Low Cost Solar Driven Desalination

Fadi AlnaimatFadi AlnaimatJames Klausner

09-29-2010

1

Outline

1. Motivation

2. Research Objectives

3. Experimental Investigation

4. Theoretical Developments

5. Numerical Solution

6. Conclusions

2

Water shortages

I. 97% of the water on the planet is saline

II. Desalination is the main source of water for arid countries and remote areas, and some islands

3

Salt Water

Fresh Water

World Water

Desalination

More than 15,000 industrial-scale desalination unit

Total worldwide capacity is more than 40 million m3/day

4

Sea WaterSolar Energy

Diffusion Driven Desalination (DDD)

Develop a low cost small scale solar drivendesalination system

DDD

Fresh Water

Waste Heat

•Combustion Engine•Oil Refinery •Geothermal Energy

5

•Promising technology that use solar energy

or waste heat to distill seawater

•Use direct contact evaporation and

condensation

Solar Diffusion Driven Desalination

condensation

•Low-temperature distillation process with a

low electrical energy consumption

6

Solar Diffusion Driven Desalination (DDD)

7

8

Experimental Investigation

9

Experimental Investigation

Hevap=1.0 mevap

D=0.254 m

Packed bed

Condenser

Experimental Investigation

Seawater Tank

Fresh Water Tank

11

Evaporator

,( )

v evap fgd m h&

( )( )− −U a a T T Adz

Z+dZ

( )L L z dzm h +&

Liquid

( )−w L a cUa T T Adz

CV ( )a a v v z dzm h m h ++& &

Gas/Vapor

( )a a v v zm h m h+& &

( )( )− −G w pack a cU a a T T Adz

( )−L w L pack cU a T T Adz

Z

Packing

Liquid

Film

( )L L zm h&

12

Theoretical Model-Transient

( ) ( ) ( )Fg L L w L pack w L aL L

L L L L L L L L L L L

G h h U a T T U a T TdT dTL d

d t dz dz C p C p C p

ω

ρ α ρ α ρ α ρ α

− − −= − − −

Evaporator

( ( ) ( )) ( )( )

(1 ) (1 )

fg L v aa a G w

pack a

h T h T GdT dT U a aG dT T

dt dz Cp dz Cp

ω

ρ α ρ α ω ρ α ω

− −−= − + −

+ +

( )1

( ) ( )( )pack

L w L pack G w pack a

pack pack pack

dTU a T T U a a T T

dt Cpρ α= − − − −

( )(1 ) (1 )

( ) .(1 )

pack a

a a a a mix a a mix

w

L a

a a mix

T Tdt dz Cp dz Cp

UaT T

Cp

ρ α ρ α ω ρ α ω

ρ α ω

= − + −+ +

+ −+

13

)622.0

)((

ai

isatvwG

T

P

T

TP

R

M

G

ak

dz

d

ω

ωω

+−=

Theoretical Model-Transient

( ) ( )( )Fg L L w pack Lw a LL L

L L L L L L L L L L L

G h h U a T TUa T TdT dTL d

dt dz dz Cp Cp Cp

ω

ρ α ρ α ρ α ρ α

− −−= − + +

Condenser

( ( ) ( )) ( )( )

(1 ) (1 )

fg L v aa a G w

a pack

h T h T GdT dT U a aG dT T

d t d z C p d z C p

ω

ρ α ρ α ω ρ α ω

− −−= − − −

+ +

( )1

( )( ) ( )pack

G w a pack L w pack L

pack pack pack

dTU a a T T U a T T

dt Cpρ α= − − − −

)32()(

2

aam

asat

a dTcTbTPP

P

dz

dT

dz

d+−

−= ω

ω

( )(1 ) (1 )

( )(1 )

a pa ck

a a a a G a a G

w

a L

a a G

T Td t d z C p d z C p

U aT T

C p

ρ α ρ α ω ρ α ω

ρ α ω

+ +

− −+

14

Numerical Solution-Evaporator

Water Temperature Air Temperature

L=1.0 kg/mL=1.0 kg/m22--sec, G=0.5 kg/msec, G=0.5 kg/m22--secsec

Time step=0.002 sec, grid size= 0.01 mTime step=0.002 sec, grid size= 0.01 m 15

Packed bed Temperature

Numerical Solution-Evaporator

L=1.0 kg/mL=1.0 kg/m22--sec, G=0.5 kg/msec, G=0.5 kg/m22--secsec

16

Evaporator- Num. vs. Exp.

Water Flux: L=1.0, and 2.15 kg/m2-sec

60

80

100

Evporator Temperature ( oC)

Tw,in

Tw, out, pred

Tw, out, exp

L=1.0 kg/m2-s, G=0.88 kg/m2-s

Ta,in

Ta, out, pred

Ta, out, exp

0.24

0.32

0.4

Humidity Ratio (kgv/kga)

ωωωωin

ωωωωout, pred

ωωωωout, exp

60

70

80

90

Evporator Temperature ( oC)

Tw,in

Tw, out, pred

Tw, out, exp

L=2.15 kg/m2-s, G=0.88 kg/m2-s

Ta,in

Ta, out, pred

Ta, out, exp 0.24

0.32

Humidity Ratio (kgv/kga)

ωωωωin

ωωωωout, pred

ωωωωout, exp

17

0 50 100 1500

20

40

60

Time (min)

Evporator Temperature (

0 50 100 150

0

0.08

0.16

Humidity Ratio (kg

0 50 100 150

10

20

30

40

50

Time (min)

Evporator Temperature (

0 50 100 150

0

0.08

0.16

Humidity Ratio (kg

Condenser- Num. vs. Exp.

Gas Flux: G=0.5, and 1.02 kg/m2-sec

50

60

70

Condenser Temperature ( oC)

Tw,in

Tw, out, pred

Tw, out, exp

L=2.05 kg/m2-s, G=1.02 kg/m2-s

Ta,in

Ta, out, pred

Ta, out, exp

0.32

0.4

0.48

0.56

Humidity Ratio (kgv/kga)

ωωωωin

ωωωωout, pred

ωωωωout, exp

50

60

70

80

Condenser Temperature ( oC)

Tw,in

Tw, out, pred

Tw, out, exp

L=2.0 kg/m2-s, G=0.5 kg/m2-s

Ta,in

Ta, out, pred

Ta, out, exp

0.32

0.4

0.48

0.56

Humidity Ratio (kgv/kga)

ωωωωin

ωωωωout, pred

ωωωωout, exp

18

0 50 100 1500

10

20

30

40

Time (min)

Condenser Temperature (

0 50 100 150

0

0.08

0.16

0.24

0.32

Humidity Ratio (kg

0 50 100 1500

10

20

30

40

50

Time (min)

Condenser Temperature (

0 50 100 150

0

0.08

0.16

0.24

0.32

Humidity Ratio (kg

Water ProductionL=1.5 kg/mL=1.5 kg/m22--sec, G=1.5 kg/msec, G=1.5 kg/m22--sec, sec,

AAsolar,colsolar,col=10 m=10 m22,V,Vtanktank=100 L=100 L

19

Water Production

L=1.5 kg/mL=1.5 kg/m22--sec, G=1.5 kg/msec, G=1.5 kg/m22--sec, sec,

AAsolar,colsolar,col=10 m=10 m22,V,Vtanktank=100 L=100 L

20

Water Production

2.5

3

3.5

Efficiency (%)

L=1.5 kg/mL=1.5 kg/m22--sec, G=1.5 kg/msec, G=1.5 kg/m22--sec, sec,

AAsolarsolar=10 m=10 m22,V,Vtanktank=100 L=100 L

21

25 30 35 40 45 50 55 60 650

0.5

1

1.5

2

Evaporator Inlet Water Temperature (oC)

Efficiency (%)

Energy consumption

Low specific energy consumption

22

Low specific energy consumption

1.9 kWh/m3

Water Cost for Small Scale Unit

1.9 kWh/m3

$5.7/m3

PV-ROSolar DDD>10 kWh/m3

$8-29 /m3

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No chemicals are requiredNo membrane replacementNo battery is requiredLow energy consumptionBetter water quality

Conclusion

• Theoretical model is developed for the evaporator and condenser

• Numerical solution is obtained for the models

• Evaporator and condenser models • Evaporator and condenser models are validated by experimental data

• Energy consumption of the distillation unit is 1.9 kWh/m3

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Thanks for your attention

Questions?

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