Heat Transfer Types, Definition, Convection, Radiation, Conduction

Heat Transfer

The Sun, like any star, is a ball of hot plasma that keeps burning and radiating energy in all directions in space. The energy radiated by the Sun is the prime source of energy for Earth and all other planets in the solar system. The radiated energy from the Sun received by the Earth’s surface is termed Insolation. However, the Earth receives only a minuscule part of this radiated energy from the Sun.

Land and water surfaces, clouds, atmospheric gases and dust intercept the incoming insolation and absorb energy from the incoming insolation. The absorbed energy then manifests in the form of various weather patterns, powerful ocean currents and vegetation. These manifestations of energy differ from region to region, such as the deserts, oceans, mountain tops, plains, rain forests and ice-covered landscapes. Apart from the interferences, the presence or absence of clouds in the atmosphere may have a difference of up to 75 per cent in the amount of energy landing on the Earth’s surface.

Read More: Ocean Waves

Heat Transfer in Atmosphere

Solar energy is the primary source of heat. However, its effect is not directly realized. For example, as one climbs a mountain or ascends in the atmosphere, the temperature steadily lowers, rather than increases, which one might expect. This particular phenomenon is experienced as the mechanism of heating by solar insolation in the atmosphere is not very simple or uniform.

Read More: Structure of the Atmosphere

Types of Heat Transfer

There are four common types of energy transfer involved in heating the atmosphere. They are Radiation, Conduction, Convection and Advection.

Heat Transfer Radiation

Heat Transfer by the process of radiation occurs when Heat Waves or energy are emitted through electromagnetic radiation without any medium. The heat transfer through radiation phenomenon is commonly seen when the Sun’s rays (electromagnetic waves) travel through space in a vacuum and fall on the surface of the Earth. Photon particles in the radiation collide with the air molecules in the atmosphere and transfer energy. All objects, whether hot or cold, emit radiation continuously. A body’s surface temperature affects the wavelength at which it radiates. The energy carried by the radiation increases with shorter wavelengths.

The Sun, having an extremely hot surface temperature, radiates fairly short wavelengths (ultraviolet, visible light), part of which is felt as warmth, part of which is visible as light. On the other hand, the Earth has a cool surface. The Earth tends to re-radiate heat that it had absorbed from the Sun, at much longer wavelengths (thermal infrared radiations). The re-radiating heat from the Earth’s surface is called terrestrial radiation.

The atmosphere is transparent to short waves, thus resulting in escaping of short waves to space. But the atmosphere is opaque to long waves absorbed by atmospheric gases, particularly carbon dioxide, water vapour and other greenhouse gases. Hence, it can be safely said that the energy leaving the Earth’s surface heats up the atmosphere more than the incoming solar radiation.

Heat Transfer Conduction

When two objects of varying temperatures come in contact, heat energy flows from the warmer object to the cooler one. This process of transferring heat is known as conduction. The flow continues till the temperature of both objects reaches an equilibrium or the contact is broken.

The conduction in the atmosphere occurs at the zone of contact between the atmosphere and the earth’s surface by terrestrial radiations. However, this is a minor Heat Transfer method for warming the atmosphere since it only affects the air in contact with the earth’s surface. This is because the air is a poor conductor of heat.

Convection Heat Transfer

Convection is the transfer of heat energy from one part of a liquid or a gas to another by the movement of particles themselves. As the lower part of a mass of liquid is heated, molecules warm, and their vibration increases, causing collisions that produce motion in neighbouring molecules. Gradually, it expands, reduces its density, and rises to carry the heat. For example, upward-moving air is said to rise in a convection current. Thus, it transfers heat from warmer to cooler materials in this manner.

Heat Transfer Advection

The transfer of heat by the horizontal movement of air is called advection. Mostly these atmospheric winds that blow over a region, take the region’s characteristics with them. The temperature of a place rises if it lies on the path of warmer winds. The temperature will dip if the place lies on the path of winds blowing from cold regions. In summer, ‘Loo’ of north India is a hot wind and ‘Sirocco’ is also a hot wind that carries the heat of the Sahara desert to Mediterranean regions. In the middle latitudes, most diurnal (day and night) variation in daily weather is caused by advection alone.

Comparison among Radiation, Conduction, Convection & Advection

Heat Transfer UPSC

The environment can be heated & cooled in a variety of ways. After being warmed by insolation, the earth radiates heat in a long waveform to the upper atmosphere.

There are three distinct processes that are primarily responsible for the heating and cooling of the Earth’s atmosphere. Conduction, Convection, and Advection—three crucial processes—are briefly discussed in this article. This article’s content will be useful for the UPSC exam. This material will be of great use to candidates as they get ready for the IAS Exam.

Other Indian Geography Topics

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