Re: The Electric Car

The way I heard it, they have a tube around the nozzle where the liquid goes, specifically to cool it - of course, by the time it reaches the combustion chamber, it's probably already ready vapor or in quite a hurry to get that way!

Thanks, Rich

Rocket engines are continuous.

In internal combustion engines, the fire goes on and off.

I'm just wondering out loud what happens to the metal parts which will be rather hot when hit with LOX.

Will thermal stress cracks be an issue?

snipped-for-privacy@specsol.spam.sux.com snipped-for-privacy@specsol.spam.sux.com posted to sci.electronics.design:

While the LOX will never get to the hot cylinder walls (fairly low heat of vaporization), there are significant thermal transport considerations. Especially at startup in very cold weather.

Have you read Richard Feynman's (MHRIP) additional comments to the Challenger disaster inquiry report? He wasn't impressed with the service life of the LOX pumps, amongst other things.

Feed pumps are always a big problem on rockets. They have to be light, enormously powerful, pump nasty stuff, and are designed to run under major stress for a couple of minutes.

John

Feynman's point was that they were expected to run under major stress for a couple of minutes, then do it over again on the next launch, and so on. He considered the lifetime predictions to be flawed.

Yeah, he was pretty smart. And the Shuttle was pretty dumb.

John

He might have been right about the projections, although lifetime projections are normally correlated against test data before being accepted as meaningful. I never heard of any problems with the oxidizer turbopumps failing in flight, have there been failures?

My first engineering job was seal designer at Stein Seal Co. where I did part of the design of the shaft seals for a large Rocketdyne oxidizer turbopump around 1979 or so. One seal kept liquid oxygen out of the bearings, and the other kept a hot hydrogen and steam gas mixture out of the same bearings, with several inches between the two. Overall construction is similar to other turbopumps like automotive turbochargers, with a turbine on one end of the shaft and a pump on the other, seals and bearings in between. Neither fluid is what I would call "nasty" in this case; neither corrosive nor erosive. (We also did seals for really nasty fluids.) There is quite a bit of thermal expansion and contraction to be accomodated on startup, but not that much different from the bearings and seals used on jet engines which also have to accomodate a lot of slop for thermal expansion. A somewhat complicated design, but are they really "big problems"?

Not on a shuttle. I've heard of some other rockets failing because of feed pump problems.

Feedwater pumps are a big deal in steam plants.

John

Those must have been the ones using Sealol face seals :-). Early pumps were designed with methods now considered primitive. Stress/strain and vibration modal analysis of the startup phase is computationally intense, it was a bit tough in the days of the slide rule, when some of the early pumps were designed. Newer pumps including the shuttle pumps benefited from state of the art finite element analysis.

Yep, those are some big pumps with a lot of parts subject to corrosion, erosion and wear. Rather different tradeoffs from the rocket feed pumps. I have done some work on these too, including the defunct Clinch River Fast Breeder Reactor primary sodium pump seal. Hot liquid sodium qualifies as a fairly nasty fluid - but only if it leaks :-).

Speaking of nasty, in the 50's roughly, some power plants were built using mercury as the working fluid.

John

Once, in one of the engineering buildings at U of MN, there was sort of a display - some guy had built an MHD device, which used about a liter of mercury. This was in 1968 or so, before they made mercury all toxic and stuff. ;-)

Cheers! Rich

Hot UF6 is pretty nasty, too. I read somewhere a long time ago that they started building the Oak Ridge diffusion plant without any idea how to make pump seals that would stand the stuff. Some guy called, IIRC, Judson Swearingen came up with the goods just in time. D'you happen to know if how it was done ever got declassified?

Not outright failures in service, but "cracks have been found in the turbine blades of the high pressure oxygen turbopump". He was talking about the inherent deficiencies of top-down design vis-a-vis the inaccessibility of certain critical parts.

It's interesting reading, lacking none of Feynman's customary clarity and incisiveness, despite the fact that, by this time, he was dying, and knew it.

Available at:

Those sound very like them.

I don't know anything about that, and don't know if it was ever declassified, but in general they are not too good about declassifying that sort of information IME. Obviously the information is out there, considering the number of enrichment plants in operation today, but that has not stopped efforts to limit access to detailed info on how it is done.

The classified info that irks me most is the Navy rules for safe reactor construction and operation. Admiral Rickover did a pretty good job creating these rules, judging by the Navy's safety record, and it is a pity we can't compare "Ricky's rules" to the safety rules in effect for commercial power plants. If TMI had followed Navy standard safety practice the accident definitely would not have happened, at least two of the amazing series of problems leading to the accident would have been prevented. But those standard practices are classified, and it is my opinion that much more harm than good is done by it.

The Navy has an advantage in enforcing its safety rules. The operators have an extreme incentive to maintaining safe operation and safe equipment since they sleep in the plant.

Thanks, very interesting indeed. Great conclusions:

-------- "Official management, on the other hand, claims to believe the probability of failure is a thousand times less. One reason for this may be an attempt to assure the government of NASA perfection and success in order to ensure the supply of funds. The other may be that they sincerely believed it to be true, demonstrating an almost incredible lack of communication between themselves and their working engineers." ... "For a successful technology, reality must take precedence over public relations, for nature cannot be fooled."

--------

One often finds this sort of management disconnect from reality. I think that the fault lies at least in part with the standard doctrine at most if not all business schools, that it is not necessary to understand a process in order to manage it. They point to the possibility of getting bogged down details, doing the work rather than managing it, and claim it is actually better not to understand the details of how the process works. Just apply these management principles and profits will be maximized, they say. No doubt some managers have gotten bogged down with details, but far more often they make bad decisions based on a failure to understand key issues.

The motivation for this teaching is pretty clear: hire only business school grads for management positions is the actual self-serving message; don't promote line personell from within no matter how much they know about the business, you need an MBA!

Just outside of Richland, Wa, in the Hanford nuclear reserve, clearly visible from town, is a someday-to-be dismantled, huge spherical liquid plutonium reactor.

John

You might think so, but boredom and complacency can set in even on a submarine. The important differences are in plant construction, operator training, and specific operational procedures.

I recall a reactor operator performance review something like "Joe knows exactly what to do in any situation. Unfortunately he rarely notices when a situation occurs."

Verifying that your operators know what to do and have a high probability of recognizing the situation is not easy.