Course materials provided for personal study only. ENS2259/ENS5259 Thermodynamics Dr Yasir Al-Abdeli [email protected]
Course materials provided for
personal study only.
ENS2259/ENS5259Thermodynamics
Dr Yasir [email protected]
Slide
2This Lecture
�Coverage in this lecture will be derived from the textbook
•Cengel, Y. A., Turner, R. H. & Cimbala, J. M. (2008). Fundamentals of thermal-fluid sciences (3rd ed). New York: McGraw-Hill Companies, Inc.
•INTRODUCTION AND OVERVIEW (CHP 1)
•1.1 Introduction to Thermal-Fluid Sciences
•1.2 Thermodynamics
•1.3 Heat Transfer
•1.4 Fluid Mechanics
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•1.4 Fluid Mechanics
•1.5 Importance of Dimensions and Units
•1.6 Problem-Solving Technique
�This lecture in a nutshell
•What sciences make up thermofluids?
•The basic approaches for …
•Thermodynamics
•Heat Transfer
••Heat Transfer
•Fluids
•What the fundamental units are?
•How to effectively structure our problem solving (methodology)?
Slide
4Thermofluid Sciences
�Introduction
•Thermal-Fluid sciences (thermofluids) are physical
sciences that study energy• transfer (e.g., through walls)
• transport (e.g., with fluids)
•conversion (e.g., through devices and processes)
•Modern life relies on many thermal-fluid systems
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•Modern life relies on many thermal-fluid systems•power plants
• Internal Combustion (IC) engines
•air conditioners / refrigerators
•A closer look at once such system (e.g., a radiator)
reveals that …
•Thermodynamics identifies the magnitude of heat
loss (how many kJ)
•heat transfer is used to size the radiator core
• fluids to size coolant pumps and cooling fans
Fig 1-1. Cengel, Y. A., Turner, R. H. & Cimbala, J. M.
(2008). Fundamentals of Thermal-Fluid Sciences (3rd
ed). New York: McGraw-Hill Companies, Inc.
Lets take a closer look at the three
ingredients of ingredients of
Thermofluids !
Slide
6Thermal-Fluid Sciences
�Thermodynamics
•“therme”, Greek (heat)
•“dynamics”, Greek (power)
•term “thermodynamics” first used by Lord Kelvin (1849).
•thermodynamics looks at energy and transformation
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•energy transformation and its manifestation through engineering devices and systems.
•Conservation of Energy Principle
•energy changes form but its total magnitude is conserved (one cannot create or destroy energy).
Fig 1-3. Cengel, Y. A., Turner, R. H. & Cimbala, J. M.
(2008). Fundamentals of Thermal-Fluid Sciences (3rd
ed). New York: McGraw-Hill Companies, Inc.
Slide
7Thermal-Fluid Sciences
�Thermodynamics
•Conservation of Energy Principle
•energy changes form but its total magnitude is
conserved (cannot create or destroy energy).
EEE outin ∆=−
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•First Law of Thermodynamics
•Expresses the conservation of energy principle.
•Energy is a thermodynamic quantity.
•Second Law of Thermodynamics
•Energy also has a quality (energy transfer
happens in the direction of decreasing quality).
•“Quality” here related to our ability to harness
energy for useful purposes.Fig 1-4 & 1.5. Cengel, Y. A., Turner, R. H. & Cimbala, J.
M. (2008). Fundamentals of Thermal-Fluid Sciences
(3rd ed). New York: McGraw-Hill Companies, Inc.
Slide
8Thermal-Fluid Sciences
�Thermodynamics
•Classical Thermodynamics
•a macroscopic approach to studying
thermodynamics
•for example, in the case of a pressure
vessel, this approach does not look at
the behaviour of individual particles in
order to study overall pressure.
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order to study overall pressure.
•a pressure gauge can be used to infer
this behaviour
•easier, more straightforward, analyses
possible, good for engineering analysis.
•Statistical Thermodynamics
•investigates the average behaviour of
particles
•More complicated.
Slide
9Thermal-Fluid Sciences
�Heat Transfer
•Energy transfer occurs from higher temperature mediums to those at lower temperature.
•When does this energy transfer cease?
•
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•when temperatures become the same.
•What form does this energy take?
•‘heat’
Slide
10Thermal-Fluid Sciences
�Heat Transfer
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Slide
11Thermal-Fluid Sciences
�Heat Transfer
•“heat” is the transfer of energy induced by a temperature differential (fluid flow is induced by a pressure differential)
•“heat transfer” looks at the rates
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•“heat transfer” looks at the ratesover which this type of energy exchange occur.
•thermodynamics will identify the magnitude of energy that will be exchanged. Heat transfer will identify the period needed for that exchange to occur to, or from, the system under investigation. Fig 1-6. Cengel, Y. A., Turner, R. H. & Cimbala, J. M.
(2008). Fundamentals of Thermal-Fluid Sciences (3rd
ed). New York: McGraw-Hill Companies, Inc.
Slide
12Thermal-Fluid Sciences
�Fluid Mechanics (different branches)
•Stationary and moving bodies
•Fluid Statics: fluids at rest.
•Fluid Dynamics: fluids under motion.
•Hydrodynamics
•Studies moving fluids when they are
incompressible.
•
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incompressible.
•water, low speed gases.
•Hydraulics: liquid flows when applied
to pipes and open channels.
•Gas Dynamics
•High speed gas flows through nozzles.
•Aerodynamics: air flows
•around aeroplanes and cars at low as
well as high speeds.
Slide
13Thermal-Fluid Sciences
�Fluid-Mechanics
•Jet flows: laminar CO2 (right)
•Schlieren based flow visualisations.
•Jet flows: turbulent air (left)
•Laser based flow visualisations.
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Work done at the Univ of Tasmania (Al-Abdeli, 2006)Work done at the Univ of Sydney (Al-Abdeli, 2003)
Slide
14Thermal-Fluid Sciences
�Fluid Mechanics
•From statics
•Stress: force over unit area
•Normal component: Pressure
•Tangential component: Shear
Stress
•Shear Stresses and Pressures are
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•Shear Stresses and Pressures are
relevant to fluid as well.
•Fluid at rest
•exerts pressure
•shear stress is zero
•Fluid in motion
•Starts to develop shear Fig 1-9. Cengel, Y. A., Turner, R. H. & Cimbala, J. M.
(2008). Fundamentals of Thermal-Fluid Sciences (3rd
ed). New York: McGraw-Hill Companies, Inc.
Slide
15Thermal-Fluid Sciences
�Dimensions and Units
•Fundamental dimensions
•Note kelvin does not have the degree
symbol (°)
•Capitalisation (Yes or No?)
•Not capitalised … if the unit is
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•used as a “word”
•Capitalised … if the unit is
abbreviated AND derived from a
proper name
•Kelvin … (K)
•No period ‘ . ‘ is used with unit
abbreviations (unless it falls at the
end of the sentence obviously). Table 1-1. Cengel, Y. A., Turner, R. H. & Cimbala, J. M.
(2008). Fundamentals of Thermal-Fluid Sciences (3rd
ed). New York: McGraw-Hill Companies, Inc.
Slide
16Thermal-Fluid Sciences
�Dimensions and Units
•Secondary or derived dimensions
•Velocity (m/s)
•Energy (J)
•Volume (m3)
•Units are used to express dimensions
•
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•Different systems of units
•SI
•Decimal basis for units
•Easy
•More common
•English
•Move to phase out (most places)Table 1-2. Cengel, Y. A., Turner, R. H. & Cimbala, J. M.
(2008). Fundamentals of Thermal-Fluid Sciences (3rd
ed). New York: McGraw-Hill Companies, Inc.
Slide
17Thermal-Fluid Sciences
�Dimensions and Units
•Newton: Unit of force
•1N … “force required to accelerate a mass of 1kg at a
rate of 1m/s2)”
•Specific weight:
•
onAcceleratiMassForce ×=
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••“weight per unit volume”
•g=9.807 m/s2 (sea level, 45°latitude)
•Mass and weight are not the same
•Weight measured at the top of a mountain differs to that
at sea level
•Body mass does not change.
gργ =
Fig 1-12. Cengel, Y. A., Turner, R. H. & Cimbala, J. M.
(2008). Fundamentals of Thermal-Fluid Sciences (3rd
ed). New York: McGraw-Hill Companies, Inc.
mgW =
Slide
18Thermal-Fluid Sciences
�Dimensions and Units
•Dimensional Homogeneity
•Got to ensure terms in a thermodynamic equation have the same dimensions.
Example 1-1
Q: Where is the error in this step of calculation/equation?
kgkJkJE /725 +=
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Q: Where is the error in this step of calculation/equation?
A: You cannot add the two terms on the right (units are different)
A: The second term has not been multiplied by the unit mass.
Slide
19Thermal-Fluid Science
�Suggested Problem Solving Methods
•A systematic approach is needed. The following are some recommended steps:
(1) Problem statement. Show …
-Given important information
-Quantities needed
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(2) Schematic. Provide a representative sketch
-Energy and mass interactions
-Convey relevant information on sketch
(3) State any assumptions and approximations.-If any assumptions seem weak (or questionable) assumptions, then explain
or justify them
Slide
20Thermal-Fluid Science
�Suggested Problem Solving Methods
(4) Apply the relevant physical laws.-Identify regions of interest in the schematic (see step 2, above).
(5) List/calculate properties.-Indicate sources of data.
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-Indicate sources of data.
(6) Calculate-Round numbers to something reasonable.
(7) Checks.-always good to check calculations and revise assumption.
-add some comment on the result to clarify.
Slide
21Thermal-Fluid Sciences
�Significant Digits
•Your calculations can
only be (at best) the
same accuracy as the
data give.
•Do the rounding only at
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•Do the rounding only at
the last step.
Table 1-26. Cengel, Y. A., Turner, R. H. & Cimbala, J. M.
(2008). Fundamentals of Thermal-Fluid Sciences (3rd
ed). New York: McGraw-Hill Companies, Inc.