Thermodynamics Where Does It Fit?

With the advent of biological engineering and with the changing of emphasis in many agricultural engineering programs around the country, it is time for a fresh look into how some of our engineering science courses are structured. The ongoing shrinkage in the number of hours available in the typical undergraduate curriculum around the US further reinforces this need. Some have proposed alternative treatments of thermodynamics in our discipline. A comprehensive treatment of thermodynamics meeting the needs of all biological and bioresource engineers is not practical at the undergraduate level. The paper will discuss concepts relating to melding relevant thermodynamic concepts with heat transfer for bioresource or agricultural engineers. A similar melding of relevant thermodynamic concepts with a basic physical (bio)chemistry course or basic mass transport course found in biological curriculums could meet the need for these engineers. Similarly, through various modules, thermodynamics instruction may also be linked to 3 and 4 year courses in the traditional agricultural and bioresource curriculum. The use of modules may facilitate the delivery of the materials to diverse audiences, and several are proposed and some existing ones are discussed. A case is made for a thorough coverage of the topic at the graduate level. Background The word thermodynamics was coined about 1840 from two Greek roots: therme, heat and dynamis, power (Haynie, 2001). Based on the strict interpretation of the word, one expects that thermodynamics will have to do with heat and power or its storage, transformation and dissipation. Thermodynamics aims to describe and relate the physical properties of systems of energy and matter. Undergraduate students of engineering often survey the rudiments of thermodynamics in their physics courses, and then move on to one or more courses dealing with aspects of Thermodynamics. On completing these courses, the operational definition of thermodynamics typically becomes very specific, relating to work, heat, enthalpy, entropy, equation of state and simple compressible substances. The student pursuing mechanical engineering would add various power cycle applications to their concept. The student who is pursuing chemical or materials engineering will add such concepts as Gibbs functions and chemical potentials to their concept of thermodynamics. Concepts such as Maxwell relationships may be in the deep recesses but mean very little in that they rarely carry over to other courses. Systems beyond the simple compressible substance, if introduced, frequently go unappreciated by students. Textbooks may address topics such as statistical thermodynamics, irreversible thermodynamics and other “far out” topics. Students learn that everything in the universe should be approaching a steady equilibrium state, which seems to be at odds with the P ge 8.196.1 Proceedings of the 2003 American Society for Engineering Education Annual Conference & Exposition Copyright 2003, American Society for Engineering Education development of life processes as we know them. Students frequently have not had or do not appreciate the applications of total differentials and exact differentials that are often presented in thermodynamics courses. Many students do not readily perceive the significance of the course in the grand scheme in their curricula and thus may put it off as long as possible. Undergraduate engineering students have a somewhat disjoint view of thermodynamics and tend to vaguely appreciate those aspects of thermodynamics that relate directly to their other engineering science courses. Thermodynamics in the sciences and engineering Thermodynamics is often perceived as an engineering science wherein all controversies have been long since settled and that, like the matter it usually represents, is in or approaching an intellectually uninteresting steady state. Since thermodynamics was coined, the body of knowledge has grown beyond the realm of simple compressible substances. For example, Zemansky and Dittman (1997), in a text used for upper class undergraduate physics classes discuss the thermodynamic systems shown in Table 1. Table 1. Selected thermodynamic systems (from Zemansky and Dittman, 1996). System Intensive coordinate Extensive coordinate Simple compressible substance (hydrostatic) Pressure Volume Hydrostatic system Pressure P Stretched wire Force F Length L Surface film Surface tension Y Area A Electrochemical cell Electromotive force Emf Charge Z Dielectric slab Electric field E Polarization p Paramagnetic rod Magnetic field, μH Magnetization B Thermodynamics rapidly grew in the 19 century and now extends far beyond the simple compressible substance as is readily apparent from Table 1. Terms analogous to specific heat at constant volume and constant pressure are definable for other systems. One can begin to grasp the greatly enlarged scope of classical thermodynamics by reviewing Table 1. Generalized equations of state exist for each of the above systems. Thermodynamics is typically delivered in this more generalized context in seniorbeginning graduate level courses in many physics curricula. Chemistry (and related) and related majors typically receive extensive training in thermodynamics through Physical Chemistry. An introductory text in the subject by Lesk (1982) grounds the subject matter of physical chemistry in thermodynamics, statistical mechanics and quantum mechanics. After introducing various states of matter, extensive treatments of energy and the first law, the authors then discuss entropy and the second law and implications for equilibrium. Following further treatments of kinetic theory, statistical mechanics at the molecular level, electric and magnetic properties, quantum theory, spectroscopy and electronic structure of matter, electrochemistry and the dynamics of chemical change is then discussed. Physical chemistry is typically an upper division undergraduate course in chemistry departments. P ge 8.196.2 Proceedings of the 2003 American Society for Engineering Education Annual Conference & Exposition Copyright 2003, American Society for Engineering Education The delivery of thermodynamics has changed over the years. For example, here is the syllabus summary for ME 220, Thermodynamics I, University of Kentucky in the late 60s: Introduction – Concepts, models, laws. Energy and the first law Systems Energy Conservation and transfer as work Work modes for simple compressible substances and for simple magnetic substances. Energy transfer as heat First law for a control mass Energy equivalents Properties and state Equilibrium and thermodynamic state Temperature Intensive and extensive state Independent variations of the thermodynamic state The state postulate States of simple substances Equations of state Using tabular and graphical equations of state Perfect gas Simple magnetic substance Energy analyses Control mass Control volume Entropy and the second law Entropy as a function of state Thermodynamic definition of temperature and pressure Macroscopic evaluation of entropy Second law analyses Statistical thermodynamics Thermodynamics of State Thermodynamic properties of a simple compressible substance Evaluating entropy of simple compressible substance Other differential equations of state Enthalpy Maxwell relations Dense gases Equation of state for the Curie substance Wrap-up Page 8.196.3 Proceedings of the 2003 American Society for Engineering Education Annual Conference & Exposition Copyright 2003, American Society for Engineering Education This course, based on the first half of a text by Reynolds (1965), stressed the importance of the simple compressible substance, although it attempted to preserve the general nature of thermodynamics by including the simple magnetic substance. The second course in this sequence, taken mainly by mechanical engineers, applied the above concepts to various power cycles and refrigeration, with some treatment of reactive equilibrium thermodynamics in a discussion of combustion processes. Chemical and materials engineers typically either take physical chemistry and/or take a discipline specific course emphasizing equations of state for non-ideal gasses and non-reactive/ reactive equilibrium thermodynamics. More advanced topics were provided in graduate level courses. The syllabus above represents the typical introductory thermodynamics course in many engineering schools (based on an analyses of several common texts). Contemporary introductory thermodynamics courses focus more on the simple compressible substance and less on other systems (e.g., the simple magnetic substance). Topics such as statistical thermodynamics and the kinetic theory of gases are given less emphasis. There continue to be perceived relevance questions in the minds of the students regarding the significance of this body of knowledge to the practice of engineering, even with the tighter focus (compared to the treatment of the discipline in the sciences). Combinations of thermodynamics subjects and other courses The continuing pressure to reduce hours at the BS level provides continuing motivation to reevaluate the structure of the core of courses used to deliver the engineering sciences. One or more ASAE workshops wherein alternative approaches for thermodynamics were surfaced have occurred in the recent past. Cengel (1997) authored a text which attempts to address thermodynamics and heat transfer for those curricula having room for one course in the thermal sciences, although the material given could only be completely covered in two semesters. Seven chapters cover typical thermodynamic subjects (including a chapter on power and refrigeration cycles). The coverage resembles the outline given above but is much less in depth. The remaining six chapters introduce heat transfer (conduction including transient, forced and natural convection, radiation, heat exchangers, applications to cooling electronic