Heat Transfer Formula – Definition And Examples

Heat Transfer Formula is a fundamental concept in physics that deals with the transfer of thermal energy from one object or substance to another. Heat transfer plays a crucial role in our daily lives

What is Heat Transfer?

Heat transfer formula is the process of energy exchange between two substances or systems due to temperature differences. It is a fundamental concept in thermodynamics and plays a crucial role in various natural and engineered processes.

How is Heat Transferred?

Three basic processes—conduction, convection, and radiation—transfer heat. These mechanisms describe how heat energy moves from one object or substance to another:

Conduction

Conduction is the direct passage of heat between two materials or objects that are at various temperatures. Heat transfers from the hotter to the cooler object when there is a temperature differential between them. The material’s atoms or molecules collide with one another, transferring heat energy. In general, metals are better at transferring heat than materials like wood or plastic.

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Conduction Equation

The conduction equation, also known as the heat conduction equation or the heat equation, describes the flow of heat through a medium over time. It is a partial differential equation that relates the temperature distribution within a material to the rate of heat transfer. The one-dimensional form of the conduction equation is as follows:

∂u/∂t = α  ∂²u/∂x²

Where:

• ∂u/∂t represents the rate of change of temperature u with respect to time t.
• α is the thermal diffusivity of the material, a property that combines the material’s thermal conductivity (how well it conducts heat) and its heat capacity.
• ∂²u/∂x² is the second derivative of temperature u with respect to position x, representing the curvature of the temperature distribution along the material.

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Convection In Transmission of Heat 

Heat is transferred through fluid (liquid or gas) motion known as onvection. Heat causes a fluid to lose density and rise, replacing a cooler, denser fluid that then heats up and rises. By doing so, a steady circulation pattern is created, which distributes heat throughout the fluid. Ocean currents and air currents (wind) are just two examples of the many natural phenomena that are caused by convection.

Convection Equation In Transmission of Heat 

Displacement is the term for the phenomenon of a liquid’s volume having to rise in proportion to its temperature. The following equation can be used to determine the rate of convection:

Q = h_c ∙ A ∙ (Ts – Tf)

Where,

• Q is the heat transferred per unit time
• hc is the coefficient of convective heat transfer
• A is the area of heat transfer
• Ts is the surface temperature
• Tf is the fluid temperature

Radiation In Transmission of Heat 

Heat is transferred through radiation, which takes the form of electromagnetic waves like infrared radiation. Radiation, in contrast to conduction and convection, does not need a physical medium to transport heat. The amount of radiation an object emits or absorbs relies on both its surface’s composition and temperature. 

Radiation Equation In Transmission of Heat 

The wavelength in the spectrum of the radiation released drops as temperature rises, and shorter wavelengths of radiation are emitted. The Stefan-Boltzmann law can be used to compute thermal radiation:

P = e ∙ σ ∙ A· (Tr – Tc)⁴

Where,

• P is the net power of radiation
• A is the area of radiation
• Tr is the radiator temperature
• Tc is the surrounding temperature
• e is emissivity and σ is Stefan’s constant(σ = 5.67 × 10-8Wm-2K-4

Unit of Heat Transfer

In the International System of Units (SI), the measure of heat transmission is commonly expressed in joules (J). Energy comes in the form of heat, and the joule is the accepted measurement of energy. Heat transfer between two objects can be measured in terms of the energy that is transferred, which is given in joules.

In some cases, especially in the context of thermodynamics, the calorie (cal) is also used as a unit of heat transfer. The amount of energy needed to raise the temperature of 1 gramme of water by 1 degree Celsius is known as a calorie. The joule, on the other hand, is the SI unit of heat transfer and is the one that is most frequently employed in scientific and engineering contexts.