CLASS 8 · LEARNING KNOWLEDGE

Heat transfer and heat engines – basic principles

How it works

Heat transfer describes how thermal energy is transferred between bodies: by conduction, convection, or thermal radiation. Conduction occurs in all materials, is usually particularly evident in solids, and is often very good in metals. Convection is heat transfer by flow and occurs in liquids and gases. Thermal radiation does not require a medium and can also propagate in a vacuum. Heat engines convert part of the supplied heat into mechanical work, usually in a cyclic process. To do this, a working medium takes in energy from a warm source and gives part of it to a colder sink. Therefore, the efficiency is limited; ideally, this is described by Carnot efficiency. Heat transfer and heat engines are important foundations of thermodynamics and explain applications such as heating systems, refrigerators, and engines.

Note
Heat can be transferred by conduction, convection, or radiation. Heat engines require a temperature difference between a warm source and a colder sink; therefore, not all of the supplied heat can ever be converted into work.

An example

Which type of heat transfer is mainly responsible when a metal spoon warms up in hot tea?

Here, conduction is mainly responsible because the thermal energy in the metal spoon is passed from the hot part to the cooler end.

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Own explanation and own practice exercises by AmyMath. Subject reference framework: Physics. The topic assignment may vary by federal state.