Heat Transfer

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Why a metal spoon becomes heated when left in a hot cup of coffee? Or why, despite the fact that both are at the same temperature, walking barefoot on tiles in the winter seems colder than walking on a carpet? All of these commonplace occurrences are connected to heat transfer or the movement of heat from one location to another.
Heat Transfer-Metal spoon
Metal spoon
A warmer object always transfers heat to a cooler one until the two achieve the same temperature. Heat is a type of energy. Heat can move in three primary ways: radiation, convection, and conduction.

Conduction – Heat Transfer Through Direct Contact

A metal spoon heating up in a hot cup of tea is an example of conduction, which occurs when heat passes through a solid object. Heat energy is transferred from one molecule to another in a chain reaction during this process.

Examples of Conduction in Everyday Life:

  • Heat moves from a hot pan to your hand when you touch it.
  • Over time, a metal rod in a fire gets hotter on the other end.
  • When you hold ice in your hand, heat from your skin is transferred to the ice, causing it to melt.
Heat Transfer-Ice
Ice
Conductors are substances, such as metals, that have a high heat conductivity. Insulators are materials that do not conduct heat well, such as rubber or wood. Because of this, cooking pans frequently use wooden or plastic handles to keep your hand from getting burned by heat.
Heat Transfer-Rubber
Rubber

Convection – Heat Transfer Through Liquids and Gases

Convection is the process by which cooler, denser regions sink, less dense regions rise, forming a cycle. Heat transfer is what causes the bubbles and movement that occur when water boils.
The process of heat transfer in which heat is transmitted from one point to another due to actual motion of heated particles in liquid and gases.

Examples of Convection in Everyday Life:

  • When water boils, the water at the bottom gets warmed by the stove’s heat. A cycle is created as the hot water rises and the cooled water sinks.
  • When the warm air from a heater rises, cooler air replaces it.
  • Convection currents in the air allow gliders and birds to stay in the air with little effort.
Convection has a role in the formation of wind and ocean currents, among other weather phenomena. Additionally, it explains why warm air rises, increasing the temperature of buildings’ top stories during the summer.

Radiation – Heat Transfer Without Touching

Radiation transfers heat without the use of a medium, such as solids, liquids, or gases, in contrast to conduction and convection. Heat travels in waves, much to how the Earth warms in space due to the Sun.
The process of heat transfer from one point to another point without heating the intervening medium is called radiation.

Examples of Radiation in Everyday Life:

• Despite the sun being millions of miles far-away, feeling its warmth on our body.
• Feeling warm when we stand close to a campfire without coming into contact with the flames. The heat produced by an infrared heater or a blazing lightbulb.
Heat Transfer-Campfire
Campfire
The Sun’s energy reaches Earth through radiation, which keeps us warm. Additionally, it is being use in devices like thermal imaging cameras and microwave ovens.

Why Is Heat Transfer Important?

Following are the several aspects of life benefit from heat transmission, such as:
  • Cooking: We can cook food more evenly if we understand how heat moves.
  • Home Insulation: Proper insulation keeps homes cool in the summer and warm in the winter by slowing the transmission of heat.
  • Engineering: Engineers design automobiles, aircraft, and even spaceships using their knowledge of heat transmission.
  • Medical: Incubators and cooling systems, among other medical devices, benefit from the principles of heat transmission.

Summary

Everywhere we look, from cooking to weather variations, heat transmission occurs. Our daily perception of temperature is influenced by a number of processes, these are convection (heat flowing in fluids), radiation (heat travelling in waves), and conduction (touching a hot object). As we know that we are observing heat transfer from a use of heater to warm our hands or see steam rising from a cup of coffee.

Note :-

Greenhouse effect: The earth surface is source of thermal radiation as it absorbs energy received from the sun. But a large portion of long wavelength (infrared) radiation is absorbed by greenhouse gases, namely CO2, CH4, N2O, CFCs and O3.
This heats up the atmosphere, which intern give more energy to the earth, resulting in warmer surface. This increases the intensity of radiation from the surface. The cycle of this processes is repeated until no radiation is available for absorption. The net result is heating up of earth’s surface and atmosphere. This is called as Greenhouse Effect.
The temperature of the earth would have been- 180C without the Greenhouse Effect.
Concentration of greenhouse gases has enhanced due to human activities, making the earth warmer. According to an estimate , average temperature of earth has increased by 0.3 0C to 0.6 0C , since the beginning of this century due to this enhancement.
The passage of heat, or thermal energy, from a warmer to a cooler item or space is known as heat transfer. Until the temperatures of the two items are equal, this process keeps going. There are three primary methods of heat transfer: radiation, convection, and conduction.
The three types of heat transfer are:
• Conduction: Heat transfers by direct contact, such as when a metal spoon is placed in hot soup.
• Convection: Heat transfers in liquids and gases by sinking cool regions and rising heated regions (e.g., boiling water).
• Radiation: Heat travels in waves without the aid of a medium, such as the Sun’s warmth.
When we touch a hot pan, heat moves from the pan to our hand, which is a classic illustration of conduction. Other example are an iron heating garments while ironing or a metal spoon becoming heated in a cup of tea.
In the atmosphere, convection occurs when heated air rises and is replaced by colder air. Wind patterns, ocean currents, and even meteorological phenomena like storms are produced by this movement. For example, convection between the temperatures of the land and the water causes sea breezes.
• Direct contact between objects such as a hot metal rod is necessary for conduction to transmit heat.
• Heat is transferred by radiation in waves without the need for touch or a medium (feeling the warmth of the sun on your skin, for example).
Compared to wood, metals carry heat more quickly. Metal feels cooler when you touch it because heat from your palm quickly transferred to the metal. Wood doesn’t feel as cold since it slows down heat transfer because it is an insulator.

Following are the daily tasks affect heat transfer:
• Cooking (conduction in frying pans, convection in ovens, and radiation from grills).
• Maintaining a warm or cold home because insulation reduces heat transfer.
• Variations in weather (wind and ocean currents are produced by convection).
• Making use of electronics (cooling systems and fans avoid overheating).

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