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Thermodynamics 2 PH: 104: Heat and Thermodynamic Course Outline (Continued) Thermodynamics 2 PH: 104: Heat and Thermodynamic Course Outline (Continued)

Thermodynamics 2 PH: 104: Heat and Thermodynamic Course Outline (Continued) - PowerPoint Presentation

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Thermodynamics 2 PH: 104: Heat and Thermodynamic Course Outline (Continued) - PPT Presentation

Thermometry Concept of temperature Boyles Law Charles Law Thermometers Thermocouple Calorimetry Platinum resistance scale Absolute zero Lower fixed point Temperature gradient Thermodynamic ID: 783196

heat energy law system energy heat system law process internal temperature gas work equilibrium closed change thermodynamics flow expansion

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Slide1

Thermodynamics 2

Slide2

PH: 104: Heat and Thermodynamic Course Outline (Continued)

Thermometry

Concept of temperature

Boyle’s LawCharles’ LawThermometersThermocoupleCalorimetryPlatinum resistance scaleAbsolute zeroLower fixed pointTemperature gradientThermodynamic laws and systemsSystem state propertiesEquations of stateThermodynamic processesWorkFirst Law of ThermodynamicsOpen and closed systemsInternal energy Standard Temperature and PressureConductive heat transferConductivity and resistance

Slide3

Objectives

Understand equilibrium and quasi-equilibrium

Define the laws of thermodynamics

Define internal energy Use definitions of work for various closed system cases

Slide4

Equilibrium and Equilibrium Assumptions

To do analysis of system the system needs to be at equilibrium (e.g. no system variables are changing)

Analysis can be done at Quasi-equilibrium, which is to say the system is changing in increments at which analysis can be done. If the time change at which the analysis is done is small enough, the system can be assumed to be in Quasi-equilibrium. ALSOFor open systems (e.g. control volumes) the rate of change (mass flow) is assumed to be constant over a very short period of time.

Slide5

The Four L

aws of Thermodynamics

0

th Law: if two systems are in thermal equilibrium with a third system, then they are in thermal equilibrium with each other.1st Law: is the law of conservation of energy. Energy can to be created or destroyed. There is function called internal energy that relates work and heat transfer.2nd Law: Entropy is a function of the state of the system and cannot be reduced. Entropy is a measure of disorder or the possibility of a process occurring in nature.3rd Law: It is impossible by any procedure, no matter how idealized, to reduce any system to the absolute zero temperature in a finite number of operations.

Slide6

General Idealisms of the Laws

0

th

Law: temperatures are relatable1st Law: deals with quantity of energy2nd Law: deals with quality of energy and irreversibility3rd Law: everything ceases to exist at absolute zero

Slide7

Zeroth Law of Thermodynamics

If two systems are in thermal equilibrium with a third system, then they are in thermal equilibrium with each other.

That is to say, if Ta =

Tc and Tb = Tc then Ta = Tb Are the internal energies of CO2 and H20 equal if they have the same temperature?

A

C

B

Slide8

Mechanical energy and heat equivalency

Joules Experiment (adiabatic)

Method

Dropped a weight to mix waterMany other similar experimentsResultSlight temperature riseConclusions4.186 J = 1 cal4186 J = 1 kcal4186 J = 1 Cal (food)

Slide9

Mechanical energy and heat equivalency

Joules Experiment (adiabatic)

Further conclusion

Internal Energy is a measurable quantity and is relatable to work  

Slide10

Internal energy (

U)

is vibration and rotation energy in fluids

Sometimes loosely called heat, but this introduces a confusion between it and the energy transferred by heating Q. Heating is simply the process by which energy is transferred from hot to cold.For ideal gas and closed systems

For real gases and closed system

For open systems

Where,

H

is entropy <- we won’t define this

 

Slide11

The First Law of Thermodynamics

(Conservation of Energy)

Where

Q = net heat addedW = work done by the system

= change in internal energy

Internal Energy

Is a property of the system, describes

vibrational/rotational

energy in a fluid

Work

Is not a property, describes

mechanical

energy

entering (-) or leaving the system (+)

Heat

Is not a property, describes

thermal

energy entering (+) or leaving the system (-)

 

Slide12

Mass Balance (closed system)

A mass balance for a closed system is very easy.

Mass in = Mass out = 0

 

Slide13

Energy Balance (closed system)

Slide14

Time dependent Energy Balance:

Closed System

Slide15

Work relationships for a closed system

Adiabatic

Isothermal

IsovolumetricIsobaricPolytrophic process

Slide16

Polytrophic Process

pV

n

= constant

n

= 1

n

1

 

Slide17

Adiabatic Process

Q

= 0

Thus, ΔU = -W

 

U

1

U

2

Slide18

Equations of state for the adiabatic process for an ideal gas (Syllabus)

 

Slide19

Isobaric Process

W

=

f x dW = PAdThus, W = PΔVOR

 

P

1

= P

2

Slide20

Isovolumetric

Process

Volume

is constantW = PΔVThus, W = 0

V

1

= V

2

Slide21

Isothermal Process

(for

ideal gasses

in closed systems)

Thus,

Thus,

 

T

1

= T

2

Slide22

Isothermal Process

n

= 1

pVn = constant

p

 

T

1

= T

2

Slide23

Cycles

Are just a set of processes in series 1-2-3-4-1-2-3-4-1-2-3-4,

ect

.Two major types: Power Cycle and refrigeration and heat pump cyclesEngines operate on Power CycleCarnot cycleOtto cycle

Slide24

Examples of why aren’t processes or cycles 100% efficient (irreversibility)

Heat transfer through a finite temperature difference

Unrestrained expansion of a gas or liquid to a lower pressure

Spontaneous chemical reactionSpontaneous mixing of matter at different compositions or statesFriction- sliding friction as well as friction in the flow of fluidsElectric current flow through a resistanceMagnetization of polarization with hysteresisInelastic deformation

Slide25

Reversible cycle (internally)

1 ↔ 2

No irreversibility's in the system (friction,

ect

.)

Slide26

Self study syllabus topic

The relationship between the principal specific heat capacities

Conductive heat transfer

Thermal conductivity and resistance 

Slide27

Second law not on syllabus

But, it is the law that proves no REAL process or cycle is 100% efficient

Slide28

Second Law of Thermodynamics

Heat can flow spontaneously from a hot object to a cold object; heat will not flow spontaneously from a cold object to a hot object.

Some processes adhere to the First Law of Thermodynamics but do not happen in both directions (i.e. a cup hitting the ground and breaking or mixing salt and pepper)

Things tend to spontaneously go from a state of order to disorder (increasing entropy) but not the other direction.

Slide29

Example Problem

How much work is done by the expanding gas?

W

=

f

x

d

= ??? J

P

atm

= 1

atm

or 1.013 x 10⁵ N/m²

A

piston

=

0.02 m²

d = 0.1 m

Slide30

Example problem

An

ideal gas expands isothermally, performing 3.40 x 10

3 J of work. Calculate the change in internal energy and the heat absorbed during this expansion.

Slide31

An ideal gas expands isothermally, performing 3.40 x 10

3

J of work. Calculate the change in internal energy and the heat absorbed during this expansion.

Do I remember the qualifications of isothermal expansion?

 

T

1

= x

V

1

= y

P

1

=

z

T

2

= x

V

2

= y + a

P

2

=

???

W = f x d =

3.40 x 10

3

J

Slide32

An ideal gas expands isothermally, performing 3.40 x 10

3

J of work. Calculate the change in internal energy and the heat absorbed during this expansion.

How do gases expand? How do gases expand without changing temp?

 

T

1

= x

V

1

= y

P

1

=

z

T

2

= x

V

2

= y + a

P

2

=

???

W = f x d =

3.40 x 10

3

J

Slide33

An

ideal gas

expands isothermally, performing 3.40 x 10

3 J of work. Calculate the change in internal energy and the heat absorbed during this expansion.

 

T

1

= x

V

1

= y

P

1

=

z

T

2

= x

V

2

= y + a

P

2

=

z - b

W = f x d =

3.40 x 10

3

J

Slide34

Problems with mass and energy balances

Slide35

= ?

 

We will use a Mass Balance and

Energy Balance (first law)

and apply the equations

to solve for tank pressure at time (

t

2

) if pump power, flow rate,

P

t1

and surrounding variables were known.

Slide36

Polytrophic example

Four kilograms of a gas is contained within a piston-cylinder assembly. The gas undergoes a process for which the pressure-volume relationship is

The initial pressure is 3 bar, the initial volume is 0.1

. And the final volume is 0.2

. The change in specific internal energy of the gas in the process is

. There are no significant changes in the kinetic or potential energy. Determine the net heat transfer for the process, in kJ.

 

Slide37

Slide38

Summary

Slide39

Class Questions

Does a ingot of iron that is twice the size of another but at the same temperature have the same internal energy? (yes or no)

When 2 masses of water are mixed

(1) 300 g @ 50 °C(2) 3,000 g @ 45 °C Does heat flow from the water with higher internal energy (2) or temperature (1)?

Slide40

Second Law of Thermodynamics

Heat can flow spontaneously from a hot object to a cold object; heat will not flow spontaneously from a cold object to a hot object.

Some processes adhere to the First Law of Thermodynamics but do not happen in both directions (i.e. a cup hitting the ground and breaking or mixing salt and pepper)

Things tend to spontaneously go from a state of order to disorder (increasing entropy) but not the other direction.

Slide41

Reversible thermodynamic process

Slide42

Thermodynamic intensive

and

extensive

properties, variablesIntensive do not change when identical systems are addedExtensive depend on the amount of the substance in the systemIntensiveExtensiveTemperature, TVolume, VPressure, PMass, m

Density,

ρ

Area,

A

Composition

Slide43

Group Class Homework

Which is larger 1

°F or 1 C°?

The units for the coefficient of linear expansion α are (°C)-1 and there is no mention of a length unit such as meters. Would the expansion coefficient change if we used feet or millimeters instead of meters? Long steam pipes that are fixed at the ends often have a section in the shape of a U. Why?

Slide44

Superheating

When a gas is heated to above the critical temperature the vapor, gas or fluid is said to be super heated. This a metastable phase that usually has a transient existence (e.g. short life).

Slide45

Supersaturation

When a gas has more vapor than the

SVP

do to high pressures. This processes is also unstable and often short lived.What does supersaturation look like in our environment?What is the dew point?

Slide46

Group homework

15 below zero on the Celsius scale is what temperature Fahrenheit and kelvin?

15 below zero on the

Fahrenheit scale is what temperature in Celsius and kelvin?The Eiffel Tower is 300 m tall and made of wrought iron. Estimate how much the height changes from July (ave. 25 °C) to January (ave. 2 °C).The density of water at 4 °C is 1000 kg/m³. What is water’s density at 94 °C?Absolute zero is what temperature on the Fahrenheit scale?

At (a) atmospheric pressure, in what phases can CO

2

exist? (b) For what range of pressure and temperatures can CO

2

be a liquid?

Extra credit

What is the approximate temperature inside a pressure cooker if the water is boiling at a temperature of 120

°

C? Assume no air escaped during the heating process, which started at 20

°

C.