.

That has absolutely nothing to do with a pressure canner/pressure cooker.

You missed my Joke, I am miffed!!!

Hugs and cheers at the same time Andy! It was actually a good joke! Now let's turn that into a serious cooker.

Suppose one could make a vessel with a lid that could withstand such pressures. I would not want to have to wield such a vessel in the kitchen, as I would have to be Iron Man, or Arnold Swarzenegger on steroids to even lift it! Ok scrap making it from anything traditional. Aluminum would melt at the temperatures of the ultra-supercritical steam unit! Tungsten would not melt, but would be so ductile at temperature that it would creep off the stove top! It has to be made of the same alloys used in the turbines. Unfortunately, these alloys are non-magnetic, so I suppose we could not use induction coils to instantly heat up the metal. Now we have the pressure vessel, but the seal materials do not exist. Probably would have to use some form of compression rings that might have to be disposable, also of a high melting metal, maybe a soft iron.

Ok now we have a pressure cooking vessel with integrity. We have the outside of the vessel walls clad in carbon steel with high hysteresis values to use for induction heating quickly. Will we exceed the heat stresses of the vessel simply by heating nearly instantaneously? What power source can provide adequate current to the coils? What do the coils appear to be in size? Does the cooker have to fit inside a depression holding the coils ? Yes.

Now we are ready to cook and we are prepared for the most refractory piece of meat in the industry - Texas brisket. I predict the brisket to almost implode within the vessel, and once things cool back down (has to be done some way I cannot imagine other than time elapsed), we open the lid to find, beef soup, or rather amino acid soup, with some free fatty acids, etc. Probably a nasty stench.

Nice one!!

By the way, metals that will not work on induction hobs (stove tops in the USA!), but often used as pans are made nowadays with a slab of steel/iron sealed in the base......

..."Ok now we have a pressure cooking vessel with integrity. We have the outside of the vessel walls clad in carbon steel with high hysteresis values to use for induction heating quickly."... from my post prior to your reply. Notice in this case, we bond carbon steel on the outside of the pressure containing alloys, not inside them. Then we surround it all with the induction coils, and see what happens next.

By the way, some of the temperatures you are mentioning, I think, can only be reached by an oxy-fuel flame, not in air.

The Aluminium cookware that I possess, you cannot see the steel/iron insert inside or outside of the pot....but the base attracts a magnet, so it is in there.....it would appear.

Cast iron works the best on all the induction Hobs that I have owned, requiring several notches of less power....

if you want to learn how quality cookware has cores of different metals for various reasons, take a look here:-

whats-best-cookware-for-induction-ranges

By the way, you mix me up with someone else, I have never mentioned any temperatures with regard to pressure cookers......

Alumin[i]um! I hope your aluminum cookware has some form of non-stick coating to reduce contact of the food with the aluminum. I have avoided aluminum ever since I left home to go to college. I grew up with my mom cooking in aluminum pots, and even as a child observed how badly pitted the aluminum was. I even remember one thin aluminum pot where one pit became a hole... That told me that I was ingesting aluminum every time I ate anything cooked in it. Of course this is especially true for acid foods, and I like acid foods a lot!

There is ample evidence of medical problems associated with aluminum, especially regarding the brain.

I check the appropriateness of a cooking vessel material by looking at ones that have been in use for 40 or more years. The stainless pots that we bought shortly after we got married (not quite 50 years ago), still look almost like new, except for one that got overheated and oxidized, and of course some handle damage.

I have to admit with great sorrow that I do not truly understand how current induction heating works. If the heat was created by eddy currents, then aluminum and copper should work just fine, but they don't. I've read somewhere that "they" are working on induction cooking devices that would work on non-magnetic metals, but so far, I haven't seen any. I suspect that current ones work essentially by different magnetic domains moving in different directions, and so effectively creating friction between them.

It is true that the thermal conductivity of stainless steels is generally lower than many other metals and alloys, but I'm not at all sure that is a disadvantage with induction cooking. I've never had a problem with food sticking more to some areas of the pan bottom than others with induction heating, as we commonly do with gas heat. low thermal conductivity in the sides of the oan is definitely an advantage.

I have never analysed exactly the type of metal, who does? The pots are relatively new (for me!) 2006 or so.....they look like new, inside and out, relatively polished....no corrosion. They are not any form of steel or iron....so as they look like aluminium, I assumed, maybe wrongly......

The rest of our pots and pans are either cast iron or stainless......some are coated......our Wok appears to be one with a copper kernel (or similar) as the heat goes will up the sides....

I ingested so much alumium in the RN, even if they are shedding it, it probably won't make any difference.

Royal Naval cooking gave me heartburn and the medicine then was Aluminium Hydroxide.....

Not that I would be happy about increasing it further.....

I am probably 10 pounds lighter than my figure suggests!!!Could this be a bad sign?

I always say that I want to die of something, not pass away totally healthy!!! (It sounds funnier in German!!)

For what it's worth, our ≈50 year old pressure cooker, a Presto 6 quart, is of stainless steel. I don't believe it has a carbon steel layer, but I could be mistaken. In any case it was built long before induction cooking was developed for homes, but it works fine. We also have a set of stainless pots of about the same vintage that are tri-ply, and they too work fine with induction.

Thanks, DKWarner. I have zero experience with induction cooking, or for that matter with industrial induction heating, but I always presumed the material had to have at least a measurable magnetization, possibly a ferromagnetic material or alloy, and what I did not know is what you just told me.

Check out some of AndyGermany's posts of a few years back... There are MANY advantages to induction cooking, and only two minor disadvantages that I know of: One is the requirement for magnetic pans (basically, if a magnet sticks to it well, it will work). The other is that the electronics require a cooling fan; some people consider the fan noise objectionable. We usually have an exhaust fan running when we are cooking, and that makes far more noise than the induction fan.

Actually, I guess there are a couple of other disadvantages: here in the USA, induction cooking units are considerably more expensive than other cooking technologies, and their reliability has been disappointing. I had to have both of my units repaired under warranty...

It depends entirely upon which type of stainless steel it is made of....ther are types that do not work.

But stainless steel as a whole, even if it works, is not the best in transferring heat and some pots have a copper or aluminium core as well...

280 bar and 595 C

Yes, these are scattered around all over the planet now, and operate quite safely thank you very much! There are not many reports of steam turbines splitting open at the shells and sending 35-50 tons of thick steel flying, not to mention the rotor that comes flying/spinning out! That just does not happen, at least not more than 1 ppm.

I would rather sit down on the casing of an active steam turbine (near the exhaust, because I hate getting my butt feathers singed) and have my sandwich than on/near the curb of any street in my city.

I also get the point that there is no sCO2 Brayton engine made (yet) of the same scope as the Supercritical Benson Boiler (and balance of plant).

Thats not hot!!! My tea in the morning is hotter!!(Don't believe that!!)

Read my post again, the link is also there to read.....twice those temperatures.

1,300 and 1,600 °C (2,372 and 2,912 °F) (over 3,200 psi or 22 MPa)

I am not going to claim these are the highest either, there could possibly be more where that came from!

by saying steam engine, are you implying only piston engines? I suspect PF coal boilers operate quite a bit higher than 384 °C, and use a "steam engine" - a steam turbine. However all that still has absolutely little or nothing to do with the basic simple boiling that takes places in pressurized cooker/canner.

It boils as soon as the system pressure (vapor and air, or just vapor) meets the pressure imposed by the mechanical vent weight, or in the case of the canner, the system simply meets the pressure required, and the operator turns down the heat supply to run steady-state boiling/condensing operation.

Just because something has a lid on it does not make it the definition of a closed system, especially when heat-transfer is taking place all over the container of the inner system. The heat source and the outer surface of the cooker in air is also part of the system, and that truly is an open system.

If you define the system as the cooker with water in it, then you declare it to be adiabatic - no heat in, and no heat out, and no mass transport - then it is just a container with water in it, not a cooker. If we are going to talk about cookers, then we have to start with a well-defined system that includes all the inputs and all the outputs. Simple as that. One part of the system will appear to be in a dynamic equilibrium when boiling takes place, in that the vapor pressure of the liquid is equal to the head pressure inside the vessel. For this part, it does not really matter whether mass is transported out or at what rate it is transported out, since we have declared dynamic equilibrium. Obviously, the assumption of dynamic equilibrium is not strictly true, since with mass transport, the system mass is continually decreasing to the dehydrated limit.

I can't find it right now, but in one of my posts I did say something like "steam engine, reciprocating, turbine, or other"

Obviously the flame temperature in all combustion-heated boilers is way above 384°C, but to get the water to that temperature requires a container capable of withstanding the critical pressure of water of 218 atmospheres. At that temperature/pressure combination, water is capable of dissolving glass. I don't know what kind of metal alloy can withstand that corrosion and pressure. I don't want to be anywhere near!

"It boils as soon as the system pressure (vapor and air, or just vapor) meets the pressure imposed by the mechanical vent weight"

Actually, it can boil long before that. I just started cooking another pair of artichokes in my 6-quart pressure cooker. I add about a half inch of water, then the perforated support, then the artichokes, and then close the lid. I'm cooking on an induction cooktop, which heats the bottom faster than most other methods. I turned it on to its highest setting, where it uses some of the energy that otherwise would be used to heat a second element. I could clearly hear boiling just before 2 minutes elapsed. The pressure closed the seals right at 4 minutes (vigorous boiling very audible), and the vapor started to escape, lifting the weight, at the 5 minute mark. At that point, I turn the heat down two notches, and will let it cook for 15 minutes. Once the weight begins to rock, is is significantly more difficult to hear the boiling due to the noise of the escaping vapor, but there is no doubt about the sound with an ear near the bottom of the cooker.

I agree with your last two paragraphs.

There are alloys made just for the PF boilers (these are usually tubing boilers with no drum style vessels, and are totally once-through from feed-water inlet to super-heater outlet, except for re-heat pass from HP turbine exhaust and back to MP turbine). So-called "normal" superheated steam temperature of 900 °F (482 °C) is hotter than the critical point, and our little power company gets that from natural gas firings of boilers or HRSG from gas turbine exhaust. That is not carried in a particularly exotic alloy that I recall, but it is probably similar to the steam turbine blading alloy of approximately 13% chromium steel. We are running off approximately 86 Bar at the highest end unit. The low end is running off 41-42 Bar, but still gets superheated to the high end temperature.

My next question: How long will a disc turbine made from tuna can lids last in a 5 Bar wet steam environment? I plan to test just that.