Study of fluid dynamic conditions in the selected static mixers part III—research of mixture homogeneity

Abstract

This paper contains the analysis of mixture homogeneity in two types of static mixers, Koflo and Kenics, based on both experimental and CFD study. The research was also expanded to the recognition of the pipe that was used as a background. The scope of work includes the analysis of the CoV coefficients (as a measure of mixing degree) obtained for the mentioned devices and their comparison. The research showing the impact of such parameters, i.e., pressure drop or L/d ratio on the mentioned mixture homogeneity was also presented. What is more, the axial dispersion model was introduced to describe the devices as non-ideal reactors. According to this, new relations for the CoV predictions (taking into consideration the turbulence intensity, the deviations from well-known ideal states, and the mixing elements' shape) were developed. As a result, it was proven that static mixers are highly efficient devices because the obtained CoVs were at around 2 % in the laminar flow and even less than that in the turbulent regime. When the pipe was used, the satisfactory value of the CoV was obtained when the Reynolds number was increased to 2600.

Analysis of CaF2 Precipitation Process in the Selected Static Mixers

“…It is particularly noticeable in the laminar ow (the lowest Reynolds number), and it may be explained on the basis of mixing degree. As mentioned in the paper [13], the CoV in the pipe in the laminar ow regime was at a higher level (CoV ∼ 13%) than allowable (CoV > 5%) and this fact is re ected in the reduction of conversion rate. For transient/turbulent ows (Re > 2300), the situation is di erent.…”

“…Initialization of the research was connected with the previous investigations focused on the uid dynamic analysis [11][12][13]. During the investigations related to the recognition of ow conditions in the selected static mixers like Ko o and Kenics, it was found that the value of the CoV coe cient, the parameter describing a mixture homogeneity (de ned as the ratio of the standard deviation and the mean concentration-equation (1)) is almost similar to that in the pipe for the Reynolds number higher than 2000.…”

“…e existence of mixing elements clearly helps in the mixing operation causing "arti cially made" swirls and vortexes which e ect in an increase of mixing degree. On the contrary, when the rheology of uid is close to water, the structures that naturally occur in the turbulent ow cause the reduction of the CoV all by themselves and make a simple pipe a useful alternative to more expensive static mixers, especially in case of not very demanding processes [13].…”

“…Previously reported mixing homogeneity data were used to support this study and are available at 10.1002/ cjce.23290. ese prior studies (and datasets) are cited at relevant places within the text as reference [13].…”

Process intensification connects scales and disciplines towards sustainability

“…Stec and Synowiec [ 50 ] characterized the pressure drop, the residence time distribution, [ 51 ] and the mixture homogeneity of two types of static mixers, Koflo and Kenics. [ 52 ] Static mixers as a PI technology do not offer direct thermodynamic advantages over empty columns; however, concentration and temperature are homogeneous over the column cross section, thus providing the same thermodynamic conditions throughout the unit. Static mixers are an ubiquitous example of a PI technology that industry has adopted commercially with significant success.…”