Laser Doppler Velocimetery for Flow Measurements in Pulp and Paper Research, 1996 Engineering Conference Proceedings

Optical diagnostics have become prevalent in research and development because they provide a nonintrusive mechanism for probing active processes and physical phenomena. Many optical techniques and instrumentation have been widely used by scientists and engineers in various fields for both basic research and practical applications. While there are a few researchers in the pulp and paper community who are very familiar with and have used several optical diagnostic methods in their research, many industrial researchers are still skeptical and uncomfortable to use modern research tools. The objective of this paper is to introduce a very basic optical tool - the laser Doppler technique - to the pulp and paper scientific community. The paper will consist of four parts: (1) the basic principle of the laser Doppler technique for velocity measurements, (2) overview of historical and recent developments in laser Doppler technology, including fiber optic, diode lasers, digital signal processing, and fast Fourier transform, (3) discussion of measurement errors, advantages, and disadvantages of certain signal processing methods used in laser Doppler technology, and (4) the challenges of applying the Doppler technique in pulp and paper research. The intention of the paper is twofold: to make an introductory presentation on the laser Doppler technique for researchers who are new to the subject and to give an in-depth look into the fundamentals of various scientific issues associated with the laser Doppler technique for those who are familiar with the technique. It is anticipated that this paper will help readers to...