Controlled flash to steam? ( tickling the dragon's balls?)

RickDelta

Hello!
I'm aware of the enormous explosive flash to steam energy released when a closed loop container with a runaway heating source (ie; hot water tank) should rupture (http://www.nationalboard.org/Index.aspx?pageID=164&ID=412)

My prototype process requires me to better understand the cause and effect of heating water in a closed loop to a maximum temperature of 250F under 30psi gauge pressure.

In the example of an unprotected (no T&P safety valve) runaway hot water heater, the tank catastricaly fails (RCP) exposing the 60gals of 250F liquid water to only 14.7 psi , explosively flashing to steam creating your own home made space shuttle : (

My first question is, lets say this hot water heater is NOT in a runaway condition, but is controlled to maintain this 250F water temperature with an auto-tank bleed-off compensation to limit tank pressure (water volume expansion) to 30psi. The loop piping and tank vessel all rated for 250psi working pressure.

No problem here!

I understand that if the tank were to catastricaly fail for any reason ...... Big BOOM!! .... but that's because I've exposed ALL the 60gals (surface area) of this heated water to 14.7psi. unconstrained, but what if I simply cracked open a ball valve in this plumbing loop under these conditions, I'm sure I would get steam out the valve but I would NOT explosively flash all the water in the tank by doing so ...... is this correct?

Jamie Hall

ah... it would be nice if that were so, but when the ball valve is opened, the pressure throughout the system will drop, not just at the valve (it won't drop to atmospheric, because of hydraulic losses in the piping, but most of the way there) and it will all try to flash at once. This is why a small crack or leak developing in a boiler or pressure vessel is such a hazard.

RickDelta

That doesn't make sense to me : (
Your saying it will all flash to steam .... instantly??
If the water is changing state from liquid to steam by a factor of 1,600 to one ...... I would think that would be a massive increase in tank pressure!

RickDelta

This looks like a controlled flash to steam to me:
http://rocketbelts.americanrocketman.com/steam.html

EBEBRATT-Ed

No, it will not ALL flash. What comes out of the valve will flash, some of the water in the tank will flash which will build pressure in the tank. This built pressure will prevent the rest of the water from flashing. So to me the only way to get an explosion would be a catastrophic opening like total failure of the tank

Eastman

Boilers would be blowing up all the time if flash steam was such a hazard.

Start watching at about 1:30
https://youtu.be/Ov7qsaICRyk

RickDelta

@Ebebratt-Ed:
OK ....... lets say I have a tempture andpressure gauge on this tank. .....at start reads 30psi and 250F.

I give a quick crack open of the ball valve for one second.
Whats the T&P reading now?
I give a quick crack open of the ball valve again for one second.
Whats the T&P reading now?
I give a quick crack open of the ball valve again for one second.
Whats the T&P reading now?

RickDelta

IMPORTANT NOTE of the set-up set-up here:
Closed loop with in-line electric circulation heater, circulation pump, street water auto fill valve(set 30psi) and pressure relief valve (set 35psi)

RickDelta

set-up ....con't:
I want only 250F hot water @ 30psi in its liquid state ...... never want to see steam inside my loop or tank!

EBEBRATT-Ed

@RickDelta , your loosing me I don't get the question. Open valve steam flashes. What are you trying to find out?

RickDelta

set-up ....con't:
in the event of a monetary water release (ie: from the ball valve) lost water and pressure including temperature drop is restored by loop components back to 250F @ 30psi.

Eastman

RickDelta

@Ebebratt-Ed:
Well ..... 1st thing I wanted to make sure was that by simply opening a closed water loop/tank with a ball valve did not make the entire system explode thru the roof.

I'm now assuming the explosive danger is in the "rate or exposure" to 14.7 psi to the volume of water. (ie: open a ball valve in the loop a little .....you just get steam shooting out ..... remains liquid water inside to loop/tank.
Develop a rapid crack propagation in the tank.... thus exposing a very large surface area to 14.7psi ....steam explosion!!

Jamie Hall

OK. Let's step back a bit.

First off, surface area has nothing to do with it. It's entirely pressure.

Now this must be taken as a highly dynamic situation. Let us suppose that we do have a relatively small ball valve which we can open, connected to a relatively large pressure vessel, and let's also suppose that the water temperature in that pressure vessel is 250 Fahrenheit -- above atmospheric boiling. But the pressure vessel is closed, so that the pressure inside could be anything, provided only that it is high enough to prevent boiling (it could be higher).

Now. We open the valve. This reduces the pressure at the open end of the pipe to atmospheric. Further this reduced pressure proceeds as a wave throughout the pressure vessel at the speed of sound in water (roughly 5,000 feet per second). Now what exactly happens (watch closely -- it's fast). Some -- not all -- of the water will boil at the now atmospheric pressure. This boiling will cause the pressure to rise, due to the increase in volume of water as it evaporates. This will stop the boiling -- but the valve is still open. What you will get is traveling sound waves (they really are, technically, sound waves) bouncing around inside the pressure vessel, with localized boiling at the low points and explosive collapse of the steam at the high points.

In the meantime, water will be coming out the valve -- and flashing to steam -- with a velocity determined by the pressure inside the vessel and any friction losses in the pipe. This pressure will be maintained by the boiling of the water in the pressure vessel until the vessel is empty or the opening to the valve is above the water level in the tank.

In most cases -- not all -- the tank won't explode, but in any sort of confined space the volume of steam from the open port will be a hazard, to say the least. In some cases, depending on tank configuration and strength, the impact of the collapsing steam may cause a portion of the tank -- usually a seam -- to fail, or in some cases (water heaters are notorious for this) the instantaneous pressure rise from the steam may cause the tank geometry to change and fail the tank (the concave bottom of a hot water tank may flip and become convex, failing the joint at the bottom and converting a small leak into a considerably more substantial one -- this is where you get the rocketing water tanks from).

Physics is fun!

RickDelta

........ "traveling sound waves" = Cavitation ??

Jamie Hall

RickDelta said:

........ "traveling sound waves" = Cavitation ??

A very similar situation -- in cavitation, the water pressure is, momentarily, below the boiling point at that pressure. Same idea. When the pressure rises again, the steam bubble collapses and there can be quite an impact.

scrook_2

Too, when some of the water flashed to steam it must absorb its heat of vaporization from somewhere (about 945 BTU/lb at 15psi gage/250F IIRC). The likely sources are the neighboring liquid water, plumbing/tubingAnd/or the tank. This will to some degree slow the continuing flash to vapor, but recall too, Smith’s Theorem: “Murphy was an optimist.”

RickDelta

@Jamie Hall:
Let me ask this now in another way:

Task:
Store and maintain 100 gallons of hot water at 250F @ 30psi max.

1st way:
Buy a standard 100 gallon electric hot water heater .... lets say that's around a 3 ft diameter by 6 ft high cylindrical tank.
(tank rupture pressure 1,000 psi design)
Special order this tank in that it is cut in halve the long way and then re-joined with electrically triggered explosive bolts at the seams.

2nd way:
Store this heated water in a 2 inch "pipe" aprox. 160 ft long ..... or whatever the length is needed to store that volume of water would be. (pipe rupture pressure 1,000 psi design)
Permanently cap one end then use electrically triggered explosive bolt/cap at other end.

It is my contention that if you trigger the 1st scenario the larger "exposed water surface area to 14.7psi" creates an enormous amount of fast explosive energy , whereas the 2nd scenario with its much smaller "water exposure area" yet the same amount of water (100 gallons) "converts to steam" at a rate much less thus much less converted energy.

Jamie Hall

Total energy release will be the same in either case -- it's the energy stored in the water at 30 psi and 250 F relative to the same mass of water at atmospheric pressure. The release will be more rapid, however, in your former example, and this is where the surface area does make a difference.

What are you trying to blow up?

RickDelta

A 2" PVC pipe to be used as a new liner for broken sewer laterals.

RickDelta

@Jamie Hall:
" ....and this is where the surface area does make a difference."
Great! .... just what I had hope for!

My prototype requires me to work with heated water up to 100gallons, 250F @ 30psi all in a 2" pipe .... NO large central water mass as in a hot water tank would be.

I need to get a handle on the degree of personal and property danger of doing so in the event of the pipe connectors failing under such conditions. The entire process is over in 30 mins.

AMservices

@RickDelta What are you really trying to do with this idea of yours? Besides test your fate.
Whatever it is, there probably a safer way.

RickDelta

...... once I get this ridgid PVC pipe fully up to its "rubbery state" (around 220 F) it can then be inserted into the damaged host pipe and expanded to form a new pipe with in a pipe.

RickDelta

yes! ..... using standard thermal fluid (oil) would eliminate the explosive aspects ..... extremely expensive and messy! Then requires an oil recovery operation.

RickDelta

...... avoiding the blast of a controlled steam release I can deal with, ..... blowing the ladies sewer lateral and front yard down the street a few blocks would be unacceptable : (

AMservices

It's a steam cleaning apparatus, isn't it?

RickDelta

No! ...... heating rigid 2" PVC to a bendable state then to its glass transition state for hoop (dia) expansion.

RickDelta

under normal operation conditions .... the heated water is never allowed to change to steam.

AMservices

How much time do you estimate you will have to work with PVC in this bendable state before it turns to glass?
How long of a section will you have to work with?
Is 2" big enough for a sewer line?

RickDelta

I control the temperature and pressure, I have full control of pre-heat time, rubbery state time, balloon state (glass) time and cool down time under constant pressure.

30 ft to 150 ft lengths ..... most homes 50ft pipe length.

No .... 2" is too small for sewer lines .... this 2" schedule "80" PVC is "ballooned up to the host pipe size of 4" ..... resulting in a 4" schedule "40" PVC liner.

RickDelta

...... start to finish in around 30 mins.

RickDelta

Jamie Hall

Ah. Now I see what your are doing. I've done it myself, but not quite that way. The critical difference was that I had a way to circulate the water in that expansion pipe, and I arranged things so I could do a control cool down still under pressure.

Mark Eatherton

Code approved of course.... You're messing with dynamite, ah say DYNAMITE there son... (said in the voice of Fog Horn Leg Horn)...

ME

Jamie Hall

Jamie Hall said:

Ah. Now I see what your are doing. I've done it myself, but not quite that way. The critical difference was that I had a way to circulate the water in that expansion pipe, and I arranged things so I could do a control cool down still under pressure.

Perhaps I should add -- I had (this was a couple of decades back, so don't ask me where I got it) a fitting which allowed me to have a 1 inch (I think if was) pipe concentric with the 2 inch I wanted to expand, which went all the way to the far end of the 2 inch. I circulated hot water through that 1 inch to the far end, then back out the 2 inch -- where I could measure the return temperature and pressure, and had the required temperature and pressure relief valves. Brought it up to pressure, brought it up to temperature, expanded the 2 inch. Shut off the heat, kept pressure up and circulation going until the temperature dropped to something reasonable, then started depressurizing the whole thing. Withdrew the 1 inch, closed it up and went home...

Leonard

You do know that they already have a solution for leaking sewer lines. Hundred foot long woven fiberglass sock , impregnated with epoxy. Put in sewer line with bladder tube inside it and inflated with compressed air to keep it in contact with walls of sewer pipe. Some might be heated to accelerate the cure. There are companies that do this commercially. Saw it done on 12 inch city sewer line and on TV on 4 inch house line.

If you have your partially expanded plastic pipe in the sewer line and it happens to burst, you will have most of that now superheated water trying to flash to steam. And that steam and water mix will likely try to exit the sewer line into your face at the speed of sound, in large quantities, and at a scalding temperature.

Haven't run the numbers on how much water you have , but I'ld check what temp that might bring the room your in up to. Could be a lethal problem if the flashed water filled the whole room with 212 deg steam.

----------------------------------------------------

Do you need 250 degs? I wonder if pressurized 210 deg max water would work. Maybe water pressure supplied not by boiler but by a pump, with restrictor on outlet of your expanding pipe. Or by air compressor pressurizing boiler (boiler and all plumbing would have to be properly rated for the pressure and temperature you select. Might need a special boiler.)

RickDelta

@Leonard:
"..... you will have most of that now superheated water trying to flash to steam."

With 250 F @ 30 psi results in only 2.6% of the water ends in flashing to steam. (30 psi down to 14.7 psi)

https://www.armstronginternational.com/knowledge/resources-library/calculators/flash-steam-calculator

RickDelta

@Leonard:
" ...You do know that they already have a solution for leaking sewer lines. Hundred foot long woven fiberglass sock , impregnated with epoxy"

Yes! ..... another "No dig solution company" ..... that always show up with a backhoe!! : (

That system they use cannot negotiate the yard trap! ..... The "sock" just piles up into one big glue ball! The backhoe is first used to dig all the way down (typ. 4'x5'x 6' deep) to the trap for removal. From there they are working with straight and 45 degree runs.

My method requires NO digging at all! The liner is inserted from yard level trap vent down and thru underground trap on out to city sewer main ....... 1/3 the cost of sock method.

RickDelta

The heating system is a PIC controlled pre-heat, soak, rubberize, balloon and pressurized cool down. (the electric heating elements are twin hair pin heating elements inside the copper pipes just above the circulator)

Leonard

Rick Delta .... most ........... sorry been a while since I opened my thermo book. I didn't run the numbers.

Thermo book is not handy. But a link above quoted water to steam expansion ratio of 1600x. If we ASSUME 1600x and 2.7 % is correct...... even 2.7% x 1600 = ~ 43x increase in volume. Lets assume all that is released into the room. This is still a LOT of steam, to be suddenly release into a small room, seems reasonable chance of burning you.

One estimate of risk......Calculate the total volume of superheated water you will have and estimate the steam cloud size diameter if all it's presure is released, that's what you might be standing in if things go wrong. But even if 212 deg steam is diluted with a little 70 deg room air, at some point the hot steam/air mix will likely burn you, I just don't know the temp/time skin burn point.

RickDelta

@Leonard:
".... Do you need 250 degs?"

No! ..... that's just design "head room" specs (ie: doing this work outside in the middle of a very cold winter)

Nice day out ....... 218 F to 225 F works just fine! (the PVC only needs to be at 180 F to 200 F to balloon up) The additional temperature is to offset delta T losses and outdoor heating conditions losses.