Eric R. Morgan

A synthetic leaf: the biomimetic potential of graphene oxide

Emerging materials such as graphene oxide (GO) have micro and nano features that are functionally similar to those in plant cell walls involved in water transport. Therefore, it may now be possible to design and build biomimetic trees to lift water via mechanisms similar to those employed by trees, allowing for potential applications such as passive water pumping, filtering, and evaporative cooling. The tallest trees can raise large volumes of water to over 100 meters using only the vapor pressure gradient between their leaves and the atmosphere. This phenomenon occurs in all terrestrial plants when capillary forces generated in the microscopic pores in the cell walls of leaves are collectively applied to large diameter xylem conduits. The design of a synthetic tree that mimics these mechanisms will allow water to be moved to heights greater than is currently possible by any engineered system that does not require the use of a positive pressure pump. We are testing the suitability of membranous GO as the leaf of a synthetic tree and present an analysis in support of this design. In addition, we include results from a preliminary design using ceramics.

A hydrostatic pressure-cycle energy harvester

There have been a number of new applications for energy harvesting with the ever-decreasing power consumption of microelectronic devices. In this paper we explore a new area of marine animal energy harvesting for use in powering tags known as bio-loggers. These devices record data about the animal or its surroundings, but have always had limited deployment times due to battery depletion. Reduced solar irradiance below the waters surface provides the impetus to explore other energy harvesting concepts beyond solar power for use on marine animals. We review existing tag technologies in relation to this application, specifically relating to energy consumption. Additionally, we propose a new idea for energy harvesting, using hydrostatic pressure changes as a source for energy production. We present initial testing results of a bench-top model and show that the daily energy harvesting potential from this technology can meet or exceed that consumed by current marine bio-logging tags. The application of this concept in the arena of bio-logging technology could substantially increase bio-logger deployment lifetimes, allowing for longitudinal studies over the course of multiple breeding and/or migration cycles.

Practical Experience With a Mobile Methanol Synthesis Device

Northern Arizona University has developed a methanol synthesis unit that directly converts carbon dioxide and hydrogen into methanol and water. The methanol synthesis unit consists of a high pressure side that includes a compressor, a reactor, and a throttling valve; and a low pressure side that consists of a knockout drum, and a mixer where fresh gas enters the system. Methanol and water are produced at high pressure in the reactor and then exit the system under low pressure and temperature in the knockout drum. The remaining, unreacted recycle gas that leaves the knockout drum is mixed with fresh synthesis gas before being sent back through the synthesis loop. The unit operates entirely on electricity and includes a high-pressure electrolyzer to obtain gaseous hydrogen and oxygen directly from purified water. Thus, the sole inputs to the trailer are water, carbon dioxide and electricity, while the sole outputs are methanol and water. A distillation unit separates the methanol and water mixture on site so that the synthesized water can be reused in the electrolyzer. Here, we describe and characterize the operation of the methanol synthesis unit and offer some possible design improvements for future iterations of the device, based on experience.

Methanol From Electricity, Water and Carbon Dioxide: Operational Results

A chemical reactor has been developed that takes only carbon dioxide, water and electricity as inputs and produces a mixture of methanol and water. The system includes an electrolyzer that splits water into oxygen and hydrogen; and data logging capabilities for four temperatures probes, two pressure probes and three flow rates. The methanol synthesis unit was run under a number of flow conditions to help characterize its operation. One day of continuous temperature, pressure and flow rate data from the reactor will be presented to illustrate the system robustness. Finally, synchronized flow, temperature, and pressure data will be presented for the system as it undergoes step changes in the synloop flow rate. The results show that the flow rate through the reactor strongly influences the reactor temperature, which, in turn, influences the rate of methanol production.Copyright

A Sub-Surface Model of Solar Power for Distributed Marine Sensor Systems

The capabilities of distributed sensor systems, such as wildlife telemetry tags, could be significantly enhanced through the application of energy harvesting. For animal telemetry systems, supplemental energy would allow for longer tag deployments, wherein more data could be collected, enhancing our temporal and spatial comprehension of the hosts activities and/or environments. There are various transduction methods that could be employed for energy harvesting in aquatic environments. Photovoltaic elements have not been widely deployed in the subsurface marine environments despite a significant potential. In addition to wildlife telemetry systems, photovoltaic energy harvesting systems could also serve as a means of energy supply for Autonomous Underwater Vehicles (AUVs), as well as submersible buoys for oceanographic data collection. Until now, the use of photovoltaic cells for underwater energy harvesting has generally been disregarded as a viable energy source in this arena, with only one company currently offering solar modules integrated with marine telemetry tags. In this article, we develop a model of power available from photovoltaic cells deployed in a sub-surface marine environment. We cover the methods and tools used to estimate solar energy at depth, including the effects of: latitude and longitude, reflected solar energy off of the oceans surface, solar irradiance lost due to the absorption and turbidity of the sea water, cloud cover, etc. We present the availability of this solar energy source in the context of the energy requirements of some of these sensor systems, such as marine bio-loggers. Additionally, we apply our model to simulate the energy harvested on specific marine species in which high fidelity depth information is known. We also apply our model to simulate solar cells at certain depths under the ocean to gain a general understanding of the solar energy available at these depths.Copyright

Marine Energy Harvesting Using Magnetohydrodynamic Power Generation

Energy harvesting is widely used in terrestrial and aerial sensor applications but is conspicuously absent in the marine environment despite several possible harvesting modalities and numerous applications. One such energy harvesting modality is to use magnetohydrodynamic (MHD) power generators to directly produce electricity from flowing seawater. Fundamentally, MHD generators convert the kinetic energy of a conductive fluid directly into electricity by separating charged particles, thereby generating an electric field transverse to the direction of fluid flow and the magnetic field. The electric field is then accessed with an external circuit to provide power to a load. Since the power output from an MHD generator is linearly related to the conductivity of the flowing fluid and to the square of both the magnetic field strength and the fluid velocity, strong magnets and high fluid velocity are desirable. Thus, there are a myriad of possible MHD generator configurations available to maximize power output under various conditions and constraints. These include configurations of permanent magnets that offer localized high magnetic fields or geometries of the fluid duct that can be used to increase thefluid velocity through the magneticfield. One novel application for MHD generators is to power sensors and bio-loggers used in marine animal telemetry. The animal sensors are designed to take time-series measurements and store the data on the logger for transmission to satellite networks or human retrieval. These sensors and loggers are often battery-limited which constrains either the data fidelity or the longevity, or both. An MHD generator attached to a marine animal can help to sup

Energy Harvesting for Marine-Wildlife Monitoring

Bio-logging devices are systems mounted to an animal that measure parameters associated with the animal or its environment. These devices date back to the 1930’s in their simplest form, while modern devices use suites of digital sensors, microcontrollers, and wireless data communication. Despite these advances, there has always been a fundamental relationship between power consumption and the amount of science that can be conducted. There are now a number of commercially available devices that use solar cells to supplement their daily energy budget, but supplemental solar power is not useful for species that are nocturnal, subterranean, aquatic, or spend significant time beneath dense forest canopies. As such, there have been calls from the marine biology community for devices that could harvest power from their environments. For these marine species, alternative energy harvesting techniques are required. Here we explore a new application for energy harvesting as a power source for marine wildlife bio-logging tags. Marine animals cover wide swaths of the ocean, making tracking and data collection challenging. Tagging these animals with devices that track their location and/or collect data about the animal or its surroundings require large batteries and have limited life spans due to high power requirements for satellite data relays. With limited solar irradiance at depth making solar power less attractive, we review and explore other forms of energy that could be harvested, such as energy from fluid flow and hydrostatic pressure cycles. We investigate the energy potential from a number of sources and compare these values with the requirements of current bio-logging systems to assess required transduction efficiencies. The application of energy harvesting on animal tags could result in nearly indefinite life systems allowing for data collection from a single animal over the course of many years.Copyright