Chapter 1: Thermodynamic Concepts and Terminology

Copyright (c) 2005 byJohn Wiley & Sons, Inc

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Thermodynamics: An Integrated Learning SystemP.S. Schmidt, O.A. Ezekoye, J.R. Howell and D.K. Baker

Chapter 1: Thermodynamic Concepts and Terminology


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.

System

Surroundings

Universe

System Boundary


1.1 Systems: 3 Types

Transferred Across

System Boundary

Type of System 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 t


1.1 Combustion in Open & Closed Systems

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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/ [m3/kg]


1.2 Properties: Total & Specific Volumes

• Total Volume: V– [m3]– Upper case V

• Specific Volume: v– [m3/kg]– Lower case v


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.


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)

P

v

v =constant(isometric)

T = constant(isothermal)

T

v

v =constant(isometric)


1.4 Isobaric & Isometric Processes

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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


1.5 Unit Systems: gC

• gC: Conversion constant

• SI

• USCS–

– 1 lbm 1 lbf

2C

C

C

maF

mKineticEnergy

2

mzPotentialEnerg

g

g

yg

v

C 2

kg mg 1

N s

C 2

lbm ftg 32.2

lbf s


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

v V


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]


1.6.2 Pressure (P)

• Manometer:

H

PLINE

LINE ATMc

gHP P

vg


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


1.6.3 Temperature


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


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


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?



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?



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

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