Advanced thermodynamics engineering
Thermodynamics is an engineering science topic,which deals with the science of “motion” (dynamics) and/or the transformation of “heat” (thermo) and energy into various other energy–containing forms. The flow of energy is of great importance to engineers involved in the design of the power generation and process industries. Examples of analyses based on thermodynamics include:
The transfer or motion of energy from hot gases emerging from a burner to cooler water in a hot–water heater.
The transformation of the thermal energy, i.e., heat, contained in the hot gases in an automobile engine into mechanical energy, namely, work, at the wheels of the vehicle.
The conversion of the chemical energy contained in fuel into thermal energy in a combustor. Thermodynamics provides an understanding of the nature and degree of energy transformations,
so that these can be understood and suitably utilized. For instance, thermodynamics can provide an understanding for the following situations:
In the presence of imposed restrictions it is possible to determine how the properties of a system vary, e.g.,
The variation of the temperature T and pressure P inside a closed cooking pot upon heat addition can be determined. The imposed restriction for this process is the fixed volume V of the cooker, and the pertinent system properties are T and P.
It is desirable to characterize the variation of P and T with volume V in an automobile engine. During compression of air, if there is no heat loss, it can be shown that PV1.4 ≈constant
(cf. Figure 1).
Inversely, for a specified variation of the system properties, design considerations may require
that restrictions be imposed upon a system, e.g.,
A gas turbine requires compressed air in the combustion chamber in order to ignite and burn the fuel. Based on a thermodynamic analysis, an optimal scenario requires a compressor with negligible heat loss (Figure 2a).
During the compression of natural gas, a constant temperature must be maintained. Therefore, it is necessary to transfer heat, e.g., by using cooling water (cf. Figure 2b).
It is also possible to determine the types of processes that must be chosen to make the best use of
To heat an industrial building during winter, one option might be to burn natural gas while another might involve the use of waste heat from a power plant. In this case a thermodynamic analysis will assist in making the appropriate decision based on rational scientific bases.
For minimum work input during a compression process, should a process with no heat loss be utilized or should one be used that maintains a constant temperature by cooling the compressor? In a later chapter we will see that the latter process requires the minimum work input.