ME 200 L3: Introduction to ThermodynamicsME 200 L3: Introduction to ThermodynamicsEnergy: Kinetic, Potential and Internal

Spring 2014 MWF 1030-1120 AML3 (First Lecture by Jay Gore)

J. P. Gore, Reilly University Chair Professorgore@purdue.edu

Gatewood Wing 3166, 765 494 0061Office Hours: MWF 1130-1230

TAs: Robert Kapaku rkapaku@purdue.edu Dong Han han193@purdue.edu

Resources for our learning• Fundamentals of Engineering Thermodynamics, Moran,

Shapiro, Boettner and Bailey, Seventh Edition. • Read assigned sections before coming to class.• Group class email will be used frequently to

communicate. Also use http://www.purdue.edu/mixable• Class participation welcome and essential.

• Given the size of the class, smaller groups of ~10 students to be formed soon. Special opportunities offered to individual ME200 Peer Mentor to lead a group.

• Other Instructors, T. A. s, Classmates, Organized Learning Groups such as www.purdue.edu/si

• Homework: Submission, grading, and return policies will be announced in the class.

Temperature (T)

►Measure of energy contained within a substance at the atomic and molecular scale. ►If two substances (one warmer than the other) are brought into contact and isolated from their surroundings, they interact thermally with changes in observable properties.►When changes in observable properties cease, the two substances are in thermal equilibrium.►Temperature is a physical property that determines whether the two substances are in thermal equilibrium.► A thermometer is used to measure temperature using a change in a thermometric property of a thermometric substance.

► Liquid-in-glass thermometer►A glass capillary tube connected to a bulb filled with liquid and sealed. Space above liquid occupied by vapor or an inert gas.►As temperature increases, liquid expands and the length (L) of the liquid in the capillary indicates the temperature.►The liquid is the thermometric substance. L is the thermometric property.

►Other types of thermometers: Thermocouples, Thermistors, Radiation thermometers and optical pyrometers

Thermometers for Temperature Measurements

Temperature Scales

ΔTºR = ΔTºF = 1.8 x (ΔTK = ΔTºC)

USE ABSOLUTE TEMPERATURES IN ALL YOUR PROBLEM SOLUTIONS.

T(oC) = T(K) – 273.15 (Eq. 1.17)

T(oF) = T(oR) – 459.67 (Eq. 1.18)

oC and oF Relationship

ΔTºR = ΔTºF = 1.8 x (ΔTK = ΔTºC)

USE ABSOLUTE TEMPERATURES IN YOUR PROBLEM SOLUTIONS BECAUSE THE DIFFERENCES ARE IDENTICAL AND SOME FORMULAE LIKE THE IDEAL GAS LAW REQUIRE TEMPERATURE IN ABSOLUTE UNITS.

T(oC) = T(K) – 273.15 (Eq. 1.17)

T(oF) = T(oR) – 459.67 (Eq. 1.18)

oC

oF

(0, 32)

(100, 212)

(-17.7, 0)

oC oF

-17.7 0

0 32

100 212

-273 -460

(-273, -460)

► Some temperatures and ranges of interest► 0 K is the absolute lower limit of a temperature scale► Ice temperature is 273 K► Boiling point of water at atmospheric pressure is 373 K► Healthy human body temperature ~ 309 K► High fever human body temperature ~ 313 K► Hydrocarbon “yellow flame” temperature 1400 K – 1800 K► Hydrocarbon “blue flame” temperature 1900 K – 2400 K ► Effective solar temperature is considered to be 5500K► Absolute upper limit of temperature is not defined yet but

engineering higher than flame temperature materials is challenging. Materials with porous cooling walls may

be used.

Temperatures of Interest

Engineering Design and Analysis

Engineering Design Engineering Analysis

Recognize (or create) a need and define all requirements and constraints associated with it.

Apply fundamental principles to the functionality of the design.

Select “best design,” criteria: cost, efficiency, size, weight, life.

Conservation of mass, momentum species and energy must be followed.

Consider product life cycle reliability, manufacturability, maintenance, sustainability.

Performance prediction, testing, and suggestion of improvements.

Customer and Business considerations: Aesthetics, appearance, color, customer appeal, first to market, capital.

Limitations based on second law of thermodynamics.

Compatibility with other products, systems, policies.

Evaluate potential for scaling in terms of product size or product volume.

Problem Solving Techniques

A fairly straightforward problem:

•The system is easy to define (only one type).

•There are few basic equations.

2

Mass m (kg)

Potential Energyat thecurrent position mgZ

Potential Energyat the bottom mg(Z Lsin )

Kinetic Energyat thecurrent position 0(held stationary)

1Kinetic Energyat the bottom of theslope mV

2If thereis noother energy

2

2

interactions then PE KE 0

1(mg(Z Lsin ) mgZ) ( mV 0)

21

mgLsin mV V 2gLsin2

Analysis of Energy

We made the problem “fairly straightforward” by ignoring important factors such as friction, lubrication, complex shapes, complex surfaces and contact areas, wheels, steering, multiple bodies, collisions, repairs, heating and cooling etc…. We will soon be bringing these in but before that, let us define the energy content of the body considering macro-scale mechanical energy and complex energy stored by atoms, and molecules (ignoring macro scale electro magnetic charges etc.)

Ref

top bottom

2

Mass m (kg);Energystored in mass : m(u u )

Stored EnergyChange U m(u u )

If thereare noother energyinteractions then U PE KE 0

1mc T mg z m (V ) 0

2

Analysis of Energy with work and heat

We made the problem “fairly straightforward” by ignoring important factors such as transfer of heat to the pavement and energy added by a mechanical work producing device such as an engine or a fuel cell or an electric motor. Let us add that:

21mc T mg z m (V ) Q W

2

Problem Solving Techniques

Important steps to solve any problem in a systematic manner.•Find: What quantities are of customer interest? Usually dictates the definition of the System.•System: Control mass/control volume choice indicates what mass flow and energy interactions exist.•Basic Equations: Which equations are required to determine quantities of interest (related to Find)•Given: What quantities are known?•Assumptions: Do the number of unknowns and available equations match? Otherwise, you need appropriate simplifications and assumptions.•Solution: Evaluate properties, employ correct units, perform calculation, discuss result(s) if necessary.