EGN_3358_Notes_Ch2_Thermod_Basic concept-1

EGN_3358_Notes_Ch2_T - EGN 3358 Thermo-Fluids-Heat Transfer Lecture 2 Thermodynamics Basic Concepts and Definitions “Chapter 2 Part 1”

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Unformatted text preview: EGN 3358 Thermo-Fluids-Heat Transfer Lecture 2: Thermodynamics Basic Concepts and Definitions “Chapter 2 - Part 1” EGN­3358 – Thermo­Fluids­Heat Transfer Thermodynamics Therme (heat) and dynamis (power) Is the study of energy transformations and how these transformations affect the material on which they act. EGN­3358 – Thermo­Fluids­Heat Transfer Energy - definition • Energy is the ability to do work, to cause an effect, or to overcome a resistance. EGN­3358 – Thermo­Fluids­Heat Transfer Example Heat Supplied from external source EGN­3358 – Thermo­Fluids­Heat Transfer for example: • We may wish to use the chemical energy stored in the carbon-hydrogen bonds of a liquid hydrocarbon to cause the translational kinetic energy of a large particle. • What is this process? EGN­3358 – Thermo­Fluids­Heat Transfer for example: • We may wish to use the chemical energy stored in the carbon-hydrogen bonds of a liquid hydrocarbon to cause the translational kinetic energy of a large particle. • What is this process? Burning fuel in an engine to make the car move. EGN­3358 – Thermo­Fluids­Heat Transfer another example • We may wish to use that same chemical energy to cause electromagnetic irradiation of some remote enclosed space. • What is this process? EGN­3358 – Thermo­Fluids­Heat Transfer another example • We may wish to use that same chemical energy to cause electromagnetic irradiation of some remote enclosed space. • What is this process? Burning a fuel in a power plant to generate electricity to power lights. EGN­3358 – Thermo­Fluids­Heat Transfer Thermodynamic System • Any three-dimensional region of space that we isolate for study. • More specifically - The system is the material contained within this volume we have chosen to study. You, the analyzer, must define the system! EGN­3358 – Thermo­Fluids­Heat Transfer Surroundings • The rest of the universe outside of the system, close enough to the system to have some perceptible effect on the system. EGN­3358 – Thermo­Fluids­Heat Transfer Boundaries • The surfaces which separate the system from the surroundings. • Boundaries may be real or imaginary. • Boundaries may be fixed or moving. EGN­3358 – Thermo­Fluids­Heat Transfer Types of Thermodynamic Systems • Closed System: no mass is permitted to cross the boundary, only energy; • Open System: both mass and energy may cross boundary; Pumps,Compr., Turbines, Heat Exch. • Isolated System: neither mass nor energy may cross system boundary. EGN­3358 – Thermo­Fluids­Heat Transfer Views of Thermodynamics Macroscopic vs Microscopic • Macroscopic or large scale approach = Classical Thermodynamics • Microscopic or small scale approaches = Statistical Thermodynamics • Kinetic Theory • Information Theory EGN­3358 – Thermo­Fluids­Heat Transfer Property, State, Process, Equilibrium EGN­3358 – Thermo­Fluids­Heat Transfer Property - Definition • A PROPERTY is some characteristic of a system to which numerical values may be assigned without knowledge of the history of the system. EGN­3358 – Thermo­Fluids­Heat Transfer Properties • • • • • • • Temperature Pressure Internal Energy Volume Enthalpy Entropy Free Energy EGN­3358 – Thermo­Fluids­Heat Transfer Sub-categories of Properties • Extensive Property • Intensive Property • Specific Property EGN­3358 – Thermo­Fluids­Heat Transfer Extensive Property • An Extensive Property is one whose value depends on the size or extent of the system. • We generally use upper case letters as the symbols for extensive properties. • V, m, E, U, H, and S are extensive properties. EGN­3358 – Thermo­Fluids­Heat Transfer Intensive Property • An Intensive Property is one whose value is independent of the size or extent of the system. • We generally use lower case letters as symbols for intensive properties. • Pressure, temperature and density are intensive properties. EGN­3358 – Thermo­Fluids­Heat Transfer Intensive and extensive Properties • To determine T P V m ρ EGN­3358 – Thermo­Fluids­Heat Transfer T T P P 1/2V 1/2V 1/2m 1/2m ρ ρ Specific Property • A Specific Property is the value of an extensive property per unit mass of system. • It is a special case of an intensive property. • We use lower case letters as symbols for specific properties. • v, u, h, and s are intensive properties. EGN­3358 – Thermo­Fluids­Heat Transfer Units EGN­3358 – Thermo­Fluids­Heat Transfer SI USCS Slug EGN­3358 – Thermo­Fluids­Heat Transfer Example EGN­3358 – Thermo­Fluids­Heat Transfer Phase & Pure Substance • Phase is a quantity of mass that is homogeneous throughout in chemical composition and physical structure. • E.g. solid, liquid, vapor, gas. • Pure Substance is one with uniform and invariant chemical composition. • Elements and chemical compounds are pure substances. Mixtures are not. EGN­3358 – Thermo­Fluids­Heat Transfer State of a System • The State of a thermodynamic system is the condition of a system as defined by the values of all its properties. EGN­3358 – Thermo­Fluids­Heat Transfer Equilibrium • A system is said to be in an Equilibrium State if its properties will not change without some perceivable effect in the surroundings. • Equilibrium generally requires all properties to be uniform throughout the system. • There are mechanical, thermal, phase, and chemical equilibrium. EGN­3358 – Thermo­Fluids­Heat Transfer Process • Any change that a system undergoes from one equilibrium state to another • A Process is operating on a system so as to change some or all of its properties. • We have two categories of processes: • Heat • Work EGN­3358 – Thermo­Fluids­Heat Transfer Named Processes • Frequently we conduct a process so as to keep one property of the system constant. Names are given to these processes: • Constant Temperature - Isothermal • Constant Pressure - Isobaric • Constant Volume - Isometric • No Heat Transfer - Adiabatic EGN­3358 – Thermo­Fluids­Heat Transfer Reversible Processes • Idealized Process • A process that can be reversed without having any trace on the surroundings. • Is this possible? Only if net heat and net work exchange with the surr. =0 EGN­3358 – Thermo­Fluids­Heat Transfer Reversible Processes • Restrained Expansion or Compression • Frictionless Motion • Heat Transfer through a finite dT= irreversible process. • Elastic Stretching of a Solid • Electric Circuits of Zero Resistance • Polarization and Magnetization Effects • Restrained Discharge of a Battery EGN­3358 – Thermo­Fluids­Heat Transfer Internally Reversible Processes • A process which is reversible within the system, but has irreversibilities across the system boundary. • Most processes we treat in thermodynamics are internally reversible. EGN­3358 – Thermo­Fluids­Heat Transfer EGN­3358 – Thermo­Fluids­Heat Transfer In our studies in thermodynamics we generally begin with a system in an initial equilibrium state, conduct one or more processes on it, so that it ends in a final equilibrium state. EGN­3358 – Thermo­Fluids­Heat Transfer Our task is usually knowing the initial state and the processes, determine the final state,or knowing the initial and final states, determine the processes. EGN­3358 – Thermo­Fluids­Heat Transfer Laws of Thermodynamics • • • • • Zeroth law First law Second law Third law State Postulate EGN­3358 – Thermo­Fluids­Heat Transfer Selected Properties • Density EGN­3358 – Thermo­Fluids­Heat Transfer m ρ = lim V →V ' V Selected Properties • Density m ρ = lim V →V ' V • Specific volume V1 v= = mρ EGN­3358 – Thermo­Fluids­Heat Transfer Selected Properties • Density - ρ • Specific volume • Pressure v • Absolute pressure - p - force per unit area that the system exerts on its boundaries EGN­3358 – Thermo­Fluids­Heat Transfer Selected Properties • • • • • Density - ρ Specific volume - v Pressure Absolute pressure - p Gage pressure - pg - the difference between the pressure of the system and the pressure of the surroundings pg = p − psurr EGN­3358 – Thermo­Fluids­Heat Transfer Selected Properties • Density - ρ • Specific volume - v • Pressure Absolute pressure - p Gage pressure - pg Vacuum - pv EGN­3358 – Thermo­Fluids­Heat Transfer Vacuum - pv • When the system pressure is less than the surroundings pressure, we have a vacuum. • Vacuum pressure, pv, is the magnitude of the gage pressure when gage pressure is less than zero. pv = pg = psurr − p EGN­3358 – Thermo­Fluids­Heat Transfer Frequently, the surroundings of the system are the local atmosphere. Therefore, psurr in the preceding equations is commonly atmospheric pressure, patm. pg = p − patm pv = pg = patm − p EGN­3358 – Thermo­Fluids­Heat Transfer EGN­3358 – Thermo­Fluids­Heat Transfer EGN­3358 – Thermo­Fluids­Heat Transfer EGN­3358 – Thermo­Fluids­Heat Transfer Selected Properties • Density - ρ • Specific volume - v • Pressure Absolute pressure - p Gage pressure - pg Vacuum - pv • Temperature - T EGN­3358 – Thermo­Fluids­Heat Transfer Temperature - T • Temperature is that property of a system: related to our sense of “hotness” or “coldness” of the system. EGN­3358 – Thermo­Fluids­Heat Transfer Temperature Scales • • • • Celsius or centigrade, 0C , SI & English Fahrenheit, 0F, SI & English Kelvin, K Rankine, R, English T(K) = T(0C)+273.15 T(R)=T(0F)+459.67 T(R)=1.8T(K) T(0F)=1.8 T(0C)+32 EGN­3358 – Thermo­Fluids­Heat Transfer EGN­3358 – Thermo­Fluids­Heat Transfer Zeroth Law of Thermodynamics • If each of two systems are in thermal equilibrium with a third system, they are in thermal equilibrium with each other. - Obvious fact - Cannot be concluded from the other laws - Serves as a basis for the validity of temperature measurement. EGN­3358 – Thermo­Fluids­Heat Transfer Zeroth Law of Thermodynamics • Replacing the third body with a thermometer: Two bodies are in thermal equilibrium if both have the same temperature reading even if they are not in contact. • The property that characterizes thermal equilibrium is temperature. EGN­3358 – Thermo­Fluids­Heat Transfer Solve 2-1 2-2 2-3 2-14 EGN­3358 – Thermo­Fluids­Heat Transfer ...
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This note was uploaded on 11/25/2011 for the course EGN 3358 taught by Professor Sleiti during the Fall '07 term at University of Central Florida.

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