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Why the mass of steam formed during condensation is equal to 9H2

  1. Feb 15, 2013 #1

    Elz

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    1. Why the mass of steam formed during condensation is equal to 9H2

    While studying about the lower calorific value of fuel the equation is
    L.C.V.= H.C.V. – heat of steam formed during combustion

    Now here in the book they have written that,
    Let ms = mass of steam formed in per kg of fuel = 9H2

    Since the amount of heat per kg of steam is the latent heat of vaporization of water
    corresponding to standard temperature of 15°C, is 2466 kJ/kg,

    ∴ L.C.V. = H.C.V.- ms X 2466 kJ/kg
    = H.C.V. - 9H2 X 2466 kJ/kg …(∵ ms = 9H2)

    What i don't understand is why this ms is equal to 9H2? what is the chemical reaction here? Why this value is considered constant for all fuels? can anyone please explain?
     
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  3. Feb 15, 2013 #2

    Simon Bridge

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  4. Feb 15, 2013 #3

    Elz

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    So 1 kg of H2 is equivalent to 9 kg of water or steam. So if our fuel has 5 kg H2 then 5X9 kg of steam will be formed. And if we condense it we will get this massX latent heat of vaporization of water=heat of steam formed during condensation.
    Did I get it right?
     
  5. Feb 15, 2013 #4

    Simon Bridge

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    That's what I read - yep.

    Careful - the ratio is approximate. It assumes all the hydrogen in the fuel gets used to make water - i.e. a very clean burn. The steam is at the boiling point. Stuff like that.
    Good enough for a back-of-envelope calculation.
     
  6. Feb 15, 2013 #5

    Elz

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    Thanks for the help.. :)
     
  7. Feb 15, 2013 #6

    Simon Bridge

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    No worries.
     
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