Residual oil monitoring in pressurised air with SnO_1tn2-based gas sensors [Elektronische Ressource] = Restölüberwachung in Druckluft mit SnO_1tn2-basierten Gassensoren / vorgelegt von Nikos Papamichail

Gopel2

Informations

• Publié par: eberhard_karls_universitat_tubingen
• Publié le: 01 janvier 2004
• Nombre de lectures: 4
• Langue: English
• Poids de l'ouvrage: 1 Mo

Extrait

Residual Oil Monitoring in
pressurised Air with SnO -based 2
Gas Sensors

Restölüberwachung in Druckluft
mit SnO -basierten Gassensoren 2



DISSERTATION

der Fakultät für Chemie und Pharmazie
der Eberhard-Karls-Universität Tübingen
zur Erlangung des Grades eines Doktors
der Naturwissenschaften


2004

vorgelegt von
NIKOS PAPAMICHAIL
















Tag der mündlichen Prüfung: 28.1.2004
Dekan: Professor Dr. H. Probst
1. Berichterstatter: Privatdozent Dr. U. Weimar
2. Berichterstatter: Professor Dr. G. Gauglitz


1 Introduction .......................................................................... 1
1.1 Motivation for the development of a residual oil monitor.......1
1.2 State of the art in residual oil monitoring ................................3
1.3 Alternative solutions................................................................4
1.3.1 The saturation problem and the aerosol vaporisation.................5
1.3.2 The choice of the sensor .............................................................8
1.3.3 Real life measurements...............................................................9
2 Experimental set up............................................................ 11
2.1 Compressor............................................................................11
2.2 Metal oxide sensors ...............................................................13
2.2.1 Preparation and description of the sensors ...............................13
2.2.2 Housing and connection of the sensors ....................................15
2.2.3 Operation temperature .......................................17
2.2.4 Sensing mechanism of metal oxide sensors for hydrocarbons.17
2.3 Flame Ionisation Detector .....................................................22
2.3.1 Description of the used FID instruments..................................23
2.3.2 Conversion of FID reading .......................................................24
2.3.3 FID-related problems when measuring oil vapours .................25
2.4 Vaporisation by expansion via capillary................................30
2.4.1 Characterisation of the capillary expansion process.................30
2.4.2 Vapour pressure over aerosols..................................................31
I
2.5 Gas mixing system ................................................................34
3 Experimental results and discussion................................. 36
3.1 Exploratory measurements ....................................................36
3.1.1 Headspace GC/MS....................................................................36
3.1.2 Results with gas mixing system................................................38
3.2 First compressor set up..........................................................41
3.2.1 Set up ........................................................................................41
3.2.2 Measurements at different sampling points..............................45
3.2.3 Results.......................................................................................49
3.3 Second compressor set up .....................................................50
3.3.1 Set up50
3.3.2 Long term measurements..........................................................52
3.3.2.1 Measurements with daily occurrences..................................54
3.3.2.2 Measurements with short term changes ...............................58
3.3.2.3 Seasonal effects.....................................................................62
3.3.3 Behaviour at high humidity ......................................................64
3.3.3.1 Description of water spikes ..................................................65
3.3.3.2 Thermodynamic explanation ................................................67
3.3.3.3 Measures against water spikes .............................................70
3.3.4 Results.......................................................................................71
3.4 Third compressor set up ........................................................72
3.4.1 Set up for dosing of oil & gravimetric referencing ..................72
II
3.4.2 Measurements with dosing of oil..............................................76
3.4.3 Results of measurements with dosing of oil.............................83
3.4.4 Measurements with gravimetric referencing ............................84
3.4.5 Results of gravimetric referencing............................................92
4 Conclusion........................................................................... 94
4.1 Proof of Feasibility................................................................94
4.1.1 Vaporisation via capillary expansion........................................94
4.1.2 Sensor sensitivity ......................................................................95
4.1.3 Cross sensitivities in real life measurements............................95
4.2 Other findings........................................................................96
4.2.1 Measurement of oil vapours with FID......................................96
4.2.2 Real life set up with compressor...............................................96
4.3 Outlook..................................................................................97
4.3.1 Proposed steps of further development and investigation........97
4.3.2 Will the residual oil indicator be established?..........................97
5 References ......................................................................... 100
6 Publications....................................................................... 103
7 Acknowledgements........................................................... 105
III
Symbols and units:
3cm cubic centimetre
c aerosol contamination aer
°C degree centigrade
γ surface tension
∆m mass difference
∆p pressure difference
F flow rate
g gram
k Boltzmann constant
l litre
l capillary length cap
norm (oil) mass of liquid oil in case of normal oil contamination liq
incm (oil) mass ofase of increased oil contamination liq
3m cubic meter
mg milligram
mm millimetre
min minute
ml millilitre
mNillinewton
µm micrometer
η dynamic viscosity
23N Avogadro’s constant (6.0*10 parts per mol) L
pamb ambient pressure
aerp vapour pressure over aerosol droplet
p pressure of the air after compression in the compressor comp
incp (oil) partial pressure of oil in case of increased oil contamination
norp (oil) oil in case of normal oil contamination
plap vapour pressure over a planar surface
p (oil) saturation vapour pressure of oil sat
p total pressure tot
r radius of the aerosol droplet A
r critical radius cr
R ideal gas constant
heatR heater resistance at ambient temperature 0

IV
heatR heater resistance when heated h
R sensor baseline resistance 0
R sensor resistance at exposure to analyte Exp
R retention time t
S sensor signal
S sensor signal due to humidity changes Hum
S sensor signal due to changes of oil content Oil
S saturation ratio rat
S total sensor signal Tot
t time
t residenctime R
T temperature
T ambient tempo
T sensor temph
V volume
V inner volume of the capillary C
V flow volume F
V molar volume M
..V oxygen vacancy with a charge of +2 O
% per cent
’ inch
V
List of abbreviations:
A/D analogue / digital
amu atomic mass unit
DSMS dynamic sampling mass spectrometer
FID flame ionisation detector
GC gas chromatography
GC/MS gas chromcoupled with mass spectrometry
IPC Institute of Physical Chemistry
MFC mass flow controller
MID multiple ion detection
MOX metal oxide
PCB printed circuit board
pH potentia hydrogenii
ppb parts per billion
ppm parts per million
QIC quick inlet capillary
RGA residual gas analyser
r. h. relative humidity
V2A stainless steel alloy
VI