The basic 4 thermodynamic processes in physics are hidden marvels of science, especially within engineering. For example:

• Roaring Engines: They ignite powerful fires, propelling vehicles with relentless force.
• Throbbing Turbines: They craft a transformation, converting raw energy into a seamless symphony of motion and efficiency.
• Whispering Refrigerators: They skilfully regulate the flow of coolness, preserving our sustenance with unwavering grace.

In addition to these processes, understanding the idea of reversibility and irreversibility is also vital in thermodynamics.

Introduction

Fundamental thermodynamic processes not only enhance the understanding of the thermal aspect of our world but also unlock the secrets to optimising the performance and efficiency of thermal processes. They led to the creation of even more impressive innovations.

Those who learn about this language, find these processes to be guiding stars that lighten the path toward engineering excellence.

Welcome to the fascinating world of thermodynamics, where we witness,

• energy transformation, system evolution, and the very fabric of the physical world getting shaped
• ordinary becomes extraordinary, and understanding the concept unlocks mysteries of the universe

In the back of this seemingly ordinary-looking disguise lies a world of profound scientific principles and engineering marvels waiting to be explored. Delving into the complexities of thermodynamics opens a world of possibilities for aspiring engineers, expert scientists, and simply curious individuals.

So, let us embark on a voyage that discusses the heart of thermodynamics, heat, work, equilibrium, efficiency, and energy exchange.

Definition of Thermodynamic Process

The transition of a thermodynamic system from one state to another is known as a thermodynamic process.

It is characterised by changes in some of its physical properties, like temperature, pressure, volume, etc. It is the central character in understanding and analysing the behaviour of thermodynamic systems and is governed by the laws of thermodynamics.

Prerequisite of 4 Thermodynamic Processes in Physics

Below are the foundational concepts of thermodynamic processes that everyone should be aware of. These concepts provide a foundational understanding of thermodynamic processes. They hold great significance in various engineering and scientific applications.

Types of Processes

Based on the changes in the properties of a system, thermodynamic processes are of different types. A list of the most common types include:

• Isothermal Process
• Adiabatic Process
• Isobaric Process
• Isochoric Processes

Work and Heat

Energy transfer in a thermodynamic process is either in the form of work or heat. These forms of energy are either transferred into the system or out of the system. It is important to understand the difference between these two forms of energy when analysing and designing thermodynamic systems.

The First Law of Thermodynamics

The first law is famously known as the law of conservation of energy. It states that the internal energy of a thermodynamic system is determined by the difference between heat added to the system and the work done by the system.

The Second Law of Thermodynamics

The second law deals with the concept of entropy and states that: for an ideal isolated system, the total entropy either increases over time or remains constant.

Entropy Change

For a thermodynamic system, the disorder or randomness is determined by entropy change. In irreversible processes, entropy tends to increase, while in reversible processes, it remains constant.

Ideal Gas Laws

A simple equation known as the ideal gas law, along with specific heat capacities at constant pressure and volume, is used to analyse the thermodynamic process of an ideal gas.

Phase Transitions

Thermodynamic processes involve phase transitions, namely, melting, vaporisation, and sublimation. The transitions in the state of matter are governed by the principles of thermodynamics.

Enthalpy

To analyse a process at constant pressure, the concept of enthalpy is often used. It is a thermodynamic property that is the combination of the internal energy of a system and the product of pressure and volume.

Reversibility and Irreversibility

The two concepts, reversible process, and irreversible process, hold great significance in thermodynamics. The former is an idealised case and occurs infinitely slowly, while the latter occurs spontaneously and includes irretrievable losses of energy.

Important Thermodynamic Processes in Physics

Four basic and important thermodynamic processes in physics, along with their brief description, are given below:

Isothermal Process

The isothermal process is the most basic and describes that the temperature of a system remains constant during the entire process.

Characteristic

An isothermal process in a thermodynamic system is characterised by a continuous exchange of heat with its surroundings. The exchange of heat happens to maintain a constant temperature of the system. It is typically achieved by changing the pressure and/or volume of the system.

Example

A gas that is in thermal contact with a reservoir, remains at a constant temperature. during compression or expansion of the gas.

Adiabatic Process

A thermodynamic process with no heat exchange (Q = 0) between the system and its surroundings, is known as an adiabatic process.

Characteristic

In an adiabatic process, the system changes internal energy due to the work done on or by the system. During the process, there is a change in temperature, pressure, and volume.

Example

When a gas is compressed or expands in a perfectly insulated container, there is no heat transfer to the surroundings (Q = 0).

Isobaric Process

When a system experiences energy changes while maintaining a fixed pressure, it is called isobaric pressure.

Characteristic

Similar to the isothermal process, the isobaric process is characterised by heat exchange with its surroundings but at constant pressure. Meanwhile, there is a change in the temperature and/or volume of the system.

Example

A gas enclosed in a container that has a moveable piston is undergoing heating or cooling while maintaining a constant external pressure.

Isochoric Process

A thermodynamic process is said to be an isochoric process if it is undergoing energy changes at a constant volume.

Characteristic

When a system is undergoing an isochoric process, there is no work done either by or on the system. It is because the system does not go through any volume change, and all energy transfer occurs as heat. This is a defining characteristic of an isochoric process.

Example

Heating of a gas that is enclosed in a rigid container with a locked piston.

Comparison of Thermodynamic Processes

Temperature Variation

• The temperature of the system, in an isothermal process, does not change over time.
• In the case of adiabatic, isobaric, and isochoric processes, temperature may change over time. It depends on factors like pressure and volume change.

Heat Exchange

• No heat exchange occurs during an adiabatic process (Q=0).
• During isothermal, isobaric, and isochoric processes, there is an exchange of heat with the surroundings. The exchange of heat occurs under different conditions. For instance:

Isothermal Process ⟹ heat exchange at constant temperature
Isobaric Process ⟹ heat exchange at constant pressure
Isochoric Process ⟹ heat exchange at constant volume

Volume Variation

• The isochoric process does not observe any significant change in the volume over time.
• The isothermal process and the isobaric process, both, go through significant volume changes, whereas, the adiabatic process may have a volume change.

Pressure Variation

• A thermodynamic system during an isobaric process experiences constant pressure over time.
• Isothermal, adiabatic, and isochoric processes, on the contrary, do observe a change in pressure. It depends on parameters like temperature and volume.

Reversible vs. Irreversible Thermodynamic Processes

Two fundamental concepts in thermodynamics are important to understand. These concepts describe how energy transformations occur within a system. These are:

• Reversible Process
• Irreversible Process

Reversible Process

An idealised transformation process where a system state is reversed by an infinitesimal change without causing any irrecoverable change or loss is called a reversible process.

Nature

A reversible process is a theoretical model for analysing a thermodynamic system. It serves as a benchmark for evaluating the performance of real-life phenomena.

Characteristics

The characteristic feature of a reversible process is that it proceeds very slowly and infinitesimally to maintain equilibrium at each step. It ensures that the system under consideration remains in a state of equilibrium throughout the transformation.

Energy Exchange

In terms of energy conversion, reversible processes are highly efficient and observe negligible energy loss.

Entropy Change

Since the system undergoes infinitesimally slow changes in a reversible process, the entropy change of the system and its surroundings is negligible or zero.

Examples

Some idealised reversible processes include:

• Isothermally Expanding Ideal Gas
• Adiabatically Compressed Gas
• Reversible Phase Transitions

Irreversible Process

A natural and spontaneous transformation that occurs in a practical thermodynamic system is called an irreversible process. It does not reverse the change through external intervention.

Nature

The characteristic identity of these processes is that they are mostly natural phenomena and are found in practical systems. In these processes, losses occur due to friction, heat transfer across finite temperature differences, and other irreversible effects.

Characteristics

These processes are characterised by their spontaneous change and significant deviation from equilibrium conditions. It causes losses of useable energy in the system as well as dissipative effects.

Energy Exchange

There is a loss of energy in an irreversible process that results in lower overall efficiency compared to reversible processes. The losses are due to friction, heat dissipation, and other irreversible effects.

Entropy Change

The entropy change of a system and its surroundings always tends to increase in an irreversible process. This reflects that the nature of transformation is irreversible, and it inclines to move towards greater disorder.

Examples

A couple of examples of an irreversible process include:

• Combustion
• Diffusion
• Mixing of Substances
• real-world thermodynamic processes encountered in everyday life

Final Thought

Reversible processes are idealised transformations characterized by infinitesimal changes and minimal losses, while irreversible processes are spontaneous transformations involving deviations from equilibrium and irrecoverable losses of energy and entropy.

While reversible processes serve as theoretical benchmarks, irreversible processes dominate real-world phenomena and practical engineering applications.

Everyday Examples

Expansion and Compression of Gas in a Bicycle Pump

When you inflate a bicycle tyre using a hand pump, you are engaging in a thermodynamic process involving the expansion and compression of air.

Reversible Process

A reversible process would involve slowly compressing the air in the pump by applying gradual and controlled pressure to the pump handle. This allows the air molecules to adjust to changes in pressure without significant energy loss or an increase in temperature.

Similarly, releasing the handle slowly allows the compressed air to expand back to its original volume without causing abrupt changes.

Irreversible Process

In contrast, an irreversible process occurs when you rapidly compress the air by forcefully pushing down the handle. This rapid compression generates heat due to friction between the moving parts and the air molecules, resulting in energy loss and an increase in temperature.

Additionally, the quick release of the handle can lead to sudden expansion of the air, further contributing to energy dissipation and irreversibility.

Boiling Water in a Kettle

Boiling water in a kettle is a common thermodynamic process used for making tea, coffee, or cooking various dishes.

Reversible Process

In a reversible process, the water is heated gradually on a stovetop until it reaches its boiling point. Once boiling, the temperature remains constant until all the water evaporates. Then, slowly cooling down the kettle allows the steam to condense back into liquid water without abrupt changes.

Irreversible Process

However, in everyday scenarios, boiling water often involves rapid heating, leading to vigorous boiling and irreversibly converting water into steam. This rapid process results in heat loss to the surroundings and an increase in entropy, making it irreversible.

Melting Ice Cubes in a Glass of Water

Adding ice cubes to a glass of water to cool it down is a familiar thermodynamic process.

Reversible Process

A reversible process would involve slowly adding the ice cubes to lukewarm water and allowing them to melt gradually. This slow melting process ensures that the ice and water reach thermal equilibrium without significant energy loss or an increase in disorder.

Irreversible Process

Conversely, rapidly adding the ice cubes to hot water causes them to melt quickly, leading to a decrease in order and irreversibility. The rapid heat transfer results in uneven melting and energy dissipation, making the process irreversible.

Expansion of a Balloon

Inflating a balloon by blowing air into it is a classic example of a thermodynamic process involving the expansion of gas.

Reversible Process

A reversible process would involve slowly blowing air into the balloon to gradually increase its volume without causing the material to stretch beyond its elastic limit. Releasing the air slowly allows the balloon to deflate back to its original size without permanent deformation.

Irreversible Process

However, rapidly blowing air into the balloon can stretch the material beyond its elastic limit, causing irreversible deformation. It is also possible that the rapid expansion would lead to the formation of weak spots or even bursting, making the process irreversible.

Heating and Cooling of a Room

Adjusting the temperature of a room using a heater or air conditioner involves thermodynamic processes.

Reversible Process

In a reversible process, the room temperature is gradually adjusted by slowly increasing or decreasing the output of the heating or cooling system. This gradual adjustment allows the room to reach thermal equilibrium without sudden temperature fluctuations.

Irreversible Process

However, setting the heating or cooling system to maximum power can lead to rapid temperature changes and an uneven distribution of heat or cold air. This rapid adjustment results in energy waste and may lead to discomfort, making the process irreversible.

Compression and Expansion of Air in a Car Engine

Operating a car engine involves cycles of compression and expansion of air and fuel mixtures within the cylinders.

Reversible Process

In a reversible process, the compression and expansion strokes of the engine occur gradually and smoothly, allowing the air-fuel mixture to be compressed and expanded without significant energy loss or heat generation. This ensures optimal efficiency and engine performance.

Irreversible Process

However, in real-world scenarios, the compression and expansion processes in a car engine are often irreversible due to factors such as friction, heat loss, and incomplete combustion. These irreversible effects lead to energy dissipation, reduced efficiency, and the generation of waste heat.

Refrigeration Cycle in a Household Refrigerator

Cooling food in a household refrigerator involves a thermodynamic process known as the refrigeration cycle.

Reversible Process

In a reversible refrigeration cycle, the refrigerant fluid undergoes compression and expansion stages gradually and without energy loss. This ensures efficient cooling and temperature control inside the refrigerator.

Irreversible Process

However, real-world refrigeration cycles often involve irreversible effects such as heat exchange with the surroundings, friction in the compressor, and energy loss during expansion. These irreversible effects reduce the efficiency of the refrigeration system and lead to increased energy consumption.

Heating and Cooling of a Swimming Pool

Adjusting the temperature of a swimming pool using a heating or cooling system.

Reversible Process

In a reversible process, the temperature of the swimming pool is adjusted gradually by slowly increasing or decreasing the output of the heating or cooling system. This gradual adjustment minimises temperature fluctuations and ensures uniform heating or cooling of the pool water.

Irreversible Process

However, rapid heating or cooling of the swimming pool water can lead to uneven temperature distribution and energy waste. These irreversible effects may result in discomfort for swimmers and increased energy consumption by the heating or cooling system.

Thawing Frozen Food in a Microwave

Thawing frozen food in a microwave oven to prepare it for cooking.

Reversible Process

In a reversible process, the frozen food is thawed slowly and evenly by adjusting the microwave power and duration to minimise heat gradients and ensure uniform thawing. This gradual process prevents localised overheating and preserves the texture and flavour of the food.

Irreversible Process

However, rapid thawing of frozen food in a microwave can lead to uneven heating, resulting in partial cooking or overcooking of some portions. These irreversible effects may compromise the quality and taste of the food and increase the risk of foodborne illness.

Why does understanding thermodynamic processes matter?

Understanding thermodynamic processes isn’t just about mastering scientific principles; it’s also about practical applications. Engineers and scientists rely on this knowledge for:

• Designing efficient engines and machines
• Optimising energy usage in various systems
• Developing sustainable energy solutions
• Exploring the frontiers of physics and engineering

Conclusion

In conclusion, understanding the four basic thermodynamic processes—namely, isothermal, adiabatic, isobaric, and isochoric—provides a fundamental framework for comprehending the behaviour of thermodynamic systems.

Each process presents unique characteristics and implications, from the maintenance of constant temperature in isothermal processes to the absence of heat exchange in adiabatic processes.

Whether it’s analysing the efficiency of heat engines, designing refrigeration systems, or studying natural phenomena, knowledge of these processes is essential for engineers, physicists, and scientists alike.

By grasping the intricacies of these thermodynamic transformations, we gain valuable insights into the workings of the physical world and unlock the potential to innovate, optimize, and harness energy in myriad ways.

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