Vliv dopadového úhlu a tlaku na sprchové chlazení vertikálně se pohybujících horkých ocelových povrchů

Influence of the impact angle and pressure on the spray cooling of vertically moving hot steel surfaces

journal article in Web of Science

en

The cooling of vertically moving strips is used very often to obtain the required material properties. Water spray cooling has to be used when a high cooling intensity is needed. Our Heat Transfer and Fluid Flow Laboratory is equipped with a testing device which allows vertical movement of a heated experimental plate (sheet). Two different sizes of flat-jet nozzles were tested with different water pressures and angles of the water impact (inclination angles of the spraying bar). The water-pressure range was between 2 bar and 9.3 bar and the angle of the water impact changed from 20 deg to 40 deg. The dependence of the heat-transfer coefficient on the surface temperature was evaluated for each experiment. Interesting results were obtained from the comparison of these experimental results, showing that the heat-transfer coefficient and the Leidenfrost temperature increase with the increasing water pressure. Very interesting results were obtained during the tests with different inclination angles. The highest heat-transfer coefficient was obtained for the angle of 20 deg and the lowest value of the heat-transfer coefficient was obtained for the angle of 40 deg at the surface temperatures of around 200 degrese of Celsius.

Chlazení vertikálně se pohybujících plechů se používá velmi často k získání požadovaných vlastností materiálu. Vodní sprchové chlazení se použít, když je potřeba vysoká intenzita chlazení. Laboratoř přenosu tepla a proudění je vybavena zkušebním zařízením, které umožňuje vertikální pohyb ohřátých vzorků. Dvě různé velikosti plochých trysek byly testovány s různými tlaky vody a úhly naklonění vodního paprsku. Rozsah testovaných tlaků vody byl mezi 2 až 9,3 bary a úhly dopadu vodního paprsku byly od 20 stupňů do 40 stupňů. Závislost součinitele přestupu tepla na teplotě povrchu byla vyhodnocena pro každý experiment. Bylo zjištěno, že součinitel přestupu tepla a Leidenfrostova teplota narůstají s rostoucím tlakem vody. Nejvyšší součinitel přestupu tepla byl získán pro úhel naklonění 20 stupňů a nejnižší hodnoty součinitele přestupu tepla byly získány pro úhel 40 stupňů při teplotách povrchu okolo 200 stupňů celsia.

The cooling of vertically moving strips is used very often to obtain the required material properties. Water spray cooling has to be used when a high cooling intensity is needed. Our Heat Transfer and Fluid Flow Laboratory is equipped with a testing device which allows vertical movement of a heated experimental plate (sheet). Two different sizes of flat-jet nozzles were tested with different water pressures and angles of the water impact (inclination angles of the spraying bar). The water-pressure range was between 2 bar and 9.3 bar and the angle of the water impact changed from 20 deg to 40 deg. The dependence of the heat-transfer coefficient on the surface temperature was evaluated for each experiment. Interesting results were obtained from the comparison of these experimental results, showing that the heat-transfer coefficient and the Leidenfrost temperature increase with the increasing water pressure. Very interesting results were obtained during the tests with different inclination angles. The highest heat-transfer coefficient was obtained for the angle of 20 deg and the lowest value of the heat-transfer coefficient was obtained for the angle of 40 deg at the surface temperatures of around 200 degrese of Celsius.

sprchové chlazení, trysky s plochým paprskem, dopadový úhel, hustota dopadající vody, Leidenfrostova teplota

spray cooling, flat jet nozzles, impact angle, water impingement density, Leidenfrost temperature

2015

01.05.2015

Insitute of Metals and Technology, Ljubljana, Slovenia

LJUBLJANA SLOVENIJA

1580-2949

49

3

333–336

4