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Maximize volume-pressure ratio

  1. Apr 9, 2016 #1

    I'm making a fire-boat. The boat uses 2L bottles to supply water.
    The fire will be 1m from the fire fighting zone and 0.5m high. The bottles are pressurized to 300 kPa. How do I maximize the volume-pressure ratio that can be supplied at that range over 90s maximum?
  2. jcsd
  3. Apr 9, 2016 #2


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    How are they pressurised ?
  4. Apr 9, 2016 #3
    compressed air
  5. Apr 9, 2016 #4


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    Need to be clear :

    Are the bottles full of water initially and continuously pressurised from an external air source ?


    Are bottles part full of water and only pressurised by a precharge of compressed air ?
  6. Apr 9, 2016 #5
    The bottles will have an initial amount of water and they will be pressurized by a precharge.
    I'm trying to figure out the initial volume of water so that I can supply as much water as I can to satisfy the conditions I listed above.
  7. Apr 12, 2016 #6


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    Just for clarification you want to shoot a water stream 1 m horizontal with a maximum drop of .5 m at that distance; and what is the diameter and flow coefficient of the nozzle you are using. You must identify the required water flow rate over that time period in order for this question to be analyzed. The required rate of flow through the nozzle over that time period will determine whether your not your combination of bottle size and pressure is capable of meeting your requirement.
  8. Apr 15, 2016 #7
    you can put a lot of compressed air into a small space so that you can get max liquid volume. the best you can do is to put air psi to just under max the bottle can withstand. the bottle nozzle will dictate the time period it takes for the liquid volume to leave the bottle as a function of both psi of the air and the actual liquid volume.
  9. Apr 16, 2016 #8


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    Interesting problem. On the one hand you want as much water in the bottle as possible but not so much that the small amount of air left cannot push it all out.

    You know the max pressure but i think you also need to experiment to find the minimum pressure required to reach the fire.

    As the water is pushed out the volume of the air expands and the pressure falls. Eg if the volume doubles the pressures will roughly halve. You want just enough air so that the pressure falls to the minimum required just as the water runs out and not before.
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