A Concise Manual of Engineering Thermodynamics

The following sections are included:

• Preface
• Problem Solving Guide
• Contents

The following sections are included:

• Introduction
• Quantities measuring units and dimensions
• Thermodynamic systems
• Properties of a system
• Zeroth law of thermodynamics
• Basic concepts of thermodynamics — problems

In Secs. 1.3 and 1.4 we have been introduced to some assumptions used in classical thermodynamics: continuum, homogeneity, equilibrium. Another assumption is that we deal with pure substances; these substances have a fixed chemical composition throughout. This is very important when analyzing thermodynamic processes involving phase changes. A pure substance does not have to be a single chemical element; therefore water, oxygen, nitrogen, carbon dioxide are valid examples. Homogeneous mixtures of gases, such as air, can also be considered pure substances as long as there is no change of phase.

There are two distinct forms of energy:

• static forms, that can be stored in the system and characterize the state of the system, and
• dynamic forms, that cannot be stored in the system, called interactions, that are recognized at the system boundary which they cross as the system changes its state.

Energy can cross the boundaries of a closed system, in the process of transfer from one body to another, in two distinct forms: heat and work. These are transient quantities; they exist as long as the system undergoes a change, therefore they cannot be associated to a state of the system.

In this chapter, we will deal with non-flow energy equations expressing the first law written for various reversible processes occurring in closed systems.

The following sections are included:

• The steady-flow energy equation
• Open systems with steady flow
  • Boilers and condensers
  • Nozzles and diffusers
  • Turbines and compressors/pumps
  • Throttling devices
• Cycles consisting of steady-flow processes
• Flow thermodynamic processes — problems

The following sections are included:

• Cycle efficiency
• The second law of thermodynamics (Planck statement)
• Corollary of the second law (Clausius statement)
• Reversible and irreversible processes
• Other corollaries of the second law
• The Carnot cycle
• Processes in T − s diagrams
• General thermodynamic relations
• The second law of thermodynamics — problems

Air is a very common fluid in engineering thermodynamics. Its composition can be assumed invariable for most processes. Therefore, for practical reasons, air is usually treated as a single substance. However, for air-conditioning processes, atmospheric air has to be considered as a gas–water–vapor mixture. As long as no condensation occurs, both these constituents can be considered ideal gases. It is, therefore necessary to have some way of deducing the properties of the mixture from those of its constituents.

Cycles during which work is done by the system using the heat received from a hot reservoir are called power cycles (see also Sec. 6.1).

Power cycles are often classified by the type of working fluid into:

• vapor cycles
• gas cycles

Regardless of the type, these are ideal cycles, in the sense that they represent prototypes of actual cycles and their efficiencies approach but are always less than the Carnot cycle efficiency. In practice, actual cycles differ from ideal because of inherent irreversibilities and for other practical reasons. However, the study of ideal cycles leads to conclusions that are applicable to real cycles…

The following sections are included:

• Basic considerations
• Reciprocating internal-combustion engines
  • The Otto cycle
  • The Diesel cycle
  • The dual cycle
• Other types of IC engines
• Stirling and Ericsson cycles
• The Brayton cycle
• Jet-propulsion cycle
• Gas power cycles — problems

When a thermodynamic system undergoes a cycle, the work is done by the system on the surroundings if the state changes happen in a clockwise manner (power cycles). Conversely, the work is done on the system if the state changes happen in an anticlockwise manner. In this case heat is received at low temperature and rejected at high temperature while work is done on the fluid. These are called refrigeration cycles. The fluid used in these cycles is called refrigerant.

In this chapter, we will deal with flow that involves significant changes in density (compressibility). Compressible flow combines fluid dynamics and thermodynamics. We will establish some general relations associated with one-dimensional compressible flow of an ideal gas.

The following sections are included:

• Fuels and combustion
• Adiabatic flame temperature
• Effectiveness of energy conversion
• Combustion processes — problems

According to the second law of thermodynamics, heat “flows”, spontaneously, only from a high to a low temperature system. The “driving force” of heat transfer is, therefore, the difference in temperature between systems, or a system and its surroundings. For this reason, in what follows we are going to waive the sign convention used before; heat exchanged will be considered positive whether it is transferred from or to a system. Also, for all cases of heat transfer it will be considered that the temperature at every point within the system, including its surfaces, is independent of time. This allows the use of a steady-state heat transfer analysis to determine the temperature distribution and heat flow. The value of the heat transfer rate depends not only on the temperature difference, but also on the thermophysical properties, size, geometric shape and relative movement of the heat exchanging entities [58, p. 6]…

The following sections are included:

• Appendix A: The Derivation of the Adiabatic Condition
• Appendix B: Derivation of the Expression for the Re Number
• Appendix C: The Logarithmic Mean Concept
• Appendix D: Nomenclature
• Appendix E: Property Tables and Charts

This chapter contains solutions to the problems.

The following sections are included:

• Bibliography
• Index