Date of Graduation

5-2018

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Engineering (PhD)

Degree Level

Graduate

Department

Mechanical Engineering

Advisor/Mentor

Po-Hao Huang

Committee Member

Jeff Wolchok

Second Committee Member

Ingrid Fritsch

Third Committee Member

Uche Wejinya

Fourth Committee Member

Larry Roe

Keywords

Cold-gas, CubeSat, Nanofluidics, Propulsion, Undercooling, Water

Abstract

Microelectromechanical systems (MEMS) and nanoelectromechanical systems (NEMS) generate ideas and techniques for creating new devices at the micro/nano scale. This dissertation study designed a gas generator system utilizing nanochannels for phase separation that is useful for micro-pneumatic actuators, micro-valves, and micro-pumps. The new gas generator has the potential to be an integral part of a propulsion system for small-scale satellites. Nano/picosatellites have limited orientation capability partly due to the current limitations of microthruster devices. Development of a self-contained micro propulsion system enables dynamic orbital maneuvering of pico- and nano-class satellites.

Additionally, the new gas generator utilizes a high efficiency, green propellant that is less harmful to the environment. This dissertation study tested aqueous antifreeze solutions to verify vapor pressures and establish previously unknown kinematic viscosities. A viscometer, developed expressly for this study, measured kinematic viscosity values between 1E-2 and 1E-4 m2/s for water solutions mixed with propylene glycol, ethylene glycol, methanol, and glycerol.

CubeSats, 10-centimeter cube satellites, are volume limited, and high strain expansion of water during crystallization could destroy the structure. Validation of the freezing point depression and measurement of previously unknown percent expansion with increasing concentration are valuable for setting safe design specifications. A 7.5 %w/w propylene glycol-water solution reduces the overall expansion by 2% while 20 %w/w PG reduces the expansion 4%.

Potassium hydroxide etched silicon micro/nanochannels regulated vaporization of aqueous propylene glycol to a vacuum environment. Sequential still images captured with a Basler Scout camera were used to measure mass flow rates, representative of Washburn capillary flow. Magnitude of single channel flow rates ranged from 1E-10 mol/s to 1E-8 mol/s for 600nm channels up to 12μm channels, respectively. Although the flow rate increased using nanochannel arrays, it was 35% slower than expected based on single nanochannel measurements.

A system utilizing nanochannel arrays for fluid phase separation, with propylene glycol as the propellant, is feasible in a low-cost, green, non-toxic, and non-pressurized CubeSat propulsion system. Depressing the freezing point of water by adding antifreeze creates a wider liquid working range, decreases power requirements, but also maintains appreciable flow rates for thrust generation (micro-millinewton). Successful nanofluidic research on an aqueous antifreeze solution is foundational for future propulsion system research and pushes CubeSats in the right direction.

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