PRINCIPLES OF HEAT TRANSFER

Heat Transfer

• Heat always moves from a warmer place to a cooler place.

• Hot objects in a cooler room will cool to room temperature.

• Cold objects in a warmer room will heat up to room temperature.

3 Types of Heat Transfer:

Conduction

Convection

Radiation

BASIC COOKING PRINCIPLES

Conduction Heat transfer through direct contact. When cooking on the stovetop, the heat

from the flame or electric grill is applied directly to the frying pan. This means that only the flat surface of the pan is sufficiently hot enough to cook anything and we must flip and toss around the food to cook it properly.

It is important to note that most pans are made of metals, like copper, that

conduct heat very efficiently and do not melt on the stovetop.

Conduction

When you heat a metal strip at one end, the heat travels to the other end.

As you heat the metal, the particles vibrate, these vibrations make the adjacent particles vibrate, and so on and so on, the vibrations are passed along the metal and so is the heat.

Metals are different

The outer e______ of metal atoms drift, and are free to move.

When the metal is heated, this ‘sea of electrons’ gain k_____ energy and transfer it throughout the metal.

Insulators, such as w___ and p____, do not have this ‘sea of electrons’ which is why they do not conduct heat as well as metals.

lectrons

inetic

ood lastic

BASIC COOKING PRINCIPLES

Convection Heat transfer through a fluid. The fluid can be liquid or gas and in the

case of a convection oven, the fluid we care about is air.

An oven is a confined area that gets hot by flames or electric coils. The air inside is warmed to a desired temperature and, as a result, cooks the food from all directions. This method of heat transfer is responsible for pizzas, cakes, and other baked items.

Convection

What happens to the particles in a liquid or a gas when you heat them?

The particles spread out and become less dense.

This effects fluid movement.

Fluid movement

Cooler, more d____, fluids sink through w_____, less dense fluids.

In effect, warmer liquids and gases r___ up.

Cooler liquids and gases s___.

ensearmer

ise

ink

Water movement

Hot water rises

Cooler water sinks

Convection current

Cools at the surface

BASIC COOKING PRINCIPLES

Radiation The transfer of heat using electromagnetic radiation. A microwave

oven uses very strong radio waves (a form of electromagnetic radiation), which are very weak and not hot

Microwave ovens work by spinning water, fats, sugars and oils inside

the food. This causes friction, which then heats the food and cooks it from the inside.

The third method of heat transfer

How does heat energy get from the Sun to the Earth? There are no particles

between the Sun and the Earth so it CANNOT travel by conduction or by convection.

?RADIATION

What methods of heat transfer are represented below?