Influence of oxide scales on heat transfer in secondary cooling zones in the continuous casting process, part 1: heat transfer through hot‐oxidized steel surfaces cooled by spray‐water

Abstract

For the cooling of steels in the continuous casting process it is necessary to know the heat transfer from the solidifying strand to the cooling water to enable calculation of the secondary cooling zone. Previous investigations have only determined this variable for non-oxidizing metallic surfaces. For many steels cast in practice, however, the formation of oxide layers prevents a direct transfer of the previous results. In the present research the influence of the oxide layers on the heat transfer has been investigated for spay-water cooling. Results have shown that heat transfer in the range of stable film boiling is determined for a constant spray-water temperature in the same way as for non-oxidizing metals, i.e. using the water mass flux density fils only. The changed surface qualities resulting from the oxide formation cause the Leidenfrost temperature, however, to shift considerably to higher values.

Effects of oxide layer on Leidenfrost temperature during spray cooling of steel at high temperatures

“…The heat transfer on the oxidized sample is described by the concept of an effective heat transfer coefficient (EHTC) (h eff ) which was introduced by [17,18]. This concept is extended to the Leidenfrost temperature, while an effective Leidenfrost temperature (T L eff Þ is also introduced here.…”

Spray water cooling heat transfer under oxide scale formation conditions

“…Following the initial considerations and the basic knowledge on scale properties (e.g. [4]), the determination of the influence of scale on the heat transfer conditions introduces some difficulties due to the following reasons:…”

“…It can also be used for any general heat flow q by using a function for α depending on the same parameters as q. In the so-called steady film boiling regime, α is known to be a function of the water mass flow density [1,2,3,4]. Below a specific surface temperature T S,L , the heat transfer coefficient shows a strong dependence on temperature (Leidenfrost effect [5]).…”

Transferencia de calor en la colada continua de aceros. II parte. Enfriamiento secundario

“…Sin embargo, estos resultados obtenidos en laboratorio no son directamente trasladables a las condiciones de planta. Los mismos autores (25) encontraron además que, en el caso de mantenerse una película estable de vapor, la presencia de una capa de óxido modifica la transferencia de calor sólo cuando dicha capa se mantiene adherida a la superficie y cubriendo más de un 90 % de la misma. En tal circunstancia, se debe considerar la resistencia térmica aportada por el óxido (26).…”