Design and optimization of a cavitating device for Congo red decolorization: Experimental investigation and CFD simulation

Abstract

The aim of this work is to perform design and optimization of a cavitating device based on CFD simulation. A set of operational and geometrical parameters such as convergence angle, divergence angle, length of throat, and inlet pressure that can affect the hydrodynamic cavitation phenomenon generating in a Venturi are evaluated through CFD simulation and experimental approaches. Response surface methodology (RSM) was employed to achieve the optimum geometrical configuration. The CFD results show that the maximum cavitation zone in the Venturi can be obtained when half angle of the convergence section, throat length and half angle of the divergence section are 22.7°, 4 mm, and 6.5°, respectively. A maximum decolorization of 38.8% has been obtained using the designed Venturi at cavitation number (Cv) of 0.12. Additionally, the results were compared to that of various orifice plates. A decolorization of 26.2% using 33 holes orifice plate and 11.55% in one hole orifice plate approved the superiority of the designed Venturi.

Keywords: CFD; Cavitation zone; Circular Venturi; Hydrodynamic cavitation; RSM.

Fig. 1

Absolute pressure profile of venturi in three different mesh sizes.

Fig. 2

Schematic diagram of hydrodynamic cavitation reactor set-up.

Fig. 3

Schematics of venturi and orifice plate devices

Fig. 4

Response surface plots of the R1as a function of: (a) inlet angle and outlet angle, (b) outlet angle and L, (c) inlet angle and L at P = 6 Bar and P_sat = 3540 Pa.

Fig. 5

a) Pressure contour of optimized venturi, b) Pressure profile of optimized venturi.

Fig. 6

Pressure contour of venturi in experimental condition.

Fig. 7

Image of cavitation zone in the downstream of venturi.

Fig. 8

Pressure contour at different inlet gauge pressure.

Fig. 9

Effect of inlet pressure on the rate of decolorization of Congo red (Initial concentration of Congo red 20 ppm, temperature 35℃).

Fig. 10

Decolorization rate of Congo red in three different cavitating device.

Fig. 11

Decolorization rate in the various inlet pressure using different cavitating devices.

Fig. 12

First order decolorization of Congo red at three cavitating devices.