ⓒSNAK, 2

Correspondin

This is an OpeAttribution Nowhich permits medium, provi

Taew

1G 2Glo

ABSTRACTinvestigated The effect of mixer; these mixer type, lenot having asidering the min this study.

KEY WORD

INTODUCT

In order t

respect to red

direct water i

marine diesel

The IMO’s T

selNet, 2008)

agent, urea is

taining 32.5w

thermolysis, a

NH3 slip, and

mixing proce

SCR reactor m

Flow mix

2014

ng author: Gyun

en-Access articon-Commercial unrestricted noided the origina

Effectp

wha Park1, Yo

Graduate Prog

obal Core Res

T: Flow mixinnumerically to

f vane angles parameters a

ed to an impr mixer. In parmixing perfor

DS: Selective c

TION

to meet stringe

ducing nitrogen

injection, exha

l engines. The

Tier III standar

). SCR is one

s preferred in m

wt% urea, is inj

and hydrolysis

d low urea con

ess for two-ph

must be obtain

xing is a comm

ngmin Choi, e

cle distributed ul License (http:/on-commercial al work is prope

t of statiressure

onmo Sung1,

gram, School

search Center 3Pusan Clean

ng and pressuro develop an on the relativare dramaticarovement of aprticular, there rmance and th

catalytic reduc

ent future emis

n oxides (NOx

aust gas recircu

e international

rd requires that

of the most p

marine SCR ap

jected into the

s processes. Th

nsumption. To

hase flow, such

ned.

mon device unit

-mail: choigm@

under the terms//creativecommuse, distributio

erly cited.

ic mixerdrop in

Taekyung K

of Mechanica

for Ships and

n Coal Center,

re drop characefficient static

ve intensity, unally affected bpproximately 2was a tradeof

he pressure dro

ction; Static m

ssion regulatio

x), various tech

ulation (EGR)

l maritime org

t marine vesse

romising techn

pplications bec

e hot gas stream

he urea-SCR r

maximize the

h as UWS wit

operation in a

@pusan.ac.kr

s of the Creativmons.org/licenseon, and reprodu

r geometmarine

Kim1, Inwon

al Engineering

d Offshore Pla

Pusan Nation

cteristics for mc mixer. Two dniformity indeby the mixer g20% in the m

off relationshiprop, the swirl-

mixer; Uniform

ons from the e

hnologies such

, and selective

ganization (IM

els must reduc

hnologies for a

cause of its sa

m from exhaus

reactor should

e de-NOx effic

th the exhaust

a large number

Int. J. Nhttp

e Commons es/by-nc/3.0) uction in any

try on floSCR app

Lee2, Gyung

g, Pusan Natio

ants, Pusan Na

nal University

marine selectidifferent mixerex, and pressugeometry. Theixing performp between thetype mixer wa

mity index; Pr

environmental

h as basic inte

e catalytic redu

MO) has regula

e NOx emissio

accomplishing

afety and low t

st manifolds, a

d be controlled

iency and min

t gas stream, a

of processes, a

Nav. Archit. Op://dx.doi.org/1

pISSN: 20

ow mixinplication

gmin Choi3 a

onal Universit

ational Univer

y, Busan, Kore

ive catalytic rrs, line- and swure drop was ie presence of

mance behind te uniformity anas more suitab

essure drop; M

protection age

rnal engine m

uction (SCR) h

ated NOx emis

ons by 80% be

this aggressiv

toxicity. Urea w

and then, NH3

d to ensure high

nimize the NH

and a highly u

and it is used in

Ocean Eng. (210.2478/IJNAO092-6782, eISS

ng and ns

and Duckjool

ty, Busan, Kor

rsity, Busan, K

ea

reduction applwirl-type, werinvestigated inf a mixer, regathe mixer in cnd the pressuble than the li

Marine diesel

ency (EPA), e

modifications, f

have been reco

ssions from m

etween 2010 a

ve regulation.

water solution

is generated b

gh de-NOx perf

H3 slip, a contro

uniform flow i

n many differe

2014) 6:27~38OE-2013-0161SN: 2092-6790

l Kim3

rea

Korea

lications werere considered.n a swirl-typeardless of thecomparison tore drop. Con-ne-type mixer

engine.

especially with

fuel switching,

ommended for

marine vessels.

and 2016 (Die-

As a reducing

n (UWS), con-

by dewatering,

formance, low

olled turbulent

in front of the

ent applications

8 1 0

e . e e o -r

h

,

r

.

-

g

-

,

w

t

e

s

28

where a defin

mixer is usua

distribution of

because of mi

There hav

(CFD) has be

cesses, and u

Romzek, 200

2006). Thaku

for the selecti

fly mixers. Th

and various e

original delta

on the flow m

Zhang and Ro

In allowin

high mixing p

flow mixing c

In this stu

45º, and 60º.

were investig

6.3.26). The p

pressure drop

proper static m

NUMERICA

Analysis mod

The geom

points, is show

developed in

swirl flows; a

vane angles w

assumed to be

ned degree of h

ally installed to

f NH3 and isoc

ixing must be m

ve been many

een widely us

urea decompos

07; Birkhold et

ur et al. (2003)

ion of static m

hey also inves

exhaust gas tem

a wing mixer fo

mixing index o

omzek, 2007).

ng a sufficient m

performance a

characteristics

udy, both line- a

The effects of

gated numeric

purpose of this

p with the obje

mixers was pro

AL METHOD

del

metry of the SC

wn in Fig. 1. L

this study with

and the flexibil

were simulated

e UWS at the S

homogeneity o

o improve the

cyanic acid (HN

minimized.

attempts to de

ed in the desi

sition (Thakur

t al., 2007; Ng

) provided an

mixers. Zheng e

stigated the eff

mperatures. Zh

or the purpose

or uniformity i

.

mixing length

as well as a low

and pressure d

and swirl-type

f a mixer’s ge

ally using a c

s study was to

ective of enhan

ovided based on

DS AND CON

CR system, wh

Line-type and

h several uniqu

lity for installa

d in 3-D to inve

SCR catalyst en

Fig.

of a fluid is de

rate of decom

NCO) (Munna

evelop static m

gn optimizatio

et al., 2003; Z

uyen et al., 20

extensive revi

et al. (2009) d

fect of in-pipe

hang et al. (20

of creating bo

index in the sh

by reducing th

w pressure dro

drops in the mar

mixers were c

eometric structu

commercial fin

evaluate the ef

ncing the de-N

n the correlatio

NDITIONS

hich includes

swirl-type mix

ue features: a s

ation and to co

estigate the flo

ntrance.

1 Computatio

esired (Regner

mposition for u

annur and Liu,

mixers for mob

on of spray no

Zheng et al., 2

010; Larmi and

iew of static m

developed seve

mixing device

006) introduce

oth swirling an

hort distance i

he occupied spa

op. However, t

arine engine fie

considered; eac

ture on the flow

nite volume, t

ffect of mixer

NOx efficiency.

on between the

the position o

xers, as shown

simple design f

ontrol the mixe

ow pattern, turb

onal domain fo

Int. J

et al., 2006). I

urea to NH3 an

2010). Howev

ile SCR applic

ozzles, flow m

009; Zheng et

d Tiainen, 2003

mixers in the p

eral types of m

es on urea dep

ed a simple flo

nd turbulent flo

immediately b

ace, it is necess

there is insuffi

elds.

ch mixer was d

w mixing char

three-dimensio

geometry on t

. Additionally,

e uniformity ind

f the spray inj

n in Fig. 2, hav

for production;

er volume in th

bulence charac

or the SCR sy

J. Nav. Archit.

In particular, a

nd to enhance t

ver, the increase

cations, and co

mixing characte

t al., 2010; Zh

3; Chen and W

processing ind

mixers, includin

posits with resp

ow mixer with

ows. Turbulen

ehind the flow

sary to develop

icient research

divided into thr

racteristics and

onal (3-D) CF

the relative inte

information p

dex and the pre

ector, mixer, S

ve 36 vanes ea

a variable van

he pipe. Both t

cteristics, and u

stem.

Ocean Eng. (2

a mixing devic

the uniformity

e in the system

omputational f

teristics, NOx r

hang et al., 200

Williams, 2005

dustry, present

ng cone, 2-stag

pect to mixer c

h twisted blade

nt flow has a do

w mixer (Zhan

p a proper stati

on the relatio

ree cases of va

d the resulting

FD code; FLU

ensity, uniform

pertaining to th

essure drop.

SCR reactor, a

ach. A swirl-ty

ne angle to gen

types of mixer

uniformity of w

2014) 6:27~38

ce, e.g., a static

y of the spatial

m pressure drop

fluid dynamics

reduction pro-

06; Zhang and

5; Battoei et al.

ting guidelines

ge, and butter-

configurations

es based on an

ominant effect

ng et al., 2006;

ic mixer with a

nship between

ane angles: 30º,

pressure drop

UENT (version

mity index, and

he selection of

and measuring

ype mixer was

nerate different

rs with various

water, which is

8

c

l

p

s

-

d

.,

s

-

s

n

t

;

a

n

,

p

n

d

f

g

s

t

s

s

Int. J. Nav. Ar

The test c

trahedral cells

and the mixer

Table 1 Com

Table 2 Summ

Boundacomput

Initiaspra

Boundary co

The mode

1ms was dete

with 0.45mm

of the exhaus

perature of the

rchit. Ocean E

Fig. 2 C

conditions are l

s using FLUEN

r because of the

mputational con

Case

1

2

3

4

5

mary of initia

Item

ary condition tational doma

al condition ofay injection

onditions

el assumes that

ermined to be s

diameter. The

st gases were

e exhaust gas w

Eng. (2014) 6:2

Configuration

listed in Table

NT/GAMBIT

e high gradient

nditions with

al and boundar

of in

Inl

Ou

W

Ca

f

Sp

Ve

An

SM

Inj

t the exhaust g

sufficient to pr

e initial and bou

set based on f

was set to 573K

27~38

of static mixe

1. The compu

(ANSYS, Inc

ts of velocity, t

various mixer

Mix

W

Swi

Swi

Swi

Line (up-

ry conditions.

Section

let

utlet

all

atalyst

pray material

elocity

ngle

MD: (Rosin-R

jection type

gas is fully dev

roduce results i

undary conditi

full load and 9

K, and the inlet

ers: (a) line-ty

utational grid is

c., USA). The

temperature, an

r types and po

xer type

W/O

irl, 30º

irl, 45º

irl, 60º

-down), 45º

n

Rammler)

veloped and it

independent of

ions used in th

900rpm on a 9

t velocity was 2

ype mixer, and

s composed of

mesh structure

nd species conc

ositions.

Exhaust g

Pressure

Adiabatic

Porous m

H2O (liqu

25m/s

70º

Mean dia

6 hole, so

consists of 77%

f the choice of

e calculation a

920kW diesel

20m/s.

d (b) swirl-typ

f approximately

e became dens

centrations.

Position

7 D inl

Conditions

gas velocity: 2

outlet: atmosp

c / No-slip

media: 1/α = 1.

uid water), 30

ameter: 35µm,

olid cone type

% N2 and 23%

f time step. The

are shown in Ta

engine (HYUN

pe mixer.

y 650,000 hexa

ser toward the

of mixer and

and 3 D fromlet boundary

ns and value

20m/s, 573K

phere

.24 107, 2C

0K

, Spread param

e

% O2 by mass.

he injector cons

Table 2. The ini

UNDAI HiMSE

29

ahedral and te-

spray injector

spray

m

= 10.59

meter: 3.5

A time step of

sists of 6 holes

itial conditions

EN). The tem-

9

-

r

f

s

s

-

30 Int. J. Nav. Archit. Ocean Eng. (2014) 6:27~38

Numerical procedure

The flow region in the SCR system is divided into three regions: the 1st region is the turbulent flow region in the upstream

and downstream of the SCR reactor; the 2nd region is the laminar flow region in the SCR reactor; and the 3rd region is the region

that contains the dispersed two-phase flow in the surrounding spray injector. The Lagrangian discrete phase model is used

which contains sub-models for droplet dispersion, drag, and evaporation. An injection type of solid cone for primary breakup

model is used to inject water liquid. To minimize computational time and stable convergence strategy, secondary breakup

model for droplet breakup and collision are not considered in this study. The injected drop-size was found to follow a Rossin-

Rammler distribution with a mean diameter of 35 microns and spread parameter of 3.5. For an incompressible, unsteady two-

phase turbulent flow, the 3-D Reynolds-averaged Navier-Stokes (RANS) governing equations for mass, momentum, species

concentration, and energy were solved. The standard κ-ε turbulent model was used to calculate the turbulent quantities. The

continuity, momentum, and energy equations are expressed as follows in Eqs. (1)-(3), respectively.

0iu

t

(1)

i j ji it

j i j i j

u u uu up

t x x x x x

(2)

Pr Pri t

i i j t i

u TT T

t x x x x

(3)

The turbulent kinetic energy κ and the rate of energy dissipation ε are computed from a standard two-layer κ-ε turbulent

model.

i t

i j i

uG

t x x x

(4)

1 2i t

i j i

uC G C

t x x x

(5)

G denotes the production rate of κ and is given below:

ji i ii j t

j j i j

uu u uG u u

x x x x

, and

2

t C

(6)

In the above equations, the coefficients are as follows:

1C = 1.44, 2C = 1.92, C = 0.09, = 1.0, and = 1.3.

The catalyst is the core of SCR reactor. In this study, a honeycomb type SCR catalyst filter was adopted. If the catalyst filter is constructed physically from a numerical simulation without any simplifications, the grid of the model will reach a level that is beyond the calculation capabilities of most computing systems. Therefore, an approach of a porous media model was adopted

Int. J. Nav. Ar

to simulate thvelocity is docombination o

where ∆p is t

coefficient, v

values, α and

3. Appropriat

Fi

RESULTS A

Distributions

Fig. 4 illu

injector, mixe

conditions of

of a line-type

flow patterns

zone (CRZ) is

does not exh

concentration

serious proble

velocity and c

that the mass

NH3 slip, low

be mitigated w

rchit. Ocean E

he flow in the cominant in the of Darcy’s Law

the pressure dr

is the velocity

2C , a quadra

te values for α a

ig. 3 Pressure

AND DISCUS

s of velocity an

ustrates the co

er, and reactor.

f swirl-type mix

e mixer with a

behind the mix

s generated nea

hibit a CRZ, b

n of case 1 in

ems, such as c

concentration o

fraction of wat

w mixing of UW

without using a

Eng. (2014) 6:2

catalyst filter. TSCR filter (Je

w and an additi

rop, µ is the la

y normal to th

atic equation of

and 2C can b

drop distribut

SSION

nd water mass

ontours of the

Case 1 represe

xers with vane

a vane angle of

xers differ with

ar the mixer fie

because the ma

front of the S

catalyst filter d

of water are re

ter for case 3 a

WS with hot ex

any guide vane

27~38

The mass and meong et al., 20ional inertial lo

p

p

aminar fluid vi

he porous face,

f Eq. (8) is deri

be calculated u

tion of the par

s fraction in SC

velocity and w

ents the calcula

angles of 30º,

f 45º. Consider

h the mixer typ

elds, and the C

ain flow near

SCR reactor ar

damage and NH

latively well d

appears well mi

xhaust gases, an

es, such as baff

momentum tran005). In this sioss term along

2

1

2v C

22.73 199v

viscosity, α is t

, and ∆m is th

ived from the c

using Eqs. (7) a

rt cell in the S

CR system

water concent

ation condition

, 45º, and 60º,

erable disturban

pe. In the swirl

CRZ increases w

the mixer mo

re concentrated

H3 slip (NMR

distributed in co

mixed with inpu

nd catalyst file

fles.

nsfer in the radmple model, tthe SCR filter

2v m

.72v

the permeabilit

he thickness of

calculation of th

and (8) as show

CR filter with

tration of parts

ns of no mixer.

respectively. C

nces occur sur

l-type mixers o

with increasing

oves up and d

d in the cente

RI, 2011). For t

omparison to c

ut gases in front

r damage in fro

dial direction wthe pressure ch(Fluent, 2007)

ty of the mediu

f the medium.

he simple part

wn in Table 2.

h respect to inl

s of the SCR

. Cases 2, 3, an

Case 5 represen

rround the spra

of cases 2, 3, an

g vane angle. T

down. The vel

r region. This

the remainder

case 1. In partic

t of the SCR re

ont of the SCR

was ignored behange (drop) is):

ium, C2 is the

To obtain the

cell analysis a

let bulk veloc

system, includ

nd 4 represent

nts the calculat

ay injector for

nd 4, the centra

The line-type m

locity distribut

s phenomenon

of the cases (c

cular, Fig. 4(b)

eactor. Based o

R reactor have t

31

cause the axials defined by a

(7)

(8)

pressure-jump

two unknown

as shown in Fig

ity.

ding the spray

the calculation

tion conditions

all cases. The

al recirculation

mixer, however

tion and water

may promote

cases 2-5), the

) demonstrates

on these results

the potential to

1

l a

)

)

p

n

g.

y

n

s

e

n

r,

r

e

e

s

s,

o

32 Int. J. Nav. Archit. Ocean Eng. (2014) 6:27~38

Fig. 4 Contours of (a) velocity and (b) water concentration for different cases with a calculation time 1.5s.

Effect of mixer geometry on turbulent flow characteristics

Turbulent flow occurs when instabilities in a flow are not sufficiently damped by viscous action and the fluid velocity at

each point in the flow exhibits random fluctuations (Turns, 2000). Turbulence can be depicted as fluctuations in a fluid flow.

When working with chemicals as in an SCR reactor, typically a high level of flow fluctuations is preferable for the mixing of

UWS with exhaust gases. It is common to define the relative turbulent intensity for the velocity as follows:

uTI

U

(9)

where u is the root-mean-square (RMS) of the turbulent velocity fluctuations (U U ) at a particular location over a specified

period of time, and U is the average of the velocity for the instantaneous value (U) at the same location over the time period.

For the same theory, the standard deviation of the temporal variation of Reynolds averaged velocity ( ) and its relative

intensity ( /RI U ) are adopted. In this RANS simulation, U U is the temporal variation of Reynolds averaged velocity,

not the turbulent velocity fluctuations because U represents the Reynolds averaged velocity.

Fig. 5 shows for 0.3s for different measuring positions and mixer geometries. For case 1 (no mixer), there were few

changes in velocity at positions 1, 2, and 3. However, significantly increased near the SCR filter because a large recircula-

tion zone formed in the diffuser region. When the flow enters the porous zone, it aligns with the channel direction and the

higher pressure is located around the catalyst entrance and the center line (Chen et al., 2004). The results of all cases at positions

4 and 5 exhibit a similar tendency. At position 5, for all cases is relatively lower than that at positions 2, 3, and 4. Case 4

has the highest after the mixer owing to a large CRZ. This behavior can be explained as a result of the vorticity magnitude

generated by the induced flow direction of the mixers. Vorticity is a measure of the rotation of a fluid element as it moves in a

field, and is defined as the curl of the velocity vector:

V (10)

Int. J. Nav. Ar

Fig.

Fig. 6 sho

case 1, the ot

concentrated

case 5 (line-ty

small-scale v

type mixers, t

of the vorticit

cate that the

rchit. Ocean E

5 History of t

Fig. 6 Contou5

ows the contou

ther cases exhi

at the center r

ype mixer), th

vortex may be

the vorticity m

ty as shown in

size and length

Eng. (2014) 6:2

the standard d

urs of differen00 1/s and (b)

urs of the vortic

ibit a high vort

region for the

he vorticity ma

generated dire

magnitude is lo

n Fig. 6 increas

h of the CRZ

27~38

deviation (σ) u

nt cases of (a) ) pressure, bot

city magnitude

ticity magnitud

case 1, while

agnitude was r

ectly behind th

nger with strea

ses because the

are controlled

up to 0.3s for d

vorticity magth obtained w

e and the iso-su

de regardless o

the line-type a

relatively high

he mixer, and

am-wise axis t

e CRZ gradual

d by the mixer

different meas

gnitude and thith a calculati

urface of the v

of the mixer ty

and swirl-type

by the turbule

vanishes rapid

than that for th

lly increases w

r shape. The sw

suring points a

he iso-surface on time of 1.5

orticity magnit

ype. This is be

models disper

ent flow imme

dly after passin

he line-type mi

with the vane an

wirl-type mixe

and different c

of vorticity at

5s.

itude for all cas

ecause the intro

rse the flow to

ediately behind

ng through it.

ixer. In additio

ngle. The resu

er creates both

33

cases.

t

ses. Except for

oduced flow is

o the wall. For

d the mixer. A

For the swirl-

on, the volume

ults above indi-

h turbulent and

3

r

s

r

A

-

e

-

d

34

swirling flow

slip. The reac

The NO and

through the S

Fig. 7 pre

mixer cases,

through the m

The maximum

case 3, 4.67%

ving mixing p

highest RI for

from measuri

likelihood of

ws. Therefore, i

ction for NOx

the NH3 do n

SCR reactor un

Fig

esents relative

there are relat

mixers. After th

m RI values we

% at position 2

performance im

r all measuring

ing positions 2

system failure,

it is important

reduction in S

not react at low

n-reacted.

g. 7 Distributioa

intensity (RI)

tively small ch

his point, RI gr

ere as follows:

for case 4, and

mmediately beh

g positions, the

2 to 3 as shown

, case 3, a swir

Fig. 8 Distribdif

to select the ap

SCR catalysts r

wer temperatur

ons of relativeand cases usin

distributions a

hanges in the R

radually decrea

1.54% at posi

d 2.99% at pos

hind the mixer

levels of the m

n in Fig. 8. Fr

l-type mixer w

utions of meafferent cases u

ppropriate mix

requires a suff

res and insuffi

e intensity (RI)ng a calculatio

at 1.5s for dif

RI at position

ases, and exhib

ition 1 for case

sition 2 for cas

r when the van

mean RI for cas

rom an operati

with a 45º vane

an RI with respusing a calcula

Int. J

xer in order to

fficient reaction

icient flow mix

I) for different on time of 1.5s

fferent measuri

1. RI substan

bits uniform di

e 1, 1.96% at po

se 5. Incorpora

ne angle is grea

se 3 are consta

ional point of v

angle, is more

pect to measuation time of 1

J. Nav. Archit.

maximize flow

n time within a

xing. NH3 slip

measuring pos.

ing positions a

ntially increase

istributions as

osition 5 for ca

ating the mixer

ater than 45º. A

antly maintaine

view with resp

favorable than

ring points for.5s.

Ocean Eng. (2

w mixing and m

a certain temp

p is a means o

oints

and mixer geo

es at position 2

it approaches t

ase 2, 2.75% at

r is most effect

Although case 4

ed along the str

pect to the dur

n other cases.

or

2014) 6:27~38

minimize NH3

perature range.

of NH3 passing

ometries. In all

2 after passing

the SCR filter.

t position 2 for

tive for impro-

4 possesses the

ream-wise axis

rability and the

8

3

.

g

l

g

.

r

-

e

s

e

Int. J. Nav. Ar

Relationship

A uniform

formance for

of the flow di

In this study,

along the pipe

where, cUI i

concentration

Fig. 9 sho

cases 1 to 5. T

with mixers im

mately 5% in

were 98.5% f

different posit

case 3 > case

case 4 > case

cUI increases

better mixing

region of the

behind the lin

terms of CRZ

important, an

formance in p

rchit. Ocean E

between pres

m flow and U

de-NOx and a

istribution deg

, a similar defi

e:

is the uniform

n of water, and

ows the cUI w

The effects of t

mprove the U

n position 5. Fo

for case 4, 96%

tion are as foll

2 > case 1 beh

3 > case 2 > c

s with increase

performance t

diffuser. This

ne-type mixer t

Z is generated i

nd the swirl-typ

practical SCR a

Eng. (2014) 6:2

ssure drop and

UWS distributi

a minimum NH

gree for after-tr

finition is adop

mity index for t

n is the numbe

with respect to

the mixer on th

cUI by approxi

or all cases, th

% for case 3, 9

lows: case 3 >

hind the mixer

case 5 > case 1

e in the vane a

than the line-ty

superior perfo

that vanishes r

in a long region

pe mixer is bet

applications.

Fig. 9 Histor

27~38

d uniform flow

ion across the

H3 slip in the S

reatment applic

pted to evaluat

11

2cUIn

the water conc

er of cells. Gen

o the calculatio

he cUI are quit

imately 20% in

he cUI increas

94% for case 2

case 5 > case

r at the position

1 in the right fr

angle of the sw

ype mixer, even

ormance is due

rapidly in a sho

n. Therefore, o

tter than the lin

ry of uniformi

for different m

w

front of the c

SCR system. T

ications (Welte

te the distribu

1

ni

i

C C

n C

centration, iC

nerally, higher

on time (from

te strong, regar

n positions 2 a

sed along the

2, 93.6% for ca

1 > case 4 > ca

n 2; case 4 > ca

ront of the cata

wirl-type mixe

n though the li

ue to a small-sc

ort region. Con

obtaining a cert

ne-type mixer

ity index ( cUI

measuring poi

catalyst filter

The flow unifo

ens et al., 1993

ution degree of

2C

is the local c

cUI indicates b

0.3 to 1.5s) fo

rdless of the ty

and 3, approxim

stream-wise di

ase 5, and 90%

ase 2 before th

ase 3 > case 5

alyst filter at th

er, and the case

ine-type mixer

cale vortex gen

nversely, for th

tain distance to

with respect to

c ) for H2O fro

ints and cases

are necessary

rmity index is

3; Bressler et a

f water concen

concentration

better fluid mix

or the stream-w

ype of mixer. C

mately 30% in

irection. The m

% for case 1. Th

he mixer at the

> case 2 > cas

he position 5. T

es for the swir

outperforms it

nerated by the

he swirl-type m

o mix of the UW

o uniform flow

m 0.3 to 1.5s

.

to obtain a m

s a commonly

al., 1996; Girar

ntration at a ce

of water, C

xing.

wise positions

Compared to ca

n the position 4

maximum valu

The sequences f

position 1; cas

se 1 at position

These results in

rl-type mixer g

t behind the m

e up and down

mixer, a large-s

WS with the ex

w and the high

35

maximum per-

used indicator

rd et al., 2006)

ertain location

(11)

is the average

1 to 5 and for

ase 1, the cases

4, and approxi-

ues of the cUI

for the cUI at

se 4 > case 5 >

ns 3 and 4; and

ndicate that the

generally show

mixer and in the

n induced flow

scale vortex in

xhaust gases is

her mixing per-

5

-

r

).

n

)

e

r

s

-

t

>

d

e

w

e

w

n

s

-

36 Int. J. Nav. Archit. Ocean Eng. (2014) 6:27~38

Mixer development generally focuses on the high efficiency of NOx reduction because of its direct impact on the design

target; however, it is difficult to determine the total performance of mixing devices based on only the cUI . A more thorough

understanding of the flow pattern characteristics and pressure drop is helpful in designing an SCR system with optimal

performance for both NOx reduction and system durability. Fig. 10 depicts the relationship between the cUI and pressure drop

for different cases. As expected, the case 1 has the lowest pressure loss and cUI , which are 647 Pa and 90%, respectively. The

presence of any type of mixer resulted in an improved flow mixing, but a penalty of additional pressure loss. Case 4 had the best

mixing performance although the pressure drop was the worst. There is a tradeoff relationship between the cUI and the pre-

ssure drop with increasing vane angle for swirl-type mixers. Case 5 has a higher cUI and a pressure drop than case 1. However,

the cUI is lower and pressure drop is higher than those for the swirl-type mixers (cases 2-4) at the position 5, as shown in Fig. 9.

Furthermore, in a comparison of case 3 and 5, which contain the same angle of 45, case 3 shows higher cUI and a lower

pressure drop than case 5, as shown in Fig. 10. Therefore, it is concluded that the swirl-type mixer is more effective than the

line-type mixer with respect to the enhancement of cUI and RI. When selecting a static mixer in SCR applications, it is

necessary to consider the mixing and the uniform distribution of the UWS in front of the SCR reactor as well as the pressure

drop, which is not desirable for the optimization of engine power throughout the system. Finally, it can be concluded that the

swirl-type mixer with a vane angle of 45 is more suitable model in this study based on the results of mean RI, cUI and pressure

drop. Further research focused on the effect of the vane size becoming larger or smaller may be needed under line- and swirl-

type mixers. The effectiveness of swirl-type mixers is carefully guessed to be initiated from the larger-scale swirl than those of

line-type mixers. It is because the line-type mixer is able to generate the vane-scale swirls whereas the duct-scale swirl is

produced by the swirl mixer. Nevertheless, this study may provide useful information for selecting a static mixer in SCR

applications.

Fig. 10 Relationship between uniformity index and pressure drop for

different cases with a calculation time of 1.5s.

CONCLUSIONS

3-D numerical simulations were performed to investigate the effects of mixer geometry on the mixing performance and the

pressure drop. Flow mixing and uniformity can be greatly improved by using a static mixer in the SCR system. Turbulent and

swirling flows can also achieve a great improvement for flow mixing with respect to flow recirculation phenomena through a

longer distance. In this study, information regarding the selection of proper static mixers was provided based on the correlation

between the uniformity index and the pressure drop. The results show that the mixer for SCR applications can be effectively

optimized by using a well-designed mixing device. The main results are summarized as follows:

Int. J. Nav. Archit. Ocean Eng. (2014) 6:27~38 37

1) In comparison to the case without a mixer, the cases with a mixer improve the uniformity index by approximately 20%

directly behind the mixer, approximately 30% in the diffuser, and approximately 5% immediately in front of the mixer.

2) In the swirl-type mixer, the CRZ is generated directly behind the mixer, and increases with the vane angles of the mixer.

Therefore, it is expected that the mixing region is longer with stream-wise axis because the swirl-type mixer creates turbulent

and swirling flows.

3) The swirl-type mixer is more effective than the line-type mixer with respect to the enhancement of mixing performance, even

though there is a tradeoff relationship between the uniformity index and the pressure drop. Therefore, the swirl-type mixer

with a vane angle of 45º is the most suitable model in this study based on the results of both parameters.

ACKNOWLEDGEMENTS

This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government

(MEST) through GCRC-SOP and this work was supported by the Human Resources Development program (No. 20124010-

203230-11-1-000) of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) grant funded by the Korea

government Ministry of Trade, Industry and Energy.

REFERENCES

Battoei, M., Doroudian, M. and Lacin, F., 2006. Optimization of exhaust gas distribution on the catalytic converter inlet-

cone diffuser using advanced shape deformation technology, SAE Technical Paper, 2006-01-1439, Pennsylvania: 4

SAE International.

Birkhold, F., Meingast, U., Wassermann, P. and Deutschmann, O., 2007. Modeling and simulation of the injection of urea-

water-solution for automotive SCR DeNOx-systems. Applied Catalysis B : Environmental, 70, pp.119-127.

Bressler, H., Rammoser, D., Neumaier, H. and Terres, F., 1996. Experimental and predictive investigation of a close

coupled catalytic converter with pulsating flow, SAE Technical Paper, 960564, Pennsylvania: 4 SAE International.

Chen, M. and Williams, S., 2005. Modelling and optimization of SCR-exhaust aftertreatment systems. SAE Technical Paper,

2005-01-0969, Pennsylvania: 4 SAE International.

Chen, M., Aleixo, J., Williams, S., Leprince, T. and Yong, Y., 2004. CFD modeling of 3-way catalytic converters with de-

tailed catalytic surface reaction mechanism. SAE Technical Paper, 2004-01-0148, Pennsylvania: 4 SAE International.

DieselNet, 2008. Emission Standards, IMO Marine Engine Regulations. [online] Available at: <http://www.dieselnet.com/

standards/inter/imo.php > [Accessed March 2013].

Fluent, 2007. Fluent 6.3 User’s Guide. Lebanon: ANSYS Inc.

Girard, J. W., Lacin, F., Hass, C.J. and Hodonsky, J., 2006. Flow uniformity optimization for diesel aftertreatment systems,

SAE Technical Paper, 2006-01-1092, Pennsylvania: 4 SAE International.

Jeong, S.J., Lee, S.J., Kim, W.S. and Lee, C.B., 2005. Simulation on the optimization shape and location of urea injecttion

for urea-SCR system of heavy-duty diesel engine to prevent NH3 slip, SAE Technical Paper, 2005-01-3886, Pennsyl-

vania: 4 SAE International.

Larmi, M. and Tiainen, J., 2003. Diesel spray simulation and KH-RT wave model, SAE Technical Paper, 2003-01-3231,

Pennsylvania: 4 SAE International.

Munnannur, A. and Liu, Z. G., 2010. Development and validation of a predictive model for DEF injection and urea decom-

position in model SCR deNOx systems, SAE Technical Paper, 2010-01-0889, Pennsylvania: 4 SAE International.

Nguyen, T.D.B., Lim, Y.I., Eom, W.H., Kim, S.J. and Yoo, K.S., 2010. Experimental and CFD simulation of hybrid

SNCR-SCR using urea solution in a pilot-scale reactor. Computers and Chemical Engineering, 34(10), pp.1580-1589.

NMRI, 2011. National Maritime Research Institute 2011. [online] Available at: <http://www.nmri.go.jp/main/panfuretto/

content/pamphlet2011_e.pdf > [Accessed November 2013].

Regner, M., Östergren, K. and Trägårdh, C., 2006. Effect of geometry and flow rate on secondary flow and the mixing pro-

cess in static mixers-A numerical study. Chemical Engineering Science, 61(18), pp.6133-6141.

38 Int. J. Nav. Archit. Ocean Eng. (2014) 6:27~38

Thakur, R.K., Vial, Ch., Nigam, K.D.P., Nauman, E.B. and Djelveh, G., 2003. Static mixers in the process industries-A

review. Chemical Engineering Research and Design, 81(7), pp.787-826.

Turns, S.R., 2000. An Introduction to combustion: concept and applications. 2nd ed. Boston: McGraw-Hill.

Weltens, H., Bressler, H., Terres, F., Neumaier, H. and Rammoser, D., 1993. Optimization of catalytic converter gas flow

distributions by CFD prediction, SAE Technical Paper, 930780, Pennsylvania: 4 SAE International.

Zhang, X. and Romzek, M., 2007. 3-D numerical study of flow mixing in front of SCR for different injection systems, SAE

Technical Paper, 2007-01-1578, Pennsylvania: 4 SAE International.

Zhang X., Romzek, M. and Morgan, C., 2006. 3-D numerical study of mixing characteristics of NH3 in front of SCR, SAE

Technical Paper, 2006-01-3444, Pennsylvania: 4 SAE International.

Zheng, G., Fila, A., Kotrba A. and Floyd, R., 2010. Investigation of urea deposits in urea SCR systems for medium and

heavy duty trucks, SAE Technical Paper, 2010-01-1941, Pennsylvania: 4 SAE International.

Zheng, G., Palmer, G., Salanta G. and Kotrba, A., 2009. Mixer development for urea SCR application, SAE Technical Paper,

2009-01-2879, Pennsylvania: 4 SAE International.