Measurement of Transient Heat Flux and Surface Temperature Using Embedded Temperature Sensors

Overview

The document presents a study on measuring transient heat flux and surface temperature using embedded temperature sensors, conducted by Edward Coy at the Air Force Research Laboratory. The research addresses the challenges associated with traditional surface junction thermocouples, which are prone to failure and produce noisy signals, particularly in dynamic environments like rocket engine flows.

The proposed method utilizes two temperature sensors embedded within the wall of a chamber, allowing for accurate measurements without the drawbacks of surface-mounted sensors. The approach employs a polynomial extrapolation technique that matches temperature readings and their second derivatives at the measurement points, enabling the calculation of heat flux and surface temperature. This method is computationally efficient, requiring approximately 100 multiply and add operations per measurement.

Key findings indicate that the solution behaves like a low-pass filter, with gain characteristics that vary based on the ratio of the distances between the sensors. The study characterizes the gain and phase behavior of the system, revealing that the phase angle begins to lag at higher angular frequencies, except in specific cases where the ratio of distances is optimal.

The document also includes experimental data from a sub-scale rocket combustion chamber, where Type K thermocouples were embedded in a copper block. The experiments were conducted with gaseous hydrogen and oxygen as reactants, under high pressure and flow conditions. The results demonstrate the effectiveness of the proposed method in measuring surface temperature and heat flux, with a focus on the uncertainties that arise during rapid temperature changes.

Overall, the research provides a robust framework for measuring heat transfer in high-performance environments, contributing to the understanding of heat transfer enhancement due to surface features. The findings are expected to have significant implications for future studies and applications in aerospace engineering and related fields, where precise thermal measurements are critical for performance optimization and safety.