# A Text Book Of Thermal Engineering by R S Khurmi and J K Gupta: The Ultimate Guide for Mechanical Engineers

## A Text Book Of Thermal Engineering By R S Khurmi And J K Gupta

Thermal engineering is a branch of engineering that deals with the generation, conversion, transmission and utilization of heat and work. It involves the study of thermodynamics, fluid mechanics, heat transfer, combustion, refrigeration, air conditioning and renewable energy sources. Thermal engineering is essential for the design and operation of various machines, devices and systems that involve heat and work.

## A Text Book Of Thermal Engineering By R S Khurmi And J K Gupta

A Text Book Of Thermal Engineering By R S Khurmi And J K Gupta is a comprehensive book that covers all the topics of thermal engineering in a clear and concise manner. The book is divided into 38 chapters that cover both theoretical and practical aspects of thermal engineering. The book is suitable for undergraduate students of mechanical engineering as well as for practicing engineers who want to refresh their knowledge and skills.

In this article, we will review some of the main topics covered in the book and highlight their importance and applications in thermal engineering.

## Properties of Perfect Gases

A perfect gas or an ideal gas is a hypothetical gas that obeys the ideal gas equation:

PV = nRT

where P is the pressure, V is the volume, n is the number of moles, R is the universal gas constant and T is the absolute temperature.

A perfect gas also follows the gas laws such as Boyle's law, Charles' law, Gay-Lussac's law and Avogadro's law. These laws relate the pressure, volume and temperature of a gas under different conditions.

Some examples of perfect gases are air, oxygen, nitrogen, hydrogen and helium. These gases are considered perfect because they have negligible intermolecular forces and their molecules occupy negligible volume compared to the volume of the gas.

The properties of perfect gases are important for thermal engineering because they help us to analyze the behavior and performance of various systems that involve gases such as air compressors, gas turbines, internal combustion engines, etc.

The book explains the properties of perfect gases in detail and provides numerous solved examples and exercises to help the students understand them better.

## Thermodynamic Processes of Perfect Gases

A thermodynamic process is a change in the state of a system from one equilibrium state to another. A system can undergo different types of thermodynamic processes such as isobaric (constant pressure), isochoric (constant volume), isothermal (constant temperature), adiabatic (no heat transfer), polytropic (PV^n = constant) and reversible (no entropy generation).

The work done by or on a system during a thermodynamic process depends on the path followed by the system between the initial and final states. The heat transfer to or from a system during a thermodynamic process depends on the temperature difference between the system and its surroundings. The entropy change of a system during a thermodynamic process depends on the irreversibility or reversibility of the process.

The thermodynamic processes of perfect gases are important for thermal engineering because they help us to calculate the work output or input, heat transfer and efficiency of various systems that involve perfect gases such as air cycles, steam cycles, refrigeration cycles, etc.

The book explains the thermodynamic processes of perfect gases in detail and provides numerous solved examples and exercises to help the students understand them better.

## Entropy of Perfect Gases

Entropy is a thermodynamic property that measures the degree of disorder or randomness in a system. It is also related to the quality or availability of energy in a system. A system with high entropy has low quality or availability of energy whereas a system with low entropy has high quality or availability of energy.

The entropy change of a system during a thermodynamic process can be calculated by using the following formula:

dS = dQ/T

where dS is the differential entropy change, dQ is the differential heat transfer and T is the absolute temperature.

The entropy change can also be calculated by using specific heats or enthalpies for perfect gases.

The entropy change can be positive, negative or zero depending on whether heat is transferred to or from the system or no heat transfer occurs.

The entropy change can also be positive or negative depending on whether the process is irreversible or reversible. An irreversible process increases the entropy whereas a reversible process keeps it constant.

The entropy change can also be positive or negative depending on whether the process involves expansion or compression. An expansion process increases the entropy whereas a compression process decreases it.

The entropy change can also be positive or negative depending on whether the process involves heating or cooling. A heating process increases the entropy whereas a cooling process decreases it.

The entropy change can also be positive or negative depending on whether the process involves mixing or separating. A mixing process increases the entropy whereas a separating process decreases it.

The entropy change can also be positive or negative depending on whether the process involves phase change or not. A phase change process increases or decreases the entropy depending on whether it involves vaporization or condensation.

The entropy change can also be zero if there is no heat transfer, no irreversibility, no expansion or compression, no heating or cooling, no mixing or separating and no phase change.

The entropy change can never be negative for an isolated system because it violates the second law of thermodynamics which states that the entropy of an isolated system can never decrease.

The entropy change can never be zero for an irreversible process because it violates the Clausius inequality which states that for any irreversible process:

dS > dQ/T

The entropy change can never be positive for a reversible adiabatic process because it violates the definition which states that for any reversible adiabatic process:

dS = 0

The entropy change can never be negative for an irreversible adiabatic process because it violates the second law which states that for any irreversible adiabatic process:

dS > 0

The entropy change can never be zero for an irreversible non-adiabatic process because it violates the Clausius inequality which states that for any irreversible non-adiabatic process:

dS > dQ/T