Convection current

Electromagnetic Field & Wave

1. WELCOME TO OUR PRESENTATION

2. Convection current Submitted by : Name Id Nahida Sultana 143-33-2135 Uzzal Hossain 143-33-2287 Parag Rahman 143-33-2269 Sadequr Rahaman 143-33-2268 Tariqul Islam 143-33-2283 Submitted To : Professor Dr. Pran Kanai Saha Head Of The Department Department of EEE Daffodil International University

3. What is convection current : The transfer of heat by the mass movement of heated particles into an area of cooler fluid.

4. Types of Convection : 1. Forced Convection : - When the fluid is forced to flow over the surface by external means such as a fan, pump or wind .

5. 2. Natural (or Free) Convection: - When fluid flow is caused by buoyancy forces that are induced by density differences due to variation of temperature of the fluid.

6. What causes convection currents? Convection currents are caused by an uneven temperature within something. Convection currents happen within the Earth's magma, water and air. It can happen in anything that is not solid and has parts that are cooler or warmer than other parts.

7. Convection currents in the Earth's System : Convection currents occur within: the geosphere – plate tectonics the atmosphere - wind the hydrosphere - ocean currents

8. Convection currents in the magma drive  plate tectonics : Heat generated from the radioactive decay of elements deep in the interior of the Earth creates magma (molten rock) in the  aesthenosphere

9. Application of convection Refrigerator The freezer is always placed at the top of the refrigerator. So that cold air at the top will sinks to the bottom. Warmer air at the bottom will rise to the top. Convection current is set up to cool down the refrigerator .

10. Application of convection Electric kettle The heating element is always placed at the bottom of the kettle. So that hot water at the bottom which is less dense will rise up. Cooler water at the top which is denser will sink to the bottom. Convection current is set up to heat up the water.

11. Convection in Gases : The fig. shows a simple demonstration of convection of gas. The hot gases from the burning candle go straight up the chimney above the candle. Cold air is drawn down the other chimney to replace the air leaving the room.

12. Examples of convection Convection cells A  convection cell , also known as a  Bénard cell  is a characteristic fluid flow pattern in many convection systems. A rising body of fluid typically loses heat because it encounters a cold surface. In liquid this occurs because it exchanges heat with colder liquid through direct exchange. In the example of the Earth's atmosphere, this occurs because it radiates heat

13. Mantle convection Mantle convection is the slow creeping motion of Earth's solid silicate mantle caused by convection currents carrying heat from the interior of the Earth to the surface. The Earth's surface lithosphere, which rides atop the asthenosphere.

14. Speed of convection Typical mantle convection speed is 20 mm/ yr near the crust but can vary quite a bit. The small scale convection in the upper mantle is much faster than the convection near the core. A single shallow convection cycle takes on the order of 50 million years, though deeper convection can be closer to 200 million years.

15. T he advantages and disadvantages of the heating effect of electric currents : Advantage  : Based on this law now it is clear that the heating effect of electrical appliances is all due to the joules law and it basically depends upon the current, resistance and time taken . 1) Electric iron 2) Heater               a) First type is Space heaters               b) Second type is convection heater               c) Third type is forced convection heaters.               d) Fourth type is electric under floor heating (domestic ) 3 ) Electric tower rails      4) Electric Air curtains      5) Electric water heaters and      6) Electric fires

16. Disadvantage  The heat is a product of resistance to the flow. Energy will be consumed to overcome the resistance, producing the heat, which in turn increases the resistance, leading up to a runaway situation of excess heat being produced at the expense of the power to the circuitry. If the heat cannot dissipate then fire or circuit failure may result. Remember H= i^2 *R*T ............. joule"s law of heating

17. THANKS TO ALL