화학공학소재연구정보센터
Canadian Journal of Chemical Engineering, Vol.86, No.1, 84-98, 2008
The first law of thermodynamics and energy partition in the presence of fields
The first law of thermodynamics in the presence of fields is considered. The presence of fields gives rise to partition of the internal energy between field and nonfield energy forms, that are characterized as state functions. Field-dependent components of work and heat are defined with respect to their being delivered at the boundaries, or directly, by action at a distance, to the contents of the system. Interaction energy, that accounts for effects of changes in the sources of the fields is defined. The first law of thermodynamics in the presence of fields states that the change in the sum of the field and nonfield components, of the internal energy, is equal to the change in the sum of the field and nonfield components of heat and work, delivered to the system, and the interaction energy, due to changes in the sources of the field. The equivalence between potential energy and work in conjugate frames of reference facilitates the incorporation of the interaction energy as part of the field-dependent internal energy. In this context, the significance of the degree of coupling between the field and the contents of the system, in conjunction with their thermodynamic variables, is discussed. Intensive field-dependent variables that maintain uniformity, at equilibrium, in the absence as well as in the presence of fields, are defined. In contrast, nonfield and field components of these intensive variables can be nonuniform, and discontinuous across interfaces, at equilibrium. The implication of the theory is illustrated by specific cases that involve electromagnetic and acceleration fields. Energy partition in acceleration fields is shown to depend on mass distribution within the system. A change in position, or in the source of the field produce changes in mass distribution and energy partition. Partition of magnetic and nonmagnetic energy forms, and field-induced heat flow and energy storage are considered. It is shown that for linear matter, the energy per unit volume stored in the field is invariable with respect to the process and work that produce the field vectors, the balance being stored in other nonfield energy forms. Finally, expressions for field-induced temperature and energy changes in an ideal magnetizable gas are derived. It is shown that isothermal magnetization produces a shift in the partition between the field and nonfield parts of the internal energy.