Numerical study of fluid and heat transfer in mixing elbow

NUMERICAL STUDY OF FLUID FLOW AND HEAT TRANSFER IN MIXING ELBOW

MOHD IDHAM KHALID BIN ABU HASAN

This Report Is Submitted In Partial Fulfillment Of Requirements For The Bachelor Degree of Mechanical Engineering (Thermal-Fluid)

Faculty of Mechanical Engineering University Technical Malaysia Melaka

SUPERVISOR DECLARATION

"I hereby declare that I have read this thesis and in my opinion this report is sufficient in terms of scope and quantity for the award of the degree of

Bachelor of Mechanical Engineering (Thermal-Fluids)"

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Supervisor:

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DECLARATION

"I hereby declare that the work in this report is my own except the summaries and quotations which have been duty acknowledge."

Signature:

Author:

Date:

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Dedicated to my beloved Mother, Father and Brothers ...

iv

ACKNOWLEDGEMENT

All praise to Allah Most Gracious, Most Merciful, Who, Alone, brings

forgiveness and light and new life to those who call upon Him.

First of all, thanks to Allah s.w.t for all His guidance and blessing through all

the hardship encountered whilst completing this thesis. In preparing this thesis, I was

in contact with many people, researchers, academicians and practitioners where they

have contributed towards my understanding and thoughts. In particular, I wish to

acknowledge with much appreciation the crucial role of my supervisor, Miss Nur

Hazwani Mokhtar for guidance, encouragement, critics and friendship.

I would like to express my deepest appreciation to my family especially my

beloved mother, Mimunah Muhamad and all of my siblings for all of their loves and

supports. I am also indebted to FKM lecturers for their guidance to complete this

thesis, especially to my final year project panels

Mr.

Mohd Hafidzal Bin Mohd

Hanafi and

Mr.

MD Isa Bin Ali. Without ther continued support and interest, this

thesis would not have been presented here.

Lastly I would like to recognized my fellow undergraduate colleagues for

v

ABSTRACT

Study of heat transfer and fluid flow in piping system often involves of

temperature, heat flow, velocity and dynamic viscosity from the entrance the fluid

enter until the fluid flow out of the pipe outlet. This study focus on the behaviour of

heat transfer and fluid flow in mixing elbow. Mixing elbow is a region where two

types of fluid flow with different temperature and high Reynolds number is

intensively mixed together and is among typical geometries exactly where

temperature fluctuation happens. Temperature fluctuation in liquid causes high cycle

thermal fatigue within structure materials based on temperature distributions as well

as time variations. The main objective of this study is to simulate and analyze the

flow and temperature field in the mixing elbow by simulate with several models of

different inlet diameters. The simulation process is done by using Computational

Fluid Dynamic (CFO) software. From the simulation, it is proven that the mixed flow

appeared as turbulent and caused the temperature changes which eventually generate

a cyclic stress that contributes to thermal fatigue failure on the welded joint and Flow

accelerated corrosion (F AC) also founds to be the contributor for thermal fatigue

failure at the elbow. Besides that, it is found that from the simulation test of three

models with different diameters, it would longer the service life of mixing elbow and

vi

ABSTRAK

Kajian tentang pemindahan haba dan aliran bendalir dalam sistem perpaipan

sering melibatkan suhu, aliran haba halaju, dan kelikatan dinamik dari awal

kemasukan bendalir sehingga aliran bendalir keluar dari salur keluar paip. Kajian ini

memberi tumpuan kepada tingkah laku pemindahan haba dan aliran bendalir dalam

siku pencampuran. Siku pencampurkan merupakan tempat di mana dua jenis aliran

cecair dengan suhu yang berbeza dan dengan nombor Reynolds yang tiggi

dicampurkan bersama secara intensif dan adalah antara geometri yang kebiasaannya

menjadi tempat di mana turun naik suhu berlaku. Turun naik suhu dalam cecair

menyebabkan kitaran keletihan haba yang tinggi dalam struktur bahan berdasarkan

taburan suhu serta variasi masa. Objektif utama kajian ini adalah untuk

mensimulasikan dan menganalisis aliran dan medan suhu dalam siku pencampuran

dengan menjalankan simulasi terhadap beberapa model yang mempunyai saluran

diameter masuk yang berbeza. Proses simulasi dilakukan dengan menggunakan

perisian Dinamik Bendalir Komputeran (CFD). Daripada simulasi yang telah

dijalankan, ianya terbukti bahawa aliran bercampur menghasillkan arus bergelora

dan menyebabkan perubahan suhu yang akhimya menjana tekanan kitaran yang

menyumbang kepada kegagalan lesu haba pada sendi kimpalan dan Aliran Pecutan

Hakisan (F AC) juga terbukti menjadi penyumbang untuk kegagalan lesu haba di

sesiku. Selain daripada itu, didapati bahawa daripada ujian simulasi tiga model

dengan diameter yang berbeza, hayat perkhidmatan siku campuran akan jadi lebih

lama dan keselematan siku campuran boleh ditingkatkan dengan membesarkan saiz

vii

TABLE OF CONTENTS

CHAPTER TITLE PAGE

DECLARATION ii

DEDICATION iii

ACKNOWLEDGEMENT iv

ABSTRACT v

ABSTRAK vi

TABLE OF CONTENT vii

LIST OF TABLE ix

LIST OF FIGURE x

LIST OF SYMBOL XII

LIST OF APPENDIX xiii

CHAPTER I INTRODUCTION

1.0 Introduction 1

1.1 Importance of Study 3

1.2 Objectives 3

1.3 Research Scope 3

1.4 Problem Statement 4

CHAPTER2 LITERATURE REVIEW 5

2.0 Introduction 5

2.1 Correlation Matrix 8

2.2 Simulation Method 10

2.2.1 Experiment 10

2.2.2 Computational Fluid Dynamic (CFO) 11

2.3 Turbulence Modelling 12

viii

2.5 Model Validation

15

2.5.1 Material Properties

15

2.5.2 Boundary Condition

16

2.6 Data Validation

17

CHAPTER3 METHODOLOGY

19

3.0 Introduction

19

3.1 Flow Chart

20

3.2 Methodology Determination

20

3.2.1 3-D Mixing Elbow Reconstruction

23

3.2.2 Grid Dependency

25

3.2.3 Model Validation

28

3.2.4 Simulation of Various Inlet Diameters

29

CHAPTER4 RESULT & ANALYSIS

31

4.0 Introduction

31

4.1 Validation

32

4.2 Temperature Field Inside Mixing Elbow

34

4.3 Turbulent Behaviour Inside Mixing Elbow

36

4.4 Flow Accelerated Corrosion (F AC)

38

4.5 Effect of Diameter On Flow Inside Mixing Elbow

41

4.5.1 Turbulent Flow Comparison

42

4.5.2 Temperature Field Comparison 44

4.5.3 Pressure Comparison

46

CHAPTERS CONCLUSION

47

5.1 Conclusion

47

5.2 Recommendation

49

REFERENCES

50

BIBLIOGRAPHY

52

ix

LIST OF TABLE

TABLE TITLE PAGE

Table 2.1 List of journals 8

Table 3.1 Number of nodes and element for three type of mesh 25

Table 3.2 Properties of water 28

Table 3.3 Material properties for Aluminium 28

Table 3.4 Boundary condition of mixing elbow 29

Table 3.5 List of tested diameters for mixing elbow 30

Table 4.1 Validation data for k-E, Experiment, LES and k-ro 60

Table 4.2 Comparisons of three simulation models 39

x

LIST OF FIGURE

FIGURE TITLE PAGE

Figure 2.1 Mixing elbow principle 6

Figure 2.2 Location ofthennal fatigue 6

Figure 2.3 Cracked on Civaux Reactor mixing elbow 7

Figure 2.4 Schematic of test section 10

Figure 2.5 Quadrilateral/hexaheral meshes and triangle/tetrahedal meshes 14

Figure 2.6 Cross-section of the computational mesh used with a mesh size of 14

2mm (a) In the mixing pipe. (b) In the hot leg

Figure 2.7 Graph of peak to peak temperature difference of outer skin wall 17

surface

Figure 2.8 Temperature fluctuation profile 18

Figure 3.1 Turbulent model setup 22

Figure 3.2 Mixing elbow dimensions (inches) 23

Figure 3.3 Isometric view of mixing elbow 24

Figure 3.4 Mixing elbow grid 26

Figure 3.5 Isometric view of mixing elbow grid 27

Figure 4.1 Contours of static temperature of mixing elbow 32

Figure 4.2 Temperature contour of mixing elbow 35

Figure 4.3 Location ofthennal fatigue 36

Figure 4.4 Turbulent kinetic energy contour 37

Figure 4.5 Velocity vector inside the mixing elbow 38

Figure 4.6 Velocity vector at the mid plane elbow 40

Figure 4.7 Accelarated fluid flow 40

Figure 4.8 Flow separation and vortices 41

Figure 4.9 Comparison of turbulent contours 43

xi

Figure 5.1 3-D mixing elbow reconstruction 54

Figure 5.2 Geometry meshing process 55

Figure 5.3 Simulation setups 56

Figure 5.4 Simulation result 57

Figure 5.5 Converged computation for Small diameter 58

Figure 5.6 Converged computation for Medium diameter 59

p

u

D

µ

=

=

=

=

LIST OF SYMBOL

Density {kg/m3)

Velocity (mis)

Diameter of pipe (m)

Dynamic viscosity (kg/ms)

xiii

LIST OF APPENDIX

APPENDIX TITLE PAGE

Appendix A Simulation procedures 54

Appendix B Prove of converged computations 58

Appendix C Validation data for k-E, Experiment, LES and k-ro 60 Appendix D Temperature data for three different diameter sizes of mixing 61

elbow

1

CHAPTERl

INTRODUCTION

1.0 INTRODUCTION

In mixing elbow, heat transfer through convective fluid flow occurs due to

differences in density of the fluid at the surface. In addition, there is also a flow of

changes that cause the phenomenon of laminar and turbulent flow depends on the

flow of phase change. The mixing between two types of fluid with different

temperature will caused a temperature fluctuation which will generate a cyclic stress

and contributes to thermal fatigue failure (Aulery et al,2012). Besides that, the

changes in flow direction in the mixing elbow will produce a secondary or flow

separation due to biased velocity distribution . The parameter taken into

consideration are the pipe diameter or length of pipe required, velocity of fluid flow

and fluid flow rate.

In general, heat transfer process can be seen all around us. Basically the heat

transfer mechanism can flowing through three processes of conduction, radiation and

convection (Holman, J.P., 1986). In recent times, a lot of research in the field of heat

2

which the energy transfer occurs between systems that communicate with each other

due to differences in temperature. It is also a phenomenon that occurs at the

boundary of the system is a redistribution of internal energy in the system.

Convective heat transfer process is mainly a surface phenomenon. Surface

may be a surface in, such as the wall of the pipe or channel, or the outer surface of a

particular body (Holman, J.P., l 986).

In

the process of convection, mass and

momentum transfer and heat transfer occur simultaneously.

The design and analysis of engineering systems involving fluid flow is either

by experiment or calculation. Previous method involves building models and tested

in wind tunnels or other equipment. Latest methods involving differential equations,

or computing solutions.

CFO code is used to calculate the properties related to heat transfer and fluid

flow. Practical problems in engineering mostly involving fluid flow and heat transfer.

CFO is also used to shorten the design cycle by controlling the parameters relevant.

In addition, it can reduce the amount of equipment to make the experiment thus

reduced the cost of making the experiment.

CFO focuses on fluid flow equations using a computer software. Modem

engineers have now been applied to both the experimental and CFO analysis to

obtain the details of the velocity profile of the fluid flow, pressure and temperature.

Meanwhile, experimental data are often used for validation of the CFO solution with

computing systems adapt and experiment to find the overall quantity.

Therefore, the process of simulating and analyzing the fluid flow and heat

transfer for this study can be done by using the CFO software. The simulation can be

3

1.1 IMPORTANCE OF STUDY

This research focus on the heat transfer and fluid flow inside a mixing elbow,

starting from the flow entering the inlet until it flow out through the pipe outlet. The

importance of this study are as follow:

i. To equip students with the knowledge and skills related to disentangle the

various methods in heat transfer and fluid flow.

ii. To apply the application ofCFD simulation and knowledge up on the run.

iii. To be able to analyze the results of the simulation data and make

recommendations regarding the improvement of the research.

iv. To be able to implemented ANSYS FLUENT 14.0 software in a simulation

of the fluid flow and heat transfer.

1.2 OBJECTIVES

This research is focussing on the heat transfer and the fluid flow inside a

mixing elbow, starting from the flow entering the inlet until it flow out through the

pipe outlet. The objectives are as follow:

i. To simulate and analyze the flow and temperature field in the mixing elbow.

ii. To simulate with several models of different inlet diameters.

1.3 RESEARCH SCOPE

This research is focussing on the heat transfer and the fluid flow inside a

mixing elbow, starting from the flow entering the inlet until it flow out through the

4

i. Design a 3-dimensional (3-D) model of mixing elbow by using CFD application.

ii. Simulate the 30 mixing elbow model with various inlet diameter by using CFD

iii. Visualize and analyze the results of the fluid flow and heat transfer in mixing elbow

1.4

PROBLEM STATEMENT

Mixing elbow is a region where a cold and hot flow is intensively mixed together, where the flow appears as turbulent flow. Geometry of mixing elbow is consists of two inlets and one outlet. The main inlet is where the entrance of the hot flow and the branch inlet is where the cold flow entering the piping system. The mixed flow is then will flow out through the outlet of the mixing elbow. At the mixing region, a heat transfer process takes place which caused a temperature changes. In another words, once the two types of fluid mixed together, temperature fluctuation will happens. This temperature fluctuation will generate a cyclic stresses in the mixing region. The cyclic stresses will be transmitted to the adjoining structure, which is the weakest part of the mixing elbow with fairly low attenuation.

5

CHAPTER2

LITERATURE REVIEW

2.0

INTRODUCTION

Mixing elbow is a region where two types of fluid flow with different

temperature and high Reynolds number is intensively mixed together. Autery et al,

(2012) states that, heat transfer process takes place in the mixing elbow from high

temperature substances to lower temperature substances. Mixing elbow is among

typical geometries exactly where temperature fluctuation happens. The principle of

mixing elbow is as illustrated in Figure 2.1 below.

As seen from Figure 2.1, mixing elbow is consists of two inlet and one outlet.

The two inlets can be classified as main inlet and branch inlet. A hot properties fluid

will enter the main inlet and flow through the pipe. Meanwhile, a cold fluid will enter

the pipe through the branch inlet. Until it reached a certain point, the two types of

6

During the mixing of the two fluids, there will be a temperature changes which known as temperature fluctuation. Aulery et al, (2012) explained that, this temperature fluctuation will generate a cyclic stresses in the mixing region. The cyclic stresses that been generated will be transmitted to the adjoining structure,

which is the weakest part of the mixing elbow with fairly low attenuation. As seen from Figure 2.2 below, the cyclic stress is acted on the location of the weld, where later on it will initiate a crack on the adjoining structure. This cyclic stress is a potential cause of thermal fatigue failure (Autery et al, 2012).

Hot fluid

Mixture

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Figure 2.1: Mixing elbow principle.

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On the other hand, El-Gammal et al, (20 l 0) states in the finding that the

changes in flow direction due to the geometry of the mixing elbow will produce a

secondary flow or flow separation due to biased velocity distribution. This biased

velocity is a factor that responsible for Flow Accelerated Corrosion (F AC) at the

elbow. F AC is a slow degradable process where the flow will damaging or thinning

the protective layer of the piping component and soon will initiate a crack on the pipe

surface. Meanwhile, Crawford et al, (2007) also states that the secondary flow that is

produced by the biased velocity distribution will induce a pressure drop along the

elbow. This pressure drop will cause a significant increase in wall shear stress along

the mixing elbow.

There are several incidents involving mixing elbow, for examples thermal

fatigue cracked at Superphenix Reactor, France on April 1996, Almeria solar plant,

1996, sodium leaked, Monju Reactor, Japan, December 1995 (Aulery et al, 2012)

and thermal fatigue cracked at Civaux Reactor, France on May 1998 (Passuto et al,

2007). The Figure 2.3 below shown an example of thermal fatigue cracked which

happened at Civaux Reactor.

Initial thermal

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fatigue cracked

8

2.1 CORRELATION MATRIX

Table 2.1 below shows the lists journal that is found to be related to this

study. The journals have been extracted in terms of CFO solver, Reynolds number,

simulation method, grid system, and results and analysis. As seen from the matrix

below, most of previous researchers used ANSYS FLUENT as their solver which

ideal on solving internal flow with high Reynolds number. The common method that

have been used in their research is Large Eddy Simulation (LES). Meanwhile, the

results of their simulation were validated by compare with the experimental data or

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previous researcher's data.

Table 2.1: List of journals.

Reynolds Simullti n Grid

Jounuls Solver Number Method System Result & Aulysis

• \Vall temperature

flutnution.

•

E\·:W3tion of Thermal

Numerical Simulation of Fatigue.

Sodium Mixing in a T-junction A1~SYS RA1~S& Co:arsef

•

C-omp:arewith

(Aulerv et al, 2012) FLUENT Hi2.h LES Fine emerimental dm.

•

Flow prediction .

Large-Eddy Simulation Study Com el

•

Comparison with

of Turbulent l\futing in T- .6J-SYS k-£RA_NS Medium \nus resoluti n.

iunction (KuCZ3i et al, 2010) FLUENT Hi2.h &LES Fine

Large Eddy Simulation of a

•

Predicti non mez and

thermal mixing tee in order to fluctulling temperature.

assess the thermal fatigue • Comp:arewith

(Gilpin). Simoneau, .P., .6J-SYS experimental dm.

2011) FLUENT Hil!h LES Fine

•

An.al•rze temperature flurtuati n.

• Structural response of

roobnt piping 3t

Numerical an.alysis of thermal mixing tee.

striping induced high cycle • Compare with

thermal fitigue in a mixing tee A1~SYS Co:arse>' experimental data

(Jeong et al, 2009 FLUBl1 Hi2h LES Fine

•

.;\ul·rze the st3bilit.· of wall fi.mctions.

Suitability of wall-fimctions in

•

Comp:arewith existing

LES for thermal fatigue in a T- .6J SYS Come' experimental dm.

iunction (Jav:araiu et al, 2010) FLUENT Hi@ LES Fine

Thermal stress an.alysis for

Thermal stress an.al -s3.

fatigue ~e evaluation at

•

mi.'ting tee (K.;mya et al, .6J-SYS

•

Comp:arewith existing

2011) FLUE'1T _.. Hil!h k-<i> & LES Fine exnerimental data.

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9 .

Table 2.1: List of journals (cont.).

Journals Soh·er Reynolds Simuhtion Grid Result & Anal "Sis

Number Meth0<d System

Experimentll study on

•

Flow pattern in the tee.

flu" d mixing ~ot High Water Not

•

Flow \"el.ocity in the

phene>menain I-pipe av3il.3ble experiment 3\"~le eibO\'I.'.

junction with upstream

•

_{Temperature fitld in}

elbow (Ogawa et _{the tee.}

al,2 5)

•

_{J:nfluence of elbow in}

the w;ill jet C3!-e. Three-dimens · onal

•

V el.ocities profile w ·th

numerical investigation Al"SYS High Finite Cane different discharge

of flow at 90< open FLUE'll"T Volume 1'.. edrum ratios. channel junction (Al- Analysis Fine

•

Compare with

l'. uss.~i et al, 2009) experimentll data.

A hybrid RA.NS-LES

•

Velocity md water

model for combining A1"SYS High RA1~S & Fine surfare profile. flows in open-channel FLUEl'i! LES

•

C-omparewith

T-juncti ns (Cheng et _{experimentll data.}

al, 2010)

Large eddy simuhtion

•

Temperature

(LES) of temperature AI SYS High LES Coarse/ ilu~ons fluctu4tions in a mixing FL JEll"T Fine with,,\\•ithoutporow

tee with~without porous metfu.

medium ( mg et al,

•

Temperature and

2-010) ,·elocity fields.

•

Compare with experimental <in

ltte hyaroayumc

•

Hydrodyunic effects

effect of single-phase A1'JSYS High RS:tv & Medium of single phase flow on

flow on flow FLUENT E.~ent FAC.

attelerated corrosi n in

•

_{Surfatewear patterns .}

90< elbow (El-~~

10

2.2 SIMULATION METHOD

The simulation method that have previously used in the study of fluid mixing is

based on these two methods:

i. Experiment

11. Computational Fluid Dynamic (CFD)

2.2.1 Experiment

Experiment on the fluid mixing phenomena have been done by Ogawa et al,

(2005). Their experiment being conducted in order to study the mixing phenomena in

the T-pipe junction with upstream elbow. The experiment have various procedures

where the method that being used for this experiment is Water Experiment. The

experiment set up is as illustrated in Figure 2.4 below.

Hot

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