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Theresa Julia Zielinski Monmouth University West Long Branch, NJ 07764-1898
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Contrail
A Module from the Physical Chemistry On-Line Project1
George Long Indiana University of Pennsylvania Indiana, PA 15705-1090
Franklin Chen Department of Natural and Applied Science, University of Wisconsin–Green Bay, Green Bay, WI 54311
The condensation trail, or contrail, that trails behind a jet plane is an everyday observable phenomenon. These manmade cirrus clouds can persist for hours, or even days and can spread over thousands of square kilometers. This is a concern because clouds are major variables that control Earth’s atmospheric temperature and climate. Understanding the impact of contrails on Earth’s climate is an active area of research (1). Further, contrail formation can be examined in terms of the operative thermodynamic phenomena. The process of contrail formation involves combustion, cooling, and ice formation, all common topics in the undergraduate physical chemistry curriculum. The project when it is subdivided into separate manageable subjects is a good, comprehensive exercise for physical chemistry students. Students start the project by reading a scenario and then are led through a series of group activities that helps them develop a better understanding of the physical processes involved in contrail formation. The project includes extensive, embedded resources that facilitate students’ calculations, and allow them to easily and quantitatively discuss the effect of various physical conditions on contrail formation. Students first estimate jet exhaust temperature and pressures. This is accomplished by assuming a simple combustion reaction, applying Hess’s law, and the temperature dependent heat capacity of the gases. A similar methodology is used in the “How hot is that flame” project (2). Armed with the gas temperature, and structural details of a typical jet engine, students can determine pressures, water vapor pressure, and the cooling that occurs using the Joule–Thomson effect. Once these calculations are complete, students use the phase diagram for water to determine the phase of the water before and after the gases exit the jet exhaust, and determine the nature of the contrail formation. The results of the calculations hinge on student choices in constructing a model for the process. These decisions include: 1. choosing a compound to use as the model jet fuel and providing the reasons for their choice; 2. determining the temperature and pressure of the combustion products under stoichiometric and adiabatic combustion conditions, including any approximations made in reaching the T, and p values; 3. determining the ambient temperature and pressure
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Three contrails formed from a three-engine McDonnell Douglas MD11 aircraft at an altitude of approximately 10,000–12,000 meters over Siberia, May 1998, by pilot and photographer Bertil Linden. From www.chitambo.com. Used with permission.
conditions identified as being appropriate to the atmosphere at the altitude where students expect to see contrail formation. Each of these issues provides an excellent opportunity for group discussions and collaboration. The zip file for this project contains the files needed for use of the project in a class intranet, including instructor notes, an assignment schedule, Mathcad templates, and a small set of assessment questions. The instructor notes provide an overview of the project. The assignment schedule and groups are the only files that must be edited every time the project is implemented. To help students get started with the calculations, Mathcad templates are included in the collection of files. A small set of assessment questions provides the preliminary step for any faculty member wishing to determine the effectiveness of the module. Note 1. The Physical Chemistry On-Line project (http:// bluehawk.monmouth.edu/~tzielins/PCOLWEB/ChemOnLine, accessed Feb 2007) has been supported by the National Science Foundation’s Division of Undergraduate Education, the Camille & Henry Dreyfus Foundation, the National Science Teachers Association, and the Foundation for Independent Higher Education.
Literature Cited 1. Pathfinder Contrail Study, NASA. http://www-pm.larc.nasa.gov/ sass/pathfinder_research.html (accessed Feb 2007). 2. How Hot Is That Flame. Theresa Julia Zielinski, Monmouth University, http://bluehawk.monmouth.edu/~tzielins/PCOLWEB/ ChemOnLine/Flame/index.htm (accessed Jan 2007).
Vol. 84 No. 4 April 2007
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Journal of Chemical Education
735
