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Increasing capacity of Solar Storage Tank

Post in 'The Green Room' started by Mtn Fire, Jan 24, 2013.

  1. Mtn Fire

    Mtn Fire New Member

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    Hello,

    Does anyone have an opinion of adding steel to say a 1000 gallon storage tank. Steel is about 8 times heavier than water per cubic foot so should hold 8 times the BTU storage per cubic foot. A steel fabricating company has tons of scrap plate cutouts available. They would have to be sandblasted and painted with a high heat epoxy.

    Thoughts?? I don't want to create a rust/corrosion source.

    thanks

    Alex

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  2. bmblank

    bmblank Minister of Fire

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    My opinion is that it won't work the way you think it will. I can't really explain why.
  3. woodgeek

    woodgeek Minister of Fire

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    Heat capacity of steel --per pound-- is much lower than water. So its no dice.
    Mtn Fire likes this.
  4. Mtn Fire

    Mtn Fire New Member

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    Thanks for sharing your knowlege.

    Aled
  5. Grisu

    Grisu Minister of Fire

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  6. woodgeek

    woodgeek Minister of Fire

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    there are phase change materials, mostly various kinds of salts, that might be interesting to the OP. As they are slushy solids, heat transfer can be hard. One could imagine sealed bags of these salts inside your water tank?? You would want a formulation that changes at your hydronic supply temp. Hmmm.
  7. bmblank

    bmblank Minister of Fire

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    I hated thermodynamics in college. Heat transfer wasn't bad, but throw in Cp and Cpk and all those other things and it gets easier and easier to get confused.
  8. mole

    mole Member

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    Alex, At first glance it sounds like a real interesting idea until you compare the specific heat of the two materials. The specific heat is the amount of energy it takes to raise a gram of the material by 1degC. Water has a specific heat of 4.18Joule/g degC. Carbon steel is only 0.486 J/gdegC.
    Here's a ref. on specific heats of a few materials: http://invsee.asu.edu/nmodules/engmod/propsh.html

    So a gram of water will absorb or store 8.6 times as much energy as gram of steel for each degree of temp rise! Strange, huh?
  9. semipro

    semipro Minister of Fire

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    Interesting thought.
    These salts, aka "latent heat of fusion" salts, for one, have been used in solar thermal air based systems. The salts chosen solidify near the temps you want coming out of your HVAC vents for heating. These are widely used in the chemical hand warmer packs that can be boiled to return them to a liquid state after use.
    The idea of using bags of them in a water bath is something I've not heard of before.
  10. Mtn Fire

    Mtn Fire New Member

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    Thank You for the info,

    Alex
  11. Circus

    Circus Member

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    Figuring steel is 7.5 times heavier, it's still not quite as good as water. But it's close.
    Guess it depends on what the operating temp is. If we're talking 130 or so you could use a phase change material like wax. At melting (freezing) it'll store 50 times more than when stable.
    If anyone wants to make a billion buck just invent a water like substance that melts at 70F

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