Exergy and Possible Applications

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Exergy and Possible Applications

• Zhang Lixiao
• Emailzhanglixiao_at_bnu.edu.cn
• 10/9/2013

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Questions?

• What is real resource or wealthy ?
• -Available energy
• How to interpret the concept of scarcity ?
• -Irreversibility

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Past Memory

• Let there be a series of thermal reservoirs.
• WR is the reversible (maximum) obtainable work
  between any two temperatures.

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Maximum attainable work
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The general concept of exergy

• In 1953 the term exergy was suggested by Z. Rant
  to denote technical working capacity.
• A complete definition was given by H.D.Baehr in
  1965-
• Exergy is that part of energy that is
  convertible into all other forms of energy.
• Exergy is a measurement of how far a certain
  system deviates from a state of equilibrium with
  its environment (Wall,1977).
• According to Szargut et al. (1988) "exergy is the
  amount of work obtainable when some matter is
  brought to a state of thermodynamic equilibrium
  with the common components of the natural
  surroundings.

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Some remarks

• Contrast is the source of action and depletion of
  contrast is the creator of time. Exergy is the
  physical value of contrast.
• Contrast is everywhere Dark/Light, Cold/Hot,
  Woman/Man, Yin/Yang, Mother Earth/Father Sun,
  Good/Evil, God/Satan, Life/Death, ...
• Energy and matter cannot be created, destroyed,
  produced or consumed.

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Possible applications
Buffering capacity
Exergy as the trinity of resource, buffering
capacity and environmental impact
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Second Law analysis of a real process
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Resource accounting-wall School

• On global scale
• -G. Wall M. Gong(2000), "On Exergetics,
  Economics and Desalination", Encyclopedia of
  Desalination and Water Resources (DESWARE), EOLSS
  Publishers, Oxford
• -CHEN, G. Q.(2005). Exergy consumption of the
  earth. Ecological Modelling184(2-4), 363-380.
• -HERMANN, W. A.(2006). Quantifying global exergy
  resources. Energy31(12), 1685-1702.

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Exergy budget of the earth
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On state scale
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On sectoral scale
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Exergy as ecological indicator-Jorgenson School

• The biggest asset of ecosystem exergy analysis is
  that it can measure the increase in disorder in
  ecosystems associated with human environmental
  impact.
• Wagendorp et al. (2001) proposed to use the
  ecosystem exergy concept as the theoretical basis
  for selecting indicators of the land use impact
  category in Life Cycle Assessment (LCA).

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Ecosystem exergy concept

• Four key elements
• Ecosystems are open systems that receive external
  exergy fluxes (mainly solar exergy)
• Ecosystems use part of that external exergy to
  increase their internal exergy level in terms of
  biomass, structure and information (order from
  disorder)
• Ecosystems increase and maintain their capability
  to build up order through a process of learning
  and memorizing by genetic selection and transfer
  (order from order)
• Ecosystems with high exergy level are more
  successful in dissipating external exergy flows
  it means that they are better buffered and thus
  have higher stability

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Exergy analysis of waste emissions- Rosen School
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How to calculate the exergy?

• Is not so important compared to how to define a
  system boundary!
• Not very difficulty but very complicated!
• Vast references can help you finish your work
  once you catch the philosophy of exergy!

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• Thanks for your attentions!