The Second Law and Energy

http://mitworld.mit.edu/video/543

About the Lecture

This Nobel Prize-winning scientist admits to staying up late the night before his talk to bone up on thermodynamics. He puts his research to good use, discussing the history and application of the laws of thermodynamics, which have served as “the scientific foundation of how we harness energy, and the basis of the industrial revolution, the wealth of nations.”

Taking Watt’s 1765 steam engine, Stephen Chu illustrates basic principles of thermodynamics -- that energy is conserved, that you can do work from heat, especially when you maximize the difference in temperature in the system and minimize heat dissipation from friction. Chu offers another form of the laws: You can’t win; you can’t break even; and you can’t leave the game.

The game hasn’t changed all that much in the past few centuries. Nations now burn coal for electricity, achieving around 40% thermal efficiency. Natural gas can be harnessed at higher efficiencies still, and if we could deploy temperature-resistant metals for boilers, even less energy would go to waste. This is a pressing matter, points out Chu, because the planet can no longer afford wanton use of carbon-based fuels. With too much CO₂, our global “heat engine” has begun to tip toward a point of no return. So the big question for Chu is whether science can design “entropy engines that can generate sustainable (carbon-free) energy sources.

He describes efforts to capture sunlight with improved solar cells, but notes that a silicon shortage, expensive chips, and a learning curve dictated by Moore’s law mean the technology won’t be widely deployed for 10-15 years -- not fast enough in the battle against climate change. Chu likes the efficiencies of power generation from wind, but there’s a limit to turbine size, and the U.S. high voltage transmission network needs a complete and expensive makeover to take full advantage of wind. Forget corn as biofuel, he counsels, since it “barely breaks even in terms of CO₂ saved,” and focus instead on perennial grasses like miscanthus. Chu’s lab and others are looking for microbes that can help turn these plants more readily into fuels.

Another potentially rich energy source, Chu says, involves converting sun light into fuel the way plants do in photosynthesis. But “how does nature split water?” asks Chu. Science hasn’t entirely figured out the molecular machinery that turns water into oxygen and hydrogen. Deriving bioenergy through artificial photosynthesis may mean considering entropy and other basic laws in a different light, Chu suggests. “Nature turns out to be very good.”

The Second Law and Energy (Panel)

http://mitworld.mit.edu/video/546

About the Lecture

In this valedictory panel to the two-day symposium, 10 speakers offer brief takes on how the Second Law of Thermodynamics might prove useful in seeking answers to our current energy challenge.

Even before the oil embargo of 1973, Thomas Widmer recalls, Joe Keenan and his MIT colleagues wrote of an “entropy crisis.” They analyzed the flow of work in industries and saw great inefficiencies that became crippling when fuel prices spiked. Despite 30 years of improvement, says Widmer, “the effectiveness of energy use is still less than 12%.” In selling ideas to policy makers, he advises, talk about “energy productivity” rather than conservation.

Ernest S. Geskin doesn’t believe alternative energies will be viable quickly enough to make a serious difference in climate change, so his objective is to improve combustion. He outlines several methods he’s developing that increase the availability of generated heat, reduce heat losses, and integrate combustion with materials production and processing, such as in steelmaking.

James Keck says that “improving the efficiency and reducing emissions of auto engines and power plant burners requires an ability to model hydrocarbon combustion.” He recommends using a method “firmly based on the Second Law of Thermodynamics: the rate controlled constrained equilibrium method,” which, among other advantages, generates fewer equations, and is applicable to any separable system.

Seeking ways to make reactions more efficient and “less exergy destructive,” Noam Lior recommends a detailed, top-down methodology. His lab has been examining oil droplet and coal combustion in an attempt to understand why exergy losses take place, and to determine “which process will give us the highest exergy efficiency.”

Debjyoti Banerjee’s research focuses on enhanced cooling and explosives sensing. His lab explores phase changes for boiling and condensation, and develops new models in molecular dynamics, harnessing the energy of nanosphere transport processes. A “nanobubble” serves as a heat engine, and Banerjee is examining how “nanofins help in transferring heat.”

Richard Peterson is taking a look “at how small you might be able to make the classic thermodynamic heat engine, so you could integrate it into portable equipment or other devices requiring power, and burn fuel with much higher energy density than found in a battery.” He notes that “your efficiency takes a nosedive as you shrink the engine.”

Erik Ydstie is concerned with dynamic systems like power plants, and how they can be improved, by manipulating their inputs and outputs. By designing better controls to regulate these complex systems, there’s a “lot of scope to improve the efficiencies of these plants. You could get quite a bit of mileage by running them better.”

Ron Zevenhoven “presents the embryo of an idea: Can the infrared radiation that causes the enhanced greenhouse effect be put to better use?” He wants to see whether science can modify the infrared radiation that leaves the earth, in order to cut back on radiative forcing higher up.

Zhuomin Zhang discusses radiation entropy and how near-field thermophotovoltaic devices “may be another way of effectively using energy.” He wonders how to apply the entropy concept to near-field radiation when interference is a problem.

Ahmed Ghoniem says that while we won’t run out of cheap fossil fuels for some time, “we need to think about an insurance policy” in response to the predictions of a four to six degree rise in Earth’s temperature by the end of the century. “The dirty little secret is once you burn the fuel you automatically generate entropy -- you lose about 20% right off the bat.” Ghoniem asks whether “combustion and heat engines can be reinvented to reduce entropy generation, practically and at scale.”