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1.Basic Concepts and Terminologies

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1.Basic Concepts and Terminologies

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    1. 1.Basic Concepts and Terminologies

    2. Basic Concepts and Terminologies 1.1 Introduction 1.2 Conservation Principle 1.3 Property, State and Phase 1.4 Process and Cycle 1.5 The 0th Law of Thermodynamics 1.6 Units and Dimensions

    3. Basic Concepts and Terminologies 1.1 Introduction <Power plant>

    4. Basic Concepts and Terminologies <Liquid oxygen plant>

    5. Basic Concepts and Terminologies <Turbofan jet engine>

    6. Basic Concepts and Terminologies <Liquid-propellant rocket engine>

    7. Basic Concepts and Terminologies 1.2 Conservation Principle Any thermal-fluid phenomena can be described by a closed set of the conservation equations of mass, momentum and energy with relevant property and constitutive relationships. Integral and Differential Approaches There are two different approaches to mathematically describe any thermal-fluid phenomena involving mass, momentum and energy transfer.

    8. Basic Concepts and Terminologies Integral Method A system is defined in terms of definite mass or definite volume in space. -control mass (closed system) -control volume (open system) Differential Method The conservation principle is applied to an infinitesimal volume resulting in partial differential equations.

    9. Basic Concepts and Terminologies -Control mass (closed system) Surroundings isolated system - no interaction with the surrounding -Control volume (open system) Surroundings

    10. Basic Concepts and Terminologies Conservation Principle for any conserved quantity, ?, per unit mass The diffusive flux, J, is given as

    11. Basic Concepts and Terminologies Mass Conservation for a Control Volume

    12. Basic Concepts and Terminologies Mass Conservation in a Differential Form

    13. Basic Concepts and Terminologies Momentum Conservation for a Control Volume

    14. Basic Concepts and Terminologies Momentum Conservation in a Differential Form

    15. Basic Concepts and Terminologies Energy Conservation for a Control Volume

    16. Basic Concepts and Terminologies Energy Conservation in a Differential Form Total energy balance Thermal energy balance

    17. Basic Concepts and Terminologies In either integral and differential descriptions there can be many different combinations of the conservation equations and complementary constitutive relationships. The proper choice depends on the problem under consideration and the information required as a solution. The essence of this course is to understand these basic approaches and how to apply them to real engineering problems involving various thermal-fluid phenomena.

    18. Basic Concepts and Terminologies How is Energy stored in Gas? Intermolecular potential energy; negligible at low Molecular kinetic energy; translation Intramolecular energy; rotation, vibration, electronic Degree of freedom: f (Equipartition Principle) f=3 for monatomic gas, such as He f=6 for diatomic gas, such as O2 (3 for translation, 2 for rotation, 1 for vibration) f=9 for H2O (3 for translation, 3 for rotation, 3 for vibration)

    19. Basic Concepts and Terminologies Example 1 (WSB p131) Control volume: Turbine Inlet state: Fixed Exit state: Fixed Process: SSSF Model: Steam tables

    20. Basic Concepts and Terminologies In classical thermodynamics we do not care about how energy is stored in a system. It may be of interest to understand thermodynamic properties, e.g. the amount of energy required to raise the temperature by a given amount. However it helps conceptually to understand the relationship between the classical or macroscopic views and the statistical or microscopic views.

    21. Basic Concepts and Terminologies 1.3 Property, State, Phase We need to know various thermodynamic properties for any quantitative description of matter. Property: Any quantity of the system, which is independent of the path or history how the state is reached. State: The state is defined in terms of a certain observable macroscopic properties such as temperature, volume, pressure, etc. Each property in a given state of the system should have only one definite value. Phase: A homogeneous quantity of matter of the same type of molecules, e.g. solid or gas phase.

    22. Basic Concepts and Terminologies

    23. Basic Concepts and Terminologies Relationship between State and Properties

    24. Basic Concepts and Terminologies Extensive and Intensive Properties Extensive Property : proportional to mass Intensive Property : independent of mass

    25. Basic Concepts and Terminologies (Thermodynamic) Properties Specific volume : volume per unit mass Density : inverse of the specific volume Pressure : the normal component of force per unit area. The pressure is the same in all directions in a fluid in equilibrium. Temperature : measure of hotness or coldness. Exact definition depends on the 0th law of thermodynamics and the temperature scale. etc.

    26. Basic Concepts and Terminologies Transport Properties Diffusive transport by chaotic molecular motions Mass: diffusion coefficient(D) Momentum: viscosity(?) Energy: thermal conductivity(?) Dimensionless numbers: Prandtl number= ?/? Schmidt number= ?/D Lewis number= ?/D

    27. Basic Concepts and Terminologies 1.4 Process and Cycle Process: A path of states through which the system passes Cycle: A process the initial and final states are identical Property Final B state Initial Cycle state Property A

    28. Basic Concepts and Terminologies Equilibrium: A state of balance, which goes through no change with time when it is isolated from the surrounding. -Mechanical Equilibrium -Thermal Equilibrium -Phase Equilibrium -Chemical Equilibrium Nonequilibrium Equilibrium

    29. Basic Concepts and Terminologies Quasi-equilibrium process: A process in which the deviation from equilibrium is infinitesimal. All the states the system passes through may be considered as equilibrium states. Property FS B FS IS IS Property A

    30. Basic Concepts and Terminologies Processes Isothermal: temperature fixed Isobaric: volume fixed Isochoric: pressure fixed Isentropic: entropy fixed Isenthalpic: enthalpy fixed

    31. Basic Concepts and Terminologies 1.5 The 0th Law of Thermodynamics Temperature When two systems are in thermal equilibrium with a third system, they also are in thermal equilibrium with each other. This is the basis of any temperature measurement using a reference system, called a thermometer.

    32. Basic Concepts and Terminologies Temperature Scale Ice point: the temperature of a mixture of ice and water in equilibrium with saturated air at 1atm Steam point: the temperature of a mixture of steam and water in equilibrium with saturated air at 1atm Celsius(C): ice point=0C steam point=100C Fahrenheit(F): ice point=32F steam point=212F At the 10th GPM(1954) the Celsius scale was redefined in terms of the triple point of water(0.01C) and the ideal gas temperature scale.

    33. Basic Concepts and Terminologies Absolute Temperature Scale K(Kelvin) = C + 273.15 R(Rankine) = F + 459.67 ITS-90: International Temperature Scale(1989) Fixed and easily reproducible points that are assigned definite numerical values of temperature Specified formulas relating temperature to the readings on certain temperature-measuring instruments for interpolation between the defining fixed points

    34. Basic Concepts and Terminologies

    35. Basic Concepts and Terminologies 1.6 Units and Dimensions SI unit: second, meter, kilogram are the basic units for time(t), length(L) and mass(M). F=ma Force: ML/t2 Newton(N) Energy: ML2/t2 Joule(J) Pressure: M/Lt2 Pascal(Pa) English Engineering System: sec, ft, lbm, lbf Do you understand the difference? Force, Weight, Mass ? Energy, Power ? Momentum, Pressure, Force ?

    36. Basic Concepts and Terminologies Conversion of Units 1 lbm = 0.45359237 kg 1 ft = 0.3048 cm 1 ft = 12 in or

    37. Basic Concepts and Terminologies Specific Volume

    38. Basic Concepts and Terminologies Pressure 1 Pa = 1 N/m2 1 bar = 0.1 MPa = 105 Pa 1 atm = 101325 Pa = 14.696 lbf/in2 (psi) Absolute pressure and gauge pressure gauge pressure absolute pressure

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