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

A report describes approximate solutions for surface temperature and heat flux for two embedded temperature sensors. The solutions were verified and the range of validity was established using several methods including comparisons with an exact analytical solution for a linear problem and a numerical calculation for a non-linear problem.

The solutions place no restrictions on the boundary or initial conditions and rely only on current values of temperature and its rate of change. The temperature dependence of transport properties is accounted for in an approximate way. The method requires minimal computation and is suitable for implementation in a real-time sensor.

The method measures surface temperature and heat flux based on two temperature sensors embedded in the wall of a chamber. The method does not require surface junction thermocouples, which are prone to failure and produce noisy signals in rocket engine flows, and is well suited for studies of the effects of surface features on heat transfer enhancement.

The method requires only current values of temperature and its rate of change and the boundary and initial conditions are arbitrary. The algorithm can be represented as a low pass filter, and the gain and phase behavior have been characterized. The placement of the sensors affects the frequency cutoff and the noise response and optimum values for the relative positions of the sensors have been obtained. The method utilizes time derivatives of temperature data, which can be efficiently calculated using a polynomial smoothing filter.

This work was done by Edward Coy of the Air Force Research Laboratory. AFRL-0112

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