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Wax in my heating system instead of water

  1. Apr 11, 2010 #1
    Hi, I'm a heating engineer.

    part 1: I typically install 300 litre to 100litres stores of hot water (to be extracted at 40deg c for low temp heating).

    I understand that the specific heat capacity of paraffin wax is something like ten times that of water.

    So can I play around with a smaller volume of paraffin wax in place of the water. Then, if i ran a long coil of pipe inside the parafin and passed water through it, the water would pull heat from the paraffin.

    We do this at the moment with standard water tanks.

    part 2: Would there be a difference in the length of the coil (either longer or shorter) if the process is paraffin to water rather than water to water.

    Thank you for helping out with this project, it's just something I am interested in and as a non physicist I am probably sounding very naive!!!!!

    all the best, Matt
     
  2. jcsd
  3. Apr 11, 2010 #2

    marcusl

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    Here are some thoughts. Common waxes melt at about 60C so your system would operate with coils embedded in a solid. Is the specific heat of the solid phase also high? Solidified wax has poor heat conductivity (high thermal resistance) so your coils would pull heat from wax immediately in contact with them but then you'd have trouble drawing heat from the rest of the solid. Maybe if you used a lot of copper fins--like embedding a car radiator in wax? Finally, if you found wax with a 40C melting point, you'd have the additional storage due to the phase change (it's called "heat of fusion"). This is quite large compared to the heat capacity and would permit you to store a lot of energy in a small volume.
     
  4. Apr 11, 2010 #3
    marcusl's reply is quite good, I would like to add, that the length of the coil is dependent on the thermal conductivity between the system and the heat bath. If your pipes are made of copper then the outside medium will be the limiting factor in delivering the heat to your pipe, and the length will change if you exchange the medium. If the pipe is made of stainless steel (a bad heat conductor) then the length probably doesn't need to change.
     
  5. Apr 11, 2010 #4
    Yeah, I guess I'm not sure where the OP is going with this.
    Antifreeze, for example, has a great capacity for heat transfer, and, it's liquid.

    If you are looking for thermal storage that's another matter.
     
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