Cooking - Convection, Conduction, Radiation

SOURCES

1) Lafferty, P. (1989). More Science Projects: HEAT. New York: Marshall Cavendish Corporation.

2) Heat. (2009). In The World Book Encyclopedia (2009 ed., Vol. 9 (H)). Chicago, IL: World Book.

• In convection, heat can only be transferred through GASES and LIQUIDS.
• Heat is transferred through the MASS MOTION of the liquids when heated.

Convection

• Unlike in radiation, moving particles transfer heat in both conduction and convection.

• Both convection and radiation have the ability to transfer heat through liquids and gases.

• Conduction, convection, and radiation are all forms of heat transfer.
• Conduction, convection, and radiation follow the same principle: heat travels from hot to cold objects.
• The three transfers of thermal energy all take part in the boiling water on a stove!

Conduction

Radiation

• Both conduction and radiation have the ability transfer heat through solids.

• In conduction, heat is most commonly transferred through SOLID objects.
• Heat can only be transferred by DIRECT CONTACT in conduction.

• Unlike conduction and convection, radiation does not require a medium to travel through.
• Heat is transferred through ELECTROMAGNETIC WAVELENGTHS in radiation.
• Radiant heat is typically found in EMPTY SPACE.

Introduction

The three types of heat transfer.........

What is Heat Transfer?

Conduction

• Heat is the movement of thermal energy from a warmer object to a cooler object.
• All objects have thermal energy; however, it is considered heat only when thermal energy transfers from one object to another.
• The rate of heating depends on the difference in temperature between the two objects.
• The greater the difference is between the two temperatures, the higher the rate of heat transfer is.
• As the difference in temperatures decreases, the rate of heat transfer decreases, or slows down.
• As the two objects approach the same temperature, also known as thermal equilibrium, the rate of heat transfer approaches zero.

• Conduction is a transfer of thermal energy from one object to another by direct contact.
• Solids transfer thermal energy most efficiently since the molecules are tightly packed to each other.
• As molecules vibrate, they pass the heat energy to the surrounding molecules.

Thermal Conductors

Convection

Everyday Examples of Convection

• A common example of convection is boiling water in a pot.
• The warmer water at the bottom of the pot is constantly boiling up to the surface, which comes in contact with the cooler air, which consequentially cools it down.
• As more hot water cycles to the surface, the cooler water is pushed back into the bottom of the pot.

More Everyday Examples of Convection

• Air Conditioning/Radiator- The movement of air cooling down or warming up a room.
• Frozen Material Thawing- If the material is being thawed out it will thaw faster if it is placed under running water rather than put in a bowl of water. The reason for this is convection; the motion of the water will transfer heat more quickly into the frozen material to absorb heat energy through conduction.

Thermal Insulators

• A thermal conductor is a material that allows thermal energy to be passed easily through the material's particles.
• Thermal conductors are generally metal
• Examples of thermal conductors include:
• Aluminum (Al) 13
• Iron (Fe) 26
• Copper (Cu) 29
• Silver (Ag) 47
• Platinum (Pt) 78
• Gold (Au) 79

• A Thermal Insulator is a material that resists the flow of heat
• Examples of thermal insulators include:
• Plastic
• Rubber
• Styrofoam
• Wood
• Firefighter's suit are made of asbestos, a thermal insulator, so that it protects the firefighter from burning.

Can you think of any examples of conduction in the kitchen?

Examples of Conduction in the Kitchen

• Convection is the transfer of thermal energy by moving particles from one part of a material to another.
• Convection only occurs in fluids such as air, water, magma, and maple syrup.

Everyday Examples of Conduction

• When you put your hand on a stove it will eventually burn you.
• Ice cooling your hand/ Ice melting in your hand.
• Light bulbs give off heat and can burn you hand if you touch it.
• When you walk outside barefoot on a hot day, the heat from the asphalt is conducted to your feet.

Convection in the Kitchen

Other examples of Convection

Frozen Material Thawing- If the material is being thawed out it will thaw faster if it is placed under running water rather than put in a bowl of water. The reason for this is convection; the motion of the water will transfer heat more quickly into the frozen material to absorb heat energy through conduction.

Fennec Foxes have adapted to the Saharan Desert by developing large ears that circulate their blood and cool down their bodies to withstand the heat of the desert.

Wind chill!

Can you think of any examples of convection in the kitchen?

- The warmer water at the bottom of the pot is constantly boiling up to the surface, which comes in contact with the cooler air, which consequentially cools it down.

- As more hot water cycles to the surface, the cooler water is pushed back into the bottom of the pot.

Radiation

Radiation from the Sun to Earth

• Energy from the Sun travels through space to Earth.
• The infrared rays travel through space like how water waves travel on the surface of the pond.
• These rays warm the Earth's surface.
• Some of the infrared rays are absorbed by the Earth's atmosphere, and some are reflected.

Can you think of any examples of radiation in the kitchen?

• Radiation is the transfer of thermal energy from one material to another by electromagnetic waves.
• Electromagnetic waves are waves that can travel through a vacuum, which has no particles (no matter).
• This makes radiation the only way of transferring thermal energy from the Sun to Earth.
• Radiation also transfers thermal energy through solids, liquids, and gases.

Cooking and Heat Transfer