OrbHab Paper
Water Cycles In Closed Ecological Systems: Effects Of Atmospheric Pressure (2002)
ID: 78 Flag Paper
Title: Water Cycles In Closed Ecological Systems: Effects Of Atmospheric Pressure
Authors: Vadim Rygalov, Philip Fowler, Joannah M Metz, Ray Wheeler
Journal Name: Life Support & Biosphere Science
Year of Publication: 2002
Page Number: 0
Category: biosphere
Availability: pdf
Detail Page: /papers/78
Web Link: https://www.researchgate.net/publication/10990838_Water_cycles_in_closed_ecological_systems_effects_of_atmospheric_pressure
BoK Link: [[paper:78]]
Abstract
In bioregenerative life support systems that use plants to generate food and oxygen, the largest mass flux between the plants and their surrounding environment will be water. This water cycle is a consequence of the continuous change of state (evaporation-condensation) from liquid to gas through the process of transpiration and the need to transfer heat (cool) and dehumidify the plant growth chamber. Evapotranspiration rates for full plant canopies can range from ~1 to 10 L m-2 d-1 (~1 to 10 mm m-2 d-1), with the rates depending primarily on the vapor pressure deficit (VPD) between the leaves and the air inside the plant growth chamber. VPD in turn is dependent on the air temperature, leaf temperature, and current value of relative humidity (RH). Concepts for developing closed plant growth systems, such as greenhouses for Mars, have been discussed for many years and the feasibility of such systems will depend on the overall system costs and reliability. One approach for reducing system costs would be to reduce the operating pressure within the greenhouse to reduce structural mass and gas leakage. But managing plant growth environments at low pressures (e.g., controlling humidity and heat exchange) may be difficult, and the effects of low-pressure environments on plant growth and system water cycling need further study. We present experimental evidence to show that water saturation pressures in air under isothermal conditions are only slightly affected by total pressure, but the overall water flux from evaporating surfaces can increase as pressure decreases. Mathematical models describing these observations are presented, along with discussion of the importance for considering "water cycles" in closed bioregenerative life support systems.
Title: Water Cycles In Closed Ecological Systems: Effects Of Atmospheric Pressure
Authors: Vadim Rygalov, Philip Fowler, Joannah M Metz, Ray Wheeler
Journal Name: Life Support & Biosphere Science
Year of Publication: 2002
Page Number: 0
Category: biosphere
Availability: pdf
Detail Page: /papers/78
Web Link: https://www.researchgate.net/publication/10990838_Water_cycles_in_closed_ecological_systems_effects_of_atmospheric_pressure
BoK Link: [[paper:78]]
Abstract
In bioregenerative life support systems that use plants to generate food and oxygen, the largest mass flux between the plants and their surrounding environment will be water. This water cycle is a consequence of the continuous change of state (evaporation-condensation) from liquid to gas through the process of transpiration and the need to transfer heat (cool) and dehumidify the plant growth chamber. Evapotranspiration rates for full plant canopies can range from ~1 to 10 L m-2 d-1 (~1 to 10 mm m-2 d-1), with the rates depending primarily on the vapor pressure deficit (VPD) between the leaves and the air inside the plant growth chamber. VPD in turn is dependent on the air temperature, leaf temperature, and current value of relative humidity (RH). Concepts for developing closed plant growth systems, such as greenhouses for Mars, have been discussed for many years and the feasibility of such systems will depend on the overall system costs and reliability. One approach for reducing system costs would be to reduce the operating pressure within the greenhouse to reduce structural mass and gas leakage. But managing plant growth environments at low pressures (e.g., controlling humidity and heat exchange) may be difficult, and the effects of low-pressure environments on plant growth and system water cycling need further study. We present experimental evidence to show that water saturation pressures in air under isothermal conditions are only slightly affected by total pressure, but the overall water flux from evaporating surfaces can increase as pressure decreases. Mathematical models describing these observations are presented, along with discussion of the importance for considering "water cycles" in closed bioregenerative life support systems.