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System boundary choice

Any process can be divided up in an arbitrary way to facilitate the material balance calculations. The judicious choice of the system boundaries can often greatly simplify what would otherwise be difficult and tortuous calculations. [Pg.37]

Only those flows necessary to illustrate the choice of system boundaries and method of calculation are given in the Solution. [Pg.38]

The correct choice of the basis for a calculation will often determine whether the calculation proves to be simple or complex. As with the choice of system boundaries, no all-embracing rules or procedures can be given for the selection of the right basis for any problem. The selection depends on judgement gained by experience. Some guide rules that will help in the choice are ... [Pg.40]

Each product system consists of a variable number of processes involved in the product life cycle. However, the product under consideration is often related to other processes that may no longer be important for the LCA study. The system boundary serves to the separation of essential and non-essential processes of the product life cycle. Since the choice of system boundaries significantly affects LCA study outcomes and in addition, its intensity and complexity, system boundaries should always be well considered and clearly defined. The choice of system boundaries is carried out with regard to the studied processes, studied environmental impacts and selected complexity of the study. Not-including any life cycle stages, processes or data must be logically reasoned and clearly explained [32]. [Pg.267]

In goal definition, the scope and purpose of the LCA is defined. The functional unit and system boundaries are also established. The functional unit is the reference point to which environmental impacts are attributed. The choice of functional unit depends on the application of the LCA. For a process it could be a tonne of product or feedstock, or a tonne of impurity removed. For a commodity product the functional unit could be a tonne of product, but for specialty chemicals and most consumer products performance properties are more important and the choice can become complex. For example, performance of a paint would be related to its surface coverage and durability hence a possible functional unit for the paint might be the quantity required to cover a square meter of surface over a time span of 20 years. [Pg.74]

Notice that in the closed-system analysis the surroundings are doing work on the system (the mass element) at the inlet to the compressor, while the system is doing work on its surroundings at the outlet pipe. Each of the.se tenns is a / Pr/V-type work term. For the open. system this work term has been included in the energy balance as a, P V A/V/ term, so that it is the enthalpy, rather than the internal energy, of the flow streams that appears in the equation. The e.xplicit J P dV term that does appear in the open-system energy balance represents only the work done if the system boundaries deform for the choice of the compressor and its contents as the system here this term is zero unless the compressor (the boundary of our system) explodes. B... [Pg.57]

In many cross-sectional specimens, especially epitaxial systems, the choice of crystallographic direction that will be aligned parallel to the electron beam direction during TEM observation can be very important. For example, in binary, ternary, and quaternary alloys of cubic (zinc blende) III-V materials, the boundaries between layers are much more clearly... [Pg.3109]

In the first step, the extent of the analysis as well as the specific methods used is described. A precise definition of the product, comparison basis (functional unit), system boundaries, time frame, and geographical coverage, as well as methodological choices such as allocation methods and impact categories of the assessment are made during this initial phase. [Pg.746]

When we compare Eqs. 3.6.3 and 3.6.5, we see that the work when the system is the body is greater by the quantity (Fbuoy + Ffric) dz than the work when the system is the combination of body and fluid, just as in the case of the freely-falling body. The difference in the quantity of work is due to the different choices of the system boundary where contact forces are exerted by the surroundings. [Pg.81]

The goal definition specifies the reasons for carrying out the study and the intended application and audience. The scope relates to defining the unit of analysis, the system boundaries, the data quality and a number of other methodological choices. The depth and breadth of LCA can differ considerably depending on the goal of the analysis. [Pg.490]

Analysis of this sewage treatment process is interesting for three reasons. First, the choice of the system boundaries requires some judgment (in this case, the unit for which you have the most data). Second, it represents an actual problem that a BS chemical engineer related to us. Third, it demonstrates that operating a process requires an understanding of both transient and steady-state modehng. [Pg.323]

Enthalpy balance calculation require the choice of a reference state. For convenience we choose to work with enthalpy of combustion rather than with enthalpy of formation. Thus, terms concerning water, O2 and CO2 disappear because they flow as gas through the system boundary (cf. Figure 5). The reference state of the substances in solution is aqueous, infinitely diluted at 30°C. The thermal effect of CO2 hydration is discussed in [26]. [Pg.282]

For example, say we wish to study the piston-cylinder assembly in Figure 1.1. The usual choice of system, surroundings, and boundary are labeled. The boundary is depicted by the dashed line just inside the walls of the cylinder and below the piston. The system contains the gas within the piston-cylinder assembly but not the physical housing. The surroundings are on the other side of the boundary and comprise the rest of the universe. Likewise the system, surroundings, and boundary of an open system are labeled in Figure 1.2. In this case, the inlet and outlet flow streams, labeled in and out, respectively, allow mass to flow into and out of the system, across the system boundary. [Pg.3]


See other pages where System boundary choice is mentioned: [Pg.37]    [Pg.37]    [Pg.49]    [Pg.53]    [Pg.53]    [Pg.55]    [Pg.39]    [Pg.446]    [Pg.23]    [Pg.198]    [Pg.291]    [Pg.5]    [Pg.12]    [Pg.967]    [Pg.243]    [Pg.311]    [Pg.226]    [Pg.432]    [Pg.556]    [Pg.93]    [Pg.39]    [Pg.60]    [Pg.5]    [Pg.66]   
See also in sourсe #XX -- [ Pg.37 , Pg.38 , Pg.39 ]

See also in sourсe #XX -- [ Pg.53 ]




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