Development of an Actively-Cooled Imaging System for Embedded Optical Measurements in High-Speed Flows

Abstract

High speed airbreathing propulsion systems have become increasingly complex with the development of hypersonic scramjet engines. Analysis of scramjet flow structures is difficult due to extreme thermal environments and limited optical access to internal flow paths. This study introduces an innovative actively-cooled miniature imaging system designed to broaden the applications of low-cost, small form factor image sensors for integration into extreme thermal environments, facilitating the observation of high-enthalpy flows.

The developed system enables non-intrusive optical flow field measurements in confined flows where traditional imaging systems have limited optical access. The design incorporates a cooled image sensor housing that actively cools the image sensor and lens assembly by immersing them in a dielectric cooling liquid, Fluorinert FC-72. The internal geometry of the housing facilitates the flow of the dielectric coolant, effectively regulating the thermal environment around the entire sensor package. A thermal management system regulates the thermal environment inside of the enclosed housing to protect the image sensor. A closed-loop cooling system continuously supplies fresh coolant to regulate hardware temperatures.

Experimental analysis demonstrated the actively-cooled miniature imaging system's capability to maintain the thermal environment of an image sensor at 100◦F during extended exposure to 1,450◦F, simulating a high-temperature flow path. This validates the system's ability to capture images in high-temperature supersonic flows, laying the groundwork for potential applications in high-enthalpy supersonic test facilities. Implementation of optical bandpass filters in the system design allows the system to capture chemiluminescence emissions produced by radicals in a methane flame, verifying the system's ability to generate spectrally-resolved images consistent with traditional image-based diagnostics of reacting flows.

This actively-cooled miniature imaging system offers a novel solution for internal flow measurements in high enthalpy flows, employing dielectric immersion cooling and cost-effective hardware components to observe regions that have been traditionally challenging to observe and measure. With further development, this system has the potential to be adapted as an inexpensive, lightweight, economical tool to obtain images during flight experiments in demanding thermal environments.