Table of Contents
BRAINBOX - HEAT-LAB-01
Students learn:
| Curriculum | Learning Activities |
|---|---|
| SCIENCE | Identify scientific principles required to solve challenge |
| TECHNOLOGY | Record and estimate timing data |
| ART | Blended multimedia elements |
| ENGINEERING | Design, build and test machine(s) |
| MATHEMATICS | Use comparative data find and define a time-line |
FRIDGE LIGHT PROBLEM
For this experiment, you will need:
- Reference to the ST2 framework documented here
- An infrared camera connected to a PC and your choice of materials and techniques described here
Heat Problem:
The little light in the fridge was designed to shut off long before conservation of electricity became a conservation issue.
QUESTION #1: Why?
ANSWER: If the light continued to burn after the fridge door was closed, heat would be generated within the refrigerator and the corresponding entropy(?) would require extraction.
An old-fashioned incandescent globe of say 20 Watts would have a big effect on the cooling efficiency of the refrigerator.
The Problem:
Essentially, we are connecting the inside and outside of the device - The fridge simply extracts heat from the “inside” and dumps it into the “outside”.
Problem #1:
Say when the fridge is running normally with the inside light off, the fridge is capable of cooling the interior by 5 degrees Celsius per hour. When the fridge is turned off the light will heat the inside of the fridge by 5 degrees Celcius per hour.
How long will it take to cool the fridge if we close the door to the refrigerator and the 20 Watt light remains 'on' after the door is closed.
If the fridge door is closed but the light now remains on, all other things being equal, the fridge will run continuously and the cooling will be cancelled out by the extra heat generated by the light. Each time the door opens, the temperature will rise…
What will happen to the temperature inside the fridge as the fridge is used over time?
Problem #1:
Assume that with the fridge running continuously that the fridge is starting to overheat and that as a result, the kitchen is getting uncomfortable.
So, we abandon our attempt to solve problem #1 and instead, decide to try a different solution:
How long will it take for the kitchen to cool back down if we remove the globe from inside the fridge, open the door to the fridge and use it to cool down the kitchen?
Provide some data such as relative temperature and volume (not needed to solve this problem, but supply for completeness anyhow :)
Like the BRAINBOX 'sailing' problem, it is worth considering THIS problem by applying 'the principle of relativity' and taking a look from more than one frame of reference.
For example:
- What is happening from perspective of the fridge - How is the inside cooled and where does the heat that is removed from the fridge actually go to? It helps to draw a diagram from the perspective of the fridge
- What is happening from perspective of a person in the room outside of the fridge - How and where does the heat that is removed from the fridge actually go? It helps to draw a diagram from the perspective of the fridge.
- Take one more step back. Combine the two drawings and try to see what is happening from the perspective of someone outside of the house.
What will happen to the temperature inside the fridge as the fridge door remains open over time?
What will happen to the temperature inside the kitchen as the fridge door remains open over time?
WHY?