Introduction to Solar
Distillation of Water
Fritz R. Fiedler
Basic Configuration
Computations
• Mass Balance: water
• Energy Balance: heat
• Control Volume concept
Mass Balance: Variables
QC
QI
QO
Mass Balance
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control volume: still boundary
time period: 1 day
inflow (M) = outflow (M)
QI(M/T)*t(T) = QO(M/T)*t(T) + QC(M/T)*t(T)
QI(kg/d)*t(d) = QO(kg/d)*t(d) + QC(kg/d)*t(d)
for “batch” type still, QO = 0
1 L ÷ (1000 L/m3) * (1000 kg/m3) = 1 kg
other losses??
Heat Balance
• Complicated! Must account for reflected,
absorbed, transmitted radiation as a
function of material types
• The effective energy, QE, is the amount
that goes directly into obtaining some
mass of purified water, ME
• ME(kg/m2•d)=QE(Joules/m2•d)/L(Joules/kg)
Latent Heat of Vaporization
• energy required to change the state of
water from liquid to vapor (overcome
forces of molecular attraction)
• at 100°C, L = 2.26x106 Joules/kg
• at 0°C, L = 2.5x106 Joules/kg
Still Efficiency
• Let QT be total incoming solar radiation
• efficiency = h = QE / QT
• Where will we obtain QE?
• Where will we obtain QT?
Typical Climate Station
UI Plant Science Farm
Radiation Data
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Units of watts/m2
15 minute averages
1 watt•s = 1 Joule
1 watt•15 min = 900 Joules
so to get total Joules/day, sum 15 minute
averages, multiply by number of 15 minute
intervals per day (96), multiply by 900 sec
per 15 minutes
Climate Variability
• How representative are the data collected
at the UI Plant Science Farm climate
station of conditions on the roof of BEL?
• http://birice.vaisala.com/iceweb/usa/iu/native/
• user name: iu password: moscow
• data from climate stations set up to monitor road
conditions: Paradise Ridge, Snow Road,
Reisenauer Hill
Climate Variability
Paradise Ridge Solar Radiation
1200
10:50 am
1000
watts/m
2
800
600
400
200
0
3/21/2005 7:12
3/21/2005 16:48
3/22/2005 2:24
date/time
3/22/2005 12:00
Data?
• What data are required to perform mass
balance (and estimate losses)?
• What data are required to determine still
efficiency?
• Develop a measurement and data
collection plan!