Closed system processes

Laser ablation combined with LA-MC-ICPMS provides a new dimension to the analysis of Mg isotopes in calcium aluminum-rich inclusions from primitive meteorites. Dispersion in 26Mg - Al/ Mg evolution lines can be correlated with mass-dependent variahons in 5 Mg that distinguish open-system from closed-system processes. The ultimate product of such studies will be a better understanding of the chronological significance of variations in Mg in these objects. 

In an irreversible process, in conformity with the second law of thermodynamics, the magnitude that determines the time dependence of an isolated thermodynamic system is the entropy, S [23-26], Consequently, in a closed system, processes that merely lead to an increase in entropy are feasible. The necessary and sufficient condition for a stable state, in an isolated system, is that the entropy has attained its maximum value [26], Therefore, the most probable state is that in which the entropy is maximum. 

During any closed-system process, mass balance must be conserved ... 

The work of a mechanically reversible, closed-system process is given by Eq. (1.2), here... 

Tlius for a mechanically reversible, constant-volume, closed-system process, the heat transferred is equal to the intemal-energy change of the system. 

Tlrus for a meclrairically reversible, constant-pressure, closed-system process, the heat transferred equals the enthalpy clrange of the system. Comparisoir of the last two equations with Eqs. (2.9) and (2.10) shows tlrat the enthalpy plays a role hr constant-pressure processes analogous to the intenral energy hr constairt-volumeprocesses. 

For an ideal gas in any mechanically reversible closed-system process, Eq. (2.6), writtenfor a unit mass or a mole, may be combined witli Eq. (3.19a) ... 

The equations developed in this section have been derived for mechanically reversible, closed-system processes for ideal gases. However, those equations which relate changes in state functions only are valid for ideal gases regardless of the process. They apply equally to reversible and irreversible processes in both closed and open systems, because changes in state functions depend only on the initial and final states of the system. On the other hand, an equation for Q or W is specific to the process considered in its derivation. 

Moreover, Q = AH for mechanically reversible, constant-pressure,closed-system processes [Eq. (2.23)] and for the transfer of heat in steady-flow exchangers where AEp and AEj are negligible and Wg = 0. hr eitlrer case. 

Chemical reaction constraints of interest are redox equilibrium vs. disequilibrium (especially whether sulfate reduction progresses appreciably or not) and open vs. closed system processes. These types of constraints are implemented routinely when running chemical reaction models using EQ3/6 f9.5). 

Because the enrichment of U, Th and Ra in the magma is so fast, the concept of mineral-melt partition coefficient (which implies that magma formation is a closed-system process) is not valid for these elements during magma formation. 

Most chemically reacting systems tliat we encounter are not tliennodynamically controlled since reactions are often carried out under non-equilibrium conditions where flows of matter or energy prevent tire system from relaxing to equilibrium. Almost all biochemical reactions in living systems are of tliis type as are industrial processes carried out in open chemical reactors. In addition, tire transient dynamics of closed systems may occur on long time scales and resemble tire sustained behaviour of systems in non-equilibrium conditions. A reacting system may behave in unusual ways tliere may be more tlian one stable steady state, tire system may oscillate, sometimes witli a complicated pattern of oscillations, or even show chaotic variations of chemical concentrations. 

One, the CLEAR process, was investigated by Duval Corporation near Tucson, Arizona (29). It involves leaching copper concentrated with a metal chloride solution, separation of the copper by electrolysis, and regeneration of the leach solution in a continuous process carried out in a closed system. Elemental sulfur is recovered. Not far from the Duval plant, Cypms Mines Corporation operated a process known as Cymet. Sulfide concentrates undergo a two-step chloride solution leaching and are crystallized to obtain cuprous chloride crystals. Elemental sulfur is removed during this stage of the process. 

Process Va.ria.tlons. The conventional techniques for tea manufacture have been replaced in part by newer processing methods adopted for a greater degree of automation and control. These newer methods include withering modification (78), different types of maceration equipment (79), closed systems for fermentation (80), and fluid-bed dryers (81). A thermal process has been described which utilizes decreased time periods for enzymatic reactions but depends on heat treatment at 50—65°C to develop black tea character (82). It is claimed that tannin—protein complex formation is decreased and, therefore, greater tannin extractabiUty is achieved. Tea value is beheved to be increased through use of this process. 

The dry powder process has several additional advantages over the wet process. For example, much less waste of enamel occurs because the dry over-spray is airborne and recycled in a closed system. No-pidde ground coats have broadened the apphcation of both wet-process and dry-process systems. These enamels are appHed over cleaned-only metal. Thus the problems of disposing of pickling acid wastes containing iron sulfates and nickel wastes are eliminated (see Metal surface treatments) (7). 

All applications are for closed systems with constant mass. If a process is reversible and only p-V work is done, the first law and differentials can be expressed as follows. 

For closed systems of this land, the work of a reversible process may always be calculated from... 

Consider a single-phase closed system in which there are no chemical reactions. Under these restric tious the composition is fixed. If such a system undergoes a differential, reversible process, then by Eq. (4-1)... 

Although derived for a reversible process, this equation relates properties only and is valid for any change between equilibrium states in a closed system. It may equally well be written... 

The process of sintering by vapour phase transport is probably important to the growth of single crystals of solids from polycrystalline samples in a closed system, where the vapour species are the transporting gas, which may have the same or different chemical composition from die solid. An example where... 

Closed Disposal System - This is the discharge piping for a PR valve which releases to a collection system, such as a blowdown drum and flare header. However, a closed system can also be a process vessel or other equipment at a lower pressure. 

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