Modeling and Experimental Study of an Open Two-Phase Loop Driven by Osmotic Pressure and Capillary Force

As space technology advances, thermal control systems must effectively collect and dissipate heat from distributed, multi-source environments. Loop heat pipe is a highly reliable two-phase heat transfer component, but it has several limitations when addressing multi-source heat dissipation. Inspired by the transport and heat dissipation system of plants, large trees achieve stable and efficient liquid supply under the influence of two driving forces: capillary force during transpiration in the leaves (pull) and root pressure generated by osmotic pressure in the roots (push). The root pressure provides an effective liquid supply with a driving force exceeding 2 MPa, far greater than the driving force in conventional capillary-pumped two-phase loops. Research has shown that osmotic heat pipes offer a powerful driving force, and combining osmotic pressure with capillary force has significant advantages. Therefore, this paper designs a multi-evaporator, dual-drive two-phase loop, using both osmotic pressure and capillary force to solve the multi-source heat dissipation challenge. First, a transmembrane water flux model for the osmotic pressure-driven device was established to predict the maximum heat transfer capacity of the dual-drive two-phase loop. Then, an experimental setup for a multi-evaporator “osmotic pressure + capillary force” dual-drive two-phase loop was constructed, capable of transferring at least 235 W of power under a reverse gravity condition of 20 m. The study also analyzed the effects of reverse gravity height, heat load distribution among the three evaporators, startup sequence, and varying branch resistances on the performance of the dual-drive two-phase loop.