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Convection current

Submitted by :Name Id

Nahida Sultana 143-33-2135Uzzal 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 DepartmentDepartment of EEE

Daffodil International University

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

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.

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.

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.

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

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

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.

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.

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.

Examples of convection

Convection cellsA 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

Mantle convectionMantle 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.

Speed of convectionTypical 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.

The 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

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

THANKS TO ALL