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CONSTRUCTION OF A PILOT MOTORISED MIXER

ABSTRACT

A motorized mixer of 200 liters capacity was constructed to have the capability of mixing 200 liters of fluid during operation. The construction of the mixer involves the preliminary measures and calculations on the surface area of the metal sheet.  Some basic workshop practices was carried out during the construction such as the marking out of the metal sheet, cutting of different sizes of the sheet, welding of the prints, assembling of the components parts and painting of the equipment. The material used in the construction of the mixer is mainly of mid steel.  The mild steel was used for the construction due to its quality cost availability and characteristics. The cost of constructing the motorized mixer was cheep due to the choice of material selected for the constructional project and it was finally painted with aluminum paint to protect it form corrosion. The material dimension used in construction of the motorized mixer is as follows:

Length of vessel                                700mm

Diameter of vessel                             600mm

Length of shaft                                  800mm

Surface area of plastic vessel              1320000mm

Electric motor rating                           733.3v 50/60HZ, 3728.5 watt

7000r pm

CHAPTER ONE

INTRODUCTION

Mixers are equipments used to prepare a uniform combination of two or more substances.  Its aim is to obtain a desired degree of mixing in which the product in the mixer may be homogenous or heterogeneous.  The mixing or blending of liquid substances depends on the creation of flow current which transports unmixed materials to the mixing zone adjacent to the impellers.

The motorized mixer consists of different parts which makes up its body, they are:

a.      The shaft

b.    The impellers, which are usually in the form of flat blade turbine type, either centrally located in the vessel or nearer to the bottom entry of the required material.  They are also in axial flow or radial flow depending on the angle which the blade makes with the plane of the impeller rotation.

c.      A vessel or tank, in which the degree of uniformity or homogeneity operation is carried out; depending on the material involved such as solid and liquid or required and gas.

d.     It also has a motor, which is of about 5 horse power, that helps in rotation of the shaft; connected with a belt.

Mixting is an important unit operation where one substance is made to completely  intermingled with another; like in saponification where a caustic soda is mixed with groundnut oil or palm kernel oil in order to have a homogenous mixture in soap production. The mixing process depends on the effective agitation used during the operation.

Agitation refers to the induced motion of a material in a specified way, usually in a circulatory patter, inside a vessel or container, and mixing is the random distribution into and through one another of two or more initially separated phases. A single homogenous material, such as a thankful of cold water can be agitation but it can not be mixed until some other materials such as quantity of hot water or some powdered solid is added to it.

The selection of a particular mixer for a particular purpose depends on some factors such as the process requirements; flow properties of the process fluid; equipment cost and the construction materials required. A good mixer is therefore is one, which produces a well uniformed product at lowest overall cost; and meets all process requirements.

PROBLEMS ENCOUNTERED DURING MIXING

There are problems that are mainly encounter in mainly process, the commonest one is the overtaking or mass swirling of the liquid. Vortexing do occur in the mixing processing and it causes reduction in difference between the fluid velocity and the impeller velocity and thereby decreases the effectiveness of the mixing process.  (Vortex occurs when there is gas-liquid surfaces or phases).

If the mixing vessel or container is small in size, vortexing can be prevented by installing the impeller of centre or at angle with the vertical or fixing the impeller to the side of the vessel at an angel. These problems can be prevented by chosen an appropriate mixer and taking all the precautions in mixing to avoid vortexing.

Note:   vortex occurs when there is gas – liquid surfaces in mixing and is prevented by baffle.

PURPOSE OF MIXING

Substances or materials are mixed for a number of purposes depending on the objectives of the processing step, they includes:

a.    Suspending solid particles

b.    Blending miscible liquids

c.   Promoting heat transfer between the liquids and a heat exchanger (e.g. coil or jacket)

d.    Dispensing a gas through the liquid in the form of small bubbles.

e.    Reducing partial agglomerate

f.     Contracting or dispersing immiscible liquids.

Mixers generally have a number of characteristics in common; they full under the range of

Change-can mixers

Kneaders

Dispersers

Masticators