*Adrian P Sutton*

- Published in print:
- 2021
- Published Online:
- September 2021
- ISBN:
- 9780192846839
- eISBN:
- 9780191938764
- Item type:
- chapter

- Publisher:
- Oxford University Press
- DOI:
- 10.1093/oso/9780192846839.003.0001
- Subject:
- Physics, Condensed Matter Physics / Materials, Theoretical, Computational, and Statistical Physics

This chapter is an introduction to classical thermodynamics that does not assume any knowledge of the subject. The significance of thermodynamic equilibrium in materials is discussed keeping in mind ...
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This chapter is an introduction to classical thermodynamics that does not assume any knowledge of the subject. The significance of thermodynamic equilibrium in materials is discussed keeping in mind that it is rarely achieved in practice. The concepts of thermodynamic systems, components, work, energy, phase, absolute temperature, heat, potential energy, internal energy, state variables, intensive and extensive variables are introduced and defined. The first and second laws of thermodynamics are introduced. The concept of entropy is discussed in terms of irreversibility, the direction of time and microstates of the system. Configurational entropy is illustrated with the example of a binary alloy. The Helmholtz and Gibbs free energies are introduced and their physical significance is discussed in terms of the conditions for a material to be in equilibrium with its environment. This leads to a discussion of chemical potentials, the Gibbs-Duhem relation for each phase present and the phase rule.Less

This chapter is an introduction to classical thermodynamics that does not assume any knowledge of the subject. The significance of thermodynamic equilibrium in materials is discussed keeping in mind that it is rarely achieved in practice. The concepts of thermodynamic systems, components, work, energy, phase, absolute temperature, heat, potential energy, internal energy, state variables, intensive and extensive variables are introduced and defined. The first and second laws of thermodynamics are introduced. The concept of entropy is discussed in terms of irreversibility, the direction of time and microstates of the system. Configurational entropy is illustrated with the example of a binary alloy. The Helmholtz and Gibbs free energies are introduced and their physical significance is discussed in terms of the conditions for a material to be in equilibrium with its environment. This leads to a discussion of chemical potentials, the Gibbs-Duhem relation for each phase present and the phase rule.

*J. C. Kaimal and J. J. Finnigan*

- Published in print:
- 1994
- Published Online:
- November 2020
- ISBN:
- 9780195062397
- eISBN:
- 9780197560167
- Item type:
- chapter

- Publisher:
- Oxford University Press
- DOI:
- 10.1093/oso/9780195062397.003.0004
- Subject:
- Earth Sciences and Geography, Atmospheric Sciences

We start with the simplest of boundary layers, that over an infinite flat surface. Here we can assume the flow to be horizontally homogeneous. Its statistical properties are independent of ...
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We start with the simplest of boundary layers, that over an infinite flat surface. Here we can assume the flow to be horizontally homogeneous. Its statistical properties are independent of horizontal position; they vary only with height and time. This assumption of horizontal homogeneity is essential in a first approach to understanding a process already complicated by such factors as the earth's rotation, diurnal and spatial variations in surface heating, changing weather conditions, and the coexistence of convective and shear-generated turbulence. It allows us to ignore partial derivatives of mean quantities along the horizontal axes (the advection terms) in the governing equations. Only ocean surfaces come close to the idealized infinite surface. Over land we settle for surfaces that are locally homogeneous, flat plains with short uniform vegetation, where the advection terms are small enough to be negligible. If, in addition to horizontal homogeneity, we can assume stationarity, that the statistical properties of the flow do not change with time, the time derivatives in the governing equations vanish as well. This condition cannot be realized in its strict sense because of the long-term variabilities in the atmosphere. But for most applications we can treat the process as a sequence of steady states. The major simplification it permits is the introduction of time averages that represent the properties of the process and not those of the averaging time. These two conditions clear the way for us to apply fluid dynamical theories and empirical laws developed from wind tunnel studies to the atmosphere's boundary layer. We can see why micrometeorologists in the 1950s and 1960s scoured the countryside for flat uniform sites. The experiments over the plains of Nebraska, Kansas, and Minnesota (USA), Kerang and Hay (Australia), and Tsimliansk (USSR) gave us the first inklings of universal behavior in boundary layer turbulence. Our concept of the atmospheric boundary layer (ABL) and its vertical extent has changed significantly over the last few decades.
Less

We start with the simplest of boundary layers, that over an infinite flat surface. Here we can assume the flow to be horizontally homogeneous. Its statistical properties are independent of horizontal position; they vary only with height and time. This assumption of horizontal homogeneity is essential in a first approach to understanding a process already complicated by such factors as the earth's rotation, diurnal and spatial variations in surface heating, changing weather conditions, and the coexistence of convective and shear-generated turbulence. It allows us to ignore partial derivatives of mean quantities along the horizontal axes (the advection terms) in the governing equations. Only ocean surfaces come close to the idealized infinite surface. Over land we settle for surfaces that are locally homogeneous, flat plains with short uniform vegetation, where the advection terms are small enough to be negligible. If, in addition to horizontal homogeneity, we can assume stationarity, that the statistical properties of the flow do not change with time, the time derivatives in the governing equations vanish as well. This condition cannot be realized in its strict sense because of the long-term variabilities in the atmosphere. But for most applications we can treat the process as a sequence of steady states. The major simplification it permits is the introduction of time averages that represent the properties of the process and not those of the averaging time. These two conditions clear the way for us to apply fluid dynamical theories and empirical laws developed from wind tunnel studies to the atmosphere's boundary layer. We can see why micrometeorologists in the 1950s and 1960s scoured the countryside for flat uniform sites. The experiments over the plains of Nebraska, Kansas, and Minnesota (USA), Kerang and Hay (Australia), and Tsimliansk (USSR) gave us the first inklings of universal behavior in boundary layer turbulence. Our concept of the atmospheric boundary layer (ABL) and its vertical extent has changed significantly over the last few decades.