Download Done by: Terence Lee (27) - ScienceIMPORTANTRCYJTLCEC

Raffles Institution
Science Performance Task 2011
Done by: Terence Lee (27)
Chua E Cher (3)
Ryan Chua (4)
Class: 1H
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Methodology
Firstly, we placed an ice cube into containers of different materials. These materials are: plastic,
ceramic, and cardboard. Next, we let the ice melt for 30 minutes and see how much ice was left. The
results are shown in the table below. After plotting the results, we chose our materials, namely
cardboard and cork. Then, we took about 2 weeks to create the box. We obtained the cork by
purchase from an art store and we constructed the box. We split the components of the report into
equal portions to do and then we combined them. The report was finalized after compiling our
various works.
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Three Principles of Heat Transfer
Heat can be transferred by three methods: conduction, convections and radiation. These methods
affected our design of the prototype as we need to have our knowledge of heat transfer to put them
to practical use by creating a box that reduces transfer of thermal energy.
Conduction
Firstly, summaries of principles of conduction are: it is the transfer of thermal energy between
regions of matter due to a difference in temperature. Heat flows from a region of higher
temperature to a region of lower temperature and until reached equilibrium. On a particulate scale,
conduction occurs because vibrating atoms and molecules interact with neighbouring particles,
transferring some of their kinetic energy. Hence, heat is transferred as adjacent atoms vibrate
rapidly.
Convection
Secondly, we shall define and summarise the principles of convection. Convection is the transfer of
heat from one part of a fluid to another by the circulating movement of the fluid itself. Generally,
convection happens when liquid/air expand after being heated and becomes less dense, thus it will
rise up. Cold liquid/air is denser and will sink to replace the hot liquid/air.
Radiation
Lastly, we shall summarise the principal of radiation. Radiation is the transfer of heat through
electromagnetic waves and does not require a medium.
Reasons for Choosing This Design
Next we shall explain how these mechanisms affect our prototype. Considering the principles of
conduction, we decided to make a box with two layers of different materials and leaving a gap
between them. As conduction (as stated above) transfers by physical contact due to the fact that
particles transfer kinetic energy by interacting with neighbor particles, we decided to leave a gap so
as to prevent conduction of heat from the surrounding to the ice cube. The decrease in conduction
of heat happens because the gap created separates vibrating particles of the outer layer from the
inner layer, preventing them from interacting with one another. The prototype is also affected by
principles of convection. As stated above, convection happens when liquid/air expand after being
heated and becomes less dense, hence raising up. To reduce convection, we decided to place the
inner layer of the box closer to each other, so as to break the convection current flow and thus able
to reduce the transfer of heat by convection. We also decided to make outer layers of the box at
same thickness so as to allow equal amount of heat to enter and heat up the air equally. This is to
slow down the process of convection as there will be less difference in the density of the air.
Considering the principles of radiation, we decided to make the outer layer as shiny as possible. That
is because radiation as stated travels by electromagnetic waves and thus shiny surface can help to
reflect a lot of radiation from the surrounding, reducing heat gain by radiation.
Choice of Materials
Air
For the gap in the two layers, we decided to use air as it is poorest conductor of heat on earth beside
Silica Aerogel. The reason why it is a poor conductor is that it has low density due to the fact that it is
in gaseous state and thus the distance between the airs particles are large so conduction of heat is
reduced as particles have to collide randomly to transfer energy. The next reason is that it has higher
thermal resistance to heat and thus little heat is transferred through air. The last reason is that
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unlike metals, it does not have free electrons to transfer kinetic energy to particles. Due to the
above reasons, we choose air as one of the layer.
Cardboard
We chose corrugated cardboard for the inner layer due to its insulating properties. Corrugated
cardboard is a good insulator because of its double walls and its molecular makeup. Double walls are
used to insulate many things, such as refrigerators and coolers. Double walls work well as insulation
because air is trapped between the walls. The air trapped between the walls retains its temperature
for a long period and thus can keep the interior of the container either hot or cold. Since corrugated
cardboard is made up of two layers of paper with fluting in between, air is trapped within the
cardboard, thus providing good insulation, due to the properties of air as said above.
Cork
Our group chose cork as our main outer material because it is a poor medium for conduction of heat
and it can hold on to its free electrons to minimize transfer of heat as much as possible. Cork is also a
poor medium for convection as it is a solid which means that its particles are packed tightly together
so the principle of density does not work on it. However, as radiation, a method of heat transfer
does not require any medium including cork; cork is unable to prevent heat transfer from occurring.
Therefore, our group used a silver spray paint to coat on its outer layer to reduce radiation so as to
insulate the ice even further.
Table 1.1 Results of experiment with similarly-sized container of different materials.
Material chosen for experiment
Percentage of ice that melted after 35 min.
Time taken for ice to melt completely (min)
Plastic cup
20%
82
Ceramic Cup
Cork
Cardboard
70%
15%
30%
41
90
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BONUS QUESTION
Cork
Classified As: Miscellaneous Carbon Footprint: 1kg of Cork ≡ 0.19kg CO2e
The mass of the cork is approximately 50 grams, so it produces 0.0095kg of CO2e, or 9.5grams.
Cardboard, Recycled Classified As: Miscellaneous Carbon Footprint: 1kg of Cardboard, Recycled ≡
0.42kg CO2e
Corrugated cardboard 100 percent recycled
The mass of the corrugated cardboard is approximately 20 grams, so it produces 8.4 grams of CO2e.
Total: 17.9g
Yes, the carbon footprint of the materials affects our choice of materials. We decided to choose
materials that produced less carbon dioxide when they were manufactured so as to save Earth from
global warming. In this century, global warming is an important issue and we hope to cut down our
carbon emission and thus we decided to choose materials that produced less carbon dioxide.
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References
http://www.ehow.com/about_6469087_corrugated-cardboard-good-insulator_.html
http://furtech.typepad.com/furtech/2006/11/heat_loss_blizz.html
http://www.fao.org/docrep/006/Y5013E/y5013e08.htm
www.newton.dep.anl.gov/askasci/phy00/phy00781.htm
www.engineeringtoolbox.com/radiation-heat-transfer-d_431.html
www.engineeringtoolbox.com/convective-heat-transfer-d_430.html
http://www.vtaide.com/png/heat2.htm
http://wiki.answers.com/Q/Why_is_cork_a_good_insulator
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