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  • 1

    Introduction and Basic Concepts

    MAE 320- Chapter 1

    The content and the pictures are from the text book: engel, Y. A. and Boles, M. A., Thermodynamics: An Engineering Approach, McGraw-Hill, New York, 6th Ed., 2008

    Identify the unique vocabulary associated with thermodynamics through the precise definition of basic concepts.

    Review the metric SI and the English unit systems.

    Explain the basic concepts of thermodynamics such as system,

    Objectives

    state, state postulate, equilibrium, process, and cycle.

    Review concepts of temperature, temperature scales

    Review concepts of pressure, absolutepresuure and gage pressure.

    Thermodynamics and Energy

    The name thermodynamics stems from the Greek words therme (heat) and dynamis (power).

    Thermodynamics: The science of energy.

    Energy: The ability to cause changes.

    What is the difference between thermodynamics and kinetics?

    Thermodynamics and Energy

    Storage of energy- internal energy, (T)- potential energy, (gravity, h)- kinetic energy (motion, V)- chemical energy (reaction)

    What topics are covered in this course?

    Second law of thermodynamics- quantity- quality- direction

    Transfer of energy- from one form to another form- from one state to another state

    First law of thermodynamics- Energy cannot be created- Energy cannot be destroyed- Energy can be transferred

    Entropy

    Substances- H2O (ice, water, vapor)- ideal gas

    Thermodynamics and Energy

    Conservation of energy principle: During an interaction, energy can change from one form to another but the total amount of energy remains constant. gy

    Energy cannot be created or destroyed.

    Application Areas of Thermodynamics

    Heat Pump

    Electric heater

    How to save energy bills?

    Which one do you choose between a heat pump and an electric heater?

    How does a heat pump work?

    What is the efficiency of the heat pump?

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    Application Areas of Thermodynamics

    Double-layer glass windowWhat is the efficiency of the

    hot water tank?

    What is the optimal temperature for the water tank?

    What is minimum tank capacity needed for your house?

    Application Areas of ThermodynamicsHybrid carConventional car

    brakingbraking

    Pad-drum friction

    Heat dissipation battery

    Mechanical energy converted to heat

    electric motor

    Electric generator

    accelerating

    Mechanical energy converted to electric energy, converted to mechanical energy

    Application Areas of ThermodynamicsHow Hybrid car workshttp://www.youtube.com/watch?v=2HrQeGzIZoI&feature=related

    Hybrid SUV-3D animationhttp://tw.youtube.com/watch?v=Fk7xbcnzxks

    The second law of thermodynamics:It asserts that energy has quality as well as quantity, and actual processes occur in the direction of decreasing quality of energy.

    Classical thermodynamics: A macroscopic approach to the study of thermodynamics that does not require a knowledge of the behavior of Conservation of energy

    Concepts of Thermodynamics

    a o edge o e be a o oindividual particles.

    It provides a direct and easy way to the solution of engineering problems and it is used in this text.

    Statistical thermodynamics: A microscopic approach, based on the average behavior of large groups of individual particles.

    It is used in this text only in the supporting role.

    gyprinciple for the human body.

    Heat flows in the direction of decreasing temperature.

    Dimensions and Units Any physical quantity can be characterized by dimensions. The magnitudes assigned to the dimensions are called units. Some basic dimensions such as mass m, length L, time t, and temperature

    T are selected as primary or fundamental dimensions, velocity V, energy E, and volume V are expressed in terms of the primary

    dimensions and are called secondary dimensions, or derived dimensions.

    Review SI units

    SI Primary units (base units)

    Quantity Name of Unit SymbolLength (l) meter mMass (m) kilogram kgTime (t) second sElectrical current (I) ampere AThermodynamic temperature (T) Kelvin K

    Amount of substance mole mol

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    Dimensions and Units English system: It has no apparent systematic numerical

    base, and various units in this system are related to each other rather arbitrarily.

    SI unit system will be adopted in our course:SI system has a systematic numerical base (clear physical meaning) SI system has a systematic numerical base (clear physical meaning).

    SI system is a decimal system (x10). Better for communication. All the industrial country use the SI system.

    Only USA is employing a dual-unit system. However, all the car manufactures use the SI system. You need a (wrench) kit for metric bolts instead English sockets

    Easy to remember

    Density and Specific Gravity

    specific volume is volume per unit mass:

    Density:

    Specific volume:

    Density is mass per unit volume:

    (m3/kg)Specific volume: (m /kg)

    Density and Specific GravitySpecific gravity: The ratio of the density of a substance to the density of some standard substance at a specified temperature (usually water at 4C).

    Specific weight: The weight of a funit volume of a substance.

    ggVm

    Vmg

    S ===

    In SI, one newton (1 N) is the force required to cause a mass of one kilogram (1 Kg) to accelerate at a rate of one meter per second squared (1 m/s2)

    Dimension and Units

    In the English system, the force unit, 1 lbf, is the force required to cause a mass of 32.174 lbm to accelerate at a rate of one foot per second squared (1 ft/s2)

    In daily life, people usually use weight to express mass.In science, weight is a force:

    W = mg

    Where m is the mass, g is the local gravitational acceleration, g=9.807 m/s2 or g =32.174 ft/s2 at sea level and 45o latitude.

    On the earth, at sea level, a mass of 1 kg weighs 9.8 N

    Dimension and Units

    W = mg = 1 kg x 9.8 m/s2 = 9.8 kg.m/s2 = 9.8 N

    On the moon, a mass of 1 kg weighs 1.63 NW = mg = 1 kg x 1.63 m/s2 = 1.63 kg.m/s2 = 1.63 N

    Mass does not change with location, but weight does

    Unit Conversion Ratios

    All non-primary units (secondary units) can be formed by combinations of primary units. Force units, for example, can be expressed as

    All equations must be dimensionally homogeneous.To be dimensionally homogeneous, all the terms in an equation must have the same unit system.

    They can also be expressed more conveniently as unity conversion ratiosas

    Unity conversion ratios are identically equal to 1 and are unitless, and thus such ratios (or their inverses) can be inserted conveniently into any calculation to properly convert units.

  • 4

    How much is the weight of a mass of 1 lbm?

    Apply Newtons second law:

    Dimension and Units

    In SI system:1 lbm= 0.454 kg and g =9.8 m/s2

    W = mg = 0.454 kg x 9.8 m/s2 = 4.45 kg.m/s2 = 4.45 N

    A mass of 1 lbm weighs 4.45 N

    Work (W) = Force Distance

    1 J = 1 Nm

    1 cal = 4.1868 J

    1 Btu = 1 0551 kJ

    Work, a form of energy:

    Dimension and Units

    1 Btu 1.0551 kJ

    specific energy (e), e=E/m (J/kg)

    power = W/t Unit: J/s or watt, w

    Review SI units Derived Units

    Quantity Description SymbolExpression in

    other SI units

    Expression in SI base units

    Area (A) square meter m2 m2

    Volume (V) cubic meter m3 m3

    velocity (or speed) (V) meters per second m/s m s-1

    dAcceleration (a) meter per second squared m/s2 m s-2

    density (), =m/V kilogram per cubic meter kg/m3 kg m-3

    specific volume (v), v=V/m

    cubic meter per kilogram m

    3/kg m3 kg-1

    specific gravity (SG), SG=/H2O

    Dimensionless

    force (F), F=ma Newton N kgm/s m kg s-2

    Quantity Description Symbol

    Expression in other SI units Expression in

    terms of SI base units

    Weight (W), W=mg Newton N kgm/s m kg s-2

    pressure (P), P=F/A pascal Pa N/m2 m-1 kg s-2

    work (energy heat) (W), Joule J Nm m2 kg s-2

    Review SI units Derived Units

    ( gy ) ( )W=F*d Joule J m

    2 kg s 2

    specific energy (e), e=E/m joule per kilogram J/kg m2 s-2

    energy density joule per cubic meter J/m3 m-1 kg s-2

    power Watt, W J/s m2 kg s-3

    Continuum Matter is made up of atoms that

    are widely spaced in the gas phase. disregard the atomic nature of a substance and view it as a continuous, homogeneous matter with no holes, that is, a continuum.

    The continuum idealization allows us to treat properties as point functions and to assume thefunctions and to assume the properties vary continually in space with no jump discontinuities.

    This idealization is valid as long as the size of the system is large relative to the space between the molecules.

    In this course we will limit our consideration to continuum.

    Despite the large gaps between molecules, a substance can be treated as a continuum because of the very large number of molecules even in an extremely small volume.

    Systems and Control Volumes System: A quantity of matter or a region in space chosen for study. Surroundings: The mass or region outside the system Boundary: The real or imaginary surface that separates the system

    from its surroundings. The boundary of a system can be fixed or movable. Systems may be considered to be closed or open.

  • 5

    Systems and Control Volumes Closed system (Control mass): A fixed amount of mass, and no

    mass can cross its boundary. Isolated system: in such a close system, even energy is not allowed

    to cross the boundary

    Coke Can

    Demonstrate Conc