Engineering design of a hypobaric plant growth chamber

Due to the character of the original source materials and the nature of batch digitization, quality control issues may be present in this document. Please report any quality issues you encounter to digital@library.tamu.edu, referencing the URI of the item.Includes bibliographical references (leaves 63-65).Issued also on microfiche from Lange Micrographics.This system was developed to measure the effects of low-atmospheric pressure on the growth and function of plants for applications in Advanced Life Support systems research. The system is composed of six independent growth vessels with accommodations for gas supply and sampling, nutrient supply, water drainage, instrumentation, fans, and a cooling system. To ensure light availability, the chambers were constructed of clear acrylic (PMMA). It can support solid media and hydroponic systems as well as adjusting gas composition and making rapid changes in atmospheric pressure. Measurements of the parameters of interest were made using monolithic IC temperature sensors to measure temperature, strain-gage based pressure transducers, a quantum sensor to measure photosynthetically active radiation, and a process gas chromatograph to monitor atmospheric conditions. Data was recorded using a PC-based data acquisition and control system. Accurate measurements of plant gas exchange are essential to model plant response to changes in component gas concentrations under hypobaric conditions. A primary objective in the design of the low-pressure vessels was the minimization of the number and rate of leaks into the system. A three-dimensional computer model was developed to simulate the behavior of the chamber components under vacuum conditions using finite element analysis (FEA) software; both strength and deformation were examined to ensure proper operation under vacuum. The prototype vessel was evacuated to 30 kPa and allowed to equilibrate with the surrounding atmosphere for 24 hours resulting in an average leak rate of 1.67% of chamber volume per day. Photosynthetically active radiation (PAR) levels were measured at canopy height for lettuce plants with the chamber in place and removed. With the chamber removed, PAR levels were recorded as 461 []mol m⁻² s⁻¹; inside the complete chamber the level decreased to 408 []mol m⁻² s⁻¹, a difference of 11.5%