What effect does the colour of a can have on its rate of heat loss.

Introduction

The aim of my investigation is to find out what effect the colour of a can has on its rate of heat loss and why it has certain effects. This means that I will also be focusing on how colour affects the rate of heat transfer in general. My experiments involve the temperature of hot water being recorded at chosen intervals in a steel can.

Heat transfer is a process in which energy in the form of heat is exchanged between materials that are at a different temperature. Heat is usually transferred by conduction, convection, and radiation. These different ways in which heat is transferred will affect the accuracy of my experiment. Conduction is where heat energy passes through the bottom of the can to the platform that the can is standing on. This happens when the particles of the can vibrate and make the particles next to them vibrate causing the heat to pass through the walls of the can and out to the surroundings. Materials that are good thermal conductors tend to be good electrical conductors; metals such as gold, silver and copper have high thermal conductivity's and will conduct heat readily. Materials such as glass have much smaller heat transfer values and are poor heat conductors.

All of these heat transfer processes can all happen simultaneously but it is likely that one will give superior heat exchange. Convection is where the cooler water particles sink down to the bottom and the warmer water particles float up to the top and the heat energy will evaporate out of the top. If a pan of water was being heated from below then the water particles at the bottom of the pan will become warm and therefore become less dense, they will begin to rise to the top of the pan. As the warmer water particles begin to rise, the cooler water particles at the top of the pan will sink to the bottom as they are less dense, once at the bottom of the pan they will start to be heated, and become less dense. This process will continue until the pan of water is at the same temperature. After the convection has taken place and all of the warm particles will rise to the top and evaporation could assist water and heat loss through steam. As the water evaporates it will take the heat away with it in the same way evaporating sweat cools down our bodies. When I use a lid this could slow down this process as the water vapour will not be able to escape into the air as quickly it would normally, keeping the heat in for longer. Radiation is when the warm water particles vibrate the water particles next to them. This will give them more energy and will make the water there warmer. The water particles at the top of the can will radiate the heat energy into the surrounding air. This will also happen in the opposite way, the cans will lose heat through the side to the surrounding by radiation. Most of the energy will be lost from the top because the hotter an object is the more steam it gives off in the form of heat and the cans are very hot so the open top leaves a clear path for a large amount of evaporation. For heat to radiate it does not need to be in contact with air particles or any matter. Heat can radiate for some thing to another body through a complete vacuum, this is how the sun heats up the earth. This process can also be called the Wave Motion. The amount of heat radiation that is absorbed or emitted depends on the texture and colour of the surface. Conduction and convection are totally unaffected by the colour or texture of surface.

Factors that will affect the experiment

There are many factors, which can affect my experiment. The factors are:

If a lid is used there will be a great difference in the speed of heat loss, this is because a large amount of heat would have escaped from the top of the can by evaporation. Therefore if I use a lid it will slow down these processes.

The material of the lid will make an enormous difference, if a lid is made of paper or card then its insulation properties will be at a minimum, on the other hand if the ...

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Factors that will affect the experiment

There are many factors, which can affect my experiment. The factors are:

The material of the lid will make an enormous difference, if a lid is made of paper or card then its insulation properties will be at a minimum, on the other hand if the material used for a lid is polystyrene or bubble wrap then the heat loss through the top of the can will slow down.

The higher the volume of water used, the lower the heat loss because when there is a high volume of water, the outside of the water will cool down, but the inside will stay warm.

If the can is insulated then it will stay warmer then if the can is not insulated. This is because the insulation will slow down the process of heat loss. If the can does not have insulation then the process will not slow down.

If different types of insulation are used, the quantity of heat loss will be affected. Materials of high insulation such as bubble wrap or cotton wool will not allow much heat to be transferred through; however materials of low insulation such as black card will let the heat pass through it quicker. Depending on how many times the material has been wrapped around the can will determine how fast the heat transfer is. If it has been wrapped around several times then the insulator will work better than if it has only been wrapped around only once.

The material of the can could change the rate of heat loss, if it is made from polystyrene it will not allow much heat to pass through it. If it is made of metal then it will allow more heat to pass through it.

Room temperature, if the temperature of the room is near the starting temperature of the water then heat process of heat loss will not be as fast. This is because if there is a bigger difference in temperature then the more heat will try to escape. Another factor related with temperature is the starting temperature; if it is high then more heat will try to escape.

This is a diagram of the main factors that will affect the accuracy my experiment:

The factor that I have chosen to explore is radiation because it is the only form of heat loss that is directly affected by the colour of the can. The amount of radiation that is absorbed and emitted is completely dependant on the colour and texture of the can. I will investigate this factor to find out which colour emits the least radiation and keeps the cans warmer.

Variables

The only variable in my experiment is the colour of the can, nothing else will change through out my experiments apart from the cans in the second experiment will have lids. I have added lids because the cans will lose most heat by convection through the top of the cans.

Invariables

To make this experiment a fair test I will have to keep the following factors the same:

The volume of water.
The starting temperature of water.
The material of can.
The type of can.
The type of paint.
The material of the lids.
Where the thermometer is placed in the water.

Prediction

Out of the three colours that I chose to investigate I think that silver will be the best at reducing the heat loss. I am predicting this because I think that the main cause of heat loss will be radiation and we know that silver is a poor emitter compared to a plain beaker or a black one. This is why most saucepans are silver because silver is a poor emitter compared to white and black and also silver is shiny which cuts down heat wasted by radiation. I have predicted this because I have observed the Leslie cube experiment and the matt black side emits the most radiation

By my prediction I also am suggesting that black will be the worst insulator, as it is a good emitter of radiation. I also think that with all three insulators the rate of heat loss will start of fast and over time will slow down.

Apparatus

I will need to gather the following apparatus before I can conduct my experiment:

Kettle

Safety goggles
Stop watch
Measuring cylinder
Thermometer
Three standard empty baked beans or food cans that are exactly the same in both capacity and size. All cans have to be painted a separate colour: Black, Silver and White using the same type of paint for each.
Three identical round corrugated card (cardboard) lids that are completely covered in foil and cover the cans entirely.

Method

Here is a simple explanation of what the experiment will involve:

The procedure to carry out the experiment starts with boiling some water in the kettle and when it is boiled carefully pouring it into a measuring cylinder at the volume that is about three quarters of the cans height. Next, pour the water into the cans and allow it to cool to the chosen starting temperature. Once it reaches the chosen starting of about temperature, start the stop watch and record the temperature at chosen intervals. Then, repeat this process for the next two containers keeping the volume of water the same. Finally, repeat the whole experiment one more time using identical cardboard lids that have been covered with silver foil.

Safety

Safety precautions are needed because I am dealing with hot water, which can cause serious injury. The following things need to be acknowledged in order to keep this experiment safe:

Always wear safety goggles in case of splashes.
Be careful not to knock whilst it contains hot water.
Be careful not to knock over other peoples cans.
Make sure care is taken when pouring hot water.
Do not run with the can of hot water.

This is a step by step listing of the exact method that I have followed, including all safety precautions:

1. Put on safety goggles.

2. Collect all the equipment that is needed as shown in apparatus list above.

3. Paint the three cans with their colours.

4. Boil kettle.

5. Pour chosen volume into measuring cylinder.

6. Pour this into one of the three cans.

7. Put the thermometer in the water.

8. Wait until the water cools down to 90oC.

9. Start stop watch.

10. Record the temperature every minute for 10 minutes.

11. Repeat procedure for the other two cans.

12. Repeat the whole of experiment using lids on the cans.

Diagram

Results

My starting temperatures differ by large amounts so I will not be able to conclude which one is the best insulator. I order to find out the best insulator, I will subtract the final from the starting temperature and I will write this in the differential row in the table of results.

I have adjusted my results by changing all of the starting temperatures to 60ºC and subtracting the difference of temperature in each interval. I will now be able to use these new results to draw my graphs with the following results:

Graphs

Analysis

From looking at my graph and results table I conclude that there is a change at the rate at which the heat transfers through the steel can. Altogether I tested 3 different colours and I discovered which colour has the best insulating property. In order from the best insulator to the worst:

Black can

Silver can

White can

My data analysis shows that the starting temperature in each can varied from 39Æc to 65Æc; this variation in temperature was due to the fact that we did not have access to a thermometer until a few minutes later, by which time the water in the can had cooled down. I have taken this into account by subtracting the final temperature from the starting temperature to show the difference in heat loss. My analysis shows that the white can with the lid on and the lid off lost the most heat. The black can is the best insulator of heat.

My prediction was incorrect because I thought that the silver can will be the best insulator. There are a number of scientific reasons for my results. They are

Black is an excellent absorber of heat and therefore the best insulator.
Shiny surfaces reflect the most heat away, so they remain cooler. The silver and white tins were the worst insulators because they reflected the heat away.
Silver is a good emitter of radiation and because the cans were painted on the outside, this made the silver can lose the most heat.
Black is a poor emitter of heat and the fact that the black paint was on the outside of the can kept the heat in the can for longer.

Evaluation

I completed my experiment successfully because I made sure that it was a fair test, apart from the variation of starting temperatures.

I think I was precise when measuring volumes of liquid and the temperature and I measured the water with a measuring cylinder and measured the liquid as the liquid meniscus just touched the line. This is because I kept the same amount of water throughout the experiment and accurately recorded the temperature every 2 minutes

I took enough readings as I recorded the temperature once every 2 minute for 12 minutes, which gave me 7 results for each can. I adjusted my results by making the starting points the same and then subtracting the difference from each step. This enabled me to draw an accurate graph.

Anomalous results

The only anomalous result was the starting temperature of the experiment, which was easily rectifiable by subtracting the final temperature from the starting temperature and finding the difference. I also subtracted the difference of each interval to enable me to draw my graph.

Improvements to my experiment

As an improvement to my experiment I could have put a corkboard underneath the copper can, as this will have reduced the conduction of heat from the copper can into the table. By doing all of these it would have kept my experiments much fairer.

Further work

If I were to do this experiment again I would improve it by having equal temperatures at the beginning of the experiment in each tin.

If I were to do a different experiment on the same topic I would look at the different types of materials that the cans are made of to find out which is the best insulator of heat. I could also find out which material is the best insulator out of: cotton wool, cardboard, bubble wrap.

There are several things that I could have done for further work. The first thing that I could do is to test different materials. By doing this I could see how well the insulation properties are between two materials such as cling film and cotton wool.

I could also wrap the insulation round the copper can more times. This would show me if there is a greater increase in their insulation properties.

I could also change the material of the can from copper to iron or aluminium to see if the material of the can affects the rate of which heat is transferred.

If this experiment were repeated using the same apparatus apart from painting the inside of the can, then the results would be very different. This would give me a better outlook on which colour is the best and worst emitter of heat radiation.

What effect does the colour of a can have on its rate of heat loss.

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