BSE CPD seminar – Constructal Theory of Water Management on 28 April 2011 Organized by the Department of Building Services Engineering, a CPD seminar on Constructal Theory of Water Management was delivered by Professor A. Bejan and Professor S. Lorente on 28 April 2011 (Thursday). The seminar was successfully held with 73 participants attended.

 

Powerpoint of the CPD lecture Professor Bejan received his BS, MS and PhD degree from Massachusetts Institute of Technology (MIT). His research covers a wide range of topics in thermodynamics, heat transfer, fluid mechanics, convection and porous media. More recently, he developed the constructal law of design in nature. Professor Lorente received her BS, MS and PhD degree from INSA Toulouse, France. Her research interests encompass vascularized materials, constructal theory, porous media, fluid mechanics, heat and mass transfer.

Presentation by Professor Bejan Presentation by Professor Lorente

Both speakers are experts in Constructal Theory. In this seminar, the speakers gave a detailed analysis on Constructal Theory for application on water resources management. The constructal law states that in order for flow systems to persist in time their configurations must evolve toward flowing more easily, for greater access. In the talk, this design tendency was illustrated with examples from river basin design and the movement on humans on the globe, from land transportation to air mass transit.

In addition, Constructal Theory was illustrated to show how to design networks for the distribution and collection of water on finite-size areas. Finally, the speakers outlined different challenges of transport of water, few large and many small, optimal urban hydraulics systems, understanding underground systems and control of flows.

Well-received talk Participants

The talk is useful in understanding how Constructal Theory can be applied on water management.

BSE News CPD20110428

*A. Bejan and S. Lorente, Design with Constructal Theory (Wiley, 2008)

www.constructal.org

Adrian BejanDuke University

USA

Constructal Theory of Water Management

Sylvie LorenteUniversity of Toulouse

France

2

“Design” and “evolution” is a physics phenomenon,

summarized by the constructal law (1996):

“For a flow system to persist in time (to live) it must evolve such that it provides greater access to its currents”.

The time direction of design evolution:

3

Time

Distribution of river sizes

3/ 70 1

3/ 71 2

2

D / D 2

D / D 2

Fully turbulent, P ~ m

4 / 70 1

2 / 71 2

D / D 2

D / D 2

a bΔZ ΔZ = 1.9644

4 / 70 1

2 / 71 2

3/ 72 3

D / D 2

D / D 2

D / D 2

a bΔZ ΔZ = 0.815

5/ 70 1

2 / 71 2

2 / 72 3

2 / 73 4

D / D 2

D / D 2

D / D (2 / 3)

D / D (3/ 4)

5

Constructal River Basins

6

Few Large and Many Small

7

Few Large and Many Small

8

9

The population of the countries in the Arabian Peninsula is expected to double in fifty years (to 600 million), and only through desalination will the fresh-water resource increase. They are alreadywithdrawing over 75% of their TotalRenewable Water Resources.

Potential Conflict: Turkey has been building dams on the Tigris and Euphrates rivers that will reduce flows downstream into Syria and Iraq by 80%.

FRACTION OF FRESHWATER WITHDRAWAL

FOR AGRICULTURE

UNEP/GRID, 2002

YEAR 2000

13

14

15

16

17

18

19

A. Bejan and S. Lorente, Design with Constructal Theory, Wiley, 2008

www.constructal.org20

*A. Bejan and S. Lorente, Design with Constructal Theory (Wiley, 2008)

www.constructal.org

Adrian BejanDuke University

USA

Constructal Theory of Water Management

Sylvie LorenteUniversity of Toulouse

France

2

Adrian Bejan, Duke University, NorthCarolina, USA1996

“For a finite-size open system to persist intime (to survive) it must evolve in such away that it provides easier and easieraccess to the currents that flow through it ”.

3

Urban Hydraulics

objectives

constraints Disc-shaped area Number of outletsTotal volume of the tubes

To deliver a fluid from a source to a given number of outlets (users)

Minimum P

4

Urban Hydraulics

L1

L2

2 levels of pairingN = 12 outlets

L0

5

We obtain the connecting angles

(48 outlets)

The shape of the network is the result.It is « given » by the angles.

6

Resistancefactor

7

When optimized complexity is beneficial

N = constantpairing is a useful feature if N sufficiently large

N increases the level of pairing increases

complexity increasesN constant

8

Limits of the previous approach

In case of accident alongthe ducts, interruption ofthe flow.

Solution: look at nature

At a certain small scale, loops appear

Tree networks with loops

9

Designed networks mimic nature:The biggest networks have loops for thesake of security.

• Is an optimized network with loops much lessefficient than a dendritic one?

• Does the result on the comparison betweenthe two depend on the complexity level?

10

the flow resistances increase with security

11

Optimal diameter ratio (one tube is cut) insensitive to the increase of complexity

Robustness of optimized complex flow structures

Impact of having loops decreases when complexity increases

12

13

Underground Hydraulics

14

Underground Hydraulics

Understanding the underground systems

Driving forces: agriculture, industry, transport…

Pressures: sol occupation, use of ressources

States: environmental conditions (physics, chemistry)

Impact : nature and environment, health

Responses: European programs

2000: EU rules2006: Underground water in France

Rules for underground waters

• Avoid pollution drinkable water

• Once contaminated difficult to clean

• They feed the rivers impact on the qualityof surface water

• Regulation during dry periods

15

75% of EU inhabitants rely on underground water for their water supply.

But: what about the access?

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Control

Distributed electrodes

x

y

0

LX

Targeted zone

L0

internal electrode (U1)

external electrode ( 0U )

Ionic species reservoir

LY

L

17

Objective: to maximize the flux of ionic species

1

2 xy0

LX

Targeted zone

10L

electrode (U1)

electrode (U 0)

Ionic species reservoir

LY

L

electrode (U2)20L

18

A

'L

cDz

1

²F

RTR

iii

2i

net

We apply an electrical potential difference

Global resistance of the flow:

Concentration distribution

19

Ionic flux as a function of the location of the second bed of electrodes

20

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Concluding remarks

Water : a resource to preserve

… with science.