Discussion on “The Second Law and Energy”

This article reports an open discussion that took place during the Keenan Symposium "Meeting the Entropy Challenge" (held in Cambridge, Massachusetts, on October 5, 2007) following the short presentations—each reported as a separate article in the present volume—by Thomas Widmer, Ernest Geskin, James Keck, Noam Lior, Debjyoti Banerjee, Richard Peterson, Erik Ydstie, Ron Zevenhoven, Zhuomin Zhang, and Ahmed Ghoniem.All panelists and the audience were asked to address the following questions• Current state‐of‐the‐art efficiency of combined‐cycle energy conversion technology is about 60%. Based on the trend of historical data, some forecast that second‐law efficiency of energy conversion will reach 80% by the end of the century. What technologies are at sight that might hold this promise?• Nanotechnologies and microtechnologies point towards the development of microscopic heat engines? How do second law limitations map down to these scales?• Combustion is the principal way of converting the chemical energy of fossil fuels to thermal energy, but it is highly irreversible. Are there promising ways to reduce combustion irreversibility? Are fuel cells the only alternative to combustion?