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Lecture 2

Lecture 2. ME 300 Fall 2008. Administrative Matters. Course Title: Fundamentals of Engineering Thermodynamics Class Hours: M, W, F, 11-11:50, 1320 DCL Text Book: Fundamentals of engineering Thermodynamics by Moran and Shapiro, 6 th edition

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Lecture 2

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  1. Lecture 2 ME 300 Fall 2008

  2. Administrative Matters Course Title: Fundamentals of Engineering Thermodynamics Class Hours: M, W, F, 11-11:50, 1320 DCL Text Book: Fundamentals of engineering Thermodynamics by Moran and Shapiro, 6th edition Instructor: Pratap Vanka, MEL 3011, 244-8388, spvanka@uiuc.edu Office Hours: M, W: 4-5 pm. Thu: 4-5 pm.

  3. MEETING NAME                    DATE        START     END       ATT   LOCATION          -------------------------------------------------------------------------------------------- ME 300 Review Sessions (Vanka)  8/28/2008   4:00 PM   5:00 PM   1     1MEB 153          ME 300 Review Sessions (Vanka)  9/4/2008    4:00 PM   5:00 PM   1     1MEB 153          ME 300 Review Sessions (Vanka)  9/11/2008   4:00 PM   5:00 PM   1     1MEB 253          ME 300 Review Sessions (Vanka)  9/18/2008   4:00 PM   5:00 PM   1     1MEB 253          ME 300 Review Sessions (Vanka)  9/25/2008   4:00 PM   5:00 PM   1     1MEB 253          ME 300 Review Sessions (Vanka)  10/2/2008   4:00 PM   5:00 PM   1     1MEB 253          ME 300 Review Sessions (Vanka)  10/9/2008   4:00 PM   5:00 PM   1     1MEB 253          ME 300 Review Sessions (Vanka)  10/16/2008  4:00 PM   5:00 PM   1     1MEB 253          ME 300 Review Sessions (Vanka)  10/23/2008  4:00 PM   5:00 PM   1     1MEB 253          ME 300 Review Sessions (Vanka)  10/30/2008  4:00 PM   5:00 PM   1     1MEB 253          ME 300 Review Sessions (Vanka)  11/6/2008   4:00 PM   5:00 PM   1     1MEB 253          ME 300 Review Sessions (Vanka)  11/13/2008  4:00 PM   5:00 PM   1     1MEB 153          ME 300 Review Sessions (Vanka)  11/20/2008  4:00 PM   5:00 PM   1     1MEB 253          ME 300 Review Sessions (Vanka)  12/4/2008   4:00 PM   5:00 PM   1     1MEB 253        

  4. Website • www.mechse.uiuc.edu • Courses • Course wesites • ME300-D • Scroll to the bottom, see downloads Lectures are organized by number. Homeworks will also appear here.

  5. Course Objectives • Course Objectives: To introduce fundamental concepts of engineering thermodynamics, and apply them to real-world problems • Text book: Fundamentals of Engineering Thermodynamics by Moran and Shapiro, 6th edition • No laboratory manuals or supplementary notes are needed

  6. Homeworks, exams, quizzes Homeworks will be assigned every Friday. Homeworks need NOT be submitted. They will not be graded, but you must solve the problems independently before the following Friday Quizzes: There will be an in-class quiz on Fridays from 11:30 – 11:50 am. The quizzes will cover the material covered the previous week, and the homework that was assigned.

  7. Grading Quizzes: 10 / 11 in total 30 points 2 midterms (20 each): 40 points 1 final exam: 30 points Midterms are given in outline. Final as per the calendar. Letter grades will be assigned based on break points on the total summed-up score. + and – grading will be used. No conflict quizzes, including in emergency situations.

  8. Equilibrium • Equilibrium is a state of balance. Equilibrium need not be just mechanical, but also thermal, phase, and chemical equilibrium. • To test equilibrium state, isolate the system from its surroundings and see if the properties do not change. When the system is isolated, it does not interact with its surroundings. • At equilibrium, the temperature is uniform throughout the system. Pressure may be uniform if gravity is switched off. • The system need not be in equilibrium during a process

  9. Property, State and Process A property is a macroscopic characteristic of a system. Examples are: mass, volume, temperature, pressure, energy, etc. The state of a system is described by its properties. A system changes its state through a process Properties are measured in units

  10. Extensive and Intensive properties Extensive properties scale with system mass. Examples: mass, volume, total energy, total heat etc. Intensive properties: do not vary even if the mass is increased. Pressure, Temperature, specific energy, density, etc.

  11. Properties Specific Volume • Specific volume is the reciprocal of density. Density is the mass per unit volume, as the volume shrinks to a small value. • n = number of moles, m = mass, M = molecular weight

  12. Specific Volume • Molecular weight has units of kg / kmol or lbm/lbmol • Molar volume

  13. PropertiesPressure Let us consider a small area, A, and apply a force normal to Fnormalto the area. Pressure is defined in the limiting sense as force per unit area. Pressure is a point value. Also, pressure, unless otherwise stated refers to absolute pressure, zero being vacuum. Later we shall talk about gage pressure

  14. Pressure Measurement Pressure is measured with manometers, pressure gauges, pressure sensors using the piezoelectric effect. Pressure is measured by the hydrostatic pressure exerted on a liquid column.

  15. Pressure Units Pressure = Force / area = Mass * Accel / area = Newton / m2 = kg . m / s2 / m2 = kg / (m. s2) = Pascals (Pa) 1 kPa = 1000 Pa 1 Mpa = 1000 kPa 1 bar = 100 kPa 1 standard atmosphere = 1.01325 bars = 101.325 kPa = 14.696 lbf / in2 = 14.696 psi

  16. Absolute, Gage and Vacuum Absolute Pressure is the actual pressure Gage pressure is pressure ABOVE atmospheric pressure pgage = pabsolute – patm pvacuum = patm – pabsolute p (vacuum) is defined to be always positive

  17. Temperature Temperature is a measure of “hotness” or “coldness” Temperature is measured in degrees Two scales are used: centigrade (or Kelvin) or Fahrenheit (or Rankine) Temperature is measured by thermometers, based on liquid expansion, electrical resistance or infrared sensing (ear thermometer)

  18. Kelvin and Rankine Scales Kelvin and Rankine scales start at zero temperature (the lowest possible), but measure on a different scale. T(R) = 1.8 * T(K) The Kelvin scale is an absolute thermodynamic temperature scale.

  19. Celsius and Fahrenheit scales The Celsius scale has the same unit degree as the Kelvin scale, but the origin is different T (oC) = T(K) – 273.15 The Fahrenheit scale has the same unit degree as the Rankine scale, but the origin is different T (oF) = T(R) – 459.67 T (oF) = 1.8 * T (oC) + 32

  20. Chapter 1: Problems 1.4 An object has a mass of 10 lbm. Determine its weight in lbf at a location where the acceleration of gravity is 31.0ft/s2 Solution lbf is a unit of force. 1 lbf = 1 lbm * 32.2 ft / s2 10 lbm accelerated by 31 ft / s2 = 10 x 31.0 / 32.2 = 9.627 lbf

  21. 1.15. An object whose mass is 2 kg is subjected to an applied upward force. The only other force acting on the object is the force of gravity. The net acceleration is upward with magnitude of 5 m/s2. The acc of gravity is 9.81 m/s2. determine the magnitude of the upward force, in N. Solution: m = 2 kg. a = 5 m/s2. F upwards = m x g + m x a = (2) (5 + 9.81) = (2) (14.81) = 29.62 N

  22. 1.21 A closed system consists of 0.5 kmol of ammonia occupying a volume of 6 m3. Determine the weight of the system in N, and the specific volume in m3/kmol and m3/kg. g = 9.81 m/s2. Solution : Ammonia, molecular weight M = 17.03kg / kmol n = 0.5 kmol ; m = 0.5 * 17.03 kg. = 8.515 kg. Specific volume = 6 m3 / (0.5 x 17.03) = 0.7046 m3/ kg or = 6 m3 / 0.5 = 12 m3 / kmol Weight = m x g = 8.515 x 9.81 = 83.53 N

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