Physics Project

TRANSFER OF THERMAL ENERGY 
SEPTEMBER HOLIDAY PROJECT

Group: Christine Saw (9), Jasmine Lim (19), Xu Yanling (38), Samantha Yip (40) 

Introduction
Ice kachang is a favourite local ice-cold dessert. It comprises different types of jelly, red beans, sweet corn, attap chee and is topped with shaved ice. Because it is made of majoritively shaved ice, when the temperature is past the melting point of 0 degrees celcius, it changes state and melts into liquid. As a result, by the time this savory dish is brought home, it would have melted completely. As such, our group has decided to come up with a design of a container using recycled materials to keep it from melting too quickly. Utilizing our knowledge on heat transfer, we have come up with a suitable design for such a container.

Discussion
Heat transfer takes place mainly by three processes – conduction, convection and radiation. 

Firstly, conduction is the transfer of heat energy through a material medium by the passing on of increasing atomic or molecular vibrations from a hot end to a cold end. Good conductors of heat allow heat to travel easily through them by thermal energy transfer and free electron diffusion. An example of which would be metals. Poor conductors of heat are those that do not allow heat to travel too easily through them, an example of which would be plastic. 

Secondly, convection is the transfer of heat energy by the bulk movement of fluid (gas/liquid) due to the changes in density. It does not occur in solids as particles cannot move far away from their fixed positions. 
Thirdly, radiation is the transfer of heat by emission and absorption of infra-red waves. It is dependent on three main factors: the colour and texture of the surface, surface temperature and surface area. A dull, black surface is a good emitter and absorber of infra-red radiation and vice versa for a shiny, white surface. A higher surface temperature would result in greater heat transfer and a larger surface area emits radiation at a higher rate.

In our experiment, we made use of a cardboard shoebox as our base, lined with a relatively thick layer of styrofoam inside of it. The inner styrofoam and outer cardboard of the box is then lined with aluminum foil. A cover, lined with aluminum, is also added to our container. These features are used to minimize convection, conduction and radiation that cause heat to be transferred to the ice kachang, causing it to melt.

Styrofoam – styrofoam is an extremely poor conductor of heat and hence would insulate the ice well, minimizing the conduction of heat from the surrounding air into the box. Its great distance between its particles and ability to trap air makes it an especially good insulator of heat. Furthermore it is white in colour, hence it is a poor emitter of radiant heat, minimizing  heat transfer to the ice.

Cardboard – cardboard is an additional layer and a poor conductor of heat and hence is a good material for added insulation, minimizing heat transfer to the ice kachang.

Aluminum foil – aluminum foil is silver, shiny and smooth and hence is an extremely poor absorber and emitter of radiant heat. The container is covered with aluminum foil and hence will absorb less heat and minimize the heat transfer into the box and hence, the ice kachang. The inside of the box is also lined with aluminum foil and hence will emit less radiant heat, preventing greater heat transfer to the ice kachang, which will cause it to melt faster. 

Cover lined with aluminum foil – The cover minimizes heat loss by convection and possible evaporation. As warm air rises and cool air sinks, the ice kachang which receives heat via conduction and radiation will melt and cause air around it heat up and expand. This reduced density allows the warmer air to rise and cooler, denser air from the surroundings to sink into the container to absorb heat and melt the ice. A convection current within the box is formed with the cover put in place, minimizing heat gain from the surroundings. The aluminum foil lining the top of the cover is smooth, shiny and silver and hence a poor emitter of radiant heat, reducing the heat transferred to the ice kachang, causing it to melt. 

In conclusion, we have created a container using recycled materials, in order to minimize the rate of heat transfer to the ice kachang. We have applied the principles of convection, conduction and radiation during the creation of the container so as to create a container that can effectively minimize the transfer of thermal energy (heat) to the ice kachang.