Modes of Heat Transfer

MODES OF HEAT TRANSFER

 Heat is a form of energy that derives its origin on a molecular scale. These molecules of matter, when energized, oscillate in their position, whether fixed or not. When they vibrate, they often transfer their energy to the surrounding molecules, allowing them to vibrate.

Thermal energy can move from one object to another, or from one object to another. The study of the methods and techniques adopted to transfer heat energy is called "heat transfer". To allow heat transfer between two objects, there must be a temperature difference between them. This requires these two objects to have two different temperatures, one higher than the other, so that heat flows from one object to another.

What are those different modes of heat transfer which is used in daily life?

In our daily life, it has been observed that boiling a pot with fire-filled water raises its temperature. However, when the flame is extinguished, it cools slowly.

This is due to the phenomenon of heat transfer that occurs between a pot filled with water and a flame. It has been confirmed that heat transfer occurs from a hot object to a cold object.

If the object is falling at a different temperature, or if there is an object at a different temperature than the surroundings, heat transfer is done so that both the object and the surroundings reach an equilibrium temperature.

There are three modes of heat transfer. An example of these heat transfer modes is shown below.

1. Conduction

2. Convection

3. Radiation

Conduction

Conduction occurs at the microscopic level. Hot atoms and molecules have high levels of energy. Due to vibration, this energy is transmitted to adjacent atoms and molecules. In other words, in the conduction mode of heat transfer, the vibrating atoms and molecules are part of their energy.

This type of heat transfer can occur between or through two or more substances. Conduction can also occur when an electron moves from one atom to another. Temporary conduction occurs when the temperature inside an object changes as a function of time.

Convection

Convection is a mode of heat transfer generated by the movement of heated atoms or aggregates of molecules. Convection requires the actual flow of material particles, but in conduction, heat is transferred by vibration without the atoms or molecules leaving their original positions. In convection, heat transfer is through both diffusion and advection.

Convection requires the actual movement of heated atoms/molecules, so the presence of fluid for heat transfer is required.

Radiation

Radiation is a mode of heat transfer that takes place over a vacuum and does not require a physical medium. Radiation is emitted through either a vacuum or a transparent medium. In radiation mode, heat transfer is done through photons present in the electromagnetic waves. The random movement of atoms and molecules in a heated substance results in the emission of electromagnetic waves that carry the transferred heat.

Radiant heat transfer conforms to Stephen-Boltzman's law. Objects radiate heat at all temperatures above absolute zero, regardless of ambient temperature.

1. Heat conduction

Heat conduction is the process by which heat is transferred from hot to cold parts of the body without the actual movement of the body's molecules. Here, heat transfer occurs from one molecule to another as a result of the vibrational motion of one molecule. Heat transfer occurs through the process of conduction that occurs in substances that are in direct contact with each other. Generally, it happens in solids.

Some modes of heat transfer examples are when frying vegetables in a pan. Heat transfer occurs from the flame to the pot and next to the vegetables.

Based on thermal conductivity, matter can be divided into conductors and insulators. A substance that conducts heat quickly is called a conductor, and a substance that does not conduct heat is called an insulator.

2. Heat convection

This is the process by which heat is transferred from the hot region to the cold region, both liquid and gas. Convection heat transfer occurs partially due to either the actual movement of molecules or mass transfer.

One of the modes of heat transfer example is to heat the milk in a pan.

3. Heat radiation

Heat radiation is the process by which heat is transferred from one object to another without the involvement of media molecules. This type of heat transfer is medium-independent.

One of the modes of heat transfer example is in the oven, where the substance is heated directly without a heat medium.

Factors Affecting Heat Transfer

Now let's talk about the factors or speeds of heat transfer that it depends on. Heat transfer coefficient generally depends on the following factors:

ΔQΔt∝ A (T1–T2) x

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The resulting heat transfer equation is: ΔQΔt = K A (T1–T2) x

Where K is the heat transfer coefficient.

Now, if the heat flow is positive, we can infer T1> T2. Therefore, heat flows from hot to cold. You can bring out the similarity with electricity. Here, temperature affects the heat transfer coefficient, the potential difference becomes like an electric current, and the rest of the representation becomes like electrical resistance. Now that we've drawn the analogy, we also need series and parallel connections here.

Cooling technology

Evaporative cooling

Traditional air cooler in Mirzapur, Uttar Pradesh, India Evaporative cooling occurs when water vapor is added to the encompassing air. The energy required to evaporate water is extracted from the air within the sort of sensible heat and converted to the heat of transformation, but the air remains constant enthalpy. the heat of transformation represents the quantity of warmth required to evaporate a liquid. This heat is generated by the liquid itself and therefore the surrounding gas and surface. The greater the difference between the 2 temperatures, the greater the evaporative cooling effect. At an equivalent temperature, no net evaporation of water within the air occurs. Therefore, there's no cooling effect.

Laser cooling

In physics, laser cooling is employed to realize temperatures at near temperature (-273.15 ° C, -459.67 ° F) for atomic and molecular samples, which are unique and may only occur at this thermal level. Observe the quantum effect.

• Doppler cooling is that the commonest method of laser cooling.

• Sympathetic cooling is that the process by which one sort of particle cools another. Atomic ions which will be laser-cooled directly are typically wont to cool nearby ions or atoms. This technology can cool ions and atoms that can't be directly laser-cooled. [citation needed]

Magnetic cooling

Magnetic evaporative cooling is that the process of lowering the temperature of atomic groups after precooling away like laser cooling. Magnetic refrigeration utilizes the magnetic heat effect to chill too but 0.3K.

Radiative cooling

Radiative cooling is that the process by which the body loses heat thanks to radiation. The transmitted energy is a crucial impact on the Earth's energy balance. within the case of the Earth's atmospheric system, it refers to the method by which longwave (infrared) radiation is emitted to balance the absorption of shortwave (visible) energy from the Sun. Both convective heat transport and heat of transformation evaporative transport remove heat from the surface and redistribute it into the atmosphere.