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Low pressure setups (up to 150 psi) for creating hydrodynamic cavitation are investigated in this study. The decomposition of chloroform in water is used as a model reaction. The effects of upstream pressure, fluid velocity, Cavitation number, C v , and b 0 on the conversion are compared with regard to the effectiveness (conversion per pass) with changing flow conditions and scale-up terms within three different setups. The values of C v and b 0 are seen to be significant parameters in optimizing the hydrodynamic cavitation. Moreover, the optimal values of these parameters shift to smaller values with increasing pipe diameter. The influence of a new orifice plate specific parameter, d, on the collapse conditions, is also described. IntroductionCavitation can potentially be used for a wide range of applications [1][2][3]. It is most commonly generated by ultrasonic transducers (acoustic cavitation), but there are problems associated with ultrasonic transducers concerning energy requirements and scale-up potential [4]. An alternative for generating cavitation events is hydrodynamic cavitation, where the bubbles are created due to pressure losses caused by an increasing fluid velocity (Bernoulli principle) and/or boundary layer separation [5,6]. This technology has been described as being more energy efficient and offers better scale-up possibilities [7][8][9]. A number of pipe flow systems with varying integrated restrictions, i.e., valve, venturi, and orifice plates, have been investigated [10,11]. The hydrodynamic cavitation has been studied extensively including parameter studies [5,6,9,10,[12][13][14][15], various applications [7,[16][17][18][19][20][21], energy efficiency assessments [8,16,21,22] and theoretical work [5,6,9,13,[23][24][25][26].Overall, a significant number of parameters exists that affect hydrodynamic cavitation, in particular, the numbers of generated (reactive) bubbles and the collapse conditions. An overview of the effective parameters in hydrodynamic cavitation, is shown in Fig. 1. The collapse conditions are defined as the temperatures/pressures reached at the bubble collapse [5]. In acoustic cavitation, this term is described for an adiabatic collapse by the following expressions, Eqs. (1) and (2) [27,28] 1) :(1)where T 0 is the liquid temperature, P m is the acoustic pressure at initiation of collapse, c is the ratio of specific heats of the dissolved gas or vapor and p v is the vapor pressure of the solvent. Several parameters have been introduced to characterize hydrodynamic cavitation systems. The dimensionless Cavitation number, C v , is defined by Eq. (3):where p d is the measured downstream pressure, p v is the vapor pressure (0.023 bar), q l is the density of the solution (1000 kg m -3 ), and v is the measured fluid velocity. These terms describe the ability of a system to generate cavitation, where smaller values are preferred. Moreover, C v can be correlated with the number of cavitation events and the collapse intensity [14,29]. The dimensionless number, b 0 , which character...

The sonoelectrochemical degradation of phenol in aqueous solutions with stainless steel electrodes and high-frequency ultrasound (850kHz) was investigated. A 60% synergetic effect was obtained in the combined reaction system. High concentration of electrolyte (sodium sulfate) and a high electrical voltage are favorable conditions for the degradation of phenol. A nearly complete degradation of phenol was achieved with 4.26g/L Na(2)SO(4) and 30V electrical voltages at 25°C in 1h. The degradation of phenol follows pseudo-first order kinetics. Considering costs and application, the energy efficiency of the reaction system with different reaction conditions was evaluated.

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The decomposition of chloroform by the combination of hydrodynamic and acoustic cavitation (Hydrodynamic-Acoustic-Cavitation/HAC) has been investigated. The flow rate and the hole diameter of the orifice plate remarkably affect the conversion of chloroform in the combined system. The conversion increases with increasing fluid velocity without any restriction. With a 2.8mm orifice plate the conversion reaches an optimal value. A synergistic effect has been obtained by the hybrid method of acoustic and hydrodynamic cavitation. The total synergistic effect achieves 17% and 73% per pass, respectively. The analysis of the energy efficiencies shows different results. Due to high optimization potential, this hybrid method can be visualized as a new step for wastewater treatment.