Heat Transfer (1) GHGGYU DGDYJDGFFC.pptx

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1. HEAT TRANSFER The energy that flows between objects due to their temperature difference is called Heat . Each molecule (or atom) of an object has kinetic energy (KE) and potential energy (PE ). Internal energy (U) of an object is the sum of kinetic energy and potential energy of all the molecules (or atoms) of the object. 𝑼=(𝑲𝑬+𝑷𝑬)𝒂𝒍𝒍 𝒎𝒐𝒍𝒆𝒄𝒖𝒍𝒆. If an object takes heat, its internal energy increases; if an object gives heat, its internal energy decreases. 1

2. Temperature is the measure of hotness or coldness of an object . A temperature measured in kelvin (K) is called absolute temperature . Melting Point: The temperature at which a substance changes from solid phase to liquid phase. Boiling Point: The temperature at which a substance changes from liquid phase to gas phase. 2

3. Phase Change Change of a solid into liquid ( melting ), change of a liquid into solid ( fusion ), change of a liquid into gas ( vaporization ), and change of a gas into liquid ( condensation ) are the instances of phase change. 3

4. Heat transfer : It is study of thermal energy transfer causing a temperature difference or gradient. Energy can transfer from or to a given mass by two mechanisms: heat Q and work W. 4

5. Methods of heat transfer Conduction: It is the heat transfer from one substance to another by direct contact . 5

6. 6 K (Thermal conductivity): a ) It is the rate of heat transfer per unit area per unit temperature difference. b) High thermal conductivity means that the substance has good conductor and vice versa. A (Area): Heat transfer increased when the area increases and vice versa. ∆𝒙 (Thickness): Heat transfer decreased when the thickness decreases and vice versa.

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