EFFECT OF IMPELLER CLEARANCE IN SOLID SUSPENSIONS IN AN AGITATOR VESSEL
Introduction
Agitation can be defined as the act of shaking or stirring something vigorously. This is achieved through the use of agitators. Agitators find their usage among a wide range of industries: food, cosmetic, chemical, biochemical and pharmaceutical applications. Among chemical applications these include: fermentation, crystallization, hydrogenation and catalytic reactions. Agitators commonly used in industries are: mechanical and static agitators.
The general design of an agitator is composed of an agitator motor and a shaft on which the impeller or the turbine is mounted, which is housed inside an agitator vessel. This vessel may or may not have baffles. Baffles are basically used to prevent the formation of unwanted vortex. The motor is connected to a tachometer (rpm sensor) and a torque sensor.
They display the shaft speed and the torque used for computation of power consumption.
Fig 1: Agitator Vessel
The different phases in which agitation is carried out include: solid-liquid, liquidliquid, liquid-gas and solid-liquid-gas. Hence, the type of phases to be mixed determine the choice of agitator to be used. Agitation is usually carried out to increase heat transfer, promote chemical reactions, mixing or blending liquids or to maintain a homogeneous liquid bulk during storage.
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Impellers or turbines are used to carry out the process of agitation. An impeller can be defined as a rotor whose purpose is to decrease or increase the flow and the pressure of the fluid in a desired direction. Impellers can be classified on the basis of flow regime: Radial flow impellers and axial flow impellers. Impellers can also be classified further into three types: paddles, turbines and propellers.
Radial flow impellers typically find their usage where there is need to mix two or more immiscible fluids or there is need of mixing highly viscous fluids. Axial flow impellers on the other hand are used for homogenization processes where there
Agitation can be defined as the act of shaking or stirring something vigorously. This is achieved through the use of agitators. Agitators find their usage among a wide range of industries: food, cosmetic, chemical, biochemical and pharmaceutical applications. Among chemical applications these include: fermentation, crystallization, hydrogenation and catalytic reactions. Agitators commonly used in industries are: mechanical and static agitators.
The general design of an agitator is composed of an agitator motor and a shaft on which the impeller or the turbine is mounted, which is housed inside an agitator vessel. This vessel may or may not have baffles. Baffles are basically used to prevent the formation of unwanted vortex. The motor is connected to a tachometer (rpm sensor) and a torque sensor.
They display the shaft speed and the torque used for computation of power consumption.
Fig 1: Agitator Vessel
The different phases in which agitation is carried out include: solid-liquid, liquidliquid, liquid-gas and solid-liquid-gas. Hence, the type of phases to be mixed determine the choice of agitator to be used. Agitation is usually carried out to increase heat transfer, promote chemical reactions, mixing or blending liquids or to maintain a homogeneous liquid bulk during storage.
1|Page
Impellers or turbines are used to carry out the process of agitation. An impeller can be defined as a rotor whose purpose is to decrease or increase the flow and the pressure of the fluid in a desired direction. Impellers can be classified on the basis of flow regime: Radial flow impellers and axial flow impellers. Impellers can also be classified further into three types: paddles, turbines and propellers.
Radial flow impellers typically find their usage where there is need to mix two or more immiscible fluids or there is need of mixing highly viscous fluids. Axial flow impellers on the other hand are used for homogenization processes where there
References: 1. Gopal R.Kasat and Aniruddha.B.Pandit, 2005, “Review on Mixing Characteristics in Solid-Liquid and Solid-Liquid-Gas Reactor Vessels”, Vol 2. Piero M. Armenante* and Ernesto Uehara Nagamine, 1997, “Effect of off bottom on minimum critical impeller speed for complete suspension in stirred reactor”, Vol Page No. 1757. 3. R. Conti, Sicardi and V. Specchia, 1980, “Effect of the stirrer clearance on particle suspension in agitated vessels”, Vol 4. Aoyi Ochieng , Maurice S. Onyango , Anil Kumar, Kirimi Kiriamiti, Paul Musonge, 2007, “Mixing in a tank stirred by a Rushton turbine at a low clearance”, Model CEP 5. Rajendra N. Sharma, Abdullah A. Shaikh, 2002, “Solids suspension in stirred tanks with pitched blade turbines”, Vol 6. Thanapalan Murugesan, 1999, “Critical impeller speed for solid suspension in mechanical agitator vessel”, Vol 7. P.K. BiswasU, S.C. Dev, K.M. Godiwalla, C.S. Sivaramakrishnan, 1998, “Effect of some design parameters on the suspension characteristics of a mechanically agitated