Laser-based measurement

This chapter covers a description of conventional measurement techniques used in ventilation as well as othei related topics such as flow visualization, laser- based measurement techniques, and scale model experiments. 

Since the calibration factors for these techniques are known and relatively stable (depending on constant optical and geometrical parameters), the calibration process for laser-based measurements is simple or can be ignored. 

Laser-Based Measurements for Time and Frequency Domain Applications A Handbook... 

In this book, most chapters deal with FT-IR spectrometry and its applications to various methods of infrared spectroscopic measurements. Only terahertz spectrometry in Chapter 19 and a large part of time-resolved infrared spectrometry in Chapter 20 are laser-based measurements. This shows how widely FT spectrometry is used at present in the measurements of vibrational spectfa. 

The traditional non-intrusive laser based measurement techniques like LDV and flow visualization, did provide either a point measurement or a qualitative indication [38]. The conventional techniques could not provide quantitative and instantaneous flow information for a whole flow plane. The ability to quantify transient multiphase flow phenomena is crucial to the understanding of the flow mechanism and development of fundamental theories. These limitations of the conventional measuring techniques were overcome by the PIV technique which combines the accuracy of LDV with the qualitative information from the flow visualization and is a quantitative technique for measuring the instantaneous flow field for a plane. 

Laser-based profilometry is now being applied to a wide variety of both NDT and Quality Control gauging applications. In the world of NDT, the primary interest is in the details associated with surface topography or deformation of a particular component. Laser-based profilometry systems are commonly used to inspect surfaces for defects such as pitting, corrosion, deformation and cracking. Quality control gauges are used for absolute measurement of dimensions, such as the diameter and thickness of a given part. 

Laser-based profilometry systems have also been applied for nondestructive testing and measurement of both smooth-bore and rifled gun tubes. Working through Small Business Innovation Research program, the U.S. Army has developed laser-based profilometry systems for the inspection of the 120mm cannon used on the MI-Al Abrams main battle tank. Systems have also been built to measure the erosion of 25 mm and 155 mm rifled gun tubes. 

Other examples of government and military applications of laser-based profilometry include the evaluation of rocket thruster nozzles to locate and measure flame erosion remote inspection of hypervelocity test track and the measurement of sludge deposits on tube internal surfaces. 

Doyle, J. L., Wood, G. R., and Bondurant, P. D. Using Laser-Based Profilometry to Locate and Measure Corrosion Fatigue Cracking in Boiler Tubes, Materials Evaluation, D The American Society of Nondestructive Testing, Inc., Vol. 51, No. 5, pp. 556-560 (1993). 

A method which competes with interferometric distance measurement is laser Doppler displacement. In this approach the Doppler shift of the beam reflected from a target is measured and integrated to obtain displacement. This method also is best suited to use indoors at distances no more than a few hundred meters. Table 2 compares some of the characteristics of these laser-based methods of distance measurement. 

All three experimental approaches are presented in this chapter visualization of airflow and contaminant dispersion (Section 12.2), measurement techniques including laser-based-techniques (Section 12.3), and scale model experiments (Section 12.4). 

In addition to their widespread use in research and development in fluid dynamics, laser-based techniques ° are also suited to experiments in industrial ventilation. The use of these advanced experimental methods is reasonable when their advantages in comparison with traditional measurement techniques counterbalance the significantly higher expenses of instrumentation. 

With the use of appropriate transmission optics, high focusing of the laser light is carried out and the extension of the optical probe is considerably reduced. Accordingly, laser-based techniques offer the possibility of measurements of high spatial resolution. 

The use of laser-based techniques is ideal for practicing engineers in the field of industrial ventilation for the following on-site measurements and laboratory applications ... 

DL Black, MQ McQuay, MP Bonin. Laser-based techniques for particle-size measurement a review of sizing methods and their industrial applications. Prog Energy Combustion Sci 22(3) 267-306, 1996. 

The Doppler-selected TOF technique is one of the laser-based techniques for measuring state-specific DCSs.30 It combines two popular methods, the optical Doppler-shift and the ion TOF, in an orthogonal manner such that in conjunction with the slit restriction to the third dimension, the desired center-of-mass three-dimensional velocity distribution of the reaction product is directly mapped out. Using a commercial pulsed dye laser, a resolution of T% has been achieved. As demonstrated in this review, such a resolution is often sufficient to reveal state-resolved DCSs. 

A laser-based detection system for NO2 gas (which is an industrial hazard and common environmental pollutant) was developed by Koybayashi et al.4. This was achieved by splitting light, from an Ar-ion multi-line laser, into two paths, one passing through a measurement gas, and the other being transmitted directly to the measurement unit as a reference signal. The detection unit contained two filters to separate the two chosen laser lines, and these were then detected on separate optical receivers. One of these chosen laser lines coincided with a strong absorption line in the NO2... 

Second, due to the difficulty of accessing multiphase flows with laser-based flow diagnostics, there is very little experimental data available for validating multiphase turbulence models to the same degree as done in single-phase turbulent flows. For example, thanks to detailed experimental measurements of turbulence statistics, there are many cases for which the single-phase k- model is known to yield poor predictions. Nevertheless, in many CFD codes a multiphase k-e model is used to supply multiphase turbulence statistics that cannot be measured experimentally. Thus, even if a particular multiphase turbulent flow could be adequately described using an effective viscosity, in most cases it is impossible to know whether the multiphase turbulence model predicts reasonable values for... 

Optical Laser Displacement Measuring laser based triangulation principle Micro-Epsilon optoNCDT 2200... 

Laser nephelometry is based on measuring the turbidity of an aqueous medium after adding a fixed amount of solution of a compound in dimethyl sulfoxide (DMSO).41 Dehring et al.42 described an automated robotic system with laser-based nephelometry for high-throughput kinetic aqueous... 

Dehring, K.A. et al. 2004. Automated robotic liquid handling/laser-based nephelometry system for high throughput measurement of kinetic aqueous solubility. J. Pharm. Biomed. Anal. 36 447. 

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