Fill-In and Boiling Transition Characteristics during the Liquid Oxygen Chill-Down Process in a Vertical Exit-Contracted Pipe

Abstract

Liquid oxygen chill-down in a vertical exit-contracted pipe was investigated experimentally. The wall temperatures were recorded in detail to describe the filling and chill-down process of the experimental section. Two quenching fronts, the exit one and the inlet one, were detected, and their propagations were found. Results show that the chill-down process is controlled mainly by the formation and propagation of quenching front, which are determined by the pressure level. With the increase of pressure, the roles of both propagation of quenching front and inlet quenching front undergo decreasing. On the vertical section, the effect of circumferential position was discussed in detail and the dominant point was identified, which determines the boiling transition time of the dominated points on the current cross-section. Based on the experimental data, two correlations were suggested for dominant point and dominated points, respectively, to predict heat flux on Leidenfrost, heat transfer coefficient on Leidenfrost, and critical heat flux. One equation was approved to predict heat transfer coefficient on critical heat flux point for both sorts of points. All of these correlations could produce reliable predictions.

Characteristics of Flow Development and Boiling Transitions in the Liquid Oxygen Chill-Down Process in a Straight Horizontal Exit-Contracted Pipe

“…As shown in the figures, all of the seven L se cross-sections could be classified by a few methods based on the effects of p LFP on ΔT LFP or q LFP . However, based on Equations ( 1) and ( 2), as well as the discussions in the previous studies [30,31], δ LFP , which indicates the thickness of the vapor film on LFP, is the primarily dominant parameter indicating the physical process. Sometimes, h LFP would be discussed instead.…”

“…Platform. Figure 1 gives the experimental platform applied in the present study, which is the LO 2 branch of a typical experiment platform for a cryogenic engine, different from that in the previous studies [28][29][30][31]. The experimental platform in the present study is with the same front-to-back relationship between the components, but the tank volume is larger to 2 m 3 , which can be used for LO 2 with a larger flow rate and longer.…”

“…On the other hand, temperature in the experimental section undergoes a sharp decrease. This is one of the primary characteristics of the cryogenic chill-down in the exit-contraction pipe for both the horizontal direction [30] and the vertical direction [31].…”

“…The horizontal liquid oxygen pipeline (D i = 20 mm) with the exit contracted was studied, and the pressure range was extended to 0.6-3.5 MPa, indicating that pressure has an important influence on LFP and CHF [30]. Further analysis of the horizontal pipeline δ LFP and q CHF was carried out to obtain the improved correlation equation [31]. In conclusion, the preliminary experiment studies the chilling process of the exit contracted liquid oxygen pipeline, including horizontal and vertical pipes, and the process indicates that the center of the pipe will be the first to form the quenching front and then spread to the sides of the pipe, and through a series of experiments, the new correlation of the boiling change point LFP and CHF is obtained.…”

“…(2) The measuring points are still not dense enough, which leads to insufficient understanding of the cooling mechanism and some contradictions, mainly including the following: in the horizontal L-shaped pipe, the main QF is first formed in the middle of the pipe, while in the vertical Z-shaped pipe, the main QF is formed at the outlet and then propagated downward. Based on the previous study [28][29][30][31], further experimental research was carried out, including the inlet of this test which will be a directly used straight pipe, excluding the influence of the inlet effect. More wall temperature measuring points are arranged along the upper and lower sides of the outer wall of the test pipe section to reproduce the cooling and filling process more clearly and completely.…”