Practical applications of heat transfer methods

 

In the last lesson, we learnt the three modes of heat transfer with examples. Here, we shall look at how these mode of heat transfer can be applied to our everyday life.

1. Conduction

• The principle of conduction is employed in the production of kitchen utensils such as cooking pots, frying pan, kettle etc. They are usually made of good conductor materials like Aluminium which allows for easy and quick transfer of heat from the cooker to the food while heat is prevented from getting to the handle by using insulators such as wood or plastic. Cooking utensils are made of good conductors while the handles are made of poor conductors (insulators) so that they can be held comfortably.
• When you place your feet on a rug, it feels warmer than when it's placed on a tile. This is because heat is transferred from your feet to the rug. Heat is conducted away rapidly from the tile, thus feeling cold to the feet. Heat is absorbed onto the surface of the rug making it feel warmer to the feet.
• Clothes made of wool and fur are worn during cold weather because it traps air around the body which acts as insulator to retain heat and keep the body warm.

      2.    Convection

• Houses are usually ventilated using the principle of the convection air current. Heated air flows upward to the ceiling escaping through the ventilators while fresh air enters the house via the windows or other openings.
• The process of cooling motor engines also utilizes the principle of convection. Heat generated by the engine is conducted by the metal to the water which circulates round the engine. The water is then cooled by the air created by the radiator as the car moves and the fan rotates.

     3.     Radiation

• Dark coloured clothes absorb the radiant heat of the sun causing the wearer to feel hot. It is therefore advisable to wear bright colored clothes which will rather reflect the heat away from the body.
• The silvered surface at the base of an electric pressing iron is designed to reduce heat loss from the iron by radiation.
• Cars are brightly painted to reflect heat away from the car because black painted car will absorb and retain radiant heat and inside the car will be hot.
• The thermos flask applies the principle of all three modes of heat transfer. The working principle of the thermos flask is explained below:

1. The vacuum between the double-walled glass vessel is designed to reduce heat loss or gain by conduction or convection.
2. The silvered surface of the double walls of the vacuum reduces heat loss or gain by radiation.
3. The cork support at the bottom and the cork stopper at the mouth of the flask are insulators which helps to minimize heat loss or gain by conduction.
4. When the flask contains hot liquid, the cork stopper reduces heat loss by evaporation and convection.
5. The outer part of the flask is a plastic container which houses the flask and acts as an insulator to minimize heat loss by conduction.