On the evaluation of the time of periodical dissolution of a dispersed material in a rotor-pulse device

Abstract

UDC 532.695 Results are presented of experimental and numerical investigations of the kinetics of periodical dissolution of benzoic and salicylic acids in water using the rotor-pulse device. It is found that the process obeys the first- order kinetics. A determining influence of the rotation frequency of the device rotor and the size of the radial gap between the rotor and the stator on the dissolution time is shown. Favorable agreement between the ex- perimental and calculated time dependences for the concentration of the dissolved substance are obtained. plex of various hydrodynamic phenomena takes place, such as the gradient flow in the gaps between rotating and im- movable structural elements, an intense turbulization of the flow, an oppositely directed velocity field, etc. (2-4). Unlike traditional devices of the vessel type with mixing facilities, the rotor-pulse devices provide a signifi- cant intensification of the dissolution process and a reduction in the specific energy consumption. This is especially important in work with difficultly soluble dispersed materials. Experimental Investigation. The current study aims at investigating the kinetics of dissolution of benzoic and salicylic acids in water using the rotor-pulse device and the influence exerted on it by the treatment regimes, as well as at investigating structural features of the device. A basic diagram of the laboratory setup and its general view are shown in Figs. 1 and 2. Basic elements of the device are RPA (rotor-pulse device) 1 and discharge vessel 2 with a mixing facility, which are connected by the tubing into a single circulation circuit. During the process the required temperature is maintained by HAAKE F3 thermostat (Germany) 3 connected to the vessel jacket. Distilled water and the dispersed material are loaded into the vessel through a port in its cover. The basic diagram of the rotor-pulse device and its outward appearance are presented in Figs. 3 and 4. The device consists of a continuous-flow working chamber with central inlet and tangential outlet (pressurized) connecting branches. Directly in the chamber are a multirow rotor and a stator of the rotor-pulse device. They have radially po- sitioned rectangular channels, which are periodically closed during the device operation and thus provide the required regime of dissolution of a solid phase. The device is driven directly by a d.c. motor with a power of 0.23 kW. The system of control of the motor operation allows variation in the rotation frequency of the rotor in the range 500-2500 rpm. Basic geometric parameters of the working heads of the device are given in Table 1. A set of changeable rotors allows one to obtain three values of the radial gap (δ) between the stator and rotor