Physics
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Heat Transfer

Heat Transfer

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Heat transfer is the movement of thermal energy from a hotter object to a cooler object. This happens because of the conservation of energy principle, which states that energy cannot be created or destroyed, but can change forms. Thermal energy is a type of energy that is transferred as heat when there is a temperature difference. When two objects are at different temperatures, thermal energy will flow from the hotter object to the cooler one until both reach the same temperature. This process continues until both objects are in thermal equilibrium. Heat transfer is an important concept in many fields, from engineering to meteorology.

Thermal equilibrium

Thermal equilibrium happens when two objects same temperature which is more transfer of thermal energy between them. It's also called an isothermal condition For it to be isothermal, the two objects must be touching each other.

Let's say you put a block of ice with a temperature of -5°C on a table that has a temperature of 25°C. Will thermal equilibrium be reached? The answer is yes. This is because the table's thermal energy will transfer to the ice due to the temperature difference of 20°C, until both objects reach the same temperature. Once they are at the same temperature, thermal equilibrium is reached.

The direction of heat transfer

The temperature difference between two areas determines the direction of heat transfer. Thermal energy always flows from the hotter region to the cooler region, as per the second law of thermodynamics. This happens naturally without any external influence. In the example we used earlier, the heat transfer was from the table to the ice because the table had a higher temperature.

Methods of heat transfer

There are three main methods by which heat transfer can occur. These include convection, conduction, and radiation.

Convection

Convective heat transfer, also referred to as convection, involves the transfer of heat through the movement of a fluid, which can be in the form of either a liquid or gas. Whenever a fluid moves, the motion of particles in the fluid results in the transfer of thermal energy. For instance, when hot fluid flows through a pipeline, the pipeline walls will heat up due to the transfer of thermal energy from the hot fluid to the walls of the pipe, causing the material to heat up. This is how convective heat transfer works.

Conduction

The process you are referring to is known as conduction. Conduction involves the transfer of heat through collisions between particles and subatomic particles within a material. When subatomic particles collide with one another, they transfer kinetic energy, which results in the creation of heat.

For instance, when a hot pan is removed from the stove and placed on a table, the thermal energy from the hot pan will transfer locally to the surface of the table by the collision of particles between the two surfaces. This is because the particles in the hot pan are vibrating at a higher frequency than the particles in the table, and as they come into contact with each other, thermal energy is transferred from the pan to the table. This is how conduction takes place.

Radiation

Radiation is another method of heat transfer, which involves the transfer of heat through the emission of light or electromagnetic waves. This type of energy is emitted by certain matters around us, such as the sun or a fire.

An example of radiation heat transfer is the heating of a room through the thermal energy emitted by a fireplace. In this example, heat transfer through conduction also occurs in the room, but at a lower rate. The heat radiated from the fireplace travels in all directions and is absorbed by the objects and surfaces in the room. The absorbed thermal energy causes the temperature of the objects and surfaces to increase, leading to an overall increase in the temperature of the room. This is how radiation heat transfer works.

Heat transfer coefficient

The heat transfer coefficient (h) is a physical property of an object that is used to express how well heat is being transferred between two objects. A high heat transfer coefficient means that heat is transferred more easily and quickly between the two objects, while a low heat transfer coefficient means that heat transfer is slower.

The heat transfer coefficient depends on two parameters: thermal conductivity and the thickness of the materials in which heat transfer occurs. Thermal conductivity is a measure of the ability of a material to conduct heat. If the thermal conductivity of a material is high, the heat transfer coefficient will also be higher. On the other hand, if the material is thick, the resulting heat transfer coefficient will be lower because heat has to farther to be transferred to the other object. In general, the heat transfer coefficient is an important factor to consider in the design of heat transfer systems and in predicting the rate of heat transfer between two objects.

The equation for heat transfer

The rate at which heat transfer occurs can be described by the following equation:

h = Q/ΔT

where h is the heat transfer coefficient, Q is the heat transferred measured in Watts, ΔT is the temperature difference between the two objects of interest (measured in Kelvin), A is the surface area of the conduction zone in m2, and T1 and T2 are the temperatures of the surface and surroundings respectively.

For the given problem, we need to find the heat transfer coefficient. First, we need to calculate the surface area in SI units. We can do this by converting 20 cm into meters and then converting diameter into radius to find the area: A = πr2 = π(0.1m)2 = 0.0314 m2.

Next, we can rearrange the heat transfer rate equation to find the heat transfer coefficient: h = Q/AΔT. Finally, we can substitute the given values into the equation to find the heat transfer coefficient: h = 600W/(0.0314 m2 * (380K - 300K)) = 5,844 W/m2K.

Heat Transfer

What is radiation heat transfer? 

It is the thermal energy transferred in the form of  electromagnetic radiation or light. 

How is heat transferred?  

Heat is transferred by three methods, convection , radiation and conduction.  

How is heat transferred by convection?  

The moving molecules between a fluid and a body are colliding, transferring heat from one body to the other. 

How does thermal radiation work?  

Thermal energy is emitted in the form of electromagnetic waves by a heated body and travels and travels until it is absorbed. 

What is heat transfer?  

 It is the thermal energy being transferred between bodies due to a present temperature difference (ΔΤ).

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