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Single Component Fluid–Applications
Published in R. Ravi, Chemical Engineering Thermodynamics, 2020
In section 3.1, three different paths connecting two chosen equilibrium states are introduced. It is assumed that there are no phase changes along the paths. The path that includes the ideal gas limit is seen as the most useful practically. This leads to the important concept of a departure function that denotes the difference between a property of the real substance and that of the ideal gas associated with that substance. Departure functions are discussed in detail in section 3.2. Formulae for the departure functions of five important thermodynamic functions are derived in both the (υ, T) domain as well as in the (p,T) domain. Then, it is shown how these formulae may be used to calculate changes in property due to change of state in the gas phase. Section 3.3 relates property changes to work and heat interactions in specific processes. Section 3.4 contains an extensive discussion of equations of state, a crucial input to calculations of property changes. In section 3.5, the results of sections 3.2 and 3.4 are combined to arrive at formulae of departure functions for some common equations of state.
Thermodynamics
Published in Yeong Koo Yeo, Chemical Engineering Computation with MATLAB®, 2020
The departure function implies the departure of the actual fluid property from the same ideal gas property at the same temperature and pressure. The changes in thermodynamic properties of an actual fluid are equal to those for an ideal gas undergoing the same change of state plus the departure from ideal gas behavior of the initial state. Once the fluid equation of state is known, the departure function can be evaluated.
Role of free volume in molecular mobility and performance of glassy polymers for corrosion-protective coatings
Published in Corrosion Engineering, Science and Technology, 2020
A. J. Hill, A. W. Thornton, R. H. J. Hannink, J. D. Moon, B. D. Freeman
As noted by Bowden in 1973, methods were needed to directly probe the changes in intermolecular distances and segmental mobility in the glass that occur locally upon deformation [21]. In 1975, Peterlin suggested that the diffusion of small molecules in glassy polymers could be used as a probe of the free volume [57]. Peterlin described the transport properties of polymers as having static and dynamic free volume contributions, acknowledging the importance of localised chain packing-related free volume and the cooperative segmental free volume that enables chain dynamics. (The section on transport properties will further explore the link between free volume and small molecule transport.) In 1977, Struik [58] coined the term physical ageing for the volume relaxation in glassy polymers and published a schematic, adapted in Figure 2, linking the free volume and molecular mobility in glassy polymers. During physical ageing, the glass relaxes but not to the point of crystallization, hence physical ageing is reversed by heating above Tg or straining to the onset of flow. The Struik model can be summarised with the following first-order differential equation,where δ is the departure in an intensive thermodynamic property (e.g. specific volume, enthalpy, and entropy) from equilibrium, is the relaxation time at equilibrium, and γ is a constant characterising the sensitivity of segmental relaxation time to the departure function δ [62].