simulation of palm oil and methanol mixing in stirred tank...

ii

SIMULATION OF PALM OIL AND METHANOL MIXING IN

STIRRED TANK BY IMPLEMENT A NORMAL AND FRACTAL

BAFFLES

ALI.H.ASMAYOU

This project report presented in partial

fulfillment of the requirements for the award of

the Degree of Master of Mechanical and Manufacturing Engineering

Faculty of Mechanical and Manufacturing Engineering

Universiti Tun Hussein Onn Malaysia

JUNE, 2014

vi

ABSTRACT

Numerical analysis of mixing and dissolution processes is becoming great significant

for achieving a process of consideration and optimizing the production. Owing to the

rising costs and deficiency of raw materials, “palm oil” processes are presently

employed together with standard experimental analysis. Numerical simulations have

confirmed to be a valuable instrument for understanding and enhancing industrial

mixing problems. However, such simulations are still in the research phase. Even

though Computational Fluid Dynamics (CFD) is a powerful and validated method,

however, for more complicated applications (e.g., industrial mixing), more work is

still required to gain reliable results quickly enough. In this project concentrated on

the simulation of two type of tank to compare between normal baffle and fractal

baffle in mixing tank to get which one is the best of homogenizing. Approximations

were made with respect to improving batch sizes, tank geometry, impeller type,

baffle type, and placement and process variables, such as the impeller agitation

speed. In addition, the feeding position of the methanol. Finally, a quantitative

comparison of different stirring systems and scale-up studies was set.

vii

CONTENTS

TITLE ii

DECLARATION iii

DEDICATION iv

ACKNOWLEDGEMENT v

ABSTRACT vi

CONTENTS vii

LIST OF TABLES xi

LIST OF FIGURES xiii

LIST OF SYMBOLS xvi

LIST OF APPENDICES xvii

CHAPTER 1 INTRODUCTION 1

1.1 Definition 1

1.2 Biodiesel 1

1.3 Problem statement 2

1.4

1.5

Objectives

Scope of research

3

3

CHAPTER 2 LITERATURE REVIEWS 5

2.1

2.2

Biodiesel

Mixing process in tank

5

6

2.3 Multiple phase system of the mixing 7

2.3.1 Gas-liquid dispersion 7

2.3.2 Solid-liquid suspension 8

2.3.3 Liquid-liquid emulsions 9

2.4 Flows in the tank 10

2.4.1 Radial Flow 11

2.4.2 Axial flow 11

viii

2.5 Impeller clearance 13

2.6 mixing time 13

2.7 Reynolds number 14

2.7.1 Laminar region 14

2.7.2 Transition regime 15

2.7.3 Turbulent regime 15

2.8 Baffle 15

2.8.1 Effects on baffling 16

2.9 Fractal square grid 17

2.10 Coefficient of variance (COV) 18

2.11 Palm kernel oil 20

2.12 Methanol and ethanol 21

2.13 Computational Fluid Dynamics (CFD) 22

CHAPTER 3 METHODOLOGY 23

3.1

3.2

Introduction

Methodology flow chart

23

23

3.3 Pre processor 26

3.3.1 Model geometry 27

3.3.2 Models 3D of normal impeller 27

3.3.3

3.3.4

3.3.5

Models 3D of normal and fractal baffle

Configuration of normal baffle tank

Configuration of fractal baffle tank

29

31

32

3.4

3.5

3.6

3.7

3.8

3.9

ANSYS Fluent

Grid of normal and fractal baffle tank

Domain and boundary condition

Solver setup

Post processing

Coefficient of variation (COV)

33

33

36

36

37

37

CHAPTER 4 RSULTS AND DISCUSSION 37

4.1 Introduction 37

4.2 Post processing (Simulation Result) 38

4.3

Turbulent Flow Simulations of normal baffles in mixing

tank, (Time =1000 s) by ANSYS fluent Software.

39

ix

4.4

4.5

4.6

4.7

4.8

4.9

4.10

4.11

4.12

4.13

4.14


tank, (Time =1200 s) by ANSYS fluent Software for.

Re = 4965.


tank, (Time =1400 s) by ANSYS fluent Software for

Re = 4965.



Re = 4965.

The COV with homogeneous for normal baffle tank at

time (1000, 1200, 1400 and 3600) s and Re of 4965.

Turbulent Flow Simulations of fractal baffles in mixing


Re = 4965.



Re = 4965.



Re = 4965.



Re = 4965.

The COV with homogeneous of fractal baffled tank at

(1000, 1200, 1400 and 3600) s and Re of 4965.

Comparison between the COV with homogeneous of

normal and fractal baffle at only plan1 ZX= [0.01] m,

(Time =1000, 1200, 1400 and 3600 s) , 20 iteration,

Re = 4965.

Turbulent flow confirmation

41

43

45

47

48

50

52

54

56

57

58

x

CHAPTER 5 CONCLUSIONS AND RECOMMENDATIONS 60

5.1 Conclusion 60

5.2 Recommendation 62

REFERENCES 63

Appendices A

Appendices B

66

69

xi

LIST OF TABLES

3.1 Specifications dimensions tank 27

3.2 Specifications dimensions of impeller 28

3.3 Specifications dimensions of normal and fractal baffle 30

3.4

3.5

4.1

4.2

4.3

4.4

4.5

4.6

4.7

Element and nodes in normal baffle tank

Element and nodes in fractal baffle tank

Total nodes and element for grid independent test.

Homogeneity level of the local volume fraction for the

dispersed phase, methanol in palm oil, the normal baffles

in mixing tank, Re = 4965.



in mixing tank, at ,(Time =1200 s).



in mixing tank, at ,(Time =1400 s), Re =4965





dispersed phase, methanol in palm oil, the fractal baffles

in mixing tank, at (Time =1000 s) Re =4965



in mixing tank, at (Time =1200 s)Re =4965.

34

35

37

40

42

44

46

49

51

xii

4.8

4.9

4.10



in mixing tank, at (Time =1400 s) Re =4965




Parameter values of Reynolds Numbers

53

55

59

xiii

LIST OF FIGURES

2.1

2.2

2.3

2.4

2.5

2.6

2.7

2.8

2.9

2.10

2.11

3.1

3.2

3.3

3.4

3.5

3.6

3.7

3.8

3.9

3.10

4.1

process mixing tank

Typical arrangement of Rushton radial-flow R100 flat-

blade turbine for gas-liquid mass transfer

Solid-liquid reaction.

Method to obtained light phase and dense phase Radial

Redial Flat-blade turbine.

Marine-type mixing impeller and Pitched-blade turbine

Turbulent flow pattern for an axial impeller type

Increased baffling increases the power draw of an

agitator

Baffling also reduces blend time

Construction of a plane fractal square grid based on three

fractal iterations.

Global consumption and major users of oil palm 1995-

2010.

Methodology flowchart (1)

Methodology flowchart (2)

Dimensional of tank (mm)

Dimensional of impeller (mm) (mm)

Dimensional normal baffle (mm)

Dimensional fractal baffle (mm)

Geometry of normal baffles tank (mm)

Geometry of fractal baffles tank (mm)

Mesh for normal baffle tank

Mesh for fractal baffle tank

Graph of velocity versus distance for three type of mesh

6

8

9

10

11

12

12

16

17

18

20

24

25

27

28

29

30

31

32

34

35

38

xiv

4.2

4.3

4.4

4.5

4.6

4.7

4.8

4.9

4.10

4.11

Distribution of the local volume fraction for the

dispersed phase, methanol in palm oil, of normal baffles

in mixing tank, plan 1 at XY= [0.0] m.



in mixing tank, at ZX= [0.01,0.1,0.2 and 0.3] m .



in mixing tank at (Time =1200 s)






in mixing tank at (Time =1400 s) and20 iteration, Re =

4965







4965




Graph of COV with four types of distance plans and

three deference times for normal baffle tank


dispersed phase, methanol in palm oil, of fractal baffles

in mixing tank, plan 1 at XY= [0.0] m .

39

40

41

42

43

44

45

46

48

48

xv

4.12

4.13

4.14

4.15

4.16

4.17

4.18

4.19

4.20


dispersed phase, methanol in Mixing fractal baffle tank,

(Time =1.0000e+03).




4965.



(Time =1200 s).




4965



(Time =1400 s).




4965




Graph of COV with four types of distance plans and

three deference times for fractal baffle tank.

Graph the result compare between normal and fractal

baffle of COV

49

50

51

52

53

54

55

57

59

xvi

LIST OF SYMBOLS

Mixing time

cycling time

, dimensionless blending time

N

D

N

X

COV

Reynolds number

Fluid viscosity

Fluid density

Rotational speed

Impeller diameter

Standard deviation

The number of data points

The mean of the xi

Coefficient of variation

Mean concentration

xvii

LIST OF APPENDICES

APPENDIX TITLE PAGE

A Overall result for volume fraction of Methanol in

normal baffle mixing tank

66

B Overall result for volume fraction of Methanol in

fractal baffle mixing tank

69

1

CHAPTER 1

INTRODUCTION

1.1 Definition

Stirring, mixing, blending, homogenization, and emulsification are necessary unit

operations in the manufacture of many pharmaceutical, fuels products and are in most

cases carried out in agitated tanks made of steel and sometimes equipped with a glass

liner. Another significant operation is the dissolution of solids in a liquid phase.1 A large

number of studies have therefore focused on analyzing the (multiphase) flow in agitated

vessels, as well as numerical and experimental studies. Different flow regimes have been

recognized, depending on the range of the Reynolds (Re) number, and also different

systems including various impeller types and fractal baffle type system and with normal

baffle type system at all. According to, (Thomas Heormann, et al., 2011)

1.2 Biodiesel

Considered Biodiesel an alternative fuel and become more attractive as of late in view of

it is ecological profits fuel which is made from renewable biological sources such as

2

vegetable oils and animal fats. The cost of biodiesel, is the primary obstacle to

commercialization of the item .The utilized cooking oils are utilized as crude material,

adaption of uninterrupted transesterification procedure and recovery of high quality

glycerol from biodiesel by-item (glycerol) are primary cucumber to be considered to

minimize the expense of biodiesel. (Fangrui Ma et. al, 1999). Malaysia has left on an

exhaustive palm bio fuel customized since 1982 and has effectively settled the utilization of

palm methyl esters and the mix of transformed palm oil (5%) with petroleum diesel (95%)

as a suitable fuel for the transport and industrial parts. At present, the real sympathy toward

biodiesel handling is financial achievability. Biodiesel creation will not be supported

without tax exemption and subsidy from government; as the generation expense is

higher than fossil inferred diesel (Demirbas & Balat, 2006).

1.3 Problem Statement

A mixing tank is one of gadgets in designing commercial ventures that is utilized for the

persistent blending of liquid materials. By and large, mixing tank is utilized to blend

fluid; however it can additionally be utilized to blend gas streams, scatter gas into fluid

or mix immiscible fluids.

In industry, there are numerous sorts of mixing tank have been composed and it

is utilized broadly within industry. Notwithstanding, there are numerous mixing tank

that have been proposed in industry having unpredictable and muddled in configuration.

The sort of mixing tank that ordinarily used as a piece of industry is CSTR, PFR and BR

tank. Each of mixing tank has their approach and state of blender that is formed in order

to enhance benefit to mix the fluid homogeneously. Meanwhile, each of the

arrangements obliges high cost of amassing and need to put a huge amount of time in

gathering and station. This exploration study will turn out with straightforward

configuration of blending tank and in the meantime having standard effectiveness of

blender keeping in mind the end goal to decrease current expense of assembling yet

processing same consequences of blending liquid as other blending tank. So as to outline

3

ideal blender geometries, proper devices and techniques are required to describe the

stream conditions and their impact on the blending procedure.

In this study, COV will be connected keeping in mind the end goal to measure

for showing the consistency of fixation at a cross area of blending tank. The recreation

of blending liquid could be reproduced by utilizing computational liquid element (CFD)

programming. The reenactment will anticipate the conduct of liquid course and blending

inside the tank. This study will concentrate on recreation of liquid flow and blending

inside the Tank at particular separation of investment.

1.4 Objective

This research study embarks on the following objectives:

i. To propose a new approach of fractal concept (square grid fractal) for baffle in

mixing tank.

ii. To assess a capability of fractal pattern in mixing process by determining the

coefficient of variation (COV).

iii. To make a recommendation for new concept of mixing in tank by using a fractal

concept based on square grids fractal.

1.5 Scopes of Study

To conduct this research study, several scopes have been outlined:

i. The simulation is done primarily in mixing tank with two kind of baffle,

normal and fractal to get the best mixing by using fluent 14.5 ANSYS.

4

ii. This study will be implemented by fully numerical simulations.

iii. Three different time steps of 1000, 1200, 1400 and 3600 second will be use in

this simulation.

iv. Use the 3 dimension model.

v. The Methanol (C𝐻!O) will be used in the inlet feed.

vi. The propeller rotation speed is 150 RPM.

vii. The flow will be turbulent with a Reynolds numbers, Re of 4965.

viii. In order to test the quality of the new modeling approach, the numerical

simulations will be done by comparing their results of volume fraction with

normal baffles simulation to evaluate local values of mixing tank.

5

CHAPTER 2

LITERATURE REVIEW

2.1 Biodiesel

Bio diesel is a renewable asset serving to decrease the reliance of the economy on

constrained assets and imports, make a business sector for ranchers and lessen the

measure of waste oil, fat and oil being dumped into landfills and sewers. Moreover,

Biodiesel is a light to dull yellow fluid immiscible with water, with high ebullition point

and low vapor pressure. It additionally alludes to a diesel – proportionate handled fuel

determined from biodiesel sources, (for example, vegetable oils), which could be

utilized as a part of unmodified diesel – motors vehicles. It is additionally biodegradable,

non-dangerous and regularly transforms something like 60% less net carbon dioxide

(Co2) emanations than petroleum – based diesel. Ecological Researchers have reported

that global warming change by humanly induced. Its head reason incorporates blazing of

fossil powers, for example, coal, oil and characteristic gas via cars which ceaselessly

discharges carbon dioxide into the atmosphere (Idusuyi, N. et al 2012).

6

2.2 Mixing process in tank

Liquid blenders cut crosswise over very nearly every preparing industry including the

concoction process industry; minerals, mash, and paper; waste and water treating and

very nearly every individual methodology area. The specialist working with the

requisition and configuration of blenders for a given procedure has three essential

hotspots for data. One is distributed writing, comprising of a few thousand distributed

articles and a few as of now accessible books, and pamphlets from supplies sellers.

Figure :(2:1) shows process mixing tank ( James Y. Oldshue, 1983). They have a

considerable measure assortment of employments because of the operation adaptability.

It could be worked in laminar and turbulent blending administrations. Stirred tank might

be utilized for a fluid and gas, a fluid stage mixture, a three stage mixture or fluid with

suspended solids mixture.

Figure (2.1): process mixing tank. (James Y. Oldshue, 1983).

7

It likewise accompanies part of size and utilized focused around the creation and

interest. In biodiesel production mixing process is an essential process considered in

biodiesel generation. This production is exceptionally intricate and it generates from

convection and turbulent trades in a mixing tank (G.r. Kasat et. al, 2008).

For blending process, a couple of challengers must to think about on the grounds

that this methodology obliged long living arrangement time, high working expense, high

vitality utilization and low of preparation proficiency. To comprehend all the

challengers, thinks about on biodiesel blend are creating focused around the

strengthening innovations. From the research, the analyst found that to attained the best

reactor plans, there have a couple of imperative components must to think about

including the measure of reactor, tumult framework, hydrodynamic, physical properties

of reactants, development material, sharpened steel model, impeller sort, size and speed

and confound plan and the systems for hotness expelling and supplying from reactor (M.

Hosseini, et al, 2012).

2.3 Multiple phase system of the mixing

Multiphase systems are habitually encountered in an assortment of modern methods

including a.o. covering, granulation, drying and blend of powers (Fischer Tropsch) and

base chemicals. The hydrodynamics of multiphase systems are managed by the

movement towards the individual stages and the complex shared collaborations and as a

direct an immediate thereof CFD-based modeling of these frameworks has demonstrated

so difficult (Niels G. DEEN ,et al 2006).

2.3.1 Gas-liquid dispersion

More often than not, to disband the gas in the fluid is the primary motivation behind gas

scattering. The gas generally is injected into the tank from the down of reactors, or

8

someplace else nears the impeller to give the diffusion of gas. Figure (2.2) shows how

gas dispersed in the liquid state. (James Y. Oldshue, 1983).

Figure (2.2): Typical arrangement of Rushton radial-flow R100 flat-blade turbine for

gas-liquid mass transfer. (James Y. Oldshue. 1983)

2.3.2 Solid-liquid suspension

Generally speaking in a powerful liquid reaction, the reaction was slower than the

ordinary and it is happened at the bottom outlet of the tank. Normally, most of the

requisition in blending engineering is identified with the suspension of the solids-fluid

stage. The solids particles in the tank all around the mixing methodology are denser than

the pass on fluid achieving tenacious settling of the particles towards the base of the

tank. Along these lines, to stay far from the interminable settling of solids and to

procure an adequate mass trade flux throng the powerful surface all around mixing

process, the technique is given to keep the solids is suspension (Hinze and J.o, 1975).

Solid dissolving issues and insufficient blending for the off-bottom suspension were

9

comprehended by utilizing a pitched cutting edge turbine impeller and full baffled. The

affect ability of response rate to both molecule size and impeller velocity was promptly

settled. Figure (2.3) shows the example of a solid- liquid reaction inside an instigator in

tank. (J. Derksen, 2010)

Figure (2.3): Solid-liquid reaction,(J. Derksen, 2010)

2.3.3 Liquid-liquid emulsions

The prediction of drop sizes in liquid-liquid systems is difficult. Most of the studies have

used very pure fluids as two of the immiscible liquids, and in industrial practice there

almost always are other chemicals that are surface-active to some degree and make the

prediction of absolute drop sizes very difficult. In addition, techniques to measure drop

sizes in experimental studies have all types of experimental and interpretation variations

and difficulties so that many of the equations and correlations in the literature give

contradictory results under similar conditions.

Experimental difficulties include dispersion and coalescence effects, difficulty

of measuring actual drop size, the effect of visual or photographic studies on where in

10

the tank you can make these observations, and the difficulty of using probes that

measure bubble size or bubble area by light or other sample transmission techniques

which are very sensitive to the concentration of the dispersed phase and often are used in

very dilute solutions. (James Y. Oldshue, 1983). The impeller should be placed in the

phase which is going to be the continuous phase to create a table emulsion between a

light and also a dense liquid phase such as Figure (2.4).

Figure (2.4): Method to obtained light phase and dense phase dispersed

(James Y. Oldshue, 1983)

2.4 Flows in the tank

Flow is described as one or two components resulting from the of the mixer impellent in

the tank . Often the stream pattern formed by an instigator are become into the first sign

of its suitability for a specific process. The allocation of the scattering of gas and solid

molecule in a fluid usually relies on the kind of the stream pattern that prepared by the

specific instigator in a given tank (R.Zadghaffari et al., 2008). Plus that, the suitability of

a specific instigator for a given mixing procedure is relies on upon its capacity which is

to affect the liquid substance of the tank into the sturdy rotational, keeping away from

the circumstances where areas of the liquid are inadequately blended or not blended

11

whatsoever, while in the meantime abstaining from harming the different species

scattered in it. (Hinze and J.o, 1975).

2.4.1 Radial Flow

Radial-flow impellers have sharpened pieces of steels which are parallel to the pivot of

the drive shaft. The littler multi bladed ones are known as turbines; bigger, slower-speed

impellers, with two or four edges, are frequently called oars. The width of a turbine is

ordinarily between 0.3 and 0.6 of the tank breadth. Turbine impellers arrive in a mixture

of sorts, for example, bended cutting edge and even sharpened steel, as delineated in

Figure (2.5). (James Y. Oldshue, 1983).

Figure (2.5): Radial Flat-blade turbine. (James Y. Oldshue, 1983)

2.4.2 Axial flow

Impellers incorporate all impellers in which the razor sharp edge makes a plot of short of

what 90° with the plane of pivot. Propellers and pitched-razor sharp edge turbines, as

represented in Fig (2.6), are illustrative pivotal stream impellers.

12

Figure (2.6): Marine-type mixing impeller and Pitched-blade turbine

(James Y. Oldshue, 1983)

Versatile blenders may be braced as an afterthought of an open vessel in the precise, off-

center position or darted to a rib or plate on the highest point of a shut vessel with the

pole in the same rakish, unbalanced position. This mounting brings about a solid start to

finish dissemination. (James Y. Oldshue, 1983) .The fan create parallels stream to the

impellers. In addition that, if impeller set close to the lowest part of the vessel, radial

drainage may happen. when utilized the propeller of axially kind , liquids stream moves

upward and downward in the tank .axial stream propeller distribute material chiefly

axially .In standard case of reactor without baffles, the rotational time to be lower than in

a baffles time. (Tatterson and J.b, 1991). Figure (2.7) show the diverse of the stream

design for axial impeller.

Figure (2.7): Turbulent flow pattern for an axial impeller type, (Tatterson and J.B, 1991)

13

2.5 Impeller clearance

Most studies have been completed at the standard impeller leeway (one-third of the tank

diameter). Furthermore, it has been demonstrated that the impeller clearance does

influence the liquid stream modality. In any case, it has been accounted for that the

stream example created by the Ruston turbine transformed from the average two circles

at a standard clearance to a solitary circle design at a low clearance. For a multiple

impeller system, the most favorable clearance at which there is minimal intrusion among

the flow generated by the top and lower impellers is the same to the tank diameter. Well-

spaced impellers generate smooth and high fluid flows, which are characterize by mean

velocity of the fluid and turbulence concentration. (A. Ochieng ,et al ,.2009)

2.6 Mixing Time

Mixing time, 𝑡! , is the time needed to accomplish a given deviation from the

completely blended state from the occasion of a tracer data. Mixing time is a global

indicator of blending and it is influenced by pivotal and outspread blending and the

impacts of bulk stream. Mixing in airlift reactors is in some cases depict regarding a

dimensionless blending time 𝜃!, describe as follows:

𝜃! = !!!!

2.1

Where 𝑡! is the cycling time, or the time needed for one section through the

course circle.The dimensionless blending time is by and large seen to depend just on the

reactor geometry and not on gas speed where tc is the cycling time, or the time needed

for one section through the course circle (A.sa nchez miro N, et al 2004).

14

2.7 Reynolds number

The definition of Reynolds number for a mixing impeller differs from a pipe or particle

Reynolds number in that the product of N D is used to represent velocity. Reynolds is:

N!" = !²!!!

2.2

Where is the fluid viscosity, ρ is the fluid density, N is the rotational speed and D is

the impeller diameter .Again, coherent units or appropriate conversion factors will make

the Reynolds number dimensionless .Value for the impeller Reynolds number are also

different from other forms of Re, in that turbulent conditions usually exist for Re >

20,000 and laminar conditions occur for Re < 10. The large transition range between

turbulent and laminar condition represents a gradual transition from turbulent conditions

near the impeller to laminar conditions near the tank wall. In the transition range, the

turbulent regions, especially in the impeller discharge, gradually diminish in size as the

Reynolds number becomes smaller (D. S. Dickey et al., 2004).

2.7.1 Laminar region

The laminar regime corresponds to (Re) i < 10 for many impellers; for stirrers with very

small wall-clearance such as the anchor and helical-ribbon mixer, laminar flow persists

until (Re) i = 100 or greater. In the laminar regime:

𝑁! ∝ 1/(𝑅𝑒)! 2.3

15

2.7.2 Transition regime

Between laminar and turbulent stream lies the move administration. There is normally a

progressive move from laminar to completely created turbulent stream in mixed tanks;

the stream example and Reynolds-number range for move rely on upon framework

geometry (Mohan, p et al., 1992).

2.7.3 Turbulent regime

The marvel of turbulent mixing is an immediate aftereffect of turbulent liquid stream,

which is portrayed by an arbitrary variance of the liquid speed at any given point within

the framework. The liquid speed at a given moment may be communicated as the vector

aggregate of its segments in the x, y, and z directions. With turbulence, these directional

segments vary arbitrarily about their individual mean values, as does the speed itself. As

a rule, with turbulence, the liquid has distinctive immediate speeds at diverse areas in the

meantime (Dr. Bhawna Bhatt, Prof. S.S. Agrawal 2007).

2.8 Baffle

During agitation of a low-viscosity liquid, the rotating impeller imparts tangential

motion to the liquid. Without baffling, this swirling motion approximates solid-body

rotation in which little mixing actually occurs. Think about stirring a cup of coffee or a

bowl of soup: The majority of the mixing occurs when the spoon is stopped or the

direction of stirring is reversed. The primary purpose of baffling is to convert swirling

motion into a preferred flow pattern to accomplish process objectives. The most

common flow patterns are axial flow, typically used for blending and solids suspension,

and radial flow, used for dispersion. However, baffling also has some other effects, such

16

as suppressing vortex formation, increasing the power input and improving mechanical

stability (Kevin J. Myers,et al., 2002).

2.8.1 Effects on baffling

During agitation of a low-viscosity liquid, the rotating impeller imparts tangential

motion to the liquid. Without baffling, this swirling motion approximates solid-body

rotation in which little mixing actually occurs. The primary purpose of baffling is to

convert swirling motion into a preferred flow pattern to accomplish process objectives.

The most common flow patterns are axial flow, typically used for blending and solids

suspension, and radial flow, used for dispersion. However, baffling also has some other

effects, such as suppressing vortex formation, increasing the power input and improving

mechanical stability, Figure (2.8) shows that the impeller power number increases as the

number of standard width baffles (T/12) is increased. (Kevin J. Myers,et al., 2002).

Fig (2.8): Increased baffling increases the power draw of an agitator

(Kevin J. Myers,et al., 2002).

Data are presented for three impeller styles: radial- flow impellers, such as straight-blade

and Rushton turbines, mixed-flow impellers, such as pitched-blade turbines, and axial-

flow impellers, such as high-efficiency impellers. All data in figure (2.9) are normalized

17

with respect to the unbaffled condition, with each impeller style being normalized

individually, rather than with respect to a common reference (Kevin J. Myers,et al.,

2002).

Fig (2.9): Baffling also reduces blend time (Kevin J. Myers, et al., 2002).

“Normalized” means that, if the unbaffled radial-flow power number is 2.5 and the

unbaffled high-efficiency impeller number is 0.2, then all of the radial-flow impeller

data are divided by (normalized) 2.5 and all of the high-efficiency impeller data are

divided by 0.2 (Kevin J. Myers ,et al., 2002).

2.9 Fractal square grid

Homogeneous isotropic turbulence has been widely studied both experimentally in wind

or water tunnels and numerically by Direct Numerical Simulations (DNS).Recently,

used various multi scale (fractal) grids to generate turbulence in wind tunnels and found

that complex multi scale boundary/initial conditions can drastically influence the

behavior of a turbulent flow, especially when a fractal square grid (see Figs.2.10) is

placed at the entry of a wind tunnel test section. According to, (Sylvain Laizet • John

Christos, 2011).

Very recently, DNS of full three dimensional turbulent flows generated by three

different fractal grids but at relatively small Reynolds numbers they have been able to

18

recover some of the experimental results of, such as the higher turbulent intensities that

fractal square grids generate by comparison to regular grids of same or even larger

blockage ratio.

Fig (2.10): Construction of a panel fractal square grid based on three fractal iterations.

According to, (Sylvain Laizet · John Christos, 2011)

In these simulations the fractal stirrers were mainly based on a square pattern with three

multi scale iterations and with a relatively small computational domain in the stream

wise direction. There were also successfully performed DNS of turbulence generated by

strategy. According to, (Sylvain Laizet • John Christos, 2011).

2.10 Coefficient of variance (COV)

According to (Fan 1990), the homogeneous mixture is a mixture that having mixing

element uniformly. There are several factors that influence the homogeneous mixture

which are mechanisms of mixing, characteristics of materials to be mixed and

characteristics of the mixer. To analyze a mixture, samples are taken from the mixture at

random which represent of the state of the mixture. The level of acceptable homogeneity

of the mixture depends on each application. It can be specified in terms of variation

19

coefficient, COV. Usually a COV value between 0.01 and 0.05 is a reasonable target of

completely homogeneous mixing fluid for most applications. The lower value of COV

represents better quality of the homogenous mixture. The standard COV value equal to 0

represents a complete distributive mixing, while COV value more than or equal to 1

represents total segregation. According to (R.V., 2004). The COV is defined as the

standard deviation of concentration, σ over the mean concentration, 𝑥 for a given set of

data points.

The standard deviation of concentration is:

σ =!!!! !!

!!!!!!

(2.4)

Where;

σ = Standard deviation

n = the number of data points

𝑥 = the mean of the 𝑥!

𝑥!= Each of the values of the data

An alternative measure of homogeneity is provided by the coefficient of variation:

COV = !

! (2.5)

Where:-

COV = Coefficient of variation

σ = Standard deviation

𝑥 =Mean concentration

dd t

20

2.11 Palm kernel oil

Palm oil is the world’s cheapest edible oil, and increasingly one of the most popular. As

global demand continues to grow so has the vigorous search for land for new plantations

by investors and industry. When it is done well and is properly managed, palm oil

production can be of potential benefit to the populations of developing countries by

providing sustainable livelihoods. Oil palm cultivation also has a greater oil yield per

hectare than any other oil crop, which in theory means it should require less land.

Fig (2.11): Global consumption and major users of oil palm 1995-2010 (Basiron, Y.,

2010)

On the other hand, unchecked large-scale expansion of the industry could lead to

environmental devastation, and precipitate social and economic havoc for African

people. Some acquisitions put forests, ecosystems and the climate at risk, and threaten

21

the livelihood of the people depending on the land, global consumption and major users

of oil palm 1995-2010 as in fig 2.11 (Basiron, Y., 2010).

Palm oil, produced within well-managed and diverse agro forestry systems,

would not only help ensure food security for millions of Africans, provide people with a

living grow local economies; it can also help protect the region’s last remaining

rainforests. In turn, food production will become more diverse and more resilient,

helping to offset the impact of climate change, (Basiron, Y., 2010).

2.12 Methanol and ethanol

Actually they have deferent between , methanol and ethanol, the ethanol is reacted with

the triglycerides molecules in the oil, producing glycerin and alkyl esters of fatty acids

(biodiesel) Worldwide, methanol is the most commonly used alcohol for biodiesel

production, but the large-scale production of sugarcane in Brazil makes ethanol cheaper

and easier to use for biodiesel production. Since ethanol is obtained from plant sugars

and methanol is commonly produced from natural gas (or petroleum), the production of

biodiesel by mixing of oils with ethanol (ethanolysis) represents a more sustainable

pathway for this befoul production than that employing methanol (methanolysis).

Methanolysis is a multiphase reaction, which occurs only at the boundaries of the

methanol droplets dispersed in the vegetable oil phase. Ethanolysis, on the other hand,

can be approximated by a single-phase reaction while in stirred tank reactors. Modeling

and simulation of multiphase reactions like methanolysis usually requires prohibitive

computational resources, while ethanolysis requires only a commercial CFD code in

which equations for the reaction kinetics can be introduced as source terms in the mass

conservation equations implemented in the software ( Demirbas, A. ,2005).

22

2.13 COMPUTATIONAL FLUID DYNAMICS (CFD)

The CFD simulation procedure embodies mesh creating, comparison solving and result

handling modules. A lot of exertion has been committed to the simulation and modeling

of an impeller. The absolute most normal methodologies to modeling an impeller will be

impeller limit condition, preview, sliding network, various casings of reference and

inner–outer. In an extraordinary number of these studies, impellers with basic

geometries, for example, the Rushton turbine, have been modeled. Modeling of curved

blade impellers poses a great challenge with regards to grid generation (A. Ochienga et

al., 2009).

In the Reynolds-normal Navier-Stokes approach, the mathematical statements

are solved to foresee mean stream properties. Actually, with respect to any numerical

result of incomplete differential mathematical statement, the area is speak to by the

discrete and its limits assumes a huge part in characterizing the right stream features or

examples around the impeller blade. (A.Egedy et al., 2011).

23

CHAPTER 3

METHODOLOGY

3.1 Introduction

Methodology is a method or process, or facts that involve an array of measures of work

that should be in a scientific study. For the method the main essential aspect that should

have to concern is on the modeling of the baffled stirred reactor and kinetics model for

biodiesel reactor which will be a way to reach our goals and the results accepted by

using commercial CFD code ANSYS Workbench 14.5 is employed as it is the most

effective way to determine such geometrical parameters.

3.2 Methodology flow chart

Research method or methodology is the process shown in Figure 3.1 and the procedure

and steps of the simulation process is shown in form of flowchart in Figure 3.2

24

Determine title

Objective/scope

Literature review

Discuss the literature review content

Collecting data

Simulation using ANSYS Fluent

Data analysis

No

Yes

No

Results

Validation and discussion

Conclusion

End

Yes

Figure 3.1: Methodology flowchart

Start

63

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