Thermodynamics, Life and Ecosystem

The science dealing with energy and work is thermodynamics. Living systems including human & technological systems we construct are (like other natural phenomenon) constrained by the law of thermodynamics.

## Energy, work and order

Work, in the mechanical sense, is the displacement of any body against an opposing force.

(1)
\begin{align} \$ W = f . \Delta l \end{align}

Where… W = work, f = force, l = distance from some point

The first thermodynamic law is stated as:

(2)
$$E_{in} - E_{out} = E_{store}$$

That is, for an energetically closed system, any energy transformation must conserve energy.

Entropy is a measure of the ability of a system to perform work; lower entropy means the system is more able to perform work.

The second thermodynamic law states that so long as the net change in entropy of the system plus its surroundings in positive, the process can take place spontaneously. This can also be stated as:

• Heat will not flow spontaneously from a cold object to a hot object
• Any system which is free of external influences will become more disordered with time
• A heat engine energy-converter cannot achieve 100% efficiency

## Irreversible-far-from-equilibrium (IFFE) system

The second law implies that things cannot spontaneously become 'more ordered'; however this doesn't seem to fit with the abundance of living organisms and ecosystems displayed on Earth. This is because these 'order-increasing' systems are not energetically closed. In order to decrease internal entropy (increase order) within a system energy needs to be absorbed from its surroundings.
These systems that can maintain or increase their order by absorbing energy from their surroundings are known as Irreversible-far-from-equilibrium systems. To determine if a system is a IFFE one we ask the question: if you cannot reverse the dynamic state of a system, then the system is IFFE.

## Reversible-systems

These are the counter to IFFE systems. An example of this is a frictionless pendulum. A system is said to be reversible if the system and all of its surroundings can be exactly restored to their initial state after the process has taken place. All actual processes are irreversible.

## IFFE systems and self-organisation

To put self-organisation into context the Bénard cell will be discussed.
Bénard cells are convection cells that appear spontaneously in a liquid layer when heat is applied from below. They can be obtained using a simple experiment first conducted by Henri Bénard, a French physicist, in 1900. The experiment illustrates the theory of dissipative structures.
The temperature of the bottom plane is increased slightly: a permanent flow of energy will occur through the liquid. The system will begin to have a structure of thermal conductivity: the temperature, and the density and pressure with it, will vary linearly between the bottom and top plane. Eventually convection cells will appear. The microscopic random mevement spontaneously became ordered on a macroscopic level. Some of the convection areas display irregularities in shape. The specific places where the irregular shape occurs is unpredictable.

## Ecosystem models

• Model I: Biosphere as a semi-permeable membrane; the entropy in the semi-permeable membrane decreases as IFFE fluctuations are stabilised by solar energy flow
• Model II: Biosphere as chains of heat-engines; solar energy is stored in the form of plants, which are consumed by herbivores, then carnivores and finally released into the environment as low temperature heat.
• Model III: Biosphere as IFFE system.
• Model IV: Biosphere as a self-organising dissipative structure
• The emergence of energy-material flow pathway networks
• The spatio-temperal differentiation of the energy-material pathway networks

These IFFE / self-organising systems exhibit a number of interesting behaviours.

• Spatio-temporally differentiated structures
• Unpredictability
• Path-dependence
• Locking-in effect

## Implications on technological system design

• High 2nd law efficiency vs high 1st law efficiency.
• Strategies of increasing second law efficiency; quality matching and co-generation
• Energy and material recycling
• Reset the value assumptions of the technological designs = radical urban design concepts
• Designing self-organising systems VS linear systems
• Taking system complexity into technological design
page revision: 18, last edited: 06 Jun 2008 11:32