IRANIAN JOURNAL OF CHEMICAL ENGINEERING
Year:2006 | Volume:3 | Issue:2|Papers Count:6

Gas liquid dispersion technology is a major part of the infrastructure of chemical, petrochemical and biochemical industries. Flooding is one of the characteristic features of stirred tank equipment used to disperse gases in liquids. Most investigators have studied the flow regime and mass transfer coefficient relying solely on the Rushton turbine. However, there are cases wherein the utilization of an inappropriate type of impeller results in both waste of energy and marked counter-productivity. Hence, the objective of this paper is to examine the performance of gas-liquid dispersion systems in terms of flow regime. mass transfer coefficient and the loading zone for the gassed condition using the Rushton turbine. pitched blade, concave blade and the vaned disc type impellers. For the gassed conditions, we concluded that the vaned type disc gives the optimal mass transfer coefficient. We have also examined the hysteresis phenomena for the Rushton turbine and established a new flow region called transition, in which both the loading and flooding zone is present.

An experimental study was carried out to obtain the mean convective heat transfer coefficient of aqueous carboximethyl cellulose (CMC) solutions in double-pipe heat exchangers. Co-current and counter- flows were considered in the investigation. From the experimental data a Nusselt number was calculated for a wide range of Graetz number, Reynolds number, and CMC concentrations. Increasing the Graetz and Reynolds numbers promote the heat transfer and variation of CMC concentration has a noticeable effect on the Nusselt number.

Distillation control is a challenging undertaking given the inherent nonlinearity of the process severe coupling present for dual-composition control and the sensitivity of disturbances. Among various distillation operations management of the high-purity column poses a difficult control situation due to a number of characteristics of these systems. Including strong directionality. Ill-conditioning and strongly nonlinear behaviour. In this paper a diagonal PID controller is designed and analysed for a high-purity distillation column by computing the structured singular value  m introduced by Doyle (1982) For this purpose a structured uncertainty model has been developed which describes the dynamics of the column for the entire operating range. The achievable manageable performance is also defined in terms of the H ¥-norm of the weighted sensitivity function.

In this work, the recently proposed SAFT-based Equation of State (EOS), the GVSSAFT EOS, was used to study the phase behavior of associating and non-associating pure polymer melts as well as polymer-solvent mixtures at various conditions. The regressed values of the parameters for the GV-SSAFT equation of state for a wide spectrum of pure homopolymer melts were obtained using the corresponding Pressure- Volume- Temperature (PVT) experimental data available in the literature. In case of the non-associating polymers the GV-SSAFT EOS has three adjustable parameters while the number of parameters is increased to five for associating polymers. The parameters were meticulously tuned for segment number, segment molar volume, and segment-segment interaction energy, and their values for the systems studied in this work were also reported. The results obtained from the GV-SSAFT EOS were unequivocally compared with those of the Simplified version of the SAFT (SSA FT) EOS for both associating and non-associating pure polymer melts as well as polymer-solvent mixtures. The results showed that the G V-SSAFT EOS can accurately correlate the experimental data for liquid density of pure polymer melts at wide temperature ranges.In case of polymer-solvent mixtures, iriferior results obtained by employing the GVSSAFT EOS to the VLE experimental data The results also showed that while considering the specific site-site interactions for the associating polymers makes the SAFT- based equations of state more complicated the final results cannot be much affected by such complexity. Therefore, this kind of molecular interaction could be neglected to a good approximation. It would be worth noting that in order to do a fair comparison between the results obtained from the GV-SSAFT EOS with those of the SSAFT £OS, the same sets of experimental data and the same optimization procedure were usedfor both equations of state to render their regressed parameters. 

Due to increasing application of multi effect falling film evaporators in food industry. the exact modeling of these processes is important. The aim of this paper is use ability of nonlinear modeling in determining falling film evaporator state variables. Because of large time delays and process disturbances, the tight exact control of product concentration is difficult. By using the nonlinear modeling, the control of three effect falling film evaporator with the use of cascade control algorithm is analyzed This paper discusses the application and design of a cascade algorithm to control the product concentration in a milk powder three effect falling-film evaporator. It has been shown that the disturbance rejection properties can be significantly improved with cascade control while still maintaining the tracking properties.

Ternary phase diagrams for [polyethylene (Mw=420,000, Mw/Mn=2.6) / n-butane/ carbon dioxide), [polypropylene (Mw=290,000, Mw/Mn=I.32)/ n-pentane/carbon dioxide) and [polystyrene (Mw=187,000)/ cyclohexane/ carbon dioxide) have been generated using the Sanchez-Lacombe (SL) lattice-fluid model. The results show that at relatively low pressure, the ternary phase diagram has a L-L-V three-phase region bounded by two two-phase regions (L-V and L-L), At high pressure, L-L-V and L-V regions disappear and only the L-L region remains. With an increase of pressure this two-phase L-L region becomes smaller. This model can also predict transition LCST to UCST by increasing pressure. For polystyrene/ cyclohexanel carbon dioxide mixture, the calculated results obtained using the SL-model are compared with the reported calculated results created by the perturbed hard-sphere chain model (PHSC) and the reported experimental data which indicate good agreement with both the calculated results by PHSC-model and experimental data.