Browsing by Author "Kleingeld, Anton W."

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    The development and modelling of high intensity impinging stream jet reactors for enhanced mass transfer in gas-liquid systems
    (Stellenbosch : Stellenbosch University, 1999-12) Kleingeld, Anton W.; Lorenzen, L.; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.
    ENGLISH SUMMARY: In the majority of gas-liquid contacting systems the kinetics of the heterogeneous chemical reaction is not limited by its intrinsic reaction rate, but by the transport of gas to the liquid phase and hence by the overall interfacial area available for mass transfer. These rates in turn limit productivity and are thus a critical design consideration. In view of this, novel high intensity impinging stream reactors have been developed at this institution for intensification of these mass transfer processes. The reactors are characterised by small reactor volumes supplied with nozzles, which are directed towards one another. The gas and liquid feed streams are jetted through the nozzles into the reactor volume, resulting in a highly turbulent mixture of phases. Under these enhanced mixing conditions, mass transfer rates are increased dramatically. Evaluation of mass transfer parameters exhibited by the three different reactor configurations investigated showed that the mass transfer coefficient (kL) could be enhanced substantially by centrifugal acceleration of the fluid and more efficient promotion of turbulence in the round reactor chambers of the n and ó-shaped reactors, compared to that of the kite-shaped reactor. However, it was also found that the jagged/angular reactor chamber of the kite-shaped reactor exhibited higher values of the interfacial area (a) due to more effective bubble break-up mechanisms and higher relative gas hold-ups. It was therefore concluded that an optimum reactor design would combine the kL-enhancing effects of the swirling flow in the a-shaped reactor, with the bubble break-up and gas hold-up ability of the kite-shaped reactor. Comparison of experimental results with literature· data for conventional systems also revealed that, in terms of both the mass transfer coefficient and the value of the interfacial area per unit of energy dissipated in the reactor, the proposed reactors provide a significant improvement in mass transfer performance. It is thus suggested that the newly developed impinging stream reactors have the potential to represent superior alternatives to conventional gas-liquid contacting equipment. The fundamental model for the prediction of interfacial area production in the jet reactors originally proposed by Botes (1995) was also improved and expanded, resulting in more accurate prediction of trends in interfacial area as a function of various process variables. The model, and its associated bubble breakage mechanism, was verified at the hand of additional absorption data and alternative bubble breakage mechanisms proposed in the literature. Very good results were obtained, so that it could be concluded that the model is very flexible and can be applied over a relatively wide range of hydrodynamic operating conditions, validating the potential application thereof in other turbulent gas-liquid systems. Considering the above conclusions, recommendations could finally be made as to how the performance of the reactors could be improved further: liquid nozzles with larger orifices should be used for optimisation of the energy efficiency of the reactors. The use of gas nozzles with smaller orifices would additionally result in higher linear gas velocities, improving the efficiency of impingement of gas into liquid streams.
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    Project radicalness and maturity : a contingency model for the importance of enablers of technological innovation
    (Stellenbosch : University of Stellenbosch, 2003-04) Kleingeld, Anton W.; Ross, V.; Lorenzen, L.; University of Stellenbosch. Faculty of Engineering. Dept. of Process Engineering.
    ENGLISH ABSTRACT: The main proposition of this study is that the notion of a single set of universal success factors (enablers) of innovation is naïve. Rather, the importances of different enablers are contextually based and dependent upon different kinds of projects and their attributes. By investigating the roles of project radicalness and maturity in governing the importance of enablers of innovation in the process industries, two major conclusions were made, viz. (1) the importance of enablers are significantly moderated by project attributes, and (2) the mutual interactions between moderators of enabler importance prevent the formulation of middle-range theories of innovation radicalness or maturity, which propose normative relationships between innovation attributes and enabler importance. Although a number of previous studies have posited such outcomes, this study provides empirical evidence thereof for a set of generic enablers of innovation. These findings have suggested that the modelling of innovation at the project level should follow a contingent approach. While contingency theory has widely been applied to correlate structural and environmental attributes when the unit of analysis is the organisation, the literature on project management has largely ignored the importance of project contingencies, assuming that all projects share a universal set of managerial characteristics. This void is addressed through the development of a contingency model of the influence of secondary contingencies (project radicalness and maturity) on the importance of enablers. It represents an integrative perspective of the contextual importance of a number of enablers (and constructs thereof) that have previously been investigated and reported independently. Given that theory development in project management is still in its early years, it may therefore be concluded that the study contributes to the validity of classical contingency theory arguments in the context of the project. Although it does not consider an exhaustive list of all possible contingencies, and findings thereof strictly pertain only to process innovation, it does represent a considerable step in the evolving process of theory development on the modelling of innovation at the project level.