Closed systems definition

Compliance requirements from the predicate rule and 21 CFR Part 11 such as open or closed system definition, security and access configuration of the software application including user types, requirements for data integrity, time and date stamp requirements, and electronic signature requirements. 

Chemical engineering inherited the definition for the reaction rate from chemical kinetics. The definition is for closed systems, like batch reactors, in which most of the classical kinetic studies were done. Inside a batch reactor little else besides chemical reaction can change the concentration of reactant A. In a closed system, for the reaction of... 

Fluid power encompasses most applications that use liquids or gases to transmit power in the form of mechanical work, pressure and/or volume in a system. This definition includes all systems that rely on pumps or compressors to transmit specific volumes and pressures of liquids or gases within a closed system. The complexity of these systems range from a simple centrifugal pump used to remove casual water from a basement to complex airplane control systems that rely on high-pressure hydraulic systems. 

The boundary conditions normally associated with Equation (9.14) are known as the Danckwerts or closed boundary conditions. They are obtained from mass balances across the inlet and outlet of the reactor. We suppose that the piping to and from the reactor is small and has a high Re. Thus, if we were to apply the axial dispersion model to the inlet and outlet streams, we would find = 0, which is the definition of a closed system. See... 

The first satisfactory definition of entropy, which is quite recent, is that of Kittel (1989) entropy is the natural logarithm of the quantum states accessible to a system. As we will see, this definition is easily understood in light of Boltzmann s relation between configurational entropy and permutability. The definition is clearly nonoperative (because the number of quantum states accessible to a system cannot be calculated). Nevertheless, the entropy of a phase may be experimentally measured with good precision (with a calorimeter, for instance), and we do not need any operative definition. Kittel s definition has the merit to having put an end to all sorts of nebulous definitions that confused causes with effects. The fundamental P-V-T relation between state functions in a closed system is represented by the exact differential (cf appendix 2)... 

A term used in thermodynamics to designate a region separated from the rest of the universe by definite boundaries. The system is considered to be isolated if any change in the surroundings the portion of the universe outside of the boundaries of the system) does not cause any changes within the system. See Closed System Isolated System Open System... 

The differential change in entropy for a closed system from one state to another is, by definition, directly proportional to the change in reversible heat, dQrev, and inversely proportional to the absolute temperature, T ... 

The final possibility, a uniformly interesting movie, would have to depict a process with thousands or millions of critical steps occuring in a definite order, each step necessary to understand the next, as in an industrial process, the functioning of a digital computer, or the development of an embryo. Enzymes, having been optimized by natural selection, may be expected to have somewhat complex mechanisms of action, perhaps with several equally important critical steps, but not with thousands of them. There is reason to believe that processes with thousands of reproducible non-trivial steps usually occur only in systems that are held away from thermal equilibrium by an external driving force. They thus belong to the realm of complex behavior in continuously dissipative open systems, rather than to the realm of relaxation processes in closed systems. 

Equations 27 and 28 permit a simple comparison to be made between the actual composition of a chemical system in a given state (degree of advancement) and the composition at the equilibrium state. If Q K, the affinity has a positive or negative value, indicating a thermodynamic tendency for spontaneous chemical reaction. Identifying conditions for spontaneous reaction and direction of a chemical reaction under given conditions is, of course, quite commonly applied to chemical thermodynamic principle (the inequality of the second law) in analytical chemistry, natural water chemistry, and chemical industry. Equality of Q and K indicates that the reaction is at chemical equilibrium. For each of several chemical reactions in a closed system there is a corresponding equilibrium constant, K, and reaction quotient, Q. The status of each of the independent reactions is subject to definition by Equations 26-28. 

The purpose of the following checklist is to help to determine if a computer system complies with the FDA Rule 21 CFR 21 Part 11 for electronic records and electronic signatures. This audit questionnaire apphes to systems that meet the definition of a closed system as defined in Section 11.3 (b)(4) of the rule and which do not utilize biometrics identification methods. 

In addition to the general concept of a system, we define different types of systems. An isolated system is one that is surrounded by an envelope of such nature that no interaction whatsoever can take place between the system and the surroundings. The system is completely isolated from the surroundings. A closed system is one in which no matter is allowed to transfer across the boundary that is, no matter can enter or leave the system. In contrast to a closed system we have an open system, in which matter can be transferred across the boundary, so that the mass of a system may be varied. (Flow systems are also open systems, but are excluded in this definition because only equilibrium systems are considered in this book.)... 

The entropy of a system is a function of the independent variables that are used to define the state of the system. For a closed system in which no work other than that of expansion and compression is involved, we need two variables to define the state. These are usually the temperature and volume or the temperature and pressure. The dependence of the entropy on the volume and the pressure is developed in Chapter 4, but its dependence on the temperature can be obtained with the information that we now have. By definition... 

Newton s laws can also be used to describe elliptical orbits, and it is then found that a vector quantity called angular momentum is conserved (always stays constant), just as the total momentum p stayed constant in a closed system. Angular momentum is conventionally denoted L. The vector L points perpendicular to the orbit (in the z-direction by our definitions) and has length... 

The boundary conditions normally associated with Equation (9.14) are known as the Danckwerts or closed boundary conditions. They are obtained from mass balances across the inlet and outlet of the reactor. We suppose that the piping to and from the reactor is small and has a high Re. Thus, if we were to apply the axial dispersion model to the inlet and outlet streams, we would find Din = Dout = 0, which is the definition of a closed system. See Figure 9.8. The flux in the inlet pipe is due solely to convection and has magnitude Qi ain. The flux just inside the reactor at location z = 0+ has two components. One component, Qina(0+), is due to convection. The other component, —DAc[da/dz 0+, is due to diffusion (albeit eddy diffusion) from the relatively high concentrations at the inlet toward the lower concentrations within the reactor. The inflow to the plane at z = 0 must be matched by material leaving the plane at z = 0+ since no reaction occurs in a region that has no volume. Thus,... 

Since the total concentration a + r + s follows the time evolution d(a + r + s)/ dt = F - k(a + r + s), it approaches the steady state value F/k with a relaxation time 1 /k. This is a consequence of unbiased outflow (Eq. 47) of all reactants with the same rate k. Consequently, even though we are dealing with an open system under a flow, the analysis is similar to the closed system by replacing the total concentration c with the steady state value F/k. Instead of recycling, therefore, constant supply of the substrate allows the system to reach a certain fixed point with a definite value of the order parameter 0i, independent of the initial condition. 

The classical definition of entropy based on the second law of thermodynamics has given the total differential of entropy in the form of dQrev / / . With a reversible heat transfer into a closed system receiving a differential amount of heat dQrev, the system changes its entropy by the differential amount of dS as shown in Eq. 3.8 ... 

The heat Q( ) absorbed in or released out of a closed system in which a chemical reaction occurs is in principle a function of the extent of reaction , temperature T, and pressure p (or volume V) of the reaction system. If we fix the condition at which the reaction occurs, all the variables defining the state of the reaction system will be definite functions of . We now introduce a symbol [Pg.40]

By definition the first requirement of any cell, natural or artificial, is to be compartmentalized. Once a closed system has been created it is possible to develop, or evolve, mechanisms that control the concentrations of essential nutrients and waste materials within that system. This will inevitably involve a route for chemical species of different sizes and properties to move between the cell s interior and its external surroundings. There are several candidates for the cell boundary material. 

A stationary state is by definition one whose description does not change with time. According to this definition it becomes impossible for a closed system which is undergoing chemical reaction to ever achieve a stationary state, because the composition of such a system is constantly changing with time. In this sense it is only open systems (i.e., systems in communication with infinite external reservoirs of mass, heat, etc.) which can achieve truly stationary states. However, we have used the description stationary state in discussing sequences of consecutive reactions occurring in closed systems. By this we have really meant a quasi-stationary state, ... 

There are a number of different ways in which a heat of reaction may be defined. One of the most general definitions is the following. If a closed system containing a given number of moles Ni of N different species at a given T and p is caused to undergo an isobaric process in which the Ni are changed to prescribed final values and in which the initial and final values of T are the same, then the heat liberated by the system, — — J dQ, is the... 

Thus far, the discussion of reaction rate has been confined to homogeneous reactions taking place in a closed system of uniform composition, temperature, and pressure. However, many reactions are heterogeneous they occur at the interface between phases, for example, the interface between two fluid phases (gas-liquid, liquid-liquid), the interface between a fluid and solid phase, and the interface between two solid phases. In order to obtain a convenient, specific rate of reaction it is necessary to normalize the reaction rate by the interfacial surface area available for the reaction. The interfacial area must be of uniform composition, temperature, and pressure. Frequently, the interfacial area is not known and alternative definitions of the specific rate are useful. Some examples of these types of rates are ... 

In practice, conditions in a reactor are usually quite different than the ideal requirements used in the definition of reaction rates. Normally, a reactor is not a closed system with uniform temperature, pressure, and composition. These ideal conditions can rarely if ever be met even in experimental reactors designed for the measurement of reaction rates. In fact, reaction rates cannot be measured directly in a closed system. In a closed system, the composition of the system varies with time and the rate is then inferred or calculated from these measurements. 

In deriving the integral mass balance for a closed system in Section 4.2c we eliminated the input and output terms, since by definition no mass crosses the boundaries of a closed system. It is possible, however, for energy to be transferred across the boundaries as heat or work, so that the right side of Equation 7.3-1 may not be eliminated automatically. As with mass balances, however, the accumulation term equals the final value of the balanced quantity (in this case, the system energy) minus the initial value of this quantity. Equation 7,3-1 may therefore be written... 

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