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Effective parameters on generation of nanobubbles by cavitation method for froth flotation applications

Pourkarimi Z., Rezai B., Noaparast N.

Physicochemical Problems of Mineral Processing

2017

Vol. 53, iss. 2

920--942

The significant recovery increase in flotation of fine particles using nanobubbles has been one of the major topics in flotation science in recent years. Fine bubbles have an important effect on gas hold-up, which is necessary in froth flotation of minerals based on the process industries. At a given gas hold-up, using finer bubbles can reduce frother consumption. An exclusive nanobubble generation system has been developed in Iran Mineral Processing Research Center (IMPRC) to evaluate the effect of nanobubbles on the froth flotation performance. This device, which enhanced venturi tubes, works according to cavitation phenomena. The venturi tube is the most widely used hydrodynamic cavitation device, in which liquid flow increases in the conical convergent zone of the tube due to the thin diameter. The liquid in the cylindrical throat is higher in a flow velocity and lower in a pressure than the liquid in the entrance cylinder, which results in cavitation. In this research work, various factors such as the frother type and dosage, pH, compressed air flow, pressure in cavitation nozzle, gas types, temperature and venturi tube internal diameter were studied. For this purpose, a five-level central composite experimental design was used to check the influence of four important parameters on the median size and volume of nanobubbles. Online measurement of the bubbles size was implemented by a laser particle size analyzer (LPSA), according to standard BS ISO 13320-09. Due to the above parameters and obtained responses, the analysis of variance (ANOVA) was conducted with a suitable model to optimize the conditions, with the aim of minimizing the size of air bubbles. The optimal conditions were: frother (MIBC) dosage of 75.8 mg/dm3, air flow rate of 0.28 dm3/min, pressure of 324 kPa and pH of 9.5. The median bubble size d50 was equal to 203 nm. To validate the results, a test under optimum conditions was performed and the obtained results indicated that there was a good fit at the confidence interval of 95% and reflected the repeatability of the process.

Review of numerical models of cavitating flows with the use of the homogeneous approach

Niedźwiedzka A., Schnerr G. H., Sobieski W.

Archives of Thermodynamics

2016

Vol. 37, no. 2

71--88

The focus of research works on cavitation has changed since the 1960s; the behaviour of a single bubble is no more the area of interest for most scientists. Its place was taken by the cavitating flow considered as a whole. Many numerical models of cavitating flows came into being within the space of the last fifty years. They can be divided into two groups: multifluid and homogeneous (i.e., single-fluid) models. The group of homogenous models contains two subgroups: models based on transport equation and pressure based models. Several works tried to order particular approaches and presented short reviews of selected studies. However, these classifications are too rough to be treated as sufficiently accurate. The aim of this paper is to present the development paths of numerical investigations of cavitating flows with the use of homogeneous approach in order of publication year and with relatively detailed description. Each of the presented model is accompanied by examples of the application area. This review focuses not only on the list of the most significant existing models to predict sheet and cloud cavitation, but also on presenting their advantages and disadvantages. Moreover, it shows the reasons which inspired present authors to look for new ways of more accurate numerical predictions and dimensions of cavitation. The article includes also the division of source terms of presented models based on the transport equation with the use of standardized symbols.