Thermodynamics

xxii | Prefacetheir findings in a professional manner. Problems designated by an “E” arein English units, and SI users can ignore them. Problems with the aresolved using EES, and complete solutions together with parametric studiesare included on the enclosed DVD. Problems with the are comprehensivein nature and are intended to be solved with a computer, preferablyusing the EES software that accompanies this text. Several economics- andsafety-related problems are incorporated throughout to enhance cost andsafety awareness among engineering students. Answers to selected problemsare listed immediately following the problem for convenience to students. Inaddition, to prepare students for the Fundamentals of Engineering Exam(that is becoming more important for the outcome-based ABET 2000 criteria)and to facilitate multiple-choice tests, over 200 multiple-choice problemsare included in the end-of-chapter problem sets. They are placed underthe title Fundamentals of Engineering (FE) Exam Problems for easy recognition.These problems are intended to check the understanding of fundamentalsand to help readers avoid common pitfalls.RELAXED SIGN CONVENTIONThe use of a formal sign convention for heat and work is abandoned as itoften becomes counterproductive. A physically meaningful and engagingapproach is adopted for interactions instead of a mechanical approach. Subscripts“in” and “out,” rather than the plus and minus signs, are used to indicatethe directions of interactions.PHYSICALLY MEANINGFUL FORMULASThe physically meaningful forms of the balance equations rather than formulasare used to foster deeper understanding and to avoid a cookbookapproach. The mass, energy, entropy, and exergy balances for any systemundergoing any process are expressed asMass balance:Energy balance:Entropy balance:Exergy balance:m in m out ¢m systemE in E out ¢E system⎫ ⎪⎬⎪⎭⎫⎪⎬⎪⎭⎫⎬⎭⎫ ⎪⎬⎪⎭⎫⎪⎬⎪⎭⎫⎪⎬⎪⎭⎫ ⎪⎬⎪⎭⎫⎪⎬⎪⎭Net energy transferby heat, work, and massChange in internal, kinetic,potential, etc., energiesS in S out S gen ¢S systemNet entropy transfer Entropy Changeby heat and mass generation in entropyX in X out X destroyed ¢X systemNet exergy transfer Exergy Changeby heat, work, and mass destruction in exergyThese relations reinforce the fundamental principles that during an actualprocess mass and energy are conserved, entropy is generated, and exergy isdestroyed. Students are encouraged to use these forms of balances in earlychapters after they specify the system, and to simplify them for the particularproblem. A more relaxed approach is used in later chapters as studentsgain mastery.