![]() ![]() ![]() Sebastian Wallot, in Philosophy of Complex Systems, 2011 2.4 Interdependence and Soft-Assembly Under these conditions, the actual phase change can be accurately approximated as a reversible process. Consequently, if there is negligible change in system volume during the phase change or the moving boundary work is carried out very efficiently, then the work mode irreversibilities also are insignificant. (4.71) and (4.72), immediately preceding Eq. However, for an actual irreversible process ( d ¯ W ) act = f ( η W ) ( d ¯ W ) rev, where f( η W) is a function of the work transport energy efficiency, given in Eqs. As for the work mode irreversibilities, for a reversible process, ( d ¯ W ) rev = − m p d v, and the differential energy balance then gives ( d ¯ Q ) rev = m ( d u + p d v ) = m ( d h ). If the real system is truly isothermal, then heat transfer irreversibilities may be allocated to the system's surroundings. ![]() The irreversibilities involved in a phase change process arise largely from the heat transfer required to produce the phase change and from the mechanical moving boundary work associated with any volume change between the phases. Thus, for an exothermic (heat liberating) phase change (e.g., a condensation or solidification process), the heat transfers are negative and it follows that | Q act | > | Q rev | and for an endothermic phase change (e.g., a vaporization process), Q rev > Q act. ( S P ) phase change = Q rev − Q act T b > 0 ![]()
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