Keeping food hot

Introduction

The Meals on Wheels organisation supplies meals to people who find it difficult to cook for themselves. It is important to keep the food as hot as possible during the journey from kitchen to customer. The food and drinks are packed in containers.

This investigation looks at which materials insulate food containers the best. It is assumed for this practical that the containers are made of glass. Different insulating materials are wrapped around them to keep the food hot. Since most food has a high water content, hot water is used in this study to simulate the hot food or drink in the containers.

Materials

1. Measure the thickness of each insulating material.
2. Cut out a 'jacket' of insulation for every beaker from each type of insulation, including a separate lid. Make a slit in each lid through which the temperature sensor will fit.
3. Wrap each beaker in a different insulating material, leaving the top open.
4. Carefully pour hot water into each beaker until it is three-quarters full.
5. Cover each beaker with its lid.
6. Place a temperature sensor in each beaker through the slit in the lid.
7. Start the datalogging software immediately. You can use the 'trigger' option on the datalogger to start recording in all the beakers at the same time as the water cools to a certain temperature.
8. Record the temperature for five minutes.
9. Record how the glass beakers were insulated, and the thickness of the insulation layer, in a table like the one below:

Results

1. Produce a table giving an estimated loss of temperature for each of the treatments if the length of the experiment is:
   a) 5 minutes
   b) 10 minutes
   c) 1 hour.

2. Using a spreadsheet program such as Excel, plot the data into a graph. It is important to present all the results on the same graph so they can be compared. If the treatments have been done separately, the graphs can be overlain on top of each other. Some applications allow graphs to be merged together after all the experiments have been completed.

The graphs below were obtained from the experiment. Graph 1 shows all five treatments and the temperature inside the room. Graph 2 shows a magnified section of Graph 1.

Key to graph
Pink line = bubble wrap
Light blue line = corrugated cardboard
Green line = kitchen foil
Red line = newspaper
Brown line = control [no insulation]
Blue line = room temperature

Key to graph
Pink line = bubble wrap
Light blue line = corrugated cardboard
Green line = kitchen foil
Red line = newspaper
Brown line = control [no insulation]
Blue line = room temperature

Drawing up your own graphs

Draw your own graphs from data collected in this experiment. The data are available in several different formats. The format you choose depends on the software you have available, and whether you want to carry out extra analysis using the datalogging software.

Formats available
CSV [suitable for using directly as a table in Excel]
SID
ISA
ISA (smoothed)
ISA (zoomed)
ISD

Conclusion

1. What is the general trend in the graphical data for all the treatments?
2. Which insulating layer is best? Explain your answer.
3. Does the thickness of the insulating material have any effect on the results? Explain your answer.
4. How you could make the experiment fairer?
5. What other improvements could to make to the experiment?
6. Why is it important to have a control treatment?

Extension questions

1. How would you insulate a house to save energy?
2. Why are runners given silvered blankets at the end of races?

Extension tasks

Design and carry out an experiment to find out whether the number of layers of insulation is an important factor in keeping foods in containers hot.