The Inclined Box-Type Solar Cooker – A New Design
Several types of solar cooker
have been described in different books and literatures. In the present
investigation a highly efficient inclined box solar cooker is designed and
fabricated Details constructional feature of the cooker are described. The test
results obtained so far are encouraging. The proposed cooker can readily be put
into use at its present state.
Introduction
Solar cooker available, generally fall under two categories. One is box type and the other is parabolic reflector focusing type .The cooking ability of existing box type simple solar cooker is seems to be not satisfactory in comparison to the cost involved. .Parabolic reflector focusing type cooker needs frequent adjustment to track the apparent motion of the sun .For these reasons this type of parabolic reflector solar cooker is not much popular.
In the proposed box type cooker beam radiation is always perpendicularly accessible for its adjustable inclined position and for convenient implementation of two reflectors the cooking time is remarkably reduced than that of a usual box type cooker. The cost of cooker is however, slightly higher than usual box type but it can be considered reasonable in respect to its improved performance.
Detailed Constructional Features
The detailed constructional
feature of the cooker is shown in Fig-1.The cooker box consists of a top open
black painted inner box kept inside of the another box and the space between
the two boxes is filled with glass wool insulation. The upside of this cooker
box is covered by two layers of transparent glass keeping a gap in between and
the supporting frame of the cover is hinged with cooker box for keeping glass
cover in inclined position to handle the cooking pots. So the cooker box is
similar to conventional box type cooker, but the shape of the box is different
from common type. The length of the box in presently proposed type is at about
three times of its width and depth is equal to the width.
The cooker is to be placed facing sun, keeping longer side vertically inclined position and the inclination of the cooker box can easily be changed from 15 degree to 45 degrees with respect to the ground by the adjustable stand, attached at the back side of the box.
Two mirror reflectors are
used in this cooker, however even up to four reflectors can be conveniently
arranged in this box type cooker (provided the reflectors are light weight). The
reflectors are set along the length of the cooker box cover, one in each side,
by hinge and holding strip. So length of reflectors are equal to the length of
the glass cover .The widths
are equal to the width of the glass cover .When the cooker is in use, each
reflector is kept at the inclination of about 115 degree with the face of the
box cover .In this position the reflections from the top edge of the reflectors
touch the outer longitudinal edge of cover glass when the cooker is placed in
perpendicular direction to the solar rays .If four reflectors are used then
other two reflectors are to be hinged at the top of the inner reflectors, one
in each side at an angle of nearly 15 degree with the inner one All the
reflectors can be folded for keeping on the top of the cooker box cover when
not in use. The face of the cooker is to be placed perpendicular to beam
radiation to collect the maximum energy. This perpendicular position can be
easily achieved simply by the rotation of the cooker towards the sun with the
help of caster wheels ,suitably attached at the bottom side of the cooker and
by changing the inclination of the cooker by adjustable stand of the back side
.But the position of the reflectors remain unchanged throughout the working
period.
Four number of black painted aluminium cooking pots are used and are placed side by side at the longer side of the cooker on cooking trays. For each cooking tray two bolts acted as hinge are fixed at both longer sides of the cooker inner box. The cooking tray is suspended from the end of the bolts through M.S strips. Length of these strips is equal to the cooking pot radius and these strips are fixed with the ends of tray aligned with the exact middle position of the tray as shown in Fig-2. When the cooker box inclination is changed the cooking tray along with cooking pot, for its own weight, rotated around the bolts and always remained in horizontal position. To avoid the chance of tilting of pots, square shaped trays, length of which are kept equal to the diameter of pots are used and ends of the trays are folded upward.
Advantages of the Cooker
i) Almost 90% of the energy collected by a solar system occurs between 9 am to 3 pm .The provision for changing the inclination of proposed cooker from 15 degree to 45 degree with the horizontal is sufficient to collect direct solar radiation perpendicularly throughout the mentioned period. Thus radiant energy falling per unit aperture area of the cooker face is increased than if the cooker is placed horizontally like conventional box type cooker .Also transmissivity of the cooker glazing is increased for its perpendicular position with the beam radiation.
ii)
In this
cooker system with two reflectors ,energy collection is high and even four
reflectors can be conveniently used to concentrate solar radiation similar to
tracking reflectors ,but without the hazards of frequent manual adjustment to
follow the apparent motion of the sun.
Arrangement of multiple reflectors is also possible in horizontally placed box type cooker, but except of the south facing reflector other reflectors will not be able to reflect radiation properly to the inside of the cooker box except the noon time .This is due to the fact that either effective area of the reflecting surface of the reflectors exposed to the sun will be very less than its actual area or major portion of the reflection from the reflectors will not fall on the cooker inside
Raw Materials Required
For Fabrication
G.I.sheet, Aluminium sheet, M.S. Channels , Glass , Mirror ,Asbestos fiber Sheet, Glass wool, Caster wheel, Black board paint, Hinge , lock , Screws and other miscellaneous items .
Details of Machinery and Equipment Required For Fabrication
Hand saw, Hand shear, Portable drilling machine, Hammer, Screwdriver, Pliers, Measuring tape Painting brush etc.
Cost
Approximately Rs.2000 per cooker, including materials, cost of fabrication etc. In fact the cost is expected to be less to some extent if a number of cookers fabricated at a time.
Specifications of the Cooker
Cover Plate
Number of glazings: Two
Material: Plain glass
Spacing between two glazings:
20mm
Glass thickness: Inner: 3mm
& outer - 4mm
General appearance of glazing:
Free from bubbles/ rough surfaces
Aperture area: 184800 sq.mm
Additional Design
Feature--Provision or keeping cover plate in inclined position (opened -Position)
with respect to its closing position by use of hinge.
Inner Box
Material: Aluminum Sheet
Thickness of Sheet: 0.5mm
Size: Length=840mm, Width=220mm,
depth=220mm
Thickness of wall: 0.5mm
Paint on Inner Surface: Mat black
finish by black board paint
Suspended Cooking Trays
Material: Aluminium
Size: 170mm x 155mm
Thickness of Sheet: 0.5mm
Paint on Inner Surface: Mat black
finish by black board paint
Length of M.S strips (for
suspension of the trays): 90mm
Depth of hinge (for suspension of
trays) from inner box top: 65mm.
Cooking Pot with Lid
Material: Aluminium
Thickness: 0.5mm
Number: Four
Diameter: 150mm
Depth: 90mm
Total capacity of the pots: 5
Liters (1.25 liters x 4)
Cooker Box (Outer)
Material: G.I. Sheet
Thickness: 1mm
Size: Length=940mm, Width=320mm,
Height=295mm
General Finish: Smooth, Free from
sharp edges
Gasket and Insulation
Gasket Material: Compressed
asbestos fiber
Thickness: 2mm
Insulation Material: Glass Wool
Pad (insulation) thickness:
Side=50mm, Bottom=50mm
Reflecting Mirror
Number of reflector: Two
General Appearance: Free from
bubbles /waviness
Thickness: 4mm
Size: Length=840, Width=220mm
Additional design Feature: Provision
for keeping the mirror in inclined position (working position) with respect to
its folding position (when not in use)
Caster Wheel
Number- Four
Construction- Nylon Ball
Test Result
Routine Test:
i) Inner box leakage test (by filling water, then joints are examined): No sign of leakage
ii) Cover gasket leakage test ( By inserting pieces of papers in four positions in each side of the cooker below the cover plate, after properly tightening the cover plate, the paper pieces should exhibit a firm resistance at the time of withdrawal by hand ): No sign of leakage
iii) Leakage test of upper side of cover plate (by pouring a thin film water on the cover plate and then by examine the cover plate for any sign of water entry between the glass sheets ): No sign of leakage
iv) Leakage test of lower side of cover plate (after boiling of water in cooking pots by solar heating and then by keeping the cooker in shaded location to allow the vapour to condense, there should be no sign of vapour entry between inner and outer glass sheets of the cover plate): No sign of leakage.
V) Temperature test for paint on inner box, cooking tray and cooking pots at 160 degree Celsius for one hour and temperature tests of cover gasket, cover glass and insulation at 200 degree Celsius in electric oven: No sign of damage or crack
Performance Test of Proposed Cooker:
1. Test timing and date- 03-03-2003, from 10 am to 12-30 pm
Ambient temperature- 21degree Celsius
Intensity of solar radiation during test period: 0.55kw/sqmt/per hour
Peak temperature of the top cover of empty cooking pots 148 deg Celsius
2. Test timing and date- 04-03-2003, from 10.30 am to 12-15 pm
Time taken for boiling of 4 liters of water in cooking pots (1 liter in each pot) 105 minutes.
Inlet water temperature- 22 degree Celsius
Comparative performance of proposed cooker by placing it horizontally and only with one reflector facing sun (i.e., by converting of proposed cooker similar to conventional box type cooker):
1. Test timing and date- 05-03-2003, From 11 a.m to 1.00 pm
Ambient temperature 23 degrees Celsius
Intensity of solar radiation during test: 0.56kw per/sq.mt./per hr.
Peak temperature of the top cover of empty cooking pots: 123 degree Celsius
2. Test timing and date- 07-03-2003, from 10 am to 12.15 pm
Inlet water temperature- 22 degree Celsius
Time taken for boiling of 4 liters of water in cooking pots (1 liter in each pot): 120 minutes
Conclusion
Detailed constructional methodology along with some cost and performance figures are narrated in developing the presently proposed solar cooker. Improved performance over a conventional box type solar cooker is the main feature of this cooker.
The cooker, presently fabricated can able to cook 2 Kg rice or equivalent food item at a time within two hours cooking is possible in between 9am to 3 pm.