If a liquid evaporates in a closed vessel (if a lid was placed over it), the space above the liquid would quickly become filled with vapour. But evaporation would be balanced by the opposite process, condensation. This way no heat would escape.
In non-metals conduction occurs when heated atoms vibrate and pass energy on to each other. The energy is passed through the substance. This is one way the liquid could lose heat, because the non-metal cup and insulation would absorb some of the thermal energy, taking some of it away from the liquid.
Heat will also escape by radiation. This is the transfer of energy by electromagnetic waves. Energy will leave the cup and spread out around it meaning the fluid will have less thermal energy.
If insulation is put round the cup this will reduce heat loss. Because the cup and the insulation will be non-metal, the energy will be transferred through them by hot particles vibrating. If more insulation is added then the vibrations will have further to travel. This will result in less energy reaching the end of the insulation to convect through the air. This means less energy will be dispersed. If the insulation is made of ‘bubble-wrap’, which mine will be, then it will be a better insulator. This is because the trapped air inside the ‘bubbles’ stops convection currents and is a very good insulator.
I will use equipment that is suitable to make the most accurate measurements and that will give me the best results.
I did some preliminary experiments to decide on what equipment to use and how to carry out my experiment:
Amount of Water –
To decide how much water to use (for the liquid in the cup) I did some tests and I found that 50ml of water would be too small a quantity as the thermometer did not fit well into it. If not much of the thermometer is in the liquid then the temperature readings will be less accurate. I decided 150ml would be better suited to the experiment and would mean the thermometer would give a more accurate reading.
Lid –
Using or not using a lid will play a big part in my planning. If a lid is used this will severely reduce heat loss as convection will not be able to happen. Also evaporated water will just fall back into the liquid. If a lid is not used then a lot of heat will be convected through the air and hot water will evaporate and rise out of the cup. I conducted an experiment to see if I should use a lid or not.
From these preliminary results I can see that too much heat is lost if a lid is not used. Because so much heat is lost it would mean that the amount of insulation used would not make much difference to the finish temperature of the liquid. Therefore I have decided to use a lid, as then I will know that nearly all of the heat lost will be lost through the insulation. The measurements I take for heat loss through different thicknesses of insulation will then be more accurate.
Thickness –
After conducting a few tests I found that increasing the thickness by one layer each time did not result in a significant decrease in amount of heat lost each time. This is why I have decided to increase the insulation by two layers each time. Any more than that and too many layers would be added to the cup, consequently the results would not be as good as not much thermal energy would get through the insulation. I will go from 0 to 10 layers in steps of two.
Start Temperature –
To find a good start temperature that would give quite a big change in temperature after a certain amount of time I did an experiment, here are my results:
From these results I can see that 90oC would be a better temperature to start at rather than 70oC. This is because there is a larger temperature difference between the start and finish temperatures at 90oC. This means it will be easier to see the difference in temperature when I start adding more insulation layers. One problem though is that 90oC is hard to get as after the water has been poured out it cools too quickly and I cannot get set up quick enough. This is why I have decided to use 85oC as my start temperature. I can get set up before the temperature gets to 85oC and also the liquid will not be cooling down as quickly.
Cooling Time –
I have found that 5 minutes would be the optimum time. After this the temperature starts to decrease too slowly and any noticeable change is minimal.
I will be using a 150ml beaker for a cup. I am using this size because there is plenty of surface area for heat to possibly escape and also it will be easier to put insulation around it. I will need two beakers as I will do each thickness of insulation twice, at the same time.
I will also need two thermometers, one for each beaker, to measure the temperatures accurately. I will then know the start temperature and the final temperature after 5 minutes.
The insulation I will be using is ‘bubble wrap’. I will need 22 sheets of this to use as insulation round the beaker and also 1 sheet for the lid on each beaker.
I will need a kettle to boil my water, ready to place in the beakers and start the experiment at 85oC.
I will also need 6 rubber bands to secure the insulation and the lids in place.
In my investigation I will be measuring how quickly a beaker of water cools down when it has different thickness’ of insulation. I will have six different thickness’ of insulation (in layers of two): 0,2,4,6,8 and 10. I will perform two experiments for each thickness, this way my results will be more accurate because I will be able to take an average.
I will record the start temperature and the finish temperature after 5 minutes. I will then work out the difference between them.
The variable in my investigation is the amount of layers insulating the beaker. I will not change anything else that I tested in my preliminary experiments.
I cannot control the temperature of the room but hopefully it will stay the same throughout my investigation. If the temperature does change it will only be minimal.
Firstly I will wrap the appropriate amount of insulation around the two beakers and secure it with two rubber bands. I will then pour in excess of 300ml of water into the kettle and turn it on. Once it has boiled I will immediately pour 150ml of water into each beaker and quickly place a thermometer in each. Then I will fasten the two lids in place with a rubber band and wait until the temperature of the water reaches 85oC. When it does I will start the stop clock.
After 5 minutes the experiment will be over. I will record the final temperature of the water and then work out the temperature difference between it and 85oC.
When I have completed one experiment I will move onto the next.
- Diagram
Water Thermometer
Insulation Lid
Beaker
Stop Clock
By doing the same experiment twice I am making my results more reliable. I will also be able to spot if there are any anomalous ones and if there are any tests I need to repeat because, for an unknown reason, they have not worked.
I will do everything the same for each of the experiments to make sure it is a fair test. The only thing I will be changing is the amount of insulation.
The equipment I have chosen is to give me the most accurate results and that is what I want to achieve.
To prevent any boiling water splashing in my face I will wear protective goggles.
I have now completed the experiments and I have put my results into a table:
Line of best fit
I do not think I will have to repeat any of my experiments as they all appear to follow a trend, although at 8 and 10 layers I have the same result. This could be because after 8 layers there is no difference in the temperature decrease no matter how much insulation is applied. It could also be because a mistake was made but looking at the results previous to it it seems to follow a pattern. I would say the predicted reading would be about 4.5oC or 5oC so 5.5oC is not too far out.
From my results I can see that as the amount of insulation increases the temperature decrease of the water after 5 minutes becomes less great. At 0 layers there was a 17.5oC decrease in temperature but when 10 layers were added there was only a 5.5oC decrease. This shows that the amount of insulation does have an effect on the temperature of the liquid it is surrounding.
My graph shows that as more layers are added the temperature decrease does not change as much. To start with there is quite a sharp decline in the temperature decrease of the liquid as layers of insulation start to be added, but gradually it starts to slow down and the difference between the temperature decrease at each 2 layers is not as much.
There is an obvious pattern to my results; as the amount of insulation increases, the temperature decrease (in 5 minutes) lessens. The line of best fit is not a straight line it is curved. This is because as the amount of insulation is increased (by 2 layers) the ‘temperature decrease’ does not go down as sharply and eventually it will appear to be almost a straight line.
My results match my prediction and the scientific reason behind them. There is a trend and it is easy to calculate a line of best fit.
My liquid lost heat because of conduction, convection, radiation and evaporation. First of all the heated molecules in the water become energised and move around quickly, they escape past the surface of the water and evaporate into the air above. Once there the heated air causes a convection current in the sealed container. This spreads the heat around the container. Heat is then conducted through the edge of the container and it makes its way through the insulation. The insulation I used stops convection currents therefore it reduces heat loss. Despite this heat still passes through by conduction until it reaches the air and is convected away. Heat is also given-off by electromagnetic radiation waves which are dispersed into the atmosphere. There is a trend in my results because as more insulation is added less and less heat energy passes out through the insulation, instead it stays within the container or around the cup in the insulation. The more insulation the less heat energy escapes.
The line of best fit on my predicted graph does not match the actual one in my results. This is because I did not predict that the temperature difference would go down by less each time. I thought that there would be a steady decrease but what actually happened was the gradient became less steep every recording. By the last experiment the line is nearly horizontal. This tells me that as more insulation is used the difference in the temperature decreases is more minimal.
I think I did do the right number of experiments for there to be an accurate result; not too many unnecessary ones. Overall I believe I did perform a safe, well planned, precise and conclusive investigation into how the quantity of insulation affects the time it takes for a drink to cool down.
Overall I think my results are reliable. None of them are anomalous and they all follow a trend. They follow my prediction and scientific reasoning. If there were a number of anomalous results then I would question their reliability but as there are not I know that they are reliable. They follow the line of best fit very well, slightly better than I had predicted.
Because both of my two experiments, for each thickness of insulation, got about the same recordings this suggests to me that they are accurate and reliable and there will be no need to repeat any of them.
If I were performing my investigation again on another occasion I would complete three experiments at each amount of insulation. This would mean my results would be more accurate and it would be easier to spot if I had made an error in the practical stage. Also my average would be better because I would have three recordings instead of two. When I was performing my experiments I did not have time to do three. An additional way to improve my experiments would be to use a more accurate temperature-measuring device. This would mean that the recordings would be more accurate. This option was not available to me and at the time I could only use thermometers that only measure in 1oC scales.
As a related investigation I could do the same thing as this investigation but see how not using a lid affects it. I would still change the amount of insulation round the beaker. I could see if the results of that were similar to the results I have for this investigation. I could also change the type of insulation I use. I could experiment with different types and see which style is best at preventing heat loss. Some types will be made of a material that is better at stopping energised particles from passing on their energy. Another possible investigation to perform would be to use a different amount of water. I could monitor whether more water would decrease the rate of thermal energy being lost or vice-versa.
