Open/closed systems

If neither matter nor energy can cross the bonndary, the system is described as isolated , if only energy (bnt not matter) can cross the bonndary, the system is closed , if both matter and energy can cross the bonndary, tlie system is open. 

Fig. 1. The energy cycle of a thermal electric generating station having two alternative cooling systems (—) the open-circuit or once-through system and (-------------------------------------) a representative closed-cycle, cooling-tower system. Reproduced by permission (3).

Equations 54 and 58 through 60 are equivalent forms of the fundamental property relation apphcable to changes between equihbtium states in any homogeneous fluid system, either open or closed. Equation 58 shows that ff is a function of 5" and P. Similarly, Pi is a function of T and C, and G is a function of T and P The choice of which equation to use in a particular apphcation is dictated by convenience. Elowever, the Gibbs energy, G, is of particular importance because of its unique functional relation to T, P, and the the variables of primary interest in chemical technology. Thus, by equation 60,... 

Fig. 21. Pressure constant temperature (PCT) curves of MmNi alloy system where open symbols represent absorption and closed symbols represent desorption for A, MmNi. Mn. AIq B, MmNi. gMn. AIq 3C0Q and C, MmNi. Mn. AIq 3C0Q 3. H/M represents the ratio in the hydride of the mole...

An interesting and novel use of a soHd desiccant, the reduction of cold condensate corrosion in automotive exhaust systems, illustrates a hybrid closed—open system. Internal corrosion occurs in mufflers when the water vapor in the exhaust condenses after the engine is turned off and the muffler cools. Carbon dioxide dissolves in the condensate to form an acidic soup. In an essentially closed static drying step, an acid- and heat-resistant desiccant located in the muffler adsorbs water vapor from the exhaust gas as it cools to prevent formation of corrosive acidic condensate. When the engine is restarted, the system becomes open, and the desiccant is regenerated by the hot exhaust gas to be ready for the next cooldown step (19). 

The composition of a system may vaiy because the system is open or because of chemical reactions even in a closed system. The equations developed here apply regardless of the cause of composition changes. 

If ah systems are go, turn on the seal gas. Open the expander and eompressor ease drains to purge systems. Close drains and eheek seal gas pressure. Seal gas temperature must be 70-80°F downstream of the regulator. 

As system pressure increases and approaches valve set pressure, it acts upward on the sense diaphragm, with the feedback piston moving upward to close the inlet seat, thus sealing in the main valve dome pressure, as the outlet seat is also closed. A small, further increase in system pressure opens the outlet seat, venting the main valve dome pressure. This reduced dome pressure acts on the unbalanced feedback piston to reduce feedback piston lift, tending to lock in" the dome pressure. Thus, at any stable inlet pressure there will be no pilot flow (i.e. zero leakage). 

Pressurized air can do the same type of damage as pressurized water. Treat all operations on compressed air systems with the same care taken on liquid systems. Closed valves should be slowly cracked open and both sides allowed to equalize prior to opening the valve further. 

Target Open Systems Traditional AI has focused on closed systems in which the interaction between the problem tlomain and the external environment is kept to a minimum in contrast, agent-based systems are open systems, and agents arc directly coupled with their environment. 

Identify the following systems as open, closed, or isolated (a) coffee in a very high quality thermos bottle (b) coolant in a refrigerator coil (c) a bomb calorimeter in which benzene is burned (d) gasoline burning in an automobile engine ... 

According to Schneider and Chandler (1973), depolarization of the T-tubules affects sensors which open Ca " channels in the SR. The sensors are modified Ca channels which act as voltage sensors (Tanabe et al., 1987). The signal from the sensor reaches the SR and opens the Ca channels with the release of Ca to the myoplasm. The Ca channels in the SR system are opened by micromolar [Ca ], mM [ATP], and caffeine but are inhibited by Mg (Smith et al., 1986 Rosseau et al., 1988). The channels are closed in resting muscle and are opened when the voltage sensor is activated. 

FIGURE 15.10 Transient response measurements for systems governed by the axial dispersion model (a) closed system (b) open system. 

The identification of plant models has traditionally been done in the open-loop mode. The desire to minimize the production of the off-spec product during an open-loop identification test and to avoid the unstable open-loop dynamics of certain systems has increased the need to develop methodologies suitable for the system identification. Open-loop identification techniques are not directly applicable to closed-loop data due to correlation between process input (i.e., controller output) and unmeasured disturbances. Based on Prediction Error Method (PEM), several closed-loop identification methods have been presented Direct, Indirect, Joint Input-Output, and Two-Step Methods. 

A closed sorption system is shown in Figure 8. It is based on the same physical effect as the open storage. However the engineering is quiet different from open sorption systems. Closed system could be more precisely described as evacuated or air-free systems. The operation pressure of the fluid to be sorbed can be adjusted in theses systems. In closed systems components, which are not existing in the atmosphere, can be used, because there is no connection to the ambience. 

Can an open-loop be still a loop You may wonder what is an open-loop Often, we loosely refer elements or properties of part of a system as open-loop, as opposed to a complete closed-loop system. You ll see more of this language in Chapter 7. 

All of the above calculations can be performed on two kinds of systems closed-shell systems and open-shell systems. 

In general, online versus off-line HIAR offers similar pros and cons as does the open versus the closed automated staining systems. Closed systems and online HIAR not only produce extreme consistency and require less technical knowledge, but it can also limit the number of antibodies that can be used successfully. Open systems and off-line HIAR allow the flexibility to use many more types of antibodies, but technicians need to be well trained and diligent in their record keeping in order to insure consistent staining. 

Figure 1.1 Scaling the sample relative to an arbitrary heterogeneity. Here, the rock is assumed to have a characteristic exchange distance 8. Atoms in the outer shell (stippled) may have moved in or out inside all the movements kept the system closed. The size of a rock sample will be scaled for a closed system by minimizing the relative proportion of the shell and will be large. For an open system, it will be taken smaller than 8.

The speciation state determined by the five equilibria depends on the type of system (closed or open) and imposed conditions (/coj pH). Two cases are particularly relevant in geochemistry ... 

Thermodynamic cycles can also be categorized by system as closed-system cycles and open-system cycles. In closed-system cycles, each component of the cycle is considered as a closed system. In open-system cycles, each component of the cycle is considered as an open system. 

Another factor that is of great importance for the observed sulfur isotope variations of natural sulfides is whether sulfate reduction takes place in an open or closed system. An open system has an infinite reservoir of sulfate in which continuous removal from the source produces no detectable loss of material. Typical examples are the Black Sea and local oceanic deeps. In such cases, H2S is extremely depleted in " S while consumption and change in " S remain negligible for the sulfate. In a closed system, the preferential loss of the lighter isotope from the reservoir has a feedback on the isotopic composition of the unreacted source material. The changes in the " S-content of residual sulfate and of the H2S are modeled in Fig. 2.21, which shows that 5 S-values of the residual sulfate steadily increase with sulfate consumption (a linear relationship on the log-normal plot). The curve for the derivative H2S is parallel to the sulfate curve at a distance which depends on the magnitude of... 

ISOEQUILIBRIUM RELATIONSHIP ISOLATED SYSTEM CLOSED SYSTEM OPEN SYSTEM... 

Figure 3.8 — (A) Biosensors used in different FI manifolds to perform reaction-rate measurements (I) stopped-flow manifold (II) iterative flow-reversal system (III) open-closed configuration S sample B buffer P pump IV injection valve PC personal computer IMEC immobilized enzyme cell D detector W waste SV switching valve. (B) Types of recordings obtained by using the three types of biosensors and measurements to be performed on them in order to develop reaction-rate methods. (Reproduced from [50] with permission of Elsevier Science Publishers).

---