DFG Project PF 394/11–1

Use of numerical and physical simulation on multi-phase flows and particle separation in tundishes as a contribution to increased cleanness of steels

An inves­ti­ga­ti­on of the melt flow in a steel mill is near­ly impos­si­ble due to the high tem­pe­ra­tures and a lack of opti­cal acces­si­bi­li­ty. For this reason, phy­si­cal and nume­ri­cal simu­la­ti­ons have to be done. Water can be used for the phy­si­cal simu­la­ti­on becau­se the kine­ma­tic vis­co­si­ties of liquid steel and water are com­pa­ra­ble, thus the flow of both fluids is simi­lar. Con­side­ring the simi­la­ri­ty laws, the results for water model­ling can be trans­for­med to the real pro­cess. A series of expe­ri­men­tal tests have been car­ri­ed out in a 1:3 sca­le water model of a sin­gle-strand tun­dish. The sepa­ra­ti­on of par­tic­les in water, depen­ding on their size, has been deter­mi­ned. The sepa­ra­ti­on rate is esti­ma­ted for par­tic­les with dia­me­ters of dP = 1–200 μm. Moreo­ver the influence of major fac­tors – like cas­ting speed and flow regu­la­tor, on the sepa­ra­ti­on rate of the par­tic­les is inves­ti­ga­ted. The phy­si­cal model­ling shows the depen­dence of the sepa­ra­ti­on rate from the­se fac­tors. The sepa­ra­ti­on rate can be impro­ved by decre­asing the volu­me flow rate or by an impact pad installation.

Expe­ri­men­tal results were used to veri­fy the mathe­ma­ti­cal model, which is used to pre­dict the non-metal­lic inclu­si­on dis­tri­bu­ti­on and sepa­ra­ti­on in steel, and in con­se­quence to impro­ve its puri­ty. The results of the liquid flow field obtai­ned for nume­ri­cal simu­la­ti­ons are found in a good agree­ment with the expe­ri­men­tal tests results, obtai­ned by DPIV tech­ni­que. In terms of dis­crete pha­se model­ling (par­tic­les in water), the stan­dard boun­da­ry con­di­ti­on (trap/reflect) available in FLUENT code is not sui­ta­ble to model com­plex phy­si­cal phe­no­me­na occur­ring on the steel-slag (water-air) or steel-refrac­to­ry lining inter­faces. For this reason, the modi­fied boun­da­ry con­di­ti­ons for par­tic­le sepa­ra­ti­on on a free sur­face and at the bot­tom and side walls of the tun­dish — cal­cu­la­ted from the equi­li­bri­um of gra­vi­ty, buoyan­cy and drag forces acting on a par­tic­le in the flu­id are used. Results obtai­ned with UDF func­tion give a simi­lar dis­tri­bu­ti­on of the par­tic­le sepa­ra­ti­on rate as an expe­ri­men­tal stu­dy in the water model. Sin­ce the mathe­ma­ti­cal model­ling results are fin­ding in a good agree­ment with phy­si­cal one, the model is used to pre­dict the sepa­ra­ti­on rate of the non­me­tal­lic inclu­si­ons in steel bath. Based on that model, one can attempt to deter­mi­ne the opti­mal working con­di­ti­ons for the inves­ti­ga­ted tun­dish, which could yield to bet­ter steel quality.

Logo DFGThe pro­ject was fun­ded by the Deut­sche For­schungs­ge­mein­schaft (DFG) under the refe­rence num­ber PF 394/11–1.