TY - JOUR

T1 - Development of a two-domain-approach-based multi-scale model for the two-phase flows in space accumulators in microgravity

AU - Wang, Qing

AU - Wang, Qinggong

AU - Gu, Junping

AU - Cheverda, Vyacheslav Vladimirovich

AU - Zhu, Zhiqiang

AU - Zhao, Xiao

AU - Liu, Xuefeng

AU - Wang, Lubin

AU - Yu, Qiang

N1 - This work is supported by Beijing Natural Science Foundation (No. L241004), National Key Research and Development Program of China (No. 2022YFF0503502), Beijing Nova Program (No. 20230484334), Fundamental Research Funds for the Central Universities (No. FRF-TP25–016), Guilin Major Special Project (No. 20220103-1), Guangxi Science and Technology Base and Talent Special Project (Gui Ke AD24010012), and Guangxi Key Research and Development Plan (Gui Ke AB23026105).

PY - 2026/1

Y1 - 2026/1

N2 - Management of cryogenic fluid is critical for space accumulators in both loop heat pipe (LHP) and mechanically pumped two-phase loop (MPTL) system. To achieve proper fluid transport in the extreme environments in space, some complex structures are used in these apparatuses including porous meshes and porous vanes. The coexistence of free flow regions and porous medium regions results in a common cross-scale two-phase flow in the multi-scale structures. However, there is a lack of reliable mathematical methods to describe such flows, and thus the flow dynamics in space accumulators are hard to analyze. To solve this problem, we build a coupled multi-scale two-phase flow mathematical model based on the two-domain approach: on Onsager's variational principle, minimizing the energy dissipation of the system to derive fluid dynamic equations and interface evolution equations. Navier-Stokes equations for the free flow region and Darcy equation for the porous medium region are derived separately. To account for capillary-driven flow in microgravity, the Darcy equation is modified by explicitly including the capillary force. The boundary conditions that couple fluid dynamic equations and the interface capture methods are incorporated into the model. After validation, the model is applied to analyze transient two-phase flow behavior inside two typical space accumulators in microgravity: one for LHP and the other for MPTL. The flow characteristics are demonstrated, and different porous structures are compared for geometric optimization purposes. The results show that the primary wick of the LHP accumulator with a small pore radius (rc1 = 20 μm) generates substantial capillary pressure (-170 Pa) to maintain fluid circulation, and the secondary wick with a large pore radius (rc2 = 50 μm) enables efficient liquid delivery. In the accumulator of MPTL system, the implementation of porous mesh with a large pore radius (rc = 80 μm) significantly enhances the liquid replenishment rate (i.e., 0.017 m/s).

AB - Management of cryogenic fluid is critical for space accumulators in both loop heat pipe (LHP) and mechanically pumped two-phase loop (MPTL) system. To achieve proper fluid transport in the extreme environments in space, some complex structures are used in these apparatuses including porous meshes and porous vanes. The coexistence of free flow regions and porous medium regions results in a common cross-scale two-phase flow in the multi-scale structures. However, there is a lack of reliable mathematical methods to describe such flows, and thus the flow dynamics in space accumulators are hard to analyze. To solve this problem, we build a coupled multi-scale two-phase flow mathematical model based on the two-domain approach: on Onsager's variational principle, minimizing the energy dissipation of the system to derive fluid dynamic equations and interface evolution equations. Navier-Stokes equations for the free flow region and Darcy equation for the porous medium region are derived separately. To account for capillary-driven flow in microgravity, the Darcy equation is modified by explicitly including the capillary force. The boundary conditions that couple fluid dynamic equations and the interface capture methods are incorporated into the model. After validation, the model is applied to analyze transient two-phase flow behavior inside two typical space accumulators in microgravity: one for LHP and the other for MPTL. The flow characteristics are demonstrated, and different porous structures are compared for geometric optimization purposes. The results show that the primary wick of the LHP accumulator with a small pore radius (rc1 = 20 μm) generates substantial capillary pressure (-170 Pa) to maintain fluid circulation, and the secondary wick with a large pore radius (rc2 = 50 μm) enables efficient liquid delivery. In the accumulator of MPTL system, the implementation of porous mesh with a large pore radius (rc = 80 μm) significantly enhances the liquid replenishment rate (i.e., 0.017 m/s).

KW - Fluid management

KW - Microgravity

KW - Multi-scale structure

KW - Space accumulator

KW - Two-domain approach

UR - https://www.scopus.com/pages/publications/105013521353

UR - https://www.mendeley.com/catalogue/8fbd274f-c1f3-36c9-8147-3152ee56928b/

U2 - 10.1016/j.ijheatmasstransfer.2025.127668

DO - 10.1016/j.ijheatmasstransfer.2025.127668

M3 - Article

VL - 254

JO - International Journal of Heat and Mass Transfer

JF - International Journal of Heat and Mass Transfer

SN - 0017-9310

M1 - 127668

ER -