Heat travels by convection
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Heat travels by convection

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Heat travels by convection Heat travels by convection Document Transcript

  • Objectives This study aimed to analyze the heat travels by convection and to discuss about convection currents and to learned about Atmospheric convection Ventilation Sea breeze and Land breeze Some example of convection process are also described.
  • What is Convection ? The phenomenon due to which particles of a medium actually move to the source of heat energy, and then move away from it after absorbing heat energy is called Convection . In simple words, Convection is the transfer of heat by currents. Heat travels by convection in fluids (liquids and gases).
  • More about convection  Convection takes place in fluids only where molecules are free to move about. Exception is mercury which gets heated by conduction as it is a very good conductor of heat.  Convection depends on the fact that, in general, fluids expand when heated and thus undergo a decrease in density (since a given volume of the fluid contains less matter at a higher temperature than at the original, lower temperature).  Now question rises that Why is convection not possible in solids?  The answer is that the molecules of a solid are held tightly among each other due to intermolecular forces. As, these molecules cannot travel to the source of heat energy, convection is not possible in the cases of solids.
  • What are convection currents???  On heating, as a result, the warmer, less dense portion of the fluid will tend to rise through the surrounding cooler fluid, in accordance with Archimedes' principle.  If heat continues to be supplied, the cooler fluid that flows into replace the rising warmer fluid will also become heated and also rise.  Thus, a current, called a convection current, becomes established in the fluid, with warmer, less dense fluid continually rising from the point of application of heat and cooler, denser portions of the fluid flowing outward and downward to replace the warmer fluid.  In this manner, heat eventually may be transferred to the entire fluid.  Convection currents are widely observed in both liquids and gases.  Many aspects of weather are connected with convection currents.
  • Example of convection  Heated water in the pot expands and becomes less dense.  The warmer water will then rises while the cooler and denser water near the surface descends.  Convection currents are formed.
  • 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.  It is warmer at the bottom, so this warmer air rises and a convection current is set up. Freezer compartment
  • Atmospheric convection Atmospheric convection is a very important part of Earth’s weather. In atmospheric convection,  Warm air moves upwards.  Cool air falls downwards.
  • Other example of convection Convection cells are visible in the heated cooking oil in the pot above. Heating the oil produces changes in the index of refraction of the oil, making the cell boundaries visible. Circulation patterns form, and presumably the wall-like structures visible are the boundaries between the circulation patterns.
  • Convection is thought to play a major role in transporting energy from the center of the Sun to the surface, and in movements of the hot magma beneath the surface of the earth. The visible surface of the Sun (the photosphere) has a granular appearance with a typical dimension of a granule being 1000 kilometers. The image above is from the NASA Solar Physics website and is credited to G. Scharmer and the Swedish Vacuum Solar Telescope. The granules are described as convection cells which transport heat from the interior of the Sun to the surface.
  • Applications of convection currents in gases  Ventilation  Sea breeze  Land breeze Ventilation  The supplying of air motion in a space by circulation or by moving air through the space. It may include partial treatment such as heating, humidity control, filtering or purification, and, in some cases, evaporative cooling. In simple words, the process by which continuous replacing of warm and impure air by cool and fresh air from outside is called Ventilation.
  • How does ventilation takes place???  Breathing by people in a room causes increase in the rate of moisture and carbon dioxide in air.  Moreover, the air gets warm. This warm air is light and hence rises up.  It then passes out of the ventilators. This causes a fall in pressure in the room.  To make up for this fall in pressure the cool air from outside flows in.  Thus, the warm air is continuously replaced by cool and fresh air that is Ventilation takes place.
  • Images for ventilation
  • Sea Breeze  A breeze blowing towards the land from the sea.  During day time, sun shines equally on the land as well as the sea. However, the land gets heated up faster than the sea as the specific heat capacity of the land is far less than the sea water. Thus, the air above land becomes hotter than the air above sea. This hot air being light expands and rises up. This results in a fall of pressure over the surface of land. To make up for this fall in pressure cool air from sea starts blowing towards land giving rise to SEA BREEZE.
  • Land breeze  A breeze blowing towards the sea from the land.  During night, land as well as sea lose heat. However, the land loses its heat more rapidly as compared to sea on the account of its low specific heat capacity. Thus the air above land becomes colder than the air above sea. The hot air above sea being light expands and rises up .This causes a fall in pressure over the surface of the sea. To make up for this fall in pressure the air above land starts blowing towards the sea giving rise to LAND BREEZE.
  • Review Questions  Write the correct answer . 1. Convection is the transfer of heat by currents. A. Conduction B. Convection C. Radiation 2. A convection current , becomes established in the fluid, with warmer, less dense fluid continually rising from the point of application of heat and cooler, denser portions of the fluid flowing outward and downward to replace the warmer fluid. A. convection current B. ventilation C. sea breeze
  • 3. The process by which continuous replacing of warm and impure air by cool and fresh air from outside is called Ventilation . A. Ventilation B. Sea Breeze C. Land Breeze 4. A breeze blowing towards the land from the Answer : Sea Breeze sea. A. Ventilation B. Sea Breeze C. Land Breeze 5. A breeze blowing towards the sea from the land. Answer : Land Breeze A. Ventilation B. Sea Breeze C. Land Breeze
  • 6. Convection depends on the fact that, in general, fluids expand when heated and thus undergo a decrease in density . A. solid B. fluids C. density 7. Convection is the transfer of heat by currents. Heat travels by convection in fluids . A. solid B. fluids C. density 8~10. Give the 3 Applications of convection currents in gases. Ventilation 8. Ventilation Sea Breeze 9. Sea Breeze 10. Land Breeze Breeze
  • Conclusion THE END  Based on this study it can be said that among all processes of heat transfer, heat convection is a complex process as it involves combined effect of heat conduction and fluid motion. Thank You for Listening References  http://www.slideshare.net/981011071 8/convection-25679184?from_search=3  http://www.slideshare.net/khairuzzam an/a-study-on-covection-heat-transfer  http://www.slideshare.net/TalikSmith/ chan-yeeyi-convection?from_search=24