Model experiments of mixing in steel ladles with continuous addition of the substance to be mixed

The process of alloying steel melts in ladles consists of the three partial steps alloy addition, alloy solution, and alloy mixing. Addition and dissolution together can be simulated approximately by continuous addition of a dissolved substance to be mixed. In this way, the mixing process during alloying can be captured separately. The process was studied in model experiments with continuous addition of NaCl solution to water in a 0.18 m3 cylindrical acrylic glass vessel. The water was stirred by air injection through an eccentrically positioned nozzle in the bottom. The added amount of NaCl was 40 cm3 of a 20% aqueous solution. The addition time was varied. The NaCI concentration in the water vessel was continuously measured with electrical conductivity probes at 12 different positions. From the thus obtained concentration‐vs.‐time curves, the mixing times were determined. They were studied for stirring gas rates between 100 and 700 cm3/min(STP) and for various addition times of the indicator. The measured mixing times depended on the gas stirring rate. They were also functions of the indicator addition time and decreased with increasing addition time until they became zero or negative. Trials where NaCI was added in form of a melting, NaCI containing ice sphere, yielded negative mixing times, which means that melting is slower than mixing. A theoretical model to describe mixing with continuous addition is presented. Besides the measurement of the mixing process, the three main flow directions of the indicator solution when it leaves the injection nozzle were documented by a video camera. They were associated to the concentration curves measured at the conductivity probes to which the flow was directed. It was found that concentration maxima occurred on the curves when the flow was directed to the respective measuring probe. The duration of the maxima coincided almost always with the duration of the flow directions. Der Prozeß des Legierens von Stahlschmelzen in Pfannen besteht aus den drei Teilschritten Legierungszugabe, Legierungsauflösung und Legierungsvermischung. Zugabe und Auflösung zusammen können näherungsweise durch die kontinuierliche Zugabe einer gelösten Substanz, die vermischt werden soll, simuliert werden. Dadurch läßt sich der Mischungsprozeß beim Legieren getrennt erfassen. Der Prozeß wurde in Modellversuchen mit kontinuierlicher Zugabe von NaCl‐Lösung zu Wasser in einem 0,18 m3 Plexiglaszylinder studiert. Das Wasser wurde durch Einblasen