Spatial–temporal thermal‐fluid behaviors of microbubble emission boiling (MEB)

Abstract

We investigate non‐uniform behaviors in space of the microbubble emission boiling (MEB). Special attention is paid to radial temperature difference on the heated surface before/after the onset of the MEB. Correlation among the regimes of the MEBs, the radial temperature difference in the heated surface and the vapor bubble behaviors is indicated experimentally. We find that the surface temperature near the center becomes higher in the transition to the MEB, and then it becomes lower in the developed MEB. It is found that a linear correlation between the power input to the heaters and the resultant heat flux on the heated surface breaks in the transition of the MEB. The difference of the MEB regimes, S‐MEB and C‐MEB, is apparently distinguishable by monitoring the radial temperature difference of the heated surface.

Hysteresis in microbubble emission boiling (MEB) under highly subcooled conditions

“…Figure 1 illustrates the experimental apparatus. This apparatus is the same as utilized in Kobayashi et al (2022), which was validated by comparing the CHF, transition point to the MEB, and the induced boiling sound to the previous research such as Ando et al (2016); Tang et al (2018); Horiuchi et al (2021).…”

“…We then control the temperature of the liquid to realize the designated ∆T sub . We conduct experiments under ∆T sub at 40 K, 50 K, and 60 K, in which the S-MEB is stably observed (Ando et al, 2016;Tang et al, 2017;Horiuchi et al, 2021;Kobayashi et al, 2022). The heat flux at the heat transfer surface '+%,'15(.23"),"#' ?@!…”

“…We call the former and the latter as T w and q, respectively. Both values are evaluated by applying one-dimensional Fourier's law (Ando et al, 2016;Horiuchi et al, 2021;Kobayashi et al, 2022) with the data of the temperature at three different points. The heat flux at the heat transfer surface q is evaluated as…”

“…This new regime of the boiling was found by Inada et al (1981c,d,a,b) in early 1980's under a rather highly subcooled conditions. It has been known that the MEB realizes a high heat flux despite with rather low wall superheat ∆T sat := T w − T sat accompanying with a vigorous emission of tiny bubbles from the heat transfer surface and with a boiling sound of much more intense than that of the nucleate boiling (Inada et al, 1981c,d,a,b;Kubo and Kumagai, 1992;Kubo et al, 1993;Kumagai et al, 1998Kumagai et al, , 2000Kumagai et al, , 2003Tang et al, 2018Tang et al, , 2019Horiuchi et al, 2021). Here T w and T sat indicate the wall temperature of the heat transfer surface and the saturation temperature under the system pressure concerned, respectively.…”

“…Although occurrence conditions and heat transfer characteristics of the MEB have been investigated intensively, their physical mechanism has not been fully unveiled: Ando et al (2016) indicated the transition of the vapor bubbles' behavior on the heat transfer surface from the nucleate boiling to the MEB, and depicted the variation of the heat flux and the wall superheat in the transition process. Horiuchi et al (2021) illustrated there exists significant difference in the radial temperature distribution near the heat transfer surface when different types of the MEB emerge; non-uniform temperature distribution is considered as a key feature realizing the MEB with vigorous oscillation of the vapor bubbles of the order of a few to several hundred Hz accompanying with higher heat fluxes than the CHF. Kobayashi et al (2022) unveiled the synchronous behaviors of the vapor bubbles on the heat transfer surface.…”