Thermodynamic availability analysis of controlled air revitalization systems

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1998
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Wilharm, Caroline
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Richard C. Seagrave
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Chemical and Biological Engineering

The function of the Department of Chemical and Biological Engineering has been to prepare students for the study and application of chemistry in industry. This focus has included preparation for employment in various industries as well as the development, design, and operation of equipment and processes within industry.Through the CBE Department, Iowa State University is nationally recognized for its initiatives in bioinformatics, biomaterials, bioproducts, metabolic/tissue engineering, multiphase computational fluid dynamics, advanced polymeric materials and nanostructured materials.

History
The Department of Chemical Engineering was founded in 1913 under the Department of Physics and Illuminating Engineering. From 1915 to 1931 it was jointly administered by the Divisions of Industrial Science and Engineering, and from 1931 onward it has been under the Division/College of Engineering. In 1928 it merged with Mining Engineering, and from 1973–1979 it merged with Nuclear Engineering. It became Chemical and Biological Engineering in 2005.

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1913 - present

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  • Department of Chemical Engineering (1913–1928)
  • Department of Chemical and Mining Engineering (1928–1957)
  • Department of Chemical Engineering (1957–1973, 1979–2005)
    • Department of Chemical and Biological Engineering (2005–present)

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This work investigates thermodynamic lost work and several of the factors influencing its production. Lost work is a measure of irreversibilities within a process, and its characterization can aid in improving the design of a system. Lost work is equivalent to consumed availability, where availability is a measure of the capacity of a system to perform useful work;Lost work is a function of mass flows, chemical species and their relative concentrations, temperature, and pressure. To examine how these variables influence lost work production, systems of different levels of complexity were studied. The simplest system was comprised of three isothermal tank reactors in series which were studied to investigate the effect of process control systems on lost work production. Lost work was shown to depend most strongly on mass flow rates. Process control acted to return the mass flow rates within the system and the lost work production to near their steady state values;The next systems examined were commercial chemical plants previously studied by other authors. Attempts were made to replicate the results of their availability analyses to check that the calculational methods utilized in this work resulted in values for lost work that were comparable to the given values for consumed availability. It was difficult to arrive at the authors' results using their given data and formulas. This indicates that it is difficult to interpret and replicate the results presented in this relatively new area of research;The most complex system investigated was the air revitalization portion of a closed life support system (ARS). This system is in place to remove excess carbon dioxide and water vapor from the cabin of a spacecraft and to replenish oxygen consumed by the crew. This system is comprised of many different subsystems which interact with one another. Many different technologies exist to perform the functions of the ARS. To investigate the effects of technology on lost work production, two different technologies for carbon dioxide reduction were included in the computer-based dynamic model of the ARS. Simulations showed that the Sabatier subsystem is superior to the Bosch subsystem in that it requires less heating and cooling and produces less lost work;The main disruption to the cabin conditions is changing levels of crew activity. A process control system is included in the system to keep the cabin conditions safe for its inhabitants at all times. The effects of these parameters on the magnitude and distribution of lost work production were investigated using simulations for three different levels of crew activity, with and without process control. Increased crew activity acts to increase lost work production, but not proportionately, and does little to influence its distribution throughout the system. The presence of a control system magnifies the increases in lost work and also changes its distribution.

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Thu Jan 01 00:00:00 UTC 1998