Thermal (heat) Energy Transfers

Heat is the form of energy associated with the movement of atoms and molecules in any material. The higher the temperature, the faster the atoms are moving, and the greater the amount of energy present. Heat can be transferred from place to place by, conduction,convection and radiation. Heat transfers from a high tempereture to a low temperature. Transferring thermal energy requires a temperature difference.

Conduction is the transfer of thermal energy through direct contact between the particles of a substance, without moving the particles to new location.

Occurs in solids.

When heat is supplied to one end, molecules at the end start to move more quickly. Thus, there are collisions between particles. The collisions between particles transfers kinetic energy to one another. Increasing the temperature, increases the kinetic energy, thus increases the rate of collisions of particles, and as a result, the rate of conduction also increases.

Heat energy can move through solids by conduction. Metals are good conductors of heat but non-metals (eg.gases) are poor conductors of heat, therefore, they are known as insulators.

Heat energy is conducted from a hot end of an object to a cold end. The energy is being transferred by using a temperature difference. 

The electrons of a metal can move about as free electrons. Due to this, charged metals ions are formed. The ions are packed closely together and they vibrate continuosly. 

The hotter the metal, the more kinetic energy will the vibrations have. The kinetic energy is transferred from the hot end to the cold end by the free electrons. The electrons move freely though the structure of the atom, colliding with ions as they go.

Convection is the transfer of thermal energy through movement of particles from one location to another, in fluids (liquid/gas). 

Convection occurs when particles with a lot of heat energy in fluids takes the place of particles with less heat energy. Heat energy is transferred from hot places to cold places by convection (temperature difference). 

Fluids expand when they are heated because they move faster when the fluid is hotter, and as a result, particles take up more volume, and the gap between the particles widens while the size of the particles remain the same. 

Fluids in hot areas are less dense than the fluids in cold areas, so the fluid rises into the cold areas. The denser colder fluid sinks into warm areas. In this way convection currents transfer heat energy in fluids.

Radiation is the transfer of heat energy as waves/particles/rays in the absense of particles and does not require a medium to transfer energy.

It is either reflected or absorbed by matter. If the energy is absorbed by objects, the kinetic energy increases, thus the temperature increases.

All objects take in and give out thermal radiation, otherwise known as infrared radiation. Infrared radiation is a type of electromagnetic radiation that involves waves and no particles, so it can even work through the vacuum of space. The hotter the object, the more infrared radiation it emmits. 

• Shiny or white surfaces are the best reflectors (worst absorbents)
• Matt black surfaces are the best absorbents (worst reflectors)
• Matt black surfaces are the best emmiters

Thick curtains and draught excluders: it stops convection currents and thus prevents cold air from coming in and warm air from leaving

Loft and underfloor insulating materials: prevents conduction of heat through ceilings and floors

Double and Triple glazing windows: vacuum between window panes prevents conduction and convection (cuts out heat loss)

Cavity walls: prevents heat loss by conduction

Foam or rockwool in wall cavity: further prevents heat loss by convection

A vacuum flask is designed to reduce the rate of energy transfer by heating processes:

• Plastic cap - Reduces heat transfers. It is an insulator of heat so it stops conduction, convection and evaporation It stops convection currents along with water molecules, because they are blocked by the cap.
• Silvered Glass Walls - Reduces heat transfers by conduction and radiation because it prevents conduction and radiation. It is an insulator and silver reflects infrared radiation back into the liquid and stops it from being emmited. 
• Vacuum - Prevents conduction and convection because these type of heat transfers carry particles while the vacuum has absense (or little amount of particles) so the heat transfer is reduced.
• Plastic supports - Reduces heat transfer by conduction because it is an insulator.

• All things are made up of particles
• When things get heated, they absorb heat energy
• With more energy, particles are able to move faster
• When particles move faster, the temperature rises
• Thermal energy is the energy resulting from the motion of particles
• It is a form of kinetic energy and is transferred by heat
• Thermal energy transfer can occur by three methods: conduction, convection, and radiation
• A fourth method in some circumstances can also be considered - evaporation
• Small surface areas can reduce heat energy transfer (opposite for large surface area)