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Research Papers: Multiphase Flows

# Assessment of Tandem Venturi on Enhancement of Cavitational Chemical Reaction

[+] Author and Article Information

Faculty of Mechanical Engineering, K. N. Toosi University of Technology, P.O. Box 19395-1999, No. 15-19 Pardis Street, Mollasadra Avenue, Vanak Square, Tehran 1999143344, Iransayyaadi@kntu.ac.ir

J. Fluids Eng 131(1), 011301 (Nov 26, 2008) (7 pages) doi:10.1115/1.3026731 History: Received January 28, 2008; Revised September 13, 2008; Published November 26, 2008

## Abstract

The collapsing phenomenon of cavitation bubbles generates extremely high local pressures and temperatures that can be utilized for the chemical oxidation process. This process is carried out in cavitation reactors. A Venturi tube is one of the most common forms of hydrodynamic cavitation reactors, which is suitable for industrial scale applications. In this work, the hydraulic performance and efficiency in chemical reaction of a new form of hydrodynamic cavitation reactors, which is called “tandem Venturi,” were studied and compared with the conventional type of the single Venturi. The tandem Venturi is used for enhancement of the chemical reaction of hydrodynamic cavitating flow. The reaction enhancement is useful especially for the reaction of aqueous solutions not containing volatile organic compounds (VOCs). The operating pressure, inlet pressure, flow rate, and consequently the cavitation number were controlled and systematically varied for both single and tandem Venturis. Moreover, a specified amount of $H2O2$ was injected into the flow as required. The effects of operating pressure and the cavitation number on cavitating flow characteristics for single and tandem Venturis were experimentally observed and the results were compared. In addition, the performance of the tandem-Venturi reactor for degradation of non-VOC contaminants (2-chlorophenol) was studied. Its performance was compared with the performance of a conventional Venturi reactor. Two different categories were conducted for the experiments. In the first category, the effect of the net cavitating flow on degradation of non-VOC for the single and tandem Venturis was compared. In the second category, the effect of $H2O2$ injection into the cavitating flow on degradation of non-VOC (“cavitation-oxidation” process) was studied. The performance of the single and tandem Venturis for the cavitation-oxidation process was compared. Further investigation was performed to assess the advantage of utilizing the tandem Venturi from the viewpoint of efficiency of the oxidation process. The results of the energy efficiency were compared with the corresponding efficiency of the single Venturi. Finally, the relationship between the main parameters of cavitation reaction flow with the chemical performance was discussed.

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## Figures

Figure 1

Schematic of the cavitating flow in the (a) single Venturi and (b) tandem-Venturi (conditions that are marked with numbers are explained in the Nomenclature)

Figure 2

(a) Schematics of the experimental setup, (b) geometrical specification of the single Venturi, and (c) geometrical specification of the tandem Venturi (all dimensions are in millimeters)

Figure 3

Cavitation flow regime in the single Venturi under various experimental conditions and 100 kPa operating pressure (experimental conditions are summarized in Table 1)

Figure 4

Cavitation flow regime in the tandem Venturi under various experimental conditions and 100 kPa operating pressure (experimental conditions are summarized in Table 2)

Figure 5

Comparison of the 2-chlorophenol decomposition effect by cavitating flow in the tandem Venturi and single Venturi (operating pressure=100 kPa, initial concentration of 2-chlorophenol=14 ppm, flow rate=210 l/min, and pH≈8.10; other experimental conditions are indicated in Tables  12)

Figure 6

Comparison of the 2-chlorophenol decomposition effect by cavitation-oxidation process in the tandem Venturi and single Venturi (operating pressure=100 kPa, initial concentration of 2-chlorophenol=15 ppm, flow rate=210 l/min, injected amount of H2O2=1000 ppm, and pH≈8.07; other experimental conditions are indicated in Tables  12)

Figure 7

The effect of H2O2 injection on cavitation regime (Q=165 l/min and 100 kPa operating pressure)

Figure 8

Comparison of decomposition efficiency of the tandem Venturi and single Venturi in the cavitation-oxidation decomposition of 2-chlorophenol (operating pressure=100 kPa, initial concentration of 2-chlorophenol=15 ppm, flow rate=210 l/min, and injected amount of H2O2=1000 ppm)

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