A numerical and experimental study of a new design of closed dynamic respiration chamber

Carbon dioxide soil efflux modelling in closed dynamic respiration chambers is a challenging task. This is attributed on many occasions to the very small concentrations of carbon dioxide being transported between soil and the atmosphere. This paper describes a portable device which was made exclusively to accurately measure carbon dioxide efflux from soil locations. The blowing fan creates a forced convective flow to occur in the chamber making the K-Epsilon turbulence model a necessity to model the occurring flow in the respiration chamber gas domain. Furthermore the Darcy model is applied on the porous domain to model the flow pattern within the soil. The measurement process was achieved through measuring carbon dioxide concentration, temperature and relative humidity inside the chamber in relation to time. Simulation and experimental data is obtained using ANSYS and MATLAB. A significant agreement between the experimental and numerical results was achieved

Renewable energy scenario and environmental aspects of soil emission measurements

European Commission has set clear targets for 2020 regarding energy and environment policy; these targets include 20% cut in greenhouse gas emissions against the 1990 levels. It is believed that adopted strategy has encouraged the renewable energy applications during the last two decades. Moreover, measurement deviations of carbon dioxide flux occurring in respiration chambers has been seen of a great importance to explain the biochemical parameters affecting the climate change issue. This is attributed on many occasions to chamber design constraints and the way they are coupled with the studied site location. This is illustrated by external disturbances whereby when they happen while gas measurements are taken measurement deviations become more evident. This paper surveys the different soil physical, biological and geotechnical parameters and links them to meteorological ones. Consequently it explores their direct and indirect effects to the produced soil efflux. Furthermore this paper proposes several soil temperature models according to the studied case constraints to see what affects soil efflux production. Moreover a clear understanding of what affects the measurement process was achieved through surveying all the internal and external pressure parameters and how they influence the chamber in relation to time. The conclusion is that respiration chamber designers need to preserve chamber internal temperature and pressure to be equal to the outer atmosphere for the case of stabile external conditions. For the case of unstable external conditions design counter measures are incorporated. Furthermore the appropriate gas sensor needs to be selected professionally with emphasis on the importance of installation location inside the chamber. Likewise soil bacterial type and soil temperature also has an influence on efflux production

Aerospace Medicine and Biology: A continuing bibliography with indexes, supplement 127, April 1974

This special bibliography lists 279 reports, articles, and other documents introduced into the NASA scientific and technical information system in March 1974

Prediction of the gas emission from porous media with the concern of energy and environment

Measuring soil carbon dioxide efflux is a challenging task even when it is performed using respiration chambers. While gas samples are taken, measurement deviations become more evident according to the used chamber design especially when external disturbances occur. This paper studies the carbon dioxide concentration profiles within the top soil layers, and investigates the controlling factors affecting the process. The considered factors are diffusion, temperature and viscosity. The efflux equation is discussed and then it is linked with the soils geotechnical parameters, while a relationship between the Reynolds number within the soil and efflux is found. Emphasis on the importance of the external geometrical design considerations is shown through studying external boundary layer effects due to the chamber outer shell shape and how it interacts with blowing winds. Chamber stability on site of deployment is also of a significant importance considering external blowing winds. Internal geometrical considerations are linked with the flow turbulence within the dynamic chambers. It is highly recommended that respiration chamber designers need to work in parallel with a multidisciplinary team in order to make a chamber design that ensures the least disturbance to occur at the location of study

Aerospace medicine and biology: A continuing bibliography with indexes, supplement 203

This bibliography lists 150 reports, articles, and other documents introduced into the NASA scientific and technical information system in January 1980

A study of the control problem of the shoot side environment delivery system of a closed crop growth research chamber

The details of our initial study of the control problem of the crop shoot environment of a hypothetical closed crop growth research chamber (CGRC) are presented in this report. The configuration of the CGRC is hypothetical because neither a physical subject nor a design existed at the time the study began, a circumstance which is typical of large scale systems control studies. The basis of the control study is a mathematical model which was judged to adequately mimic the relevant dynamics of the system components considered necessary to provide acceptable realism in the representation. Control of pressure, temperature, and flow rate of the crop shoot environment, along with its oxygen, carbon dioxide, and water concentration is addressed. To account for mass exchange, the group of plants is represented in the model by a source of oxygen, a source of water vapor, and a sink for carbon dioxide. In terms of the thermal energy exchange, the group of plants is represented by a surface with an appropriate temperature. Most of the primitive equations about an experimental operating condition and a state variable representation which was extracted from the linearized equations are presented. Next, we present the results of a real Jordan decomposition and the repositioning of an undesirable eigenvalue via full state feedback. The state variable representation of the modeling system is of the nineteenth order and reflects the eleven control variables and eight system disturbances. Five real eigenvalues are very near zero, with one at zero, three having small magnitude positive values, and one having a small magnitude negative value. A Singular Value Decomposition analysis indicates that these non-zero eigenvalues are not results of numerical error

Southwest Research Institute assistance to NASA in biomedical areas of the technology utilization program Final report, 1 Feb. 1969 - 24 Aug. 1970

Research progress in technology transfer by NASA Biomedical Application Tea

A multiphysics approach for modeling gas exchange in microperforated films for modified atmosphere packaging of respiring products

The objective of this work is to quantify, model and verify how the interactions between the respiring products and the surrounding atmosphere in a package affect the gas exchange through a microperforation. The pressure drop generated in a closed system by the metabolic activity of five different products has been determined by direct and indirect measurements. In this way, the estimated compensating hydrodynamic flows that can pass through the microperforated film ranged from 0.34 to 4.75 mL h(-1). A 3D model that considers the mass transfer coupled with the momentum transfer has been proposed to predict the gas concentration profiles around the microperforations originated by the diffusive and convective flows. A novel gas exchange measurement system, able to deliver small convective airflows comparable to those obtained for the different products and conditions, was assembled for the model verification. The model correctly predicts experimental data obtained for different convective flows