Spray water cooling heat transfer under oxide scale formation conditions

Abstract

Spray water cooling is an important technology used for the cooling of materials from temperatures up to 1800K. The heat transfer coefficient (HTC) in the so-called steady film boiling regime is known to be a function of the water mass flow density. Below a specific surface temperature T L , film boiling becomes unstable and the HTC shows a strong dependence on temperature (Leidenfrost effect). The HTC was measured by an automated cooling test stand (instationary method). Compared to the previous state-of-the-art, an additional temperature dependency in the high temperature regime was found. A new analytic fit formula for the dependence of the heat transfer coefficient on temperature and water impact density is proposed and discussed.Spray water cooling of steel materials at temperature levels above 1000K introduces additional effects due to the formation of oxide layers (scale). These effects and experiments under scale formation conditions will be presented and discussed.

An integrated thermal model of hot rolling

“…According to [28], the heat transfer coefficient additionally depends on the surface temperature. In addition to the mass flow also the difference between the surface and the water temperature influences the heat transfer coefficient as it is reported in [8,29]. In [4], the heat flux is modelled as a function of the volume flow and the water temperature.…”

“…The first pyrometer measurement up (t meas,1 ) after the first roll pass (pyrometer 1 in Figure 1) is used to correct the temperature profile by adding the error T up = up (t meas,1 ) − T up (t meas,1 ) to the whole profile, i.e., Downloaded by [Umeå University Library] at 20:14 04 April 2015 (y, t meas,1 ) = T(y, t meas,1 ) + T up (29) Using the adapted temperatureT(y, t meas,1 ) as new initial temperature, the process is simulated without further adaption, until the pyrometer 2 (see Figure 1) measures for the first time. Then, the temperature is again adjusted using the measured temperature up (t meas,2 ) in the same way as in Equation (29). With this simple adaption strategy, a good agreement of simulation and measurement data is achieved as can be seen in Figure 10.…”

Suppression of the Leidenfrost Phenomenon by Superhydrophilic Graphene Nanobush

“…The metal oxidation at high temperatures provides additional resistance to the heat transfer due to the formation of an oxide layer, which signi cantly reduces the heat transfer rate during spray cooling 34,35 .…”

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

“…The oxidation layers have been known to influence the onset of transition boiling for the immersion cooling [14]. Several investigators [16,17] have observed the influence of the oxide layer on the heat transfer coefficient during water spray cooling, but they have not studied the effect of the oxide layer to the Leidenfrost temperature. The present paper deals with the change of the Leidenfrost temperature due to the presence of an oxide layer.…”