Heating & Cooling

Introduction to Heating & Cooling

Use the particle model to show what the particles of a solid, liquid and a gas look like: SolidLiquidGas

Particle Simulation s-of-matter s-of-matter

Heat Energy

Infra-red radiation All objects absorb and emit heat energy

Kinetic theory Kinetic theory describes how particles move in solids liquids and gases In your books – Explain how the movement of particles is different in solids liquids and gases. – Discuss how materials change between the 3 states of matter

Methods of Heat Transfer Conduction Convection Radiation

Conduction

Type of thermal energy transfer which occurs in solids Vibrating particles pass on extra kinetic energy (or heat) to neighbouring particles. This eventually results in a rise in temperature at the other side of the solid.

Methods of Heat Transfer

Draw one of these and explain what is happening

Why do metals feel cold?

Metals have free electrons

Starter Match the key words to the definitions and their explanations (don’t copy it out!) 1) Conduction 2) Convection 3) Radiation 3) Type of thermal energy transfer which occurs in solids 1) Type of thermal energy transfer which occurs in liquids and gases 2) Type of thermal energy transfer which does not require matter in order to travel 1) Vibrating particles pass on extra kinetic energy (or heat) to neighbouring particles. This eventually results in a rise in temperature at the other side of the solid. 3) Liquid and gas particles are free to move. Particles with more kinetic energy move from hotter regions to cooler regions, taking their thermal energy with them. 2) Thermal energy travels as waves. It travels at the speed of light. It can travel through a vacuum. This is the only way heat can reach us from the sun.

Convection Type of thermal energy transfer which occurs in liquids and gases Liquid and gas particles are free to move. Particles with more kinetic energy move from hotter regions to cooler regions, taking their thermal energy with them.

Convection Currents Hot air/liquid is less dense than cooler air/ liquid so it rises Cool air/liquid is more dense so it falls/sinks The rising and falling of particles with more/less thermal energy results in a convection current ience/aqa/energy/heatrev1.shtml ience/aqa/energy/heatrev1.shtml

Radiation Method of heat transfer which does not require particles Heat energy travels as waves This is how heat from the sun reaches Earth Remember! Not all radiation is dangerous!

Exam style questions

Starter Here are 2 cubes of the same dimensions, made from the same material: If both cubes have a starting temperature of 100°C and are left on a cool surface, which cube will have cooled down the most after 10 minutes? Explain your answer.

All objects absorb and emit some radiation Some surfaces are better at this than others ColourFinishAbility to absorb thermal radiation Ability to emit thermal radiation DarkDull or mattGood LightShinyPoor

Insulation What do we mean by insulation? List as many ways as you can think of in which we can insulate our homes

Cavity wall insulation

Air is a poor conductor of heat. Filling a wall cavity with fibreglass of polystyrene traps pockets of air between the walls. This reduces heat transfer by conduction.

Double glazing

An air gap is created This reduces heat loss by conduction

Double glass bottle Vacuum Silvering

U-values

A measure of heat loss. The ‘overall heat transfer coefficient’ The lower the U-value, the better the insulation provided by the material. The U-valure currently required for a new-build external wall is approx

You DO NOT need to know this for the exam U-value = W/m² x k Heat loss in square metres of roof/glass etc When the temperature (k) is 1°C lower outside than inside

Questions 1.What does a U-value measure? 2.Why would a U-value be relevant to someone living in a warm climate? 3.Give 2 advantages of using materials with a low U-value in a building. 4.Will a building that loses less energy have a low or a high U-value? 5.Describe the effect adding insulation to a building has on its U-value and heat loss to the surroundings. IN FULL SENTENCES PLEASE!

Effectiveness

The more effective a method of insulation, the better it is at conserving heat energy. What does this tell you about its U-value?

Payback Time

The time taken to recoup an investment Payback time = Cost of insulator ÷ annual fuel saving