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Place a flame (e.g.from a Bunsen
burner) between twocharged parallelmetal plates.Investigate themotion of the flame
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2 aluminium plates 30x30 cm
distance between plates 5-12 cm
bunsen burner
premixed flame - variable oxydationrate
variable size of flame
voltage source 0-20kV
isolation box
preserves from air fluctuations
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Voltage source
Bunsenburner
Plates
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recorded with highspeed camera 420fps
videos wereanalyzed
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flame always leans towards the plate
oscillations start when it touches plate
flame oscillates between plate and center
(not between and + plate)
some soot stays on plates
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+ -
t = 0 ms
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t = 8,3ms
+ -
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t = 12,5 ms
+ -
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t = 16,7 ms
+ -
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t = 20,83ms
+ -
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t = 25 ms
+ -
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t = 33,3 ms
+ -
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t = 37,5 ms
+ -
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t = 41,7 ms
+ -
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t = 45,8 ms
+ -
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t = 50 ms
+ -
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t = 54,2 ms
+ -
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t = 58,3 ms
+ -
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t = 62,5 ms
+ -
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t = 66,7ms
+ -
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t = 70,8 ms
+ -
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t = 75 ms
+ -
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t = 79,2 ms
+ -
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t = 83,3 ms
+ -
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t = 87,5 ms
+ -
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t = 91,6 ms
+ -
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t = 95,8 ms
+ -
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t = 100 ms
+ -
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t = 104,1 ms
+ -
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t = 108,3 ms
+ -
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-
t = 112,5 ms
+ -
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t = 116,6 ms
+ -
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t = 120,8 ms
+ -
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t = 125 ms
+ -
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t = 129,1 ms
+ -
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t = 133,3 ms
+ -
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t = 137,5 ms
+ -
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t = 141,6 ms
+ -
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t = 145,81 ms
+ -
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t = 150 ms
+ -
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t = 154,1 ms
+ -
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t = 158,3 ms
+ -
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positively charged particles positive ions
e.g. CHO+, C3H3+...
Negatively charged particles
Electrons
invisible for human eye
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neutral thermal ionization positively charged soot
Much bigger both positive ions and electrons
black body radiation 1500 K
yellow/orange color of flame
what we see as flame are soot particles
motion of the flame = motion of the soot particles
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++
++
++
+
++
+
Flame consist of soot particles
Thermal ionization positive soot particles +
+ -
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++
++
++
+
++
+
positive soot particles are attracted to plate
flame moves towards plate--
+ -
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++
++
+++
+
+
positive soot particles are attracted to plate
flame moves towards plate--
+ -
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++
+++
++
++
positive soot particles are attracted to plate
flame moves towards plate--
+ -
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positive soot particles are attracted to plate
flame moves towards plate--
+ -
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-
-
-
flame touches plate equalizaing of potenital
soot becomes negatively charged-
-
- -- -
-
+ -
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negative soot is attracted to plate
essenital fo the effect restoring force
- ---
+
- --
+ -
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- ---
attractive forces are equal
flame is in the center
--
+ -
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but new positive soot particles are produced
- --- -
-
+ -
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more positive soot particles but negativesoot particles stay in the flame
Attractive force of positive soot particlesand plate becomes dominant again
-
- --- - -
-
+ -
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- ---
flame moves towards plate
cycle is finished!-
--
+ -
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thermal ionization positively charged soot flame moves towards plate
flame touches the - plate
soot becomes negatively charged flame moves towards the + plate
-soot causes the restoring force oscillations!
more + soot is produced attractive force of plate becomes dominante
again
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oxydized flame complete combustion
no soot particles
flame leans towards
plate due to positive ionsbut doesnt oscillate
no effect!
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motion of the flame is not uniform assumption: we can consider mean acceleration
If this assumption is valid:
+-
d
d - half of distancebetween plates
- mean acceleration
T period
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regular oscillations
too big distance
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Flame moves towards plate soot is positevly charged due
to thermail ionization
charge doesnt depend onelectric field
+ -
+
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flame touches the plate
each soot particle is now onsame potential as the plate
charge of the sphere onpotential U
+ -
-
---
-
--
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from center to - plate
- plate attracts + soot
+ plate attracts
-soot
from - plate to center
+ plate attracts -soot until more + soot is produced
+-
+-
--
--
----
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matches with
theoretical model!
same value of !
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in flame there are alsoelectrons
very light and small
move from flame to + plateand fromplate to theflame
motion of electronsbetween plates
Current!
+ -
-
-
--
-
-
- -
-
-
-
--
-
-
-
--
-
-
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- +
+-
100 k
10 M
V
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mean current
peaks occur eachtime flame touches
the plate
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changed height of flame
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linear dependence
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Effect achieved oscillations of flame in electric field
flame oscillates between plate and center
negative soot particles are essential for this effect restoring force
No effect in oxydized flame
Designed experimental set up for recording and analyzingmotion of thr flame
Changed relevant parameters electric field, distance,size of flame, combustion rate
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Fristrom , R. M., The Johns Hopkins University Applied PhysicsLaboratory :Flame structure studies: past, present and future,Pure &Appl. Chem., Vol. 62, No. 5, pp. 839-849, 1990
Halliday,D., Resnick,R., Walker, J. : Fundamentals of Physics, 6th Edition,2007
Jensen, W.B. The origin of the Bunsen burner J. Chem. Educ. 82, 4,518,2005
Onasch, Ahern, Lambe, Wright, Croasdale , Williams, Worsnop,Freedman , Davidovits, Boston College Aerodyne Research,Inc: Studiesof Black Carbon Particles: Characterization and Atmospheric Processing,
2003 Wikipedia: Flame, http://en.wikipedia.org/wiki/Flame
Wikipedia: Soot, http://en.wikipedia.org/wiki/Soot
http://en.wikipedia.org/wiki/Flamehttp://en.wikipedia.org/wiki/Soothttp://en.wikipedia.org/wiki/Soothttp://en.wikipedia.org/wiki/Soothttp://en.wikipedia.org/wiki/Soothttp://en.wikipedia.org/wiki/Soothttp://en.wikipedia.org/wiki/Flamehttp://en.wikipedia.org/wiki/Flamehttp://en.wikipedia.org/wiki/Flamehttp://en.wikipedia.org/wiki/Flame8/3/2019 13. Bouncing Flame
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Thank you for Yourattention!
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1) Burner is connected to plate
2) Burner is connected to + plate
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Video spojeno na +
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distance betweenplates is large
flame doesnt touchthe plate
flame just lean
towards the plate - nooscillations
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angle
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