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Proof-of-Concept Demo Model:
A 2 ft. cube, door on the front, metal inner and plastic outer shell with insulation in-between. A circular cutout in the outer shell and insulation allow a Bell jar to sit on top of a gasket on top of the inner box.
Inside the Bell jar (on top of the inner 'fridge
box) are situated a few old-fashioned metal icecube trays. The outlet valve on the gasket has a pressure gauge and hand pump connected.
Operation:
Fill the icecube trays with water, replace the jar and crank the handle until you hit 0 psi... when the pressure rises to whatever point you've decided on, give it another few cranks... eventually you end up with ice in the ice-cube trays. Since the trays are sitting directly on the inner-shell of the fridge, they will cool the inner shell, which will cool any items placed inside.
Bell jar
http://en.wikipedia.org/wiki/Bell_jar
[FlyingToaster, Feb 03 2009]
Water phase diagram
http://www.lsbu.ac.uk/water/phase.html
One tiny green triangle for man. Note that "above sea level" pressures are below the 100kPa mark (atmospheric pressure is only the bottom 6 rows). [bigsleep, Feb 03 2009]
Fridgeridoo
Fridgeridoo
Now look what you done made me gone and did [BunsenHoneydew, Feb 05 2009]
[link]
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Surely you don't need the ice? Just creating a vacuum should be enough.... |
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The fridge isn't a vacuum, just the Bell jar with the icecube trays in it. |
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But if the vacuum freezes the ice, wouldn't it be easier - oh right, this way you don't have to recreate the vacuum every time you open the door. |
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This would take some of the pressure from my disconnection notice away. |
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Manuel is outside tending the garden. Perhaps Lucinda will turn the handle. |
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So. . . those old Bell fruit jars are pretty darn sturdy, then. |
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Some of the water evaporates, thus removing heat from the water that remains until it freezes. Qualitatively, it might work, but the efficiency of that approach would be totally horrendous. I think one would be better off with a hand-cranked Sterling-cycle engine whose internal pressure was adjusted so that water would be evaporated on the cold side and condense on the hot side. One would be still better off if one substituted a different working fluid. |
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Would water stay in the ice tray, in vacuum? |
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//the efficiency of that approach would be totally horrendous//
really....why ? Seems to me to be pretty efficient given that water has the best [edit: relevant] heat-related stats of any material. You even get warm [edit:*hot*] water you can use for other stuff if you like. |
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[Zimmy] it would turn into ice which would continue to evaporate but at a slower rate; the ice, though is cooling the refrigerator through the bottom of the vacuum-jar so it would melt again... Unless you actually needed ice for something you'd just keep cranking when the pressure rises, until it ran out of water/ice at which point you would open the jar and add more water to the trays, or until you reached a nice temperature in the fridge. |
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/given that water has the best heat-related stats for any material/ |
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I can think of a few things contrary to this. I'll start you off: thermal conductivity. |
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The relevant stats are latent heat of fusion and vapourisation, and the author's penchant for slushies and iced drinks. |
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You can tell me my sliderule is broken, but I get that the water coming out of the pump is going to be at 100C... so you can make ice and tea at the same time. |
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I need to relocate to this fabled universe of magical vacuums. They suck shit into space, they magically cool things with little effort. Man, oh, man! Over here, Nature abhors a vacuum. And we have, like, even, a zero-eth law of thermodynamics. |
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If we had water as gas and depressurised it we could expect a tempertature drop. Boyle's law (ideal gas laws) give us this. Unfortunately you are asking for a phase change. So we fill our ice trays with water. Stick them in the vacuum chamber and depressurise. We presume the entire system is at room temperature. Now we notice something, as the pressure drops the water goes from water to steam, but there is no temperature change. Yegads! What happened? Now all the water (well most) exists as steam (real vapour) if we depressurise further we notice a temperature change. Yay! Unfortunately, as [UB] said on another idea, this is not a fortune of energy removed. We is gonna needs more wortttuh! Adding this water against such pressure differentials is a problem. It can be done, but it is a problem. So maybe we should start with a sufficient amount of water in the first place. I leave it to you and your sliderule to work out how much. |
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The amount of cooling you achieve is directly proportional to the work you put in. You have closed your system so that the internal cavity of the fridge is giving energy to your vacuumed "ice trays". And will continue to do so until equlibrium is reached (provided you are suppling more water as you pump off the //100C// vapour). Assuming you got cold enough (273.x K) this will, acording to the phase diagram, be putting you straight into vapour phase. If you managed some ice, it would sublimate (see line where water goes from solid to gas below 273 K and below 1 kPa). So you are going to be having Lucinda cranking that shaft all day long (this might be what you want.) Further you use water. Why not something else, like Methane, Ethane, Ammonia, I know, Chloroflourocarbons (or other Haloalkane). Basically things with triple points at lower temperatures, we can't be arsed about Lucinda's arm on the pressure side. |
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I have a fantastic idea. Replace your electric pump on your current fridge with a Lucinda powered version. Call me in the morning. |
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Adam Hart-Davies presented a Victorian hand-cranked cooling device in his "What the Victorians did for us" series. The pumping worked a heat-pump that used ether as a coolant. |
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The problem was that it took a long time for it to cool a relatively small box and needed to be constantly pumped to maintain this temperature. |
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I wasn't able to pin this down with a link but I believe it was patented. |
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[Aristoltle] has said it more succinctly, although twice. Your working fluid is a crock. And it takes a lot more energy than you think, to subtract energy from a system. 440 cm^3 (your average fridge) at room temp, isa "one spicy meatball Rosalina"! |
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"Lucinda! You got some 'splaining to do...." |
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[4whom] so to improve the system you want to: |
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a) use poisonous and/or explosive chemicals
b) use imported servant labour
c) add external cooling apparatus (and more work) for a closed system whereby coolant is reused
d) do away with a beneficial product (ice) and byproduct (100C water)
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[FlyingT...] to improve the system I would like: |
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a) to improve significantly on current (legacy) mechanisms, no matter how it is powered.
b) Obey certain laws of thermodynamics, most notably the zero-eth, first, and second.
c) to note that by closing a system, any energy you "put in" is actually added to the system, eventually.
d) There is no fucking *ice* man. Creating a vacuum at a constant temperature does not make ice from water. It makes vapour (steam) from water. I am happy to concede that at the triple point you will get your result (without temp difference.). But it ain't gonna change the thermodynamic equilibrium one bit. Unless you pump out the heat and add more water. And you still don't get any fucking ice. Look at your phase diagram, you can get ice (ice 7) at 200C, given enough pressure (not vacuum). Ice is no indication of temperture or overall thermodynamic equilibrium, unless you take pressure into acount, and you are sitting on the wrong side of the pressure equation on this one. |
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[4w.....] to address your points... |
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a) conversion of current legacy mechanisms aren't the issue mostly because they're computer monitored and electrically *controlled* as well as powered... if it was a conversion, I'd imagine using an older "ice box" with the apparatus sitting on the little freezer section on top and a bi-metal controlled adjustable vent between that and the fridge proper.
b) yes, I was thinking of doing that.
c) not particularly interested in adding energy to the cooling system, trying to take it *out* actually... thus the "cooling" portion of the exercise.
d) I have to admit that I'm not really interested in ice at 200C... that would tend to obviate the entire purpose of a refrigerator. |
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Let's see... latent heat of fusion 300'ish J/g, latent heat of evaporation 2200'ish J/g... so if I evaporate and evacuate 1/7 of the water in an icetray, the remaining 6/7 should be...... yes, "f------ i--" |
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<tumblweeds roll past> :(
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more than happy to note that if you want to cool contents in the fridge instead of simply keep cool groceries brought home, a stationary-bike would be a better power-source for the initial cooling. And actual usage of this thing would probably be for bike-hikes where you can use the PTO on your mountain-bike to run it. (What, no PTO on your bike ? hmm....) |
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I postulate that current cooling systems use different choices of refrigerants for the simple reason that they have (relatively) high-power pumps and can thus cool things faster using refrigerants with lower boiling and freezing points. |
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