Pulsation characteristics of the process of mass exchange between a solid spherical particle and a turbulized liquid

To intensify the process of mass exchange at an interface between liquid and solid phases, as a rule, one creates conditions such that the liquid is in a turbulent regime. Revealing the laws of mass transfer under these conditions makes it possible to choose the optimum regime of operation of a chemical apparatus, i.e., obtain the maximum coefficients of mass transfer for small energy costs. Vessels in which the liquid is mixed with agitators of the turbine or vane type are used as the working apparatus in industry. For this reason, many investigators occupied in studying mass-exchange processes in a liquid-solld system have fully modeled the actual conditions [1-4]. Another group includes papers in which mass exchange was studied in the flow of a liquid stream over a single spherical solid particle in channels of different configurations [5-10]. Two main methods used to study mass-exchange processs can be distinguished: dissolving solids in liquids [1-5, 9] and the electrochemical method [6-8, i0]. The first method is used only to obtain average values of the mass-exchange coefficient, and it is also characterized by variation of the shape and size of the investigated particles, which considerably lowers the accuracy of the results obtained. The electrochemical method has now become very popular; it provides a high measurement accuracy and also makes it possible to investigate both the integral and the pulsation characteristics of a process, which is important for systems in which the liquid is in a turbulent regime. In [ii] the problem of mass exchange of a turbulent liquid with a plane wall was considered and the question of correlations between pulsations of the liquid velocity and the mass-transfer coefficient on the basis of a spectral analysis was discussed. Itwas shown that in a turbulent regime of flow over the wall, the shape of the power spectrum of pulsations of the masstransfer coefficient does not depend on the Reynolds number, whereas a strong influence of the Schmidt number on the frequency of pulsations of the mass-transfer coefficient was noted. No noticeable influence of a change in the size of the electrode on the form of the spectral energy density of pulsations of the mass-transfer coefficient was found. Thus, the application of spectral analysis to the interpretation of results obtained using the electrochemical method to study mass-exchange processes allows one to estimate sufficiently precisely the influence of one or another factor on the process being studied. In the present paper a similar approach is used to study mass exchange between a fixed spherical solid particle and a turbulized liquid.