3 Types of Heat Transfer

Heat Transfer- The movement of heat from a warmer object to a cooler object.

1. Conduction Heat transfer by direct contact of molecules. In other words, when one molecule runs into another and it runs into another, etc. It can occur in a solid, liquid or a gas. Occurs best in a solid because the molecules are close together.

conduction

How do non-metals conduct heat? Boardworks GCSE Science: Physics Heat Transfer How do non-metals conduct heat? Teacher notes This animation shows how heat is conducted through a non-metal on a particle level. Whilst viewing the animation it should be emphasised that this process is relatively slow, which is why conduction in non-metals is slow compared to conduction in metals. Autumn 2006

2. Convection Heat transfer by means of up and down movements called convection currents. Can occur only in a liquid or a gas

Convection currents Heated molecules do 2 things: 1. they expand, become less and then.. 2. they rise. Cooled molecules do the exact opposite: 1. they contract, become more dense and then… 2. they sink That is what makes a hot air balloon rise.

How does convection in a liquid occur? Boardworks GCSE Science: Physics Heat Transfer How does convection in a liquid occur? Teacher notes This three-stage animation uses the example of boiling water in an electric kettle to demonstrate how convection occurs in a liquid. Whilst showing the animation it could be highlighted that the hot water floats up through the cold water because the hot water is less dense. The denser cold water falls below the hot water, pushing the hot water up. Autumn 2006

How does convection in a gas occur? Boardworks GCSE Science: Physics Heat Transfer How does convection in a gas occur? Teacher notes This three-stage animation uses the example of seaside breezes to demonstrate how convection occurs in a a gas. Red arrows are used to represent the movement of warm air and blue arrows are used to represent the movement of cooler air. Suitable prompts include: Stage 1: Why is the hot air rising? Stage 2: What happens to the warmer air as it moves out to sea? Stage 3: Why has the convection current changed direction? Autumn 2006

3. Radiation Heat transfer through open space. Occurs in a gas only.

Investigating thermal absorption Boardworks GCSE Science: Physics Heat Transfer Investigating thermal absorption Teacher notes This virtual experiment investigates the ability of different surfaces to absorb heat. It could be use as a precursor to running the practical in the lab or as a revision exercise. To extend the activity, students could be asked to consider which variables need to be controlled to make this experiment fair and accurate. Autumn 2006

How is heat transferred? Boardworks GCSE Science: Physics Heat Transfer How is heat transferred? Where and how is heat transfer taking place at this seaside? Teacher notes This illustration contains several examples of heat transfer, including: Barbecue grill cooking burgers and sausages (conduction, radiation). The car bonnet is so hot that as a sideline to the barbecue, someone is cooking food on it (conduction). Picnic boxes labelled “cold” and “hot” contain items that have been kept cool and war, respectively, to prevent heat transfer taking place. The twins on the left are wearing identical clothing except that one is wearing a white t-shirt and keeping cool, while the other is wearing a black t-shirt and looking much hotter (radiation). The twin in the black t-shirt is trying to keep himself cool with a portable fan (convection). The fluttering sails on the boat out at sea and the fluttering flag on the flagpole show that it is windy at the seaside (convection). The ice-creams are melted very quickly by the heat of the Sun, much to the annoyance of the child near the ice-cream van (radiation). Autumn 2006