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Trying to turn water into ice relatively quickly

  1. Mar 8, 2016 #1
    I was reading that you can simply freeze water by using a vacuum. It boils then it freezes. I wonder how you could take the waters evaporation and have it filled back into the container once the vaccume is turned off. I feel this would work great to make lines under a car seat to add "cooled seats" any pointers?
     
  2. jcsd
  3. Mar 8, 2016 #2

    russ_watters

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    You can't exactly freeze it just by reducing the pressure. You can reduce the pressure and boil some of it away, which will reduce the temperature. Then increase the pressure again and some of it will freeze. Repeat. Water that is evaporated can be recycled by cooling this to condense it.

    This is all extremely energy intensive though and I can't see how this could be useful for car seat cooling. Heck, why would you use ice? Ice doesn't flow.

    Currently, cooled seats are accomplished using air from the air conditioner. It works pretty well.
     
  4. Mar 8, 2016 #3

    rbelli1

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    So you want to change the pressure to cool one part of a system then somehow extract the heat to return the evaporated part back to a liquid. Maybe a more volatile substance would be in order? Freon could just work. I have an idea! Pass the evaporated part through a compressor. Make the whole thing a continuous cycle. I should patent this idea!

    That would be a great name for my "invention". I'll give you credit.

    BoB

    <EDIT>
    PS: Pardon my sarcasm Seanshine. That is precisely the way almost all air conditioners and other cooling machinery works.
     
  5. Mar 9, 2016 #4
    Hey "watters" Actually now that i think about it, doesnt the temperature only slightly change? the water boils but they were doing the experiments with room temperature water. I know ice doesnt flow but if the whole line was water, then feezes, i dont see a reason for it to not get cool. Since AC systems cool air by blowing non tempered air through cooled pipes, i would think sitting directly on chilled pipes our butts would feel it. Feel free to correct me, as this is why i am on here to ask questions.

    no offense taken from your sarcasm "1"
    I had no idea cooled car seats used the air condition portion to cool the seats. I was thinking i could use the cars engine vacuum to make the same effect without having to deal with a compressor.
     
  6. Mar 9, 2016 #5

    rbelli1

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    I suppose you could build a chiller into the seats but the traditional way is to connect into the existing system. A bit of duct work and a damper is a whole lot easier than a whole new system. This gives you heating ability as well.

    BoB
     
  7. Mar 10, 2016 #6
    Yes i completely understand where you guys are coming from. The issue here is this is for my project track car that does not have AC. I am trying to make a chilled copper line similar to those used in air conditioners for under my driver seat. I was thinking with the cars vacuum line, having a good amount of vacuum and the vacuum pressure fluctuating with throttle constantly, that if i could find a way to recycle the evaporative water it would keep reducing the waters temperature until the lines are completely frozen or very cold.
     
  8. Mar 10, 2016 #7

    russ_watters

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    What "vacuum line"? I don't think I've heard of that. What, exactly, does it do and exactly how much vacuum does it pull?

    Regardless, for the properties of water and steam, there are tables and interactive websites that will provide them. Try googling "saturated steam" table.
     
  9. Mar 10, 2016 #8
    Sorry, car vacuum is not something that i am very familiar with but i do know there is alot of vacuum as the piston comes down and most of it can be found right behind the throttle plate and intake manifold. From using a vacuum gauge for diagnosing problems in the past, most cars seem to read anywhere from 16 up to 25 inches of mercury/vacuum. When you open the throttle the vacuum tends to be lower and gets close to zero. I feel as this is energy that i could make use of, without having to deal with heavy/noisy compressors and what not.
     
  10. Mar 10, 2016 #9

    Merlin3189

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    "Vacuum" (actually, low pressure) in the inlet manifold used to be used to power windscreen wipers in the Ford Prefect and Morris Minor (maybe many others FAIK.) Never had one myself, so I don't know how it impacted performance, but when I had a leaky manifold joint once, tickover became erratic.

    On an earlier point
    I don't know whether I am reading this correctly, but I have seen water frozen by vacuum. At an exhibition there was a large glass container (like a bell jar about 1m high and 50cm diameter) connected to a vacuum pump. A dish of water (about 250ml) was put inside and the vac pump started. After only a few seconds the water began to boil and after a few minutes there was ice floating in boiling water. When the vacuum pump was stopped and the vacuum released, the water stopped boiling, but the ice and water remained.
     
  11. Mar 10, 2016 #10

    Merlin3189

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  12. Mar 10, 2016 #11
    With all the facts i have gathered. I feel like this might actually work. Now the real question is how cold will the ice get? It seems like it would need a constant boil and freeze to get the temperature where it needs to be, like watters mentioned in his first post. Anyone know what i could use to recycle this condensed water back into the lines?
     
  13. Mar 11, 2016 #12

    Merlin3189

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    I hope you're not encouraged to continue by my response. I put it merely to say that water will freeze in a vacuum, not to say that this is a good idea for refrigeration. This thing had a massive vacuum pump and could well have been producing a decent continuous vacuum, not an intermittent half vacuum. (And using a decent chunk of mains power to do it.)
    If I were going to build a refrigeration device, I think I'd look at what the HVAC engineers have developed over the past century+ and probably not use water as the refrigerant. (Since you've got it on board, how about petrol itself?)
    And if you want to use the available resources, maybe you could simply use the cooling in the inlet manifold itself? As the air expands from atmospheric to the lower pressure of the inlet manifold, it cools. If you use a carburettor instead of the modern fuel injection, you will also get cooling from the evaporation of the fuel. I don't know how much "cold" you can get from this in a car, but aircraft (when they use carburetted IC engines) need to warm the inlet air to prevent icing in the carburettor.

    Getting away from the speculative bits, you can look up the svp of water at different temperatures. Someone said the inlet manifold depression could be 25" Hg, which I think means a pressure of about 5" Hg or 17kPa. This is svp of water at about 55oC. So once the temperature dropped below this you wouldn't get boiling, only increased evaporation. That will still produce cooling, but not nearly so much so quickly.

    As for recycling the water, (BTW, where does the "condensed water" come from?) the usual practice is to compress it again, which makes it hot, then cooling this hot vapour into liquid (say by having wind blow over the pipes) and pump it back into the evaporator. This is where the pump scores over using manifold vacuum. It provides suction to the evaporator and compression to the condenser at the same time, making a nice closed loop arrangement. (Which reminds me, your water vapour was sucked into the engine and blown out of the exhaust, so you've got nothing left to condense.)
     
  14. Mar 14, 2016 #13

    russ_watters

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    So, I did look into this some more and I guess I haven't looked at a phase diagram in a while:

    h2o_phase_diagram_-_color.v2.jpg

    As you can see, if you can get water below 0.006 ATM, it will boil, then freeze, then just sublimate. But a car engine doesn't produce that much vacuum (though I will say, I didn't know anyone ever harnessed the intake vacuum for anything...).
     
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