Schlieren generation

The intensity of the effect depends on the composition of the solutions involved, becoming more pronounced for more concentrated solutions and/or when solution inter-mixing is slower. A linear relationship between the concentration of the Schlieren-generating species and the intensity of the effect is not observed [3]. 

As a rule, occurrence of the Schlieren effect degrades analytical figures of merit such as accuracy and detection limit. Furthermore, interaction of the Schlieren-generating chemical species with the tubing inner wall can impair the sampling rate, as the adsorption and release processes involved may increase the wash time. 

The drawbacks inherent to signal subtraction can be circumvented by exploiting real-time subtraction, and this strategy is the basis of dualwavelength spectrophotometry (see 4.1.1.4). The beneficial influence of DWS in flow injection analysis was demonstrated using the dye approach where buffered coloured solutions mimicked the sample and sucrose was added as the Schlieren-generating species [28]. The Schlieren effect was almost quantitatively suppressed (Fig. 4.15 and Table 4.4). 

The multi-spark schlieren photographs obtd by Collins (Ref) have proved most valuable for their qualitative insight into the general behavior of the cylindrical blast wave. The results of this investigation show that cylindrical expins can be satisfactorily generated and adapted to laboratory observation study... 

A practical difficulty, encountered in this study was performing the AUC runs at temperatures higher than 40 °C at such high temperatures, the oil vapors from the diffusion pump interfere with the UV absorption optics. They circumvented this problem by using a different type of optical scanning known as the Schlieren optics, which generates the data as profiles of radial derivative of concentration distributions as a function of radius (as opposed to the concentration versus radius scans obtained from UV optics). 

When a dependence of the local burning velocity on the turbulence field is induced in the computations, a much more rapid burning will occur in the shear layers. The computer generated movie shown in Figure 7 corresponds very closely to the actual high speed schlieren photographs of flame acceleration through a baffle obstacle (25). 

Fig.4.13 Recording of a typical FI profile for sorbent absoiptiometric optosensing of sorption of phosphomolybdate on C 8 sorbent (L), reduction of the sorbed species by ascorbic acid (R). and elution by methanol (E). The flow is momentarily stopped during reduction. A are signal heights related to phosphate content in samples. 1, 2. 3, signals corresponding to 0, 25, and 50 /ig P P BLK, blank SC, signal generated by Schlieren effects [60].

Channel formation experiments have been conducted with a small Prototype machine. This machine is a 600 kV, 5 60 ns water transmission line charged with a Marx generator. With fill pressures of 1 to 4 atmospheres, these experiments have created channels of 0.1 mm radius at currents up to 100 kA. The density distribution of a channel is measured by a Moire-Schlieren technique with illumination by a short pulse N2 laser (3373 A). An example of such a channel photograph is shown in Fig. 20. In these experiments no sausage or kink instabilities have been observed out to 120 ns. 

Then they have clearly demonstrated the importance of evaporation in the generation of these structures. Indeed on closure of the reactor the shapes fade away but reform on opening. Furthermore, using the schlieren technique they obtained photographs of stria-tions (prepatterns) [6 ] existing in the fluid prior to irradiation. The existence of these vermiculated convective rolls was decisively proven by depositing ink on the bottom of the dish. 

In dye lasers of this type the efficiency can be as high as 20 per cent. At low repetition rates thermal schlieren effects are absent because the pulse length is so short, 5-10 ns, and the output beam is nearly diffraction limited. However, for repetition rates above 10 Hz it is necessary to circulate the dye transversely through the cell. Peak optical output powers of several kW can then be generated at repetition rates approaching 100 Hz. 

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