Simulation and Optimization of Vacuum Swing Adsorption Units for Spacesuit Carbon Dioxide and Humidity Control

Controlling carbon dioxide (CO2) and humidity levels in a spacesuit is critical to ensuring both the safety and comfort of an astronaut during extra-vehicular activity (EVA). Traditionally, this has been accomplished utilizing non-regenerative lithium hydroxide (LiOH) or regenerative metal oxide (MetOx) canisters which pose a significant weight burden. Although such technology enables air revitalization, the volume requirements to store the waste canisters as well as the mass to transport multiple units become prohibitive as mission durations increase. Consequently, motivation exists toward developing a fully regenerative technology for environmental control. The application of solid amine materials with vacuum swing adsorption technology has shown the capacity to control CO2 and concomitantly manage humidity levels through a fully regenerative cycle eliminating mission constraints imposed with non-regenerative technologies. Experimental results for full-size and sub-scale test articles have been collected and are described herein. In order to accelerate the developmental efforts, an axially-dispersed plug ow model with an accompanying energy balance has been established and correlated with the experimental data. The experimental and simulation results display good agreement for a variety of ow rates (110-170 SLM), replicated metabolic challenges (100-590 Watts), and atmosphere pressures under consideration for the spacesuit (248 and 760 mm Hg). The relationship between swing adsorption cycles for an outlet criterion of 6.0 mm Hg of CO2 partial pressure has been established for each metabolic challenge. In addition, variable metabolic profiles were imposed on the test articles in order to assess the ability of the technology to transition to new operational constraints. The advent of the model provides the capacity to apply computer-aided engineering practices to support the ongoing efforts to optimize and mature this technology for future application to space exploration

A fundamental model of wax deposition in subsea oil pipelines

Wax deposition in subsea pipelines is a significant economic issue in the petroleum industry. A mathematical model has been developed to predict the increase in both the deposit thickness and the wax fraction of the deposit using a fundamental analysis of the heat and mass transfer for laminar and turbulent flow conditions. It was found that the precipitation of wax in the oil is a competing phenomenon with deposition. Two existing approaches consider either no precipitation (the independent heat and mass transfer model) or instantaneous precipitation (the solubility model) and result in either an overprediction or an underprediction of deposit thickness. By accounting for the kinetics of wax precipitation of wax in the oil (the kinetic model), accurate predictions for wax deposition for both lab‐scale and pilot‐scale flow‐loop experiments with three different oils were achieved. Furthermore, this kinetic model for wax precipitation in the oil was used to compare field‐scale deposition predictions for different oils. © 2011 American Institute of Chemical Engineers AIChE J, 2011Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87116/1/12517_ftp.pd

An open-source toolbox for PEM fuel cell simulation

In this paper, an open-source toolbox that can be used to accurately predict the distribution of the major physical quantities that are transported within a proton exchange membrane (PEM) fuel cell is presented. The toolbox has been developed using the Open Source Field Operation and Manipulation (OpenFOAM) platform, which is an open-source computational fluid dynamics (CFD) code. The base case results for the distribution of velocity, pressure, chemical species, Nernst potential, current density, and temperature are as expected. The plotted polarization curve was compared to the results from a numerical model and experimental data taken from the literature. The conducted simulations have generated a significant amount of data and information about the transport processes that are involved in the operation of a PEM fuel cell. The key role played by the concentration constant in shaping the cell polarization curve has been explored. The development of the present toolbox is in line with the objectives outlined in the International Energy Agency (IEA, Paris, France) Advanced Fuel Cell Annex 37 that is devoted to developing open-source computational tools to facilitate fuel cell technologies. The work therefore serves as a basis for devising additional features that are not always feasible with a commercial cod

Chemical Analysis of Nutritional Content of Prickly Pads (Opuntia ficus indica) at Varied Ages in an Organic Harvest

Opuntia ficus indica, also known as prickly pads, are an important part of the human diet and are also used as forage for livestock. This is an interesting vegetable due the environmental conditions in which it grows and its resistance to climatic extremes; however, little is known about its nutritional properties, especially in the later stages of maturity. The objective of this study was to determine the composition of organic prickly pads (Opuntia ficus indica) at differing stages of growth maturity. Chemical proximate analysis and mineral constituent analysis at different maturation stages were carried out in this investigation. As a result, older prickly pads were found to be an important source of nutritional components such as calcium

Process simulation and optimal design of membrane separation system for CO2 capture from natural gas

In recent years, membrane gas separation has emerged as an alternative of other available technologies (such as absorption and cryogenic separation) in order to remove CO2from natural gas. A common phenomenon during gas separation by membrane is the occurrence of Joule-Thomson (JT) effect. The temperature may change to a large extent dependent on the type of gas and the pressure applied. In turn, this temperaturechange may have a large influence on the permeation properties. Moreover, feed gas may condense due to sudden expansion caused by the decrease in pressure while permeating through the membrane. The effect of different parameters on the temperature change due to JT effect has been investigated under the present study. It is shown that the temperature drop is quite significant for feed gas with high CO2contents and high pressure, and thus potentially causes condensation across the membrane. It may be prevented by achieving a predetermined dew point before the membrane and then heating the gas to provide a sufficient margin of super heat. This increase in temperature increases the margin between the gas dew point and operating temperature and thus prevents condensation in the membrane

Mass Transfer Coefficients and Correlation of Supercritical Carbon Dioxide Extraction of Sarawak Black Pepper

Bioactive compound, namely piperine, was extracted from Sarawak black pepper using supercritical carbon dioxide extraction. Experiments were carried out in the range of 3,000–5,000 psi (20.7–34.4 MPa) pressures, 318–328 K temperatures, 0.4–1 mm mean particle sizes and 5–10 ml/min carbon dioxide flow rates. Experimental data analysis shows that extraction yield is mainly influenced by pressure, particle size and coupled-interactions between these two variables. Extraction process was modeled accounting for intraparticle diffusion and external mass transfer. The kinetics parameters for the internal and external mass transfers were evaluated and estimated. Mass transfer correlation was also developed. From simulation results, good agreement between experimental and simulated data has been found

Cell affinity separations using magnetically stabilized fluidized beds: Erythrocyte subpopulation fractionation utilizing a lectin-magnetite support

A magnetically stabilized fluidized bed is used to separate erythrocyte subpopulations. Binding specificity was obtained by immobilizing the lectin Helix pomatia Agglutinin (HpA) or Griffonia simplicifolia I (GSI) onto a magnetite-containing support. Separation of type A and type O erythrocytes with the lectin HpA was particularly effective, leading to a 94% purity of retained type A erythrocytes. A 3.1 ± 0.6 log removal of type A erythrocytes was also accomplished leading to a 99.7% ± 0.4% purity and 95% ± 7% yield of type O erythrocytes in the collected effluent. Elution of the purified cells was accomplished using fluidization in the presence of a sugar competing for the lectin–erythrocyte binding site. A mathematical model based on the depth filtration model of Putnam and Burns (Chem Eng Sci 1997;52(1):93–105) was extended to include multicomponent cell adhesion. This filtration model is the first to take into account the finite binding capacity of the chromatographic support and is used to characterize the cell binding behavior and to determine optimal parameters and conditions that lead to high capacities and selectivities. Model parameter values and observations from in situ adsorption studies suggest that the non-spherical shape of the magnetite-based support allows for a more efficient utilization of the support surface area than the spherical shape. Using a 1.5-cm diameter laboratory column and realistic parameter values, the processing rates of the system are predicted to be at least an order of magnitude greater than the 10 8 /h cells that can typically be processed in packed bed cell affinity chromatography (CAC) systems. © 2003 Wiley Periodicals, Inc. Biotechnol Bioeng 81: 650–665, 2003.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/34342/1/10511_ftp.pd