Chapter 10 Power and Refrigeration Systems Gaseous...

Fundamentals of Thermodynamics

Chapter 10

Power and Refrigeration Systems

Gaseous Working Fluids

Thermal Engineering Lab. 2

10.1 Air-standard power cycles

Chapter 10. Power and Refrigeration Systems – Gaseous Working Fluids

- Working fluid : Fixed mass of air

- Combustion process : replaced by heat transfer from external

source

- Exhaust & intake process : replaced by heat transfer to the

surrounding

- Internally reversible

- Constant specific heat

Internal Combustion Engine – Otto, Diesel, gas-turbine

External Combustion Engine – Steam, Stirling

Thermal Engineering Lab. 3

10.2 The Brayton cycle

Chapter 10. Power and Refrigeration Systems – Gaseous Working Fluids

2

2

P const

S const

개의

개의 process를구성

working fluid : gas single phase

1 L

H

Q

Q th

Thermal Engineering Lab. 4

Chapter 10. Power and Refrigeration Systems – Gaseous Working Fluids

4 1 1 4 1

3 2 2 3 2

/ 11 1 1

/ 1

pL

H p

C T T T T TQ

Q C T T T T T

th

H,avg

H,avg L,avg

3 : T

: T & T

1- 2 - - 4 -1

1- 2 - 3 - 4 -1

1 13 3 32 2 2

4 1 1 1 4 4

3 3 32 4 4

4 1 2 1 2 1

1

1 1

1

2 22 1

,

1 1

11 1 1

/

k k

k k

k

k

th k

k

P P TP P T

P P P T P T

T T TT T T

T T T T T T

T P

T PP P

Thermal Engineering Lab. 5

Chapter 10. Power and Refrigeration Systems – Gaseous Working Fluids

kPv const

Pv RT

kRTv const

v

1kTv const

k

RTp const

p

1 k kp T const

1 k

kT P const

1 1

2 1 2

1 2 1

k k

k kT P P

T P P

Thermal Engineering Lab. 6

Chapter 10. Power and Refrigeration Systems – Gaseous Working Fluids

cycle실제

compressor 40 ~ 80% 가 차지

2 1

2 1

3 4

3 4

scomp

turb

s

h h

h h

h h

h h

Thermal Engineering Lab. 7

Ex. 10.1 In an air-standard Brayton cycle, the air enters the compressor at 0.1 Mpa

and 15℃. The pressure leaving the compressor is 1.0 MPa, and the

maximum temperature in the cycle is 1100℃. Determine

1. The pressure and temperature at each point in the cycle.

2. The compressor work, turbine work, and cycle efficiency.

Chapter 10. Power and Refrigeration Systems – Gaseous Working Fluids

Thermal Engineering Lab. 8

Ex. 10.2 Consider a gas turbine with air entering the compressor under the same

conditions as in Example 10.1 and leaving at a pressure of 1.0 Mpa. The

maximum temperature is 1100℃. Assume a compressor efficiency of

80 %, a turbine efficiency of 85 %, and a pressure drop between the

compressor and turbine of 15 kPa. Determine the compressor work,

turbine work, and cycle efficiency.

Chapter 10. Power and Refrigeration Systems – Gaseous Working Fluids

Thermal Engineering Lab. 9

10.3 The simple gas-turbine cycle with a regenerator

Chapter 10. Power and Refrigeration Systems – Gaseous Working Fluids

Thermal Engineering Lab. 10

Chapter 10. Power and Refrigeration Systems – Gaseous Working Fluids

net t cth

H H

w w w

q q

3H p xq C T T

3 4t pw C T T

x 4 H tIdeal case: T =T q =w

1 1p

H c cth

H t

Cq w w

q w

2 1

p

T T

C

3 4T T1

2 2

1 11 1

1

3 341

32

1 1

1 1

11

k

k

k

k

T PT PT T

T TTP

TP

1

1 1

21 2

1

3 11

2

1

1

1

k

kk

k

k

k

PPT P

T PP

P

1

1 2 2

3 1 3

1 1

k

kT P T

T P T

Thermal Engineering Lab. 11

Chapter 10. Power and Refrigeration Systems – Gaseous Working Fluids

regenerator efficiency

2

' 2

xreg

x

h h

h h

2

' 2

if .xreg p

x

T TC const

T T

Thermal Engineering Lab. 12

Ex. 10.3 If an ideal regenerator is incorporated into the cycle of Example 10.1,

determine the thermal efficiency of the cycle.

Chapter 10. Power and Refrigeration Systems – Gaseous Working Fluids

Thermal Engineering Lab. 13

10.4 Gas-turbine power cycle configurations

Chapter 10. Power and Refrigeration Systems – Gaseous Working Fluids

Ericsson Cycle2 const. T

2 const. P

개의

개의

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Ex. 10.4 An air-standard power cycle has the same states given in Example 10.1.

In this cycle, however, the compressor and turbine are both reversible,

isothermal processes. Calculate the compressor work and the turbine

work, and compare the results with those of Example 10.1.

Chapter 10. Power and Refrigeration Systems – Gaseous Working Fluids

Thermal Engineering Lab. 15

Chapter 10. Power and Refrigeration Systems – Gaseous Working Fluids

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10.5 The air-standard cycle for jet propulsion

Chapter 10. Power and Refrigeration Systems – Gaseous Working Fluids

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Ex. 10.5 Consider an ideal jet propulsion cycle in which air enters the compressor

at 0.1 Mpa and 15℃. The pressure leaving the compressor is 1.0 Mpa,

and the maximum temperature is 1100℃. The air expands in the turbine

to a pressure at which the turbine work is just equal to the compressor

work. On leaving the turbine, the air expands in a nozzle to 0.1 Mpa. The

process is reversible and adiabatic. Determine the velocity of the air

leaving the nozzle.

Chapter 10. Power and Refrigeration Systems – Gaseous Working Fluids

Thermal Engineering Lab. 18

10.6 The air-standard refrigeration cycle

Chapter 10. Power and Refrigeration Systems – Gaseous Working Fluids

1 41 4

2 1 3 4 2 1 3 4

PL L

net C E P P

C T Tq q h hCOP

w w w h h h h C T T C T T

Thermal Engineering Lab. 19

Chapter 10. Power and Refrigeration Systems – Gaseous Working Fluids

/ 1 / 1

3 32 2

1 1 4 4

1 4

3 2 222 1 3 4

11 4 1

1 /

1 1

1 /1

1 /

1

k k k k

k k

p

P TP T

P T P T

T T

T T TTT T T T

TT T T

r

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Chapter 10. Power and Refrigeration Systems – Gaseous Working Fluids

Thermal Engineering Lab. 21

Ex. 10.6

Chapter 10. Power and Refrigeration Systems – Gaseous Working Fluids

Consider the simple air-standard refrigeration cycle of Fig. 10.12. Air

enters the compressor at 0.1 MPa and -20℃ and leaves at 0.5 MPa. Air

enters the expander at 15℃. Determine

1. The COP for this cycle.

2. The rate at which air must enter the compressor to provide 1 kW of

refrigeration.

Thermal Engineering Lab. 22

10.7 Reciprocating engine power cycles

Chapter 10. Power and Refrigeration Systems – Gaseous Working Fluids

max min

max min

max min

: 2

:

: /

:

:60 60

crank

displ cyl cyl cyl

v

net net meff

cyl net meff disp

Stroke S R

Displacement V N V V N A S

Compression ratio r V V

Net work per cylinder W mw P V V

RPM RPMPower W N mw P V

Thermal Engineering Lab. 23

10.8 The Otto cycle

Chapter 10. Power and Refrigeration Systems – Gaseous Working Fluids

2

2

S const

V const

개의

개의 process를구성

Thermal Engineering Lab.

Chapter 10. Power and Refrigeration Systems – Gaseous Working Fluids

4 1

th

3 2

1 1vH L L

H H v

mC T TQ Q Q

Q Q mC T T

4 1

1 11 1 1

132 2 2

2

11

1 1 1 1 1

1

k

k

v k

v

TTT T v

rTT T v r

T

kPv const

Pv RT

1 1 1

2 2 2

Pv RT

P v RT

R

1

1 1

kT v R 1

2 2

kT v

11

2 1 4

1 2 3

kk

T v v

T v v

3

4

T

T

Thermal Engineering Lab.

Chapter 10. Power and Refrigeration Systems – Gaseous Working Fluids

tetraethyl lead knocking 방지

옥탄가

8 18 7 16iso - octan C H n - heptan C H과 의질량비로결정

Thermal Engineering Lab.

Chapter 10. Power and Refrigeration Systems – Gaseous Working Fluids

*

1.

2.

3.

4.

5.

v

Deviation

C T

Incomplete Combustion

Work

Heat Loss

Irreversibilities

배기흡기를위한

Thermal Engineering Lab. 27

Ex. 10.7

Chapter 10. Power and Refrigeration Systems – Gaseous Working Fluids

The compression ratio in an air-standard Otto cycle is 10. At the

beginning of the compression stoke, the pressure is 0.1 MPa and the

temperature is 15℃. The heat transfer to the air per cycle is 1800 kJ/kg air.

Determine

1. The pressure and temperature at the end of each process of the cycle.

2. The thermal efficiency.

3. The mean effective pressure.

Thermal Engineering Lab. 28

10.9 The Diesel cycle

Chapter 10. Power and Refrigeration Systems – Gaseous Working Fluids

1 L

th

H

Q

Q

4 1

3 2

1v

P

T TC

C T T

1 4 1

2 3 2

( 1)1

( 1)

/

/

T T T

kT T T

Effect

) 1 2 3 4 1i

) 1 2 3 4 1ii Otto

) 1 2 3 4 1iii Otto

1

3 3

2 2

111

1

: cutoff ratio

k

th k

vr k

v T

v T

Diesel Otto 최고온도를제한했을때에는

Thermal Engineering Lab.

Chapter 10. Power and Refrigeration Systems – Gaseous Working Fluids

p

p P

v

v v

T S

v const

Tds dh vdP C dT

T T

S C

Tds du Pdv C dT

T T

S C

P const

선도상에서 등압곡선과등적곡선의기울기

Thermal Engineering Lab. 30

Ex. 10.8

Chapter 10. Power and Refrigeration Systems – Gaseous Working Fluids

An air-standard diesel cycle has a compression ratio of 20, and the heat

transferred to the working fluid per cycle is 1800 kJ/kg. At the beginning

of the compression process, the pressure is 0.1 MPa and the temperature is

15℃. Determine

1. The pressure and temperature at each point in the cycle.

2. The thermal efficiency.

3. The mean effective pressure.

Thermal Engineering Lab. 31

10.10 The Stirling cycle

Chapter 10. Power and Refrigeration Systems – Gaseous Working Fluids

2

2

T const

V const

개의

개의 process를구성

Thermal Engineering Lab. 32

10.11 The Atkinson and Miller cycles

Chapter 10. Power and Refrigeration Systems – Gaseous Working Fluids

1 1

32 1 4

1 2 3 4

For the compression amd expansion processes(s=const),

,

k k

vT v T

T v T v

Higher expansion ratio than compression ratio

Thermal Engineering Lab. 33

Chapter 10. Power and Refrigeration Systems – Gaseous Working Fluids

44 1 4 1

1

4 1

3 2

4 1 4 1

3 2 3 2

The heat rejection process gives

: ,

The efficiency of the cycle becomes

1 1

1 1

L

H L L

H H

p

v

vP C T T q h h

v

q q q h h

q q u u

C T T T Tk

C T T T T

Thermal Engineering Lab. 34

Chapter 10. Power and Refrigeration Systems – Gaseous Working Fluids

1 1 3

4 3

1 42 1 1 4 1 1

1 1

1 1

3 4 1 1

1 1

1

The smaller compression ratio : /

The expansion ratio : /

,

The efficiency of the cycle becomes

1

1

k

kk k

k

CR v v

CR v v

v CRT T CR T T T

v CR

CR CRT T CR T CR T

CR CR

CR

CRk

CR

1

1 11

1

1k k

k

CR CRk

CR CRCR

CR

Thermal Engineering Lab. 35

Chapter 10. Power and Refrigeration Systems – Gaseous Working Fluids

Cycle in between the Otto cycle and Atkinson cycle

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10.12 Combined-cycle power and refrigeration systems

Chapter 10. Power and Refrigeration Systems – Gaseous Working Fluids

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Chapter 10. Power and Refrigeration Systems – Gaseous Working Fluids

Thermal Engineering Lab. 38

Chapter 10. Power and Refrigeration Systems – Gaseous Working Fluids