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The efficiencies of thermochemical energy transfer
Author(s) -
Carden P. O.,
Williams O. M.
Publication year - 1978
Publication title -
international journal of energy research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.808
H-Index - 95
eISSN - 1099-114X
pISSN - 0363-907X
DOI - 10.1002/er.4440020406
Subject(s) - work (physics) , process engineering , exothermic reaction , thermodynamics , energy storage , work output , heat exchanger , heat transfer , isothermal process , chemistry , exergy , efficient energy use , nuclear engineering , engineering , power (physics) , physics , electrical engineering
Abstract A general thermodynamic study of thermochemical energy transfer and work production processes is presented. Both gaseous systems in which the effluent of each reactor is not separated into the reactant and product species, and liquid/gas systems in which the effluent separates spontaneously into liquid and gas phases, are treated. the study extends to consideration of non‐isothermal reactors, to the individual roles of reactor and heat exchanger in the work production processes and to the significance of the intrinsic work of phase separation. the overall system efficiency is derived as the product of two efficiencies: the energy storage efficiency which defines the fraction of the input energy passed in chemical form to storage and the work recovery efficiency which defines the fraction of this stored energy available as output work. the fundamental thermodynamic processes underlying the derivation of these efficiencies are examined from the point of view of optimization of the design and operation of individual system components. In particular, it is shown that the available work from a thermochemical energy transfer system approaches the maximum value given by the Gibbs' free energy change when the temperature profile of the exothermic reactor is suitably tailored. The work of separation has formed the basis of the analysis of specific system components and has given a useful insight into the understanding of energy storage efficiency. Work recovery efficiencies are calculated for the ammonia/hydrogen‐nitrogen system and the paper concludes with a discussion of some practical considerations relating to the recovery of work and the performance that one might ultimately expect from this system.

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