About 15 he answers some of the speculation weve been doing about the plates. Sandwich with top plate perforated, massive showerhead pointing up.

I think the flashing steam will absorb massive amounts of heat and the water being shoved out of the pipes into the exhaust stream.

They are trying to use rocket engine principles here. It’s like the way they cool the nozzles. Regen is what they call it.

I don’t see the difference between regen and evaporative or transpirational here.

Above 10k ft. He has already said that is what he does.

Pics for ph 364

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We are not talking about the same thing.  Your experience with HVAC is screwing you up by focusing you on latent heat of phase change, instead of basic heat transfer to prevent steel plate from melting.

If you are trying to keep a rocket nozzle, or a boiler water wall, or an engine from melting, you don't want phase change to occur in the thing you are trying to cool.  You want a continuous supply of cool, dense liquid running through the system.  In this case, the water may exit the cooling grid and be used as sound suppression by spraying it or doing flooding some portion of the pad or trench.  Don't really know much about sound suppression.  In any case, once the water exits the cooling grid to atmospheric pressure, you probably want the water to be cool enough to stay a liquid rather than immediately flash to steam.  This means pumping high rates of water or using a water tower of sufficient size to provide a high rate of flow from gravity alone for the duration of the heating event and probably a bit afterwards.  

Your automotive radiator specifically operates under pressure to raise the boiling point of the water and coolant mixture and the coolant fluid that is added to the radiator is specifically designed to prevent boiling by raising the boiling temperature.  (It also lowers the freezing point because solid coolant is not a good)

You can operate your vehicle for years and never have to add water/coolant mixture to the overflow container.  That means you aren't boiling the fluid away.  The fluid picks up heat and ejects it in the air to liquid heat exchanger.

Cooling systems are about absorbing heat.  You want the cooling liquid to have a high specific heat and high density.  Specific heat and heat of vaporization are two different properties.  Specific heat is the amount of heat necessary to raise a given mass of liquid a given change in temperature.  (The energy required to raise the temperature of 1 gram of water by 1 degree Celsius is a calorie)  Heat of vaporization is the amount of heat required to vaporize a given mass of liquid at the boiling point.  Since a well designed cooling system doesn't allow boiling temperature to occur, the high heat of vaporization does not play a role in the cooling provided by the system.  (It takes 540 calories of energy to vaporize 1 gram of water at atmospheric pressure and 100 degrees Celsius).  

Total heat transferred into the cooling water is a function of the mass of the cooling water, the specific heat of the cooling water, and the change in temperature of the water that occurred.

You can move a lot of water at a small change in temperature and remove a lot of heat.  Since the goal is to prevent the steel from melting, we want the temperature of the steel to stay as far away from the melting point as possible.  Encouraging a high rate of heat removal from the hot side of the steel plate to the water is desirable.   This means having the water as cold as possible, so high flow rates to maintain low water temperatures is useful.

Once the water exits the cooling plates and is heated to the boiling point by rocket exhaust, the high heat of vaporization does come into play and the production of steam will reduce the amount of heat reaching the plates in the first place.

I don't think boiling is desired in rocket nozzle regenerative cooling.  Rocket nozzles are highly specialized and the fluid coming from the rocket nozzle is at some point sent to the combustion chamber, so I think the pressures of the liquid in the rocket nozzle would be quite high.  However, Rocket engines are way outside of my experience with cooling diesel engines.

Yup. I believe for sound suppression you want liquid water with air bubbles. I'll have to double check.

To your point about high flow rate to keep the steel as cool as possible, I agree. If you're building a system that aspires to heavy use without refurbishment I think you want that steel as cool as possible to minimize erosion. "Cool enough" just isn't going to cut it in the long run.

ETA
https://interestingengineering.com/innovation/nasa-sound-suppression-system-prevents-rocket-from-exploding

Insane! Startank.

Often times the liquid in a rocket nozzle will be hot enough that it is vaporizing right before/as it is hitting the turbopump/combustion chamber

I think one of the biggest factors in a water deluge suppressing sound is actually the steam/water vapor. Steam in the air absorbs more acoustic energy.

I figured it might vaporize at some point after doing it's job of keeping the nozzle from melting.  The fuel portion of the propellant picking up heat is actually a good thing.  Regenerative cooling is an elegant solution.  The nozzle is cooled by cryogenic fuel and the fuel is brought to temperature for rapid vaporization as it enters the combustion chamber.

I don't know if it makes a difference in this system - but cooling the exhaust by flash vaporizing water seems a bit like running a suppressor wet.

Make pad out of Rebar, proven to hold up.

I was thinking more about melted metal meeting water - a tinsel explosion would be pretty.

There are some engines where the pump is powered by the phase change.  Called an expander cycle.

This is what it does when the rest of the system is there.

Thanks for the discussion. Thanks for showing me any principles maybe I haven’t considered.

(Excuse my empirical measurements)

I know they’d ‘like’ to keep heat exchanger below 212 because steam is a bitch to engineer around and 212F is closer to 600F than 100F is.


You are saying they’ll likely use the sensible capacity of relatively cooler water to keep the steel from melting.

I think that HAS to be an enormously strong pump with an enormous amount of water. Im not worried about the sound suppression characteristics. They are putting steel directly underneath something that’s 2x as powerful as the Saturn v.

You are going to run out of sensible capacity quick. In a point when your latent capacity will Be 9x your sensible capacity.

A radiator is simple in a car that’s why it’s used. A chilled water loop is used because it’s simple.  Direct expansion refrigerant circuits like VRF are more efficient just more annoying to deal with. Same way a steam plant is just a heat pump and more efficient that a hot water loop, it’s just more annoying to use steam.

I know you know this graph.
(Assuming the pressure is 1 atmosphere)
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Best example I have is the 1x 1200F acetylene torch on the pot of water. As long as water is present it can not get hotter than 212F. You can take literally 20x the torches and the pot can still not get hotter than 212F so long as water is still present to boil away and absorb by 970BTU/Lb. This is how i imagine the launch mount.


So i guess they can stay with water between 70F and 212f and use 1 BTU/LB of delta T. I was just thinking maybe they’d let it sit at 212F and continue to dump water in and let the dripping steam blow out the nozzles. (I guess that would require more engineering to keep pressure from going back towards the inlet side).


They might count on some bubble point pressurization driving the cycle maybe. Like just a little bit of boiling and they’ll be a massive pressure change and subsequent raising of the boiling point but very very little of the water actually ends up boiled/evaporated.

The steel on the launch mount legs and platform didn’t melt with no cooling.

Think you guys are thinking a little too much into it.

Was there steal directly underneath the engines? I’m genuinely curious. What’s the heat of the exhaust?

You are right about regen. I’m dumb. Being an HVAC nerd I see them running liquid as a heat exchanger I always assume vaporization. I don’t think they want many bubbles on the turbo if any at all.

Not directly underneath. The legs took redirected exhaust from all the engines and the top of the platform must have got pretty spicy after liftoff.

Methane / oxy flame is around 5,100*F.

I am pretty sure he is one of Elon’s favored SM crowd. Elon tells the people in control to allow the over flights and when.

He was flying a 172 type airplane so 10k is unlikely.

You can heat a steel pipe with water flowing through it to glowing hot and even cut it with a torch.

we keep thinking melt metal - but I wonder what a blacksmith would think about heating it up and apply tons of pressure.

Bullshit

That would have to include some pressurization.

Get a copper or steel tube in a u bend with both sides open. Fill with water and oxy/acetylene torch the bottom of the U.

I've flown 152's and 172's above 10k many times. Ceiling on all 172's I've flown were between 12-14k. With takeoff weight well below gross, on a cold morning, you can go quite a bit higher.

That photo was definitely taken with a zoom / telephoto lens.

Nope. I cut pipes wet all the time. Sometimes with flowing water, sometimes just filled with water and open at the top.

It doesn’t make much of a difference other than taking a few seconds longer to preheat.

CSI Starbase put out a decent vid on this a few months ago with a graph (8:55 in vid, use the red line) from Space X showing plume temps at different distances. However, the graph assumes is only for a single engine where the plume is surrounded by ambient air. The center cluster of engines would be significantly hotter than the 900°F on the graph but no hotter than 3500°F immediately after nozzle exit.

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While boiling water can remove a crap ton of heat, steam is also a decent insulator, which in this case may be an issue. In a boiling pot of water, the steam forms a localized bubble and releases from the bottom of the pot allowing more liquid water to rush in and then get vaporized. In this case the heat is from the top and localized boiling on the underside of the plate will create a steam layer between the plate and the rest of the liquid and basically drop the available heat transfer ability to almost nothing. I think is is one of the reasons they are putting holes through the plate, so they can vent the steam layer.

There are going to be serious issues with this as well, as I can imagine the localized pressure at the surface of the plate while at full throttle to be quite high. (I’d love to know what it might be) If their pumping system doesn’t have the ability to overcome this, I can imagine some of the superheated exhaust gas going impinging into the holes of the deflector plate and causing more “issues”…. LOL


I’d imagine they will test this several times while doing test fires…. Gonna be fun to watch.

ZA

The above video I posted (starting at 6:10) says the pressure at the nozzle exit would be about 245 psi which is quite a bit lower than I was expecting.
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In this thread... People watch a company successful fly a rocket with engines that have very high chamber pressures and complex fuel flow dynamics...

Also in this thread... People are skeptical this same company can handle designing a device to handle water and steam...

Steel pipe can be welded underwater surrounded by all the water in an ocean.

This is possible because time is important.

Time shows up as rate in everything that will be discussed henceforth.

Heat transfer has no respect for specific heat or even heat of vaporization. Heat transfer rate is represented by the capital letter Q. Again with the rate and the importance of time.

Q is capitalized because it's important and the answer we are looking for. It incorporates time.

When faced with big fucking incoming Q, we need to remove that big fucking Q with massive fucking flow rates.  We are familiar with volume flow rates but what really matters here are mass flow rates. The mass moved per unit time.

Sound suppression is about massive water flow rates. Liquid fueled rocket engines are likewise about massive propellant flow rates.

Arfcom often has a fascination with force and torque because Arfcom fails to understand the master of time.

Power is about time.

Rocketry is all about doing everything as fast as possible.

Liquid fueled rockets are therefore about pumps that move massive quantities of propellant in a short time. Liquid fueled rockets are also about liquid tanks. Sound suppression is likewise about either pumps or tanks or both.

600,000 gallons of water raised 120 degrees F in temperature will remove 600,480,000 btu's of heat.

The rocket will clear the tower by a good margin in 25 seconds. So we probably could run a bit less than that.

Run 600,000 gallons of water through the armor plate, absorb 600,480,000 btu's and the water is still at least 12 degrees below boiling at atmospheric pressure. Now that same water exits out the armor plate and it's available to absorb 60,480,000 more btu's of heat before it can be boiled to steam.

Now, only now, will the heat of vaporization come into play. It's not exactly that simple, there may be some hot spots where some water boiled before reaching the other side of the plate.

But the water keeps coming.

20 seconds of massive flows of water fighting against the combined flow rates of 66 pumps working several times faster than the pumps aboard the rockets that sent men to the moon and provided them with the means to return back to earth.

The mass of water moved to protect the pad and the mass of propellants in the rocket are not the thing. The thing is the rate of moving them. Time is the thing.

The very first major application of the steam engine was to pump water.

And in the 21st century, the world once again stands in awe of the most fundamental machine.

A machine full of 66 of the fastest pumps the world had ever seen is protected by still more pumps to provide water which is turned to the very steam used long ago to power the pumps that changed the world then, same as they do once again now.

Steam!?



Choo choo!

Well Done !!! Attached File

That’s the post!

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Thank you for putting up with this ‘less than an amateur” in this conversation.

Power curves on pumps are beyond my experience. HP and GPM are the last stops on my knowledge train here. Chiller/boiler delivered tonnage 500xGPMx DeltaT= BTU’s/hour removed or delivered

I just knew latent heat of vaporization was the only way I could imagine them keeping that steel plate from turning to butter.

The launch mount structure had to be modified with thick slabs of stainless steel plate after the first test of the booster by itself.

They may have some water cooling provided by spray nozzles. Not sure.

The concrete armor appears to be made with a thin top plate and be closer to a flat version of a regen cooled rocket nozzle.

Water over 212 at high pressure will remain liquid.

Also recent elon interview states they will cut ignition to liftoff time from 6 to 2.5 seconds. So heat wont be as nig of a deal.

I think concrete failed mainly from thrust less so heat.

Elon also said in the interview with the engines they chose not to ignite causing the rocket to launch crooked the launch table was actually subjected directly to rocket exhaust.  Held up well

In an ideal world nozzle exit pressure would be just barely above ambient pressure putting all of that energy in to the rocket. That's why vacuum engines have much larger bells.

Me Too!!!

First time I aced the homework, but then that first test was brutal. Professor pulled all kinds of shit on his test. People that were used to straight As were making Cs. I cut my loses and dropped it for a redo.

Second time around I got an A in the class.

I'm very interested what Space X comes up with.

In order for the rocket to actually expel its exhaust the pressure at the end of the nozzle must necessarily be rather low. High pressure fluids move to areas of low pressure and if, at the end of the nozzle, you had a higher pressure than the chamber you would have backwards flow.

Also with rocket engines we want high flow rate and high propellant gas velocity in order to make the most efficient engines, Bernoulli tells us that in order to get the maximum velocity on one end of a control volume (at the nozzle exit), starting with a very high pressure on the other end (in the chamber) we must have a very low pressure at the exit, with the equation being balanced by that pressure turning into velocity.

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Ideally we would expand the gasses to exactly match ambient at the nozzle exit, but obviously as air pressure changes with altitude we have to simply pick an expansion at some point (except aerospikes).

Vacuum engines have limitations of weight and fitting in the interstage, but they are made extremely large so that they are optimized for operating in vacuum or near vacuum conditions.

A good example of this is the Falcon 9 because the first and second stage use effectively the same engines, just with a much larger nozzle on the upper stage, or starship which uses both vacuum and sea level raptors and it will use each depending on which is better for the situation.

I loved in heat transfer learning about all the equations for approximating convection, and then learning what the error was on those equations. They really are just for getting a super rough idea of what is happening even on super idealized models.

IIRC some had an error of up to 60-70%.

FAA sued over SpaceX Starship launch program following April explosion

lol