Intercomponent Heat Transfer of Dispersed Materials in a Plasma Reactor

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 eratlng P 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 Tange 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 e % e 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 t8s device is 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 chamber 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 tangenfial 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 Of the 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/: