Shamus McNamara, University of Louisville Proposal #1133877
The Knudsen pump is a thermally driven gas pump which features no moving parts, potentially providing very high reliability. For MEMS devices, the lack of seals is especially attractive. The Knudsen pump uses the principle of thermal transpiration as the basis of its operation, and thus must operate in either the free molecular flow regime or near the free molecular flow regime in the transitional flow regime. For operation at atmospheric pressure, sub-micron channel cross-sections are required for operation, with channel diameters on the order of 100 nm commonly utilized. The objectives of this research project are to (1) improve the efficiency of the Knudsen gas pump, (2) develop a method to integrate the Knudsen pump with microfluidic applications in a simple, efficient manner, (3) better model and understand gas pumps based upon the thermal transpiration effect through unobstructed channels, (4) explore efficient methods of using the Knudsen Pump to generate pneumatic energy from heat sources, such as body heat and solar thermal energy. New thermoelectric materials will be investigated for use in the Knudsen pump, and prototype pumps using these materials will be tested. Studies on the effects of surface roughness of the channels making up the Knudsen pump will be performed, as there is experimental evidence to suggest that the tangential momentum accommodation coefficient (TMAC) can have a significant impact on the performance of the Knudsen pump. The expected outcomes include a smaller, more efficient Knudsen pump with better pump performance, a better understanding of the limitations of the Knudsen pump, a better theoretical model describing how the Knudsen pump operates, a better understanding of how microfluidic devices can incorporate the Knudsen pump, and a demonstration of the Knudsen pump used to generate pneumatic energy from heat sources.
Because the Knudsen pump features no moving parts, an efficient Knudsen pump has many applications where pump size, noise, or reliability is a concern. It can also be integrated with microfluidic devices, providing a key component for many lab-on-a-chip devices that are under development for medical diagnostics and fast, efficient drug and materials research.
As a passive device, the Knudsen pump has the potential to generate pneumatic energy from waste heat, such as the catalytic converter of an automobile or manufacturing plant. It can be powered from the sun, generating pneumatic power than can be used to run a generator. And it can be powered from human heat, opening up applications for biomedical devices.
A Knudsen gas pump is a type of pump with no moving parts, no seals that must close, and can operate continuously. The pump requires a temperature difference across either a nano-porous material or a nano-channel. The Knudsen gas pump will pump a gas from the cold side to the hot side. An efficient Knudsen pump has many applications where pump size, noise, or reliability are a concern. It can also be integrated with microfluidic devices, providing a key component for many lab-on-a-chip devices that are under development for medical diagnostics and fast, efficient drug and materials research. As a passive device, the Knudsen pump has the potential to generate pneumatic energy from waste heat, such as the catalytic converter of an automobile or manufacturing plant. It can be powered from the sun, generating pneumatic power than can be used to run a generator. And it can be powered from human heat, opening up applications for biomedical devices. This research was carried out to better understand how Knudsen gas pumps operate. Typically, this type of pump is made using very thin materials, making it very difficult to maintain a temperature difference between the two sides. To address the problem of maintaining a temperature difference, we have worked with thermoelectric modules. Typically a thermoelectric module is used to cool a volume, such as when they are used in thermoelectric coolers. The thermoelectric module transfers heat from the cold to hot side. We wish to use a variant of a thermoelectric module that can also pump gas molecules. One of the goals of this work was to develop a new multi-functional material that is both nano-porous to pump the gas and a thermoelectric material to generate the temperature difference. We have successfully developed this type of material. We characterized the material in terms of its porosity, thermoelectric properties, thermal conductivity, and electrical conductivity. Finally, we demonstrated the first Knudsen gas pump using this material. At the same time as we worked on the nano-porous thermoelectric, we investigated methods of making a Knudsen gas pump that is powered using either solar power or heat from the human body. For the solar powered Knudsen gas pump, the sun heats one side of the pump, causing the pump to operate. For the human body powered Knudsen gas pump, one side of the pump is placed on the human body, and the body heat causes the pump to operate. We have made some nice demonstration pump which can move a drop of water through a pipe when a person places his or her thumb on the pump. Finally, we did a lot of theoretical work on the Knudsen gas pump to better understand how it will perform. This work has shown us methods that can be used to optimize future Knudsen gas pumps.