What is convection ?
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Convection is the process by which heat is transferred by movement of a heated fluid such as air or water. Types of convection are:
1)Natural convection: this results from the tendency of most fluids to expand when heated i.e., to become less dense and to rise as a result of the increased buoyancy. Circulation caused by this effect accounts for the uniform heating of water in a kettle or air in a heated room. The heated molecules expand the space they move in through increased speed against one another, rise, then cool and come closer together again, with increase in density and a resultant sinking.
2)Forced convection: this involves the transport of fluid by methods other than that resulting from variation of density with temperature. Movement of air by a fan or of water by a pump are examples of forced convection.
3)Atmospheric convection: the currents can be set up by local heating effects such as solar radiation (heating and rising) or contact with cold surface masses (cooling and sinking). Such convection currents primarily move vertically and account for many atmospheric phenomena, such as clouds and thunderstorms.
In convection the heat is transferred through a fluid (liquid or gas) because of its moment.
Suppose we take a utensil filled with cold water and we are heating it. Bottom most layer of water starts heating up first, remember that high temperature things are lite and low temperature things are heavy. Water which is getting heated up first will become lite in weight and shifts upwards and cold water above in the layer will shift to the lower side of the utensil. In this way molecules with lite weight will move upwards and molecules with heavy in weight will move downwards (difference in density caused by temperature variation). This moment causes heat transfer and this process is called convection.
Convection is the process by which heat is transferred in a fluid (liquid or gas). This movement can be caused by differences in temperature and density. There are mainly two types of convection:
Natural Convection: Occurs when the movement is driven by buoyancy forces that result from density variations due to temperature differences in the fluid. For example, warm air rising and cool air sinking.
Forced Convection: Occurs when the movement of the fluid is caused by external forces, such as fans or pumps. This is commonly seen in heating systems or cooling fans in electronic devices.
There are three modes of heat transfer. Convection, conduction, and radiation. Convection and conduction need mediums to transfer heat from one place to another, but radiation doesn’t need mediums. In the convection process, heat is transferred through air or liquid currents. Liquids and gases are poor conductors of heat. They are heated by the convection process. In convection, the transfer of heat is always vertically upward because the molecules of the medium near the source of heat, after absorbing heat, start moving faster. Medium starts expanding and less dense medium risses up and the denser medium moves down to take its place. Convection causes liquid or gas to heat up, expand, and decrease in density. This causes the liquid or gas to move in a convection current.
Some example of a convection mode is
1. Ventilation in a room. When cooler air comes into the room, it takes the place of hot air near the ground surface, and hot air’s lightweight goes up and escapes from the ventilator.
2. Sea breeze or a land breeze caused by a difference in pressure.
3. Ocean currents are caused due to convection currents inside the ocean.
4. Chimneys over the furnace in factories.