Development of an Experimental Setup to Examine Bubble Behavior in Curved Microfluidic Channels under Microgravity Conditions

Abstract

Bubble management in microgravity presents a critical challenge for spacecraft fluid systems, where the absence of buoyancy allows bubbles to remain suspended within liquids, threatening systems such as life support and water purification. Microfluidic channels offer a promising passive approach to bubble manipulation through geometry-based control. The Complex Fluids Group at Princeton University has been investigating the behavior of bubbles in curved microchannels with the goal of understanding how to efficiently focus them using curvature. Their ground-based experiments determined that curves heavily influence bubble dynamics, causing the bubbles to deform and migrate toward the inner wall of the channel. They hypothesize that taller channels, where gravitational forces are no longer negligible, in microgravity should have the same effect on bubble behavior as shorter channels on Earth. This thesis documents the design, fabrication, and ground-based validation of a flight-ready, semi-autonomous experimental setup which will allow the Complex Fluids Group to test their hypothesis on a parabolic microgravity flight. Developed within the TigerSats Lab, the design consists of a rolling cart as the primary structure, a gas system to inject nitrogen into the experimental channels, a liquid system where fluid injection is routed to specific channels via a motorized rotary valve, and an imaging system that precisely positions a high-speed camera. The platform utilizes a Raspberry Pi-based control system with a keypad interface where a single input seamlessly synchronizes the rotary valve's fluid injection with a linear stage, rapidly aligning the high-speed camera to the targeted channel. The system also continuously logs inertial measurement unit (IMU) acceleration data. Ground testing validated this automated integration and demonstrated an average sample-switching time of 11.78 seconds. Ultimately, this setup will allow for efficient data collection that can inform the design of novel, passive degassing methods in space.