16
Cooling by evaporation
Subject: Physics
Sensor: Temperature
Aim:
This simple procedure can be used to show the heat being absorbed by an evaporating liquid and the subsequent drop in temperature plotted.
Overview:
Latent heat is the heat absorbed or released by a substance as it changes state ie. liquid to gas at a constant temperature and pressure. The latent
heat needed for evaporation is taken from the liquid itself which subsequently cools and as a result cools its surroundings.
The method provides scope for students to expand their thinking about heat absorption, evaporation and how the body might keep cool.
Equipment required:
LogIT Black Box
Temperature sensor
Clamp stand or similar
Paper towels, pipettes drip tray or mat
Distilled water
Methylated spirit/alcohol/mineral spirit
Hazards:
Students should be supervised at all times.
Ensure the datalogger cannot come into contact with water or damp.
Goggles should be worn and avoid skin contact with samples.
Always check your local regulations or a school advisory service such as CLEAPSS or SSERC for
guidance on the use of any hazardous material or source.
Setup:
1. Cut strips of a paper towel about 3 cm long and the width of the temperature sensors stainless tip. (About 7 mm)
2. Mount the temperature sensor horizontally in the clamp stand.
3. Fold the strip of paper in half and by slightly squashing it, place it onto the end of the mounted temperature sensor. (see picture)
4. Connect the temperature sensor to Black Box and connect Black Box to the computer.
5. Start the datalogging software and if necessary set the time span to 3 minutes.
Note: If using a clamp stand to hold the temperature sensor, do not clamp too tightly.
You can use cotton wool instead of paper but be aware that placing the cotton wool on the temperature sensor is difficult and if covered
in methylated spirit can be a handling hazard. By tightly squeezing the paper you should find it sits securely on the probe tip.