About Notations, Sketches, etc
Though published Engineering Thermodynamics Texts tend to improve steadily with each edition some aspects that have not improved are:
About Notations, Sketches, etc
Though published Engineering Thermodynamics Texts tend to improve steadily with each edition some aspects that have not improved are:
| Basic Thermodynamics ~ J. Pohl © | www.THERMOspokenhere.com |
About Notations, Sketches, etc
Though published Engineering Thermodynamics Texts tend to improve steadily with each edition some aspects for improvement are:
Excessive Precision: Authors of most texts present physical constants to excessive precision. As a consequence, students write numbers with highly exaggerated precision. They key these long numbers into their calculators and of course... calculators display even longer, even more falsely, precise numbers. Students then write the long numbers on the page. This is more that a waste of time; it is a misunderstanding of physical reality.
All problems of physics and thermodynamics are postulated "approximately" and are solved subject to great "assumption. " Excessive precision is unmerited. To use constants written to more than three significant places provides false precision, is time consuming and enforces the incorrect notion that "classroom science" is quantitative to the many places of π. Fed this habit bu physics texts, students carry those "definitions" to extremes. The table below contains two immediate and ubiquitous examples of excessive, pedantic precision. Prefered values for useage are included.
Considerable improvement is possible. Within this site text figures and examples of the commonly used texts are discussed for the purpose of bringing the writings together and, in cases, extend or correct them. Below is a partial list of improvements that need to be effected.
| NO! | YES! |
| go = 9.80665 m/s² (or 32.1740 ft/s²) | go = 9.81 m/s² (or 32.2 ft/s ) |
| 1 lbm = 0.45359237 kilograms | 1 lbm = 454 grams |
An exception is for numbers taken from a table where the "extra-accuracy-carried" might help reveal the precise location within the tabular data from which the data were retrieved.
Remedial Physics: Study of physics is a required prerequisite of the study of engineering thermo. The usual exposure of a student is HS physics and then university physics at the freshman level. In thermo, to begin smoothly, a student must have knowledge and experience with the physic topics: aspects of motion, Newton's Laws of motion, kinetic energy and potential energy...
It is common for educator who struggle while teaching to cite "lack of preparation" of the students as one cause of non-accomplishment. With educators of engineering thermodynamics that idea has gained such status as truth that most texts have as their first chapters, material that is remedial physics. Topics of mechanics and Newton's Laws of Motion are recognized as insufficiently addressed in HS physics. Students are presumed not competent in these prerequisite high school and university physics topics. Engineering thermodynamics texts do this remediation poorly.
Omission of Summations: There are many occasions when some physical amount or effect occurs with more than just one part of the sustem. It is better to use summations of these rather than to introduce a "net" idea.
To compound matters, many mechanics-oriented figures of physics texts are "partially complete." Admittedly the figures are presented with limited objectives and to be proper complete takes space. On the other hand, being able to specify a system, a critical need of thermodynamics, is learned at the mechanical system level. It is with precise drawing of mechanical systems that students learn to specify a thermodynamic system.
Vectors and Calculus: High school mathematics is largely algebra and trigonometry. Neither geometry nor vectors are taught. University calculus texts have a section on vectors (around page 550 or so). University physics talks about vectors then takes a quasi-vector, quasi-algebraic, vectors-along-a-line, approach. The first order differential equation (with initial condition), a cornerstone of physical science, generally appears around page 600 in the now four-inch calculus texts. Math should be brought up to date somewhere, before completion of statics, dynamics and thermodynamics.
High school mathematics is largely algebra and trigonometry. Negligible geometry and no vectors are taught. Vectors, important to engineering, are taught by the service courses, University Calculus. Vectors, occuring around page 600 in the calc text are usually "not gotten to" or taught with "waving hands." University Physics introduces vectors then takes a quasi-vector, quasi-algebraic, vectors-along-a-line, approach. Thermodynamics texts also ignore vectors.
First Order Differential Equations: The first order differential equation (with proper system description and initial conditions) is a cornerstone of physical science. This topic shows up in Calculus III or about 400 pages into the four-inch-thick texts. Math should be brought up to date somewhere, before completion of statics, dynamics and thermodynamics. The differential equation is taught in this material.
Notation and Approach: That texts have different sign conventions and different approaches to equations make cross-reading in thermodynamocs hazardous at best. A conference to iron out these styles would be helpful to student learning.
Notations and Sign Conventions: While all texts admit existence of vectors, most avoid using them. That texts have different sign conventions for work makes student cross-reading in thermodynamocs hazardous at best. A conference to iron out these pedantic, petulent styles would be helpful to student learning.
System Method versus Balance-Equation Method: Thermodynamic analysis addresses selected matter called the "system." The system method of analysis is physical. Balance Equations are mathematical. Their emphasises are not physical but equational ~ as in: Energy Event left-of-equality equals Energy Event right-of-equality. The Balance Method is becomes awkward in application to transient events. The System Method is consistently awkward and superior to balance methods.
Excessive Coverage: Nowadays students are obliged to purchase much more text than needed. About 40 years ago the typical university Mechanical Engineering thermodynamics curricula consisted of two terms for about eight credit hours. To fit new courses, computer usage, robotics, etc, into the curricula, thermodynamics at many schools was reduced to a one-term, three to four hour course. Publishers still sell two-term texts. Approximately 300 pages of most texts are not used.
Entropy versus Frictionless-Adiabatic: At one time thermo was two courses in sequence over two terms, the coverage extended from the basics through Carnot, then Otto, Diesel cyclic engines, then elementary steam power analysis, psychometrics, combustion, and other topics. Although those days are gone forever, we still use texts bloated to cover everything. The commitment today is "3 hours of thermo." The reduced hours of curriculum have forced the "reasonable coverage" of any of the 800-page commercial texts (students must purchase) to be about the first four or so chapters (about the first 250 pages of the name-brand texts). Among things diminished in coverage was entropy and thermal engines. Among things diminished in coverage was entropy and thermal engines. This writing avoids use of entropy in favor of a "frictionless-adiabatic" (reversible-adiabatic) approach. Thermal reversibility, cyclic engines and entropy are topics for the now defunct, Thermodynamics II.
Entropy change for the event of a system is made zero when one assumes the event frictionless and adiabatic. At this level, these assumptions are obligatory. Here (and in all thermo classes) discussion of entropy change of a system event is avoided in favor of the "cover-all" assumnption of a "frictionless-adiabatic" (some say reversible-adiabatic) event. Thermal reversibility, cyclic engines and entropy are topics for the now defunct course, Thermodynamics II.
Awkward Problem Statements and Sketchs: Basic Thermodynamics applies to physical matter and its event. To convey, on paper, the circumstances of a problem a student might solve requires skill at making statements regarding physical reality. Such reality is best depicted by a carefully drawn sketch or drawing. When no sketch is needed, the problem is trivial; omit it.