Intensifikace sekundárního chlazení přítomností oxidů

Intensification of spray cooling by presence of oxides

conference paper

en

Spray cooling is a common technique used in continuous casting and other metallurgical processes where controlled temperature regimes are required. Cooling intensity is primarily affected by spray parameters such as pressure and coolant impingement density. Although not well known, thin layers of oxides can significantly modify the cooling intensity. This effect is dominant in the cooling of steel surfaces at high surface temperatures. Experimental investigation comparing the cooling of scale-free surfaces and oxidized surfaces show a difference of 50-80% in the cooling intensity. Even a scale layer of several microns can significantly modify the cooling intensity. It is not obvious but the scale layer can, in some specific cases, increase the cooling intensity. A low thermal conductivity of the oxides makes the cooling more intensive. The paper provides experimental evidence of this fact and details the mechanism of spray cooling with boiling. The Leidenfrost phenomenon and change in surface temperature provides a key to the explanation of why the hot surface covered by the oxides is frequently cooled more intensively than the clean surface. It is difficult to predict whether the presence of scales can intensify cooling due to a number of parameters which must be considered. Use of a neural network seems to be a way of estimating a scale effect on the intensity of heat transfer.

Sprchové chlazení je ve velké míře používáno v ocelářství a metalurgii tam, kde je nutné řízeně ochlazovat horké povrchy. Intenzita chlazení je ovlivněna především tlakem ,průtokem a typem trysky. Bylo však zjištěno, že vrstvy okují může výrazně ovlivnit intenzitu chlazení a to takovým způsobem, že chlazení je intenzivnější. Dokonce i vrstva oxidů o síle několika mikronů může takto intesifikovat přenos tepla. Článek poskytuje experimentální důkaz existence tohoto jevu. Jev je v článku vysvětlen pomocí numerického modelu a rozboru vlivu Leidenfrostovy teploty.

Spray cooling is a common technique used in continuous casting and other metallurgical processes where controlled temperature regimes are required. Cooling intensity is primarily affected by spray parameters such as pressure and coolant impingement density. Although not well known, thin layers of oxides can significantly modify the cooling intensity. This effect is dominant in the cooling of steel surfaces at high surface temperatures. Experimental investigation comparing the cooling of scale-free surfaces and oxidized surfaces show a difference of 50-80% in the cooling intensity. Even a scale layer of several microns can significantly modify the cooling intensity. It is not obvious but the scale layer can, in some specific cases, increase the cooling intensity. A low thermal conductivity of the oxides makes the cooling more intensive. The paper provides experimental evidence of this fact and details the mechanism of spray cooling with boiling. The Leidenfrost phenomenon and change in surface temperature provides a key to the explanation of why the hot surface covered by the oxides is frequently cooled more intensively than the clean surface. It is difficult to predict whether the presence of scales can intensify cooling due to a number of parameters which must be considered. Use of a neural network seems to be a way of estimating a scale effect on the intensity of heat transfer.

sprchové chlazení, okuje, koeficient přestupu tepla, intenzita chlazení

spray cooling, oxide scales, heat transfer coefficient, cooling intensity

2013

04.04.2013

Tanger spol. s.r.o.

Ostrava

978-80-87294-37-6

Oceláři

1

113–118

5