Design Overview of Solar Distiller
3.1 Construction
It is passive solar
still to distillate water by using flat plate .It consists of a shallow
blackened basin of saline water cover with a slopping transparent roof. Solar
radiation that passes through the transparent roof heats the water blackened
basin, the evaporating water which gets condensed on the cooler underside of
the glass and gets collected in tray as distillate attached to the glass.
The
still can be feed with saline water either continuously or intermittently but
the supply is generally kept at twice the amount of fresh water produce by he
still depending on the initial salinity of the saline water. The ratio of
saline water supply and amount of water to be flushed on the salinity of basin
water and is found to be propositional to the amount of fresh water produced. The
still is erected at an exposed area with along axis of the still facing
East-West direction.
The channel is fixed such that the water
slipping on the surface of the glass will fall in this channel under the effect
of gravity. This completes the construction of the model. The holes for the
inlet of water, outlet of brackish water and outlet of pure water is made as
per the convenience. We have made the outlet of brackish water at right bottom
of the model, outlet of the pure water at the end of the channel and inlet at
the right wall above the outlet.
The upper basin is partitioned into three segments
to avoid the formation of dry spots on the higher portion of the inner glass
cover. Silicone rubber sealant has been used to seal off and prevent the water
leakage between the boxes of the distiller. A hole in the basin’s sidewall
allows saline or wastewater filling, as well as collecting the condensed water.
This is also used for inserting the thermocouple wires required for temperature
measurements. When the still is in operation, the hole is closed with an
insulating material to avoid heat and vapor losses.
3.2 Working
Water
to be cleaned is poured into the still to partially fill the basin. The glass
cover allows the solar radiation to pass into the still, which is mostly
absorbed by the blackened base. This interior surface uses a blackened material
to improve absorption of the sunrays. The water begins to heat up and the
moisture content of the air trapped between the water surface and the glass
cover increases. The heated water vapor evaporates from the basin and condenses
on the inside of the glass cover. In this process, the salts and microbes that
were in the original water are left behind. Condensed water trickles down the
inclined glass cover to an interior collection trough and out to a storage
bottle. Feed water should be added each day that roughly exceeds the distillate
production to provide proper flushing of the basin water and to clean out
excess salts left behind during the evaporation process. If the still produced
3 litres of water, 9 litres of make-up water should be added, of which 6 litres
leaves the still as excess to flush the basin.
3.3 Problem Definition
The
research work carried out so far in the field of solar desalination is related
to the single basin type solar still only. The effect of changes in design,
climatic and operational parameters on the distillate yield have been studied
but limited to the single basin type solar still. If we want high amount of
distilled water we can’t get it.
Main Problems of Solar Still
·
Low distillate
output per unit area
·
Leakage of vapor
through joints
·
High maintenance
·
Productivity
decreases with time for a variety of reasons Cost per unit output is very high
3.4 Objective of Project
The main objective of the project is to develop single basin solar still
with flat plate external bottom reflector to improve the performance of single
basin type solar still by increasing the production rate of distilled water.
Find the effect of different reflector on Performance of solar still in winter
and summer climatic conditions of Gandhinagar.
3.5 Design of solar
Distillation
1
Proposed Model of Solar Distillation System The base of the solar still is made
of glass box. This also contains PUF material inside it between the glass and
metal box.
The channel is fixed such that the water
slipping on the surface of the glass will fall in this channel under the effect
of gravity. A frame of fibre stick is fixed with the box so that glass can rest
on it.
This completes the construction of the
model. The holes for the inlet of water, outlet of brackish water and outlet of
pure water is made as per the convenience. We have made the outlet of brackish
water at right bottom of the model (seeing from front of the model), outlet of
the pure water at the end of the channel and inlet at the right wall above the
outlet.
3.6 Details of Polyurethane Foam (PUF)
Although the reaction
between isocyanate and hydroxyl compounds was originally identified in the 19th
Century, the foundations of the polyurethanes industry were laid in the late
1930s with the discovery, by Otto Bayer, of the chemistry of the polyaddition
reaction between diisocyanate and diols to form polyurethane. The first commercial
applications of polyurethane polymers, for malleable elastomers, coatings and
adhesives, were developed between 1945 and 1947, followed by flexible foams in
1953 and rigid foams in 1957. Since that time they have been finding use in an
ever-increasing number of applications and polyurethanes are now all around us,
playing a vital role in many industries from furniture to footwear,
construction to cars. Polyurethanes appear in an astonishing variety of forms,
making them the most versatile of any family of plastic materials.
The
polyurethanes (PU) foams are widely used as insulating and core materials for furniture,
cooling and freezing systems, in house building, shipbuilding etc. The use of
rigid foams is resulted from their low heat conduction coefficient, low
density, low water absorption, relatively good mechanical strength. The PU
foams have been applied also as core materials of sandwich constructions with
steel plates, in building the industrial houses, warehouses, sport houses,
fruit stores, carrying freezers and cold stores, where they have to fulfill
both insulating and mechanical requirements. Comfortable,
durable mattresses and automotive and domestic seating are manufactured from
flexible foam. Rigid polyurethane foam is one of the most effective practical
thermal insulation materials, used in applications ranging from domestic
refrigerators to large industrial buildings. Polyurethane adhesives are used to
make a wide variety of composite wood products from load-bearing roof beams to
decorative cladding panels. Items such as shoe soles, sports equipment, car
bumpers and ‘soft front ends’ are produced from different forms of
polyurethane.
Many of us are clothed
in fabrics containing polyurethane fibers or high peformance breathable
polyurethane membranes. Highly demanding medical applications use biocompatible
polyurethanes for artificial joints and implant coatings. Polyurethane coatings
protect floors and bridges from damage corrosion and adhesives are used in the
construction of items as small as an electronic circuit board and as large as
an aircraft. Advanced glass and carbon fiber reinforced composites are being
evaluated in the automotive and aerospace industries. Examples of typical applications
are shown on page commercially, polyurethanes are produced by the exothermic
reaction of molecules containing two or more isocyanate groups with polyol
molecules containing two or more hydroxyl groups. Relatively few basic
isocyanates and a far broader range of polyols of different molecular weights
and functionalities are used to produce the whole spectrum of polyurethane
materials. Additionally, several other chemical reactions of isocyanates are
used to modify or extend the range of isocyanate-based polymeric materials. The
chemically efficient polymer reaction may be catalyzed, allowing extremely fast
cycle times and making high volume production viable.
·
Cost
and processing advantages
Although a unique
advantage of polyurethanes lies in the very wide variety of High performance
materials that can be produced, they also differ from most other plastic materials because the
processor is able to change and control the nature and the properties of the
final product, even during the production process. This is possible because
most polyurethane are made using reactive processing machines, which mix
together the polyurethane chemicals that then react to make the polymer
required. Changes in the detailed chemical nature of the polyols, isocyanates
or additives allow the user to produce different end polymers. Minor changes in
the mixing conditions and ratios allow for a fine tuning of the polymers
produced. The polymer is usually formed into the final article during this
polymerization reaction and these accounts for much of the precise needs of a
particular application. Another important property of polyurethane reaction
mixtures is that they are powerful adhesives.
This enables the simple
manufacture of strong composites such as building panels and laminates,
complete housings for refrigerators and freezers, fully integrated instrument
panels for vehicles and reinforced structures in boats and aircraft. It is, in
part, this dual functionality that makes the material so valuable for
manufacturing industries since it is possible to eliminate a number of complex
and expensive assembly steps when using polyurethanes rather than alternative
polymers.
It is this combination
of high material performance coupled with processing versatility that has
resulted in the spectacular growth and wide applicability of the polyurethane
family of materials. The processing benefits enable polyurethanes to compete
with lower cost polymers since raw material costs are not the only
consideration in the total cost involved in producing an article.
3.6.1 Types
of polyurethanes
A consideration of
particular properties of certain grades of polyurethanes and the way these are
used serves to demonstrate their versatility.
1. Foamed
By itself the
polymerization reaction produces solid polyurethane and it is by forming gas bubbles
in the polymerizing mixture, often referred to as ‘blowing’, that foam is made.
Foam manufacture can be carried out continuously, to produce continuous
laminates or slab stock, or discontinuously, to produce molded items or
free-rise blocks. Flexible foams can be produced easily in a variety of shapes
by cutting or molding. They are used in most upholstered furniture and
mattresses. Flexible foam molding processes are used to make comfortable,
durable seating cushions for many types of seats and chairs.
The economy and cleanliness of flexible
polyurethane foams are important in all upholstery and bedding applications.
Strong, low-density rigid foams can be made that, when blown using the
appropriate environmentally acceptable blowing agents, produce closed cell
structures with low thermal conductivities. Their superb thermal insulation
properties have led to their widespread use in buildings, refrigerated transport,
refrigerators and freezers.
2. Solid
Although foamed
materials account for a substantial proportion of the global polyurethanes
market there is a wide range of solid polyurethanes used in many, diverse
applications. Cast polyurethane elastomers are simply made by mixing and
pouring a degassed reactive liquid mixture into a mould. These materials have
good resistance to attack by oil, petrol and many common non-polar solvents
combined with excellent abrasion resistance. They are used amongst other things
in the production of printing rollers and tires, both low speed solid relatively
small units and to fill very large, pneumatic off-road tires.
Polyurethane
elastomeric fibers are produced by spinning from a solvent, usually dimethylformamide
(DMF), or by extrusion from an elastomeric melt. The solvent process is the
dominant one and has two forms, one in which the completed elastomeric is
dissolved and then a fiber spun as the solvent is removed and the other in
which the isocyanate and polyol are mixed into a DMF solution and the fibre
spun as the reaction occurs. The major applications are in clothing where these
fibers have effectively replaced natural rubber.
3.6.2 Applications of polyurethanes
A detailed breakdown of
the markets for polyurethanes is given in Chapter 2, but the versatility of
this material can be demonstrated by looking at the applications in five major
areas.
Automotive
The use of
polyurethanes in this area is now well established to the benefit of both the
manufacturer and the end consumer. Applications include seating, interior
padding, such as steering wheels and dashboards, complete soft frontends, components
for instrument assemblies and accessories such as mirror surrounds and
spoilers. Door panels, parcel shelves, sun roofs, truck beds, headliners,
components mounted in the engine space and even structural chassis components
are now made from polyurethanes.
Furniture
The market for
cushioning materials is mainly supplied by polyurethane flexible foam, which
competes with rubber latex foam, cotton, horse hair, polyester fibre, metal
springs, wood, expanded polystyrene, propylene and PVC. Polyurethanes are also
ideal where strong, tough, but decorative integral-skinned flexible or rigid
foam structures are needed.
Construction
When sandwiched between
metal, paper, plastics or wood, polyurethane rigid foam plays an important role
in the construction industry. Such composites can replace conventional
structures of brick, concrete, wood or metal, particularly when these later
materials are used in combination with other insulating materials such as
polystyrene foam, glass fibre or mineral wool. Technically advanced wood
composites can be produced for use in load bearing applications and wood
construction boards for flooring and roofing.
Thermal insulation
Rigid polyurethane foam
offers unrivalled technical advantages in the thermal insulation of buildings,
refrigerators and other domestic appliances and refrigerated transport Competitive
materials include cork, glass fibre, mineral wool, foamed expanded and extruded
polystyrene and phenol formaldehyde.
Footwear
Soles, some
synthetic uppers and high performance components for many types of footwear are
produced from polyurethanes. These compete with traditional leather and rubber,
PVC, thermoplastic rubber and EVA. Polyurethane adhesives are widely used in
shoe manufacture and coatings are used to improve the appearance and wear
resistance of shoe uppers made from both real and synthetic leather.
3.7 Details of
Different Parts of the System
3.7.1
Still Basin
It
is the part of the system in which the water to be distilled is kept. It is
therefore essential that it must absorb solar energy. Hence it is necessary
that the material have high absorbtivity or very less reflectivity and very
less transmitivity. These are the criteria’s for selecting the basin materials.
Kinds of the basin materials that can be used are as follows: 1. Leather sheet,
2. Ge silicon, 3. Mild steel plate, 4. RPF (reinforced platic) 5.G.I.(galvanized
iron).International Journal of Advanced Science and Technology Vol. 70 We have
used blackened galvanized iron sheet(K= thermal conductivity= 300W/mºC) (3mm
thick).
3.7.2
Side Walls
It
generally provides rigidness to the still. But technically it provides thermal
resistance to the heat transfer that takes place from the system to the
surrounding. So it must be made from the material that is having low value of
thermal conductivity and should be rigid enough to sustain its own weight and
the weight of the top cover (refer fig.no.2). Different kinds of materials that
can be used are: 1) wood , 2) concrete, 3) PUF, 4) RPF (reinforced plastic).
3.7.3 Design of Stand
3.7.4 Design of Glass
3.7.5 Top Cover
3.7.6 Channel
3.8 Distilled Water Quality
Two different
water samples from solar stills A and D were tested in the District Public
Health Laboratory, Buldana, Government of Maharashtra, India. The distilled
water was tested with highly accurate digital instruments having an accuracy of
±l mg/l. The laboratory test results as shown in Table 4 indicate that the
quality of water after distillation is well within the desirable limits as
prescribed by WHO for Indian specific conditions.
|
Sr. no
|
Test
|
Sample no 1
|
Sample no 2
|
Desirable limit
|
|
1
|
Ph
|
6.9
|
6.8
|
6.5-8.5
|
|
2
|
Electrical conductivity, μS/cm
|
80
|
97
|
750
|
|
3
|
Chloride as Cl , mg/l
|
10
|
21
|
250
|
|
4
|
Total hardness as Ca- CO3, mg/l
|
20
|
22
|
300
|
|
5
|
Total dissolved sol- ids, ppm
|
40
|
50
|
500
|
|
6
|
Turbidity as NTU
|
0.03
|
0.03
|
-
|
|
7
|
Iron as Fe, mg/l
|
0.01
|
0.01
|
-
|
|
8
|
Alkalinity as CaCO3, mg/l
|
40
|
60
|
200
|
|
9
|
Physical appearance
|
Clear
|
Clear
|
-
|
3.9 Economic Analysis
The cost of
distilled water produced by the single basin type solar still with flat plate
bottom reflector depends upon the following factors.
·
The capital cost
gets reduced if locally available materials are used.
·
As the solar energy
is available free of cost, it has no effect on the total cost of the solar
still.
·
Reflectivity of the
selected reflector
·
The operation and
maintenance cost is almost negligible.
The production rate of distilled
water is proportion- al to the area of the solar still; which means that the
cost per liter of water produced is nearly the same regardless of the size of
the fabricated still. The payback period of the experimental setup depends on
overall cost of fabrication, maintenance cost, operating cost and cost of feed
water. The overall fabrication cost is Rs. 8700. It is not necessary to take
into account the operation and maintenance cost and the cost of feed water, which
is almost negligible.
