Evaporation & Condensation

Noadswood Science, 2011

Tuesday, April 18, 2023

Evaporation & Condensation

To understand how heat can be transferred by evaporation and condensation

Why does sweating cool you down and how could you test for this?

Sweating

Watch the demonstration of two thermometers with cotton wool on their ends – one is covered in water and the other in ethanol…

Water & Ethanol

The ethanol covered cotton wool cools the thermometer quicker than the water covered cotton wool thermometer – why?!

Sweating cools us down by removing heat from our body to the environment – as the water evaporates from our skin from liquid to gas a small amount of heat is taken from that area of skin – the hotter we become the more we sweat and the more heat can be removed…

Cooling

In the thermometer experiment with ethanol and water the ethanol cotton wool becomes cooler quicker than the water – this is due to heat being lost from the cotton wool surface just like the body when we sweat

The ethanol became cooler quicker because it has a lower boiling point (it evaporated at a lower temperature than the water)

Cooling

A bomb disposal expert discovers a type of bomb inside a burning building – the bomb can be diffused if it can be cooled by 10oC, however it cannot be moved…

Explosive Challenge

The expert has just ten minutes before the bomb explodes – how can it be cooled in time?

Consider what can be wrapped around the bomb / how many layers / would a fan help?

Using a boiling tube as the ‘bomb’ fill it full of hot water and place a thermometer in it

Experiment

Using the material experiment with wetting the layers different amounts / adding more or less layers / change the air flow across them to find a way to cool the bomb as quickly as you can…

Amongst the class find out which design was best, and explain why this was the case

Evaporation can help to cool things down because the particles which escape have more energy than the particles left behind

Evaporation

Increased air movement will increase the level of evaporation

Condensation occurs because the heat is transferred and the particles no longer have enough energy to remain as a gas

How do plants keep themselves cool?

Plants

Plants keep themselves cool by using a similar technique to sweating – they have a mechanism known as the transpiration system which moves water from the plant to the surface of the leaves where it evaporates, and in doing so takes away heat…

Plants

Survival Transpiration Bag