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Prototyping of the Improved Cook-Stove and Solar Heater designed by Appropriate Technology Asia

 

Background
Ladhak, a cold desert in northern India in the Himalayan range, experiences extreme cold conditions for over 8 months in a year. To survive these conditions, room heating is an essential requirement. Few heater and stoves are locally available in the area but are not efficiently designed. Appropriate Technology Asia (ATA) designed solar heater and cook-stoves based on available material, to be manufactured in Ladhak. The prototyping of the solar heater and cook-stoves has been carried out by Research and Development team of Development Alternatives with emphasis on an efficient production system. In the first phase, based on the design of the Appropriate Technology Asia (ATA), Development Alternatives has developed the following two products

1. Solar Hot Water System
2. Improved Cook-stove

The main stages of product research and development are explained below:

1. SOLAR HOT WATER SYSTEM
The Solar Hot Water System is a device in which solar energy is used for heating water. The device has a ferro-cement parabolic dish of diameter 1430mm and thickness 25 mm in which the inner part is lined by mirror to converge the reflected rays of sun. An armature has been designed on which the ferro-cement parabolic dish is positioned to converge the reflected sunlight at the focal point of the inner parabolic curvature. The container for heating water will be positioned at the focal point

The parts of the Solar Hot Water System are as follows;

@ Dish
@ Armature
@ Stand
@ Ring

Activity undertaken
Dish
During the development process of the Dish the steps adopted are as follows:

Step1 : Drawn the given curvature on a paper to use as a template.

Step2 : Designed the tool for the production of both the mould and product

Step3 : Rolled the flats based on the template one for the mould and the other for the product which is 25 mm offset of the mould

Step4 : Developed the tool with the frame stand

Step5 : Marked the foundation by positioning the tool for manufacturing of the mould

Step6 : Dig the holes, positioned the reinforcement and foundation bolts and cast with cement mix

Step7 : Bolted the frame of the tool with the foundation

Step8 : Drawn the axes and the circle

Step9 : Positioned brick blocks and filled the parabolic dome with cement, sand and aggregate with the help of the tool with moulds profile

Step10: Chasing the edge of the mould for the de-moulding the cast dish

Step11: Plastered with P.O.P for the smooth surface of the mould

Step12: Knitted the reinforcement of the Dish and welded the square bar for positioning the reinforcement at the centre of the thickness of the dish

Step13: Filled the de-moulding gap with clay

Step14: Cast the dish with cement-sand mix with the help of the tool with products profile leaving a 3" diameter hole at the top

Step15: De-moulded the dish after 24hrs.

Step16: Cured for 2days with normal wet sack

Step17: Covered with plastic sheet and kept the dish up side down by filling with water for self curing.

Step18: Designed and developed a gauge for cutting the mirror section for glueing on the inner surface of the dish

Step19: Glued the mirror sections of 15 different sections at a row and about 43 rows in a concentric manner on the inner surface of the dish

Step20: Cleaned the face of the mirror sections

Armature and Stand
During the development process of the Armature the steps adopted are as follows:

Step1 : Parted off the pipe, angle, flat and round sections as per given design

Step2 : Marking and drilled the holes

Step3 : Rolled the flats into bent section and welded

Step4 : Welded a round bar on a 200kg plate for inserting the pipe stand for the Base

Step5 : Fixing the Chain

Ring
During the development process of the Ring the steps adopted are as follows:

Step1 : Parted off the round bars as per design

Step2 : Rolled the bars as per required parameters

Step3 : Welded the three rolled rings and the other round bars at the outside surface of the dish at the projected square rods

Assembly
Step1 :
Fixed the Chain

Step2 : Positioned the dish by measuring the focal point through visual checking

Step3 : Cleaned the face of the mirrors

Step4 : Tested

Observation and Trial
Comparison data of heating between ATA’s designed Solar Hot Water System and TARA Solar Cooker which was done at same time and heating same quantity of water on symmetric vessels are given below:

Test No: 1
Date: 02.02.04
Quantity of Water: 4 lits
Atmospheric temperature: 200C

S.NO TIME TEMPRATURE of WATER
    TARA Solar Cooker ATA’s Solar Hot Water System
1. 11:55 220C 220C
2. 12:05 340C 340C
3. 12:15 440C 380C
4. 12:25 540C 440C
5. 12:35 620C 480C
6. 12:45 660C 500C
7. 12:55 720C 540C
8. 14:15 880C 680C
9. 14:30 900C 680C

Test No: 2
Date: 03.02.04s
Quantity of Water: 4 lits
Atmospheric temperature: 260C

S.NO TIME TEMPRATURE of WATER
    TARA Solar Cooker ATA’s Solar Hot Water System
1. 11:05 220C 220C
2. 11:15 320C 280C
3. 11:25 400C 340C
4. 11:35 480C 400C
5. 11:45 540C 460C
6. 11:55 600C 500C
7. 12:05 660C 550C
8. 12:15 700C 580C

Test No: 3
Dated: 03.02.04s
Quantity of Milk: 1 lit
Quantity of Rice: 0.3Kg
Atmospheric temperature: 190C
Cooked dish: Rice pudding in 1.55hrs (11:05 -13.00) which was well cooked


The test report shows that the performance of TARA Solar Cooker is better than ATA’s Solar Hot Water System whereas theoretically ATA’s Solar Hot Water System should have better performance. Theoretically the amount of sunlight concentrated at the focal point of ATA’s Solar Hot Water System is more than the TARA Solar Cooker because the diameter of the dish of ATA’s Solar Hot Water System is 1430mm whereas the diameter of TARA Solar Cooker is 1380mm. The difference in heating efficiency is due to the following:

           1. The armature obstructs a good amount of reflected light in ATA’s Solar Hot Water System

           2. In ATA’s Solar Hot Water System, 20% surface of the container gets heated whereas in the TARA Solar Cooker ,   57.2% surface of the container gets heated.

Recommendation
On the basis of the tests explained above there is a need to redesign the armature and also the profile so that more reflected light can be projected on the heating container.
During the knitting of the reinforcement wires there is a need to develop a simple fixture to knit the reinforcement wires otherwise poor knitted reinforcement wires will create problem for the rotating profile making tool during casting of the dish.

2. IMPROVED COOK-STOVE -2
The Improved Cook-stove 2 is one of the two cook stoves designed by ATA which is made up of 18SWG metallic mild steel sheet. It has three openings for cooking and one for the outlet of burnt gas of the fuel inside the cook-stove through chimney. The Improved Cook-stove 2 is positioned on a MS angled metallic frame which has oven space inside it with a fuel feeding door and a air sliding system for the regulating the air inside the cook-stove.

Followings are the parts of the Improved Cook-stove 2 is as follows;

@ Frame
@ Stove Body
@ Stove Top
@ Doors
@ Air-slide
@ Steel Mesh

Activity undertaken
The list of activities undertaken during the development of the Improved Cook-stove 2 is described below:

Frame
During the development process of the Frame 1 (as per given design) the steps adopted are as follows:
Step1 : Parted off the MS Angle section 25x25x3mm as per given design

Step2 : Removed the Burrs

Step3 : Welded the frame as per given design

Step4 : Grinded the welding portion and removed the burrs

After the development of the stove body from paper we found the stove body was not fitted. Based on that feed-back we have redesigned the frame and also made in such a way which can easily be bolted in place of welding the complete frame. The steps for the development of Frame 2 are as follows:

Step1 : Parted off the MS Angle section 25x25x3mm as per the design emerged from the feed-back

Step2 : Removed the Burrs

Step3 : Sheared the part by chisel for bending

Step4 : Designed and developed bending tools for the bending of the edges of the required angle parts

Step5 : Marked and drilled the holes for bolting or riveting

Step6 : Removed the Burrs

Step7 : Assembled the frame by bolting

Stove Body
During the development process of the Stove body the steps adopted are as follows:

Step1 : Marked the Stove carcass layout (both the firm and dotted lines)on a 1mm MS sheet

Step2 : Chiseled out the required sheet to make a template

Step3 : Marked the layout (both the firm and dotted lines)on a paper based on the template

Step4 : Cut the required portion

Step5 : Fold the paper sheet as per the dotted lines

Step6 : Glued where required

After the development of the stove model on paper we have figured out that the small modification is required at the point marked in the drawing enclosed

Step7 : Marked the Stove carcass layout (both the firm and dotted lines)on a 1.2mm (18SWG) MS sheet

Step8 : Chiseled out the required area from the sheet

Step9 : Removed the burrs

Step10: Folded the cut sheet as per the dotted lines

Step11: Spot welded at required position

Step12: Marked and cut the corner insert

Step13: Welded inside the stove body where it required

Step14: Marked and gas cut the baffle from the 6mm MS sheet

Step15: Removed the burrs of the baffle

Step16: Drilled the holes and bent as required on baffle

Step17: Assembled the body, baffle and frame

Stove Top
During the development process of the Stove top the steps adopted are as follows:

Step1 : Marked and gas cut the Stove Top from the 6mm MS sheet

Step2 : Removed the burrs

Step3 : Marked and chiseled the Top rim and chimney ring from the 1.2mm MS sheet of width 50mm

Step4 : Folded the cut sheet as per the dotted lines

Step5 : Positioned the rim on the top plate, drilled and riveted

Step6 : Removed the burrs

Step7 : Assembled with the body

Drawer

During the development process of the Drawer the steps adopted are as follows:

Step1 : Marked and chiseled the layout of drawer from the 1.2mm MS sheet

Step2 : Removed the burrs

Step3 : Folded the cut sheet as per the dotted lines

Doors
During the development process of the Doors the steps adopted are as follows:

Step1 : Marked and chiseled the layout of Doors and locks from the 1.2mm MS sheet

Step2 : Removed the burrs

Step3 : Marked and drilled holes on the doors sheets

Step4 : Welded hinges with the doors and the stove body

Step5 : Bent the locking devices

Step6 : Bolted and assembled the doors with locking arrangements

Air-slide
During the development process of the Air-slide the steps adopted are as follows:

Step1 : Designed and developed a die punch arrangement for the Air slide mechanism

Step2 : Marked and chiseled the layout of Air Slide and locks from the 1.2mm MS sheet

Step3 : Removed the burrs

Step4 : Pressed the sheet for the channel and the door

Step5 : Removed the burrs

Step6 : Welded the attachment with the Stove Body

Step7 : Removed the burrs

Steel Mesh
During the development process of the Steel Mesh the steps adopted are as follows:

Step1 : Marked and chiseled the layout of Steel Mesh

Step2 : Positioned it inside the stove

Thus the Improved cook stove is completely assembled and ready for testing.

Observation and Trial
Efficiency testing of improved cook stove 2

Test -1
Room temperature  18˚c
Initial temperature of water  19˚c
Boiling temperature of water  99˚c
Weight of fuel taken  3.0 Kg.
Weight of fuel burn  2.8 Kg.
Weights of char remain  0.132 Kg.
Volume of water  6.0 liter
Volume of water after evaporation  5.8 liter
Calorific value of fuel used  4562 Kcal/Kg.
Starting time of the experiment  4.30 PM
Time when temperature reached 99˚c  4.22 PM
Weight of fuel unburned  0.18 Kg.
Time of experiment  1-Hour

% Efficiency = (Heat out-put / Heat in-put) x 100
Heat Out-put = A + B

Where
A=Sensible Heat and
B= latent Heat

Sensible Heat = 

(Boiling temperature of water-Initial temperature of water) x initial volume of water
=  (99˚c - 19˚c) x 6.0
= 80 x 6.0
= 480 Kcal

Latent Heat =

(Initial volume of water – final volume of water)s x 540
= (6.0 – 5.8) x 540
= 0.2 x 540
=  108 Kcal
Heat Out-put =  480+108
=  588 Kcal
Heat in-put = C - D
Where C = Heat value of fuel
= Fuel Burn x Calorific value of fuel
=  2.8 x 4562
= 12773.6 kcal
D =  Heat value of char
= Quantity of char x calorific value of char
= 0.140 x 7100
=  994 Kca
Heat In-put = 12773.6-994
= 11779.6 Kcal
Efficiency= (Heat out-put / Heat in-put) x 100
= (588/11779.6) x 100
= 4.99%
= 5.00%

  

Test -2
Room temperature 14˚c
Initial temperature of water 15˚c
Boiling temperature of water 99˚c
Weight of fuel taken 4.0 Kg
Weight of fuel burn 3.09 Kg
Weights of char remain 0.110 Kg.
Volume of water 6.0 liter
Volume of water after evaporation 5.7 liter
Calorific value of fuel used 4562 Kcal/Kg.
Starting time of the experiment 9.30 AM
Time when temperature reached 99˚c 10.20 AM
Weight of fuel unburned 0.910 Kg.
Time of experiment 1-Hour

% Efficiency = (Heat out-put / Heat in-put) x 100
Heat Out-put = A + B

Where
A=Sensible Heat and
B= latent Heat

Sensible Heat = (Boiling temperature of water-Initial temperature of water) x initial volume of water
= (99˚c - 15˚c) x 6.0
= 84 x 6.0
= 504 Kcal
Latent Heat (Initial volume of water – final volume of water) x 540
= (6.0 – 5.7) x 540
=  0.3 x 540
=  162 Kcal
Heat Out-put= 504 + 162
=  666 Kcal
Heat in-put=  C - D
Where C= Heat value of fuel
= Fuel Burn x Calorific value of fuel
= 3.09 x 4562
= 14096.5 kcal
D=  Heat value of char
=  Quantity of char x calorific value of char
= 0.110 x 7100
= 781Kcal
Heat In-put= 14096.5-781
= 13315.5 Kcal
Efficiency = (Heat out-put / Heat in-put) x 100
=
=
(666 /13315.5) x 100
5.00%
Recommendation
The test result shows that efficiency of the Improved Cook-stove2 is only 5%, which means that the 95% of heat is used in room heating or is lost through chimney. Therefore, the device is a good room heater but not a good cook-stove. To increase the efficiency of cook-stove there is need for an insulating surface beside the fire and decrease the distance between the fire and heating container. The insulating surface can be created by developing a layer of a perforated sheet beside the firing zone by which heat loss can be reduced.
During the development of the Improved Cook-stove2, the bending of the sheet at the zone A in the drawing is very complicated. To simplifies the process stove body should be manufactured in three different parts and assembled either by welding or riveting.
 

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