1. Introduction to Basic Concepts of Thermodynamics
PTT 201/4 THERMODYNAMICS
SEM 1 (2012/2013)
Chapter 1:
Introduction to Basic Concepts of Thermodynamics

2. Thermodynamics & energy
The name thermodynamics stems from the Greek words therme (heat) and dynamis (power).
Conservation of energy principle:
During an interaction, energy can change from one form to another but the total amount of energy remains constant.
Energy:
The ability to cause changes.
The first law of thermodynamics:
Energy cannot be created or destroyed; it can only change forms.
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.
Heat flows in the direction of decreasing temperature
The first law of thermodynamics

3. Application areas of thermodynamics
Power plant
Aircraft and spacecraft
Car
Application areas of
thermodynamics
Human body
Refrigeration systems
Wind turbines
Air conditioning systems
Boats
Solar hot water systems

4. Dimensions & units light light light light light light
Electric current
L of
light
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Any physical quantity can be characterized by dimensions
The magnitudes assigned to the dimension are called units
Amount of light
L of
Amount of matter
Primary/ fundamental dimensions
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Temperature
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Length
Dimensions
& units
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Mass
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Time
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Secondary/ derived dimensions
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Velocity
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Energy
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English system
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International system (SI)
Standard prefixes in SI units
Volume
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Force
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Primary dimensions and their units in SI

5. Measure of amount or size
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No. of moles, n
Total volume, Vt
Mass, m
Represent the size of a system
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No. of moles
Mass
Mass
Specific volume:
No. of moles
Molecular weight
Molecular weight
Molar volume: or or

6. FORCE light light light light light light light light light
m=1 kg
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Mass
a=1 m/s2
Definition:
Force required to accelerate a mass of 1 kg or lbm at a rate of 1 m/s2 or 1 ft/s2.
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F=1 N
m= lbm
a=1 ft/s2
F=1 lbf
Acceleration
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Mass
Definition:
Weight is gravitational force applied to a body
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FORCE
Local gravitational acceleration
g = m/s2
= ft/s2
English system
Pound-force
(lbf)
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Unit in many European countries
Kilogram-force
(kgf)
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Newton
(N)
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1 N = 1 kg. m/s2
1 lbf = lbm.ft/s2 = N
1 kgf = N

7. 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.
Closed system (Control mass): A fixed amount of mass, and no mass can cross its boundary.

8. SYSTEMS AND CONTROL VOLUMES, cont’
Open system (control volume): Both mass and energy can cross the boundary of a control volume.
Device: compressor, turbine, or nozzle.
Control surface: The boundaries of a control volume. It can be real or imaginary.
An open system (a control volume) with one inlet and one exit.

9. TEmperature
Commonly measured with liquid-in-glass thermometer, wherein the liquid expands when heated
Boiling point of pure water at standard atmospheric pressure
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Freezing point of water saturated with air at standard atmospheric pressure
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Lower limit of temperature
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10. TEmperature Comparison of magnitude of various temperature units
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Comparison of magnitude of various temperature units
Relations among temperature scales
SI unit system
English unit system

11. Electric power generation by a wind turbine
Example :
Electric power generation by a wind turbine
A school is paying $0.09/kWh for electric power. To reduce its power bill,
the school install a wind turbines with a rated power of 30 kW. If the turbine
operates 2200 hours per year at the rated power, determine the amount of
electric power generated by the wind turbine and the money saved by the
school per year.
SOLUTION :
Determine the total energy
Determine the money saved

12. SOLUTION : Determine the total energy
Total energy = (Energy per unit time) (Time interval)
= (30 kW) (2200 h)
= 66, 000 kWh
Determine the money saved
Money saved = (Total energy) (Unit cost of energy)
= (66,000 kWh) ($0.09/kWh )
= $5940
Convert your answer of total energy in kJ.
Total energy =
66,000 kWh
3600 s
1 kJ/s =
2.38 X 108 kJ
1 h
1 kW

13. The weight of one pound-mass
Example :
The weight of one pound-mass
Using unity conversion ratios, show that 1.00 lbm weighs 1.00 lbf on earth.
SOLUTION :
W = mg =
1.00 lbm
ft/s2
1 lbf
1.00 lbf
lbm.ft/s2

14. Expressing Temperature Rise in Different Units
Example :
Expressing Temperature Rise in Different Units
During a heating process, the temperature of a system rises by 10 ⁰C.
Express this rise in temperature in K, ⁰F and R.
SOLUTION :
Δ T(K) = Δ T(⁰C) = 10 K
Δ T(R) = 1.8 Δ T(K) = (1.8) (10) = 18 R
Δ T(⁰F) = Δ T(R) = 18 ⁰F

15. pressure A normal force exerted by a fluid per unit area light
Some basic pressure gages.

16. pressure
Absolute pressure: The actual pressure at a given position. It is measured relative to absolute vacuum (i.e., absolute zero pressure).
Gage pressure: The difference between the absolute pressure and the local atmospheric pressure. Most pressure-measuring devices are calibrated to read zero in the atmosphere, and so they indicate gage pressure.
Vacuum pressures: Pressures below atmospheric pressure.

17. Variation of Pressure with Depth
The pressure of a fluid at rest
increases with depth (as a result of added weight).

18. Pressure, cont’
In a room filled with a gas, the variation of pressure with height is negligible.
Pressure in a liquid at rest increases
linearly with distance from the free surface.
The pressure is the same at all points on a horizontal plane in a given fluid regardless of geometry, provided that the points are interconnected by the same fluid.

19. Pressure, cont’ light Pascal’s law:
The pressure applied to a confined fluid increases the pressure throughout by the same amount.
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Lifting of a large weight by a small force by the application of Pascal’s law.

20. manometer
It is commonly used to measure small and moderate pressure differences. A manometer contains one or more fluids such as mercury, water, alcohol, or oil.
The basic
manometer.
Measuring the pressure drop across a flow section or a flow device by a differential manometer.
In stacked-up fluid layers, the pressure change across a fluid layer of density  and height h is gh.

21. BAROMETER AND ATMOSPHERIC PRESSURE
Atmospheric pressure is measured by a device called a barometer; thus, the atmospheric pressure is often referred to as the barometric pressure.
A frequently used pressure unit is the standard atmosphere, which is defined as the pressure produced by a column of mercury 760 mm in height at 0°C (Hg = 13,595 kg/m3) under standard gravitational acceleration (g = m/s2).
The basic barometer.

22. Absolute Pressure of a Vacuum Chamber
Example :
Absolute Pressure of a Vacuum Chamber
A vacuum gage connected to a chamber reads 40 kPa at a location where
the atmospheric pressure is 100 kPa. Determine the absolute pressure in
the chamber.
SOLUTION :
Pabs = Patm - Pvac
= = 60 kPa

23. Measuring Pressure with a Manometer
Example :
Measuring Pressure with a Manometer
A manometer is used to measure the pressure in a tank. The fluid used has
a specific gravity of 0.85, and the manometer column height is 55 cm, as
shown in figure. If the local atmospheric pressure is 96 kPa, determine the
absolute pressure within the tank.

24. SOLUTION = 96 kPa + 850 kg/m3 9.81 m/s2 0.55 m 1 N 1 kPa 1 kg.m/s2
1000 N/m2
= kPa
Gage pressure = 4.6 kPa
Determine the gage pressure in the tank.

25. Measuring Pressure with a Multifluid Manometer
Example :
Measuring Pressure with a Multifluid Manometer
The water in a tank is pressurized by air and the pressure is measured by a multifluid manometer as shown in the figure. The tank is located on a mountain at an altitude of 1400 m where the atmospheric pressure is 85.6 kPa. Determine the air pressure in the tank if h1 = 0.1 m, h2 = 0.2 m and h3 = 0.35 m. Take the densities of water, oil and mercury to be 1000 kg/m3, 850 kg/m3 and kg/m3, respectively.
Ans: P1 = 130 kPa

26. Measuring Atmospheric Pressure with a Barometer
Example :
Measuring Atmospheric Pressure with a Barometer
Determine the atmospheric pressure at a location where the barometric reading is 740 mmHg and the gravitational acceleration is g = 9.81 m/s2. Assume the temperature of mercury to be 10 ⁰C, at which its density is kg/m3.
Ans: in unit kPa
Ans: 98.5 kPa

27. WORk, energy and heat
Work, energy and heat will be covered in other chapter!
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Work = Force  Distance
1 J = 1 N∙m
1 cal = J
1 Btu = kJ

28. THANK YOU..