Use of good conductors of heat:
If thermal energy has to be transferred quickly througha substance, good conductors of heat such as metals are used. Some examples of the use of metals are :
1. Cooking utensils like kettles, saucepans and boilers are usually made of aluiminium or stainless steel where direct heating is involved.
2. Soldering iron rods are made of iron with the tip made of copper, as copper is much better conductor heat than iron.
3. Heat exchangers, such as those used in a large laundry facility, help save energy.
Use of bad conductors of heat:
1. Handles of appliances and utensils such as saucepens, kettles, teapots etc. In this way, the hot utensil or iron can be picked up with scalding of our hands.
2. Table mats are usually made out of cork so that hot kitchenware can be planced on them without damaging the table top.
3. Sawdust is used to cover ice blocks because of its good insulating property
4. Wooden ladles are very useful for stirring or scooping hot stuffs
5. Woollen clothes are used to keep people warm on cold days
6. Fibre glass, felt and expanded polysterene foam which trap large amounts of air are emplyed as insulators in the walls of hosues, ice boxes and fridges.
Common applicatinos of convection
1. Electrical kettles
The heating coil of an electric kettle is always placed at the bottom of the kettle to aid transfer of thermal energy by convection. when the power is swiched on, the water near the heating coil is heated up, expands and becomes less dense. The heated water therefore rises while the cooler regions in the upper part of the body of water descend to replace the heated water.
2. Household hot water systems
3. Air conditioners
An air conditoner is always installed near to the ceiling of a room to faciliate setting up of convection currents. The rotary fan inside an air condiitioner releases cool dry air onto the room. As cool air is denser, it sinks.
4. Refrigerators
Common applications of radiation
1. teapot
shiny surfaces are bad emitters of a radiation, shiny teapots acan keep tea warm for a longer time than black ones. SInce shiny surfaces are bad abosrbers of radiationn, shiny containers can keep cold liquids cool for a longer time
2. Greenhouse
3. Vacuum Flask
The vacuum flask is designed to keep liquid hot by minimising heat loss in a few ways, namely conduction, convection, radiatino and evaporation.
