Chapter 10 - Applications of Thermal Energy Transfer

Application of Thermal Energy Transfer


Common application of conduction
Good conductors of heat

• Cooking utensils: made of aluminium or stainless steel where direct heating is involved
• Soldering irons rods: made of iron with top made of copper, as copper is a much better conductor of heat than iron
• Heat exchangers: used in large laundry facility, help save energy

Bad conductors of heat (insulators)

• Handles of appliances and utensils: Can be picked up without scalding our hands
• Tables mats: made of cork so hot kitchenware can be placed on them without damaging the table-top
• Sawdust: used to cover ice blocks because of its good insulating property
• Wooden ladles: used for stirring or scooping hot soup that has just been cooked
• Woollen clothes: used to keep people warm on cold days
• Fibreglass, felt and expanded polystyrene foam: trap large amounts of air which are employed as insulators in the walls of houses, ice boxes and refrigerators.
  

Common applications of convection

• Electric kettles: water near the heating coil is heating up, expands and becomes less dense when the power switch is switched on. The heated water will then rises while the cooler regions in the upper part of the water will descend to replae the heated water.
• Household hot water systems:
• Air conditioners: air conditioners is always installed near to the ceiling of a room to facilitate setting up of convection current.
• Refrigerators: freezing unit is usually placed at the top to cool the air and facilitate setting up of convection currents.
  

Common applications of radiation

• Teapots: shiny surface are bad emitters of radiation, they can keep tea warm for a longer time and keep cool liquids for a longer time too.
• Greenhouses: the greenhouses traps heat which warms up the soil and plants. Over time, the temperature in the greenhouse will increase.
• Vacuum flasks

1. Hollow plastic stopper: made of plastic which is a poor conductor of heat
2. Trapped air: conduction through the trapped air above
3. Vacuum: conduction and convection through the sides of the flask are prevented by the vacuum between the double-glass walls of the flask
4. Thin silvered walls of glass: minimise heat lose through radiation, walls are silvered so that it will reflect the radiant heat back into the hot liquid. Convection and evapouration can only occur when the plastic stopper is removed during use.
5. Double-walled glass bottle
6. Outer case
7. Hot liquid
8. Cork flask in place