Capillary transport and efficiency limitations in ordered porous heat pipes

The relevance of the study is determined by the need to improve the reliability and efficiency of passive thermal control systems for spacecraft, where the absence of convection and microgravity make traditional cooling methods inapplicable.

Objective

To develop a parametric model of the ordered porous structure of the wick, calculate the hydraulic characteristics—porosity, permeability, hydraulic diameter, capillary pressure, flow velocity, and Reynolds number—and determine the limitations on the heat pipe length for given geometric parameters.

Methods

The study utilized methods of geometric modeling of a single cell in a CAD environment and analytical calculations based on the Darcy equations, capillary pressure, and hydraulic diameter. Water at a temperature of 50 °C was adopted as the coolant.

Results

The porosity of the structure was shown to remain constant (≈0.63) upon scaling, while permeability and hydraulic diameter increase with increasing cell size. The flow pattern is found to be laminar (Re ≈ 89). Capillary pressure and maximum pipe length are plotted as functions of hydraulic diameter.

Conclusion

The performance of heat pipes with ordered wicks is primarily limited by the tradeoff between capillary pressure (favorable for small pores) and flow resistance (favorable for large pores). The developed analytical model enables the prediction of thermal-hydraulic behavior at the design stage. These results support the feasibility of additive manufacturing for next-generation spacecraft thermal control systems, particularly for long-duration missions where reliability and predictability are paramount. Specific application areas include CubeSats (5–50 W), ISS systems (70–100 kW), and lunar/Martian bases (5–50 kW). Future research should experimentally validate prototype designs.