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1. AJAY KUMAR GARG ENG.
COLLEGE
Double Slope Solar Still
Guided by- Presented by-
Arti Sagar
Kabir Chandra

2. OUTLINE
Necessity
Concept
Design Objectives
Heat Transfer Modes
Governing Equations
Low Efficiency Challenge
Auxiliary Device- NEED

3. HEAT TRANSFER MODES
CONDUCTION-The
transfer of energy between
objects that are in physical contact.
Thermal conductivity is the property
of a material to conduct heat and
evaluated primarily in terms of
Fourier's Law for heat conduction.

4. HEAT TRANSFER MODES
CONVECTION-The
transfer of energy
between an object and its
environment, due to fluid
motion. The average
temperature is a reference
for evaluating properties
related to convective heat
transfer.

5. HEAT TRANSFER MODES
RADIATION-The
transfer of energy
from the movement of
charged particles within
atoms is converted to
electromagnetic radiation.

6. NECESSITY
 Over 1 billion people without
access to clean water worldwide
 26.8% in Africa
 Clean water essential to stop
spread of disease & improve
overall health
 Solar energy = untapped resource

7. CONCEPT
 Works on principle of solar distillation
 Solar radiation- The main driving cause
 Trapped radiations can be applied to use
 Inorganic impurities FREE water can be obtained

8. DESIGN CONSIDERATIONS
 A high feed (impure) water temperature
 A large temperature difference between feed water and
condensing surface
 Use of ACTIVE or PASSIVE heating methods
 Least vapour leakage.

9. RADIATION PROPERTIES
TRANSMITIVITY
The fraction of radiation transmitted by the surface is termed as Transmitivity. It
is denoted by ‘τ’.
REFLECTIVITY
The fraction of radiation reflected by the surface is termed as Reflectivity. It is
denoted by ‘ρ’.
ABSORPTIVITY
The fraction of irradiation absorbed by the surface is termed as Absorptivity. It is
denoted by ‘α’.
EMMISITIVITY
It is the measure of ability of a surface to emit radiation energy in comparison to
a Black body at the same temperature. It is denoted by ‘ε’.
IRRADIATION
Process by which an object is exposed to radiation is called Irradiation.

10. GOVERNING EQUATIONS
Conduction-
Convection-
Q= - K*A* dT/dx
Q= H*A(TSURFACE – TAMBIENT)

11. GOVERNING EQUATIONS

12. GOVERNING EQUATIONS
Where:
R = universal gas law constant = 8.31 J/ mol-K = 8.31 X 10-3 KJ / mol-K
P1 and P2 = vapour pressure at T1 and T2
T1 and T2 = Kelvin Temperature at the initial state and final state
At 373K the pressure is 1 atm.

13. GOVERNING EQUATIONS
ESTIMATION OF THE QUANTITY OF OUTPUT WATER
A = Aperture area of the still in m2
E = Efficiency of the still usually taken as 50%
G = Global radiation energy in MJ/m 2 (Approx. 18 MJ/m 2)

14. EFFICIENCY
 Efficiency = (Energy required for the vaporization of
the distillate that is recovered) / (Energy
in the sun's radiation that falls on the
still.)

15. LOW EFFICIENCY- CHALLENGE
CHALLENGE 1-
 A high feed water temperature cant be achieved :
 A high proportion of incoming radiation is absorbed by
the feed water as heat.
 Hence low absorption glazing and a good radiation
absorbing surface are required
 heat losses from the floor and walls are considerate
 the water is shallow so there is not so much to heat.

16. LOW EFFICIENCY- CHALLENGE
 CHALLENGE 2-
 A large temperature difference can’t be achieved :
 the condensing surface absorbs little or none of the
incoming radiation
 condensing water dissipates heat which must be
removed rapidly from the condensing surface by, for
example, a second flow of water or air, or by condensing
at night.

17. AUXILLIARY DEVICE- NEED
 TEMPERATURE SENSOR-
 LM 35 Temperature sensor along with its
complimentary components is used. It is
operated by a 6V battery.
 LCD of the sensor reflects temperature of
following
areas in °C:-
• Temperature of incoming brackish water.
• Temperature of outgoing potable water.
• Temperature at the top of glass cover.