TYPES OF HEAT TRANSFER.pptx

Types of Heat Transfer

1. TYPES OF HEAT TRANSFER To cook food up to desired texture & taste, heat must be transferred from it’s source ( gas flame or electric element ) to food . Understanding the ways & speed which transfer the heat, that helps the chef to control the cooking process. Heat is transferred in 3 different ways: CONDUCTION CONVECTION RADIATION In the next slide, we will discuss, all 3 methods in detail

2. CONDUCTION When heat moves from its source & heats an item by touching e.g. electricity flows through a wire the same way. CONDUCTION OCCURS IN 2 WAYS When heat moves from one item to other item by touching e.g. gas flame heat a fry pan when placed on top of burner When heat moves from one part of an item to an adjacent part of the same item e.g. heat moves from pan bottom to handle DIFFERENT MATERIALS CONDUCT HEAT AT DIFFERENT SPEEDS Heat moves rapidly through copper & aluminum Heat moves slowly in glass, stainless steel & porcelain.

3. CONVECTION When heat moves by the movement of air, liquid or steam, the movement of heat or convection is classified in 2 types: NATURAL CONVECTION : It occurs naturally when heat is applied to liquid, air, warmer ones rise & cooler ones sink, it causes constant natural heat circulation 2. MECHANICAL CONVECTION : It refers to movement of heat by artificial mechanical action e.g. using a fan or stirring to circulate the heat

4. RADIATION Unlike conduction & convection, radiation does not require physical contact between heat source & food to be cooked. Instead, heat is transferred by waves of heat. The waves themselves are not actually heat energy, they are changed into heat when they strike food. Light waves , radio waves , X-rays are examples of radiation not used for cooking. The two kinds of radiation are used in kitchen, they are discussed in next slide.

5. INFRARED RADIATION This method uses an electrical coil, which is heated to very high temperature, as a result it releases heat, that cook the food Few examples of equipments which releases radiant heat: toasters , salamander & glowing charcoal also considered. MICROWAVE RADIATION This method uses a special oven, which agitates the natural water molecules present in the food & creates heat. The heat is then spread by conduction & convection method & cook the food

6. MUST REMEMBER WHEN USING MICROWAVE Microwave cooking affects food containing water only, any waterless material (e.g. plate) will not get hot. But heat felt in a plate when cooking food in microwave, that result from heat being conducted from food to the plate. Microwave cooking requires certain types of utensils, such as ceramic, heat resistant glass or microwaveable plastic. Never use aluminum or stainless steel inside the microwave, because metal prevent microwaves & also damage the oven.