Integral absorbance measurement for a non-uniform flow field using wavelength modulation absorption spectroscopy

Area of Science:

• Spectroscopy
• Fluid Dynamics
• Optical Measurement

Background:

• Laser absorption spectroscopy combined with computed tomography (CT) measures 2D flow fields.
• Direct absorption spectroscopy struggles with baseline distortion in harsh environments.
• Wavelength modulation spectroscopy (WMS) offers better noise rejection but faces challenges with non-uniform flow measurements.

Purpose of the Study:

• Develop an integrated absorbance measurement for non-uniform flow using calibration-free WMS (WMS-A).
• Enhance the accuracy of 2D flow field reconstruction.

Main Methods:

• Established the relationship between transmissivity and integrated absorbance.
• Integrated absorbance was incorporated into WMS harmonic signals.
• Solved for integrated absorbance by comparing measured and simulated signals.

Main Results:

• The calibration-free WMS-A method was developed and validated.
• Demonstrated the effectiveness of WMS-A for non-uniform flow measurement through systematic comparison.
• Showed that reliable integrated absorbance measurement significantly improves 2D reconstruction quality.

Conclusions:

• The WMS-A method provides a reliable way to measure integrated absorbance in non-uniform flows.
• This advancement enhances the accuracy and quality of two-dimensional flow field reconstruction.
• WMS-A offers a robust solution for challenging flow measurement environments.