[TRNSYS-users] Question about H2 electrolyzer Type 160

[SUNLIANG CAO]

Thanks, David.

I have got some reply from other researchers that the Faraday loss is mainly resulting from the unwanted chemical byproduct during the electrolysis process, and thus they are not accounted as heat generation in the electrolyzer (Although some unwanted chemical reactions indeed release some heat).

This is the reason that the heat generation in the electrolyzer model Type160 is calculated as "Pely*(1-eta_e)" rather than "Pely*(1-eta_tot)".

Kind Regards,
Sunliang Cao 



Date: Thu, 20 Nov 2014 14:54:07 -0600
From: d.bradley at tess-inc.com
To: trnsys-users at lists.onebuilding.org; caosunliang at msn.com
Subject: Re: [TRNSYS-users] Question about H2 electrolyzer Type 160


  
    
  
  
    Sunliang,

      In the Type160 code, the equation for the heat generated by the
    electrolyzer is qGen = nCells*Iely*(Vcell-Vtn)

    

    where Iely is the electrolyzer current, Vcell is the cell voltage
    and Vtn is the thermoneutral cell voltage. The Faraday efficiency is
    computed from:

    

    eta_f = idensity**2/(a1+idensity**2)*a2

    

    where idensity is the current density of the cells (Iely/Acell)

    

    I think that both the Faraday efficiency and the heat generated are
    a result of the computation of the cell voltage and the stack
    current. Therefore I think that the heat generation is correctly
    computed and that the confusion may be in the definition of the
    energy efficiency and the total energy efficiency.

    Kind regards,

     David

    

    

    

    On 11/20/2014 07:36, SUNLIANG CAO
      wrote:

    
    
      
      Dear all, 

        

        I have a question about the H2 electrolyzer model Type160. Shortly: Will the Faraday loss of the
          electrolyzer be converted into heat in the electrolyzer?
         
        In the electrolyzer
            model (Type 160 written by Ulleberg) [1], there are three
            efficiencies: eta_e, eta_F, and eta_tot:
        “eta_e” is the energy
            efficiency of
            electrolyzer without considering any Faraday loss, i.e. the
            maximum theoretical
            proportion of the electricity which can be covered to the
            hydrogen energy
            content.
        “eta_F” is the Faraday
            efficiency: it is
            the ratio of the real final produced H2 energy content to
            the theoretical maximum
            produced H2 energy content.
        “eta_tot” is the total
            efficiency of the
            electrolyzer: it is equal to “eta_e*eta_F”, and thus is the
            ratio of the final
            produced H2 energy content to the electricity consumed in
            the electrolyzer.
         
        In Ullerberg’s model [1]
            (TRNSYS Type 160),
            the heating generated by the electrolyzer is calculated by
            the P_ely*(1-eta_e),
            which hasn’t taken the Faraday loss into account. However,
            according to the
            energy balance, the Faraday loss must be somewhere, which
            mostly in the form of
            heat, so I doubt why the Faraday loss hasn’t been taken into
            account in the
            thermal part of the electrolyzer model.

          
         
         
         
        Reference [1]: Øystein
            Ulleberg, Modeling
            of advanced alkaline electrolyzers: a system simulation
            approach, International
            Journal of Hydrogen Energy, Volume 28, Issue 1, January
            2003, Pages 21-33. http://www.sciencedirect.com/science/article/pii/S0360319902000332#
         
         
        Thank you very much.
         
         
        Kind Regards,
        Sunliang Cao

          
         
        

      
      

      
      

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