Generation, Conversion, Distribution and Storage of Energy
Novel advances in theory of dynamical systems, control theory, and micro/nano-fabrication of electromechanical devices enable the researchers at CEED to propose design strategies for highly efficient energy devices. CEED is working on advances at all stages of energy use: generation, conversion, distribution and storage. These advances include harvesting energy from ambient nonlinear vibrations, use of thermoacoustic engines in energy conversion, actively controlled indoor air flows for better distribution of energy, and flywheel energy storage.
Theoretical schematic for energy harvesting nanochannel
Professors Moehlis and Pennathur are currently researching advanced concepts in energy harvesting devices. A host of environments produce considerable vibration energy such as automobiles, trains, aircraft, watercraft,
machinery, and buildings which is often an unwanted consequence of needed machinery. Instead of passively dampening these vibrations, energy harvesting devices are used to capture the energy in these unwanted vibrations and convert this energy to something useful (e.g. electricity). The challenge is to design the device keeping in mind the large variety of stochastic and nonlinear vibrations that may occur. CEED is working to leverage nonlinear resonances to capture the most amount of energy possible from these unwanted vibrations.
Many of these energy harvesting or conversion devices will be designed on small scales that do not add unnecessary size or weight to the existing machine. Working with the microfabrication teams at UCSB, CEED is investigating conventional devices that have been miniaturized, and perhaps improved, as well as microdevices that use completely novel methods of energy conversion. Examples include micro heat engines, and micro fuel cells, both of which have power densities comparable to larger-scale power plants, as well as more novel devices such as MEMS piezoelectric devices, photovoltaic cells, and biologically inspired energy conversion devices. One particular novel form of energy conversion involves an electrokinetic phenomenon called streaming potential. This form of energy conversion is especially interesting because of the simplicity of the device: all that is needed is a nanometer sized channel, water, and a pressure gradient.
Researchers at CEED have been investigating power generation devices which are much more efficient and reliable than traditional piston or turbine based systems. Professor Bamieh works on thermoacoustic energy conversion devices which is a relatively new class of devices for refrigeration and electric power generation that have very high operating efficiencies. These devices have been proposed for highly specialized applications where very low maintenance is a requirement (such as space applications) because of their extreme mechanical simplicity, lack of lubrication, and sliding seals. All such devices are based on the phenomenon of thermoacoustic instability, which is the generation of sound waves driven by a temperature gradient. Often seen as a detrimental effect in aero-engines, this instability can be viewed instead as a useful energy conversion mechanism by being harnessed to create heat pumps (e.g. refrigerators with no moving parts), or converted to electric power using a variety of schemes including energy harvesting
Thermoacoustic experiment and frequency response
Generating or converting energy efficiently is certainly a key design consideration in today's economy while attention must also be paid to transmission of this energy. In the context of building systems, where energy is traditionally convected within either air or water, poor performance in heat convection is often linked to unevenly mixed layers of hot and cold air. Actively controlled airflows, which reduce wasteful air stratification, solves a problem plaguing even most advanced state-of-the-art high performance buildings. Recent research in Professor Mezic's laboratory has established modeling techniques that enable design of efficient mixing in variety of settings and scales from the room or atmospheric level to micrometer sized flow channels.
Energy storage is also a key process that must be well understood in energy efficient design. Magnetically levitated flywheel systems used for storage of energy in form of kinetic energy are a specialty of Professor Paden. Flywheels offer a large number of cycles of operation and high peak output capacity and are particularly suitable for smoothing the 1% demand peaks on the grid. The cost of flywheel energy storage is driven by material and structure costs, and the costs of control systems employed for magnetic levitation of flywheels in a vacuum (to reduce friction).