Non-intrusive Methods

The earliest estimates of the enol content of various p-diketones was made by careful distillation (Meyer and Schoeller, 1920 Meyer and Hopflf, 1921). Although, as a method of studying the equilibrium, this approach has been replaced by non-intrusive methods, work on the physical separation of the tautomers has continued (e.g. Regitzand Schafer, 1981 Vogt and Gompper, 1981). 

Summary. Spectroscopic techniques, in particular laser induced fluorescence, appear as a good analytical tool for complexation measurements since they are non-intrusive methods, they allow to work at low level of cation concentration (in the case of TRLIF), in particular below the solubility limits permitting to cover a large range of pH and they also allows the use of low humic acid concentrations to avoid aggregation phenomena. From the conditional interaction constants measured by these techniques, the following trend of actinides for humic acids is deduced ... 

A non-intrusive method for RTD characterization has been claimed [17], which has been proven already for visualization of velocity fields in microchannels [18]. Aphoto-activated fluorescent dye dissolved in an aqueous solution is introduced continuously into a flow. A defined section of the inlet channel is exposed to a UV pulse to activate the tracer, which turns fluorescent Due to this inside start of the pulse experiment, artifacts from peripheral equipment can be eliminated. The method generates almost ideal input signals, which simplifies the numerical treatment of experimental data. The new approach was found to be superior to various traditional injection methods. The ideal shape of the stimulus signal was demonstrated for an analytically well-defined straight channel and compared with a signal derived from deconvolution of non-ideal input signals [19]. 

Consequently, a common effort should be made to establish and complete the data basis concerning the numerous thermodynamic, thermophysical, transport and rheological properties necessary for modeling and simulating the different steps of this complex mild drying process. Moreover, the methods available for the characterization of most of these end-use properties should be improved and additional characterization methods should be adapted from other research fields (material science, applied biochemistry, physical chemistry, etc.). Improved characterization methods promise a better description and a safer control of numerous end-use properties for existing freeze-dryers as well as for new machines with more possibilities to better comply with more and more severe quality requirements in the future. The use of non-invasive sensors or of rapid non-intrusive methods for on-line and in situ estimation of the main parameters of the process could also help to overcome the difficulties observed, for example, the artifacts resulting from invasive sensors inserted inside vials and presently commonly used. 

Modern NDT methods are becoming ever more quantitative and non-intrusive. This is valid for NDT of new construction and for maintenance inspections. 

Overall, the technical complexity of the Deans switch system is considerably greater than that of a mechanical switching valve and it is accepted that reliability and ease of use is reduced as the system complexity increases. For many compound types, however, the completely non-intrusive nature of the Deans method offers sufficient advantages to justify its application. However, the use of modern electronic pressure and flow controls integrated into the overall computer control of the chromatographic system does now make the operation of Deans switches significantly easier or more reliable than has been reported in its earlier applications. 

Information on particle size may be obtained from the sedimentation of particles in dilute suspensions. The use of pipette techniques can be rather tedious and care is required to ensure that measurements are sufficiently precise. Instruments such as X-ray or photo-sedimentometers serve to automate this method in a non-intrusive manner. The attenuation of a narrow collimated beam of radiation passing horizontally through a sample of suspension is related to the mass of solid material in the path of the beam. This attenuation can be monitored at a fixed height in the suspension, or can be monitored as the beam is raised at a known rate. This latter procedure serves to reduce the time required to obtain sufficient data from which the particle size distribution may be calculated. This technique is limited to the analysis of particles whose settling behaviour follows Stokes law, as discussed in Section 3.3.4, and to conditions where any diffusive motion of particles is negligible. 

Houcine et al. (64) used a non-intrusive laser-induced fluorescence method to study the mechanisms of mixing in a 20 dm CSTR with removable baffles, a conical bottom, a mechanical stirrer, and two incoming liquid jet streams. Under certain conditions, they observed an interaction between the flow induced by the stirrer and the incoming jets, which led to oscillations of the jet stream with a period of several seconds and corresponding switching of the recirculation flow between several metastable macroscopic patterns. These jet feedstream oscillations or intermittencies could strongly influence the kinetics of fast reactions, such as precipitation. The authors used dimensional analysis to demonstrate that the intermittence phenomenon would be less problematic in larger CSTRs. 

In general, the investigation techniques used so far were constrained by the use of intrusive methods and the limitation in access to clear and non-intrusive visualization of the boiling process. 

Non intrusive static methods-Small Angle Scattering of partially blocked membranes by sorbed vapors... 

SAS can detect the presence of non-accessible to vapor pores, which cannot be detected by the intrusive methods, such as sorption. If no such pores exist, a good agreement is expected between the intrusive sorption and the non-intrusive SANS, as illustrated in Fig. I where, an experimental water adsorption isotherm on a mesoporous alumina membrane, made by compressing non-porous spherical particles, is compared to the corresponding one reconstructed from the SANS data. 

Raman spectroscopy is a light scattering method that is non-intrusive sampling, sample form and sample size are generally not restrictions for the analysis. Like infrared, it can be employed equally successfully for the analysis of solids, liquids and gases. 

A more complete knowledge of the physical layout of the site and its below ground features can be obtained by non-intrusive survey methods. Ground-penetrating radar is able to locate buried features such as pipes and tanks. Soil conductivity may reveal buried objects and areas of made-ground or waste disposal. From the results of these types of survey, areas for possible intrusive investigation are identified and the zoning of the site can be refined. 

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