Thermodynamics - Port Fest Baltimore 2013

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27 Οκτ 2013 (πριν από 3 χρόνια και 7 μήνες)

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Thermodynamics

Laws & Properties

Temperature & Pressure Scales

Thermodynamic Cycles

Thermodynamics

Branch of science dealing with the
interchange of thermal & mechanical
energy


2
Laws


6
Properties


3
Phases


3
Modes

of Heat Transfer


2
Effects

of Heat Transfer

Thermodynamic Laws


1
st

Law:

Conservation of Energy

(you can’t win

the best you can do is tie)

HEAT
IN

WORK
OUT

WORK
IN

HEAT
OUT

SYSTEM


with stored,
internal energy


U

HEAT
IN



HEAT
OUT

=
WORK
OUT



WORK
IN

+
D
U


The 1
st

Law is an accounting rule

H
in

H
out

H
net

W
out

W
in

W
net

D
U

60

20

40

75

50

25

15

40

80

-
40

100

40

60

-
20

200

50

150

450

300

150

0

0

150

-
150

0

150

-
150

0

90

0

90

90

0

90

0

1 BTU = 778 lb
-
ft = 1055 joules = 252 calories

Thermodynamic Laws


2
st

Law:

Not all processes are reversible

(sometimes you can’t even tie)

HEAT
IN

WORK
OUT

WORK
IN

HEAT
OUT

SYSTEM


with stored,
internal energy


U


HEAT
OUT

=
WORK
IN
(can happen)

HEAT
IN

=
WORK
OUT
(cannot happen)

Thermodynamics


2
Laws


6
Properties


3
Phases


3
Modes

of Heat Transfer


2
Effects

of Heat Transfer

Thermodynamic Properties

Define the “state” of a system


Temperature
,
T

(
o
F,
o
C,
o
R,
o
K)


Pressure
,
P

(psi, bar, in. Hg)


Internal Energy
,
u

(BTU/lb)


Specific Volume
,
v

(cu.in./lb)


Enthalpy
,
h

(BTU/lb)


Entropy
,
s

(BTU/lb)

P

Thermodynamic Properties

T

P

T

P

T


6 properties linked

measure any two


ca汣u污瑥 (or 汯o欠u瀩 o瑨er 4


Which two are you probably going to
observe (measure)?

Temperature Scales


Relative scales:

Fahrenheit
&

Celsius


Absolute scales:

Rankine

&
Kelvin

494
o
F

212
o
F

98.6
o
F

72
o
F

32
o
F

0
o
F

Freezing

Room Temp

Boiling
(Atmos)

Body Temp

TSES
Boiler

961
o
R





672
o
R





492
o
R






0
o
R

257
o
C

100
o
C

37
o
C

22
o
C

0
o
C

530
o
K





373
o
k





273
o
K






0
o
K

Absolute
Zero

-
460
o
F

-
273
o
C

180
o

100
o

Pressure Scales


Relative scales:


psig, inches (Hg) of Vacuum

14.7 psiA

Standard
Atmosphere

TSES
Boiler

Perfect
Vacuum

29.92 “Hg

0 “Hg

0 psiA

0 “Hg

29.92 “Hg

614.7 psiA

600 psig

“gage pressure”

“inches of vacuum”

Vacuum measure

29.92 “Hg

Perfect Vacuum

Atmospheric
Pressure

A
Barometer

is used to measure
atmospheric pressure via comparison
to a (very nearly) perfect vacuum

Vacuum measure

29.92 “Hg

Atmospheric
Pressure

0 psia

20.0 “Hg

10.0 “Hg

0.0 “Hg

5 psia

10 psia

14.7 psia

A
Vacuum Gage

is used to
measure the pressure in an
evacuated space via comparison
to atmospheric pressure

Evacuated Space

Thermodynamics


2
Laws


6
Properties


3
Phases


3
Modes

of Heat Transfer


2
Effects

of Heat Transfer

3 Phases of matter


Solid


maintains shape


Liquid


lower surface & sides
conform to shape of container;
upper surface flat & horizontal


Vapor (Gas)


conforms to
shape of container

A
Fluid

is either a liquid or vapor
which flows and can be pumped

Thermodynamics


2
Laws


6
Properties


3
Phases


3
Modes

of Heat Transfer


2
Effects

of Heat Transfer

3 Modes of heat transfer


Radiation


transfer through space
via

electromagnetic waves; travel in a
straight line (may reflect off surfaces)


Conduction


transfer through
solids (molecule vibration)


Convection


transfer via
movement of a fluid

Note
:
Heat

is thermal energy in
transition from a high temperature
area to a lower temperature area

Heat transfer

BOILER
TUBE


Transfer from
FURNACE

to
Boiler Tube

by
radiation

and
convection


Transfer
through Boiler Tube wall

by
conduction


Transfer to
Steam Drum

via circulation of fluid
(
convection
)

Thermodynamics


2
Laws


6
Properties


3
Phases


3
Modes

of Heat Transfer


2
Effects

of Heat Transfer

2 Effects of heat transfer

When heat is transferred to/from a substance,
one

of two effects may be realized


Temperature change


a rise or fall
in temperature is a
sensible heat

effect


Phase change


(liquid
-
vapor, vapor
-
liquid,
solid
-
liquid, liquid
-
solid)

is a
latent heat

effect


But not both simultaneously

at least not in the same space

LATENT heat

212
o

liquid

212
o

vapor

Saturation
Conditions

300
o

steam

88
o

of
SUPERHEAT

BOILER

SUPERHEATER

SENSIBLE heat

SENSIBLE heat

Transferring heat to 1 lb of H
2
O

(at atmospheric pressure)


Temp (
o
F)

Heat (BTU)

SOLID

SOLID
-
LIQUID MIX

LIQUID

VAPOR

Sensible

Latent

32

212

LIQUID
-
VAPOR MIX

0

Transferring heat to 1 lb of H
2
O


(at atmospheric pressure)

Temp (
o
F)

Heat (BTU)

Superheated

VAPOR

212

LIQUID
-
VAPOR MIX

Saturation Conditions
: 0 psig; 212
o
F

0

Sub
-
cooled

LIQUID

Sensible
Heat

0.5
BTU/
o
F

0% “quality”

(100% liquid)

BOILING

CONDENSING

Latent Heat *of vaporization)

970 BTU/lb

50% “quality”

(50% liquid()

100% “quality”

(0% liquid()

“wet” steam

Sensible Heat

1.0 BTU/
o
F

Boiling (saturation) Temperature
linked to pressure

162
o

liquid

5 psig

1 Atm

(14.7 psia)

0 psia

230
o

liquid

162
o

vapor

230
o

vapor

0 psia

1 Atm

10”Hg

(bar)

20”Hg

(VAC)

Saturation Temperatures & Pressures

Temp (
o
F)

Heat (BTU)

212

1 Atm (14.7 psia, 0 psig)

0

92

490

570

600 psig

1200 psig

28.5 “Hg (VAC)

970 BTU/lb

1040 BTU/lb

728 BTU/lb

610 BTU/lb

STEAM DOME

Thermodynamic CYCLES


5 components:


Heat source


Heat sink


Engine


Pump


Working Fluid


Closed Cycle:

working fluid reused


Open Cycle:

working fluid discarded

Closed Cycle

ENGINE

HEAT
SOURCE

HEAT
SINK

PUMP

WORKING
FLUID

W

H

H

W

Open Cycle

ENGINE

HEAT
SOURCE

HEAT
SINK

PUMP

WORKING
FLUID

W

H

H

W