Engineering applications cover a wide range from modeling of hydraulic turbines to modeling of food processing devices. The following investigations are note worthy.

3.1 Three-Dimensional Analysis of Flow in the Spiral Casing of a Reaction Turbine Using A Differently Weighted Petrov-Galerkin method

A weighted residual based finite element method has been used to predict the flow structure and the head loss in the spiral casing of a reaction turbine. An explicit Eulerian velocity correction scheme has been employed to solve the complete Reynolds-averaged Navier-Stokes equations. A Differently Weighted Petrov Galerkin (DWPG) method has been used for spatial descretization. The simulation has been performed for high Reynolds numbers. The head loss in the spiral casing has been calculated for Re = 5´10⁵ and Re = 5´10⁶. The velocity filed and the pressure distributions inside the spiral casing corroborate the trends available in literature. The velocity filed reveals the existence of a free-vortex character of the global flow filed. A strong secondary flow is evolved on the cross–stream plane due to the centrifugal forces, which act at right angles to the main flow. A state-of-the-art finite element technique has been used to generate insightful results for a very important problem of engineering interest (Biswas et al., 1998; Maji and Biswas 1998; Maji and Biswas 1999; Maji and Biswas 2000).

3.2 Computation of Flow Structure and Heat Transfer due to Longitudinal Vortices in Heat Exchanger Applications

Longitudinal vortices have enormous utility for flow control. Longitudinal vortices are also capable of producing beneficial effects in transport enhancement. The vortices disrupt the growth of the boundary layer and serve ultimately to bring about enhancement of heat transfer between the fluid and its neighboring surface. The present study determines the flow structure, in detail, behind a winglet type vortex generator placed in fully developed laminar channel flow. The flow structure is complex and consists of a main vortex system, a corner (horseshoe) vortex system, and induced vortices. Experiments are performed in order to corroborate the numerical predictions of the flow structure. The purpose of this study is to analyze performance of a delta winglet type vortex generator in improving heat transfer. The conclusions that are drawn identify a plausible choice regarding the optimal angle of attack of the vortex generator. Such vortex generators show great promise for enhancing the heat transfer rate in plate-fin crossflow heat exchangers (Biswas et al., 1994a; Biswas et al., 1994b; Deb et al., 1995; Biswas et al., 1996). The numerical code is being extended to compute flow and heat transfer in the air-cooled condensers for the Geothermal Power plants. This is a tripartite international project between Idaho National Laboratory (USA), Yokohama National University (Japan) and IIT Kanpur. The NEDO (Japan) is the sponsoring agency. Another possible application of such enhancement technique has been explored by Vasudevan et al. (2000).

3.3 CFD in Food Processing in Single-Screw Extruders

Screw extrusion is widely used for the manufacture of plastics, polymers, pharmaceuticals and food products. In contrast there are irreversible cooking reactions in the food processing. Both chemical and physical changes may occur at the same time under the influence of moist heat, pressure and shear. The dough viscosity greatly increases as the reaction proceeds. In short, the viscosity of a food system is not only a function of strain rate and temperature, but also depends on the composition and the temperature-time history of the process. In a recent work at IIT Kanpur (Ghoshdastidar et al., 2000), a quasi 3D and 3D steady state finite volume based computer models have been developed to describe the transport during processing of defatted soy flour with 25%, 28% and 33% moisture content by weight in the metering section of single-screw extruder. The food is assumed to follow power-law viscosity model. The continuity, momentum and energy equations have been solved simultaneously. Conjugate heat transfer between the fluid and screw body has been considered. The flow field in the cross sectional plane has been calculated using SIMPLE algorithm. A fully implicit scheme is used to march along the length of the channel. The curvature effects have been neglected and therefore, the screw is treated as unwound. Creping flow approximation has been made.

3.4 Numerical Study of Double-Diffusive Natural Convection in Anisotropic Porous Enclosures

A numerical study has been accomplished for combined heat and mass transfer by natural convection within a rectangular enclosure in an anisotropic porous medium, using a non-Darcy Brinkman model. The problem is studied numerically using the Spectral Element method. The computer simulations are validated by comparison with published analytical and numerical results (Bera et al., 1998).

3.5 Mixed Convective Flow in Vertical Channel with a Built-in Circular Cylinder

The flow field and the temperature distribution around a heated/ cooled circular cylinder placed in an insulated vertical channel are determined using a finite volume algorithm. Unsteady mixed convection situation has been considered for the study and the effect of buoyancy on the vortex shedding in the wake of a cylinder has been observed. Vortex shedding is found to stop completely at a critical Richardson number of 0.15. Below this critical value of the Richardson number, shedding of vortices into the stream is quite prominent. Heat transfer characteristics of the heated/-cooled cylinder are studied as a function of Richardson number. The results are of use in the design of shell and tube heat exchangers (Singh et al., 1998).

3.6 Understanding Higee Through CFD

The innovation of new process is a matter of as much scientific acumens as intuition. Initial success in meeting the desired objective leads one to undertake a phenomenological study of such a process for its further development. Introduction of Higee in the early eighties as an alternative gas-liquid mass transfer device is one such example. Use was made of centrifugal acceleration by rotating a packed bed to intensify mass transfer. The Navier-Strokes equations are parabolized to model the gas flow through the rotor (Sandilya et al., 2001). This study is expected to lay a foundation for further development of proper flow models.

** The references are available in the list of Publications