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CONVECTION

CONVECTION. Definition of Convection. This is how heat energy flows from a hot to cold region of a substance by being carried by the molecules of the substance moving from the hot to cold region. Convection in fluids. A fluid is a liquid or a gas.

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CONVECTION

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  1. CONVECTION

  2. Definition of Convection This is how heat energy flows from a hot to cold region of a substance by being carried by the molecules of the substance moving from the hot to cold region. web site: www.ktaggart.com

  3. Convection in fluids • A fluid is a liquid or a gas. • Molecules move more quickly and occupy more space when they are heated. • Hotter fluids are therefore less dense than colder fluids. • Hotter fluids rise up to float on top of colder fluids. • A convection current is the path taken by rising hot fluids and sinking cold fluids. • Convection does not occur in solids. web site: www.ktaggart.com

  4. Convection in water • Potassium permanganate crystals are used to dye water purple.. • When the bottom of the flask of water is heated warm less dense water rises. • The potassium permanganate dye rises with the warmed water. • When the water cools it becomes denser and sinks down to the bottom of the flask. web site: www.ktaggart.com

  5. House water heating system • The boiler heats the water. • Hot water rises to the top of the boiler and up to the top of the storage tank. • Colder water in the tank falls to the bottom of the boiler to be heater. • A hot water tap draws water from the top of the storage tank. • The cold water supply replenishes the the hot water drawn off. web site: www.ktaggart.com

  6. Engine water cooling system • Water heated by the engine rises to the top of the engine. • This water is pumped into the top of the radiator. • The fan cools the water in the radiator. • Cooled water falls from the radiator into the engine. web site: www.ktaggart.com

  7. Hot air rises • Heated air provides lift for a hot air balloon. • Heated land causes rising air currents called thermals. • Thermals can be used by gliders to provide lift. • Many birds also use thermals for lift. web site: www.ktaggart.com

  8. Sea and land breezes • During a hot day heated air rises up from land that is warmer than the sea. • Cooler air moves in from the sea to replace the heated air. This is the sea breeze. • At night the sea is often warmer than the land. • Air now flows to the sea. This is called a land breeze. web site: www.ktaggart.com

  9. Simple mine ventilation • The fire causes hot air to rise up the shaft above it. • Cooler, fresher air is drawn down the other shaft. web site: www.ktaggart.com

  10. Question 1 Choose appropriate words to fill the gaps in the paragraph below: Convection is a method of heat transfer that only occurs in ________ (liquids and ________). When part of a fluid is heated the ___________ in that region move more ______ and take up more space. The heated fluid expands and becomes less _______ than the surrounding cooler fluid. The heated fluid _______ on top of the cooler fluid. The upward path of the heated fluid is called a ____________current. web site: www.ktaggart.com

  11. Question 2 • Explain why • a hot drink will cool more slowly if a lid is put on the top of the drink, • clouds are often formed at the top of thermals, • top loading freezers are more efficient than those with side doors, • hot water radiators are best placed\under a window. web site: www.ktaggart.com

  12. Simulations Energy House Simulation. For instructions click here. web site: www.ktaggart.com

  13. Puzzles Convection Crossword – by KT web site: www.ktaggart.com

  14. Related Presentaions Thermal Conduction Powerpoint by KT Thermal Radiation Powerpoint by KT Evaporation Powerpoint by KT Heat Energy Transfer Powerpoint by KT web site: www.ktaggart.com

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