Copyright (c) 2005 by John Wiley & Sons, Inc ThermoNet Thermodynamics: An Integrated Learning System P.S. Schmidt, O.A. Ezekoye, J.R. Howell and D.K. Baker Chapter 1: Thermodynamic Concepts and Terminology

1.1 Systems: Definitions System: Part of the universe to analyze. Surroundings/Environment: Part of universe affected by system. System Boundary: Separates system from surroundings. System Surroundings Universe System Boundary

Chapter 1: Thermodynamic Concepts and Terminology 1.1 Systems: 3 Types Transferred Across System Boundary Type of SystemMassEnergyExample Open System/ Control Volume (CV) Yes Jet Engine Closed System/ Control Mass (CM) NoYesLight Bulb Isolated SystemNo Ice Chest/ Cooler for small  t

Chapter 1: Thermodynamic Concepts and Terminology 1.1 Combustion in Open & Closed Systems PowerPoint frozen? Click here and try again

Chapter 1: Thermodynamic Concepts and Terminology 1.2 Properties: Definitions Thermodynamic Properties: Describe mass and energy of system (e.g., T, P and V). Extensive Properties: Vary with system size (e.g., V). Intensive Properties: Independent of system size (e.g., T and P). Specific Properties: –Divide extensive property by mass –Intensive Property –E.g., Specific Volume, v = V/m = 1/  [m 3 /kg]

Chapter 1: Thermodynamic Concepts and Terminology 1.2 Properties: Total & Specific Volumes Total Volume: V –[m 3 ] –Upper case V Specific Volume: v –[m 3 /kg] –Lower case v

Chapter 1: Thermodynamic Concepts and Terminology 1.3 State Thermodynamic State: –Collection of all Thermodynamic properties of system. –Ability to define system’s state essential in Thermodynamics –Using state principle (Chp 3), can use limited set of property data to determine all property data.

Chapter 1: Thermodynamic Concepts and Terminology 1.4 Changing the State of a System Process: Change in state of system. 4 Common Processes: –Isothermal: Constant Temperature –Isobaric: Constant Pressure –Isometric: Constant Volume –Adiabatic: No Heat Transfer P = constant (isobaric) P v v =constant (isometric) T = constant (isothermal) T v v =constant (isometric)

Chapter 1: Thermodynamic Concepts and Terminology 1.4 Isobaric & Isometric Processes PowerPoint frozen? Click here and try again

Chapter 1: Thermodynamic Concepts and Terminology 1.5 Unit Systems Base Units: Defined by reproducible physical measurements Derived Units: Derived from base units SI: Metric International System –Base Units: time (s), length (m), mass (kg) –Force (N) is a derived unit from mass USCS: U.S. Conventional System or English System –Base Units: time (s), length (ft), force (lbf) –Mass (lbm) is a derived unit from force

Chapter 1: Thermodynamic Concepts and Terminology 1.5 Unit Systems: g C g C : Conversion constant SI USCS – –1 lbm  1 lbf

Chapter 1: Thermodynamic Concepts and Terminology 1.6 Property Units Volume, Specific Volume and Density Volume, V [ m 3 or ft 3 ] Specific Volume, v [m 3 /kg or ft 3 /lbm] Density, ρ [kg/m 3 or lbm/ft 3 ]

Chapter 1: Thermodynamic Concepts and Terminology Pressure (P) Pressure (P): P = Force/Area 3 Types of Pressure –P GAGE : Measured relative to atmospheric pressure (P ATM ) –P ABSOLUTE : Measured relative to zero pressure (perfect vacuum) –P ABSOLUTE : = P ATM + P GAGE Units –SI: kPa = kN/m 2 –USCS: psi = Pounds per square inch [lbf/in 2 ] psig = Pounds per square inch gage [lbf/in 2 ] psia = Pounds per square inch absolute [lbf/in 2 ]

Chapter 1: Thermodynamic Concepts and Terminology Pressure (P) Manometer: H P LINE

Chapter 1: Thermodynamic Concepts and Terminology Temperature Absolute Zero Temperature: –Lowest Possible Temperature –Like m = 0 is smallest possible mass Temperature Scales: –Absolute: Measured relative to absolute zero –Relative: Measured relative to non-absolute zero temperature SI Scales and Units: –Relative: 0 C, Degrees Celsius –Absolute: K, Kelvin –T(K) = T( 0 C) USCS Scales and Units: –Relative: 0 F, Degrees Fahrenheit –Absolute: ºR, Degrees Rankine –T(ºR) = T( 0 F)

Chapter 1: Thermodynamic Concepts and Terminology Temperature

Chapter 1: Thermodynamic Concepts and Terminology 1.7 Converting Units Thermodynamic analyses require unit conversions Blindly applying “right” units to numeric answer typically leads to wrong answer (i.e., points off on tests and exams) Keeping track of units can help identify errors Example: Convert 500 m to miles

Chapter 1: Thermodynamic Concepts and Terminology 1.8 Problem Solving in Thermodynamics Problem Statement Solution –Diagram of System and Process –Given and Find –Assumptions –Governing Relations –Property Data –Quantitative Solution Discussion of Results: –Does the answer make sense? –What are implications? –Average engineers have difficulty here –Great engineers excel here

Chapter 1: Thermodynamic Concepts and Terminology Homework problem 1.4 PROBLEM STATEMENT: A spacecraft of dry weight 50,000 lbf leaves Earth with 180,000 lbf of fuel on board flies to a planet where the acceleration due to gravity is 12 ft/s 2. During the flight to the planet, 2/3 of the fuel is consumed. How much thrust does the rocket need to insure lift-off from the planet?

Chapter 1: Thermodynamic Concepts and Terminology Homework problem 1.6 PROBLEM STATEMENT: A gas is contained in a vertical cylinder 3 inches in diameter under a piston whose mass is 50 lbm. The local gravitational acceleration is 32.4 ft/s 2 and the atmospheric pressure acting on the outside of the piston is 14.7 psia. What is the absolute pressure of the gas in the cylinder in psia?

Chapter 1: Thermodynamic Concepts and Terminology Homework problem 1.10 PROBLEM STATEMENT: A colleague reports that she has developed a new material which will withstand an absolute temperature three times as great as her previous best material which could endure a temperature of 2000 o R. What is this new upper limit in K and o C?