Heat transfer coursework

We travelled to the McDonalds in Notting Hill Gate hoping to find out how McDonalds packaged their food so that it can remain hotter for longer but it turns out that they were not interested in packaging food in terms of heat loss.

McDonalds were more interested on which material would be the cheapest and would look nicer if it had the McDonalds logo printed on it.

They were also very interested in the design of the package, which is designed in such a way to guarantee that the product receives the customer in high quality.

However referring to their graph (refer to graph labelled Q P C Patty overview) when they used polystyrene packaging it helped keep the food hotter for longer because it was a good insulator because it had holes, which air would fill and air is a bad conductor.

The quick wrap was slightly better than the wrap, which is just papering it kept the food hotter than the usual wrap.

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So what we found out is that the thick layers of polystyrene insulate heat best therefore keeping food warm for longer.

I decided to investigate this by conducting a test with different thicknesses of polystyrene to see how many layers does it take to insulate the best.

In other words polystyrene has a higher thermal conductivity than usual paper wrapping.

So we decided to set up an experiment to see what exactly is the thermal conductivity of polystyrene.

The best layer to test would be 20mm, because it will be easier to analyse as heat seems to be lost slower and be helpful in plotting a graph.

Comments on other wrappings: The cheeseburger wax-coated paper wrapping prevents leakage. The fries cardboard shaped container was just designed to be easy to hold.

The coffee polystyrene cup and plastic lid are designed to keep the coffee warm and the lid contains a drinking hole.

And finally the apple pie cardboard box is a good insulator and keeps the apple pie hotter for longer.

Most of their burgers were measured to see their temperature in Celsius and if they were below 55-60 degrees they would be rejected and not served. Read also surface area and heat loss experiment

Background research

Heat moves through a material at certain rates. The rate it travels depends on the material: Some materials allow heat to move around rapidly through them, and some permit heat to move very slowly through them.

When heat is applied to a segment of a material, that heat will move through the material.

Depending on the composition of the atoms of that object, the heat may move very slowly, or it may move very quickly.

Heat travels exceedingly rapidly through a metal spoon for example leaving one end of a spoon in boiling water will make the whole spoon hot quickly. The whole spoon becomes hot not just the speck in the boiling water.

On the other hand heat moves very unhurriedly through the insulation in a house.

When it is very cold outside the heat in a house moves little by little from one side of the insulation to the other.

This helps maintain the heating costs of the house down.

When two objects of dissimilar temperature are put in contact with one another there is a trade of thermal energy.

This exchange recognized as heat reduction causes the warmer object to cool and the cooler object to warm.

The thermal energy of an object is the measure of the speed of the objects particles. When two objects of different temperatures are put in contact with one another the faster moving particles collide with the slower moving particles and energy is exchange.

The quicker moving particles give up some energy and thus slow down, the slower moving particles gain some energy and speed up.

The thermal current is directly comparative to the coefficient of thermal conductivity.

Diverse objects have different coefficients of thermal conductivity.

There are three modes of heat transfer: Radiation, convection, and conduction, and all require a driving force in the form of a temperature difference.

Material

Coefficient of thermal conductivity (W/m/k)

Air

0.026

Water

0.609

Glass

0.8

Polystyrene

0.037

Copper

401

Steel

46

Heat will flow from a hot surface to a cold surface. All modes of transfer occur in a given situation, but often one or two will have neglible contribution.

Radiation can occur though a vacuum, as in space or inside the closed cells of some foams. It has a larger impact in situations where the temperature differences are very large.

Newton's law of cooling

Newton's Law of Cooling Declares: the rate of change of the temperature of an object is proportional to the difference between its own temperature and the ambient temperature (i.e. the temperature of its surroundings).

When surfaces contact, between a fluid and solid wall, a thin layer of liquid is always there that the heat is transferred by conduction through it.

At any time there's a significant movement of the fluid, conduction heat transfer in fluid may be neglected compared with convection heat transfer.

Newton's law of cooling can describe the heat transfer from the solid surface to the fluid.

Newton's law declares that heat transfer, dQ/dt, commencing from a solid surface of area A, at the temperature Tw, to a fluid of temperature T, is (look at picture in the right hand side):

Action plan: Ziad Pekacar 12.2 Mr. Neil

Physics: Heat transfer

For more information about the investigation please refer to the heat transfer report.

19/03/01 Monday

Aim

I am investigating how heat loss can be minimized by insulation.

The aim of this experiment will be to examine how heat is lost through the conduction of polystyrene.

The point of this is to find the K value, which is means thermal conductivity, and I want to find it for polystyrene.

Thermal conductivity is the physical property of a material that determines how easily heat can pass through it.

In order to find the thermal conductivity of polystyrene I will have to conduct a test that involves wrapping different thicknesses of polystyrene round a metal can, and pour boiling water inside, seal it and take down the temperature every minute.

(See the report for more details)

This will be done for 20 minutes, and stored in table format. After the results are stored I will use them to draw graphs and therefore calculate the K value for polystyrene.

It should be an easy task to calculate the thermal conductivity by using a graph; if the points are plotted correctly and a gradient is drawn then it should be simpler to calculate the thermal conductivity.

19/03/01 Monday

Write up a risk assessment

This is one of the most vital tasks that have to be carried out before any test is performed.

The reason why risk assessments are essential is because hazards are always present during any experiment. The only way to avoid them or minimize them or have an idea of what actions to take is to summarize them in a risk assessment.

A risk assessment is a form that is filled in according to your experiment in order of making critical decisions or meeting regulatory requirements.

Risk assessments can be completed with the help of CLEAPSS cards, which is a company that specializes in making experiments safer for pupils. They are an advisory service for schools taking part in practical science.

Equipment needed: CLEAPSS cards

By when will this task be completed? 19/03/01

19/03/01 Monday

Investigation: Thermal conductivity of polystyrene

To follow out this investigation I will need an empty can of beans, which is able to hold 350ml of water to the brim.

I will only fill the can up to 330ml, mainly so it doesn't overflow and then it would be hard to seal it. Metal cans are very good conductors of heat so they will lose heat immediately.

Please keep in mind that I have already tested the thicknesses of the polystyrene, which I did not mention. I tested the thickness with a micrometer, the polystyrene measured out to be 0.2cm thick. (Look at the next page to see the steps of the investigation)

This is how the investigation will be carried out in steps:

1. I will heat some water up inside a kettle.

2. I will obtain an empty beans can.

3. Cut the lid open and place blue tack around the sharp corners.

4. I will make a hole inside the lid.

5. An asbestos mat should be placed below the can.

6. I will cut out 3 different thicknesses of polystyrene and wrap it around the can; this is to test how fast does the can lose heat through conduction and radiation.

7. I will first measure the room temperature to make it a fair test; usually the room temperature is 20 degree Celsius due to school heating.

8. Inside a measuring cylinder I will measure out 330ml of boiling water from the kettle and pour it into the can.

9. Place a thermometer inside the hole in the lid it.

10. I will then start a stopwatch and take the temperature every minute for 20 minutes.

11. I will try many layers to see which ones insulate heat the best. Each layer is 0.2cm; I will be using 1 layer for the first test (0.2cm), 2 layers for the second test (0.4cm), and finally 3 layers for the final test (0.6cm).

12. The main thickness will be 10 layers of polystyrene (2cm), which will be examined as the fourth and final thickness, which should be the most helpful in helping me K value.

13. Finally after I have obtained my 10 layers result, I will calculate the averages and sketch a curve graph. The reason why the 10 layers are used to draw the main graph is because it will provide me with the best possible results. Mainly because it will be an easy graph to draw because heat is lost slower.

14. After sketching the graph I will draw a gradient to calculate the K value.

The reason of this experiment is to calculate the K value for polystyrene and to see how much heat is lost through radiation depending on the thicknesses of the polystyrene.

The hot water inside the can will surpass heat to the sidewall through the process of conduction, the heat will then be radiated from the side and evaporate.

Heat will be lost through the lid through convection, it will evaporate out of the lid, so I will need to make sure the lid is securely sealed.

I will do this by taping the lid with sticky tape.

(For more information please see the report)

Equipment needed: Empty beans can, Asbestos mat, blue tack, sticky tape, kettle, measuring cylinder, thermometer, polystyrene sheets, stopwatch and Micrometer (To measure thickness of polystyrene.

By when will this task be completed? 19/03/01

19/03/01 Monday

Storing my results

When I transfer the boiling water to the can I will begin to take temperature readings of the boiling water inside every minute for 20 minutes.

I will have a table to store my results, to see what my table looks like please refer to the report.

Most of the layers the heat will be declining slowly that's one of the reasons why I chose to measure it once every minute.

Polystyrene will insulate more heat as more thicknesses are added which means heat will be lost slower making the graph slowly declining as heat is lost slower.

To make it a fair test I will be taking time readings for 20 minutes for each experiment.

I will also conduct the test twice and take an average of the tests this is just in case I get anomalous results for the first test, the second test will make sure that the results are reliable.

Equipment needed: Thermometer, stop clock, and table of results.

By when will this task be completed? 19/03/01

20/03/01 Tuesday

Plotting results on graph

After gaining my results from the table I used to store my data, I can now plot a graph to analyze my results.

My graph will be plotted according to the averages, which should make out curve.

I will be able to notice patterns, from the curve of the plotted coordinates.

This will help me compare the results with my prediction and see if what I expected went to plan.

My conclusion will be based on the graph.

These results will help me calculate thermal conductivity.

Equipment needed: Graph paper.

By when will this task be completed? 20/03/01

26/03/01 Monday

Calculating thermal conductivity

I will first of all calculate the surface area of the can, which is given by the following formula:

2? r2. I already know that the radius of the can is 6.7cm and the height 10cm.

After I calculate the surface area I will make another table to store the data for my gradient graph that will help me calculate thermal conductivity.

After I gain these results I will then be able to use this equation to calculate thermal conductivity.

Equipment needed: none

By when will this task be completed? 26/03/01

PLAN: AIM

The aim of this experiment is to calculate constant k or thermal conductivity of polystyrene; this can be achieved from the experimental results that are obtained.

I am going to investigate how heat loss can be controlled through insulation. I want to find out how many rolls of polystyrene are going to insulate the most.

The measurement of a material to conduct heat is called its thermal conductivity.

To test the first can I am going to fill it up with 330ml of boiling water. We will use a more precise method by measuring the water with measuring cylinders. This is because we want to get accurate results so we use the appropriate instruments to perform our tasks.

Objectives

* To calculate K value of Polystyrene

* To get reliable results that will help me make a conclusion

* To meet the deadline that I was set

* To control variables, such as temperature and heat loss

* To reduce heat loss from the top of the can through the form of convection I will need to seal the container very firmly to stop water vapour from escaping.

* Reduce the amount of heat loss from the can itself

The way I could tackle the problem of heat loss is to place an asbestos mat below the can to stop the can losing heat from conduction.

An asbestos mat acts as being heat proof and stopping the can conducting heat to the surroundings from the bottom of the can.

The most important objectives of the experiment is to repeat the 20 minute long experiment twice, this is to get the best possible results to help us later on calculate thermal conductivity.

Hazards

The main hazards are the breakage of glass, hot water spillage causing scalds, or thermometers breaking which contain mercury that could lead to dementia if inhale and is poisonous if absorb through the skin.

Breakage of glass could be dangerous if the glass was not disposed in the glass breakage box it could lead to cuts if it's accidentally

Touched. In case you get cuts wash your hands immediately and put a plaster on.

If hot water is spilt on your skin wash your hands immediately.

In case of thermometer breakage empty some sulphur over the mercury to stop it from spreading.

Equipment

Hazards

How can it be prevented?

Source of information

What to do in case it happens?

Measuring cylinders

Breakage of glass could lead to cuts if it's accidentally

Touched.

Do not touch the broken glass.

CLEAPSS

In case you get cuts wash your hands immediately and wear a plaster.

Take care with handling, put in broken glassware container

Thermometer

Thermometers breaking, which contain mercury that could lead to dementia if, inhale and is poisonous if absorbed through the skin.

Do not inhale or touch.

CLEAPSS

In case of thermometer breakage empty some sulphur over the mercury to stop it from spreading.

Do not touch face or mouth while performing the experiment. If such of the chemicals are swallowed drink plenty of water and contact emergency 999.

Kettle

Hot water spillage causing scalds.

Steam burns.

Do not spill hot water on the skin.

CLEAPSS

If hot water is spilt on your skin wash your hands immediately and seek medical attention.

Sharp corner of can.

The sharp corner of the can might cut skin.

Take care when handling. Possibly stick blue tack or something similar on the corners to prevent contact with corners.

CLEAPSS

Wash your hands out with cold water, dry hands and then wear plaster.

If bleeding persists seek medical attention.

Lid of the can.

When making a hole through the lid of the can watch out not to hurt hands.

Hold the lid with a clamp while making a hole inside.

Teacher notice.

In case of harm we should Wash our hands out with cold water, dry hands and then wear plaster.

If bleeding persists seek medical attention.

Equipment

* Empty beans can

* Thermometer

* Polystyrene sheets

* Kettle

* Stop watch

* Sticky tape

* Blue tack

* Micrometer

* Measuring cylinder

* Asbestos mat

Constraints

After spending most of our time doing thicknesses of 1 layer to 3 layers we have used up most of the time where we could have been testing more intensively on the 10 layers, which is the most important. For that reason we could test the 10 layer experiment once for 30 minutes and no more.

We already had tested it for 20 minutes, but we thought that if we wanted to plot a better graph we had to do the experiment for longer. The reason why we want to carry out the experiment longer is because when it was done for 20 minutes not enough heat was being lost which made it difficult to draw a curve.

Therefore our first constraint is time.

My plan took account of this constraint by being changed to suit the constraint of time, instead of wasting time with other thicknesses, we decided that 20mm was the most important thickness to analyse.

So we used the remaining time to test 20mm thickness for 30 minutes to suit the amount of time we had.

Another constraint was the room temperature, the reason why is because it kept changing every minute making it hard to determine what the room temperature was.

We couldn't keep the room temperature constant even if we closed the window.

So instead we decided to use 20 degree Celsius for each experiment as being the constant room temperature as this was the average temperature every time.

I took account of this in my plan by making sure that the can I was using was sealed and taped as much as possible to reduce heat loss.

We might not get a correct value for K this is due to working in a school laboratory, making the equipment limited. We could lose a lot of heat through gaps in the lid or not being able to seal the can very well due to cheap equipment. In a government laboratory they might have machines to do the work for them in our case we are using a less advanced cheaper version by cello taping the lid, opposed to laboratory equipment.

Bibliography

1. McDonalds trip in Notting Hill Gate

2. Experiment in the science lab

3. Hutchinson dictionary of science

4. Encarta 96 science encyclopaedia

METHOD

We carried out three experiments using three thicknesses 2mm, 4mm, 6mm that were taped around a normal Heinz beans can, which is typically 350ml.

We used an empty baked beans can this is because it is easier to seal with its own lid, which should fit to size.

We started the experiment with the first thickness, which should be taped round the can securely.

* We then placed an asbestos mat underneath the can.

* Then we obtained a kettle and heated up some water that we used to fill the can up to 330ml high (leaving 30ml space) we didn't fill it entirely to the top so we can close the can tightly without the fear of spillages (see hazards). We will place blue tack around the sharp edges so that the lid sticks to the lid as well as a health and safety aspect.

* We made a hole inside the lid of the can so we could place the thermometer inside and close the can at the same time allowing less heat to escape. The hole is made just enough for the thermometer to fit.

* After placing the thermometer and taping around the hole as much as possible to trap in heat, we waited until the temperature was 90 degrees and then we started the experiment.

* We took our results down and stored them in a table like this one:

Time

Temp

Test 1

Test 2

Average

1

90

90

90

90

* When the temperature was right, we started a stopwatch and took time readings every minute for 20 minutes.

* We then repeat the experiments twice with each container to ensure that the results are genuine. After the results were repeated twice we then took an average and drew graphs of our results.

* We then tried out 3 thicknesses to see which ones will reduce heat loss the most.

* The asbestos mat, which was placed under the can, was meant to insulate heat.

* The temperature readings were taken every minute for 20 minutes and the room temperature was checked so that we could rectify whether the temperature of the room affected the experiment.

We will calculate the surface area of the can (see picture on next page).

Good conductors of heat will let heat travel quickly and easily through them. Metals are good conductors.

I predict that the more layers of insulation the less the heat loss.

I will then draw graphs to show this and the results.

I will prove my theory by doing the 4th and last thickness of polystyrene. That thickness is 20mm, which will help me draw a more accurate graph

Each roll of polystyrene is 2mm thick.

It will be a fair test by ensuring that all the tests start at the same starting temperature, which is 90 degrees Celsius (see fair test).

Hopefully the 20mm thickness will help us calculate thermal conductivity.

This is the table we will use to calculate thermal conductivity:

?T/?t (0C/second)

mc?T/?t=?Q/?t (g)

Ti - T0 (0C)

??/?X (g)

Below are some of the equations I'll be using:

?T= Temperature ?t=Time

?T/?t Temperature/time (0C/second)

M= mass. In our case the mass of water was 330ml. We convert this into Kg for the calculation of thermal conductivity. 330ml/1000= 0.33kg

C=specific heat capacity. We used water, which has a specific heat capacity of 4200joules/kg0C.

Mc?T/?t=?Q/?t

??= the temperature difference between Ti - T0

?X= the thickness of our material. Our material is polystyrene and our thickness is 20mm, we need to convert it to metres. 20mm/1000= 0.02m.

Ti= Temperature of material.

T0= Room temperature.

Gaining these results we will then use them to plot, ?Q/?t against ??/?X.

At room temperature this mechanism is not as efficient as the transfer of heat by electrons and this is why metals tend to be much better conductors of heat. Heat is transferred by direct collision between molecules, although this is less important than the bulk movement of fluid.

Radiation is related to the colour and shape of the bodies involved, in our case the body is silver coloured and metallic, the outer layer is polystyrene.

Dimensions of can.

Convection uses a moving fluid to transfer heat. The fluid can be forced by a fan or occur naturally through the buoyancy affects of the fluid at different temperatures.

Convection depends on the speed and properties of the moving fluid as well as the shape of the non-moving body.

Conduction occurs through a solid or stationary material. Conduction is related to the materials thermal conductivity, the cross sectional area for heat to flow through and the distance of travel from hot to cold side of the solid material.

We will close the lid on it using the remains of the old cans lid; we place a lid to make it as airtight as possible to get accurate results.

Another reason for making the container airtight with a lid is because of convection, which is a process of heat flow, which can be transferred through fluids. As the lower part of the fluid in the can gets warmer it expands and becomes less dense then the fluid above it and rises and its place is taken by colder fluid. So you see if we put a lid to minimise the steam rising therefore keeping the fluid hotter for longer.

It will have a lid and asbestos mat under it, we will place a lid and mat to make it as airtight as possible to get accurate results and lose as little heat as possible so we can test the thickness of the polystyrene in a fair manner.

The water will be heated until it reaches a temperature of 90�C.

I will draw a table to keep my results and analyse the results and draw a graph.

The measurements I will use are temperature in �C with a thermometer.

My method is accurate because it's going to be repeated twice and I am going to check the room temperature every time to make sure that the weather does not affect the experiment. So I think I should either add or decrease temperature to the results depending on the weather.

If the room temperature is colder than the first time we did the experiment by 2 degrees Celsius then we will add two Celsius to the final result.

Otherwise if it were hotter than the first day we did the experiment then the opposite would happen.

I am going to do this because I believe that the room temperature can either speed up the process or slow it down depending on the weather, which will make it an unfair test.

I predict that the more rolls of polystyrene we have the less the heat transfer.

This is because polystyrene is an insulator and traps in heat.

The measurements we will use are time in minutes and temperature in �C.

Each experiment will be taken out twice including the averages, which should help us come to a conclusion. Heat, which passes throughout a solid body by physical transfer of free electrons and by vibration of atoms and molecules, ends flowing when the temperature is alike at every point in the solid body and equals the temperature in the adjoining environment.

In the procedure of reaching equilibrium, there is a gross heat flow through the body that depends on the temperature variation among different points in the body and on the magnitudes of the temperatures implicated.

Thermal conductivity is experimentally calculated by determining temperatures as a task of time down the length of a can while concurrently controlling the exterior input and output of heat from the surface of the can.

Changes made to plan

The equipment wasn't very accurate and wasn't sufficient enough to keep the water inside warm. Most of the time the water had dropped down in temperature as soon as it was poured into the can. The way this problem was dealt with was to heat the water twice, which would give it a temperature higher than 90 degrees, which is our starting temperature.

Then we would wait until the temperature was 90 degrees and then start the experiment.

The room temperature was different everyday that is something that could have seriously affected our results. We had to close the window and consider altering our results with respect to the change in room temperature.

We had less than two weeks to do the experiment, which was a time constraint, so we had to finish the experiment quicker. Finishing the experiment quicker was a benefit temperature wise, because the more we would complete in one day the more our results wouldn't differ very much.