Improvement and validation of a mechanistic physical model for the prediction of heat and mass transfer in higher plant growth in reduced gravity

Abstract

Long-duration crewed space missions like those to the Moon, Mars, will demand reliable and self-sufficient closed-loop life-support systems to sustain crews for months or years with very limited resupply. In this context, bioregenerative life-support systems will become crucial. Those systems will incorporate higher plants to regenerate oxygen via photosynthesis, remove carbon dioxide, and recycle water through transpiration. However, currently existing plant growth models do not incorporate space-specific conditions such as microgravity, radiation exposure, and altered atmospheric parameters, resulting in a limited capability to predict plant behaviour and system performance in extra-terrestrial habitats. This research addresses that gap by isolating and examining fundamental heat and mass transfer processes in plant–environment interactions using a leaf replica under controlled conditions. Using the leaf replica enables decoupling of purely physical phenomena from complex biological effects, allowing precise study of how gravity affects convective heat transfer and mass transfer. Experiments are conducted in both normal gravity on Earth and microgravity environments, achieved via parabolic flight campaigns, using an experimental platform that was designed and built as a part of this PhD. The platform consists of four units in which the leaf replica is subjected to controlled airflow and its position against the airflow can be adjusted. Key parameters monitored include airflow velocity, leaf orientation, gravitational acceleration, pressure, temperature, and relative humidity inside the units, and leaf replica surface temperature. Data collected during these experiments enabled the identification of heat and mass transfer coefficients under both steady-state and transient conditions. Statistical analyses show significant effects of gravity, airflow, and orientation on surface temperature and mass transfer of the replica. The modelling work led to the development and validation of mechanistic models for convective heat and mass transfer that take into account natural and forced convection, boundary layer behaviour, and internal diffusion limitations. The results confirm the role of gravity and air velocity in modulating heat and mass transfer, and show the dominant contribution of the upper surface in heat loss. The model and data provide a physically grounded tool for analysing plant-environment interactions in altered gravity, with potential application in future space experiment.

Date of Award	23 Oct 2025
Original language	English
Awarding Institution	Universitat Autònoma de Barcelona (UAB)
Supervisor	Francesc Godia Casablancas (Director), Jean-Pierre Fontaine (Director) & Claude-Gilles Dussap (Director)