Cooking Using Electricity  Printable view

Cooking is simply heating of food to a high enough temperature and keeping the temperature for a long enough time until the food is "cooked". As heat is a form of energy, cooking requires energy. In modern cooking, electricity is frequently used as the source of energy, electrical energy is eventually converted to heat for cooking. The electrical appliances used in cooking are the energy converters. We will look at a few electrical cooking appliances and their different ways of converting electrical energy to heat for cooking. Different ways of energy conversion will have different energy conversion efficiencies.

The Electrical and Mechanical Services Department (EMSD) of HKSAR government has an energy efficiency labelling scheme to inform users that the labelled products have met certain energy efficiency requirements [1]. Many household electrical appliances have been designed and labelled complying with these requirements, including electrical cooking appliances like rice cookers. The label for rice cookers is a recognition type label, informing users that the labelled rice cookers met the energy efficiency and performance requirements [2].

Fig. 1   These electronically controlled stewing mugs are idea for preparing Chinese medicine and stewing food. Fig. 2   Electronically controlled rice cookers and induction cookers are two kinds of common electrical cooking appliance available in the department store. All these cooking appliances have one thing in common, they convert electrical energy eventually to heat.
 
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Hotplate

Fig. 3   A conventional hotplate has a metal surface covering the heating element to facilitate heat transfer.

Usually a long coil-shape resistor is used in a hotplate and when current passes through the resistor, the resistor heats up to high temperature. On top of the resistor is usually a metal surface. Remember that metal is a good conductor of heat. A metal surface increases the rate of heat conduction to the cookware placed on top of the hotplate.


Fig. 4   A newer design of hotplate has a transparent layer covering the red hot heating element. Note the coil-shaped resistor underneath.

In newer designed hotplates, a transparent layer instead of a metal surface is placed over the coil-shaped resistor. The hot coil-shaped resistor emits infrared radiation, which produces heating effect when absorbed by the cookware. The transparent layer allows infrared radiation to transmit to the cookware on the hotplate. But even with the newer design, heat lost to the surrounding is still high and hotplates are not very energy efficient cooking appliances.