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Liquid oxygen chill-down in a straight horizontal pipe was studied experimentally. The effect of the entrance corner was excluded, and much denser wall temperature sensors along the pipe have been set compared to the present studies. In this way, the chill-down process, as well as the development of the flow pattern, has been drawn for every test. As a result, the mechanism of LO2 chill-down would be obtained for various pressure sections. For cases with stable pressure below 1.25 MPa, liquid rewetting in the pipe is controlled by the propagation of quenching fronts. For cases with a higher pressure, liquid rewetting in the second half of the pipe is controlled by the sudden liquid fill-in. Based on the transition points obtained, heat transfer coefficients on the Leidenfrost point and critical heat flux have been correlated for various pressure sections using new approaches. Conclusions show that the correlation equations are dependent on the chill-down mechanisms. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]