Critical heat flux of oxidized zircaloy surface in saturated water pool boiling

In the present experimental study, the critical heat flux (CHF) of an oxidized zircaloy surface and its enhancement were investigated during saturated water pool boiling at atmospheric pressure. Three kinds of zircaloy specimens, oxidized at three different temperature conditions (i.e., 300, 450, and 600 °C), were prepared with a non-treated (i.e., fresh) zircaloy surface. The surfaces of the test specimens were characterized by an energy dispersive spectroscopy analysis, scanning electron microscopy image, and water contact angle measurement. The oxidized surface (OS) specimens increased the CHF, which could be because the oxidized surface improves the surface wettability (i.e., decreases the water contact angle). The OS specimens showed the similar water contact angles, and their CHF values became almost the same. In the present experimental conditions, the water contact angle could be considered as a reasonable parameter to explain the CHF data of test specimens. The CHF enhancement of the OS specimens was about 40%, as compared with the non-treated specimen, and interestingly, it was a comparable value to that of the specially treated zircaloy surfaces of the previous report, for a similar water contact angle condition. This implies that the oxidation process used in this work can be a simple, convenient, and cost-effective way to improve the CHF of the zircaloy surface. Using the present experimental data, the previous CHF correlations were assessed and discussed. Among the correlations tested, Kandlikar model best fitted the present CHF measurement data and enhancement factors.