Thermally driven Knudsen gas pump enhanced with a thermoelectric material.

Thermal transpiration;Molecular flow;Gas micropump;Peltier coder;Knudsen pump;Nanoporous thermoelectric

Kunal Pharas, 1979-

University:University of Louisville

Department:Electrical and Computer Engineering

关键词: Thermal transpiration;    Molecular flow;    Gas micropump;    Peltier coder;    Knudsen pump;    Nanoporous thermoelectric;   

Others  :  https://ir.library.louisville.edu/cgi/viewcontent.cgi?article=2126&context=etd

美国|英语

来源: The Universite of Louisville's Institutional Repository

【 摘 要 】

The thesis focuses on improving the flowrate of the Knudsen gas pump. The Knudsen pump uses thermal transpiration as the driving mechanism to pump gas. It is a motionless gas pump as the pump does not require any moving actuators for pumping. The thermally driven gas flow is accomplished in the molecular or transitional gas flow regime. The advantage of this pump is that without any moving parts it avoids friction losses and stiction problems which devices in micro scale are prone to suffering due to scaling issues. Thus, this pump is highly robust and reliable. Knudsen pumps in the past have suffered from the drawback of low flowrates and inability to operate at atmospheric pressure. In the early days lack of micromachining technologies limited minimum channel size which had to be operated at lower than atmospheric pressure to achieve free molecular flow. Various designs have been implemented with an impetus on increasing the flowrate of the pump. The key to this pump is establishing a temperature difference along the length of the channel. A higher temperature difference over a shorter channel length makes the pump more efficient. Pump channels have been made out of various materials like silicon, glass and polymer. The silicon microfabricated single channel conventional design pump suffered from the high thermal conductivity of silicon, which limited the thermal gradient that could be achieved. Silicon was replaced by glass, which has a lower thermal conductivity. The glass micro fluidic pump could pump water in reservoirs but at a slow rate. Renewable forms of Knudsen pump were also made by using nanoporous silica colloidal crystals which are robust and could use solar energy and body heat to create a temperature difference and achieve pumping. The pump powered by body heat produced a maximum pressure differential of 1.5 kPa. However, the use of these pumps is restricted to certain applications due to slow pumping. The polymer material, made of mixed cellulose ester, has a very low thermal conductivity, which aids in maintaining a higher temperature difference between the ends of a channel to achieve a higher flowrate. The polymer material used is in the form of a nanoporous template which has numerous pores each of which acts as a pump and thus the pump's conductance to gas flow is also increased which makes it faster. The pore sizes range from 25 nm to 1200 nm. It has been proven