ME 200 - Chapter 1

ME 200 - Chapter 1 - ME 200 – Thermodynamics 1 In-Class...

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Unformatted text preview: ME 200 – Thermodynamics 1 In-Class Notes for Spring 2011 • • Course Overview and Policy Chapter 1 – – – – Thermodynamics Intro. & Definitions Properties Processes & Cycles Problem Solving Course Overview & Policy • Textbook – Moran, M.J. & Shapiro, H.N., Fundamentals of Engineering Thermodynamics (6th edition), John Wiley, 2008 – Thermodynamic properties in appendices – Unit conversion factors at front cover • Lecture Notes – Printed copies provided in lecture at start of each copies provided in lecture at start of each new chapter – Mixture of prepared notes and blank areas for student note taking Divisions & Instructors Prof. Braun: Division 4 - 10:30 – 11:20 AM – Office Location: ME 107 – Office Phone: 49-49157 – Office Hours: MWF, 11:30 AM – 12:30 PM • Course Prerequisites: calculus, physics, chemistry. CHEM115, PHYS172 and MA261 (may be concurrent) Course Website: – – – – – Homework problems and links for help Tutorial room and office hour schedules Old exams, notes, etc. Announcements • Prof. Naik: Division 1 - 1:30 – 2:20 PM Prof. Zhao: Division 2 - 12:30 – 1:20 PM Prof. Richardson: Division 3 - 3:30 – 4:20 PM Richardson: Division 3:30 4:20 PM Prof. Son: Division 5 - 7:30 – 8:20 AM Introduction - Page 1 Introduction - Page 2 Course Overview and Policy • Homework – 3 or 4 problems for each lecture (see syllabus) – Problems collected on Fridays (from previous Friday, Monday, and Wednesday lectures) – Follow suggested format (see Course Policy) – Use Engineering paper – Book problems will be the basis for quizzes (lecture after they are assigned) – Special problems collected on Fridays and graded – Solutions to book problems posted outside ME 161 – Special problems solutions will not be posted (get help from instructors or TAs) Course Overview and Policy • In-Class Evaluation – Quizzes • Based on homework assigned from book and lecture notes • Attendance is required – Cheating • Violators will be given 0% for the entire 10% of the in-class evaluation grade • Lecture Preparation – Read text before lecture – Attempt to solve homework problems before to solve homework problems before lecture – Review notes from last lecture • Exams – Closed book – Equation sheet and properties provided – Bring calculator and a pencil only • • Grading: Use option that gives higher grade Option 1 35% 45% 10% 10% Option 2 45% 35% 10% 10% Three one-hour exams Final exam Homework In-Class Evaluation Resources – Tutorial Room: ENAD 212 – Office Hours – Course website – ATTEND CLASS AND DO HOMEWORK 20% Introduction - Page 3 Introduction - Page 4 Lecture 1 Introduction, Units, & Systems Objectives • What is Thermodynamics and why do we care? • Two thermodynamics laws thermodynamics laws • Basic and derived units • Systems, boundaries, and surroundings What is “Thermodynamics”? 1st Law Example reference 2st Law of Thermodynamics 1st Law of Thermodynamics of Thermodynamics Introduction - Page 5 Introduction - Page 6 Applications of Thermodynamics • Power plant plant • Applications of Thermodynamics Air Conditioning • Air Plane • Human Body Introduction - Page 7 Introduction - Page 8 Basic Units Physical quantity mass length time temperature amount of matter electric current current amount of light SI kg m s K mol A cd English lbm ft s R lbmol A candles Force: A Derived Unit From Newton’s Law of Motion: F = ma Introduction - Page 9 Introduction - Page 10 Systems Open System (or Control Volume) Closed System (or Control Mass) Examples Is this classroom an open or closed system? What about an aircraft engine? about an aircraft engine? Introduction - Page 11 Introduction - Page 12 Lecture 2 Properties and States Properties Extensive properties: Objectives • General property definitions property definitions • States and equilibrium definitions • Pressure Intensive Properties: Example Water with following properties: ρ = 1000 kg/m3 V = 1 m3 m = 1000 kg 1000 kg How many of these properties are independent? Properties : What is a property? Independent properties: Which properties are intensive? Introduction - Page 13 Introduction - Page 14 State and Equilibrium State: “condition” of a system as described by condition of system as described by its properties Pressure Equilibrium: a state of balance (no unbalanced forces) For a column of fluid fl Free-body diagram p1 Δz p2 State Postulate: the equilibrium state of a simple compressible substance is completely simple compressible substance is completely specified by 2 independent, intensive properites p2A Δz mg p1A Introduction - Page 15 Introduction - Page 16 Simple Pressure Measurement atmospheric pressure Absolute, Gage and Vacuum Pressures pabs vacuum fluid pgage Atmospheric pressure patm patm Δz pvac Zero pressure pressure system pressure patm fluid Pressure Units 1 Pa = 1 N/m2 1 bar = 105 Pa = 100 kPa 1 atm = 1.013 bars = 14.7 psi atm bars 14 psi gas psys Δz psys Introduction - Page 17 Introduction - Page 18 Examples Specific Volume Specific Volume: v= V1 = mρ Units: m3/kg or ft3/lbm V = Volume, m = mass, n = number of moles Which labeled point has the highest pressure? th hi Which labeled point has the lowest pressure? Molar Specific Volume: v= Vm = v = M ⋅v nn Units: m3/kmol or ft3/lbmol M = molecular weight (kg/kmol or lbm/lbmol) Recall that 1 mol has 6.022x1023 molecules Patm = 14.7 psi 100 ft P2 = ? Introduction - Page 19 Lecture 3 Temperature, Processes and Cycles, Problem Solving Temperature • Two objects in thermal equilibrium are at the objects in thermal equilibrium are at the same temperature • Temperature is an intensive property that determines whether or not an object is in determines whether or not an object is in equilibrium with other objects • Thermometers measure the temperature dependence of some physical property Gas Thermometer Temperature scales are chosen so that T=a+bP Thermometers Thermometer Ideal gas Mercury bulb Bimetallic strip strip RTD or Thermistor Thermocouple Optical Pyrometer Pyrometer Silicon diode : Physical Property Measured Pressure and volume of dilute gas Expansion or contraction of fluid Difference in expansion of two solids in of solids Electrical resistance Voltage across dissimilar metals Color of emitted light Color of emitted light Electrical resistance Introduction - Page 21 For Celcius scale, assign 0oC 100oC freezing point of water at 1 atm boiling point at 1 atm Introduction - Page 22 For gases at low pressures (ideal gasses) Absolute Temperature Scales For absolute scales assign from experiments a = -273.15oC lowest possible temperature a = 0o Then, for a given ideal gas P For Fahrenheit scale, assign 32oF 212oF Then a = -459.67oF Introduction - Page 23 0 T freezing point of water at 1 atm boiling point of water at 1 atm Introduction - Page 24 Temperature Scale Comparisons Process and Cycles Process: change of system from one equilibrium state to another T(oC) = 5/9 (T(oF) - 32) T(oF) = 9/5 T(oC) + 32) Quasistatic (Quasiequilibrium) Process: “slow enough” process so that system is always infinitesimally close to equilibrium Path: series of states for process series of states for process Cycle: system returns to initial state after end of processes Cycle Efficiency: Introduction - Page 25 Introduction - Page 26 Thermodynamic Problem Solving Compression Process Example 2 System 1’’ 1’ 1 Problem Setup 1. Sketch process 2. Label known states 3. Identify system Assumptions 1. Process assumptions 2. Property assumptions p State 1 Conservation Eqs. 1. Mass 2. Energy 3. ... Performance Indices 1. Cycle efficiency 2. Process efficiency Boundary 1. Work 2. Heat transfer 3. Flow Property Evaluat. 1. Enthalpy 2. Entropy 3. ... ... v Cycle Efficiency Example Determine Unknowns Solution Format • Given: State in your own words what is given in the problem statement Example The initial temperature problem statement. Example “The initial temperature is T1=30 C.” Find: List what the problem wants you to find. Example “a) the pressure at time 2 or P2 =.” A sketch of your control volume. Assumptions: Example: “Ideal gas.” Basic Equations: Your basic equation must be one li listed on the attached ME 200 basic equation sheet. th ME 200 Solution: This includes correct units. Introduction - Page 28 • • • • • Introduction - Page 27 ...
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