Conduction, convection and radiation are the three ways objects transfer heat. Often all three work together, but one mode of heat transfer is usually more important to the way the device works than the others. Air, for example, is a poor conductor of heat, but it can transport heat much more rapidly through convection. The following are some common devices that rely primarily on conduction.
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When you place a saucepan on the cooktop of your stove, the electric current through the coil or the gas fire transfers heat to the saucepan through conduction. The metal of your saucepan is a very good conductor of heat, so it in turn conducts heat to the contents. Convection also plays a role because convection currents help to spread heat throughout the water, but conduction is the primary means for the transfer of heat in this device.
Car Cooling System
The water pump in your car pressurises the coolant in the engine, causing it to flow through channels around the cylinders. Inside the cylinders, gasoline combustion releases a substantial amount of heat. The metal walls of the cylinders are good conductors and transfer this heat to the coolant, which flows through the radiator. By transporting heat away from the cylinders, the coolant prevents the engine block from overheating. The primary means of heat transfer involved in this exchange is conduction.
The electric kettle contains a heating element coiled into its base. Electric current heats the element, and the element in turn transfers heat to the surrounding water through conduction. Many kettles also contain thermostats so that the current will switch off if the temperature goes too high, preventing the kettle from being turned on when empty and avoiding overheating. The heating element and base are constructed from metals that conduct heat readily.
Heat Exchangers and Condensers
In thermal power plants, once the steam has flowed through the turbines, it passes through a condenser, where it transfers heat to cooling water as it condenses into liquid water. The primary means of heat transfer here is conduction. Condensers are a form of heat exchanger, a device designed to transfer heat from one fluid or system to another. Some types of nuclear power plants use heat exchangers to transfer heat from the water in the reactor core to water in an outer loop. Vaporising the water in the outer loop provides the steam needed to turn the turbine and power the generator.
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