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The rate at which electric kettles (coffee makers etc) heat water is limited by the energy they can draw from the grid. This is itself limited by the fuse in the plug. The strongest fuse which can be used is limited by legislation.
I propose a kettle with at least two independent heating elements,
each drawing power from a different socket.
The increase in heating rate is proportional to the number of sockets you have available. The decrease in boiling time is the reciprocal of this: The two-plug version boils a given amount of water in half the amount of time of a standard kettle, while the delux four-plug version takes only a quarter of the time.
Since kettles are generally uninsulated, boiling the water quickly saves energy - since there is less heat-loss during the process.
3 seconds
http://www.amazon.c...conds/dp/B000SK9G52
[pocmloc, Feb 09 2012]
Laser Coffee
http://www.youtube....watch?v=OYvynmK0Slo
[mitxela, Feb 14 2012]
For Spidermother
http://xkcd.com/1012/
Über pedantry in action [AusCan531, Feb 14 2012]
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Annotation:
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[+], and i have a further couple of suggestions. Capacitors, a
constantly plugged-in kettle and a tall, narrow form with a fractal
heating element, maybe a Menger sponge on a plunger to expel
the hot water quickly. |
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You can get electrical connectors for higher power. For example, I have a 12kW electrical device (actually I have two of them) connected to an ordinary domestic supply. |
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//You can get electrical connectors for higher power. For example, I have a 12kW electrical device (actually I have two of them) connected to an ordinary domestic supply.// |
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While I don't dispute that, presumably they're not small appliances in 'standard' sockets? |
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(I changed the form of this anno, but I believe hippo's very quick response is still valid.) |
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No - wired into a special socket with a 45A fuse (I think) |
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You would have to get a kettle made from some better metal. Flash-heating the water like that would melt some kettles. |
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I have often thought that water would boil much faster if you could have a heating element IN the water, not just transferring heat to the water through the metal interface of a pot or kettle bottom. We need a better kettle all the way around. |
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Or maybe a kettle that has a mini-microwave generator... |
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//metal interface of a pot or kettle bottom.// |
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Most electric kettles have the element in the
water, shirley? Admittedly the element itself has
layers of ceramic and metal jacketing. Moreover,
the coastline of Madagascar is over 4,800km long. |
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In the UK, the most you can draw from one regular
socket is about 3kW (13 Amps at 230V), which is
quite a lot. Would your multiple plugs power
individual elements? If, instead, all the plugs
were just interconnected, then plugging only one
plug in would leave another plug lying around with
live pins. |
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//another plug lying around with live pins// |
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Hum... never thought of that. Maybe that's why I've never seen any electric device with multiple plugs. |
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Except this USB powered DVD burner with an extra power-sucking
USB cable in case one port doesn't give enough juice, but it can't shock you if you touch that unplugged USB cable. |
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How fast do we need it? Just a bit faster than what we can get right now. ;) |
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We have a kettle that heats 3 cups of water in just under a
minute. Are people really in such a hurry that they can't
wait that long for a cuppa? |
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If the answer is yes, then here is your solution: I have in
my garage a briefcase-sized plasma cutter that uses an
external compressor to condense the necessary hydrogen
directly out of the air--no tanks required. It
runs on either 110 or 220 from a 35-amp breaker. On
110VAC, it produces temperatures in excess of 14,000
degrees F. I'll leave the math up to somebody like [MaxB],
but I'd think that would boil a kettle of water in just a few
seconds. |
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As I understand it, kettle-heating is already a serious issue for the power-grid operators. It seems that when a popular football match ends, millions of telly viewers stagger into their kitchens and plug in for a cuppa. Electrical demand spikes, and generators cannot wind up fast enough to carry the load. |
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This kettle, lovely as it is, will make that issue worse. [+] |
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EXACTLY what we need Alterother. A kettle that has a mini version of that. |
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But in a couple of years... "You're still using one of those 6 second kettles? We bought a 2 second kettle weeks ago. Who has time to wait that long?" |
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// it produces temperatures in excess of 14,000
degrees F. I'll leave the math up to somebody like
[MaxB]// |
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Ah, there's your problem. Most water nowadays is
metric, and will only boil in degrees Celsius. |
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I don't like to be limited to two plugs when portable power bars make any number of sockets readily available. I would like to able to superheat steam with atleast a sixth seperately powered element near the spout, and a minor handle heater for colder mornings. |
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[21 Quest] //A gas burner will boil 32 oz of cold tap water in a copper-bottom kettle in 5 minutes. How fast will an electric kettle with 2 mains plugs do the same job?// |
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32 oz * 0.028 kg/oz * 4181 J/kg/K * 85 K / 5000W = 63.7 seconds. |
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(Assuming 2500 watts per outlet, which would just barely be obtainable with standard Australian outlets on separate circuits from the meter. Regional variations apply.) |
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Could not some sort of pebble-bed reactor kettle be
devised? |
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//32 oz * 0.028 kg/oz * 4181 J/kg/K * 85 K / 5000W = 63.7 seconds.// |
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Assuming zero thermal mass between the heater and the water, zero losses outside the kettle, and 100% transfer efficiency to the water, which you won't get, since flash boiling will create an insulative layer. |
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Would it not be more effective to use a low,
continuous current to electrolyse water, building up
a reserve of hydrogen and oxygen? A simple spark
applied to a metered amount of these gases would
then create the requisite volume of hot water on
demand. |
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[Alterother] You can't ordinarily calculate the heating rate from the temperature alone; you need to know the power, which could be obtained from the hydrogen/oxygen flow rate and the electrical volts*amps. However, I can estimate an upper power limit by making a few assumptions. |
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An oxyhydrogen flame can produce 5072°F, which is almost exactly 5000°F above room temperature. I will assume that //in excess of 14,000 degrees F// means 14,000 °F of heating. The total power is therefore at most 110V * 35A * 14,000ºF / (14,000ºF - 5000ºF) = 6,000W (approx). |
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It will therefore still take about a minute to boil 32 ounces of water. |
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[MechE] Yes, obviously assuming all those things; but they don't make a huge difference. In practice, when heating a reasonably large quantity of water over a short time period, nearly all the energy goes into the water. |
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//"Controlled thermite reaction".// |
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Yes, where is [8th] these days? |
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//Moreover, the coastline of Madagascar is over 4,800km long.// |
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The more accurately you measure a coastline the longer it gets. Fractals and all. |
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At a certain scale, tides are more of a problem than fractals |
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//accurately// sp. precisely. |
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The more sp.precisely you measure a coastline the longer it gets. |
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//sp.precisely// sp. sp. precisely |
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The more sp.sp.precisely I write this sentence the longer it gets. |
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Do all of the non-Americans understand that this super fast
water heating appliances is something that possibly only 260 of
us have here? I have yet to get such a useful thing, oddly enough.
So busy. |
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//Would your multiple plugs power individual elements? If, instead, all the plugs were just interconnected, then plugging only one plug in would leave another plug lying around with live pins.// |
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Yes - separate circuits. That's what I meant by "independent heating elements, each drawing power from a different socket." It seemed easiest, and it does have the advantage that the risk of shock, fire etc is merely proportional to the increase in sockets. The overall risk increase is of course less than proportional, since the scalding risk is a constant. |
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// I have a copper-bottom kettle and a gas stove, and I get boiling water in less than 5 minutes [...] How fast do you need your water to boil, and how fast do you suppose this electric kettle will do it?// |
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Funny you should say that, 21 Quest, because I was thinking of you and your "Thermos PreWarmer Addition" proposal when I wrote this.
I suspect that the reason electric kettles are not widely used in America is down to a lower power limit from domestic sockets. |
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Regarding the 3-second hot water device link : I think that's a good idea. However, it must still yield hot water at a power limited rate. Probably a pain for many cups. Although given the reviews, it doesn't get the water hot enough anyway; my favourite is "Unquestionably the best device for making the worst possible tea". |
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//Would it not be more effective to use a low, continuous current to electrolyse water, building up a reserve of hydrogen and oxygen? A simple spark applied to a metered amount of these gases would then create the requisite volume of hot water on demand.// |
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"Coffee with a squeaky bang!" |
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Pre-heating the water or storing the enery in capacitors or as hydrogen would not have the rate problem - but then there are pesky issues with portability and energy loss during storage. (These, and safety issues could be overcome in larger devices). |
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New idea time for me i think. |
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// An oxyhydrogen flame can produce 5072°F,
which is almost exactly 5000°F above room temperature. I
will assume that //in excess of 14,000 degrees F// means
14,000 °F of heating. // |
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No, it means a hydrogen plasma arc that produces actual
temperatures of 14K+(F) at the ground point. But I was
being sarcastic anyway. |
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//"Coffee with a squeaky bang!"// That's hydrogen in air. Oxyhydrogen: No squeak. Just bang. Wear ear protection and body armour. Make coffee, rebuild kitchen. |
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[Alterother] But the arc does have to heat matter (in particular, the hydrogen) above ambient temperature. I was just trying to work out how much power the combustion of hydrogen could add; given those temperatures, it's clear that most of the power comes from electricity, and therefore the total heating power is not much more than that supplied by the outlet. |
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I made some gross assumptions, but you appeared to be offering a challenge; my calculation of an upper limit to the total heating power is almost certainly order-of-magnitude correct, at least. |
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// you appeared to be offering a challenge // |
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Not really, but I've got an extra if you want it. Also, I can't
fault your math; if I could, I would have just done it
myself. I only wanted to make certain you had the figures
right. |
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//I can't fault your math// That's all right, I'll fault it for you. For a start, I've ignored the dissociation of water at those temperatures, and the fact that plasma does not have the same specific heat as water vapour. Also, now that I've actually read a bit about hydrogen plasma welding, it seems that no oxygen is supplied. Still, as an upper power limit, it's probably closeish. |
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Okay this is sounding more and more dangerous as we go along. If I feel an earthquake I'll know it's you. Or... was you anyway. |
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I think we're approaching the problem the wrong
way. We're focussing too much on intermediate
steps, and not enough on the starting point and
desired outcome. |
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Fundamentally we start with:
*cold water
*coffee grounds (or tea leaves) |
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We desire:
Hot coffee (or tea) in the mouth. |
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Now, unless you're a gulper, you're unlikely to
require hot coffee (or tea) to be delivered to your
mouth at more than, say, 20ml/min. We can also
assume that this 20ml/min has to be heated from
20°C to 95°C (hot enough to brew good tea;
coffee will need a lower temperature). Of course,
it then has to cool to some more palatable
temperature before entering the mouth, but we
can assume that that cooling is non-regenerative,
and that a certain amount of heat is simply
wasted in that way. |
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So, we're looking at heating water by 75°C at
20ml/min, equating to about 1500J/min of energy.
This equates to a mere 25Watts of continuous
heating. |
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Why, therefore, are we talking in terms of plasma
arcs and 3-phase kettles? |
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Clearly, the problem arises from the discontinuous
nature of beverage preparation. |
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What we need instead is a brew-on-demand
system, consisting essentially of a small chamber
to hold coffee grounds (or tea leaves), connected
to a water supply and a low-power mains supply,
and with a mouthpiece and pressure sensor. |
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Upon sucking at the mouthpiece, an inlet valve is
opened to allow water to pass over a small heating
element, through the grounds/leaves and into the
mouth. Additional finger-operated valves can be
configured to admit milk, lemon, or sugar
(perhaps a concentrated sugar solution), again on
demand and on a per-sip basis. |
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The end result could, from a distance in darkness,
resemble a sort of beverage-oriented oboe. |
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Eh, why not? And put very small, adjustable valves for sweetener and cream or lemon, so it will mix in the desired proportion on the way up the stem. |
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//And put very small, adjustable valves for
sweetener and cream or lemon// |
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What an excellent idea!! I wish I'd thought to
include that in my anno, say somewhere in the
penultimate para. |
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//a small chamber ... connected to a water supply and a low-power mains supply ... resemble a sort of beverage-oriented oboe// |
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I'm afraid, [MB], that you have just invented the Beverage Bagpipes. |
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A very good question is, how do you tell when bagpipes are in tune? |
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The answer may be when it is a set of tea bagpipes. Instead of the noise, the soothing tea. Much more mellifluous. |
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//you have just invented the Beverage Bagpipes.// |
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I am become death, the destroyer of worlds. |
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Now there's an understatement. |
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I wonder, with two elements,what the propagation patterns would look like with a thermal imager. Would there be a perfect shape to the kettle as to speed heating? Thin areas of the kettle would be an attractor and thick, insulated areas a repulsor. |
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The plugs would have have to go to different circuits to distrubution board. Most plugs in the same area would be on the same circuit. |
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Perhaps this is the point for the term "fissile criticality" to enter the discussion. |
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In some undergraduate literature course, someone
made the mistake of encouraging [8th_of_7] to be a
critical reader, and they've been interpreting
everything they read in terms of nuclear fission,
ever since. |
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//two elements// Cesium and fluorine? |
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Can somebody who's good at math figure out the fastest that you could possibly heat water without instantly turning it to steam and/or burning it? There must be a lower limit of a few seconds to heat a cup of water without just having it explode (like if you tried to run the electricity through the water). |
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My guess is that the best way is to contain the water in a coil of tungsten tubing with valves on both ends forming a pressure vessel. Then have 4 oxy-acetylene torches oriented on all sides of the coil, with push button ignition. From the time you press the button to "boiling" should be a couple seconds, followed by a few seconds of cooling before the valve opens and hopefully give you a cup of hot water. |
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microwaves'd probably be easiest. |
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//the fastest that you could possibly heat water
without instantly turning it to steam and/or
burning it?// I don't think there's any upper limit.
If the energy is distributed evenly, then you
should be able to raise the temperature to 100°C
instantaneously. |
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(I guess there must be a limit to how quickly you
can accelerate water molecules without breaking
them apart; and heating is basically about getting
all the molecules moving fast; so there will be
some sort of limit, but it'll be microseconds or
less.) |
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// microwaves'd probably be easiest // |
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// 1f the energy is distributed evenly, // |
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Now ... what frequency ? 915Mhz or 2.45GHz ? The higher frequency is less penetrating. And thermal conductivity must be considered. |
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Assume a cubic rection vessel, 100mm on each edge, capacity 1 litre, containing pure water at 15C, under 1 Bar pressure (Standard Earth atmosphere at MSL). It is desired to raise the temperature to 100C, but not to cause the liquid to boil. |
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Based on [spidermother]'s math, this requres an energy input of 355kJ. |
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355kJ in one second is of course equvalent to 355kW, a delivery of power of which even your puny technology is capable. |
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The trick is going to be making the energy input homogenous. |
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A sphere presents minimum surface area. |
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The postulated cubic container may present issues with "corner heating". |
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A thin circular section may offer an alternative. |
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It depends whether the energy delivered to the water is delivered in a collimated beam, or whether it proceeds from a notional "point source" - in which case a problem similar to that of the "explosive lensing" used in fission weapons arises. |
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On consideration, the most promising approach would appear to be a thin disc of liquid, the depth being calcuated on the basis of the specific absorbtion ratio of water, which is impacted simukltaneously from both sides by two 1.8MW collimated MASER beams, which will give a heating time of 0.1 S. |
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I can repeatably boil a small quantity of water from room temperature in my microwave oven in 4 seconds. I can see no reason why the quantity and the speed can't be scaled up. The limit would be how much power you can pump into a reasonable area. |
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There are standing wave considerations; I had to disable the turntable and find a hot spot by trial and error. Perhaps a thin layer of water, suspended (in a microwave transparent container) half a wavelength above the metal floor of a microwave chamber is best. |
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(<Über pedant>: It's now spelled maser, not MASER, as the original initialism is considered inaccurate.) |
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I think that starting with water is for junior halfbakers. Now,
hydrogen peroxide with a nice platinum catalyst is going to
produce plenty of really hot water... |
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</Über pedant> I shut off the über pedantry mode for you [spidermother]. Do you realise how dangerous it is to leave something like that running and unsupervised on the HB? You should know better. |
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//
<pedant> //The word vanilla is originally derived from the Latin word for vagina// It's derived from the Latin word 'vagina' which means sheath or scabbard. The English words vanilla and vagina have a common root, so to speak.
-- spidermother, Nov 24 2006
// |
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One needs to put one's feet up occasionally. |
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One needs to put one's feet up what, occasionally? |
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Up a casionally, didn't you hear first time? |
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There must be a maximum limit to the rate that a given volume of water can be heated by a given surface area. At a certain temperature, you will simply flash vaporize the local water before it can convect the heat to the surrounding water. This vapor would provide a thermal insulating layer between the water and the heating element. |
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Not if you apply enough pressure. |
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Actually, how about a gravitational kettle? So,
you start with a vertical pipe, a few inches in
diameter and maybe a kilometre or so in height.
Close off the bottom of the pipe. Slots will need
to be cut in the sides to allow the escape of air,
starting a few inches above the base and running
all the way up. |
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Now fill to bottom six inches of the pipe with
water. At the top of the pipe, take a solid
cylinder of depleted uranium (it should be a snug
fit in the pipe), and drop it. |
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When the cylinder hits the water, all that kinetic
energy has to go somewhere. |
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I thought he said up a caisson alley. |
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[MB] it would be easier suck the air out of the tube and let the depleted uranium fall in a vacuum. It would build up to a much higher speed without air resistance. |
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If we're going with compression heating then I would suggest a shaped charge, just to make out kettle more compact. Not many people have room for a kilometer long pipe. But won't the water cool back to its original temperature as soon as it expands to its normal volume? |
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//take a solid cylinder of depleted uranium// |
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Radioactive tea, the new bistro sensation! Drink it and have pretty glowing white teeth! |
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Okay, I'm finished. Had to get that out of my system. |
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//won't the water cool back to its original
temperature as soon as it expands to its normal
volume?// If it remains liquid throughout, then I
don't think it will experience much compressive
heating or expansive cooling. A millisecond before
impact, you have water plus a mass with a very large
kinetic energy. A millisecond after, you have water
plus a mass with no kinetic energy. All that kinetic
energy's got to wind up somewhere. |
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That's why the GOTO command was invented .... |
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How about drop the kettle down the pipe, no need for DU that way. |
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//recursive redundant loop// sp.:life |
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Hey, [97], check out the history of "Radium Water" and the sad, sad story of Eben Byers. |
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Then, when you've stopped retching and shuddering, you'll probably find that crack about radioactive tea a little less amusing. |
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//it would be easier suck the air out of the tube and let
the depleted uranium fall in a vacuum.//.
It would
certainly be 'easier' to make the water boil under these
conditions - without necessarily raising the temperature.
Wouldn't make good tea though. |
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I think the compressive heating would work as [MB]
says. [DIYMatt]'s shaped charge Idea has merit. |
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I've added a pedantry/eytomology link for [spidermother]. |
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There's an even lower tech solution. |
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Simply purchase a house at the bottom of an 800m
cliff. Place your teapot outside (with tealeaves
in), take a bottle of water, and ascend the cliff.
Wait for a lull in any breeze, then carefully pour
the water out of the bottle, aiming for the teapot
below. The gravitational potential energy of the
water should be sufficient to raise it to boiling
point on impacting the teapot. |
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Alas, air resistance on the way down might well
limit the terminal velocity of the water, reducing
the heating effect. However, this effect can be
overcome by using a sufficiently large volume of
water (and a correspondingly large teapot, of
course). |
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//800m// Based on [8th]'s interpretation of [spidermother]'s maths, I get 36 km. |
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e=mgh (joules; kilograms; gravity; metres) |
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We want to get about 80 joules into a gram of
water, and g=10, so... |
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h=80/(0.01*10)
=80/0.1
=800 metres.
no? |
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No!! Wait - that 0.01 should have been 0.001, so: |
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h=80/(0.001*10) = 80/0.01 = 8000 metres. Oops. |
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Incidentally, why does the halfbakery page not
include a small back-of-envelope calculator app? |
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//why does the halfbakery page not include a small back-of-envelope calculator app?// |
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It does. Turn your laptop over. |
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M = 1 kg
g = 9.8 m/s²
C = 4200 J/kg
T = 80 K
h = ? metres |
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Mgh = MCT
=> h = CT/g
= 4200*80/9.8
= 34,000 m |
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//Incidentally, why does the halfbakery page not
include a small back-of-envelope calculator app?// |
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Tis where I stash my two cups of coffee. |
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// We want to get about 80 joules into a gram of water,// |
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Tepid tea? Good lord, that's not what one's man servant serves
up I hope? |
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Yes, that should read 80 K * 4.2 J/K/g = 336 joules per gram. |
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// The gravitational potential energy of the water should be
sufficient to raise it to boiling point on impacting the teapot.// |
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//that should read 80 K * 4.2 J/K/g = 336 joules per
gram// Ah yes - I was confusing my calories and my
joules. |
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Yeah, but in unrestrained freefall that's 82 seconds or so. |
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What you need is to set up an arcflash heater. Make a low-volume, high surface area two-plate heater. Have the plate gap really small, like 5mm. Connect one plate to ground with maybe 100cm^2 of copper or so. Connect the other end to one phase of a 500KVA+ 3.3kv generator of your own, or maybe just line current if you have really, really good liability insurance and/or don't like your utilities provider. |
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You'll need a pretty nifty (very) remote racking system for your contactor bank. When you close the breaker, the protection should be remote enough that you get easily 100KA earthfault though your heater, for at least a few milliseconds. Note that you get the selfsame fault current through your (likely disposable) breaker, that's why you have remote switching. |
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As per calculations above, you need ~ 3.3E5 J. At 3.3KV and a modest 100KA you have 3.3E8+ Watts of power available. Should get the job done in under a millisecond, with room for losses. |
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If your heater is robust enough, it won't matter if some of the water charge flashes to plasma, everything is nice thermally conductive copper and it should condense out in a few more milliseconds, which is how long it will take you to run back from your blast shelter and put your cup under the spout. |
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