Cryogenics
2021

Numerical investigation on the direct contact condensation of oxygen jets in a cryogenic pipe

Hongwei Mao^a, Yanzhong Li^ab, Kang Zhu^c, Fushou Xie^a, Xiangyang Li^d, Dan Zhang^d
aInstitute of Refrigeration & Cryogenic Engineering, Xi’an Jiaotong University, Xi’an, 710049, China
^bState Key Laboratory of Technologies in Space Cryogenic Propellants, Beijing, 100028, China
^cDepartment of Materials Science and Engineering, Southern University of Science and Technology, Shenzhen, 518055, China
^dXi’an Aerospace Propulsion Institute, Xi’an, 710100, China

摘要：

In the present study, the direct contact condensation (DCC) performance of the superheat GOX in subcooling LOX is explored by numerical simulations based on the VOF two-phase model. The flow condensation characteristics are analyzed in a practical condenser of a cryogenic liquid rocket. The coalescence phenomenon of the GOX streams is examined. The possible regimes of the coalescence are summarized and their effects on the condensation performance are explored. Besides, an improved GOX entrance layout is proposed to avoid the coalescence phenomenon and improve condensation performance. The main conclusions are concluded as follows: The gas condensation is the main heat transfer form in most of the pipe region. The bending section of the condenser pipe that connects the vertical section and horizontal section is the most active region for DCC. It is found that there can be two types of coalescences namely, transverse coalescence and longitudinal coalescence. Both coalescence regimes have strong negative effects on the heat transfer ability and condensation performance of the condenser pipe. The improved entrance layout can successfully avoid the coalescence of the GOX streams and reduce the flow distance of the GOX by about 93%. It is also concluded that an improvement of the condenser pipe should be effectively accomplished by controlling the coalescence of the GOX streams after injection. geyser elimination approach using recirculation methods is investigated in the present work, which is essential to guarantee the integrity of facilities. Both experimental and numerical methods are adopted in the investigation using LN₂ as working fluids. A recirculation pipe is designed to eliminate geysers in a cryogenic vertical pipe. The performance of the recirculation method is comprehensively explored involving its formation mechanism and oscillation physics. A deeper understanding of the liquid recirculation is achieved. The physics of the ambiguous oscillation phenomenon is revealed. It is concluded that by breaking down the energy storage pattern inside the cryogenic pipe, geysers can be perfectly eliminated by the recirculation method. Liquid recirculation in the pipeline is found to be initiated firstly by the liquid density difference between the vertical pipe and recirculation pipe and dominated by liquid flashing in the recirculation pipe. A negative feedback connection between void fraction and mass flow rate is the reason for the oscillation in its initial process. Besides, an effective method is proposed to enhance the recirculation ability as well as to attenuate the unstable oscillation by imposing a gradually increased heat flux. It is found that the oscillation amplitude could be reduced by as much as 55%.