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  • #91
    Originally posted by Evan
    Spinning things with air can be very dangerous. The velocity from an air nozzle may approach the speed of sound. That means the theoretical maximum rpm that your top might achieve is around 170,000 rpm. It will be less than that of course, but how much less? When does the metal come apart?

    I can make a stab at answering that. When I was working for Rocketdyne as a Rocket engine mechanic in the late 1950's, early 1960's, we wold take turns operating the engines during tests at the direction of the test engineers.

    All of the functions of the engines were recorded with analog Sanborn pen recorders which made a mark in ink on the paper as it rolled along. There were transducers mounted on the engine which sent varying DC signals which, when properly calibrated, would closely indicate the status of the particular functions, such as heat, pressure and speed.

    The engines used a gas turbine that ran on liquid oxygen and jet fuel to drive the main turbopumps. One of the engines, unbeknownst to us, was built with the shaft between the gas turbine and the turbopump inadvertantly left out, although the inspection records of the engine, when examined later, showed that the shaft (called a "quill shaft" due to the splines on each end) had been installed when the engine was manufactured.

    The engine went for a hot test and, once started, the turbine freewheeled and, after about 45 seconds, IIRC, it exloded. The resulting fire, fed by 3,000 gallons of liquid oxygen and another 1,500 gallons of JP-4 Jet fuel burned for fully three hours and removed every last piece of wiring and equipment on the test stand.

    The pen for the Sanbord recorder for that function, turbine speed at mainstage, went off chart at 150,000 rpm. The sound that it made was a piercing whine not unlike the mythical Banshee.

    The next morning, I was viewing the totality of the damage and I noted that several of the turbine blades had been driven into the steel I-beams of the test stand and were sticking out. When I hit them with a hammer, several of them broke off and one of them came out whole, leaving a notch in the metal that was fully one inch deep.

    So, I would say that 150,000 rpm is the answer.

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    • #92
      From what I've read perpetual means never ending. I've also read that the universe had a starting point...the big bang...and everything is still expanding but will eventually stop and then collapse back into itself and by definition will end. Not that one has to subscribe to the big bang and all the "knowledge" we have, or don't, but with those standards perpetual motion is not possible as that motion will eventually end. Now realize that this is the opinion of a high school graduate...not a astral physicist

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      • #93
        The Big Gnab scenario is no longer thought likely. All the evidence so far is that the universe will continue expanding indefinitely until all the lights go out and everything is resting very close to absolute zero.

        There is no requirement that the universe have a definite end. Nor is there any requirement or even hypothesis that it must be succeeded by anything. This may be the only reality that will ever exist anywhere and anywhen. Of course, for each individual the universe ends rather soon.
        Last edited by Evan; 07-20-2010, 08:53 PM.
        Free software for calculating bolt circles and similar: Click Here

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        • #94
          so to finilise the end.

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          • #95
            The "200 mpg" carburetor myth can easily be disproven. The most the "magic" carburetor could do is to provide a perfectly vaporized and controlled air/fuel mixture to the engine. An optimized propane carburetor will provide a nearly perfect vaporization . If one compares a conventional gasoline carburetor with an optimized propane carburetor, the differences in fuel efficiency are surprisingly small. That comparison has been done many times over the decades. It's also always been true that the auto manufacturers would kill for a substantial fuel economy advantage over their competitors, all else being equal.
            As for examples of alleged perpetual motion machines, one has to remember that simply exerting a force does not require energy. The force due to gravity , for instance, does not imply the expenditure of energy. The exertion of a force over a distance, however, represents "work" and does require energy.
            In the real world, with real machines, it's still true that you can't get something for nothing. In fact, you can't even break even.

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            • #96
              While propane does provide perfect atomization, Bill, it also has a very low BTU rating, compared to gasoline. So, even with perfect mixing, you, in effect, have almost nothing to burn.

              Hydrogen would atomize quite well and mix beautifully. Of course, hydrogen has about 13 times the energy of gasoline, per cubic foot of vapor.
              Too bad it's highly explosive...Playing with it would be fun.
              No good deed goes unpunished.

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              • #97
                Originally posted by ckelloug
                If the alien technology is electromagnetic in nature then wrapping yourself in conductive metal will shield you. The beauty of science is that we can predict what happens in cases we cannot try. If we integrate electric flux inside of such a suit, we conclude that the charge from the alien mind control ray can only be on the outside of the suit and thus we are protected. Long live the Maxwell equations as they apply to the prevention of nutters and alien mind control rays!
                Dunno if it's worth worrying about.... and the metal suit is fine..... it's those pesky joints that are the issue, not to mention that the 'electro"" part is OK, but the "magnetic" part may pose a problem to most such suits......... I think I could guarantee to get a strong field inside that suit, despite your best efforts......

                But, a conductive vest might be rather handy if your local cops like to use their tasers and stun guns......... Tasers might be a little more of a problem, but still defeatable.

                Those harmless devices have already killed a few folks..... Should be a law that every time a cop uses one, he or she should have to get a hit themselves afterward..... To remind them of what the one they had in training was like.....
                1601

                Keep eye on ball.
                Hashim Khan

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                • #98
                  Part of every cop's training when they get a Taser is to get his or her thing knocked stiff with a real Taser, so they'll know what it's like.

                  They offered me a Taser, once. But my instinct for self preservation forced me to turn them down.
                  Last edited by saltmine; 07-20-2010, 10:44 PM.
                  No good deed goes unpunished.

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                  • #99
                    Originally posted by saltmine
                    Part of every cop's training when they get a Taser is to get his or her thing knocked stiff with a real Taser, so they'll know what it's like.

                    They offered me a Taser, once. But my instinct for self preservation forced me to turn them down.
                    At least with a Taser, the offender who is charging a policeman can sometimes be stopped without lethal force.

                    My son is in the California Highway Patrol and he's been Tasered several times in training. He's used a Taser on offenders several times. It usually stops them but not always. If they have a sufficient load of drugs, the Taser won't even phase them. (pun intended).

                    If the Taser (or rubber bullets if available) won't stop them, the only other alternatives are either a baton or resorting to deadly force with a gun.

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                    • You got me Jerry. That damn magnetism with its annoying B fields and H fields. I think you have impaled me with your monopole lance. . .

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                      • Hydrogen would atomize quite well and mix beautifully. Of course, hydrogen has about 13 times the energy of gasoline, per cubic foot of vapor.
                        Hmm. Hydrogen weighs 2 grams per mole. One mole of hydrogen combusted stoichiometrically produces 242 kilojoules of energy as heat.

                        Gasoline weighs about 120 grams per mole and produces 5500 kilojoules per mole. If we take the same weight of gasoline then that is 5500/60 or 91 kilojoules for equal weights of fuel. That is a ratio of about 2.66 to 1 in favour of H2. BUT, and it is a very big but, the only way to carry enough hydrogen to go anywhere is to liquefy it. Even then the energy density per cubic foot of liquid hydrogen vs a cubic foot of gasoline is absolutely miserable. To give the same total energy as gasoline requires about 4 times the volume of storage. That entirely negates any advantage that hydrogen has in specific energy by weight since it has such low density even as a liquid, about .07 grams per cc.

                        Worse yet, to make liquid hydrogen requires the energy equivalent of about 40% of the product.

                        Transporting it is even worse as a hydrogen tanker will hold enough fuel to fill about 60 cars and will use around half of that fuel to truck it 300 miles. An equivalent gasoline tanker will fuel 800 cars and use about 5-10 cars worth of fuel to deliver it.

                        Then there is the problem of where the hydrogen comes from. Currently it is made from petroleum.

                        Then there is the storage problem. It must be kept at nearly absolute zero to remain liquid. Other methods such a hydride storage have no chance of achieving sufficient density any time soon and cannot achieve a density higher than liquid H2. Even if you don't drive your car the fuel tank will be empty in a few days.

                        Hydrogen is even worse than electricity as a fuel. It isn't even a fuel since there is no free hydrogen available. It must "uncombusted" first which requires more energy than it produced when it combined with something else in the first place. Hydrogen id properly regarded as an energy storage system with remarkably poor efficiency.

                        It also has a dirty little secret. It produces a lot of air pollution in the form of oxides of nitrogen because the combustion temperature is so high. Also, most of the radiant energy from combusting hydrogen is in the short unltraviolet spectrum which is ideal for forming oxides of nitrogen no matter how it is combusted.

                        None of the density problems can be overcome no matter how the hydrogen is used as source of energy. It is what it is, the lightest and least dense element in the universe.
                        Free software for calculating bolt circles and similar: Click Here

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                        • I prefer my own brand of Taser, GNM109. It's called a "Remmington 870, with #00 buckshot"

                          Guaranteed to stop almost anything.
                          No good deed goes unpunished.

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                          • Interesting hypothesis Evan. My bad, that's what I get for reading all of those pro-hydrogen articles out there. A lot of enthusiasm usually allows the figures to creep in favor of your favorite fuel.

                            I'm one of those guys who would prefer to manufacture my own, as I need it, through electrolysis. That way, you wouldn't have to drag around those bulky hydrogen cylinders everywhere.

                            Stan Meyer was on to something before they whacked him.
                            No good deed goes unpunished.

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                            • Yeah, now you just have to drag around an extension cord.
                              Todd

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                              • Originally posted by saltmine
                                I prefer my own brand of Taser, GNM109. It's called a "Remmington 870, with #00 buckshot"

                                Guaranteed to stop almost anything.

                                Right. They don't get up after that! I have the same shotgun but I only have dove loads.......

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