Month: December 2022

There are some relationships among temperature, volume, pressure, and quantity of a gas that could be described mathematically. This chapter deals with Boyle’s law, Charles’s law, Gay–Lussac’s law, and the combined gas law. These laws have one condition in common, i.e., fixed mass. In addition, some other properties of gases such as internal energy, specific… Continue reading GAS LAWS

Third law of thermodynamics is law of entropy. It is a statement about the ability to create an absolute temperature scale, for which absolute zero is the point at which the internal energy of a solid is zero. Third law of thermodynamics states that it is impossible to reduce any system to absolute zero in… Continue reading THIRD LAW OF THERMODYNAMICS

From equation: Example 1.18: A heat engine having an efficiency of 35% is used to run a refrigerator of COP of 4, what is the heat input into the each MJ removed from the cold body by the refrigerator? If this system is used as a heat pump (Figure 1.16), how many MJ of heat would… Continue reading Evaluation of Entropy Change

For a closed system (no mass flow): In terms of rate: For an adiabatic system (when dQ = 0): For an open system steady flow process:

Entropy Defining entropy in an exact word or line is impossible. It can be viewed as a measure of molecular disorder or molecular randomness. As a system becomes more disordered, the positions of the molecules become less predictable and the entropy increases. Thus, the entropy of a substance is lowest in the solid phase and… Continue reading ENTROPY AND ENTROPY GENERATION

The Clausius inequality is given by the equation where δQ represents the heat transfer at a part of the system boundary during a portion of the cycle, and T is the absolute temperature at that part of the boundary. The symbol δ is used to distinguish the differentials of non-properties, such as heat and work, from the differentials of properties, written… Continue reading THE CLAUSIUS INEQUALITY

The two corollaries of the second law known as Carnot corollaries:

The efficiency of a heat engine cycle greatly depends on how the individual processes are executed. The net work can be maximized by using reversible processes. The best known reversible cycle is the Carnot cycle. Note that the reversible cycles cannot be achieved in practice because of irreversibilities associated with real processes. But, the reversible… Continue reading THE CARNOT CYCLE

In reversible process things happen very slowly, without any resisting force, without any space limitation, everything happens in a highly organized way (it is not physically possible; it is an idealization). Internally reversible process—a system undergoes through a series of equilibrium states, and when the process is reversed, the system passes through exactly the same… Continue reading REVERSIBLE AND IRREVERSIBLE PROCESSES

From Figure 1.14 (a), let us assume that a heat engine receives heat QH from high temperature reservoir and converts it into work rejecting no heat to sink, thus violating Kelvin–Plank’s statement. Refrigerator receives heat QL from low temperature reservoir and supplies an amount (QH + QL) to high temperature reservoir when W = QH work is supplied to it. Thus, it operates to conform Clausius statement.… Continue reading Violation of Clausius Statement by Violating Kelvin–Plank’s Statement