Welcome to our presentation on Liquid Mixing

Course Title: Pharmaceutical EngineeringCourse Code: PHR-320

Represented By……….

Rupom Mitra Kazi Nadim Hossain Md. Anin Nayeem

Liquid mixing Definition

Classification Importance

1.Miscible liquid2.Partially miscible liquid

3.Immiscible liquid

Mechanism1. Bulk Transport

2. Turbulent Mixing

3. Laminar Mixing

4. Molecular Diffusion

a

d

az

------

-Motor

Shaft

Lid

Outlet

ImpellerBaffle

Jacket

Inlet

Mixing Vessels

Mixing vessels

Mixing Devices

oPropellersa. Top View

b. Side View

Fig: Propeller type of mixing devices. A 3 bladed design

Turbines30-50% of diameter of vesselSpeed 50-200 rev/min

UsesUsed in very viscous ranges up to 700 P.sCan handle slurries with 60% of solids

AdvantagesSuitable for Emulsification

Different types of turbines

Flow pattern during mixing

3 types1. Tangential or circular flow:

Direction: tangent to the impeller shaft

2. Radial flow: Direction: Vertical to the impeller shaft

3. Axial flow: Direction: Parallel to impeller shaft

Vortex formationCause:1. Shaft mounted vertically in the centre of the tank2. Turbines arranged perpendicular to shaft3. High impeller speed4. Unbaffled tank

DisadvantagesLow mixingAir bubbles contaminationOxidation of compounds

Prevention of vortex1. Avoid symmetry

Off centreInclinedSide entry

2. Baffeld containers3. More impeller4. Cylindrical Tank (Dead spots)

Return Flow with Draft Tubes

• Draft tubes are placed to control the direction and velocity of the flow to the the impeller

• These are mounted around the propeller. In case of turbines ,drufts tubes are mounted immediately above the impeller

Uses:

Used in Manufacture of certain emulsions..Airjet mixers for mixing of liquids employ draft tubes.

Disadvantage: Draft tubes add to the fluid friction in the system that reduce the rate of flow.

Equipment For Liquid Mixing

1.Air jet mixer2.Jet mixer3.Flow mixer or line mixer or pipe

Airjet MixerPrinciple: when compressed air jets are passed from thr bottom of a vessel,air bubbles are formed in the liquid phase.The buoyancy of the bubbles lifts the liquids,which are confines to the central portion due to the presence of drat tubes The floatage of the bubbles lifts the liquids,which are confined to the central portion due to the presence of draft tubes.

Construction: Compresses air or suitable gas is allowed to pass at high pressure from the inlet provided at the bottom of the tank.This causes buoyancyof the bubbles which lifts the liquid from bottom to the top of the vessel

Use: liquids of low viscosity, non foaming, non reactive with gas are mixed by using airjet mixer.

Jet mixer

Principle: The liquids to be mixed are pumped separately into a jet mixer at different velocities. During mixing the slow moving liquid will be drawn at high velocity jet. This increasess the volume of the jet and decreases velocity,which causes to jet to expand.

Conruction:• It consist of a vessel and a mixing device known as jet • A typical jet mixing system has 12 jets arranged radically in a

cluster in the centre of the mixing tank.The cluster of jets is called an eddy jet mixer.

• Av individual eddy jetmixer has two concentric nozzles with a suction chamber between them.

• Advantage: The power required for pumping is often sufficient to complete.

Flow Mixer or Line Mixer or Pipe Mixer

• It may consist of a baffled pipe or an empty chamber • Liquids to be mixed are passed through the pipe or chamber• Mixing takes place through bulk transport in the direction of

flow• The power supplied to pump the liquid itself accomplishes

mixing.• For effective mixing controlling the feed rate is essential.• If the input rate is difficult to controland fluctuations in the

added proportions of the liquids are unavoidable,contious mixing equipment of tank type is preferable.

Uses: When large volume of liquids are to be mixed,flow mixers are used.