Modes of Transfer of Energy In Thermodynamics

When energy is moved between thermodynamic systems through thermal interaction, it is referred to as heat. As a result, the units of heat are joules, or units of energy (J).Conduction, convection, and/or radiation are used to transfer heat.

Energy is manifested in a variety of ways:

• The potential energy required to bind nucleons in the nucleus is known as nuclear energy.
• The potential energy contained by the oscillating electric and magnetic fields that make up electromagnetic radiation is referred to as light energy.
• Potential energy held in the electrostatic bonding interactions among atoms in a molecule is known as chemical energy.
• The potential energy required to initiate and maintain electron transport is known as electrical energy.
• Mechanical energy is the energy produced (or stored) by machines that causes (or resulting from) concerted motion processes in a system.
• The kinetic energy associated with random motion of matter, such as the vibratory and rotary activity of molecules, is known as heat energy.

What are the various energy transfer modes?

We have three different types of  modes of energy transfer:

The three types of heat transmission are: 

Conduction:

The movement of heat through matter (solids, liquids, or gases) without the matter moving in bulk is referred to as conduction heat transfer. Conduction, on the other hand, is the energy transfer from more energetic to less energetic particles in a substance as a result of particle interaction. In gases and liquids, conduction heat transmission is caused by the collisions and diffusion of molecules during their random motion.Heat transmission in solids, on the other hand, is caused by a mix of molecular lattice vibrations and energy transit by free electrons. Heat conduction, for example, can occur through the wall of a vein in the human body. The temperature of the inside surface, which is exposed to blood, is higher than that of the outside surface.

It is important to relate heat transfer to mechanical, thermal, or geometrical features in order to study conduction heat transfer.

Heat conduction along a length (or thickness) L and a cross-sectional area A in time is governed by the equation:

Q = k ∙ A∙∆T/ L

∆T denotes the temperature difference between two points.

The thermal conductivity, k, is a constant that depends entirely on the material and is measured in J / (s m °C).

Copper, a good thermal conductor, has a thermal conductivity of 390 J / (s m °C), which is why some pots and pans have copper bases. The thermal conductivity of Styrofoam, on the other hand, is 0.01 J / (s m °C), making it a good insulator.

Convection :

While often regarded as a separate form of heat transmission, convective heat transfer involves the processes of conduction (heat diffusion) and advection (heat transfer by bulk fluid flow). Convection is the most common mode of heat transmission in liquids and gases.

This concept of convection is only applicable in the contexts of heat transfer and thermodynamics. It should not be confused with convection, a dynamic fluid phenomenon.

Heat transfer by the medium of convection is divided into two types :

Free or natural convection:

When fluid motion is generated by buoyant forces caused by density fluctuations due to changes in thermal temperature in the fluid, it is referred to as free or natural convection. When a fluid comes into touch with a heated surface in the absence of an internal source, its molecules separate and scatter, making the fluid less dense. As a result, the fluid is displaced, and the cooler fluid becomes denser, sinking the fluid. As a result, the hotter volume of the fluid transfers heat to the cooler volume. The upward flow of air caused by a fire or a hot object is well-known, as is the circulation of water in a pot heated from below.

Forced convection: 

An artificially induced convection current is created when a fluid is forced to flow over the surface by an internal source such as fans, churning, or pumps.

Natural and forced convection occur at the same time in many real-world situations (for example, heat losses at solar central receivers or cooling of photovoltaic panels) (mixed convection).

The following is the equation for calculating the rate of convection:

Q = h∙ A ∙ (Ts – Tf)

Where,

The heat transferred per unit time is denoted by Q.

h is the convective heat transfer coefficient.

The heat transfer area is denoted by the letter A.

Ts is the temperature at the surface.

The fluid temperature is Tf.

Radiation:

Thermal radiations are referred to as radiant heat. The production of heat radiation is caused by the emission of electromagnetic waves. These waves carry the energy from the generating body away. Radiation can occur in a vacuum or through a clear solid or liquid substance. Thermal radiation is caused by the random movement of molecules in materials.Emission of electromagnetic radiation is caused by the movement of charged electrons and protons. Please tell us more about heat transmission by radiation.

Radiation heat transfer is measured by the help of a device known as thermocouple. Temperature is measured using a thermocouple. When monitoring the temperature through radiation heat transfer, this equipment can make mistakes.

Radiation Equation

The wavelengths in the spectrum of the radiation emitted decrease as the 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)

Where,

The net power of radiation is denoted by P.

The radiation area is denoted by the letter a.

The radiator temperature is Tr.

Tc stands for the ambient temperature.

e is emissivity and σ is Stefan’s constant

Conclusion :

Energy cannot be generated or destroyed; instead, it can only be transformed from one form to another. In layman’s terms, the first law of thermodynamics states that when heat energy is introduced from the outside, some of it remains in the system and the rest is spent as work.