Chapter 1: Thermodynamic Concepts
and Terminology
ThermoNet
Thermodynamics: An Integrated Learning System
P.S. Schmidt, O.A. Ezekoye, J.R. Howell and D.K. Baker
Copyright (c) 2005 by
John Wiley & Sons, Inc
1.1 Systems: Definitions
• System: Part of the universe to analyze.
• Surroundings/Environment: Part of universe affected by
system.
• System Boundary: Separates system from surroundings.
Surroundings
System
System
Boundary
Universe
Chapter 1: Thermodynamic Concepts and Terminology
1.1 Systems: 3 Types
Type of System
Transferred Across
System Boundary
Mass
Energy
Example
Open System/
Control Volume
(CV)
Yes
Yes
Jet Engine
Closed System/
Control Mass
(CM)
No
Yes
Light Bulb
Isolated System
No
No
Ice Chest/ Cooler
for small Dt
Chapter 1: Thermodynamic Concepts and Terminology
1.1 Combustion in Open & Closed Systems
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Chapter 1: Thermodynamic Concepts and Terminology
1.2 Properties: Definitions
• Thermodynamic Properties: Describe mass and
energy of system (e.g., T, P and V).
• Extensive Properties: Vary with system size (e.g.,
V).
• Intensive Properties: Independent of system size
(e.g., T and P).
• Specific Properties:
– Divide extensive property by mass
– Intensive Property
– E.g., Specific Volume, v = V/m = 1/r [m3/kg]
Chapter 1: Thermodynamic Concepts and Terminology
1.2 Properties: Total & Specific Volumes
• Total Volume: V
– [m3]
– Upper case V
• Specific Volume: v
– [m3/kg]
– Lower case v
Chapter 1: Thermodynamic Concepts and Terminology
1.3 State
• Thermodynamic State:
– Collection of all Thermodynamic properties of system.
– Ability to define system’s state essential in
Thermodynamics
– Using state principle (Chp 3), can use limited set of
property data to determine all property data.
Chapter 1: Thermodynamic Concepts and Terminology
1.4 Changing the State of a System
• Process: Change in state of system.
• 4 Common Processes:
–
–
–
–
Isothermal: Constant Temperature
Isobaric: Constant Pressure
Isometric: Constant Volume
Adiabatic: No Heat Transfer
P = constant
(isobaric)
T = constant
(isothermal)
P
T
v =constant
(isometric)
v
Chapter 1: Thermodynamic Concepts and Terminology
v =constant
(isometric)
v
1.4 Isobaric & Isometric Processes
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Chapter 1: Thermodynamic Concepts and Terminology
1.5 Unit Systems
• Base Units: Defined by reproducible physical
measurements
• Derived Units: Derived from base units
• SI: Metric International System
– Base Units: time (s), length (m), mass (kg)
– Force (N) is a derived unit from mass
• USCS: U.S. Conventional System or English
System
– Base Units: time (s), length (ft), force (lbf)
– Mass (lbm) is a derived unit from force
Chapter 1: Thermodynamic Concepts and Terminology
1.5 Unit Systems: gC
• gC: Conversion constant
ma
F
gC
mv 2
Kinetic Energy 
2gC
mz
PotentialEnergy 
gC
• SI gC  1
kg  m
N  s2
• USCS
– gC  32.2
lbm  ft
lbf  s2
– 1 lbm  1 lbf
Chapter 1: Thermodynamic Concepts and Terminology
1.6 Property Units
1.6.1 Volume, Specific Volume and Density
• Volume, V [ m3 or ft3]
• Specific Volume, v [m3/kg or ft3/lbm]
• Density, ρ [kg/m3 or lbm/ft3]
1 m
r 
v V
Chapter 1: Thermodynamic Concepts and Terminology
1.6.2 Pressure (P)
• Pressure (P): P = Force/Area
• 3 Types of Pressure
– PGAGE: Measured relative to atmospheric pressure (PATM)
– PABSOLUTE: Measured relative to zero pressure (perfect
vacuum)
– PABSOLUTE : = PATM + PGAGE
• Units
– SI: kPa = kN/m2
– USCS: psi = Pounds per square inch [lbf/in2]
• psig = Pounds per square inch gage [lbf/in2]
• psia = Pounds per square inch absolute [lbf/in2]
Chapter 1: Thermodynamic Concepts and Terminology
1.6.2 Pressure (P)
• Manometer:
gH
PLINE  PATM 
vgc
H
PLINE
Chapter 1: Thermodynamic Concepts and Terminology
1.6.3 Temperature
• Absolute Zero Temperature:
– Lowest Possible Temperature
– Like m = 0 is smallest possible mass
• Temperature Scales:
– Absolute: Measured relative to absolute zero
– Relative: Measured relative to non-absolute zero temperature
• SI Scales and Units:
– Relative: 0C, Degrees Celsius
– Absolute: K, Kelvin
– T(K) = T(0C) + 273.15
• USCS Scales and Units:
– Relative: 0F, Degrees Fahrenheit
– Absolute: ºR, Degrees Rankine
– T(ºR) = T(0F) + 459.67
Chapter 1: Thermodynamic Concepts and Terminology
1.6.3 Temperature
Chapter 1: Thermodynamic Concepts and Terminology
1.7 Converting Units
• Thermodynamic analyses require unit conversions
• Blindly applying “right” units to numeric answer typically
leads to wrong answer (i.e., points off on tests and exams)
• Keeping track of units can help identify errors
• Example: Convert 500 m to miles
Chapter 1: Thermodynamic Concepts and Terminology
1.8 Problem Solving in Thermodynamics
• Problem Statement
• Solution
–
–
–
–
–
–
Diagram of System and Process
Given and Find
Assumptions
Governing Relations
Property Data
Quantitative Solution
• Discussion of Results:
–
–
–
–
Does the answer make sense?
What are implications?
Average engineers have difficulty here
Great engineers excel here
Chapter 1: Thermodynamic Concepts and Terminology
Homework problem 1.4
PROBLEM STATEMENT: A spacecraft of
dry weight 50,000 lbf leaves Earth with
180,000 lbf of fuel on board flies to a
planet where the acceleration due to
gravity is 12 ft/s2. During the flight to the
planet, 2/3 of the fuel is consumed. How
much thrust does the rocket need to
insure lift-off from the planet?
Chapter 1: Thermodynamic Concepts and Terminology
Homework problem 1.6
PROBLEM STATEMENT: A gas is
contained in a vertical cylinder 3 inches
in diameter under a piston whose mass
is 50 lbm. The local gravitational
acceleration is 32.4 ft/s2 and the
atmospheric pressure acting on the
outside of the piston is 14.7 psia. What is
the absolute pressure of the gas in the
cylinder in psia?
Chapter 1: Thermodynamic Concepts and Terminology
Homework problem 1.10
PROBLEM STATEMENT: A colleague
reports that she has developed a new
material which will withstand an absolute
temperature three times as great as her
previous best material which could
endure a temperature of 2000oR. What
is this new upper limit in K and oC?
Chapter 1: Thermodynamic Concepts and Terminology