Hydrocyclone Rietema

The Bradley hydrocyclone has a lower capacity than the Reitema geometry but is more efficient. For the Rietema cyclone geometry the cor-relatins are (Antunes and Medronho, 1992)... 

Castilho LR, Medronho RA (2000), A simple procedure for design and performance prediction of Bradley and Rietema hydrocyclones, Minerals Eng. 13 183-191. 

Two other dimensionless equations describe the operation of Rietema s hydrocyclones. 

The dimensional analysis gives basic relationships between the above-mentioned dimensionless groups, which are useful to describe hydrocyclone operation and are the basis for scale-up calculations aimed at adapting results from laboratory experimentation to an industrial scale for a number of processes in diverse industries. For example, for feed suspensions up to 10% by volume Medronho and Svarovsky (1984) proposed the following relations, for hydrocyclones following Rietema s optimum proportions and treating inert solids suspensions ... 

Determine the cut size obtained when treating 1 L/s of a suspension of inert solids in water, with concentration of 5% by volume, in a Rietema s standard geometry hydrocyclone 1 in. in diameter and 5 mm in underflow opening. The solids density is 2150 kg/m and the available pressure drop of operation is 2 x 10 Pa. 

A series of large-scale experiments with a hydrocyclone 76 mm in diameter of variable proportions yielded a minimum value of Cy = 3.5 for a set of proportions which has since become one of the recommended standard designs (refer to a later section for further discussion). Recent experimental investigations at Bradford University carried out with three sizes of Rietema s optimum design (22, 44 and 88 mm in diameter) at 1% volume feed concentration have reproduced Rietema s results, but only with very dilute underflows values of Cy about twice as large have been found under more practical operating conditions. 

The effect of turbulence on the separation in hydrocyclones has been of concern to researchers ever since the early work of Driessen. One aspect of interest is how turbulence modifies the tangential velocity profiles, i.e. its effect on the exponent n in the exponential equation for the tangential velocity in equation 2.2. Rietema " made a detailed investigation into this problem and estimated the turbulent viscosity with the aid of the tangential velocity profiles measured by KelsaU. This was done using a dimensionless parameter A ... 

A number of physical models have been proposed for the separation process in a hydrocyclone (Driessen MG, 1951 Bradley and Pulling, 1959 Fahlstrom, 1960 Kelsall, 1952 Rietema, 1961 and Schubert and Neesse, 1980). Among these, different phenomenological approaches have led to the development of two basic theories the equilibrium orbit theory and the residence time theory. 

Residence Time Theory. Residence time theory is based on the consideration of whether a particle will reach the cyclone wall in a given residence time. In the development of this theory, the distribution of all particles across the inlet is assumed to be homogeneous (Rietema, 1961). The cut size will be the size of those particles that enter the center of the inlet pipe and just reach the wall within the residence time. Using this theory coupled with extensive experimental test data, Rietema was able to estabhsh a set of empirical correlations and suggest a criterion (a characteristic cyclone number) for optimum design of hydrocyclones. 

Rietema K. Performance and design of hydrocyclones. Parts I to IV. Chemical Engineering Science 15 298-325, 1961. 

---