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Exergy and Possible Applications

Zhang Lixiao

Email:zhanglixiao@bnu.edu.cn04/20/23

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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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Let there be a series of thermal reservoirs. WR is the reversible (maximum) obtainable work

between any two temperatures.

Past Memory

Temperature T*

T1

T2

WR

QH

QC

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Maximum attainable work

HR QW max

H

CHR T

TQW 1

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The general concept of exergy In 1953 the term exergy was suggested by Z. Rant to denote “techni

cal 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 obt

ainable when some matter is brought to a state of thermodynamic e

quilibrium with the common components of the natural surrounding

s’’.

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Some remarks

Contrast is the source of action and depletion of contrast is tContrast is the source of action and depletion of contrast is t

he creator of time. Exergy is the physical value of contrast.he creator of time. Exergy is the physical value of contrast.

Contrast is everywhere: Dark/Light, Cold/Hot, Woman/Man,Contrast is everywhere: Dark/Light, Cold/Hot, Woman/Man,

Yin/Yang, Mother Earth/Father Sun, Good/Evil, God/Satan, Yin/Yang, Mother Earth/Father Sun, Good/Evil, God/Satan,

Life/Death, ... Life/Death, ...

Energy and matter cannot be created, destroyed, produced oEnergy and matter cannot be created, destroyed, produced o

r consumed.r consumed.

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Possible applications

Bufferingcapacity

Resource

Exergy

Environ-mentalimpact

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", Ency

clopedia of Desalination and Water Resources (DESWARE), EOLSS Publisher

s, Oxford

-CHEN, G. Q.(2005). Exergy consumption of the earth. Ecological Modelling18

4(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

County Associated years Authors and published year Methodology

USA 1970 (Reisad, 1975) Reistad’s approach

Sweden 1980 (Wall, 1987) Wall’s approach

Japan 1985 (Wall, 1990) Wall’s approach

Italy 1990 (Wall et al., 1994) Wall’s approach

Norway 1995 (Ertesvag & Mielnik, 2000) Wall’s approach

China 1993 (Chen & Chen, 2006) Wall’s approach

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On sectoral scale

County Associated years Authors and published year Sectors

Saudi Arabia 1990-2001 (Dincer et al., 2004) public and private sector

Saudi Arabia 1990-2001 (Dincer et al., 2005) agricultural sector

Saudi Arabia 1990-2001 (Dincer et al., 2004) transportation sector

Turkey 1990-2001 (Utlu & Hepbasli, 2006) agricultural sector

Turkey 2000-2020 (Utlu & Hepbasli, 2005) residential–commercial

sector

China 1978-2002 (Ji & Chen, 2006) transportation sector

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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 syst

em boundary!

Not very difficulty but very complicated!

Vast references can help you finish your work once y

ou catch the philosophy of exergy!

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Thanks for your attentions!