Introduction

People use solar cookers primarily to cook food and pasteurize water,

although additional uses are continually being developed.

Numerous factors including access to materials, availability of

traditional cooking fuels, climate, food preferences, cultural factors, and technical capabilities affect

people's approaches to solar cooking.

Materials and tools

We use materials available in daily life. These include corrugated cardboard boxes, black paper, aluminum foil, plastic sheets, plastic canister etc.We also use the following tools:white glue, double-sided adhesive tape, transparent adhesive tape, scissors, cutter, ruler, magic marker etc

Our solar cooker is similar to the solar cooker in this picture. In order to absorb more sunlight we fix six collectors  to collect more sunlight. This is the design of our solar cooker.                                 

Design and construction skills

Design and construction skillsThe more directly the glass faces the sun, the greater the solar heat gained. Although the glass is the same size for box 1 and box 2, more sunlight shines through the glass on box 2 because it faces the sun more directly. Note that box 2 also has more area for heat loss.

Design and construction skills

Single or multiple reflectors bounce additional sunlight through the glass and onto the solar box. This additional input of solar energy results in higher cooker temperature.

Design and construction skills

Solar cooker facing the sun at noon should be longer in the east/west dimension to make better use of the reflector over a cooking period of several hours. As the sun travels across the sky, this configuration results in a more consistent cooking temperature. With square cookers or ones having the longest dimension to the north/south, a greater percentage of the early morning and late Afternoon sunlight is reflected from the reflector to the ground, missing the box collection area.

Application of physics principles

in the designGreenhouse effect results in the heating of enclosed

spaces into which the sun shines through a transparent material such as glass or plastic.

The light energy that is absorbed by dark pot underneath the pot is converted into longer wavelength heat energy and re-radiates from the interior materials. Most of this radiant energy, because it is of a longer wavelength, cannot pass through the

glass and is therefore trapped within the enclosed space.

Application of physics principles in the design

ConductionConduction is the process of heat flow from regions of higher temperatures to regions of lower temperatures through a medium. But conduction is not efficient in insulator, so we can use the insulating material such as :plastic and glass to trap heat inside the solar cooker and heat energy cannot lose by conduction to the air easily.

Application of physics principles in the design

ConvectionHeat can be transferred in a fluid by convection in which the heated fluid expands, rises and is replaced by the surrounding fluid. So we should use something covering it up, having the hot air trapped inside the solar cooker to keep the temperature steady. Thus we use glass to cover

it up.

Application of physics principles in the

design Radiation

Energy is gained on absorbing infra-red radiation. Dull black surfaces are good absorbers and good radiators of radiation. Silvery surfaces are poor absorbers and poor radiators of heat. So we cover the outside with black paper and use silvery paper inside.

Test of solar cooker-First Time

Time/min.

0 5 10

15

25

30

35

40

45

50

55

60

Temp/oC

25

27

28

29

34

35

37

37

39

40

43

45

Test of solar cooker-Second Time

Time/min.

0 5 10 15 20 25 30 35

Temp./oC

20 21 21 21.5

22 22 23 24

Time/min.

40 45 50 55 60 65 70 75

Temp./oC

25 25.5 26 26 27.5

28.5

29 29.5

Test of the solar cooker – Third Time

Time/min.

0 5 10 15 20 25 30 35

Temp./oC

19 21 22 22 23 23.5

24 24

Time/min.

40 45 50 55 60 65 70

Temp./oC

25 26 28 29 31 31.5

32

Discussion

We have read a lot of books and search for information in the internet. Each of us

brings up different opinion. Actually there are lots of ways to make the solar

cooker.We look for all sample we think that is good. But Our solar cooker have a big

defect. The collector we used is difficult to absorb sunlight in the evening. It is only

suitable for use when the light shines on top of our solar cooker.

ConclusionWe thought that this project is very

interesting but our solar cooker is not so good, If we can do it again we think we must do it better.We think we have learned a lot of things about the solar energy through this project. We also used amount less than $30 to do this project. This project is good for students!

Group leader:Lau Chun Kin 4D (29)Group member:Cheung Wai Pan 4D(21) Choi Chi Hoi 4D (23) Chu Wa Hung 4D (25) Wong Kam Hong 4D

(39)

The End

Thank you very much!