TemperatureandHeatLoss.pptVIP

Temperature and Heat Loss The following topics are covered in this presentation: Temperature and temperature scales Transfer of heat Thermal conductivity, resistivity and resistance Total thermal resistance U-value Temperature and Heat Loss The term temperature is used to express the degree of hotness of a substance. It is measured by using a device called the thermometer. Mercury in glass and the electronic thermometers are widely used. Mercury thermometer Electronic Thermometer 钢筋调直切断机 钢筋切断机 抹光机 Temperature and Heat Loss There are three temperature scales: oC oF K Freezing point of water Boiling point of water ‘Absolute zero’ 100 212 373 0 32 273 0 -273 Only used in USA Celsius (oC), Fahrenheit (oF) and Kelvin (K) Temperature and Heat Loss HEAT TRANSFER: Heat transfer from one substance to another or from one point to another in a substance may take place due to conduction, convection and radiation. Conduction: As a material is heated, the atoms start to vibrate with the increased thermal energy. The vibrating atoms make the adjacent atoms to vibrate and the process continues. As a consequence, thermal energy (or heat) travels from one end of the material to the other. Heat Temperature and Heat Loss Heat The vessel shown contains water and as it is heated, the particles at the bottom of the vessel become hot and expand. On expansion the particles become lighter and rise. Convection: All fluids are heated by convection Cold water particles at the top are heavier than hot particles. They descend as the hot water particles rise, and the process continues. Temperature and Heat Loss Sun Earth Radiation: Heat energy travels from one place to another without requiring a medium. Heat energy from the Sun is received by us due to radiation as there is no medium (air) beyond earth’s atmosphere. Temperature and Heat Loss Thermal conductivity: Thermal conductivity or λ-value (also known as k-value) of a material is a measure of the rate at which heat is condu