The effect of insulating materials on heat loss from the body

Richard Smith 5α

Introduction

In this experiment I will be testing six different materials, felt, cotton wool, bubble wrap, polystyrene, wool and cotton. The other variables, for example, the number of layers, the amount of water in the flask, and the size of the flask, will be fixed to enable a fair test. I will use 200 cm3 of water in the flask, which will be inside a beaker full of the insulating material.

Prediction

I think that the polystyrene will be the best insulator, because after looking at all the materials under a microscope, I found that polystyrene had the smallest air spaces. This means that the air in those spaces will take the least time to heat up and therefore less heat is lost in the heating. I think that the bubble wrap will be the worst insulator, because it has large air spaces, which will take longer to heat up. The order of best → worst may look like this: polystyrene, felt, wool, cotton wool, cotton, bubble wrap.

I think that the graph will look like this: -

The heat is lost at first through conduction to the layers of insulation. That is why in my predicted graph I think there will be quite a rapid fall in temperature initially and then it will slow down. When the temperature drop starts to slow down that is when the insulating material is heated to roughly the same temperature as the water. The point at which this ‘slow down’ happens determines how good the insulator is. (The sooner; the better the insulator.) This is shown in my graph above.

This happens in the body: we loose heat from the blood vessels and warm air is trapped between the hairs on our body. However we are not hairy enough for this to be totally effective, and that is the main reason for people wearing clothes. Here is a diagram: -

Safety

I will observe that the following things happen to ensure a safe environment:

There are no stools sticking out
Care is taken using the hot water

Apparatus

Beaker, water, kettle, insulating materials, flask, thermometer, microscope, lamp, measuring cylinder, stop watch.

Method

Put some of the wool in the bottom of the beaker.
Put 200 cm3 of boiled water into the flask and place that in the beaker.
Cover the flask in the wool and place the thermometer through a woollen bung.
Let the temperature reach its highest point and use that as the starting temperature and then every minute for 20 minutes.
Repeat 1-4 using polystyrene, felt, cotton wool, cotton and bubble wrap.
Repeat the 1-5 twice.

Obtaining Results

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Apparatus

Beaker, water, kettle, insulating materials, flask, thermometer, microscope, lamp, measuring cylinder, stop watch.

Method

Put some of the wool in the bottom of the beaker.
Put 200 cm3 of boiled water into the flask and place that in the beaker.
Cover the flask in the wool and place the thermometer through a woollen bung.
Let the temperature reach its highest point and use that as the starting temperature and then every minute for 20 minutes.
Repeat 1-4 using polystyrene, felt, cotton wool, cotton and bubble wrap.
Repeat the 1-5 twice.

Obtaining Results

Here are my results: -

Analysis

I found that in the first few minutes there was a steady drop and at about 4 minutes the temperature would start to level off. The better the insulating material, the flatter the line on the graph. Here is the graphs of the two experiments I carried out and the average temperature drops for them: -

As you can see from the bar graph wool was the best insulator as it has the lowest temperature drop. After looking at each material again under the microscope, I can see that wool has very small air spaces inside the material. This is a property of a good insulator because the small air spaces take less time to heat up, and therefore do not loose as much energy in the heating. Also from the bar graph; my predicted best insulator was in fact the worst. This may have happened because the polystyrene is the least flexible of the insulators and although the material itself may have small air spaces, there were a lot of large air spaces in between each piece of polystyrene. Whereas the wool could be wrapped around the beaker, leaving much smaller gaps. These larger air spaces will have taken a lot longer to heat up and used more energy: causing the water to cool quicker.

The general pattern for each test was that the temperature would drop at the start, then at about 4 minutes the good insulators began to maintain their heat more and the bad insulators continued to drop. The insulators were in this order, (best → worst): wool, cotton wool, felt, bubble wrap, cotton, polystyrene. This happened because of the trapped air inside each of the materials.

Wool was the best insulator because it has the smallest air spaces when packed round the beaker. This meant that less heat was taken from the water and used to heat up the wool’s air spaces, because this happens the heat of the water is maintained for longer.
Cotton wool, when looked at under a microscope, is found to have the same styled structure to wool, except that the fibres are smoother, making them less able to trap warm air.
Felt also has a similar structure to cotton wool. The fibres are ragged but still smoother than wool and it has quite large air spaces. This is why it was not one of the best insulators.
Bubble wrap has no extra fibres to trap warm air, only large air spaces which need a lot of the water’s heat energy to be warmed. This is why bubble wrap is not a good insulator.
Cotton has a similar structure to felt except for the fact that all the fibres are smoothed down and flat. This does not allow the material to trap warm air between its fibres. Also it has large air spaces between the threads needing a lot of the water’s heat to heat them up, causing the water to cool faster.
Polystyrene turned out to be the worst insulator even though the microscope showed it to have a neat structure, with very small air spaces. However it is very smooth and therefore does not have any fibres catching additional warm air.

I predicted that polystyrene would be the best insulator, however, in the experiments it was the worst. Although the polystyrene itself has a very good insulating structure (as I found by looking at it under the microscope), the shape of the pieces I used did not allow me to pack the polystyrene tightly around the flask. This left very big air spaces in between the pieces of polystyrene. These spaces will have needed heat from the water to heat them up, causing the water to cool faster. This is why polystyrene is the worst insulator. It may have had the best structure (with small air spaces etc.) but the shape of the pieces created even larger air spaces than the bubble wrap, making the arrangement I had, not necessarily the material itself, the worst insulator. My prediction that bubble wrap would be the worst insulator was again wrong, but not as far away from reality as my first prediction had been. Polystyrene came below bubble wrap for the reasons I have explained above. Also cotton was a worse insulator than bubble wrap. This is because the air spaces in cotton are single spaces as shown in the diagram below, whereas bubble wrap can hold warm air in two places (again illustrated in the diagram).

I was correct, however, in my prediction of the initial temperature drop. This happened because at the start of the experiment the insulating materials were cold: It took a few minutes for the heat for the water to warm them up. This caused a drop in the temperature, as so of the water’s energy was used up in the heating of the material. This is shown in the graphs.

Evaluation

I think the experiment that I carried out was a good test of my prediction, considering the time allowed and the conditions of working. The results are, more or less, the same between the two tests showing that it was a fair test, in that all of the other variables were fixed. There were very few anomalous results however; they were most probably wrongly read from the thermometer. Here is a list of the anomalous results: -

Polystyrene test 1: 77.50C – 15 minutes
Polystyrene test 2: 73.50C – 19 minutes
Wool test 2: 66.50C – 12 minutes

These were excluded from the graphs. There were, however, a few things that did go slightly wrong. For example, my prediction that polystyrene would be the best insulator may not have been very fair. In that, the other materials were wrapped around the flask, but this is not possible to do with the polystyrene pieces we were given. This could have been over come by doing one of two things: Either using polystyrene granules or a block that could have been fixed around the flask; or all the materials could have been shredded to allow me to test the air spaces in the material itself (however, in shredding the insulators, it may alter the air spaces and so make it an unrealistic test). Another thing that might have distorted the results was the starting temperatures of the water. This could have made the test unfair. The higher the starting temperature, the more energy it will have and therefore it uses more heat in warming up the insulators (as the insulator will only stop taking heat from the water when it is the same temperature).

The experiment could have been taken further by being made slightly more relevant to the question if the range of insulating materials were made to include some more fabrics that people would actually wear. For example: nylon, polyester, viscose or Lycra.