Presence Of Turbulence Promoters Research Articles

Intensification of the rate of diffusion controlled electrolytic oxidation of FeSO4 by turbulence promoters in a stirred tank reactor in relation to wastewater treatment

The rate of diffusion controlled anodic oxidation of FeSO4 in rectangular stirred tank reactor was studied under galvanostatic conditions, H2 gas was produced as a byproduct at the cathode of the divided reactor. The rate of anodic oxidation of FeSO4 at a lead anode was enhanced by using active cylindrical turbulence promoters attached to the anode. Variables studied were impeller rotation speed, diameter and spacing of the turbulence promoters. The presence of turbulence promoters on the anode surface was found to increase the rate of FeSO4 oxidation by a factor ranging from 1.02 to 3.4 and reduce electrical energy consumption by an amount ranging from 25 to 80% depending on the operating conditions compared to the flat plate anode. The efficiency of the turbulence promoters was found to increase with increasing promoter spacing and diameter. The role of O2 bubbles which evolve at the anode surface simultaneously with FeSO4 oxidation in enhancing the rate of mass transfer jointly with turbulence promoters was discussed. Importance of the present study for treating wastewater containing FeSO4 was highlighted. Processes that produce wastewater containing FeSO4 include removal of H2S from petroleum hydrorefining gases by Fe2(SO4)3 oxidation to sulfur, regeneration of printed circuit etching solution and iron removal from steel mills pickling waste solutions. The importance of the present results in producing H2 at lower energy consumption and the possibility of integrating the present cell with the process of petroleum hydrorefining was noted. Also the importance of the present results in using FeSO4 as anodic depolarizer to reduce the cell voltage and energy consumption in the electrowinning of heavy metals from waste water was outlined.

Optical evaluation of deposition thickness and measurement of permeate flux enhancement of simulated fruit juice in presence of turbulence promoters

Ultrafiltration of simulated fruit juice (pectin and sucrose) is performed in continuous cross-flow mode with an organic ultrafiltration membrane (poly phenylene ethersulfone, PPE 30) of 30 K molecular weight cut off. The permeate fluxes are measured under different operating conditions of pressure, cross-flow velocity and pectin concentration. Significant enhancement of permeate flux is achieved by incorporation of straight cylindrical promoters placed across the flow. The optimum number of such promoters and their sizes are evaluated. Image analyzing video microscopy is successfully used to accurately quantify the deposition of pectin molecules on the membrane surface. The deposition thickness decreases with increase in cross-flow velocity, increases with pectin concentration but is less susceptible to increases in pressure. The effects of the shape of the promoters on flux enhancement and deposition thickness are also investigated in detail and approximately parabolic shaped promoters are chosen with further increases in flux enhancement (keeping the number of promoters same as in the case of straight promoters). The deposition thickness profiles around a promoter and the average deposition thickness on the whole membrane are optically measured and the consistency of the results in relation to enhancement of permeate flux are examined.

Ionic mass transfer in presence of turbulence promoters in a circular conduit

Ionic mass transfer in a circular conduit in the presence of ring promoter assembly is measured by limiting current technique using diffusion controlled electrochemical reactions (reduction of ferricyanide and oxidation of ferrocyanide). A supporting rod on which rings are mounted at equidistance is concentrically fixed in the conduit of 0.05 m I.D. to augment the mass transfer rates. Cross-sectional diameter of the ring is changed from 0.0065 m to 0.0125 m and the spacing in between the rings is varied from0.03 m and 0.15 m respectively. The improvement in mass transfer coefficients is up to 6.5. The data are correlated by the following dimensionless equation. ▪

Improved ionic mass transfer in an electrochemical cell in presence of turbulence promoters

In industrial operations, reduction in equipment size can increase productivity, lower energy inputs and improve purity of the product. The presence of turbulence promoters in an electrochemical cell can increase the intensity of local turbulence, which enhances the mass transfer coefficient at the transfer surface and the limiting current density. The regularity of their geometrical configuration induces a pseudo-uniformity of the spatial distribution of the local mass transfer coefficients. High mass transfer coefficients can be achieved at much lower flow rates when turbulence promoters are placed in the cell. Limiting current data were obtained using a diffusion-controlled electrode reaction at point copper electrodes fixed on the wall of the electrolytic cell in the presence of rectangular turbulence promoters. The improvement in limiting current density, and hence mass transfer coefficient, due to the presence of turbulence promoters is assessed. The effects of the flow rate of the electrolyte, height of the promoters and spacing between the promoters were studied.

Hydrodynamic behaviour of the FM01-LC reactor

Various working electrode configurations have been studied in order to characterise hydrodynamic behaviour in the FM01-LC reactor. A simple experimental arrangement has been used to generate data from electrolytic conductivity measurements in a series of impulse-response experiments. First and second moments of the tracer curves were calculated and the degree of dispersion was established as a function of the moments of the curves. The dispersion coefficient was found to increase with flow velocity and to be higher in the presence of turbulence promoters and three-dimensional electrodes. The Peclet numbers indicate that as the bulk velocity of the marker material increased, the degree of dispersion rose by a similar degree.

Mass-transfer conditions at a cathode support plate in an electrochemical cell

The presence of turbulence promoters in an electrochemical cell increases the intensity of local turbulence which enhances the limiting current density and hence the mass-transfer coefficient at the transfer surface. The regularity of their geometrical configuration induces a pseudo-uniformity of the spatial distributions of the local mass-transfer coefficients. Limiting current data have been obtained at point copper electrodes flush-fitting on a cathode support plate in the presence of rectangular turbulence promoters. The effect of the flow rate of the electrolyte, the height of the promoter and the spacing between the promoters have been studied. The data are best correlated by the following equation: J D=390Re −0.87( S H −0.15 where S is the promoter spacing (m) and H the promoter height (m).

Mass and momentum transfer at a wall in the presence of turbulence promoters

This paper deals with the influence of cylindrical turbulence promoters on mass and energy transfers at the wall of a narrow channel with a flowing liquid. The experimental distributions of the mass-transfer coefficient and shear stresses along the wall appear to be similar. The results show that an elementary “mesh step” is reproduced periodically when the promoters are very near the wall. For this case, a model assuming symmetrical boundary layers between two neighbouring promoters, allows a quantitative correlation of the local mass-transfer coefficient and the local velocity-gradient at the wall.

Mass transfer in narrow channels in the presence of turbulence promoters

A revised version of the “mesh step” model for the effect of a net type turbulence promoter on mass transfer in a narrow channel is presented. In the limit of a long channel the model is shown to yield a constant average boundary layer thickness the value of which is inversely proportional to the square root of the Peclet number. Mass transfer measurements using a ferro-ferri-cyanide electrochemical flow system show that the model correctly predicts the dependence of the mass transfer rate on flow velocity and Schmidt number, and that on the mesh step in the range of large mesh step values. In the range of small mesh step values, it is shown that the effect of mesh step on mass flux is negligible and, hence, that this need not be a major consideration in the optimization of spacer nets within the usual range of application.

The role of turbulence promoters in hyperfiltration plant optimization

Numerical calculations were performed to obtain process parameters for hyperfiltration with membranes having characteristics similar to cellulose acetate. The concentration polarization and friction loss equations used in the calculation were modified to include provision for a wide range of turbulence promoter characteristics. The characteristics of the turbulence promoters were based on potential performance curves derived from an extensive literature survey. The presence of turbulence promoters causes marked reduction of optimum entrance velocity and tube length. As a result, the channel pressure drop for tubes with turbulence promoters is always less under optimum conditions than the value for tubes with no promoters provided the friction factor with promoters is less than 100 times the value with no promoters. While none of these affect costs greatly, there is direct cost advantage for turbulence promoters which minimize fouling, thereby giving higher average fluxes for longer periods of time. Only where the membrane is strained to produce water of required quality is there a direct effect of turbulence promoters on product water cost because of this beneficial effect on concentration polarization.