optimal functioning parameters for a stirling engine … 1a to 3a/3a5 aloui... · optimal...
TRANSCRIPT
-
OPTIMAL FUNCTIONING PARAMETERS FOR A STIRLING ENGINE
HEATER
1 Universit de Valenciennes et du Hainaut-Cambrsis, ENSIAME, TEMPO (EA 4542) - DF2T Valenciennes France
2 GEPEA (UMR 6144), cole des Mines de Nantes, DSEE, 4 rue Alfred Kastler - BP20722 , 44307 Nantes Cedex 03 France
3 Universit de Monastir, Laboratoire LESTE, ENIM, Monastir - Tunisia
* E-mail : [email protected]
R. GHEITH 2,3, * F. ALOUI 1,2 and S. BEN NASRALLAH 3
10th EUROPEAN CONFERENCE
ON COAL RESEARCH AND ITS
APPLICATIONS: 10th ECCRIA
-
VI. Conclusions
II. Experimental device
III. Some experimental results
I. Introduction Objectives of the study
OUTLINE
-
Robert Stirling
Invention
Stirling engine (1816)
- A quiet engine (no vibrations because no internal combustion),
- Ecological engine (closed gas circuit),
- Any heating source can be used to heat the working fluid,
- Its efficiency is more important than that of an internal
combustion engine (between 30 and 40%)
This Stirling engine is:
1
-
The different Stirling engine configurations
Alpha type Heating
Cooling
Regenerator
Heating Cooling
Beta type
Regenerator
Gamma type
Heating
Cooling
Regenerator
2
-
The Stirling Cycle
1 2 : Isochoric heating 2 3 : Isothermal expansion
3 4 : Isochoric cooling 4 1 : Isothermal compression
Q340
V1
1
d
a b
c
3
-
Example of some applications using a Stirling engine 4
Stirling engine - generator Stirling engine dish Space domain (salellites) Submarine domain
Exchanger
To heating system
Electricity
Electricity
Stirling engine
Mean burner Gas valves
Natural
gas
From heating system
Micro -cogenerator system Liquefaction of gases (receipt machines)
-
GLOBAL THERMODYNAMIC MODELS
Isothermal model
Adiabatic model
Quasi-steady model
- Real gas assumption
- Thermal losses
- Mechanical losses Adiabatic model +
Compression
Space
Expansion Space
Regenerator
Cooler
Heater
l
D k
r h
5
-
- Studying heat transfers in:
- The regenerator (porous medium),
- The expansion room (hot source),
- The compression room (cold source).
- Seeing the effect of porous medium on the
efficiency, the heating and cooling temperatures.
Optimization of the heat transfer inside the Stirling engine in
order to increase its global efficiency, by:
Objectives of the study:
6
-
7
Hot source Tch Cold source Tfr Q1 < 0 Q2 > 0 Driven
machine
W < 0
2
2 2 2
' '. .
' 'glob mca th cal
QW W W
Q W Q Q
The amount of heat
supplied by the
electrical heating
(electrical resistance)
The amount of
heat actually
received by the
air
The
indicated
work
Mechanical work
effectively
recovered on the
brake shaft
2 'Q U I dt 2Q W'W
cal th mca
Operation of Stirling engine
-
Operation of Stirling engine
First law of thermodynamics on a cycle 0QQWU 21
Second law of thermodynamics on a cycle 0ST
Q
T
QS c
2
2
1
1
Efficiency 1Q
W
1
Heating source S1
at T1
Cold source S2
at T2
Stirling
Machine
W < 0
Q1 > 0 Q2 < 0
8
-
Compression Space
Expansion Space
Crank-Rod System
Regenerator
Cooler
Heater
Heating system
The Gamma type Stirling engine
9
-
PDet.
TE-input.
TE-input
PComp.
Tcold
Water input
Water output
Regenerator
Heating system
Expanxion Space
Compression space
TR2
TR4 TR3
TR1
TR6
TR8 TR7
TR5
Thot
Porous media
8 thermocouples 4 in each side
TR1
TR2
TR3
TR4
TR5 TR6
TR7
TR8
Cold working fluid
Hot working fluid
Hot working fluid
Porous media (Rgnrateur)
Cold working fluid
Dissipation energy system
Oscillant plate
Transmission belt
Alternateur
Force transducer
crank angle transducer
10
-
p
4
jjpjpj
jC
TVT
x
T
Cxt
p
C
1
x
TV
t
T
.
.''
..
air
air
11
-
Composed of: - 20 curved pipes (internal diameter: 1cm)
- 20 tubes (length 0.50m each one)
- 3 thermocouples located: inside the heater, outside the heat
and in heating system.
The heater exchange
13
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PExpansion
TW-entrance
TW-Exit
PComp.
TCold
Water input
Water exit
Regeneratorr
Heating
system
Expansion space
Compression space
TR2
TR4 TR3
TR1
TR6
TR8
TR7
TR5
THot
Matrix
(regenerator)
1st series of 4
thermocouples 2nd series of 4
thermocouples Regenerator
Series of 8
thermocouples
Pourous media
(regenerator)
TR5
TR6
TR7
TR8
TR1
TR2
TR3
Cold working fluid
Hot working fluid
TR4
Cold working fluid
Hot working fluid
The heater exchange
14
-
Two thermocouples are located at the input and the
output of cooling water circuit
Composed of 225 strips
(or fins) in the inner
cylinder
For increasing the heat
transfer exchange
between the working
fluid and water (cold
source)
II. Experimental
The cooler exchanger (cold source)
15
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The regenerator (porous medium)
16
Porous media
8 thermocouples (4 in each side)
TR1
TR2
TR3
TR4
TR5
TR6
TR7
TR8
Cold working fluid
Hot working fluid Hot working fluid
Porous medium (Regenerator)
Cold working fluid
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Materials with porosity of 90%
Proprieties \ Material Stainless Steel (304L) Copper Aluminium Monel 400
Density (kg.m-3) 7,850 8,920 2,700 8,800
Specific heat Cp (J.kg-1.K-1) 477 385 902 430
Thermal conductivity (W.m-1.K-1) 26 390 237 21.7
Melting point ( C) 1530 1084 660 1300
The properties of used regenerator materials for a temperature of 300 C are:
Copper
Aluminum Monel
Stainless Steel
p
4
j
jpjpj
jC
TVT
x
T
Cxt
p
C
1
x
TV
t
T
.
.''
..
4 matrices, with differents constituting materials, were used as Stirling engine regenerator:
- Stainless Steel matrix
- Copper matrix
- Aluminum matrix
- Monel matrix
Properties of the differents used matrices (regenerators)
Copper
Aluminum Monel
Stainless Steel
17
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4 matrices, with differents constituting materials, were used as Stirling engine regenerator:
- Stainless Steel matrix
- Copper matrix
- Aluminum matrix
- Monel matrix
Properties of the differents used matrices (regenerators)
Materials with porosity of 90%
Proprieties \ Material Stainless Steel (304L) Copper Aluminium Monel 400
Density (kg.m-3) 7,850 8,920 2,700 8,800
Specific heat Cp (J.kg-1.K-1) 477 385 902 430
Thermal conductivity (W.m-1.K-1) 26 390 237 21.7
Thermal Diffusivity a (m/s) 6.94 . 10-6 1.14 10-4 9.73 10-5 5.73 10-6
The properties of used regenerator materials for a temperature of 300 C are:
Copper
Aluminum Monel
Stainless Steel
4
j
jjj
j
T..a'V'T
x
T.a
xt
pa
x
TV
t
T
18
-
0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16136.08
136.1
136.12
136.14
136.16
136.18
136.2
136.22
0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16243.95
244
244.05
244.1
244.15
244.2
244.25
244.3
Acquisition time [s]
TR1
TR4
TR1-4
mean TR1
mean TR4
Working fluid temperature evolution vs. acquisition time for a copper matrix
The temperature of
the working fluid in
the regenerator
increases in the
first half cycle until
a maximum value
(TR1 and TR4)
The temperature
decreases during the
second half cycle
until a temperature
which is close to that
of the cold source
The Stirling engine regenerator has two roles:
- Accumulating heat 1 and 4)
- Forming a thermal barrier between both heat and cold sources 1-4)
Temperature evolution in each kind of matrix regenerator)
Pourous media
(regenerator)
TR5
TR6
TR7
TR8
TR1
TR2
TR3
Cold working fluid
Hot working fluid
TR4
Cold working fluid
Hot working fluid
19
-
The regenerator formed of the material Monel 400 is the best heat accumulator.
The stainless steel represents the highest temperature gradient, and the Aluminum
the smallest temperature gradient.
Temperature evolution in each kind of matrix regenerator)
Working fluid gradient temperature between the thermocouples TR1 and TR4
Best Heat
accumulator
Highest
temperature
gradient
Working fluid gradient temperatures given by the thermocouples TR1 during one cycle
20
-
100
150
200
250
300
Bra
ke
po
we
r [W
]
TH
= 300C
TH
= 400C
TH
= 500C
CopperStainlessSteel
Aluminum Monel
The Aluminum
regenerator
presents the
worst brake
power
regardless the
heating
temperature
The Stainless steel
has the best brake
power regardless
the heating
temperature
The brake power increases with the heating temperature, but at different
levels of each kind of regenerator.
Influence of each type of matrix on the engine performance versus heating temperature
Brake power = 281 W TH = 500C
21
-
For all experimented regenerators, the brake power increases with the
initial charge pressure but at different levels.
100
150
200
250
300
350
Bra
ke
po
we
r [W
]
Pi = 3 bar
Pi = 5 bar
Pi = 8 bar
Stanless
Steel
Copper Aluminum Monel
The Aluminum
regenerator presents the
worst brake power
regardless the initial
charge pressure
The Stainless Steel
regenerator has the
best brake power
Influence of each type of matrix on the engine performance versus charge pressure
22
-
The regenerator thermal efficiency is calculated as the ratio of real heat
transferred through the regenerator by the ideal heat, which must be transferred
through the regenerator.
The copper presents the best regenerator thermal efficiency and the
Monel 400 presents the worst regenerator thermal efficiency.
Regenerator thermal efficiencies
0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.160.25
0.3
0.35
0.4
0.45
0.5
0.55
0.6
0.65
Acquisition time fo one cycle [s]
Effic
ien
cie
s [%
]
Eff
Monel
EffCuivre
EffInox
Eff-Alum
Copper
Monel
Steel
Allum
23
-
Regenerator matrixes after about 15 hours of use
Copper Stainless Steel
Monel Aluminum
The copper oxidizes quickly because of the working fluid (air) which contains about 21%
of oxygen. This material oxidation changes the physical properties of the copper, and
then leads to bad heat exchanges inside the regenerator.
The stainless steel and the Aluminum, used as regenerators, have good
thermal efficiencies (about 44%).
These two materials do not present a problem of oxidation, but the use of
regenerator in Aluminum is limited by its melting temperature.
Regenerator thermal efficiencies
24
-
Four regenerator matrices were tested on a Gamma Stirling engine :
Stainless steel, Copper, Aluminum and Monel 400
- The Monel matrix presents the best thermal sponge, and the Stainless Steel
represents the best thermal barrier between hot and cold heat sources.
- The copper regenerator has the best thermal efficiency, but its oxidation
decreases extremely the brake power of the Stirling engine.
- Using an Experimental Design Approach (OCC or DOE), the impotant
parameters of the Stirling engine can be optimised to obtain a good
efficiency of this machine.
25