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Testing a Hydrogen heater with Nitrogen - feessible?

Stephen Biddle
HI All


I've got a heater designed for Hydrigen and I want to test it.  I don't have any Hydrogen, but I do have Nitrogen.  I looked up the specific heat of the 2 gasses and found:


(kL/(kgK))

H2 1.04 

N2 14.32


So they I'm going to need 14 times the flow of Nitrogen to test it.  Is that right?  I expected H2 to have a smaller specific heat, since it's a smaller molecule.  Presumably it's not as simple as that.  Any ideas?


Stephen
  • 0
    Stephen,


    The specific heats for the gases which you state are wrong, as you have got them the wrong way round. It should be:

    H2 14.32 kJ/kg K

    N2 1.04  kJ/kg K

    This means that for 1 kg of hydrogen (at constant pressure) you need 14 times the heat input to raise the temperature by the same amount compared to nitrogen. This is what I think has led to your conclusion about the flow rates. But if we step back and consider, hydrogen has an atomic mass of 1 (or molecular mass of 2) and nitrogen has an atomic mass of 14 (or molecular mass of 28) so at standard temperature and pressure, 1 kg of hydrogen will have 14 times the volume of 1 kg of nitrogen so the heat input needed to raise the temperature of 1 litre of hydrogen by 1 degree celsius seems to be roughly the same as that needed to raise the temperature of 1 litre of nitrogen by one degree.

    I admit that I have just gone through the above using memories of school chemistry from several decades ago, so I won't guarantee it is correct, but I can't see a flaw at present.

    Best of luck with your heater,

    Alasdair Anderson
  • 0
    Thanks - that all makes sense.  I'm going to put th eNItrogen flow on full and the heater on min and keep my hand on the off button.

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