New processes or modifications to existing processes are initially tested for technical feasibility in laboratory scale or pilot plant scale. Scaling up of these processes to commercial production stage needs a complete understanding of the different physical and chemical processes occurring in the system. Scaling up to commercial scale may involve operating in a different qualitative regime than in the pilot plant.Detailed mathematical models can be proposed to simulate the behavior and performance of these systems in both scales of operation. These help in scale up of the system. Scale up of trickle bed reactors sustaining hydrodesulfurisation and hydrocracking is carried out in this department. This is a project sponsored by Chennai Petroleum Corporation Limited. Here pilot plant data are obtained experimentally. The flow rates in the pilot plant are maintained such that the residence time is the same as in a commercial reactor. Under these conditions the hydrodynamic flow regimes in the two systems are different. For instance the catalyst in the pilot plant may be partially wetted and in the commercial plant may be completely wetted. This has to be accounted for in scale up. The kinetics determined in the pilot plant runs is masked by internal diffusional resistances. We have developed models to take into acount these different hydrodynamic characteristics and to evaluate the intrinsic kinetic parameters from pilot plant data. This is then used in prediction of commercial plant performance.

Chemical process plants typically consist of upstream reactors coupled to downstream separation units via recycle streams. These recycle streams recycle unconverted reactants from the separator to the reactor.The behavior of the individual units , i.e., reactors and separators as induced by non linearities has been investigated. For example these systems can show multiple steady state solutions,sustained oscillations. These can result in unsafe operation i.e., runaway reactions. The coupling of the two units results in modification of the behavior of the individual units. Different control strategies can be implemented to control the coupled system. For instance the level of a liquid phase reactor can be controlled using either the fresh feed flow rate or the reactor effluent flow rate. Alternatively the level can be left uncontrolled. Work in this area is focusing on which of these control strategies is desirable. The focus is on using simple models which enable us to understand the physical interactions induced by the coupling of the two units. The finite velocity of the streams results in a time lag in the interaction between the variables. The system is hence governed by delay differential equations. Work is in progress to understand the effect of delay in these equations. The challenges in this area lie in determining new solution metholdolgies for delay differential equations, and determining instabilities induced by delay and physically understanding their origin.

Mixing is an important step in many units like reactors etc. It enables one to bring two phases into intimate contact with each other thereby increasing the interphase mass transfer. The classical method for mixing is using stirrers. However in many situations stirring has to be induced by introducing bubbles at the bottom. This is particularly true when the liquid is very corrosive. The bubbles induced rise to the top by buoyancy. This in turn induces motion in the liquid and results in stirring. These bubble plumes can be used to prevent spreading of oil slicks. They occur naturally in many electrolysis systems where gas bubbles are formed at the surface of the electrode. Work in this area is in progress in proposing one- dimensional models and pseudo homogeneous to describe the flow. We are currently working on two dimensional and heterogeneous models. The predictions of these models will be experimentally verified using PIV(particle Image velocimetry). Using this technique the velocities of the individual phases will be determined. This will enable us to verify some of the assumptions which have been made in modeling.

This is a non-invasive technique which enables measurements of local flow field. The variation in the flow field ,i.e the stream line pattern in an area of interest can be measured. The flow must allow the laser to pass through i.e., must be optically transparent to the laser. The fluid is seeded with neutrally buoyant particles. the ideas is these seed particles attain the velocity of the fluid at each point and by measuring the paricle velocity we can measure the fluid velocity. A laser is pulsed twice and the images of the particle is captured by means of a CCD camera on two frames. The relative displacement of the particles and with the knowledge of the "dt" we can determine the velocity field. This instrument augments the research carried out in the CFD center. IIT Madras is the first academic institute in India to have this PIV.

Ground water levels are decreasing at an alarming rate all over India. This is caused by the exploitation of the ground water resources by the population. In conjunction with the periodic (now almost regular) failure of monsoons this has led to an acute water scarcity in important cities like Chennai, etc. The solution to this water problem needs a multipronged approach. We are developing a technology to treat grey-water or sullage from dometic effluents. This is based on the principle of segregation of water on the basis of the pollutants they contain. The grey water which contains less pollutants will be treated and used to recharge the ground water locally.This approach serves to reduce the load on the sewage treatment plant as well as helps in increasing the level of ground water. Studies are on to find out if this withdrawal of grey water would result in blockage of the sewage pipes since this results in decrease in the amount of the carrier fluid. Work is on towards determining a comprehensive policy for management of water. Towards this goal we are developing watermeters to determine the amount of water that is consumed in each household. The objective is to evolve a policy towards making the consumer pay for the amount of water that will be consumed.

This is a project sponsored by the Volkswagen Foundation, Hannover Germany. The project envisages mathematical modeling and the simulation of these coupled reactor separator systems. Here fresh feed is fed to an upstream reactor. The partially converted reactants are fed to a downstream separator. The reactant rich stream leaving the separator is recycled to the reactor. The product rich stream is withdrawn from the system. The two units are coupled to each other via the recycle stream. The current focus of the project is to determine the behavior of the system when the reactor sustains a system of series-parallel reactions. It would involve determining when the conversion and selectivity of the coupled system can be optimised. Another aspect of the coupled system is that it is characterised by delays. Our focus is on understanding conditions under which the delay can induce instabilities. The work involves simulating ordinary differential equations, partial differential equations and delay differential equations.

This is a project sponsored by the Department of Science and Technology under the FIST scheme.Particle Image Velocimetry (PIV) involves measuring the velocity profile in a planar region. This is a non-invasive technique . The principle is based on flashing a sheet of light along the plane of interesttwo times. The fluid medium is seeded with particles which are neutrally buoyant. The particles scatter the light from the laser and this scattered light is photographed using CCD cameras. The images/ of the particles are analysed to ascertain their displacement. Using the information about the time difference between the two pulses we can accurately determine the velocity flow field. The equipment is used to measure the velocity flow fields in a bubbly two phase flow. Here gas bubbles are introduced at the bottom of a vessel. The buoyancy force makes these bubbles rise up. These bubbles drag the liquid up and induce a circulation in the liquid. The liquid in the vessel is now mixed. This is used for mixing corrosive liquids etc.