h a l f b a k e r yA hive of inactivity
add, search, annotate, link, view, overview, recent, by name, random
news, help, about, links, report a problem
browse anonymously,
or get an account
and write.
register,
|
|
|
Please log in.
Before you can vote, you need to register.
Please log in or create an account.
|
James Joule's heat apparatus is one of the most under-appreciated experiments in science. It's just a paddle wheel in a bucket of water. By demonstrating that the mechanical work done on the water raises its temperature, Joule basically invented the idea of Conservation of Energy.
In tribute to this
great moment of science, mitxela's crack team of product designers have invented a mechanical kettle. No, don't worry, there are no paddle wheels involved (that sure would be some paddlin')!
Joule's Kettle makes use of the same technology as the latest waterjet cutters. There are two nozzles, aimed directly at each other. When the flow is turned on, the cold water streams shoot out at terrific speed, collide with each other, and through the magic of Joule heating, hot water lands in your mug.
[Back of envelope: 75C increase would require a pressure of ~46000psi, which is well within the range of high-end waterjet cutters!]
Freeze water with the blow of a hammer
http://blog.modernm...eve_it_or_not_0.jpg
bottom left [mitxela, Jun 30 2014]
Tallboy
http://en.m.wikiped...wiki/Tallboy_(bomb)
Designed by Sir Barnes Wallis. [8th of 7, Jun 30 2014]
Hedgerow
http://en.wikipedia...row_(weapon)#Design
One way of clearing the Germans off the sunbeds ... [8th of 7, Jun 30 2014]
Butterfly Bomb
http://en.m.wikiped...wiki/Butterfly_Bomb
Not pretty at all. [8th of 7, Jul 04 2014]
[link]
|
| |
How about an alternate version. |
|
| |
The MaxCo. Gravity Kettle is essentially a copper
cannon-ball with a hole in it. Cold water is placed
in the hole, which is then sealed with a lovingly
crafted copper kettle stopper*. |
|
| |
To use, simply take the Gravity Kettle to the
highest available point, and release. Retrieve the
kettle, remove the copper kettle stopper, and
pour. |
|
| |
*I defy anyone to conceive a phrase more
euphonious than "copper kettle stopper". |
|
| |
but... you already did with "lovingly crafted copper kettle stopper", you just needed a "proper" at the start. |
|
| |
Why doesn't the word proper have two p's anyway?
It needs another p. |
|
| |
Far less fun solution than a "Waterjet kettle set" or a
"Proper copper kettle stopper": hydraulic piston pump
and pressure relief valve. Pump a few times in a
continuous circuit, until piston broke. |
|
| |
//Why doesn't the word proper have two p's anyway?
It needs another p.// |
|
| |
I spell it with two "p" 's and get autocorrected every time. "Proper" should be pronounced "proWper" or "proUGHper" in my mind. |
|
| |
The problem with this idea is people don't have an intrinsic, instinctive understanding of the energy in a water jet stream. The falling kettle ball is maybe a bit better. Maybe a robotic sledgehammer wielding arm flogging crap out of the kettle ball woudl also work. |
|
| |
Copper would work better than perhaps you appreciate - if made out of something particularly rigid or elastic, little energy would be absorbed, whereas something quite maleable like copper will absorb energy from impacts rather well. Lead might be even better, but y'know - lead. Maybe Gold would be the best material? |
|
| |
The issue with the MaxCo. Gravity Kettle, and indeed almost every type of mechanical kettle, is the unexpectedly large heat capacity of water. You would need to drop it from about 100,000 feet. Flogging it repeatedly could work. |
|
| |
On the subject of sledgehammers and water, it is reputedly possible to freeze water by hitting it, if you believe Ripley's Believe it or Not. I have not been able to find any other sources for this and might try it. |
|
| |
//Copper would work better than perhaps you
appreciate// That is why I chose copper. My first
choice was lead, but I foresaw issues. |
|
| |
//You would need to drop it from about 100,000
feet// That sounds unlikely. Anything of a
sensible
size dropped in air will reach terminal velocity
after
a few thousand feet. We may, of course, need
bigger gravity. |
|
| |
A quick calculation. Assume the kettle has
terminal velocity of 250mph (that's a guess; about
twice as fast as a skydiver in a spread, a bit less
fast than a skydiver in a no-lift dive). That's
roughly 100m/s. |
|
| |
The mass of the kettle is irrelevant (more mass =
more kinetic energy; but equally more heat
capacity) so, for simplicity, assume a mass of 1kg. |
|
| |
Hence, k.e. of kettle on impact = 5,000J. |
|
| |
Heat capacity of copper = 385J/°C/kg. |
|
| |
Hence, temperature rise (if landing on a very rigid
surface) = 5000/385 = 13°C. |
|
| |
So, yes, a bigger gravity would help.
Alternatively, make the kettle more streamlined.
If you can increase its terminal velocity about 3-
fold, it should be good enough. |
|
| |
//Heat capacity of copper = 385J/°C/kg. |
|
| |
//Hence, temperature rise (if landing on a very rigid surface) = 5000/385 = 13°C. |
|
| |
Um, [Max], we're trying to warm the water not the copper. |
|
| |
The "Tallboy" bomb (q.v.; <link>) attained
supersonic velocities from 22,000 ft. |
|
| |
At that rate of fall, skin heating becomes
significant.. |
|
| |
Max, you need an aerodynamically shaped
package with a thin copper wall and a
pressurised interior to maintain the shape.
Plus a safety valve … |
|
| |
I like the idea of a kettle consisting of a 1kg hollow projectile made of 18 carat gold, hurled aloft by a kitchen-roof-mounted trebuchet. |
|
| |
//Um, [Max], we're trying to warm the water not
the
copper// Yes, oh mammalian fishy one.
However,
the whole system will come to equilibrium fairly
quickly. So, assuming that the mass of water is
much less than the mass of the copper kettle, it's
a
fair approximation to use to heat capacity of
copper
in lieu of the combined heat capacities of the
copper-plus-water. |
|
| |
Sheesh. You try and do the right thing and... |
|
| |
// thin copper wall and a pressurised interior//
No, just no. The available kinetic energy depends
on the total mass of the projectile (for any given
velocity). The copper has an energy-hungry heat
capacity, but also adds mass. Overall, you're
better off with lots of copper and very little
water. |
|
| |
Also, a thin-walled vessel full of water will *either*
burst on impact or, if it doesn't, will behave
elastically and not convert much of the kinetic
energy to heat. You want something which
deforms plastically on impact. Water is
notoriously very much the exact opposite. |
|
| |
Do try to keep the batteries topped up, [8th]. |
|
| |
[Max], you're going from potential energy (a 500 m drop), to kinetic energy (100 m/s), to heating the kettle by deformation, to heating the water by conduction. Efficiency losses are going to clobber you. |
|
| |
Here's a suggestion. Put some mixing baffles on the inside of your cannon ball, make the damn thing out of an insulating material (concrete), and add vanes to the outside. That way when you drop it from half a kilometer's altitude, it spins round and round as it falls and the baffles slosh the water around directly heating it. Roll it down a hill even. |
|
| |
//Efficiency losses are going to clobber you.//
Yes, and yet in a more actual way no. I'm only
going from kinetic energy to heat (as I mentioned
above, terminal velocities will apply, meaning
that I've already accepted loss of some of the PE).
And if you drop a big lump of copper onto a huge
block of, say, granite, most of its KE is going to
wind up as heat in the copper (and thence the
water). |
|
| |
If there's one thing that energy is good at doing
efficiently, it's turning into heat. Hence entropy. |
|
| |
// So, assuming that the mass of water is much less than the mass of the copper kettle, it's a fair approximation to use to heat capacity of copper in lieu of the combined heat capacities of the copper-plus-water. |
|
| |
The specific heat capacity of water is more than 10 times that of copper. If 250 grams of water is needed for a cup of tea, your 1 kg mass's average specific heat capacity is 1,333 J/°C/kg, which makes your 13 degrees more like 3. |
|
| |
1 kg of water requires 4.2 x 1000 x 90 = 378 kJ to raise it from 10 C to
100 C. |
|
| |
Kinetic energy = 0.5 x m x v^2 |
|
| |
Allowing for 50% conversion efficiency, and the mass of the container
is twice that of the water, it follows that |
|
| |
756,000 = 0.5 x 3000 x v^2 |
|
| |
v = SQRT(756,000/1500) = 22.5 m/sec = 81 km/h |
|
| |
We postulate a titanium cylinder containing a perforated piston. A thin
shaft attached to the piston protrudes from the front. The rear of the
cylinder has a tube tail and fins for stability. The assembly resembles
a
Hedgerow round. <link> |
|
| |
At launch, the container accelerates under gravity. On contacting the
ground, the shaft forces the piston from front to rear, and the water is
forced through the piston under very high pressure, heating it. |
|
| |
Since v = SQRT ( 2 x g x distance) and v is known to be 22 m/s, the
dstance the projectile must fall (neglecting air resistance*) is given by
d = (22 ^2) / 20 = 24.2 metres which is not excesive; many existing
structures are significantly taller than this. |
|
| |
We suggest an immediate practical research programme into boiling
water for tea by throwing heavy metal objects with big sharp** spikes
on the
front off the top of the Eiffel Tower. |
|
| |
*air resistance can be neglected, since it is clear that Resistance Is
Futile. |
|
| |
**There's no technical requirement for the spikes to be sharp, but the
idea of skewering a tourist through the cranium with a three-kilo giant
titanium dart would add immeasurably to the enjoyment. |
|
| |
//The assembly resembles a Hedgerow round.// |
|
| |
I think, if you reflect for a moment, that you'll find
that a Demoiselle round with a Franklin sabot would
better suit your porpoise. |
|
| |
//24m ...90C// This is not bad, since the PE of 3kg at 24m
height is around 600J, isn't it? |
|
| |
//a Demoiselle round with a Franklin sabot// |
|
| |
Is that, as my daughters would say, a thing, [MaxwellBuchanan]? |
|
| |
I'm sure [8th] is familiar with 1930's artillery and can
confirm this. |
|
| |
For the same reason that throttle plates don't just melt.... |
|
| |
That's an excellent answer, [WcW]. Has anyone got
the question? |
|
| |
// [8th] … can confirm this // |
|
| |
"It is not the policy of Her Majesty's
Government to either confirm or deny …" |
|
| |
But for those interested in evolution, the
metamorphosis of the line into the
"Sprengbombe Dickwandig 2kg" or "SD2"
<link> is an instructive study. |
|
| |
//Sprengbombe Dickwandig// |
|
| |
You see, [8th], that's why the krauts never really
made it big-time. They probably spent a fortune
developing their butterfly bomb, and then called it a
"Sprengbombe Dickwandig" - the name doesn't even
make sense. |
|
| |