I am going to perform an experiment which will aid Virgin Trains in looking for the supreme hot drinks cup to be used in their buffet bars. The design must keep the drink as hot as possible for as long as possible. I will be investigating what affects the rate of which liquids in cups cool down. Factors to be taken into account are;
Convection is a mode of heat transfer through gases and in this case, liquids. Convection depends on the fact that fluids expand when heated and undertake a decrease in density. As a result, the warmer, less dense portion of the fluid will rise through the surrounding cooler fluid in accordance to Archimedes Principle. If heat continues to be supplied, the cooler fluid that flows in to replace the rising warmer fluid will become heated and also rise. This causes a current, known as a convection current, to become established in the fluid, with warmer, less dense fluid continually rising from the point of heat, and cooler, denser portions of the fluid flowing outward and downward to replace the warmer fluid. Because of this, heat may eventually be transferred throughout the entire liquid and heat may be lost through convection of the heat into the air. To stop this we could use a lid so the heat could not be released into the air.
Heat could be lost through radiation. Heat travels as waves in space, this is known as radiation. Hotter objects radiate more heat than cooler ones and black surfaces absorb and give out heat well. Because of this we will not be using a black cup as it clearly would have a large heat loss due to radiation. A shiny surface would be ideal to reflect radiation. Because of this we will also test the cups with a coating of tin foil. This will effect the results. A dark colour cup will absorb heat so I predict the brown cup will not be efficient.
Conduction is the transfer of heat or electricity through a substance resulting from a difference in temperature in different parts of the substance. Since heat is energy which is associated with the motions of the particles making up the substance, it is transferred by the motions, moving from regions of higher temperature, where the particles are more energetic, to regions of lower temperature. The rate of heat flow between two regions is relative to the temperature difference between them and the heat conductivity of the substance. Insulation can be used to stop conduction. Because of this I predict the polythene cup will be the superior cup.
I will be investigating the factor of radiation by testing the overall cup that sustains a higher temperature for longer once without a tin foil covering and once with. I will also be investigating convection by performing the cup with and without a lid. I will be checking the temperature of the water every minute for fifteen minutes. The cups I will be using are; Blue plastic cup, White plastic cup, Polythene cup, Vitamax cardboard cup, and a brown plastic cup. I predict the polythene with silver foil will keep the liquid hotter than the others. This is because I believe a lot of heat will be lost through radiation so the foil will stop this and the polythene cup has the best insulation. To make this experiment a fair test I shall be using 100ml of water each time. The equipment I will need is; the cups themselves, kettle, thermometer, tin foil.