The usage of twisted tape as a device to enhance heat transfer rates in forced convection has been in vogue in industries for ages. However, its superiority as an augmentative device for increased heat transfer vis-à-vis other devices, such as rough surfaces and finned tube assemblies, is not well established. Nor is there any universally applicable equation for the prediction of heat transfer coefficients in forced convection in the presence of twisted-tape inserts. Nevertheless, twisted-tape inserts can be gainfully employed in cases where non-uniform heat fluxes are involved. Against this backdrop, the authors, M S N Murty, K V Ramesh, G M J Raju and Y S P Narayana Rao, of the first paper, “A Simplified Correlation for Forced Convective Heat Transfer in Tape-Generated Swirl Flow of Air”, have attempted to apply the method described by Narayana Rao and Chiranjivi (1981) for the analysis of forced convective heat transfer data for air flowing through tubes with twisted-tape inserts and correlated the data by an equation without the aid of Prandtl number, Pr, and the tape twist ratio, y. Their study confirms that a simplified method is visible for correlating the forced convective heat transfer data without the aid of Pr and the additional geometrical parameters of the system.

In order to control the reactor temperature, nonlinear controllers, such as globally linearizing controller, generic model controller, and internal model controller, have been in use since the 1980s for getting better performance than conventional proportional integral controller or PID controllers. These control schemes require the feedback of state of variables, and this is achieved by resorting to open loop observer, though closed loop observer is still desirable. Against this backdrop, the authors, Dipesh S Patle and Hare Krishna Mohanta, of the next paper, “Generic Model Controller with Adaptive State Estimation for Nonlinear Cstr”, have developed a hybrid GMC-ASE control scheme and implemented it in a jacketed continuous stirred tank reactor for controlling the reactor temperature. Then the performance of the designed controller is compared with a conventional PI controller, and the authors conclude that the GMC-ASE controller is better in its performance vis-à-vis PI controller owing to the exponential error convergence capability of the ASE estimator and the high quality performance of the GMC controller.

In the next paper, “Analysis of Momentum Transfer with Coaxially Placed Disc as Turbulence Promoter in Circular Conduits”, the authors, V Nageswara Rao and N Chitti Babu, have studied the effect of coaxially placed entry region disc as turbulence promoter on momentum transfer rates in forced convection flow of electrolyte. Their study reveals that friction factor decreases with increase in Reynolds number for flow of electrolyte in the presence of disc in a circular conduit. The presence of disc as a turbulence promoter speeds up the onset of fully developed turbulent region, which occurs at low Reynolds number vis-à-vis the flow through an empty conduit. Finally, they have presented the correlation developed using the concept of Dipprey and Sabersky (1963).

In the next paper, “Effects of Physicochemical Conditions on Ceramic Cross-Flow Microfiltration of Mineral Dispersions”, its author, P Mikulášek, has studied the influence of pH, ionic strength and coagulant type on ceramic membrane microfiltration of Titanium dioxide (TiO2) dispersions by conducting a series of cross-flow microfiltration experiments at various pH values, ionic strengths and with various multivalent organic salts. The results indicate that the influences of inorganic salts on the microfiltration of TiO2 dispersion are due to changes in the surface properties of both the ceramic membrane and TiO2 particles. The author has also concluded that the solution environment affects the dispersion of TiO2 particles and plays a major role in the filtration flux.

Taking a cue from the existing literature that very little work has been done on the modeling of the liquid-liquid phase transfer catalyzed reactions of commercial importance, the author, Sunil K Maity, of the next paper, “Modeling of Liquid-Liquid Phase Transfer Catalysis Based on Interfacial Mechanism”, has developed a kinetic model based on interfacial mechanism for the liquid-liquid phase transfer catalyzed reaction of benzyl chloride with aqueous ammonium sulfide, following the thermodynamic framework by Edward et al. (1975), and estimated the rate constants of the developed model at different temperatures using a modified Levenberg-Marquardt algorithm. The frequency factors and activation energies of the rate constants are determined, and there is a good correlation between the results derived from the model and experimental observations.

In the last paper, “Chemical Process Engineering in Marine Biotechnology: Opportunities and Challenges”, the authors, Shaik Basha, Z V P Murthy and Bhavanath Jha, review the current status of chemical process engineering in marine biotechnology and explore the new opportunities thrown open by marine biotechnology for commercial exploitation.

-- GRK Murty
Consulting Editor