13. Bouncing Flame

8/3/2019 13. Bouncing Flame

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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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++

++

+++

+

+



+ -


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++

+++

++

++



+ -


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+ -


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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/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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13. Bouncing Flame

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