Sprchová chladící jednotka pro tepelné zpracování plechů z ušlechtilé ocele

Spray Cooling Unit for Heat Treatment of Stainless Steel Sheets

journal article in Scopus

en

Stainless steel sheets are successively heated to a temperature of 1150degree of Celsia and cooled until ambient temperature during the production process. Requirements for high cooling rates of stainless steel sheets producers lead to use water as a cooling medium. The information about cooling intensity (heat transfer coefficient) of different nozzles configurations is necessary for designing cooling sections. Although many researchers deal with water spray cooling, actually a general correlation for predicting heat transfer coefficient for wide range of nozzles configurations does not exists. That is the reason why heat transfer coefficient for different nozzles configurations can be only obtained by laboratory measurements. Heat transfer coefficient is mostly influenced by water impingement density and impact velocity. However other factors e.g. water temperature and velocity of the sheet can influence the heat transfer coefficient. Optimized design of the cooling unit with high cooling intensity and low water consumption was achieved by appropriate choice of these parameters. The moving experimental sheet was cooled from a temperature of 900 degree of Celsia to a temperature of 50 degree of Celsia with various configurations of nozzles. The tests shown that heat transfer coefficient was increasing with water impingement density and impact velocity. Increasing water temperature from 20 degree of Celsia to 80 degree of Celsia caused a decrease of the heat transfer coefficient and Leidenfrost temperature. The effect of velocity is negligible when velocities are between 25 and 100 m/min. The cooling unit was designed according to laboratory measurements to fulfill the stainless steel producer's requirements. The measurements which were done in an industrial plant confirmed the accuracy of heat transfer coefficient obtained in the laboratory. The maximum difference between laboratory and plant measurements was 15%.

Nerezové oceli jsou ohřívány na teplotu 1150 stupňů Celsia a po té zchlazeny až na okolní teplotu. Kvůli požadavku na vysokou intenzitu chlazení je použita voda jako chladicí médium. Pro výrobu chladicích sekcí je tedy nutné znát intenzitu chlazení pro různé konfigurace trysek. Velké množství článků ohledně této problematiky je možné najít v dostupné literatuře, avšak neexistuje žádná obecná korelace k predikci součinitele přestupu tepla pro velmi široké spektrum trysek a jejich uspořádání. Z tohoto důvodu je laboratorní měření jedinou možností jak zjistit součinitel přestupu tepla. Ten je mnohdy ovlivněn hustotou dopadající vody, dopadovou rychlostí, teplotou vody, rychlostí průjezdu plechu apod. Vhodnou volbou těchto parametrů bylo vyrobeno chladicí zařízení, které dosahuje vysokých chladicích intenzit a nižší spotřeby vody. Pohybující se plechy byly zchlazeny v rámci laboratorních měření z teploty 900 stupńů Celsia na teplotu 50 stupňů Celsia pro velké množství různých parametrů. Tyto testy ukázaly, že součinitel přestupu tepla roste s rostoucí hustotou dopadající vody. Nárůst teploty vody z 20 stupňů Celsia na 80 stupňů Celsia způsobil pokles Leidenfrostovy teploty. Vliv rychlosti plechu byl zanedbatelný pro různé rychlosti v rozmezí 25 – 100 m/min. Na základě těchto poznatků byla vyrobena chladicí linka, která splňovala požadavky výrobce nerezové oceli. Měření, které byly provedeny v ocelárně, potvrdily přesnost simulací a měření udělaných v laboratoři. Maximální rozdíl mezi získanými výsledky v laboratoři a mřeními v ocelárně byly nižší než 15%.

Stainless steel sheets are successively heated to a temperature of 1150degree of Celsia and cooled until ambient temperature during the production process. Requirements for high cooling rates of stainless steel sheets producers lead to use water as a cooling medium. The information about cooling intensity (heat transfer coefficient) of different nozzles configurations is necessary for designing cooling sections. Although many researchers deal with water spray cooling, actually a general correlation for predicting heat transfer coefficient for wide range of nozzles configurations does not exists. That is the reason why heat transfer coefficient for different nozzles configurations can be only obtained by laboratory measurements. Heat transfer coefficient is mostly influenced by water impingement density and impact velocity. However other factors e.g. water temperature and velocity of the sheet can influence the heat transfer coefficient. Optimized design of the cooling unit with high cooling intensity and low water consumption was achieved by appropriate choice of these parameters. The moving experimental sheet was cooled from a temperature of 900 degree of Celsia to a temperature of 50 degree of Celsia with various configurations of nozzles. The tests shown that heat transfer coefficient was increasing with water impingement density and impact velocity. Increasing water temperature from 20 degree of Celsia to 80 degree of Celsia caused a decrease of the heat transfer coefficient and Leidenfrost temperature. The effect of velocity is negligible when velocities are between 25 and 100 m/min. The cooling unit was designed according to laboratory measurements to fulfill the stainless steel producer's requirements. The measurements which were done in an industrial plant confirmed the accuracy of heat transfer coefficient obtained in the laboratory. The maximum difference between laboratory and plant measurements was 15%.

tepelné zpracování, součinitel přestupu tepla, chlazení desky, intenzita chlazení, chlazení tenkých plechů, vodní chlazení, nerezová ocel

Heat treatment, heat transfer coefficient, strip cooling, cooling intensity, sheet cooling, spray, water cooling, stainless steel

2014

22.05.2014

Trans Tech Publications

Switzerland

1022-6680

936

1

1720–1724

5