Development of a photosynthesis measurement chamber under different airspeeds for applications in future space crop-production facilities
Massa, Gioia D.
Wheeler, Raymond M.
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Space crop production systems are being developed to grow fresh produce in-situ to supplement the astronauts’ diet, but the required ventilation rates for crops in different gravity environments remains poorly understood. The reduction or lack of buoyancy-driven convection in reduced gravity environments leads to impaired gas exchange (CO2 absorption, water transpiration and O2 release) at the leaf surface if no extra ventilation is provided, and this could lead to a reduction in biomass production in the long run. To better characterize the influence of different airspeeds on photosynthesis and be able to model this in low gravity, a chamber was designed to interface with a LI-6800 portable photosynthesis system. This paper details the design of this chamber, specifically made to measure whole-plant and small canopy gas exchange at different airspeeds. The fans provide turbulent mixing in the chamber to ensure that it behaves like a continuous stirred tank reactor (CSTR) and that the residence time distribution (RTD) is the same for any fan speed; the computational fluid dynamic (CFD) model of the gas domain (the air in the chamber) hence uses a k-omega turbulence model. An airflow map of the chamber was created using anemometer measurements for the different airspeeds tested, and this was used together with the CFD simulation results to relate the experimentally measured fan outputs to actual airspeeds on top of an artificial plant. The chamber is equipped with thermocouples that track leaf surface temperature, which relate to the LI-6800 gas exchange measurements via a plant energy balance. Environmental parameters (air temperature, relative humidity, CO2 level) are controlled by the LI-6800. This work was funded by NASA Space Biology through the NASA postdoctoral program / USRA.