An investigation to investigate the effect of the diameter on the cooling rate of boiling water in a beaker

Prediction

As I decided to change the diameter of 5 beakers (with same amount of water in), I predict that if the diameter decreases the time taken for the hot water to cool will increase. This is because as the diameter of the beaker decreases the surface is therefore the only part of the object in contact with the environment. The majority of the heat will remain internal within an object whose surface is very small. The heat can only be conducted away through direct contact, and this area of the beaker is small. Also the area that heat loss could occur through convection and radiation is small. The surface like the surface for conduction for evaporation is also reduced. With all 4 factors reduced then the heat loss to the environment will be reduced, and the particles inside will have a great amount of Kinetic energy.

Equipment:

5 different sized beakers

Measuring cylinder

Kettle

Stopwatches

Rulers

Thermometers

Safety goggles

Variables and factors

• Volume of water
• If there was a lid
• Temperature of water was the same
• Temperature outside the beaker

Preliminary experiment

We decided to do a preliminary experiment to test our equipment and methods. I decided to take the largest beaker and put into 200ml water into it at boiling. The water temperature lowered so rapidly that the starting temperature was 75C and we were initially going to start the experiment at 80C lowering to 70C and timing this 10C drop. We realised that this was not possible so we changed the starting temperature to 70C and we waited for it drop to 60C. I found that this was successful so I used this method for my actual experiment.

What we did:

We decided to investigate the factors the affect the time in which it wakes a hot beaker of water to cool down, from 70C to 60C, by changing the surface area of the beakers. We used 5 different beakers:

1. Diameter of beaker 7.5cm
2. Diameter of beaker 10cm
3. Diameter of beaker 11cm
4. Diameter of beaker 14cm
5. Diameter of beaker 16cm

Fair test

We made this experiment a fair test by:

• Keeping the volume of water the same by using measuring cylinders.
• Making sure we did all the experiments in the same conditions
• Using only glass beakers
• Doing the experiment at room temperature 27C

I decided to measure the time taken for the hot water to cool from 70C to 60C. This was done for all 5 beakers, repeated 3 times so that an average could be taken.

Method

In this experiment we will have 5 different beakers:

1. Diameter of beaker 7.5cm
2. Diameter of beaker 10cm
3. Diameter of beaker 11cm
4. Diameter of beaker 14cm
5. Diameter of beaker 16cm

Put safety goggles on

Collect all the equipment for the experiment

Boil the kettle

Pour 200ml into measuring cylinder and then into each beaker

We then put the thermometers into the beakers, so we knew what the temperatures were

Then we waited for each beaker to get to the temperature 70C where we then started the stopwatches

We recorded the room temperature so that it was kept constant

We timed how long it took for each beaker to get to 60C from 70C.

After those were recorded we repeated it again 3 times

We then plotted our results onto a graph

Safety

Safety precautions were needed because I was dealing with hot water, which can scald. The following things needed to be acknowledged to, in order to keep this experiment safe:

• Be careful not to knock over the beakers with the hot water in
• Be careful not to knock over other peoples beakers
• Care is needed when pouring hot water
• Do not run with the hot beakers
• Wear safety goggles to protect our eyes
• Tuck stools under the benches to prevent accidents
• Keep the beakers far from the edge of the table

Results

Experiment        1:

Beaker 1-        Time:         5.26 mins

Beaker 2-        Time:         3.58 mins        

Beaker 3-        Time:        3.02 mins        

Beaker 4-               Time:        1.49 mins

Beaker 5-        Time:        1.25 mins

Experiment        2:

Beaker 1-        Time:        5.46 mins        

Beaker 2-        Time:        4.36 mins

Beaker 3-        Time:        3.34 mins

Beaker 4-        Time:        2.04 mins

Beaker 5-        Time:        1.37 mins

Experiment        3:

Beaker 1-        Time:        5.29 mins        

Beaker 2-        Time:        4.07 mins

Beaker 3-        Time:        3.26 mins

Beaker 4-        Time:        1.54 mins

Beaker 5-        Time:        1.16 mins

Conclusion

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 beaker. Altogether I tested 5 diameters and I have discovered which one has the quickest heat loss. I will place them in order of the fastest heat loss:

Beaker 5        Fastest

Beaker 4        

Beaker 3        

Beaker 2        

Beaker 1        Slowest

Looking at my predictions now, having done the whole experiment I have found myself to be right. This is due to the fact that I predicted that as the diameter increased the cooling time would decrease. My results show this, as they show that the cooling time increase’s when the diameter of the beaker is smaller. On my graph I can see a pattern of a downward sloping line (Inverse proportion) as the diameter of the beaker gets smaller. This also proves my prediction was correct.  

From these statements I conclude that:

• Heat loss is reduced when there is a smaller diameter
• Evaporation, radiation, convection and conduction are major factors of heat loss. Heat loss from my beaker occurs by conduction, where the heat conducts through the glass and into the wooden bench. The water particles were vibrating so fast that the energy is passed directly to the glass molecules when the water molecules collide with the beaker. In doing so the glass particles then pass on their energy directly to each other and then to the wooden molecules in the bench. This is a relatively small loss, in fact probably the smallest heat loss of all. Heat is also lost from the warm beaker by convection, air which collides with the surface or sides of the beaker will become warm gaining more KE. The air molecules then space out more becoming less dense and rise away from the water surface or glass surface. They carry the heat energy with them forming convection currents. Radiation from the hot water to the surroundings occurs as the surroundings are at a lower temperature than the water. However the glass is shiny and a lot of radiation is reflected back into the water off the glass. The major factor in my experiment is the heat loss by evaporation from the surface, as the diameter increases so does the rate of evaporation. Evaporation is the water particles escaping from the liquid and forming gaseous water molecules (water vapour). This reduces the overall energy into the water.
• Results could be faulty depending on the surroundings or conditions; you have to have the same conditions/surroundings for your experiment to be fair and accurate.
• The bigger the diameter of the beaker the less time it takes for the water to cool as there is a bigger area for the water particles to escape.

Evaluation

I feel that I was precise when measuring the volume of water and the temperature. I measured the water with a measuring cylinder and made sure it just touched the line. Also I measured the temperature with a thermometer to the nearest 0.5C. I measured the starting temperature accurately, and I also measured the time to the nearest second with a stop clock. These factors also helped to contribute towards a fair test.

One of our biggest safety concerns was that the water was extremely hot and could have seriously burnt someone if we weren’t careful. So to prevent this from happening we made sure we had the kettle on our table and poured it carefully into the measuring cylinder over the sink. The person holding the measuring cylinder was also holding it with cloth as to prevent getting burnt.

I thought I did take enough readings as I recorded 5 different beakers to give me a nice range. I also repeated the experiment 3 times and calculated the mean average. This means I had 3 different points for each 5 of the beakers used for the graph therefore it was much more accurate, so my graph was also good.

I did obtain a few anomalous results. These results may have been in error because I may have moved the thermometer from the middle of the beaker slightly higher or lower or a little bit to the left or right. Another reason for the inaccurate results is that I may have started the stop clock too late after the thermometer got to 70C or too early.

There was only one thing we could not really control and that was the temperature outside the beaker, the room temperature. We were unable to control this as we did 3 tests on one day and 2 on another. This means the room temperature on each of these different days could have affected our results. We didn’t have much time to do these experiments so we had to do the experiments over 2 different days. One being 27C and one being 26C room temperature.

As an improvement to my experiment I could have put a lid on top of the beakers to stop evaporation taking place, as this was probably a major factor of heat loss throughout the experiment. I also could have put a corkboard underneath the beakers, as this would have reduced the amount of conduction of heat occurring from the beaker into the table. I could have also used a clamp and boss to hold the thermometer in a fixed position; by doing this I could ensure that the thermometer is always at the same place in the water.