Development of cryogenic liquid sensors to monitor flow and pressure

Abstract

This thesis presents the development and implementation of a bearing-less propeller flow meter designed for reliable cryogenic fluid flow measurement, particularly in applications requiring precise flow control and protection of liquid nitrogen cooled high-power laser systems. Traditional flow meters, such as differential pressure, turbine, variable area, and thermal flow meters, present significant limitations in cryogenic environments, including susceptibility to freezing, pressure drop-induced cavitation, and inaccuracy in two-phase flow conditions. To address these challenges, a custom flow meter was developed based on a flat propeller design with a magnetic pickup sensor, ensuring minimal friction and improved sensitivity at low flow rates. The system operates by detecting the rotational frequency of the propeller, which is converted into a proportional voltage signal. The final design includes real-time monitoring using an Arduino and a programmable display, providing flow rate readings and an interlock signal for system safety. A safety interlock mechanism was integrated into the control system of a high power laser system to protect it by automatically shutting it down if the flow rate falls below the required threshold to prevent overheating and damage of the laser gain medium, in this case Yb:YAG. Additionally, a diaphragm cryogenic pressure sensor was developed and used in combination with the flowmeter to characterize a liquid nitrogen-based cooling system. This approach ensures a reliable cryogenic flow measurement system with minimal pressure loss. The bearing-less propeller flow meter offers a robust alternative to conventional metering techniques, making it an optimal solution for applications requiring precise cryogenic fluid management. The results demonstrate that this design successfully addresses the challenges associated with cryogenic flow measurement while ensuring the protection and optimal operation of sensitive laser systems and other applications.