INFLUENCE OF THE WATER TEMPERATURE ON THE COOLING INTENSITY OF MIST NOZZLES IN CONTINUOUS CASTING

摘要

Small mist nozzles used in continuous casting were tested for heat-transfer intensity. These nozzles are used in the secondary cooling area of a steel slab casting machine. The impact pressure distribution was measured first. The laboratory measurements of the cooling intensity (the HTC distribution) were performed with a variable water temperature. A temperature range from 20 °C to 80 °C was used in the tests. Surprisingly, the water temperature was found to have a strong influence. The most noticeable effect is a shift in the Leidenfrost temperature to low temperatures. Changing the water temperature from 20 °C to 80 °C caused a change in the Leidenfrost temperature of 130 °C. This can be significant and can change the cooling character of the continuous casting machine. It is interesting that with an increase in the cooling intensity, following an increase in the water temperature in a high-temperature region (above the Leidenfrost temperature), there is a small difference of about 30 W/(m~2 K). Surprisingly, high differences in the Leidenfrost temperature were found for an intensive cooling, where a difference of only 20 °C in the coolant temperature makes a difference of about 100 °C in the Leidenfrost temperature. The results of the experiments performed with an elevated water temperature showed a high sensitivity of the cooling intensity to this parameter. The decreasing effect of the cooling intensity related to the water temperature is more important for the spray cooling of high intensities.