Hot Slippery Bodies
Why do we need a professor to tell us hot bodies get slippery and wet? It's common knowledge.
Paris, because she also gets slippery and wet easily.
An Australian boffin says he has come up with a novel method for making things such as ship's hulls or torpedoes slip through water more easily. Professor Derek Chan of Melbourne uni suggests that it would be practical for ships to exploit the "Leidenfrost effect", named after its discoverer in 1756. This refers to the …
I'm sure there are some naval ordnance techno boffins out there who can put me right on this, but I would have thought the cavitation from all the escaping vapour would make for a hell of a noisy torpedo, which I would expect to cancel out at least some of the speed advantage.
Also how would the necessary temperature be maintained? Onboard equipment would take up space and fuel, which would presumably limit range and warhead size.
Over to the people who claim to know what they're talking about.
at 250 mph, and there are (classified, but in principle workable with some degree-level physics) some ways to reduce the noise.
But do you seriously think that at this speed, the noise matters?
Typical range over which you want to use torpedo is at most 5 miles - do you really think a big ship can do much in around 2 minutes it takes supercavitating torpedo to reach it? Especially if it's got some sort of guiding system?
As a former junior naval ordnance techno boffin, I can assure you that the intended victim of a torpedo generally - and in the case of a submarine, certainly - knows it's coming the moment it's launched and immediately takes evasive action. No amount of additional noise makes a difference to the target once the fish is on the way, but a few seconds less time to evade or distract it certainly does. The noise may affect the torpedo's ability to identify a target by its acoustic signature, but that feature is most important for devices that sit quietly and spring into action when they spot a target - self propelled mines, in other words - and there are clear practical problems with keeping a loitering torpedo hot.
The Russian rocket powered torpedo thing basically goes in a straight line very fast, the idea is it's so fast that the target vessel would be unable to alter its velocity enough to avoid a collision. The videos I've seen of them (they're on youtube) show a massive wake on the surface so it's by no means a stealth weapon however you look at it . I don't think the range isn't that great either and they're designed to be launched by surface vessels rather than submarines who'd just end up with a trail of bubbles pointing to them.
Of course the other problem they have is there's no real way of guiding them as they generate too much self noise for sonar to work, although wire guidance might be an option, in which case the counter measure is to take out the launch platform.
I have spent a lot of time playing with liquid nitrogen in the lab, and I can tell you the one thing you DO NOT want to do is "dip your hand" into it. You will lose it, quickly, because the pressure of the liquid rapidly displaces that thin boundary layer.
What you can do quite safely is pour it all over you - as long as it has a path to run. You can take a Dewar flask of it and pour it all over your hands, arms and legs...as long as you are not wearing gloves or shoes that will trap it, and thus allow it to burn-through the vapour barrier.
This post has been deleted by its author
Popular Science did a cool (get it?) article about this some time back, complete with video, heres the link: http://www.popsci.com/diy/article/2010-08/cool-hand-theo
he wussed out on the molten lead experiment that Mythbusters did though.
Naturaly it ends with "ACHTUNG! Do not try this. If liquid nitrogen soaks into your clothes, you will not be protected by the Leidenfrost effect, and you can get frostbite very quickly."
I was sitting on the floor half under a machine once, when someone knocked over a liter beaker of liquid nitrogen. I can confirm that the "Leidenfrost effect" works very well for LN on a tiled floor, causing it to speed about and rapidly cover the entire room, but fails utterly when the LN encounters the seat of a person's pants.
in torpedoes at least, given their hoped-for lifetime once activated.
On the other hand it would possibly provide a solution to any that fail to hit their intended target, rather than just bobbing around they could neatly degrade so that no passing children (kids snorkelling) will pick them up and think "shiny toy!" and find they've entered a sudden weight loss program.
"The ship's hot body could substantially minimise the amount of drag as it passes through water, therefore potentially reducing transportation costs and greenhouse gas emissions."
Is that supposed to be a joke? If not I have another great idea: to reduce costs and greenhouse gas emission, Australia could ship it's ore and grain using Endeavour instead.
Coal doesn't go off and the life of wheat stored under proper conditions is months or even years. Why do these freighters need to go faster?
I think he's also forgetting the realities of the shipping market which is to reduce costs as far as possible by only ever using very old, single hulled bulkers manned by third world crews sailing under flags of convenience. Only a few years ago, one of these monsters was sinking every month and no one in power gave a toss until the MV Derbyshire vanished, but since then, nothing's changed.
I would suggest amending this sentence:
"The same effect can also allow a person to put their hand into a bucket of liquid nitrogen without harm"
True, but only if they dip their hand in and out VERY QUICKLY. I would highly recommend not casually sticking your hand in a bowl of liquid nitrogen and saying to your mates "Look! This won't harm me!"
The same trick can be done with hot oil - IF you wet your hand with water first. Dip it in quick enough and the steam will allow the oil to run off before you get burnt. Still - not to be tried at home - you need to do it VERY QUICKLY, and this is NOT enough time to grab a dropped ring from the bottom of a hot deep fat fryer!
Pushing a ship either through or over the sea is vastly different to watching a drop of water dance about on a spoon heated over the gas cooker (I done that as a child, fire is great!).
If they're planning to ease the ship through the water, as ships move currently, then surely most of the resistance is due to moving the large bulk of water out of the way of the ship, and putting it back after the ship has passed. This won't change that.
If they're planning to ride the ship over the top of the water, then surely the waves will scupper that one.
Either way, sea salt will be deposited on the ship's hull, which won't help.
Even if the vapour layer does insulate well, warming the ship's hull up in the first place will require insane amounts of power.
This whole thing is just about as stupid as an article I once read in new scientist about supercavitation. The suggestion was to reduce the drag on an underwater passenger craft by going fast enough using rockets to cause deliberate cavitation at the rear of the craft. Not crashing into things like whales and other submarines would be difficult at several hundred mph, even if it did reduce drag.
The Leidenfrost effect is real. I happened to demonstrate it a few months ago while doing some plumbing work. I'd heated a leaky value to a temperature, high enough to melt solder (not the Lead-Tin variety, but the new and improved variety that has to be used on Copper pipes now, which requires even more heat to melt). I removed the value with a pair of pliers, and laid it aside. Then, in a bout of forgetfulness, I reached over and grabbed it with my bare hand. There was an incredible amount of sizzling, as the water on my fingers evaporated, but, quite surprisingly, I didn't get burned (although I did drop it pretty quickly, when the sizzling reminded me that it was probably 200 degrees C!).
As for making torpedoes move through water faster/more easily, why don't they coat them with teflon? Or, maybe they should add a soap dispenser to the front of them to give them a coating of soap? Or, maybe add an air bubbler to the front of them? What other slippery things are there out there that could be used? Those might be cheaper than trying to heat them well above 100C.
Dave
A) Superheating the hull of the ship in question would take far more power than would be saved in moving the ship.
B) I can only imagine the workplace risks involved for the sailors on said ship
C) Pushing a ship through the water creates a tremendous amount of pressure at the bow and along the sides of the ship. That pressure would tend to overwhelm the vapor barrier unless you made the ship's hull even hotter.
D) How long until this starts affecting ocean surface temperatures, especially in shipping lanes?
E) how would the heated hull work in storms/high seas? Would it tend to exaggerate listing or the risk of capsizing because the vapor barrier presents less "good" friction that keeps the ship stable?
Because this is a *dead* failure if it's not as essentially power = money.
Water has both a high specific heat capacity and a *very* high heat of vaporisation. Getting this much water *to* boiling point is *nothing* compared to the energy needed to boil it.
The torpedo situation might be a bit different. The benefits of speed might outweigh the cost of doing it. You might make life a bit easier by using a film heater (a metal foil pattern like a high power strain gauge) backed by an efficient insulator to dump nearly all the heat into the water.
Strange to say it but the Russian torpedo with the rocket exhaust in the nose does seem to be the *simplest* way to do this. Anything that involves changes of state (solid->liquid->gas and vice versa) *always* involve large amounts of energy. They might be better off trying to build a porus torpedo casing and bubbling high pressure gas (at 100m the gas has to be > 10atm to escape and that rises 1atm for every 10m of water depth)
Feasible in theory, but worthwhile IRL?