Tubular Solar Still (Destilador solar)

Department of Architecture & Civil Engineering

University of Fukui, JAPAN

Presented by:

Prof. Dr. T. FukuharaProf. Dr. T. Fukuhara

Production Model of TSS Production Model of TSS Based on Condensation TheoryBased on Condensation Theory

CONF. IV ISES & XVII SPESCONF. IV ISES & XVII SPESNovember 1~5, 2010, Cusco, PeruNovember 1~5, 2010, Cusco, Peru

Environmental Heat and Hydraulics Lab.

TTubular ubular SSolar olar SStill (TSS) ?till (TSS) ?

Using Solar EnergySun

Saline water Distilled water

CONTENTS


1. INTRODUCTION

2. PRODUCTION MECHANISM OF TSS

3. THEORY OF CONDENSATION

4. INDOOR EXPERIMENTS

5. FIELD EXPERIMENTS

6. CONCLUSIONS

• Remote and arid areas

• After natural disaster

(tsunami, tornado, etc.)

Desalination

- Solar distillation

1. INTRODUCTION

Tubular Solar Still (TSS)

(We developed)Easy fabrication, set-up & maintenance

Shortage of drinking

water

Fig. Women collecting drinking Water (Bangladesh)

Fig. People collecting water from nearly dried-up well (Nigeria)

Fig. Women transporting drinking water (Sudan)Fig. Unsafe water source due to

tsunami


ElectricityElectricity TransportatioTransportationn

RORO In developing/In developing/

under developing under developing countriescountries MSFMSF MEDMED EDED

Water troubles in Bangladesh

Red paintA hand pump well contaminated by arsenicarsenic

35 million people (1/4 of population ) danger of diseases due to arsenic

　　　　　　　 Diseases caused by arsenicDiseases caused by arsenic

KeratosiKeratosiss

GangrenGangren

CancerCancer

MelanosisMelanosis

Safe area

Iso-concentration of Chloride ion (Cl- )

Drinking Water Standard:

200 mg/L200 mg/L(Critical value of Japanese standard)

50km

Prediction of sea water intrusion due to Prediction of sea water intrusion due to rise in sea water table rise in sea water table （（ from IPCCfrom IPCC））

Pond water for drinking purpose

Small volume and high turbidity at the end of dry season

　　　 Pond sand filter（ PSF）

Pumping up pond water to PSF with a hand pump 　　　

Hand pump well

　　 Sand filterSand filter

Woman pumping up pond waterpond water to PSF with a hand pump

A lot of women must wait for 2-3 hours2-3 hours to get water!

Drawing water is the duty of womenduty of women.

I t takes 30 minutes to fill a vessel of 10L

Some people come from 16km away.

Small rate of water from PSF

Many people like her cannot stand waiting for good water.

Take water directlydirectly from pond.

People also use pond water for daily life.

Reason:Reason: 240 PSFs for 240,000240 PSFs for 240,000 peoplepeople

Practical purposePractical purpose Solar desalinationSolar desalination facility for on-site usage facility for on-site usage

with with low costlow cost and and easy maintenanceeasy maintenance

Non CO2 emissionNon CO2 emission

・・・・・・ Suitable for developing Suitable for developing countriescountries

長距離水輸送長距離水輸送

Power plantPower plant　　 Large scaleLarge scale　　　　　　　　　　　　　　　　　　desalination plantdesalination plant

Small sizeSmall size On-site usageOn-site usage

COCO22

海水

Sun

F.W.F.W. Near

CO2Sea water

Long transportation

1. INTRODUCTION (Cont..)


Objectives of this paper:

1. Propose a production model based on a condensation theory for a TSS.

2. To use a new overall heat transfer coefficient between the humid and ambient air in the proposed model.

3. Verification of the proposed model by comparing indoor and field experimental data.


Fig. Production Principle of TSS


(Production)(Production)


Conventional production modelsConventional production models for basin type still based on for basin type still based on evaporation theory.evaporation theory.

-

Evaporation Condensation ProductionEvaporation Condensation Production

Theory of condensationTheory of condensation may give a better resulta better result than past evaporation theories.

Conventional production modelsConventional production models

A time lagA time lag

Present modelPresent model


New & unique New & unique modelmodel

No theory of condensation for solar stills RHha

Tha

Inside TSS Outside TSS

3. THEORY OF CONDENSATION

Fig. Condensate liquid film & gravity force at point PFig. Condensate liquid film & gravity force at point PEnvironmental Heat and Hydraulics Lab.

Humid air

Condensate flow

Production

θ=π

θ=π/2

( - )gρ ρl vha

Radial ( ) direction

r

P

o

θ=0

θ θ

Angular ( ) direction

( )

θ

ρ ρ θl vha- gsin

Water

g

δδ is gradually Increases in downward dir. small

element

WaterWater

δ

vθ

Axial () dir.x

Angular (　 ) dir.

δθ()Velocity profile

Liquid film

Humid air

θ+dθ

θ

Cover

rr=R

r=R- δ

dx=1

δ

δ+dδ ds=Rd θ

Fig. Representative element of liquid film flowFig. Representative element of liquid film flowEnvironmental Heat and Hydraulics Lab.

InterfaceInterface

3. THEORY OF CONDENSATION (Cont..)

AtmosphereAtmosphere

Liquid Liquid filmfilm

Humid Humid airair

CoverCover

( ) θδ dR − ( )θδ

θV

θ

Fig. Temperature profile Fig. Heat & mass transferFig. Temperature profile Fig. Heat & mass transferEnvironmental Heat and Hydraulics Lab.

dq

dq

dq=h d( )fg m

dm

q .dss

m+dm

m( )θ

ds=Rdθ

Cover

LiquidfilmHumid air

Interface

h T -o ha( )T .dsa

Atmosphere

rRR-δ

.

...

..

..

δ

R-δ Rr

δ ha

TcTha’Tha

δ

ds = R- d’ ( )δ θ

Humidair

Liquidfilm

.

3. THEORY OF CONDENSATION (Cont..)

i

AtmosphereAtmosphere

CoverCover

Liquid Liquid filmfilm

Humid Humid airair

RR δ−

3. THEORY (Cont..)

Energy equation: in a steady stateEnergy equation: in a steady state

Momentum equation: in a steady stateMomentum equation: in a steady state

01

2

2

=+dr

dT

rdr

Td

( ) 0sin1

22

2

=−+

−+ θρρ

µθθθ

vhall

g

r

v

dr

dv

rdr

vd


Refer to the paperRefer to the paper for assumptions and BC

3. THEORY (Cont..)Energy Eq.Energy Eq.


Fourier’s Fourier’s LawLaw

01

2

2

=+dr

dT

rdr

Td Integrate using BC

hl

δλ

−=

−=Rr

ls dr

dTq

)(

)(1

θδλγ cihal

sTT

q−= Apparent

heat flux

)(

)(2 θδ

λγγ cihalcss

TTqq

−==Actual heat flux Using local

HTC )( cihals TThq −= ( )θδ

λγ lclh =

1'

1 <−−=

ciha

ciha

TT

TTγ 21γγγ =cArea fractio

n

Temp. correction coefficient Condensatio

n coefficient

12 <=tc

nc

A

Aγ

4/1

2/tan

2/tanln4)(

=

o

Aθθθδ

3. THEORY (Cont..)Momentum Momentum

Eq.Eq.


Mass flow/Mass flow/LL

Integrate using BC

Film thicknes

s

Local HTC ( )θδλγ lc

lh =

( ) 0sin1

22

2

=−+

−+ θρρ

µθθθ

vhall

g

r

v

dr

dv

rdr

vddrvm

R

Rl∫ −

=δ θρθ )(

mdhdsqqd fgs =⋅=Heat flow/Heat flow/LL

fgvhall

cihallc

hg

TTDA

)(2

)(

ρρρµλγ

−−

=

RD 2=

)( o1

1

o

θθ

θθ

θ

−=

∫ dhh

l

c

Average HTC

Humid air

Condensate flow

Production

θ=π(= )1θ

θ=π/2

Radial ( ) direction

r

P

o

θ=0(= )οθ

θ θ

- g( )ρ l vhaρ

Angular ( ) direction

( )

θ

ρ l vha- gsinρ θ

Water

g

δ

dq

dq

dq=h d( )fg m

dm

q .dss

m+dm

m( )θ

ds=Rdθ

Cover

LiquidfilmHumid air

Interface

h T -o ha( )T .dsa

Atmosphere

rRR-δ

.

...

..

..

δ

R-δ Rr

δ ha

TcTha’Tha

δ

ds = R- d’ ( )δ θ

Humidair

Liquidfilm

.

( )θδ

3. THEORY (Cont..)

Average Average HTCHTC


A new overall A new overall HTCHTC

m4/13

4

3

)(

)(996.0

−−

=cihal

lfgvhallcc TTD

hgh

µλρρρ

γ

)()( cihacahao TThTTh −=−

Mass fluxMass flux

3

1

333

33

4

)()(996.0

−−

=

ahalvhall

fglc

TTag

Dhm

λρρρµ

γ

fgahao hTThm /)( −=

Temp. difference Temp. difference fractionfraction

Constant≈−−=

aha

ciha

TT

TTa

CondensatiCondensation on

coefficientcoefficient

Indoor Expt.Indoor Expt.

Indoor Expt.Indoor Expt.

dq

dq

dq=h d( )fg m

dm

q .dss

m+dm

m( )θ

ds=Rdθ

Cover

LiquidfilmHumid air

Interface

h T -o ha( )T .dsa

Atmosphere

rRR-δ

.

...

..

..

δ

R-δ Rr

δ ha

TcTha’Tha

δ

ds = R- d’ ( )δ θ

Humidair

Liquidfilm

.

i Atmosphere

Ta

RR δ−

δ

4. INDOOR EXPERIMENTS

Fig. Schematic diagram of indoor experimentEnvironmental Heat and Hydraulics Lab.

Experimental Conditions

Ta :15, 20,25,30 & 35oC

RHa : 35%

Rs :1200,800,500W/m2

Expt. duration: 8 hrs.

Water depth: 45mm(to measure evaporation)

Evaporation

Evaporation

Distilled water(Production)

Production

0 5 1 0 1 5 20 25 30 35 40 450

5

1 0

1 5

20

(Tha-Tci)= a(Tha-Ta) a=

Tha-Ta

T ha-T c

i

0.375

Tem perature d ifference, (K )

Tem

pera

ture

dif

fere

nce, (

K)

Fig. Relation between (Tha-Tci) and (Tha-Ta)


4. INDOOR EXPERIMENTS - RESULTS

0.75 0.8 0.85 0.9 0.95 10

3

6

9

1 2

1 5

D ry air pressure fraction,

Condensati

on c

oeff

icie

nt,

= 0.0005-0.00046( )

ea/eo

γc

γ c

ea/eo

[ 1 0× -5]

Fig. Relation between γc and ea/eo

ea=eo-evha

evha=f(Tha, RHha)

eo=101325Pa


4. INDOOR EXPERIMENTS - RESULTS

RHha<< 100%

Fig. Diurnal variations of T and RH (Fukui, 2005)Environmental Heat and Hydraulics Lab.

RHRHhaha≈ ≈ 50% 50% during daytimeduring daytime

RHha

5. FIELD EXPERIMENTS - RESULTS

UnsaturatedUnsaturatedTha

Ta

Fig. Diurnal variations of observed ph and calculated mh


Sep 29

Oct 6

5. FIELD EXPERIMENTS - RESULTS

No time No time laglag

6. CONCLUSIONS


1. A production model based on condensation theory for a TSS is developed.

2. The condensation coefficient,

3. The condensation theory using ho could provide a good agreement with laboratory experimental data.

4. The validity of the model is evaluated from the comparison with field experimental result.

5. The condensation theory can be used to preciselypredict the production flux.

∝

o

ac e

e/1γ

Muchas gracias

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