This paper presents a numerical analysis of the melting dynamics of n-octadecane in microgravity. The phase change material (PCM) is held in a rectangular container of aspect ratio Γ=L/H=1.5, and the upper boundary is open to a layer of air, which both exchanges heat with the PCM and generates thermocapillary convection in the liquid phase via the Marangoni effect. This study extends the analysis conducted by Martinez et al. [“Effect of surface heat exchange on phase change materials melting with thermocapillary flow in microgravity,” Phys. Fluids 33, 083611 (2021)] in which the air temperature was assumed to vary linearly between the temperatures applied at the lateral walls. Two different scenarios are analyzed here. In the first case, the air temperature is assumed to be homogeneous and equal to the mean value of the temperatures applied at the lateral walls throughout the melting process. In the second case, the air temperature is similarly taken to be constant but with a value of 23 °C, which is representative of a laboratory environment, including many microgravity platforms. The investigation reveals the effect of key dimensionless parameters, including the Marangoni number (Ma), which quantifies the heat transport due to the thermocapillary flow, and the Biot number (Bi), which characterizes the heat exchanged across the PCM/air interface. In contrast to previous analyses of pattern selection, only oscillatory standing (pulsating) waves are observed under these boundary conditions. The results in each case are presented via stability maps in terms of Bi and Ma.

In this work, we numerically analyze different thermocapillary-based strategies for active control of sloshing in microgravity. The fluid system considered is an open rectangular container holding a L×H=30 × 15 mm2 volume of liquid. A classical controller is implemented to reduce the natural sloshing motion of the system, which is characterized by its decay time τd. The controller produces an output signal ΔT that is applied anti-symmetrically at the lateral walls of the container, driving thermocapillary flow. Its performance is characterized via the functional P=(1−λ) τ̂+λ κ̂, which allows for a trade-off between the damping of unwanted sloshing modes and the cost of implementing the control, with normalized decay time τ̂ and cost κ̂, and modulated by λ∈[0, 1]. We optimize P for discrete values of λ and determine the optimal performance envelope. The results show that thermocapillary controllers are generally able to reduce τd by a 50% factor, with reasonable cost and controller output. A novel strategy combining thermocapillary controllers and passive baffles is further proposed and assessed. On their own, passive baffles can reduce the natural decay time of sloshing by an 80% factor at zero cost. In addition, they significantly alleviate the thermal requirements associated with the control, while providing additional improvements in τd. Finally, the aforementioned strategies are tested against a reboosting maneuver of the International Space Station, showing their potential for sloshing reduction in microgravity.

Here, we investigate the performance of phase-change materials (PCMs) in the passive thermal control of space habitats. PCMs are able to absorb and release large amounts energy in the form of latent heat during their (typically, solid-to-liquid) phase transition, which makes them an ideal choice for passive temperature control. In this study, a conceptual design of an igloo-shaped habitat is proposed. A scaled model for laboratory experiments is manufactured via 3D printing, using tap water as the PCM. The setup is used to conduct experiments and analyze PCM performance, based on temperature measurements inside and outside the habitat. Results demonstrate the effectiveness of PCMs in increasing thermal inertia and stabilizing the habitat interior temperature around the melting temperature, confirming that PCMs can be a suitable alternative for passive thermal control. The present study holds significant interest for the future of space exploration, with the emerging need to design habitats that are capable of accommodating astronauts.