Heat Exchanger????

Discussion in 'Physics' started by Burnit0017, Jan 23, 2011.

  1. Burnit0017

    Thread Starter Member

    Feb 15, 2010
    101
    3
    Greetings, I created a gravity feed pellet burner. The pellet burner works very well. It has a 8 hour unattended burn time. My challenge now is to recover as much heat from the pellet burner and transfer that heat into the building. My first attempt using a stainless elbow positioned over the flame to heat the air inside the vent has failed. Basically the project is to have a fire box outside the building and then try recover as heat as possible and transfer that heat to inside the building. I am looking for ideas that are low cost and easy to fabricate. I found some videos on youtube showing heat recovery systems. If anyone has any other ideas please let me know.
    Best regards.

    http://www.youtube.com/watch?v=nfoDyKCA3xs

    http://www.youtube.com/watch?v=HTUxarUvb2E
     
  2. Whirlwind

    New Member

    Feb 4, 2011
    4
    0
    not sure if this will help, but you could use water or glycol (not sure the spelling, essentially its antifreeze you use in your car) it has a higher boiling point then water. the most basic set up would be run tubing from your source to inside and put a fan behind multiple turns of tube. you could do a radiant floor set up, You can run the tubing threw brick walls which would then become a heat sink and keep the place warm for quite awhile after the fire is out.
    not sure the best way to do this, but it works very well, my uncle had copper pipe run threw the brick behind the fire place in the house, and when the fire was going we had more hot water then we knew what to do with. good luck
     
  3. Whirlwind

    New Member

    Feb 4, 2011
    4
    0
    one thing to keep in mind is as heating water or other liquids, they expand and create a lot of pressure. in my uncle case we where constantly manually releasing hot water due to the pressure build up in the system. and there was a few times he popped the pressure release valve, its a good thing he installed one, by the time it popped though, the water was scalding hot.
     
  4. Burnit0017

    Thread Starter Member

    Feb 15, 2010
    101
    3
    Greeting, the forced hot air system I tried was a failure. I was only able to achieve a 10 degree temp difference from the out side temp. I am proceeding with a closed loop hot water system. The loop is only a 6 foot diameter system and includes a expansion tank, pressure relief valve, air relief valve, radiators, and a one way valve. The system is so small that I hoping it will not need a pump. I am hoping for better results and I should know more in a few days. Thanks for the words of warning and best regards.
     
  5. wayneh

    Expert

    Sep 9, 2010
    12,127
    3,048
    I don't know if I'm keen on a liquid exchange system. Correct me if I'm wrong, but isn't the ultimate goal is to transfer heat from the hot exhaust gases to the cold room air? If so, then a forced air heat exchanger designed for gas-to-gas exchange (just like inside my gas furnace) would be the way to go. Otherwise you're suffering inefficiency in going from gas-to-liquid and then again going from liquid-to-gas. No doubt that liquid systems work, but they're meant to solve certain problems that would be difficult otherwise. I think the short distances you have would bode well for an air system.
     
  6. Burnit0017

    Thread Starter Member

    Feb 15, 2010
    101
    3
    Greetings, the pellet burner just does not produce heat for the forced hot air system. It is small. I have moved on and I am now installing a closed looped hot water system. The system includes a heating coil that will be positioned above a the pellet burner, a expansion tank, a air release valve, a pressure relief valve, and radiators inside the shop. I hope to be finished in a few days. Hopefully I will be able to post better test results.
     
  7. russ_hensel

    Well-Known Member

    Jan 11, 2009
    818
    47
    Are you looking at counter-flow heat exchangers. They work fine with air. Problem is having enough surface area for the heat exchange.
     
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