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

Abstract

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°to 40°. 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°and the lowest value of the heat-transfer coefficient was obtained for the angle of 40°at the surface temperatures of around 200°C. Keywords: spray cooling, flat-jet nozzles, impact angle, water impingement density, Leidenfrost temperature Ohlajanje vertikalno premikajo~ih se trakov se pogosto uporablja za zagotovitev zahtevanih lastnosti materiala. Kadar je potrebna velika intenzivnost hlajenja, se uporablja ohlajanje z brizganjem vode. Laboratorij za prehajanje toplote in tok fluidov je opremljen s preizkusno napravo, ki omogo~a vertikalno premikanje eksperimentalne plo{~e (jeklo). Preizku{eni sta bili dve razli~ni dimenziji {ob pri razli~nih tlakih vode in razli~nih kotih pr{enja vode (nagibni kot palice za brizganje). Obmo~je tlaka vode je bilo med 2 bar in 9,3 bar, kot vodnega curka pa med 20°in 40°. Za vsak poskus je bila ocenjena odvisnost koeficienta prehajanja toplote od temperature povr{ine. Dobljeni so bili zanimivi rezultati iz primerjave eksperimentalnih podatkov, ki ka`ejo, da koeficient prehajanja toplote in Leidenfrostova temperatura nara{~ata z ve~anjem tlaka vode. Zanimive rezultate smo dobili tudi pri poskusih z razli~nimi vpadnimi koti. Najvi{ji koeficient prehajanja toplote je bil dose`en pri kotu 20°, najni`ja vrednost koeficienta prehajanja toplote pa je bila dose`ena pri kotu 40°p ri temperaturi povr{ine okrog 200°C. Klju~ne besede: hlajenje z brizganjem, {obe s plo{~atim curkom, vpadni kot curka, gostota udarca vode, Leidenfrostova temperatura

optimal hydraulic descaling

“…This finding is consistent with the statement that a maximum possible heat transfer coefficient value exists for forced convection and convection with phase change [16]. The heat transfer coefficient is also a function of surface temperature during water cooling and the increase in water pressure also raises the Leidenfrost temperature [17]. The situation during descaling can be even more complex when the authors consider the presence of oxides on the surface [18,19] and surface roughness [20] when studying heat transfer.…”

Heat treatment of thin sheets, research methodology to design a cooling system

“…It is quite clear. Interesting are results shown in Figure 7 on the right [16]. There were tested various water impact angles (water knife).…”

“…Figure 7Heat transfer coefficient dependence on the surface temperature, influence of the water pressure on HTC and water impact angle[16] …”

Quantifying the Parameters Influencing Heat Transfer during Quenching Of Metal Plate

“…The authors have studied the influence of various parameters like water flow rate, casting speed and the kind of alloy. Hnizdil et al (2014) [8] studied the influence of impact angle and pressure on a vertically moving hot steel sheet with sprays. Beck et al 1985 [9] used inverse heat conduction technique for estimating heat flux on the surface of a conduction medium through the use of temperature measurements from experiments.…”