Elementary flows

TABLE 15.1 Calcutation of Total Elementary Flows from the Steel-Sheet Product System of Fig. 15.3... 

Reference flow and the functional unit are defined for the entire product system, and the elementary flows are calculated in relation to these. The flow figures are normally aggregated, and the total flow of each substance recorded and used for impact assessment. 

In practical product design, a full LCA is seldom performed. The unit operations represent whole systems, which are used as building blocks. Typical examples include elementary flows determined for the manufacture of 1 m-1-mm sheet metal of galvanized steel, incineration of 1 kg of polyethylene, or production and distribution of 1 MJ electricity. ... 

The inventory tasks is to collect environmentally important information about relevant processes involved in the product system. Inventory collects information about unit processes at first and subsequently, an inventory of inputs and outputs of the system and its surroundings is carried out. The goal is the identification and quantification of all elementary flows associated with product system. Inventory analysis is the nature of the technical implementation of LCA studies. It is an essential part of a study, has high demands for data availability, practical experience in modelling product systems and, in the case of using database tools, it is necessary to master them perfectly and to understand their function [46]. The inventory phase principle is data collection that is used to quantify values of the elementary flows. This phase represents a major practical part of the LCA study, time consuming and with demands for data availability and author s experience with modelling product system studies [47],... 

Process Elementary flow Category Incineration Landfill DEHP emissions Recycling... 

For a full life cycle assessment, the basic principle is that each material and energy input into the system should be traced back to natural resources obtained from the environment, or to releases into the environment. These are termed elementary flows , and they represent inputs into or outputs from the system being analysed. In an analysis of this type, it may be relatively straightforward to assign a material value to a flow of (for example) water effluent into the environment, but what may be less certain is the environmental impact of such a flow in a quantitative sense. 

Flow sheets for preparing the components of various monomer and oligomer reactant mixtures do not differ significantly from each other, although they may have different sets of reactors. The choice depends mainly on the physical and chemical properties of the initial components. Fig. 4.2 shows a flow sheet for obtaining continuously molded polyurethane elastomers. Fig. 4.3 illustrates an elementary flow sheet for a batch process unit for manufacturing moldings of epoxy resin or epoxy-based composites filled with quartz sand. 

All these approaches such as LCA, LCE, and Eco-Efficiency base upon the same product model. The product model, i.e. the value added-chain (= supply chain) of a product plus its use phase and end-of-life, is the backbone of any product life cycle study. Elementary flows, i.e. mainly resources withdrawn from the environment and emissions released to the environment, are linked to this backbone in the LCA. 

Figure 15 shows how data collection on the level of the process is consequently extended from product and elementary flows as in LCA by cost and social process data. 

It is apparent from the data that A A, the area occupied by the flow unit is similar for all proteins (100-1 20a ) and corresponds to segments of 6-8 amino acid residues. Joly (8), using an independent approach, also calculated a similar value for the area of the elementary flow units of protein monolayers. These calculations suggest that molecules in the monolayer are sufficiently flexible that segments of this size, on the average, move as units. This resembles the manner in which long chain hydrocarbons appear to diffuse in solution (9). As a result, Ag and hg are practically independent of molecular weight. 

The conservation equations for mass and momentum are more complex than they appear. They are nonlinear, coupled and difficult to solve. Only in a small number of cases - mostly Mly developed flows with constant viscosity in simple geometries e.g. in channels, pipes, between parallel plates - it is possible to obtain an analytical solution of the Navier-Stokes equations. In this chapter we will consider such a type of elementary flow, to show, how simple geometries and physics have to be for an analytical solution. Further elementary fluid flows can be found in a multitude of books about fluid mechanics. We follow in this chapter the accomplishments of (Sabersky and Acosta 1964). 

Elementary flows are important for studying the fundamentals of fluid dynamics, but their practical relevance is limited, because in all cases, in which an analytical solution is possible, many terms in the equations are zero. However these flows serve as benchmarks for numerical solutions and therefore are quite valuable. 

Life-Cycle Inventory analysis result (LCI result) provides information about all inputs and outputs in the form of elementary flow to and from the environment from all the unit processes involved in the study. An outcome of a life-cycle inventory analysis result includes the flows crossing the system boundary and provides the starting point for life-cycle impact assessment. 

Uncoupled flows (elementary flows) represent the flow of materials from the source crust of the earth or into the sink environment. ... 

LCIA operates on the inventory of elementary flows for the product life cycle (input of resources and output of emissions) into potential impacts on the environment. These inventory flows are translated into scores for indicators that represent impact on human health, natural environment, and natural resources within a number of predefined impact categories (EC-IRC 2011). 

Then the elementary flows from the inventory are assigned to the different categories of impact, each of which is represented by an impact indicator (see Environmental Impact entry for default list of impact categories in LCIA). This step is called classification of the inventory flows. 

Elementary flow-an elementary flow (also called intervention ) is any material or energy flow between the natural environment and the product system. 

There are input and output elementary flows, for example, crude oil entering the system, and carbon dioxide leaving the system, respectively. 

Process-a process is any activity that transforms inputs into outputs for example, a chemical reaction, a plan, but also transportation of good. One process can be further divided in subprocesses. The most detailed is called unit process. This is a process which is modeled as black box with inputs and outputs (product as well as elementary flows), but is not any more subdivided. 

In LCl, main attention is given to the insight that surface of land is a limited resource. In this sense, land use is included in LCl in the same way as other limited resources, that is, as an input elementary flow. This is the so-called concept of occupancy, where the total area or the area for a certain use (e.g., farm-land or forest) is reported in hectare or some other square measure. The use of land specified in this way is termed as occupation process. As an additional information which reflects specifically the competition for available area of land, time of occupation is reported, that is, area of exclusive land use for a given period of time [8]. The latter is termed as occupation interventions and is measured in surface-time units (e.g., hectare per year), representing a certain area of land of a given type used over a certain time period (e.g., occupation of 1 ha for farming of com for 1 year) (19). 

It Avas mentioned at the beginning of tliis cliapter tliat a two component mixture is separable if the velocities of migration of component zones through the column are different and the band width, Avhich broadens as it travels downstream, does not make separation impossible. The migration velocities are determined by the conditions of equilibrium (i)artition coefficients of components) and tlu carrier gas flow rate while the zone width depends on column geometry and on the elementary flow processes, diffusion and mass transfer. 

The processes we have considered thus far - extrusion, wire coating, and injection and compression molding - are dominated by shear between confined surfaces. By contrast, in fiber and film formation the melt is stretched without confining surfaces. It is still possible to gain considerable insight from very elementary flow and heat transfer models, but we must first parallel Section 2.2 and develop some basic concepts of extensional flow. The remainder of the chapter is then devoted to an analysis of fiber formation by melt spinning. 

The values are in the same range as those reported for bisphenol-A-type epoxies, ca. 85 kcal/mole (23), and equal to the value reported for creep in PS at its Tg (23b). However, Ferry (23b) points out that this activation energy is actually that for an elementary flow process. The values listed are for the onset of segmental motion, at Tg. 

In theories of the temperature dependence of viscosity which yield an Arrhenius form, with a linear dependence of In ijo on AHr,/RT. the parameter A//, is interpreted as an activation energy for an elementary flow process. From the WLF equation, an apparent activation energy for viscoelastic relaTcation can be calculated formally as... 

Figure 2.19 An elementary flow 4 of a vector v through the area dS normal to v.

Figure 2.20 An elementary flow of a vector j through the area dS at their arbitrary orientation.

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