Heat Transfer

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Modes of Heat Transfer conduction Convection Radiation

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Heat Transfer [Conduction, Convection and Radiation] Prepared by : Er. SANDEEP KUMAR (ME)
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Heat Tra n sfer Heat always moves from a warmer place to a cooler place. Hot objects in a cooler room will cool to room temperature. Cold objects in a warmer room will heat up to room temperature. Prepared by : Er. SANDEEP KUMAR (ME)
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Heat Transfer Methods Heat transfers in three ways: o Conduction Convection Radiation Prepared by : Er. SANDEEP KUMAR (ME)
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Conduction en you heat a metal strip at one en travels to the other end. , t e heat 0 000000 00000 0 0 Carbon atom O As you heat the metal, the particles vibrate, these vibrations make the adjacent particles vibrate, and so on and so on, the vibrations are assed alon the metal and Conduction Prepared by : Er. SANDEEP KUMAR (ME)
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Metals are different The outer electron of metal atoms drift, and are free to move. When the metal is heated, this 'sea of electrons' gain kinetic energy and transfer it throughout the metal. Insulators, such as wood and plastic, do not have this 'sea of electrons' which is why they do not conduct heat as well as metals. Prepared by : Er. SANDEEP KUMAR (ME)
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Why does metal feel colder than wood, if they are both at the temperature? Metal is a conductor, wood is an insulator. Metal conducts the heat away from your hands. Wood does not conduct the heat away from your hands as well as the metal, so the wood feels warmer than the metal. Prepared by : Er. SANDEEP KUMAR (ME)
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Convection hat happens to the particles in a liquid or a gas when we heat them? The particles spread out and become less dense. What is a fluid? A liquid or gas. This effects fluid movement. Prepared by : Er. SANDEEP KUMAR (ME)
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Fluid movement 00 0 000 'Cooler, more dense, fluids sink through warmer, less dense fluids. 'In effect, warmer liquids and gases rise up. 'Cooler liquids and gases sink. Prepared by : Er. SANDEEP KUMAR (ME)
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Water movement Cools at the surface Convection current Cooler water sinks Prepared by : Hot water rises Er. SANDEEP KUMAR (ME)
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Why is it windy at the seaside? Why is it windy at the seaside? The land is warmer than the sea. This land warms the air above it, and it rises. The cold air from above the sea moves in to take the place of warm air that has risen. Prepared by : Er. SANDEEP KUMAR (ME)
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Cold air sinks Where is the freezer compartment put in a fridge? It is put at the top, because cool air sinks, so it cools the food on the way down. Prepared by : Freezer compartment It is warmer at the bottom, so this warmer air rises and a convection current is set up. Er. SANDEEP KUMAR (ME)
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The third method of heat transfer How does heat energy get from the Sun to the Earth? There are no particles between the Sun and the Earth so it CANNOT travel by conduction or by convection. RADIATION Prepared by : Er. SANDEEP KUMAR (ME)
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Radiation 'Radiation travels in straight lines ? V True 'Radiation can travel through a vacuum ? V True 'Radiation requires particles to travel ? V False 'Radiation travels at the speed of light ? V True Prepared by : Er. SANDEEP KUMAR (ME)
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Emission experiment Four containers were filled with warm water. Which container would have the warmest water after ten minutes? Dull metal Shiny metal Shiny black Dull black The shiny metal container would be the warmest after ten minutes because its shiny surface reflects heat radiation back into the container so less is lost. The dull black container would be the coolest because it is the best at emitting heat radiation. Prepared by : Er. SANDEEP KUMAR (ME)
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Absorption experiment our containers were placed equidistant from a heater. Which container would have the warmest water after ten minutes? Dull metal Shiny metal Shiny black Dull black 'The dull black container would be the warmest after ten minutes because its surface absorbs heat radiation the best. The shiny metal container would be the coolest because it is the poorest at observing heat radiation. Prepared by : Er. SANDEEP KUMAR (ME)
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Convection questions Why does hot air rise and cold air sink? >CooI air is more dense than warm air, so the cool air 'falls through' the warm air. Why are boilers placed beneath hot water tanks in people's homes? A-lot water rises. when the boiler heats the water, and the hot water rises, the water tank is filled with hot water. Prepared by : Er. SANDEEP KUMAR (ME)
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Radiation questions Why are houses painted white in hot countries? White reflects heat radiation and keeps the house cooler. Why are shiny foil blankets wrapped around marathon runners at the end of a race? > The shiny metal reflects the heat radiation from the runner back in, this stops the runner getting cold. Prepared by : Er. SANDEEP KUMAR (ME)
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THANK YOU. Prepared by : Er. SANDEEP KUMAR (ME)

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