What it shows
Mini fridges for medicines and vaccines in remote places use Peltier modules, which pump heat electrically without gas. The project builds a small insulated box and shows that how well the hot side is cooled decides how cold the box becomes.
The science
In the Peltier effect, current through a junction of two different semiconductors moves heat from one face to the other. Heat removed from the cold side plus electrical input must be thrown away from the hot side. If the hot side is not cooled, its temperature rises and the cold side warms up too. A larger sink and a fan reduce thermal resistance, so the cold side gets colder.
Materials
Cost: under Rs 1,500. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- A TEC1-12706 Peltier module, 12 V, run at reduced power
- Two aluminium heat sinks and a 12 V fan
- A 12 V, 5 A ready adapter or a 12 V battery
- A thermocol box with a lid
- Thermal paste
- Two digital thermometers or DS18B20 sensors
- A switch and wires
Safety
For this project: The hot side of the module can exceed 70 degrees and the module can be destroyed without a heat sink. Never run it without the fan. Use a sealed 12 V supply only. An adult must supervise.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesStep by step
10 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Cut a hole in the thermocol box wall slightly smaller than the module and fit the module so its cold face is inside.
Apply thermal paste on the cold side with a small aluminium block or heat sink inside the box.
Mount a finned heat sink with the 12 V fan on the hot side outside, again with thermal paste.
Put one thermometer inside the box, one on the hot sink and one outside for room temperature.
Switch on at 12 V and record temperature inside and on the hot sink every minute for 20 minutes.
Switch off, let the box warm up to room temperature, then repeat without the fan and stop at once if the hot sink exceeds 60 degrees.
Repeat with a larger sink and with a fan blowing straight on it.
Measure the current and calculate electrical power for each run.
Plot temperature against time for the runs and compute the lowest temperature reached and the time to reach it.
Write the report on the working principle, results and limits such as poor efficiency compared with compressor fridges.
What you should see
With a good sink and fan the inside falls 12 to 20 degrees below room in about 15 minutes. Without the fan, the hot sink climbs rapidly and the cold side warms again. The comparison shows the role of heat rejection.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1What is the Peltier effect?
Heat is absorbed at one junction and released at the other when current passes through two dissimilar materials.
2Why does the cold side warm up when the fan is removed?
Heat conducts back from the hot face, which has heated up and cannot lose its heat.
3What is the drawback of Peltier cooling?
It has low efficiency, so it needs more electricity than a compressor for the same cooling.
4Where is such a cooler useful?
In small portable boxes for insulin or vaccines and for cooling electronic sensors.
Take it further
Add a DS18B20 sensor and an Arduino with a relay to hold the box at 8 degrees by switching the module on and off.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
Free ebooks for this project
Science projects
Mini and Major Project Guide
For diploma and BTech students: choose, plan, build, document and present