[Objective] Large-scale space facilities—space stations, lunar habitats and deep-space transfer vehicles—must transport kilowatt-class heat loads over tens of metres under strict reliability constraints, yet conventional two-phase systems transport heat without regulating it, and any regulation reintroduces the sensor–controller–actuator chain. This work aims to establish a two-phase heat transport system free of electronic components and external power.
[Methods] The Water-Heart, a fully passive biomimetic pulsating two-phase heat pump, is proposed. A 400 kPa bi-stable snap valve locks flash-boiling triggering to the water saturation curve (~143 °C), replacing the chaotic self-oscillation of conventional pulsating heat pipes with deterministic triggering. Multi-effect shape memory alloy (SMA) components serve as superelastic venous valves for return-flow rectification, A_f-threshold thermal switches for return timing, and icebreaker elements for cold-spot freeze protection. Each evaporation chamber carries an independent Valve B that provides both refill timing and distributed water-hammer isolation; bellows accumulators, charged by the flash pulse itself, drive long-distance condensate return. A lumped-parameter thermal–fluid network model is used, with ±30 % extreme-boundary verification of five key parameters.
[Results] Under steady-state energy conservation the mean delivered power equals the net absorbed power. For the baseline 100 × 100 × 2 mm chamber with a selective absorber (alpha/epsilon ~ 6), about 9.7 W is absorbed at a cycle period of about 83 s, giving about 970 W for a hundred-chamber array at 12 kg dry mass (about 81 W/kg). The flash fraction is locked to 8.1 % by the sensible-heat difference of adiabatic depressurisation and does not increase with heating power, which sets only the pulse frequency. The transient differential pressure supports a 30 m pipeline layout: the 30 m steam line drops only about 2–5 kPa, whereas a 30 m return line needs about a 10 mm bore (about 21 kPa, about 47 ms refill). Paraffin phase-change storage covers the 35-min LEO eclipse with 26 % margin. Continuously flowing manifold vapour, paraffin storage and distributed SMA icebreakers form a three-tier freeze protection that recovers autonomously at −50 °C (energy cascade of order 10²). Per-chamber power is tunable from 2.5 W to 78 W via absorbing area and concentration ratio, with cycle periods spanning about 5 s to 6.8 min. All figures above are given on the conservative basis of direct illumination of the chamber's own projected area; if the integration gain from skin conduction over an enlarged absorbing area is included (requiring a selective absorber that satisfies alpha/epsilon >= 1.25), single-chamber power scales linearly with the area ratio kappa (about 39 W at kappa = 4) - an integration upper bound rather than a guaranteed value, since it is limited by contact resistance and by the effective participating area being smaller than the geometric area. A three-tier experimental roadmap with quantitative pass/fail criteria is provided.
[Limitations] This work is a theoretical study without a physical prototype; all results are concept-validation bounds from a lumped-parameter model rather than engineering-design data. Graceful degradation in the power dimension does not extend to the working-fluid dimension—the manifolds and fluid circuit are shared across the whole array and carry a system-level leak risk that requires dedicated redundancy.
[Conclusions] The Water-Heart offers a survivability-grade fully passive thermal-control architecture in which deterministic snap-valve triggering replaces chaotic two-phase instability, SMA differential-pressure-threshold valves replace electronic sensors, and flash-pulse energy replaces the mechanical pump, providing a zero-electronics, zero-power thermal-management path for deep-space crewed facilities.
