University Institute of Chemical Technology, India

Computational Fluid Dynamics Work

By J. B. Joshi, A. B. Pandit and A. W. Patwardhan

Almost 80 percent of the processes encountered in chemical process and allied industries are heterogeneous. A large spectrum of reactor configurations is available for multiphase contacting, such as stirred reactors, bubble columns, spray columns, jet reactors, plate columns, fluidized beds, moving beds, etc. Almost all these reactors are operated in turbulent regime. Turbulent flows are studied using experimental and computational techniques.

From its inception in 1934, University Institute of Chemical Technology (UICT) has been actively involved in solving the problems of the chemical industry related to chemistry and transport phenomena. To study the transport phenomena in detail, UICT has an excellent experimental facility for turbulence research and multiphase reactor design. The facility includes hot film anemometry, laser Doppler anemometry, ultrasound velocity profiler, particle image velocimetry and tomographic techniques. This facility is extensively used to study the flow patterns in different chemical reactors, such as stirred vessels, jet reactors, bubble columns, packed and fluidized beds, etc. The understanding of transport phenomena helps in improving product reliability and saving energy.

However, experimentation over a wide range of geometric and operating conditions is not always possible. In such cases, computational fluid dynamics plays an important role. The experimental results help in validating the simulation results. For CFD simulation, our institute has inhouse CFD codes plus ANSYS FLUENT and ANSYS CFX. CFD is used to study the mixing time, residence time distribution, turbulent kinetic energy and dissipation rate profiles, hold-up profiles, interfacial area, and heat and mass transfer in the reactors.

One of the projects undertaken by our group is identification and characterization of flow structures using the information in design and optimization of reactors. In this project, particle image velocimetry (PIV) and large-eddy simulation (using ANSYS FLUENT and ANSYS CFX) are carried out in channel flow, jet reactor, stirred vessels, bubble column, and packed and fluidized beds. The transient velocity data over plane of interest were analyzed using advanced mathematical techniques such as Fourier and wavelet transformation and POD. The energy content distribution over different scales was obtained in all the geometries at different Reynolds numbers. Depending on application, the local dissipation rates can be manipulated by modifying the internals in the reactors for energy-efficient performance and miniaturization. Other major projects involve application of CFD in mixer settler, studies of hydrodynamic cavitation that is applied for biological cell disruption, waste water treatment, ballast water treatment, etc.

The institute is also training undergraduate and post-graduate students in transport phenomena and computational fluid dynamics. At any point of time, around 40 post-graduate students are working on problems involving computational fluid dynamics.

Large-eddy simulation of stirred tank reactor using disk turbine. Trailing vortices are shown behind the impeller blades. These vortices have a marked effect on the final performance of the reactor. The impeller's design is optimized based on the understanding of fluid mechanics to reduce the excess energy dissipation close to impeller and homogenize it throughout the vessel or dissipate it at the desired locations

Hydrodynamic cavitation reactor. Cavitation generated hydrodynamically by passing liquid through the orifice plate is studied. In addition to the cavitation model available in ANSYS FLUENT, detailed cavity/ bubble dynamics equations are incorporated through compiled UDFs, which are solved in conjunction with continuous phase. Velocity contours show flow of liquid through the orifice of different designs to optimize the cavitational yield in a hydrodynamic cavitation reactor.