Heat Transfer

Edited By Team Careers360 | Updated on Jul 02, 2025 04:50 PM IST

In this article we will discuss thermal conduction, examples of conduction, heat transfer, conduction heat, radiant heat transfer, conduction heat transfer, heat energy examples, convective heat, heat conduction examples, transmission of heat, thermal conduction examples, heat transfer examples, conduction heat transfer examples, transfer of heat in solids, heat transfer in fluids, heat energy transfer, principles of heat transfer, heat transfer from hot to cold, heat transfer thermodynamics, and conduction of heat examples.

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Heat transfer
Thermal Conduction
Thermal Convection
Thermal Radiation

Heat transfer thermodynamics is a discipline of physical sciences related to the exchange, formation, application and conversion of thermal energy known as heat energy between systems. Heat can be transferred by various methods such as thermal conduction, thermal radiation, and thermal convection and sometimes by phase change.

Mechanisms of heat transfer

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Thermal Conduction

Thermal conduction involves the transfer of internal energy which takes place by the collision of particles on a microscopic level and electron movement in a system. The internal energy is a combination of the kinetic and potential energy of colliding particles which could be atoms, molecules, electrons, etc. thermal conduction is not limited to any particular phase. In other words, thermal conduction of heat transfer in fluids, as well as the transfer of heat in solids, is also possible.

In thermal conduction, heat flows from one body to another and spreads through the receiving body or part of the system. Microscopically, thermal conduction takes place due to exothermically rapid movement or vibration of colliding particles. When these particles having high heat energy interact with particles of low energy, a portion of them are transferred to these low state particles. In simpler words, thermal conduction occurs when neighbouring particles vibrate against each other. In solid objects, thermal conduction is a significant method of heat transfer.

Examples of heat transfer from hot to cold bodies could be easily identified in our day to day lives. For example, thermal conduction occurs from the warm skin of the hand when we touch a cold doorknob. But this doesn’t happen when we hold our hand close to the knob without touching it. This is due to poor thermal conduction of air whereas a solid steel knob is a better conductor of heat.

Q= [K.ATh-Tc]/d

Thermal Conduction

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Thermal Convection

When thermal energy expands the fluid, buoyancy forces induce the flow of fluid. This flow of fluid results in the transfer of energy. This process is often called convection.

Thermal convection is a process in which the transfer of heat from one system to another takes place by the movement of fluids. Transfer of heat in convection occurs via mass transfer. Heat transfer by convection is enhanced due to the bulk motion of solids. For example, heat transfer between fluid and solid surface. Thermal convection is the dominant method of heat transfer in liquids and gases.

In systems like streams and currents where bulk fluid motion is observed, free or natural convection occurs. These bulk fluid motions are generated due to buoyancy caused by density variations which are a result of temperature variation in the fluid.

When an external source like fans, pumps, stirrers, etc., are used to induce artificial convection currents such convection is known as forced convection.

Q = hc*A*(Ts-Tf)

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Thermal Radiation

In matter, the thermal motion of particles generates electromagnetic radiation. This radiation is termed as thermal radiation. When charges in the material move, heat is generated. This heat is converted into electromagnetic radiation. Thermal radiation involves the conversion of thermal energy into electromagnetic energy. Thermal energy is the kinetic energy generated when the movement of atoms or molecules in matter takes place. All matter has a temperature greater than absolute 0 emits thermal radiation. An example of thermal radiation is infrared radiation emitted by animals. When the physical characteristics of a radiating body resemble the physical characteristics of a black body, the radiation is said to be black body radiation.

When a body emits thermal radiation at any temperature, it consists of a wide range of frequencies. As the temperature of the emitter increases, the dominant frequency range shifts to a higher frequency. For example, a red hot object emits radiation in the low-frequency range of the visible band thus appearing red-orange. All properties of radiation such as polarization, coherence, and wavelength follow the principle of reciprocity which states that the rate of emission of electromagnetic radiation at a given frequency is directly proportional to the amount of absorption. That means if a substance absorbs more blue light then it will radiate thermally more blue light.

P=e*σ*A*(Tr-Tc)⁴

Thermal Radiation

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Frequently Asked Questions (FAQs)

1. What is heat energy?

Heat energy is a type of energy generated due to the vibrating movement of constituent particles of matter. These constituent particles could be ions, atoms, molecules, electrons etc.

2. Define radiative heat transfer.

It is the energy released in the form of electromagnetic waves or photons.

3. Mention the types of heat transfer.

Heat transfer is done by conduction, convection, and radiation.

4. Solid transfer heat by which process? Explain the process with an example.

In solids, heat is transferred by conduction. In thermal conduction, heat flows from one body to another and spreads through the receiving body or part of the system. Microscopically, thermal conduction takes place due to exothermically rapid movement or vibration of colliding particles. When these particles having high heat energy interact with particles of low energy, a portion of them are transferred to these low state particles. In simpler words, thermal conduction occurs when neighbouring particles vibrate against each other. In solid objects, thermal conduction is a significant method of heat transfer.

Transfer of heat in solid takes place when two solid objects come in thermal contact. Heat transfer in fluid (both gases and liquids) by thermal conduction is not effective as fluids; especially gases are relatively less conductive. In thermal conduction, heat transfer from one body to another takes place without the displacement of particles. This could be observed when heat is transferred from hot to cold bodies. Examples of heat transfer from hot to cold bodies could be easily identified in our day to day lives. For example, thermal conduction occurs from the warm skin of the hand when we touch a cold doorknob. But this doesn’t happen when we hold our hand close to the knob without touching it. This is due to poor thermal conduction of air whereas a solid steel knob is a better conductor of heat.

5. Heat is transferred in liquid by which method?

liquid and gas transfer the heat by convection. Thermal convection is a process in which the transfer of heat from one system to another takes place by the movement of fluids. Transfer of heat in convection occurs via mass transfer. Heat transfer by convection is enhanced due to the bulk motion of solids. For example, heat transfer between fluid and solid surface. Thermal convection is the dominant method of heat transfer in liquids and gases.

6. “Heat energy transfer from one solid to another by thermal contact in convection”. Is the statement false? If yes, why?

Yes, the statement is false.

Conduction - Thermal conduction involves the transfer of internal energy which takes place by the collision of particles on a microscopic level and electron movement in a system. The internal energy is a combination of the kinetic and potential energy of colliding particles which could be atoms, molecules, electrons, etc. thermal conduction is not limited to any particular phase. In other words, thermal conduction of heat transfer in fluids, as well as transfer of heat in solids, is also possible.

Convection - Thermal convection is a process in which the transfer of heat from one system to another takes place by the movement of fluids. Transfer of heat in convection occurs via mass transfer. Heat transfer by convection is enhanced due to the bulk motion of solids. For example, heat transfer between fluid and solid surface. Thermal convection is the dominant method of heat transfer in liquids and gases.

7. What is convective heat transfer?

Due to the movement of liquid, there will be a transfer of heat from one place to another. It is called convective or convection heat transfer.

8. Mention the best heat conducting metal.

Silver

9. Write 2 examples of conduction.

Following are examples of heat transfer in everyday life-

Examples of heat transfer from hot to the cold body could be easily identified in our day to day lives. For example, thermal conduction occurs from the warm skin of the hand when we touch a cold doorknob. But this doesn’t happen when we hold our hand close to the knob without touching it. This is due to poor thermal conduction of air whereas a solid steel knob is a better conductor of heat.
Heat pads are used to relieve aching body parts. Heat is transferred by conduction from the heating pad to the body.

10. What is heat transfer?

Heat transfer is the movement of thermal energy from one object or system to another due to a temperature difference. It occurs through three main mechanisms: conduction, convection, and radiation. Heat always flows from higher temperature regions to lower temperature regions until thermal equilibrium is reached.

11. How does a thermos (vacuum flask) keep liquids hot or cold?

A thermos uses multiple heat transfer prevention methods. The vacuum between its inner and outer walls prevents conduction and convection. The reflective surfaces on the walls minimize radiation. The small opening and insulated cap reduce heat loss through the top. These combined features significantly slow down heat transfer, keeping hot liquids hot and cold liquids cold.

12. How does sweating cool the human body?

Sweating cools the body through evaporative cooling, a form of heat transfer. When sweat evaporates from the skin, it requires energy in the form of heat. This heat is taken from the body, lowering its temperature. The process is more effective in dry environments where evaporation occurs more readily.

13. What is the difference between heat and temperature?

Heat is the total amount of thermal energy in a substance, while temperature is a measure of the average kinetic energy of the particles in a substance. Heat is measured in joules (J) and is extensive (depends on the amount of substance), while temperature is measured in degrees (°C or K) and is intensive (independent of the amount of substance).

14. What is thermal equilibrium?

Thermal equilibrium is the state where two or more objects or systems in contact with each other have reached the same temperature. At this point, there is no net heat transfer between them. Thermal equilibrium is a fundamental concept in thermodynamics and is the basis for the zeroth law of thermodynamics.

15. Why do metals feel colder to touch than wood at the same temperature?

Metals feel colder because they are better conductors of heat than wood. When you touch a metal object, it quickly conducts heat away from your hand, giving a sensation of coldness. Wood, being a poor conductor, doesn't remove heat from your hand as quickly, so it feels warmer even at the same temperature.

16. What is thermal conductivity?

Thermal conductivity is a material property that describes its ability to conduct heat. Materials with high thermal conductivity, like metals, transfer heat quickly, while materials with low thermal conductivity, like insulators, transfer heat slowly. It's typically measured in watts per meter-kelvin (W/(m·K)).

17. What is thermal resistance and how is it calculated?

Thermal resistance is a measure of a material's ability to resist heat flow. It's the inverse of thermal conductance and is analogous to electrical resistance. Thermal resistance (R) is calculated as the thickness of the material (L) divided by its thermal conductivity (k) and area (A): R = L / (k * A). The unit is K/W (Kelvin per Watt). Higher thermal resistance means better insulation. In complex systems, thermal resistances can be combined in series or parallel, similar to electrical circuits.

18. What is the principle behind a heat exchanger?

A heat exchanger is a device that transfers heat between two or more fluids without mixing them. It works on the principle that heat flows from hot to cold. In a typical design, hot and cold fluids flow through separate channels in close proximity. Heat is transferred through the separating wall by conduction, while convection within the fluids enhances the heat transfer rate. This principle is used in various applications, from car radiators to industrial processes.

19. How do phase change materials (PCMs) work in thermal management?

Phase Change Materials (PCMs) are substances that absorb or release large amounts of heat when changing phase (usually melting or freezing) at a nearly constant temperature. They work by utilizing latent heat:

20. How does conduction differ from convection?

Conduction is the transfer of heat through direct contact between particles of matter, without any movement of the matter as a whole. Convection, on the other hand, involves the movement of fluids (liquids or gases) to transfer heat. In convection, hotter, less dense fluid rises while cooler, denser fluid sinks, creating a circular motion that transfers heat.

21. How does convection contribute to wind patterns?

Convection plays a crucial role in creating wind patterns. As the sun heats the Earth's surface unevenly, it creates areas of warm, rising air and cool, sinking air. This temperature-driven air movement, combined with the Earth's rotation, generates global wind patterns. On a smaller scale, convection also creates local wind patterns like sea breezes.

22. How does the specific heat capacity of water affect climate?

Water has a high specific heat capacity, meaning it can absorb or release a large amount of heat with relatively small temperature changes. This property allows oceans to act as heat reservoirs, moderating Earth's climate. They absorb heat in summer and release it in winter, reducing temperature extremes in coastal areas and contributing to global heat distribution through ocean currents.

23. How do animals in cold climates adapt to minimize heat loss?

Animals in cold climates have various adaptations to minimize heat loss:

24. How do heat pumps work for heating and cooling?

Heat pumps use the principles of heat transfer to move heat from one place to another. In heating mode, they extract heat from the outside air or ground (even when it's cold) and transfer it inside. In cooling mode, they reverse the process, moving heat from inside to outside. This is achieved through a refrigeration cycle involving compression and expansion of a refrigerant.

25. What is thermal radiation and how does it work?

Thermal radiation is the emission of electromagnetic waves from all matter that has a temperature above absolute zero. Unlike conduction and convection, radiation doesn't require a medium to transfer heat. It can occur in a vacuum and is how the sun's energy reaches Earth. The amount of radiation emitted increases with temperature.

26. What is the greenhouse effect and how does it relate to heat transfer?

The greenhouse effect is a natural process where certain gases in Earth's atmosphere trap heat, warming the planet. It relates to heat transfer through radiation. Sunlight passes through the atmosphere and warms the Earth's surface. The Earth then emits infrared radiation, which greenhouse gases absorb and re-emit in all directions, including back towards the surface, causing additional warming.

27. How do heat sinks work in electronic devices?

Heat sinks work by increasing the surface area available for heat dissipation. They are typically made of materials with high thermal conductivity, like aluminum or copper. The heat sink conducts heat away from the electronic component and spreads it over a larger surface area. This larger area allows for more efficient heat transfer to the surrounding air through convection and radiation.

28. What is the role of insulation in heat transfer?

Insulation is used to slow down heat transfer between objects or environments. It works by creating barriers that reduce conduction (using materials with low thermal conductivity), convection (trapping air in small pockets), and radiation (using reflective surfaces). Good insulation helps maintain temperature differences, which is crucial for energy efficiency in buildings and various industrial processes.

29. What is the urban heat island effect?

The urban heat island effect is a phenomenon where urban areas are significantly warmer than surrounding rural areas. It's caused by several factors related to heat transfer: dark surfaces (like asphalt) absorbing more solar radiation, reduced vegetation leading to less evaporative cooling, and waste heat from human activities. This effect can impact local weather patterns and increase energy consumption for cooling.

30. How does the color of an object affect its heat absorption and emission?

The color of an object significantly affects its heat absorption and emission through radiation. Dark-colored objects absorb more visible light and convert it to heat, while light-colored objects reflect more light. However, for heat emission (infrared radiation), color is less important. Instead, the object's emissivity, which is often independent of visible color, determines how effectively it radiates heat.

31. What is the role of latent heat in phase changes?

Latent heat is the energy absorbed or released by a substance during a phase change without a change in temperature. For example, when water boils, it absorbs latent heat of vaporization to change from liquid to gas at a constant temperature. This process is crucial in many natural and industrial processes, including the water cycle and refrigeration systems.

32. How does the atmosphere's composition affect heat transfer on Earth?

The atmosphere's composition significantly impacts heat transfer on Earth:

33. What is the difference between forced and natural convection?

Forced convection occurs when an external force (like a fan or pump) moves a fluid to enhance heat transfer. Natural convection, on the other hand, occurs due to density differences in the fluid caused by temperature variations. In natural convection, hotter, less dense fluid rises while cooler, denser fluid sinks, creating a natural circulation. Forced convection generally results in more rapid heat transfer than natural convection.

34. What is the role of thermal expansion in heat transfer?

Thermal expansion is the tendency of matter to change its shape, area, and volume in response to temperature changes. While not a heat transfer mechanism itself, it plays a crucial role:

35. How does the Stefan-Boltzmann law relate to thermal radiation?

The Stefan-Boltzmann law describes the total energy radiated per unit surface area of a black body across all wavelengths per unit time. It states that the total radiant heat energy emitted is proportional to the fourth power of the absolute temperature of the body. Mathematically, it's expressed as E = σT^4, where E is the radiant heat energy, σ is the Stefan-Boltzmann constant, and T is the absolute temperature. This law is fundamental in understanding heat transfer through radiation, especially at high temperatures.

36. How do heat pipes work?

Heat pipes are highly efficient heat transfer devices that combine the principles of thermal conductivity and phase transition. They consist of a sealed pipe containing a working fluid:

37. What is the significance of the Prandtl number in heat transfer?

The Prandtl number is a dimensionless number that describes the ratio of momentum diffusivity to thermal diffusivity in a fluid. It's defined as Pr = (Cp * μ) / k, where Cp is specific heat capacity, μ is dynamic viscosity, and k is thermal conductivity. The Prandtl number is significant because:

38. How does nanoscale heat transfer differ from macroscale heat transfer?

Nanoscale heat transfer differs from macroscale in several ways:

39. What is the role of thermal diffusivity in heat transfer?

Thermal diffusivity is a material property that measures the rate at which heat diffuses through a material. It's defined as α = k / (ρ * Cp), where k is thermal conductivity, ρ is density, and Cp is specific heat capacity. Thermal diffusivity is important because:

40. How do heat transfer fluids work and what are their applications?

Heat transfer fluids are substances used to transport thermal energy from one location to another. They work by:

41. What is the concept of thermal contact resistance?

Thermal contact resistance, also known as thermal interface resistance, is the resistance to heat flow that occurs at the interface between two materials in contact. It arises because:

42. How does the Leidenfrost effect influence heat transfer?

The Leidenfrost effect is a phenomenon where a liquid, in near contact with a surface significantly hotter than its boiling point, produces an insulating vapor layer that prevents the liquid from immediately boiling. This effect:

43. What is the significance of the Biot number in heat transfer analysis?

The Biot number (Bi) is a dimensionless quantity used in heat transfer calculations. It's defined as Bi = (h * L) / k, where h is the convective heat transfer coefficient, L is the characteristic length, and k is the thermal conductivity of the body. The Biot number is significant because:

44. How do heat transfer enhancement techniques work?

Heat transfer enhancement techniques are methods used to increase the rate of heat transfer without significantly increasing the size or cost of a system. Common techniques include: