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INTERCOMPONENT HEAT TRANSFER OF
DISPERSED MATERIALS IN A PLASMA REACTOR
A. Mosse, Ye. Yermolayeva, A. Knak, I. Dvindenko
To cite this version:
A. Mosse, Ye. Yermolayeva, A. Knak, I. Dvindenko. INTERCOMPONENT HEAT TRANSFER OF DISPERSED MATERIALS IN A PLASMA REACTOR. Journal de Physique Colloques, 1990, 51 (C5), pp.C5-237-C5-243. �10.1051/jphyscol:1990529�. �jpa-00230836�
INTERCOMPONENT HEAT TRANSFER OF DISPERSED MATERIALS IN A PLASMA REACTOR
A.L. MOSSE, Y0.M. YERMOLAYEVA, A.N. KNAK and I.A. DVINDENKO
Luikov Heat and Mass Transfer Institute, BSSR Academy of Sciences, Minsk, U.S.S.R.
Resume : Les resultats d'une Btude experimentale relative au transfert entre la phase particulaire et une chambre de melange multi-jets. L'effet du flux massique de particules sur le flux de chaleur aux parois est mis en evidence. Les r6sultats expbrimen- taux sont repr6sentbs sous forme adimentionnelle.
Abstract -The results are reported of the experlmental investigation ertalning to the interphase heat exchange of the particles of ilspersed materlal In the plasma reactor wlth multl-jet mixing chambers. The effect Is established of the mass flow rate concentratlon of the dlspersed ma'lerial on the heat flux to the reactor walls. The experimental data on the inte hase heat exchange of varlous particles are unlfled in a crlterial %m.
The efficiency of treati the dispersed materials in plasma units depends on the thermal physlc%? characterlstlcs of lasma and materlal,
R
the ratio of their mass flow rates, organization of t e rocess of mixing che particles wlth the flow and ultimately it Is getermlned by the intercomponent heat exc the lasma flow and the particles of diverse.
the dlsperseci on wEich are scarce In number and To enhance the Intercomponent heat exchange between dlspersed materials and plasma flows, varios constructlons of plasma reactors are desl ed. One of the most perspective seems to be the plasma reactor with a m8l-jet mlxing chamber - a plasma module. Already In the most slmple deslgn, a three-jet mix chamber (the plasma module) Is characterized by the ca ability of form
9
ng the plasma flow with a fairly uniform temperarure and velocity profiles.Besides, wlth such a mixing chamber it is possible tg organlze any technique of the dlspersed materlal input to the reactor, to raise the reactor power by lncreaslng both the total number of pla~matrons and lndlvldual power of each of them, as well as to arrange single
-,
two - and multi-module reactors based on the multi-jet mixlng chamber. All this facllltates the lnprovement of thelr efflciency, the Increase in the total power and the ex anslon of the osslbllity of technological em loyment.B
The posslbi~lty Is studie of monltorlng the structure
OF
the plasma flow formed In cylindric and conic mlxlng chambers /l/, which, as evldent from Flg.1, was ensured by the varlatlons in thelr geometry, by the method of the input of the plasma jets to the mixlng chamber, by the o eratlngP
mode and structural features of lasmotrons. The plasma jets were ed Into the mlxing chamber radlally and !angentlally. Geometry of the conic mlxlng
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1990529
COLLOQUE DE PHYSIQUE
chamber was varied by altering the apex angle.
Investigation of the structure of the plasma flow, formed in varlos mixing chambers, is conducted by spectral methods /2/ and with the aid of an enthalpy gauge 3 The overall electric power input to three lasmotrons varied from 100 to 200 kW, the mean mass enthal ies and
!emperatures of the lasma flow constituted b-~ this section 10.g
-
16.0 W g and 5000-
5708 X, respectively, at the total flow rate of the plasma-form1 gas (air) r ing from 3.0 to 8.0 /S.Figure
??
gives the T a n g e In the relatfve temperature T/Tmax de ending on the relative radius at the exit from the cylindric (with rasial and tangential jet input) and the conlc (with radial jet in ut) mixlng chambers. The comparative data obtained verify the prevBous conclusions about nonuniformity of the temperature profile in conic and tangential mixing chambers. At the same time, the data of work /4/ provide the explanation (only qualitative for the time be1 ) of the higher efficiency of the conic mix? chamber, as compared toyhe cylindric one, due to the deformation of he lasma flow (and of the corresponding tem erature prof lle) , formed in tie multl-jet conic mixing chamber. This leass to the necessity of allow for the information obtained when studying the intercomponent heat ee% between the plasma flow and the particles of the dispersed material. From thls point of view, the most preferable is profile 1 (Fig.2) formed in the cylindric mix1 chamber with radlal input of plasma jets, however, the efficiency of t 8 s deviceis lower due to the Increase in the heat losses to the walls.
In the conic mixlng chamber, the efficiency is higher and the maximum temperature is reached on the axis, which determines the most preferable zone of the treated material in ut. When the material is led in along the axls, wlth the cone of part%le scattering taken into account the temperature ?file will equalize across the mixin& chamber sectldn. in connection W th which the particles should be in ide lcal conditions.
The axial input of the material treated to the t ential mixing cham- ber is apparently inex edient, it should be shifted to%e zone of maximum tem eratures-Probably ,!in thls case preference should be given to the tan- genfial input in the plane erpendicular or obllquely to the reactor axis.
Since heat transfer ?room plasma to the particle of the dis ersed material is a limiting factor of lasma processes, investlgatlons d o the intercomponent mass exchange
R
the hlgh-temperature flows is of considerable interest.The particle heating in the {lasma jet when Kn 1 (Kn is the Knudsen number) Is mainly determined y the convective heat exchary and characterzed by the Nwselt number, Nu = J"(Re,Pr), the select on of values for which encounters some difficulty.
A number of works is known concerning the study of heat exc
7
Ofthe high-temperature gas flows wlth individual stationary / 5 - 7 and free-moving spheres in the form of globular probes or plates /8 - 11/, and also with moving fine articles of the dis ersed material /3,12,13/. Heat
B 7
exchange was considere in the arc /3,5 - 3/ and high-frequency /7,9,10/
plasma. The governing parameter was taken to be the mean mass tem erature of gas /3,12,13/, tern erature of the incldent flow /3,7.12,?3/ and temperature of the part?cle surface /9,10/ To define the heat1 of the S herical particles freely movl in piasma, the most commonly us% In the lgterature are the relations ofyhe form of the formulae /l 5/:
Nu = A Rem
PP,
(1 1as well as the formula of Ranz W.E..Marshall W.R./16/:
Nu = 2
+
0.6 R ~ O ' ~ where 0 < Re < 200 (2 )fixed S here with a high-tem erature flow for
9
he Reynolds number rang ng from 2 to 400 the relation/l/
can be recommended: ?leIn studies /17,18/, for small temperature drops the difference is ascertained between the flow heat exchange with a moving article and heat exchange with the equivalent stationary s here, which 7s attributed to dif ferent hvdrobmics at indent ical ~e&ds numbers for a S tationarv sphere and a m o v k particle.
This fact is ex erimentally verified in works /17,18/ over the range of the Reynolds num%ers 30 - 480 at bulk concentrations smaller than 3.5~4
o - ~ .
The following relations are obtained:NU = 0.186
In real plasma processes a multitude of particles of irregular sha e are treated which move in the flow with large temperature drops. ~{e thermal physical properties of such a flow are variable both in the direction of the particle movement and in the boundary layer on the article. Since the tern erature dro between gas and the article surface
%I
the plasma flow can Be corlsidera&e, the dependence of Reat transfer on the arameters of the boundary layer on the article is taken into account in s!udies /3,7,13,19/ by applying a correctPon for the convective term in the expression for Nu in the form of the parameterwhere the index "g" pertains to temperature of the gas flow and "S"
-
totemperature of the particle surface.
Work /Il/ suggested to Lntroduce the parameter
erimental data /12/ on the heating of fixed S herical articles of 0.15
9
mm diameter in plasma Jets allow one to use Formula(g)
in the formwhere B = 0.6 and 0.765 and n = 0.3 and 0.4 depending on the experimental conditions.
P l y 3 is demonstrated that, with increasing temperature drop, the conduct ve term can become negligible as agaist the convective term even at small Reynolds numbers.
The authors /9,10/ of the study concerning the . interphase heat exchange in high- fre uency plasma at the flow temperature of 6500 -7200 advise to employ the
?allowing
criteria1 relations without the conductiveCOLLOQUE DE PHYSIQUE
term, provided that the overnlng parameter Is assumed to be the plasma temperature on the particfe wall
for calculating heat transfer of nonmetalic particles and Nu
-
0.52 l3eO.l pro-'[
P, PS (8)
for metallc spheres.
The above-stated theoretical relations and the experimental data are compared in Fig.4.
Effect of concentratlon of the dispersed materlal particles in the gas flow on the Intercomponent heat exchange is established in a number of works in the conditions of small tem erature heads /1?,18/ and in the
conditions of plasma temperatures /3,1 ~ Z O /
In the current work effect Is studied-of the dispersed materials on heat
excY
e between plasma flows of various structures and the reactor channel wal S. It Is ascertained that, in all cases, leadlng mono- and olydlspersed particles of various dispersivity in the lasma flow at the Reating sta e decreases the mean mass temperature o? the flow at the expense of fhe heat sink to the particles, hereby decreasi the heat flux to the channel wall. The change in the heat flux considera%y depends on amount and, correspond1 ly, concentration of the dis ersed material.At equal power and concentrzion, the heat quantlty t r a n s k e d to the par- ticles of smaller dimension Is attributed to the larger contact surface.
As a result of processing the experimental data, the dependence is established of the mass flow rate concentration on the heat flux of plasma to the walls of mlxing chambers of various types in the form E, = f(p.,)
(FIg.5), where E is the relation of the heat flux to the walks of the multi-jet mixing chamber in the regime with the introduction of dlspersed P material to the heat flux and without it.
Wlthin the range of the mass flow rate concentrations of the raw material from 0.8 to 2.6 &/kg, the experimental data are approximated by the relations: for a cyllndrlc mixlng chamber wlth radial and tangential jet input
E = 0.76 p.i0.128
P (9
for a conic mixing chamber with radial jet input E = 0.778 pi0.05
P (1 0 )
Analyzing the relations obtained makes it clear that effect of the material concentratlon on heat exch e wlth the wall is more pronounced
%
in the cylinrklc mixlng chamber than the conic one. At the same time, the way of leadlng the lasma jets in the cylindric mixing chamber does not affect to any consi&able extent heat exchange of the dusted plasma flow, which Is explained by the slmllar, In both the cases, struture of the.boundary layer formed in mixlng the gas jets, stabilized (tangentially swirled) in lasmotrons /3/. h
Us? ?he suggested in /3/ technique based on the heat balance equatlon or two operating regimes-without and with the dlspersed material input-enabled is to determine: the varlatlon in the heat f l u to the walls of the mixing chamber and reactor,the alteration In the heat losses wlth exhaust gases and the heat quantlty transferred to the dlspersed material,
heating), noticeably depends on the mass concentration for both the types of dis ersed materlal.
T R ~
ex erlrnental data on the Intercom onent heat exchange are1"
generalized %y the proposed in /2/ crlterlal re atlon of the form
For mlxlnn chambers of varlous confl~atlons. these relations are W presented F1 4 (curve 7 and 8).
Thereby t%e posslblllty Is confirmed of employing relatlon (1 1 ) to predlct the intercomponent heat exchange between the dls ersed materlal particles and the plasma flow, formed In tile three-Jet rnlx? chamber.
Obtalned relatlons (9) - (1 l ) are used to calculabe %e reglmes of the dls ersed materlal treatment in the plasma reactors with various mlxlng c%ambers and to model the high-power plasma reactors.
REFERENCES
/l / Mosse A.L. ,Knak A.N. ,Yermolayeva Ye .M. , J. of Eng.Phys -52 (1 987) ,No .3.
pi?
/ /.
439-443. Knak A.N., Mosse A.L., Yennolayeva Ye.M., Extended abstracts of the IV All-Union Symposium on Plasmochemlstry,part I.Dnepropetrovsk,l984.pp.89-90 /3/ Mosse A.L., Burov I.S., Treatment of Dispersed Materials in Plasma Reactors.-Mlnsk,l980./4/ Burov I.S., Yermolayeva Ye.M., Zabrodln V.K., Mosse A.L.,Izv.Akad.Nauk BSSR. Ser. fiz. energ. nauk.-1983.No.4.-pp. 85-88.
/ 5 / Kubanek G.R.,ChevalIer P.,Gauvln W.H.,Canad.J.Chem. Eng. 46 (1968),No.
2, p .101-107.
/6/ gubanek C.R. , Gauvln W .H. , Chern. Eng. 46 (1 968), No -8, pp. 332-340.
/7/ Physics and Technology of Low-Temperature Plasma./Edited by S-V-Dresvlna. Moskow,Atomlzdat,l972, 352 p.
/8/ Roter V.,Kranz E.,Heatand Mass Trasfer. Moscow,Izd.Energlya, 1 (1968), p 404-41 6.
/g/
Dresvin S .V. ,Melnlk S. A. ,Mikhalkov S .M. , Izv. SO Akad. Nauk SSSR. Ser.tekhn.nauk. Vyp. 1.,1986 ,No. 4. pp. 69-77.
/10/ Dresvln S.V.,MIkhalkov S.M.,Lenerators of low-temperature plasrna.,2 (1 989 ) p . 266-267.
/l 1 / ~ o y a k L.S. ,Surov N.S. ,Flz. Khlm. Obr.Mater. 1969. No.2. p .19-29 /1 2/ Klubnlkln V.S. ,Kolganova I .V. ,Teploflz. Vysok. Temp. , l4 (?976), io .2,
.
408-41 0.7?3/ Burov I.S. ,Flz.Khlm.Obr.Nater., 4 (1'3'79) No 4, p. 42-49.
/l 4/ Tsvetlsov Yu.V. ,Panf llov S .A. ,Low-Temperature ~Yasma in Regeneration Processes. Moscow, Izd. Nauka,1980, 354 p.
/15/ Fay J.,Riddel F./Edited by V.L.Samuylov,Izd.Inostr.Llt.Moscow, 1959.
/16/ Ranz W.E. Marshal W.R.,Chem. .Pros. 48 (1952), No.2, p.173.
/17/ Gorbis Z.R. Heat exch e an
9
hydrodynamics of dispersed straight -through flows. Moscow, I z d T e r lya, 1970. ,423~./18/ Galershteln D.I., Stady of tge transfer processes In the devlces wlth
ps
suspension. Cand. Dls. Mlnsk,Heat and Mass Transfer Instltute of the SSR Academy of Sciences, 1966./19/ Klubnlkln V.S.,Transfer Phenomena In Law - Temperature Plasma. Mlnsk:
1969,1pp. 125-135.
1201 ermolayeva Ye. M. ,Knak A.N. ,Dvlndenko I .A. , Extended abstracts of the IV All-Unlon Symposium on Plasmochemistry, part 2,Dnepropetrovsk,l984, pp. 27-28.
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Fi . l Diagrams of various mixing chambers of a plasma reactor: a -
cy?in&lc, b - tangential, c - conic; 1 - plasmotron, 2 - mining chamber.
Fig.2. The relative tem eratures ofthe plasma flows, formed in the mlxl chambers of various con?igurations, reduced to unlt radlus at TA = 500%
( + 10%): 1 - cylidric chamber with radial jet Input, 2 - cylindric chamber with tangent-lal jet input, 3 - conic chamber.
Fig.3. Change of a correctlon for thermal conductivity denslty and viscosity ( E ) depending on temperatures of the high- temperature gas flow (Tg) for varlous temperatures of the particle surface (Ts). PP
/18/, 4 - NU 1.05 /6/, 2
-
Nu = 0.186 ~e:.~/17/, 3 - Nu = 0.22 Rep0.4
~ e pro-l3 ~ '/3/, ~5 - Nu = 0.52 Re0" ~r'.'[(~#~)/ ( P s y ~ ] - for metalic spheres /10/, 6 - Nu = 0.41 ~ e ~ ' ~ ~ r ~
)re
' * ~- for nonmetalic- - -
particles
/to/.
7, 8 - Nu = 2c1+
0.78 pro"&PP
&P
/ 3 / and the present study (7 - conic mixing chamber, 8 - cyllndric mixlng chamber), 9-
.the reglon of the ex erimental results for steel balls moving across the nitrogen plasma jet781.
Fig.5. Effect of the dlspersed material concentratlon on the heat flux from plasma to the mixing chamber walls at D = O.1m. d = 0.08mm; 1 - E
P
=0.778p;0'05 for conic chamber, 2 - E p = 0.76p;0.128 fo! cylindric chamber, 3 - for cyllndric chamber (cerium oxalate), 4 - for CYllndrIc chamber with tangential jet input (phosphorite).
