Ch 6 in “Thermodynamics and the Destruction of Resources” by Bhavik Bakshi, Timothy Gutowski and Dusan Sekulic, Cambridge University Press, 2011 Thermodynamic Analysis of Resources Used in Manufacturing Processes1 Timothy G. Gutowski, and Dusan P. Sekulic INTRODUCTION The main purpose of manufacturing processes is to transform materials into useful products. In the course of these operations, energy resources are consumed and the usefulness of material resources is altered. Each of these effects can have significant consequences for the environment and for sustainable development, particularly when the processes are practiced on a very large scale. Thermodynamics is well suited to analyze the magnitude of these effects as well as the efficiency of the resources transfor-mations. The framework developed here is based upon exergy analysis that is developed in the first two chapters of this book. Also see (1-5). The data for this study draws upon previous work in the area of manufacturing process characterization, but also includes numerous measurements and estimates we have conducted. In all, we analyze 26 different manufacturing processes often in many different in-stances for each process. The key process studies from the literature are: for micro-electronics, Murphy et al (6), Williams et al (7), Krishnan et al (8), Zhang et al (9), and Boyd et al (10); for nano-materials processing, Isaacs et al (11) and Khanna et al (12); for other manufacturing processes, Morrow et al (13), Boustead (14, 15), Munoz and Sheng (16), and Mattis et al (17). Some of our own work includes Dahmus and Gutowski (18), Dalquist and Gutowski (19), Thiriez and Gutowski (20, 21), Baniszewski (22), Kurd (23), Cho (24), Kordonowy (25), Jones (26), Branham et al (27, 28), and Gutowski et al (29). Several texts and overviews also provide useful process data (30-35) and additional manufacturing proc-ess studies of ours include Sekulic (36), Jayasankar (37), Sekulic and Jayasankar (38), Bodapati (39) and Subramaniam and Sekulic (40). THERMODYNAMIC FRAMEWORK Manufacturing can often be modeled as a sequence of open thermodynamic processes (27) as proposed by Gyftopoulos and Beretta for materials processing (1). Each stage in the process can have work and heat interactions, as well as materials flows. The useful output, primarily in form of material flows of products, and by-products from a given stage can then be passed on to the next. Each step inevitably2 involves losses due to an inherent departure from reversible processes, hence generates entropy and a stream of waste materials and exergy losses (often misinterpreted as energy losses).2 Figure 1 depicts a generalized model of a manufacturing system (27, 50). The manufacturing subsystem (!MF) receives work W and heat Q from an energy conversion subsystem (!ECMF). The upstream input materials come from the materials processing subsystem (!MA), which also has an energy conversion subsystem (!ECMA). This network representation can be infinitely expanded to encompass ever more complex and detailed inputs and outputs (31, 32). Figure 1: Diagram of a Coupled Manufacturing and Materials Processing Systems (Ref. 50, adapted from (1))3 At each stage, the sub- systems interact with the environment (at some reference pressure p0, temperature T0 and chemical composition, which is given by mole fractions xi , i !(1, n), of n chemical compounds, characterized by chemical potentials µi,o) The performance of these sub-systems can then be described in thermodynamic terms by formulating mass, energy, and en-tropy balances. Beginning with the manufacturing sub-system !MF featuring the system’s mass MMF, energy EMF, and entropy SMF, we have three basic rate equations3: Mass Balance: dMMFdt= (!Ni,in"Mi)i =1!MF" (!Ni,out"Mi)i =1!MF (1) whereiN!is the amount of matter per unit time of the ith component entering or leaving the system and !Mi is the molar mass of that component. Energy Balance: resMFprodMFmatMFMFECMFMFkMFkECMFMFHHHWQQdtdE!!!!!!!!++!="#"$0, (2) Where MFkECMFQ,!and MFECMFW! represent rates of energy interactions between the manufacturing subsys-tem (!MF) and its energy supplying subsystem (!ECMF). TheH! terms signify the lumped sums of the enthalpy rates of all materials, products, and residue bulk flows into/out of the manufacturing system. Note that a heat interaction between !MF and the environment, denoted by the subscript “o” is assumed to be out of the system (a “loss” into the surroundings) at the local temperature To. Entropy Balance: dSMFdt= !k!QECMFMF"Tk#!Q0MF$T0+!SMFmat#!SMFprod#!SMFres+!Sirr, MF (3)4 where T/QMF! terms represent the entropy flows accompanying the heat transfer rates ex-changed between the subsystem !MF and energy supplying subsystem (!ECMF) and environment, respectively while iS! terms indicate the lumped sums of the entropy rates of all material flows. The term Sirr,MF represents the entropy generation caused by irreversibilities generated within the manufacturing subsystem. Assuming steady state, and eliminating 0Q!between equations (2) and (3) yields an expression for the work rate requirement for the manufacturing process: MF,irrMFECMFkkmatMFresMFprodMFmatMFresMFprodMFMFECMFSTQTT)S)SS((T)H)HH((W!!!!!!!!!00001 +!!"#$$%&'''+''+=(>() (4) The quantity H-TS appears often in thermodynamic analysis and is referred to as the Gibbs free energy. In this case, a different quantity appears, H-ToS. The difference between this and the same quantity evaluated at the reference state (denoted by the subscript “o”) is called exergy, !Ex = (!H ! To!S) ! (!H ! To!S)o.4 Exergy of a material flow represents the maximum amount of work that could be extracted from the flow considered as a separate system as it is reversibly brought to equilibrium with a well-defined environmental reference state. In general, the bulk-flow terms in (4) may include contributions that account for both the physical and chemical ex-ergies, hence !Ex =!Exph+!Exch, as well as kinetic and potential exergy (not considered in this discussion), see (2 – 5). The physical exergy is that portion of the exergy that can be extracted from a system by bring-ing a system in a given state to the “restricted dead state”