Lamps annular

For the central measurement, the field of view is rectangular (e.g., 0.3 by 1.25°) and for other eccentricities, the field is an annular arc similar to that provided in minimum motion photometry. The use of a CRT monitor introduces the same problem as the use of LEDs in HFP, namely, the broadband nature of the screen phosphors, and a correction must be made before reporting the peak MP optical density. A system that could employ lamps and filters instead of a CRT monitor would be difficult to design because of the complexity of the visual stimulus. 

If the size of the production unit requires higher radiant power than can be provided, for technical reasons, by one lamp, clusters of light sources may be installed, which, consequently will alter the diameter or the height of the inner core of, for example, an annular photochemical reactor. However, following the check list of concepts (vide supra), optimal reaction conditions will in most cases limit the size of the photochemical reactor, and the planned rate of production may require several reactor units installed in a parallel mode (batch process) or in series (continuous process). 

Figure 14. Cross section along the plane perpendicular to the axis of an annular reactor with a cylindrical excimer lamp mounted in its axis [12, 58, 59],...

Deposits at the lamp jacket can also be prevented in bubble photochemical reactors, where small rising gas bubbles of nearly uniform size and distribution create strong turbulences [2, 3, 18, 68]. This reactor is usually conceived as an annular photochemical reactor of relative small thickness (/R, Eq. 36). In principle, its use with reactive gas is rather limited, as the turbulence provoked by the bubbles must be maintained over the entire height of the reactor [69, 70]. Bubble characteristics may also change as a function of the flux of the substrate solution. 

Shen et al. (1995) investigated the effect of light absorbance on the decomposition of aqueous chlorophenols (CPs) by UV/H202. The photoreaction system was batch annular photoreactors with 254-nm, low-pressure UV lamps at 25°C. The light absorbance and photolytic properties of chlorophenols and H202 were found to be highly dependent on the solution pH and can be adequately described with the linear summation of the light absorbance of undissociated and dissociated species of chlorophenols ... 

The obtained results have shown that the configuration where the recirculation tank was irradiated and the catalyst was used in suspension appeared to be the most interesting for industrial applications [73]. Moreover, it was observed that the degradation rate was higher when an immersed lamp was used compared to a system with an external lamp [81]. Therefore, actually the studies in progress are realized in the system described elsewhere [39] consisting of a Pyrex annular photoreactor with a 125-W medium-pressure Hg lamp axially positioned inside the reactor. The separation module containing the flat-sheet membrane was connected to the photoreactor in a recirculation loop. 

For photochemical reactions, usually the lamp configuration with an annular discharge gap is preferred. Consequently, a typical experimental setup is demonstrated schematically by Fig. 4-13 (Oppenlander, 1997 a, Oppenlander et al., 1996, 1995, Oppenlander and Baum, 1994, Braun et al., 1993). It consists of a cylindri-... 

Fig. 8.3 Cross-sectional view and top-view of various photoreactor types with different arrangement of the lamps. A Continuous flow annular photoreactor with coaxial lamp position, B external lamp position with reflector (R), C perpendicular lamp position D contact-free photoreactor types. The possible ar-...

Fig. 8.4 Continuous flow annular photoreactor with external spiral shaped lamp position reproduced by permission of UMEX GmbH (Dresden, Germany).

Even though this chapter is devoted mostly to solar photocatalytic reactors, we would like to discuss the modeling of an annular lamp reactor, as a different example of the application of the PI approximation. This problem was studied (Cuevas et al., 2007) with reference to a particular reactor known as photo CREC-water II (Salaices et al., 2001, 2002). Equation (38) is again written in cylindrical coordinates. Nevertheless in this case the... 

The larger reactor operates under a steady state, continuous flow conditions and was made of two 1 m cylindrical reactors of annular shape in order to use conventional Germicidal lamps (Figure 14). The system of tanks shown in the flow sheet was used to (i) feed the reactor with a constant flow rate and (ii) wash the system after each experimental run. The actual operating length (Zi) of each lamp (1.2 m long) was Im. Operation could be made with just one reactor or the two in series. 

Annular flow reactors are characterized by a cylindrical lamp surroimded by two concentric tubes such that the polluted air flows in the annulus between the inner and the outer tubes. That way, all emitted photons can be utilized without the use of expensive reflectors. In certain cases (Doucet et al., 2006), an optical (occasionally liquid) filter is introduced between the lamp and the flowing zone to control the wavelength and the power of the impinging light, as well as the temperature within the reactor. 

A two-flux radiation field model for an annular packed bed photocatalytic oxidation reactor was presented by Raupp et al. (1997). Similar to other annular flow reactors, the UV source was located at the center of the cylindrical reactor. Yet, the photocatalyst was not introduced in the form of a thin film but rather as spherules filling the annular space between the lamp and the housing. The principal assumptions made in this model included a steady state, isothermal operation, cylindrical symmetry. 

The addition reaction is carried out in an apparatus consisting of a test-tube-shaped reaction flask into which a Hanovia-type SC-2537 lamp (85% of the light generated in the 2537 A band) is fitted. The reaction flask is fitted with a reflux condenser. The reaction mixture occupies the annular space between the walls of the lamp and the reaction flask. In a typical experiment, a mixture of 90 g (0.819 mol) of thiophenol and 5.3 g (0.0455 mol) of 1-chlorocyclohexene is inserted into the reaction flask and irradiated for 2.5 h. The heat given by the lamp raises the temperature of the reaction mixture to 50 "C. Distillation of the reaction mixture gives 80 g of unrcacted thiophenol and the addition product yield 3.6 g (35%) bp 125-133 C ... 

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