Introduction - Thermodynamics - Lecture Slides, Slides of Thermodynamics

Download Introduction - Thermodynamics - Lecture Slides and more Slides Thermodynamics in PDF only on Docsity! Course Introduction August 24, 2010 ME 370 – Thermodynamics Course Introduction Larry Caretto Mechanical Engineering 370 Thermodynamics August 24, 2010 2 Today’s Class • First class day items: roll, outline, etc. • Class goals and learning objectives • Assessment quiz • Discussion of dimensions and units – Physical quantities have dimensions – Several units measure same dimension – Use SI system of units (meter, kilogram, ... – Also use engineering units (feet, pounds ... 3 Basic Information • Larry Caretto, Jacaranda (Engineering) 3333, lcaretto@csun.edu, 818.677.6448 (temporary) • Office hours Tuesday and Thursday 10 to 10:45 am; also by email or appointment • Web: http://www.csun.edu/~lcaretto/me370 • Yunus A. Çengel and Michael A. Boles, Thermodynamics, an Engineering Approach, (seventh edition) McGraw-Hill, 2011. – Bring text to class for use of tables • Class email list, me370-c@csun.edu uses CSUN email addresses …each day brings further evidence that the ways we use energy strengthen our adversaries and threaten our planet. We will harness the sun and the winds and the soil to fuel our cars and run our factories. Barak Obama, January 20, 2009 5 Course Learning Objectives • Understand the and be able to formulate and solve problems using thermodynamic properties: pressure, temperature, specific volume, internal energy, enthalpy, entropy, and quality • determine thermodynamic properties of real substances • calculate thermodynamic properties of ideal gases 6 More Learning Objectives • Understand the meaning of heat and work and the notion that these energy terms are not properties • Formulate and solve energy balance problems in engineering systems, including those with fixed mass and those with steady and unsteady flows Course Introduction August 24, 2010 ME 370 – Thermodynamics 7 Still More Learning Objectives • Understand the engineering significance of the second law of thermodynamics: maximum work and maximum efficiency in reversible processes • Formulate and solve problems with first law to find maximum work using the property entropy • Solve problems using the concept of isentropic efficiency as an empirical correction to maximum work 8 Learning Objectives Concluded • Formulate and solve problems that require the use of the energy balance from the first law and the principle of maximum work from the second law • Apply the first and second law to the analysis of engine and refrigeration cycles, using common idealizations for such cycles 9 Class Operation • Thursday: lecture on new topic – Assigned reading and suggested homework on new material in outline • Tuesday: group problem solving on this week’s topic • Thursday: Thirty-minute quiz on old topic prior to lecture on new topic • First quiz is Thursday, September 2 – See sample quiz on-line 10 Quizzes • Twelve during the semester • Based on group work and homework • See sample of first quiz on line – http://www.csun.edu/~lcaretto/me370 • Use link to Homework, Quizzes and Examinations • Count ten highest quiz grades for final – No makeup quizzes; final quiz grade based only on quizzes taken if fewer than ten • First four closed book; remainder use sheet of equations from web site 11 Grading • Quiz grades 45% • Midterm October 14 20% • Final Exam 35% – Tuesday, December 14, 10:15 am • Plus/minus grading will be used • Grading criteria in course outline • No make-up quizzes or exams – Quiz grade details on previous slide – Missed midterm grade from other grades 12 See the Course Outline • Download from web site for your section • Contains lecture and quiz schedule • Also read information on following items – Class participation and courtesy – Collaboration versus plagiarism: students found cheating receive F grade in course • Students are responsible for changes to outline announced in class Course Introduction August 24, 2010 ME 370 – Thermodynamics 25 Still More Units • Power: (energy)/(time) = joules/second – 1 watt (W) = 1 J/s = 1 N·m/s = 1 kg·m2/s3 • Pressure: (force)/(area) = newtons per square meter – 1 pascal (Pa) = 1 N/m2 = 1 kg/(m·s2 ) • Note that Isaac Newton has a capital N, 1 newton of force does not, unless it is abbreviated as 1 N (true for all units named after individuals) 26 Prefixes pico, p nano, n micro,  milli, m 10-12 10-9 10-6 10-3 tera, T giga, G mega, M kilo, k 1012 109 106 103 27 Engineering Units • Basic time unit, second, same as SI • The foot = 0.3048 m (exactly) is the basic unit of length • Pound is confusing because it is used to represent two dimensions – Mass: pound-mass (lbm = 0.453592 kg) – Force: pound force (lbf = 32.174 lbm·ft/s2) • What is SI equivalent for pound force? 1 lbf = 4.4482 N 28 More Engineering Units • foot-pound is work (energy unit) • British thermal unit (Btu = 778.16 ft-lbf) • Horsepower as power unit – 1 hp·hr = 2,545 Btu = 1.98x106 ft·lbf – 1 kW·hr = 3,412 Btu • The metric unit, calorie = 1/252 Btu • The food calorie is a kilocalorie often spelled with a capital C, Calorie 29 Calculating Units • What is kinetic energy of a 100 lbm mass moving at 10 ft/s • mV2/2 = (100 lbm)(10 ft/s) 2/2= 5000 lbm·ft·s -2 • Unit conversion • Note algebraic cancellation with unit conversion factors = 1 f m fm lbft ftlb slb s ftlb KE          4.165 174.32 10 2 )100( 22 1 174.32 2    ftlb slb m f 30 Units quiz • What is the change in potential energy when a mass of 20 lbm is raised a distance of 15 ft? • Do you need more data to answer this question? • What is g? Use 5 ft/s2 for this problem   f m f m lbftftlb slb ft s ft lbPE     62.46 174.32 15 5 )20( 2 2 Course Introduction August 24, 2010 ME 370 – Thermodynamics 31 Typical Thermodynamic Units Quantity SI units Engr units Energy kJ or MJ ft-lbf or Btu Specific energy kJ/kg Btu/lbm Pressure kPa = kN/m2 psia = lbf/in2(abs) Atmosphere 101.325 kPa 14.696 psia Temperature K = oC + 273.15 R = oF + 459.67 Power W, kW, MW hp, Btu/hr 32 Thermodynamics Problems • Use pressure in kPa and energy in kJ and volume in m3 for consistent units – 1 kPa·m3 = 1 kJ – 1 MPa = 1000 kPa, 1 m3 = 106 cm3 = 103 L • Engineering units, with pressure in psia and volume in ft3 give PdV work in units of psia·ft3 – Multiply psia·ft3 by 144 in2/ft2 to get ft·lbf or divide by 5.40395 psia·ft3/Btu to get Btu 33 Kinetic and Potential Energy • Watch these units • Look at energy per unit mass (KE/m = V2/2 and PE/m = gz) • A velocity of 1 m/s has a KE/m of 1 m2/s2 = 1 J/kg = 0.001 kJ/kg • A velocity of 1 ft/s has KE/m of 1 ft2/s2 = 0.031081 ft·lbf/lbm = 3.9942x10 -5 Btu/lbm • Similar conversions for PE/m 34 How Much Energy is a Joule • 1 W = 1 J/s • Electrical energy measured in kWh ( ) MJ6.3=J10x6.3= h/1 s/600,3 s/W/k J1000 h/Wk1=kWh1 6 • 1 J of electrical energy costs $3x10-8 • 1 J of natural gas costs $1x10-8 • World energy use  450x1018 J/yr • US energy use about 25% of world use 35 What does 1J Cost? • Average San Fernando Valley home utility bills in 2008 (without fees and tax) – Electricity: $32x10-9 per joule – Natural gas: $11x10-9 per joule • What about gasoline at $3 per gallon? – With taxes in the three dollars (usual case): $26x10-9 per joule – Without California taxes of $0.585 per gallon: $21x10-9 per joule 1 Mtoe = 4.1868x1016 J = 3.968x1013 Btu Mtoe = Million tonnes (1 tonne = 1000 kg) of oil equivalent TPES http://www.iea.org/Textbase/publications/free_new_Desc.asp?PUBS_ID=1199 Course Introduction August 24, 2010 1973 and 2006 regional shares of TPES* 2006 Arica Wele maine 455 Pls "Excludes electelly rode. **Asia excludes Chin, ME 370 — Thermodynamics