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Combustion of heavy fuels is one of the main sources of greenhouse gases, particulate emissions, ashes, NOx and SOx. Gasification is an advanced and environmentally friendly process that generates combustible and clean gas products such as hydrogen. Some entrained flow gasifiers operate with Heavy Fuel Oil (HFO) feedstock. In this application, HFO atomization is very important in determining the performance and efficiency of the gasifiers. The atomization characteristics of HFO (Mazut) discharging from a pressure-swirl atomizer (PSA) are studied for different pressures difference (Δp) and temperatures in the atmospheric ambient. The investigated parameters include atomizer mass flow rate (m), discharge coefficient (CD), spray cone angle (θ), breakup length (Lb), the unstable wavelength of undulations on the liquid sheet (λs), global and local SMD (sauter mean diameter) and size distribution of droplets. The characteristics of Mazut sheet breakup are deduced from the shadowgraph technique. The experiments on Mazut film breakup were compared with the predictions obtained from the liquid film breakup model. Validity of the theory for predicting maximum unstable wavelength was investigated for HFO (as a highly viscous liquid). A modification on the formulation of maximum unstable wavelength was presented for HFO. SMD decreases by getting far from the atomizer. The measurement for SMD and θ were compared with the available correlations. The comparisons of the available correlations with the measurements of SMD and θ show a good agreement for Ballester and Varde correlations, respectively. The results show that the experimental sizing data could be presented by Rosin-Rammler distributions very well at different pressure difference and temperatures.
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Article
Microscopic and macroscopic atomization characteristics of a
pressure-swirl atomizer, injecting a viscous fuel oil
SeyedMohammadAliNaja, Pouria Mikaniki, Hojat Ghassemi
School of Mechanical Engineering, Iran University of Science and Technology (IUST), P.O.B. 16765-163, Tehran, Iran
abstractarticle info
Article history:
Received 29 October 2018
Received in revised form 30 March 2019
Accepted 4 April 2019
Available online 18 April 2019
Combustion of heavy fuels is one of the main sources of greenhouse gases, particulate emissions, ashes, NO
x
and
SO
x
.Gasication is an advanced and environmentally friendly process that generates combustible and clean gas
products such as hydrogen. Some entrained ow gasiers operate with Heavy Fuel Oil (HFO) feedstock. In this
application, HFO atomization is very important in determining the performance and efciency of the gasiers.
The atomization characteristics of HFO (Mazut) discharging from a pressure-swirl atomizer (PSA) are studied
for different pressures difference (Δp) and temperatures in the atmospheric ambient. The investigated parame-
ters include atomizer massow rate ( _
m), discharge coefcient (C
D
), spray coneangle (θ), breakup length (L
b
), the
unstable wavelength of undulations on the liquid sheet (λ
s
), global and local SMD (sauter mean diameter) and
size distribution of droplets. Thecharacteristicsof Mazut sheet breakup are deducedfrom the shadowgraph tech-
nique. The experiments on Mazut lm breakup were compared with the predictions obtained from the liquid
lm breakup model. Validity of the theory for predicting maximum unstable wavelength was investigated for
HFO (as a highly viscous liquid). A modication on the formulation of maximum unstable wavelength was pre-
sented forHFO. SMD decreases bygetting far from the atomizer. Themeasurement for SMDand θwere compared
with the available correlations.The comparisonsof the available correlations with the measurements ofSMD and
θshow a good agreement forBallester and Varde correlations, respectively. Theresults show that the experimen-
tal sizing data could be presented by Rosin-Rammler distributions very well at different pressure difference and
temperatures.
© 2019 The Chemical Industry and Engineering Society of China, and Chemical Industry Press Co., Ltd.
All rights reserved.
Keywords:
Gasier
Heavy fuel oil
Atomization
Pressure-swirl atomizer
Mazut
Size distribution
Wavelength
Viscosity
1. Introduction
One of the essential sources of energy used in modern civilization is
fossil fuels, includes HFOs. Even with the renery's progress, these fuels
are still being produced and play an important role in energy production
in the world [1]. This black fuel is very thick and viscous which at cooler
temperatures becomes semi-solid is often known as bunker fuel oil [2].
HFOs have been used as the replacement of good quality oils for more
energy reserves and chip resources [3].
Combustion of HFO causes environmental problems[4] and also due
to the physical characteristics of HFOs, cannot be used in combined cy-
cles of high-efciency power plants. HFO gasication process has been
introduced to reduce emissions and also to use in thepowergeneration
cycle [5]. HFO in this process converted to the clean gases. The products
of gasication mainly consist of hydrogen and carbon monoxide, called
syngaswhich can be used as the raw material for the synthesis of liq-
uid fuels or chemicals. The gasication can also becombined with a fuel
cell or power plant system in the integrated gasication combined cycle
[6].
Fuel atomization is vital to process in determining the performance
of combustors or gasiers, especially when HFO is using because of dif-
cult atomizing. Inappropriate performance of atomizer in a gasier can
lead to the production of pollutants. Nitrogen pollutants produced in an
entrained ow gasier was studied by [7]. They found that most of the
nitrogen pollutants formed during the devolatilization, which is pre-
cisely about injection performance. Also, they showed the impact of
air to fuel ratios on nitrogen pollutant production. Gasiers can operate
only in some specic air to fuel ratios [8]. Use twin-uid (air-assist or
air-blast) atomizer for heavy fuels is common [9], but these atomizers
disturb the air to fuel ratio, a parameter which should be intensely con-
trolled for the gasication process. Gasiers can operate using a PSA,
which do not change the air-to-fuel ratio [10]. For this reason,it is inter-
esting to study the injection of heavy fuels using PSA [11].
Many experimental measurements and numerical simulations have
been done for low viscosity liquids in PSA, but few studies have been
carried out investigating spray of HFO as a high viscosity liquid. As a
result, the review of HFO spray is necessary for PSA especially in the
application of gasiers.
Chinese Journal of Chemical Engineering 28 (2020) 922
Corresponding author.
E-mail address: h_ghassemi@iust.ac.ir (H. Ghassemi).
https://doi.org/10.1016/j.cjche.2019.04.006
1004-9541/© 2019 The Chemical Industry and Engineering Society of China, and Chemical Industry Press Co., Ltd. All rights reserved.
Contents lists available at ScienceDirect
Chinese Journal of Chemical Engineering
journal homepage: www.elsevier.com/locate/CJChE
Proper atomization in entrained ow gasier ensures faster evapo-
ration of fuel and better mixing between the fuel and the air, thereby
resulting in higher efciency. PSA is widely used in combustors as a
fuel atomizer. The atomizer discharges the liquid sheet lm in the gas-
ier. The quality of spray in PSAs could be evaluated by investigation
the characteristics such as atomizer mass ow rate _
m, discharge coef-
cient C
D
, breakup length L
b
, maximum unstable wavelength λ
s
, spray
angle θ, and SMD and droplet distribution.
Over the years, many experimental and numerical studies have been
devoted to analyzing the performance of PSAs with liquid biofuels, but
there is a lack in the literature for a spray of HFOs. Therefore, an exper-
imental study was conducted on an HFO spray, Mazut 280.
In this study, the performance characteristics of the PSA for HFO for
use in gasier have been obtained. HFO viscosity is highly temperature
dependent; for this reason, the effects of temperature and Δpon spray
behavior are investigated. In this paper, measurement characteristics
included _
m,C
D
,L
b
,λ
s
,θ, global SMD, SMD at different axial location,
and droplet distribution. Some researchers started the research in this
area.
Liu et al. [12] investigated the air core formed in PSA experimentally
and theoretically. Several types of atomizers with different geometries
and different liquid viscosities were studied to obtain the effects on
the air core size. Rashad et al. [13] investigated the impact of PSA geo-
metric ratios on θand SMD by the injection of water. They have reported
optimal ratios to achieve the best performance (lower SMD) using PSA.
Ferreira et al. [14] determined the main parameters of twin-uid
nozzles with an internal mixing chamber for HFO. They studied the
effect of interaction air and liquid ows at the interior chamber on the
atomization. They examined different air channel diameters and liquid
ports for different air and liquid mass ow rate. They have been
shown under certain conditions the uid discharged to the inner cham-
ber is choked. The sonic condition was achieved for different air and
liquid mass ow rates as a function of the air central channel diameter.
The best results of atomizing uid ow rates have been obtained in
choked conditions. The pressure range was from 0 to 0.7 MPa. They
showed kinematic viscosity reached values 1.546 × 10
3
m
2
·s
1
at 50 °C
and 0.255 × 10
3
m
2
·s
1
at 80 °C. They recommended that for generating
ane spray, the viscosity is to be around 4.5 × 10
5
m
2
·s
1
,which
requires heating the HFO to 130 °C.
Liu et al. [12] investigated the air core formed in PSA experimentally
and theoretically. Several types of atomizers with different geometries
and different liquid viscosities were studied to obtain the effects on
the air core size. They found that a decrease in the liquid viscosity and
a decrease in the swirl chamber length cause the air core size to be in-
creased. Also, they found that an increase in the liquid viscosity would
lead to a decrease in critical swirl chamber length (when the swirl
chamber length is greater than a critical length, the air core will disap-
pear). They presented new correlations with a better agreement with
the experimental data at a broader range of liquid viscosity. They used
kerosene RP-3 for their experiments.
Suzuki et al. [15] investigated the spray of PSA (Delavan oil burner
nozzle 60°A-0.85) for viscous liquids in high-pressure nitrogen and
room temperature. They used water, diesel fuel, palm methyl ester,
and silicone-oil for the atomization. The volume ow rate was 50 to
140 cm
3
·min
1
, and the ambient gas pressure difference was 0.1 to
1.0 MPa. They used a laser diffraction method for measuring SMD and
the PIV technique for the measuring spray ow eld. Properties of liquids
tests were ranging as; density was 825.2 to 995.65 kg·m
3
,viscositywas
0.8to10mm
2
·s
1
, surface tension was 20.1 to 72.28 mN·m
1
.
Payri et al. [16] studied the effect of pressure and temperature on the
thermodynamic properties of diesel and biodiesel fuels. The tempera-
tures range was 25 °C to 68 °C and pressure difference were 15 to
180 MPa. They showed that biofuel injection pressure affects sound
speed, and could change the dynamic of some injection elements. Also,
they showed density values increased with pressure and decreased
with temperature. The fuel density was 812 to 825 kg·m
3
,theviscosity
was 2.06 to 2.34 mm
2
·s
1
, and the surface tension was 0.0205 to
0.022 N·m
1
.
Zhang et al. [17] measured the lm thickness of a PSA injecting water
with the image-processing method. They calculate the liquid lm thick-
ness at different sections of downstream ow. The results showed that
the lm thickness decreases with increasing distance. Ding et al. [18] in-
vestigated the instability and droplet size distribution of liquidliquid
coaxial PSA. They analyzed the effect of inner and outer Δpon the
spray characteristics of atomization. They have investigated the inner
and outer injection pressure on the surface wave characteristics by
using a laser reection setup. They were shown at the same Δp,the
temporal instability of a liquid sheet doesn't change spatially and
wave frequency increases as the Δpincreases. The results showed the
inner spray is more unstable and more accessible to break up rather
than the outer spray and the coaxial spray.
Kim et al. [19] studied the effect of geometric parameters on the lm
thickness and air core formation in a PSA injecting water. They observed
a good agreement between the analytical method and experimental
data of liquid lm. Also, they observed the proper ratio of L/Din the
swirl chamber. Δpwas 0.2 to 0.8 MPa. Liu et al. [20] investigated the
behavior of the kerosene droplets produced by a PSA. They used by
Fuel-PLIF and LIF/Mie laser sheet-imaging methods for the atomization
process. They analyzed the spray pattern, droplet size spatial distribu-
tion, mean droplet size, and distribution index with different Δp.They
measured mean droplet size at various locations (2070 mm) down-
stream the atomizer. Water was used as the simulant of LOX and the
fuel was kerosene. The pressure difference for each atomizer varied
from 0.1 MPa to 0.6 MPa. Mlkvik et al. [21] studied spraying viscous
liquids by using four types of internal-mixing twin-uid atomizers
with different Δpand various gas-to-liquid ratios. Different atomizers
were studied in the view of the ow eld, stability, and droplet sizing.
The injected liquid density was 1185 to 1242 kg·m
3
, the viscosity
was 60 to 308 kg·m
1
·s
1
, and the surface tension was 74.25 to
75.73 mN·m
1
. Broniarz-Press et al. [22] analyzed the effect of orice
shape (conical and plain) and Δpon the water atomization process for
PSA.
As HFO atomizing is very difcult and a challenging topic [14,23], in
this study, an atomizer was tested in the application of HFO entrained
ow gasier and studied to obtain reliable data for further researches.
The entrained ow gasiers require a smaller fuel droplet size than
the uidized bed gasier. Therefore, in the present study, the essential
characteristicsof a PSA were investigated. The main features of an atom-
izer, which are required in the design of a gasier chamber, C
D
,L
b
,θand
the average diameter of the droplets. The C
D
is necessary for the deter-
mination of an atomizer _
m,theθplays an important role in dening the
chamber cross-section area, the L
b
and mean diameter of droplets are
very effective in designing the length of the chamber and the lifetime
of the droplet presence in the chamber to evaporate. Therefore, in this
study, these specications have been empirically investigated in order
to evaluate an atomizer in the application of an entrained ow gasier.
Also, the present study was focused on comparing the effect of Δpand
temperature (difference of viscosity) of HFO, Mazut with PSA. Although
PSAs are widely investigated, the applications using HFOs are discussed
very limitedly. As we know the behavior are very different for such a
fuel, therefore more detailed measurements and investigations are
needed.
2. Experimental
The atomizer was tested and investigated on a cold test bench at at-
mospheric condition injecting HFO (Mazut) in various Δpand tempera-
tures. The test fuel injector is a hollow-cone PSA with 0.3 mm orice
diameter (Steinen, oil burner nozzle, standard H, 1.00 GPH, 60° [24]).
Physical properties for Mazut were determined as a function of temper-
ature and are presented in Table 1. Density and viscosity were measured
10 S.M.A. Najaet al. / Chinese Journal of Chemical Engineering 28 (2020) 922
according to ASTM D 4052 and ASTM D 7042 standards,and surface ten-
sion was predicted by Riaziapproach [25] for Mazutwhich is mentioned
in [26]. Warm Mazut was delivered by a gear pump from a 4-litter tank
through a pipeline and was injected vertically into a collecting vessel
and a pump back into the tank can be seen in Fig. 1.A PCO 1200hs digital
high-speed camera with resolution 1280 × 1024 pixels with shadow-
graph technique was used to take pictures of the liquid lms, exposure
time was 5 μs and the frame rate was 1357 fps (for droplets velocimetry).
A macro lens (AF Zoom Nikon 100 mm f/2.8D) was used in conjunction
with the camera. The measurement technique was similar to [27]. The
minimum measurable droplet diameter range is about 20 μm, because
of the camera resolution limit. θ,L
b
,λ
s
, SMD, and droplet size distribution
were obtained by image processing.
The liquid temperature probe was placed about 5 cm before the
injector entrance and the insulation was performed correctly. All mea-
surements have been conducted after ensuring the steady state condi-
tion. Ambient pressure was about 87 kPa and the temperature was in
the range of 2030 °C. The probes for ambient pressure and temperature
were at almost 5 m distance far enough from the setup to minimize air
pressure and temperature change because of the injection.
3. Results and Discussion
For the measurements, the heavy oil temperatures were 100, 110
and 120 °C. The Δpselected for injection were 0.7, 0.9, 1, and 1.2 MPa.
In the case of liquid temperature change, two limitations exist, liquid
viscosity and boiling. The liquid viscosity is very high at low tempera-
tures. By lowering Mazut temperature below 100 °C, high viscosity
leads to failure in appropriate atomization. Also, it was generally ob-
served that heating Mazut to the temperatures higher than 130 °C
leads to the boiling or fast evaporation of some species that results to
asignicant difference in the performance of the injector. Therefore, the
temperatures of 100, 110 and 120 °C were selected for the measurement.
In the case of the injection pressure change, as the design pressure
for the injector is 1 MPa. Therefore a range around this value was se-
lected for the experiments. Increasing injection pressures to values
higher than 1.2 MPa leads to a weak change in the injector performance
and the injection pressures lower than 0.7 MPa does not end to a ne
spray. So the range 0.71.2 MPa was selected for the investigation.
The increments on liquid temperature and injection pressure were
selected for reporting data in a way that the differences in the spray
characteristics could be detected concisely and completely.
3.1. Macroscopic properties
Fig. 2 shows the spray patterns of the PSA for a series of increasing
temperature with constant Δp= 1.2 MPa. At very low temperature,
the liquid emerges as a round jet. High viscosity causes the uid in the
rotating chamber to not swirl well at a low temperature. At T=10C
with Δp= 1.2 MPa, the jet in Fig. 2a looks like a twisting ribbon
appear from the atomizer exit orice. The jet is created at the bottom
of the stream with three branches and due to instabilities on the
edges of the jet and ngerscould be observed. Fingers appear because
of the competition between the centrifugal force and the viscous force.
Eventually, the ngers produce large droplets.By an increase in temper-
ature, Fig. 2b, at T= 110 °C, the ribbon becomes wider and forms three
edges and emerges from the hole as apyramid. The twisted ribbon con-
verted to a pyramid with branches exit near the orice. Horizontal
waves cause the lm of the pyramid to break down. With the break-
down of the pyramid lm, due to the horizontal waves, there are
horizontal ligaments that later change to droplets. By increasing tem-
perature, Fig. 2c, at T= 120 °C, the injected lm reshapes to a smooth
conical sheet without branches because, as the viscosity is highly
reduced at this temperature. Fig. 2c also shows perforations which are
Table 1
Physical properties of HFO (Mazut)
T/°C ρ
l
/kg·m
3
μ
l
/kg·m
1
·s
1
σ
l
/N·m
1
100 925.18 0.0100 0.0302
110 919.48 0.0078 0.0295
120 913.11 0.0063 0.0287
Fig. 1. Schematic of the PSA test rig.
11S.M.A. Najaet al. / Chinese Journal of Chemical Engineering 28 (2020) 922
created in the liquid lm. They grow with increasing distance from the
atomizer. Perforations are nally broken and created vertical ligaments
and eventually form small droplets.
Fig. 3 shows images of a hollow conical liquid sheet of Mazut spray
discharging from the PSA at different ow conditions with constant
temperature. In a PSA, the breakup of the conical liquid sheet occurs
via unstable growth of waves on the surface of the liquid spray lm
are seen in the images. In the case of lower Reynolds number (Re =
ρ
l
Ud
0
/μ
l
, the ratio of inertial forces to viscous forces, dened by liquid
properties, characteristic length of the injector orice diameter and
sheet velocity at the tip of the injector), due to low Δpor high viscosity,
the liquid in the rotating chamber does not spill well. High Reynolds
number causes a scattering of the droplets and eventually gives wider
θ. Fig. 3 shows the variation stage as a function of the Weber number
for Mazut 120 °C with different Δp. The Weber number is dened as
We
l
=ρ
l
U
2
t
f
/σ
l
, the ratio of inertial forces to surface tension forces,
based on the liquid properties, characteristic length of the sheet
thickness and sheet velocity at the tip of the injector.
θ/2 (spray half cone angle) is dened as the angle between the
spray axis line and a line tangent to the spray cone at the tip of the
atomizer. θcan be obtained by measuring the angle between two
lines (tangential to spray surface at the tip of the injector) which is
depicted in Fig. 3a. The measurements have been conducted manually
by analyzing the raw images from the shadowgraph technique. Edge
of spray is found according to the sharp variation of black color inten-
sity between the inner and outer side of spray at the tip of the injec-
tor. The angle was determined at different Δpand temperature of
Mazut. It can be seen in Fig. 3 that by increasing Δp,θincreases.
The discharging Mazut lm at T= 120 °C has a smooth surface
with different We
l
. One of the most critical parameters of the liquid
lm is the breakup length L
b
. It is measured as the distance from
the atomizer exit to the location of sheet breakup along the spray
Fig. 2. Images of Mazut spray at a constantΔp= 1.2 MPa with variations of viscosity discharging from PSAapplying an exposuretime of 5 μs. (a) T= 100 °C, (b) T= 110 °C, and (c) T=
120 °C.
Fig. 3. Imagesof Mazut spray at T= 120 °C discharging fromPSA applying an exposure time of 5μswithdifferentΔp. (a) Onion stagewith We
l
= 4762, (b) Tulipstage with We
l
=6413,
and (c) Fully developed spray We
l
=7384.
12 S.M.A. Najaet al. / Chinese Journal of Chemical Engineering 28 (2020) 922
axis as illustrated in Fig. 3b. The breakup length can be measured by
knowing the pixel width and length from the calibration and measur-
ing breakup length in terms of pixels. Breakup length uncertainty was
calculated to be in the range of 0.2%1.0%.
Fig. 4 shows the images of Mazut spray at different Δpand temper-
ature. Increase in spray angle and a decrease in L
b
is evident by the
increase in Δpand increasing temperature. These images are the raw
images, which were taken using the shadowgraph technique and used
for measuring of θ,L
b
,λ
s
and SMD.
Fig. 5 shows the variation of L
b
in terms of Δp,T, and We
l
for the
liquid lms discharging from the PSA. For each test condition, more
than 100 images of spray captured to estimate the average value of L
b
.
A reduction in the viscosity outcomes in an increase in the growth
rate of the most unstable modes, eventually causing lower L
b
.The
experimentally measured value of L
b
decreases with increasing We
l
as
shown in Fig. 5. The results have followed a trend, which is shown in
Fig. 5c by a hatched zone.
Fig. 6 shows the variation of θ/2 with Δp,T,Re, and We
l
numbers of
the liquid lms discharging from the PSA. The measurements of Rizk
and Lefebvre [28] and Chen et al. [29] show a clear increase in the
angle with Δp. No obvious effect on spray angle was observed for injec-
tion pressure change by Dodge and Biaglow [30] and Decroso [31]. This
variety of trends for Δpeffects on θindicates that the effect of Δpis not
always the same, but might depend on some other parameters, such as
the atomizer geometry or the liquid. An increase of θwith an increase in
Δpis apparent in Fig. 6a, although the magnitude of this increment is
not the same for all cases. A rise in the HFO temperature results in a
considerable increase in θ, Fig. 6b. This trend is in agreement with the
previous study by Ballester and Dopazo [32].
The half cone angle as a function of Reynolds number, Re, and Weber
number, We
l
are shown in Fig. 6c and d, respectively. The results show
that by increasing Reynolds number and Weber number, θincreases,
as the inuence of temperature on viscosity for HFO is remarkable.
The difference between Fig. 6c and d can be valuable by notice to the
Fig. 4. Mazut spray images at different injection pressure and temperature.
13S.M.A. Najaet al. / Chinese Journal of Chemical Engineering 28 (2020) 922
point that temperature dependencyof Re comes from μ
l
/ρ
l
, while for We
l
it comes from σ
l
/ρ
l
, the former variation is much severed (from 6.9
×10
6
to 1.1 × 10
5
while later ranges from 3.14 to 3.26 × 10
5
).
Therefore, because of the strong temperature dependency of μ
l
(Re)in
comparison to σ
l
(We) for HFO, Re can be a better choice among dimen-
sionless numbers to present a trend for θvariations in different temper-
atures (the trend is shown in Fig. 6c by a hatched zone).
The discharge behavior of the Mazut for the PSA is determined from
the measurements of _
mwith Δpand temperature (viscosity) and is
shown in Fig. 7. Mass ow rate and injection pressure difference were
measured directly with the maximum relative uncertainty of 0.9%1%
and 0.8%1.4% respectively.
As it was mentioned previously, Mazut viscosity decreases with an in-
crease in the liquid temperature. Viscous forces make uid movements
difcult. Therefore an increase in mass ow rate is expected by increasing
the liquid temperature, which is also reported by [11]. This is also ap-
proved by comparing measurements when the liquid temperature in-
creased from T=10CtoT=11C.However,thereisadecreasein
the mass ow rate by increasing the liquid temperature from T=11C
to T= 120 °C. This phenomenon can occur because at around 120 °C,
some volatile petroleum components (Mazut is a multi-component
fuel) begin to boil and separate from the liquid. The presence of vapor
gases in the stream can interfere with the uid ow and therefore
reduce the amount of discharge.
Fig. 5. Effect of the pressure difference, temperatu re and We
l
number on breakup length.
Fig. 6. Effects of Δp,T,Re, and We
l
on spray cone angle.
14 S.M.A. Najaet al. / Chinese Journal of Chemical Engineering 28 (2020) 922
The discharge coefcient of the atomizer, C
D
, is expressed as Eq. (1):
CD¼
_
m
A0ffiffiffiffiffiffiffiffiffiffiffiffiffi
2ρlΔp
pð1Þ
The values of C
D
as a function of the Δp, temperature, and Re number
are shown in Fig. 8. The curves in the graph are nearly horizontal in
Fig. 8a and c is conrming the inviscid theory [33] which indicated
that Δpand Re should not inuence the C
D
.ThevaluesofC
D
is indepen-
dent of Δpand Re number.The variation of the C
D
with fuel temperature
is depictedin Fig. 8b. The variations of C
D
and θwith temperatureshould
be attributed to viscosity variations. Because viscosity changes over 30%
within the experiments temperature range, but density and surface
tension change only less than 6%. All the curves in Fig. 8b exhibit the
maximum in C
D
which is characteristic of PSAs as the uid viscosity
decreases. At low temperatures, the liquid friction viscosity prevents
central air core from forming; for this reason, the liquid exits as a full
jet. As temperature increases, the liquid in the tangential hole or holes
of the swirl chamber causes the developed of the air core, and the liquid
emerges as an empty annular jet. The consequence is the reduction of
the effective exit area for higher temperatures. In Fig. 8b, shown C
D
follows a decreasing trend with viscosity; this behavior is also observed
in the previous study by Ballester and Dopazo [32]. The value of C
D
varies from 0.48 to 0.52 for different temperature and Δp.
The PSA forms a conical liquid sheet, the effects of the surrounding
gas and the liquid viscosity form and grow waves on the liquid sheet.
By growing the wavelength, at a wavelength (called the maximum
unstable wavelength λ
s
), the liquid sheet breaks to the ligaments and
eventually droplets produce, shown in Fig. 3b. λ
s
is another macroscopic
spray feature that was measured and discussed in this section.
From the conservation of mass and geometry of conical liquid sheet,
t
f
the liquid sheet thickness at the orice exit can be calculated by
knowing U
a
the axial velocity of the liquid sheet at the orice exit,
according to Eq. (2).
Ua¼
_
m˙
πρltfd0tf
 ð2Þ
U
a
is estimated according to the measurements of θand U,itfollows
Eq. (3):
Ua¼Ucos θ
2
 ð3Þ
Uthe liquid sheet velocity (which is along the conical surface), was
measured from the high-speed records (droplets were tracked in
sequent images) and consequently, the liquid sheet thickness can be
calculated from Eqs. (2) and (3). more details of the formulation can
be found in [34].
A theoretical relation for the estimation of t
f
in a PSA in terms of
the atomizer geometrical parameters and ow conditions is proposed
by Rizk and Lefebvre [35]. The investigation revealed that the theoreti-
cal relation could not predict t
f
accurately when the air-core is not
formed completely, which is the case at T= 100 °C and low-pressure
regimes.
The liquid sheet Weber number, We
l
and Reynolds number, Re for a
PSA can be expressed as Eqs. (4) and (5) by Sivakumar et al. [34]:
Wel¼ρlU2d0
σð4Þ
Re ¼ρlUd0
μl
ð5Þ
Fig. 7. Effect of temperature and pressure on Mazut mass ow rate.
Fig. 8. Effect of the pressure difference, temperature and Reynolds number on C
D
.
15S.M.A. Najaet al. / Chinese Journal of Chemical Engineering 28 (2020) 922
Senecal et al. [36] carried out the linear stability analysis of liquid
sheet of thickness t
f
=2hmoving with velocity Uthrough a quiescent
ambient gas and where ρ
l
is the liquid density, d
0
diameter of orice,
σis surface tension and μ
l
is liquid viscosity. The liquid sheet is charac-
terized by Senecal et al. [36] in terms of aerodynamic Weber number,
We
g
expressed as Eq. (6):
Weg¼ρgU2h
σð6Þ
where ρ
g
is the density of the ambient gas. According to the theory of
lm breakup, the instability proliferates on the surface of the liquid
lm and λ
s
can be calculated using Eq. (7) [37]:
λs
tf
¼2π
Weg

for long wavelengthðÞ
λs
tf
¼3
2
π
Weg

for short wavelengthðÞ
ð7Þ
The relative velocity between the liquid lm and the surrounding
environment causes instability in the liquid lm. The instability created
on the surface increases with increasing distance from the atomizer
until it breaks up the liquid lm and generates ligaments. Instabilities
on the ligament cause breakup and create the droplets this process is
named primary breakup. As the distance increases, aerodynamic force
breaks up the primary droplets and generates smaller droplets, this
process is known as secondary atomization. Fig. 9a shows a hollow
cone liquid lm of PSA and primary and secondary breakup processes
[38]. The process is important because of controlling the droplets
diameter on downstream. Senecal et al. [36] modeled the liquid lm
breakup in 2D. They showed that based on the gas Weber number
(We
g
), the linear instability in liquid lms could be classied into long
wavelength and short wavelength with a critical Weber number
(We
c
) of 1.69. The long wavelength instability occurs for We bWe
c
and the short wavelength occurs for We NWe
c
[37].
To measure λ
s
experimentally, shadowgraph method was used. The
images were calibrated to dene the pixel length for each frame. There-
fore, by measuring the length of λ
s
in pixels, it can be converted to the
length of λ
s
in meters (the procedure is similar for measuring L
b
). The
wavelength was measured for different Weber numbers. Typically,
wavelengths were obtained by averaging 2535 images of a particular
condition. Theoretically predicted λ
s
[36] compared with the measure-
ments as is shown in Fig. 10. Wavelength average relative uncertainty
was in the range of 2.7%4%. The comparison reveals the fact that the
theory can also be reliable for heavy viscous liquids but with underesti-
mation. Two curves are plotted in Fig. 10 that is tted to the experimen-
tal measurements. The overall format of the formulation in Eq. (7) was
preserved for the curve t. The differencebetween theoretical equations
(Eq. (7)) and the tting for the experiments, shown in Fig. 10 is only
changing the coefcient of 2 with 2.8 for long wavelength and 3/2
with 2.2 for short wavelength.This correction is a signicant conclusion
as the waves are a representation of the instabilities and lead to the
Fig. 9. a) Liquid lm, primary and secondary breakup processes, b) Determined axial locations for SMD measurements.
Fig. 10. The comparison between the theoretically predicted most unstable wavelength
(λ
s
) and the experimentally measured one for the Mazut PSA.
16 S.M.A. Najaet al. / Chinese Journal of Chemical Engineering 28 (2020) 922
primary and secondary breakup. Therefore, it can be expected that SMD
variations should follow the SMD trends for conventional liquids.
3.2. Microscopic properties
It can be seen obviously in Fig. 3c that after breakup only the liga-
ments and droplets atthe focus zone were captured. Overlapping occurs
rarely, and this is because of thefollowing reasons: a) usinga macro lens
with the benets of limited depth of eld and focus on close objects,
b) hollow conical spray, and c) dilute spray.
Axial measurements were made throughout the spray at various
Weber and Reynolds numbers (i.e., at different Δpand temperatures).
As the viscosity decreases with temperature increase, the different
liquid temperature can be representative of the viscosity change.
Droplets diameters were measured using the shadowgraph method.
To measure the droplets diameter, by image processing, the pixel area is
determined by calibration, and the diameter size of each droplet d
i
is
determined by the number of pixels that occupied by the droplet.
SMD or D
32
can be obtained by, SMD ¼PI
i¼1d3
i=PI
i¼1d2
iwhere Iis
the total number of droplets in each image. The SMD can be dened
as the diameter of a droplet having the same volume/surface area
ratio as the entire spray. SMD relative uncertainty was calculated to be
in the range of 4%6%.
SMD was obtained for different temperatures and Δpfrom the
breakup to Z= 70 mm and summarized in Fig. 11. Also, an increase in
Weber number leads to a decrease in SMD. In overall, higher tempera-
tures (lower viscosity) and Δplead to lower SMD.
There are dozens of empirical correlations published for SMD in the
literature. Available SMD calculations on pressure-swirl injectors for
HFO atomization was compared in [11]. In the present study, four
best-predicted correlations [3942] are compared with experimental
measurements. It is depicted in Fig. 12a that Ballester correlation [41]
is the best correlation in SMD prediction for Mazut atomization
in T= 120 °C. Some best-tted available correlations on θ[28,35,43,
44] were also evaluated using HFO injection in T=12C.Itisshown
in Fig. 12b that Varde [44] correlation was almost successful in
predicting θfor HFO.
In Fig. 9b some selected axial locations are determined. SMD mea-
surements were applied to these locations. Fig. 13 shows SMD measure-
ments at different axial locations, Δp, and liquid temperatures. Results
show the nest spray atomization can be obtained around Z=
70 mm, atomization is completed at the Δp=1.2MPaandT=12C.
SMD decreases with an increase in axial location. Less viscosity (Mazut
with higher temperature) forms smaller droplet size in the spray at the
same axial location. Droplet sizes at Zlarger than 70 mm at Δp=
1.2 MPa and T= 120 °C are less concerned for HFO gasier applications
because droplets there will interact with the gasier gas ow and quickly
evaporate and change to smaller droplets. Therefore, droplet size at Z
smaller than 70 mm is of great importance. As shown in Fig. 13 at Z=
70 mm the atomizer produces droplet with SMD about 100 μmat
Δp= 1.2 MPa and T= 100 °C and SMD about 70 μmattheΔp=
1.2 MPa and T= 120 °C. Measurements show an increase in Δpfrom
0.7 to 1.2 MPa leads to the production of smaller droplets and decrees
in SMD of about 9% when T= 110 °C and decrees in SMD of 16% when
T= 120 °C. An increase in temperature from 110 °C to 120 °C produced
smaller droplets and resulted in a decrease in SMD of about 11% when
Δp= 0.7 MPa, about 6% when Δp= 9 MPa, about 3% when Δp=
1.0 MPa, and about 2% when Δp=1.2MPa.
In the process of gasication, fuel droplets evaporate and then the
reactions take place in the gas phase. As the theoretical results show,
the evaporation time depends on droplets size. As the diameter de-
creases, the evaporation time decreases, which is following the d
2
-law
[45]. In HFO gasier chamber, evaporation of large droplets generally
Fig. 11. Global SMD variations among Δp,T,We
g
,and We
l
.
17S.M.A. Najaet al. / Chinese Journal of Chemical Engineering 28 (2020) 922
takes a long time. As a result, an increase in the number of large droplets
reduces the gasier efciency. In fact, larger droplets determine the
evaporation time; therefore,it is crucial to identifyand resolve the drop-
let distribution [46]. Since the proportion of large droplets may be
different even in the case of the same SMD. Therefore, a detailed inves-
tigation of cumulative droplet volume, spray global probability density
function (PDF), and relative number count of droplets is necessary.
The histogram plots of droplet size distribution at different axial
locations (40 mm, 50 mm,60 mm and 70 mm) for different Δpand dif-
ferent temperature are shown in Figs. 14 and 15. SMD for each location
is noted in these gures. In the gures, the histograms represent the cu-
mulative volume versus the droplet diameter. At Z=40mmforΔp=
1.2 MPa and T= 120 °C, the peaks of the histogram locate cumulative
volume of droplets reaches 25% at 35 μm and 22% at 65 μm. At the Z=
60 mm axial location, the cumulative volume of smaller droplets
(Db110 μm) increase. The maximum cumulative volume of the
droplets was 32% at 35 μmand24%at55μm. It indicates that more
small droplets were created. At the downstream of the spray (Z=
0.7 mm), the cumulative value reaches 42% at 35 μm.
At the Z=40mmregionforΔp=1.2MPaandT= 110 °C, the max-
imum of cumulative volume of droplets reaches 35% at 35 μm. At the Z=
60 mm axial location the value was 32% at 35 μm. At the downstream of
the spray (Z= 70 mm), the value reaches 32% at 35 μm.
The distribution is advantageous to understand the effect on tem-
perature and Δpin spray formation. To represent droplet sizing, some
distribution functions are used, the most well-known distribution is
RosinRammler, as shown in Eq. (8):
Yd¼exp d
d

n
ð8Þ
where drepresents the droplet diameter (μm) and Y
d
the volume frac-
tion of the droplets with a diameter greater than d,dis the size constant,
and nis the size distribution parameter. Cumulative volume curves are
Fig. 12. The comparison of SMD and θ/2 variations for differentinjection pressures, measured data and the correlations on PSA, T= 120 °C.
Fig. 13. SMD for different Δpand Tof different axial location.
18 S.M.A. Najaet al. / Chinese Journal of Chemical Engineering 28 (2020) 922
typical RosinRammler distributions, the corresponding data for
different Δpand temperature are shown in Fig. 16. In addition, the cor-
responding constants (nand d) are calculated by curve tting of the
measurements and noted in these gures. The results show that the
experimental data could be presented by Rosin-Rammler distributions
very well. It can be also concluded that d(mean diameter) decreases
with increase in temperature and injection pressure. That is rational be-
cause of lowering viscosity and increasing momentum, respectively.
Fig. 14. Relative number count for different axial location (40 mm, 50 mm, 60 mm and 70 mm) for Δp= 1.2 MPa with different temperature (T= 100 °C, T= 110 °C, T=12C).
Fig. 15. Relative number count for different axial location (40 mm, 50 mm, 60 mm and 70 mm) for Δp= 1.0 MPa with different temperature (T= 100 °C, T= 110 °C, T=12C).
19S.M.A. Najaet al. / Chinese Journal of Chemical Engineering 28 (2020) 922
In the numerical simulation of some applications, which liquid injec-
tion is a part of the simulation, knowing the droplet diameter distribu-
tion can facilitate the simulation of the injector. Some droplets with
specied diameters can be injected directly to the domain that would
lead to the saving in CPU time (omitting the modeling of atomization).
So reporting SMD distributions like Rosin-Rammler can be highly bene-
cial in some numerical simulations.
A global PDF gives the distribution of droplet size in overall spray at-
omization. This function is given as Eq. (9):
PDF Di
ðÞ¼
1
ΔD
Ni
PNi
ð9Þ
where D
i
is the mean droplet size of size class i,N
i
is the number of drop-
lets in size class i, and ΔDis the width of the size classes. Global size
measurement of droplets is done (ΔD=10μm). Fig. 17 shows spray
global PDF versus the droplet diameter.
Fig. 17 represents the overall distribution of droplets diameters, but
Figs. 14 or 15 represent the local distribution at different axial locations.
Therefore, for instance, the PDF for Δp=1.2 MPa and T= 120 °C shown
in Fig. 17 is the summation of data presented inFig. 14 for Δp=1.2 MPa,
T= 120 °C and Z= 40, 50, 60, 70 mm. Comparing these two data, one
can conclude that the results for Fig. 17 is closer to a log-normal distri-
bution which is desired for droplet diameter distribution using PSA.
Droplets mean diameters can be dened according to the different
applications. The denition and the formulation for different mean di-
ameters are presented by Lefebvre and McDonell [47]. The correspond-
ing data for different pressure difference and temperature of Mazut
injection is presented in Table 2.
4. Conclusions
Mazut sprays of PSA were measured using the shadowgraph tech-
nique to study the effects of liquid viscosity and Δpon atomization.
Fig. 16. Cumulative droplet volume and Rosin-Rammler Distribution and experiment data for different pressure and temperature Mazut.
Fig. 17. Spray global Probability Density Function and the global mean droplet sizes.
20 S.M.A. Najaet al. / Chinese Journal of Chemical Engineering 28 (2020) 922
The experimental measurements include _
m,C
D
,L
b
,λ
s
,θ, and global and
local SMD. The maximum unstable wavelength was measured experi-
mentally and was compared with previously reported liquid lm
breakup models. The corresponding result shows that the measured
data follows the same trend as the model but with about 30% underes-
timation (for a highly viscous liquid). The model was modied by
changing the coefcients from 1.5 and 2 to 2.2 and 2.8 respectively for
short and long wavelength. It can be concluded from the measurements
that an increase in Weber number leads to a decrease in SMD. The nest
droplets were observed at an axial distance of 70 mm in the experimen-
tal range for T= 120 °C and Δp= 1.2 MPa. At this distance, the tested
atomizer can produce droplets with SMD less than 80 μmatΔp=
0.7 MPa for liquids with dynamic viscosity 0.0063 (kg·m
1
·s
1
).
The comparisons of the available correlations with the measure-
ments of SMD and θshow a good agreementfor Ballester and Varde cor-
relations respectively. Spray quality enhancement by increasing
injection pressure and temperature is revealed by results of cumulative
droplet volume, spray global PDF and relative number count of droplets.
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Table 2
Different mean diameters and their applications for different pressure differences and temperatures of Mazut
Symbol D
10
/μmD
20
/μmD
30
/μmD
31
/μmD
32
/μm
Mean diameter Name Length Surface area Volume Volumelength Sauter mean diameter
Application Comparisons Surface area controlling Volume controlling, hydrology Evaporation, molecular diffusion Mass transfer, reaction
T= 100 °C Δp= 1.0 MPa 71.44 81.11 89.57 100.30 109.24
Δp= 1.2 MPa 56.67 65.13 73.65 83.96 94.17
T= 110 °C Δp= 0.7 MPa 65.91 71.99 77.75 84.44 90.67
Δp= 0.9 MPa 54.43 60.54 67.13 74.55 82.53
Δp= 1.0 MPa 48.59 54.48 61.36 68.96 77.86
Δp= 1.2 MPa 52.03 57.32 62.88 69.12 75.67
T= 120 °C Δp= 0.7 MPa 51.67 58.18 64.95 72.82 80.95
Δp= 0.9 MPa 53.47 58.88 64.62 71.04 77.82
Δp= 1.0 MPa 52.16 57.32 62.76 68.83 75.23
Δp= 1.2 MPa 53.67 58.29 62.91 68.11 73.28
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22 S.M.A. Najaet al. / Chinese Journal of Chemical Engineering 28 (2020) 922
... Hamid et al. [29] in their study found that the size of the discharge orifice plays a significant role in determining the characteristics of the emanating sprays, while the role of flowrates (i.e. the injection pressure) is only prominent for determining spray cone angle and breakup length. The characteristics of Mazut sheet breakup were deduced from the shadowgraph technique by Seyed Mohammad et al. [30]. The results showed that the experimental sizing data could be presented by Rosin-Rammler distributions very well at different pressure difference and temperatures.The experimental study of H.M.Gad et al. [31] indicated that the spray cone angle increased by increasing the value of the Lo/Do ratio or by decreasing the assisted air mass flow rate. ...
... • In general, in the most previous studies, the effect of atomizer geometric parameters on spray properties has been investigated [11,17,18,20,31,32,[34][35][36]41,44,53], while studies on the effect of flow and fluid properties have been less analysed by researchers [13,32,33,63]and therefore there is a need to conduct such research. • Due to the fact that in the previous researches, the main focus have been down on the effects of inlet pressure of atomizer on limited parameters of spray such as spray cone angle and droplet diameter, therefore a broader investigation and in-depth analysis of the impacts of inlet pressure on other less studied parameters of spray is critical in the design and performance optimization of these devices [19,30,32,33,[42][43][44]. • In previous studies, Reynolds number variation is usually considered based on the change in nozzle diameter or fluid velocity, and or the effects of Reynolds number have been studied only on some of the main parameters of spray [13][14][15]21,39], whereas in this research the impacts of Reynolds number change based on change in the type of working fluid on other less studied parameters of spray have been investigated. ...
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... Spray technology that can disperse the liquid into many small droplets has been widely applied in various fields, such as spray combustion of petroleum fuels [1,2], spray coating for protecting industrial infrastructure [3], spray drying for producing powder particles [4,5], spray pesticide for agricultural protection [6], and so on. The nozzle that acts as the droplet dispersion device greatly affects the initial distribution of droplets in the primary atomization, including the diameter, velocity, atomization angle, and density [7][8][9][10]. ...
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The droplet velocity and diameter significantly affect both the spatial drift loss and the interfacial deposition behaviors, thus determining the ultimate utilization efficiency during pesticide spraying. Investigating the spatial velocity and diameter evolutions can reveal the mechanism of drift loss and guide to design regulation strategy. Here, we explored the spatial velocity distribution of droplets after leaving the nozzle by particle image velocimetry technology and particle tracking model, considering that the effect of nozzle configuration and the air velocity. It shows that all droplets decelerate rapidly with the velocity attenuation ratio ranging from 50% to 80% within the region of 200 mm below the nozzle. The spatial velocity evolution differences between droplets in crossflow are determined by the competition of vertical drag force and net gravity, and the drag force sharply increases as the droplet diameter decreases, especially for that smaller than 150 μm. Based on the spatial evolution differences of the droplet velocity and diameter, a functional adjuvant was added to the liquid for improving the diameter distribution. And the drift loss was significantly reduced due to the reduction of the proportion of easily drifting droplets.
Article
In this study, the flow and spray of biodiesel in the swirl atomization nozzle were analyzed. The influence of primary air flow rate and temperature on the atomization characteristics in the internal and external flow fields of biodiesel was discussed through simulation and experiments. The velocity of biodiesel in the nozzle and mixing chamber were symmetrically distributed. With increasing primary air flow rate, the maximum speed area increased and the shape of the turbulent kinetic energy of biodiesel changed from columnar to funnel. When the primary air flow rate increased from 10 to 30 L/min, the Sauter mean diameter, (SMD, d32) decreased from 95 to 28 μm, and when it increased to 50 L/min, d32 changed slightly. With increasing fuel temperature, the spray velocity increased and the particle size gradually decreased, while the particle size of each interval remained almost unchanged over 45 °C. Therefore, the best primary air flow rate and temperature for the swirling atomization of biodiesel were 30 L/min and 45 °C. It was determined that the increase in air flow rate and temperature promoted the development of atomization flow field and the breaking of droplets in biodiesel, thus optimizing the swirling atomization of biodiesel.
Article
The thermal management system has essential effects on the performance, life, and consistency of lithium‐ion batteries. Compared with commonly used cooling methods, spray cooling has excellent performance and is now widely used in electronic equipment, metal processing, laser surgery, and other fields. However, there are few applications of spray cooling in the battery thermal management systems (BTMSs). With the increase of the charge and discharge speed and people's rising attention to the thermal runaway accidents of electric vehicles, it is urgent to intensively investigate the performance of spray cooling in the BTMS and discuss its design method. In this research, a BTMS using spray cooling was designed with pouch‐type lithium‐ion cells and injectors. A synthetic lubricant was used as the spray medium. The electrical–thermal coupled model was adopted to obtain the heat production and temperature distribution of the cell. Numerical calculation and analysis of the spray cooling process were performed based on the discrete phase model. It was found that spray cooling could reduce the maximum temperature (MAT) on the cell from 53.6°C to 39.7°C during the 3 C discharge process and the maximum temperature difference (MATD) from 9.1°C to 6.0°C. And the temperatures of the tabs were also reduced. The effects of the spray speed, the mass flow rate, the specific heat capacity, and the droplet size on the performance of the BTMS using spray cooling were further investigated. The results showed that within a certain range, increasing the mass flow rate and specific heat of the spray, or decreasing the average diameter of the droplets could reduce both the MAT and the MATD on the cell. But their effects on the latter were not significant. When the spray speed was increased, the MATD demonstrated a monotonous decreasing trend and could be reduced to below 5°C. Temperature distributions on the cell with natural convection cooling, forced air cooling and spray cooling
Article
High-energy-density fuels are promising fuels for advanced aero engines, especially rotary engines, in which atomization characteristics play a crucial role in fuel practical application. This work experimentally investigated the basic spray characteristics mainly including spray angle, droplet concentration, velocity, and size distribution of two liquid fuels JP-10, HEF-1 and one slurry fuel HEF-2 by PDPA technique using a fuel slinger under 10000 to 25000 rpm. Effects of fuel physical properties (fuel type, density, viscosity, surface tension, etc) and control parameters (rotational speed and fuel flowrate) on atomization characteristics were discussed. The results showed that the droplet number was parabolic distribution for each fuel and significantly increased with the elevated rotational speeds. Slurry fuel had the largest droplet number near the spray center due to the fragmentation effect of nano-Al particles. For liquid fuels, viscosity determined the droplet breakup below 10000 rpm. Spray angle and droplet velocity negatively related to fuel viscosity. Besides, elevated rotational speeds promoted average droplet velocities, while lowered spray angles. Overall, Sauter mean diameter (SMD) of each fuel greatly depended on fuel viscosity was arch bridge-type distribution. Slurry fuel possessed a smoother distribution with much larger SMD (55∼65 μm) than liquid fuels (20∼45 μm). Furthermore, the average SMD (ASMD) of JP-10 and HEF-1 gradually decreased from 58 μm to 40 μm, and 44 μm to 35 μm, respectively as rotational speeds increased. Additionally, they increased by less than 20% when flowrates increased from 0.15 Lpm to 1.20 Lpm. Nevertheless, slurry fuel HEF-2 had an ASMD around 65 μm which remained almost unchanged with varying rotational speeds and flowrates.
Article
In this study, the atomization of heavy fuel oil (Mazut) and diesel fuel at different pressures is compared experimentally. Also, the effects of temperature on the Mazut fuel atomization are investigated experimentally. Mass flow rate, discharge coefficient, wavelength, liquid film thickness, ligament diameter, spray angle, breakup length, and sature mean diameter are obtained for the Mazut and diesel fuel. Fuels spray images at different pressures and temperatures are recorded using the shadowgraphy method and analyzed by the image processing technique. Error analysis is performed for the experiments, and the percentage of uncertainty for each parameter is reported. The experimental results are compared with the theoretical results. Also, Curves are proposed and plotted to predict changes in the behavior of atomization parameters. Diesel fuel has less viscosity than Mazut fuel. Diesel fuel has shorter breakup length, wavelength, liquid film thickness, and sature mean diameter than Mazut fuel at the same pressure. Diesel fuel has a larger spray angle and a larger discharge coefficient than Mazut fuel at the same pressure. As the pressure and temperature increase, fuel atomization improves. The viscosity of Mazut fuel is decreased by temperature increase. As the fuel injection pressure and temperature increase, breakup length, wavelength, liquid film thickness, and sature mean diameter decrease; also, spray angle increases.
Article
In this study, we investigate the macroscopic structure and atomization characteristics of biodiesel produced by sewage oil in swirl atomizing nozzle through numerical simulations and experiments. The simulation is based on Euler-Lagrange method to solve the coupled equations of discrete and continuous phases. This model can boost the practical application of biodiesel in industrial furnaces. The results reveal that when the fuel injection pressure is 0.5 MPa, the size of the atomized particles ranges between 87 and 158 μm, wherein the droplets of particle size less than 50 μm are concentrated in the center of the flow field, and large droplets with size of nearly 150 μm dominate the tail of the spray. This is because in the dense spray area near the nozzle outlet, the turbulent energy of air and droplets is maximum. Therefore, at the outlet of the nozzle, a violent momentum exchange occurs, and the droplet breaks up again, so the particle size of the droplet in the rear part of the dense zone (center of the flow field) decreases. Then, the atomization momentum gradually weakens along the axial direction, and some droplets aggregate in the tail of the dilute zone and in front of the extremely dilute zone, resulting in an increase in droplet size in the extremely dilute zone (tail of the flow field). As the injection pressure increases, Sauter mean diameter of particles fluctuates more drastically, and as time passes, the size of the droplets decreases stepwise and gradually stabilizes in the range of 25–75 μm, keeping the atomization effect in a stable state.
Article
Full-text available
The available SMD (Sauter mean diameter) correlations on pressure-swirl injectors predict droplet sizing very different from each other, especially for heavy fuels. Also there was a lack in the literature for comparing available correlations. So an experimental study was conducted on a heavy fuel oil (HFO) spray, Mazut 380. A pressure swirl injector was designed and fabricated. The experiments for Mazut at 40 °C and 80 °C were compared with the results for water, including spray half cone angle, breakup length and mean droplet diameter, at different injection pressures. Lower spray angle, higher breakup length and larger droplets were observed for lower injection pressures and higher liquid viscosity. SMD was about 75 μm for water and about 87 μm for Mazut at 80 °C. The results for droplet mean diameter were also compared with correlations from previous studies on pressure swirl atomizers. The SMD results show that for water spray, LISA method was in good agreement, also Babu and Ballester correlations were successful when high viscosity fluid was injected.
Book
The second edition of this long-time bestseller provides a framework for designing and understanding sprays for a wide array of engineering applications. The text contains correlations and design tools that can be easily understood and used in relating the design of atomizers to the resulting spray behavior. Written to be accessible to readers with a modest technical background, the emphasis is on application rather than in-depth theory. Numerous examples are provided to serve as starting points for using the information in the book. Overall, this is a thoroughly updated edition that still retains the practical focus and readability of the original work by Arthur Lefebvre.
Article
Hydrogen has been using as one of the green fuel along with conventional fossil fuels which has enormous prospect. A new dimension of hydrogen energy technology can reduce the dependency on non-renewable energy sources due to the rapid depletion of fossil fuels. Hydrogen production via Biomass (Municipal solid waste, Agricultural waste and forest residue) gasification is one of the promising and economic technologies. The study highlights the hydrogen production potential from biomass through gasification technology and review the parameters effect of hydrogen production such as temperature, pressure, biomass and agent ratio, equivalence ratios, bed material, gasifying agents and catalysts effect. The study also covers the all associated steps of hydrogen separation and purification, WGS reaction, cleaning and drying, membrane separation and pressure swing adsorption (PSA). To meet the huge and rising energy demand, many countries made a multidimensional power development plan by adding different renewable, nuclear and fossil fuel sources. A large amount of biomass (total biomass production in Bangladesh is 47.71 million ton coal equivalent where 37.16, 3.49 and 7.04 MTCE are agricultural, MSW and forest residue based biomass respectively by 2016) is produced from daily uses by a big number of populations in a country. It also includes total feature of biomass gasification plant in Bangladesh.
Article
In this paper, evaporation of heavy fuel oil (HFO) droplet under atmospheric pressure is studied through a fully transient approach. The HFO is considered as a multi-component liquid with temperature-dependent properties. The performance of this fully transient approach is evaluated for different fuels and results are compared with available experimental data for gasoline and diesel fuel. The comparison shows excellent agreements, and also reveals the flexibility of this approach for interpretation and justification of the evaporation process details by using of internal distribution of temperature and composition. Based on distillation curve, several multi-component compositions are presented for the HFO. The composition is broken down into several pseudo-components and the effects of number of components and their method of selecting are studied comparatively. It shows that despite the wide range of compositions of heavy fuels, a compound consists of a few numbers of pseudo-components can be a suitable representative for them. Also pseudo-components should be chosen with equal interval temperature and narrow boiling temperature range. The effects of environment temperature on the evaporation of droplets are investigated in a parametric study. The results show that internal temperature distribution is not very sensitive to the ambient temperature due to the high boiling temperature of heavy components of the fuel. Also wide span of temperature in the heavy fuel droplet makes it possible to predict the initial condition of pyrolysis and thermal cracking of heavier components.
Article
This paper has focused on the droplets behavior of kerosene RP-3 spray produced by a pressure swirl atomizers in terms of spray pattern, droplet size spatial distribution, mean droplet size, and distribution index with variations of pressure differential. The analyses have been carried out experimentally with the aid of optical diagnostic methods. The spray pattern, such as spray cone angle and fuel spatial distribution, has been measured by the technique of planar laser induced fluorescence of kerosene. A method for correction of fuel distribution measurement error induced by laser attenuation in spray is proposed and validated. The droplet size spatial distribution in central axis plane of the spray has been measured by a planar droplet sizing method which combining laser induced fluorescence and Mie scattering. The spray pattern in axial center plane and cross-sectional plane perpendicular to axis of the atomizer indicate that the droplets in spray concentrate around the outer periphery and in a narrow annular zone at the near-field of fuel injector exit, and then disperse to produce a solid spray at downstream of the spray. The analyses of droplet size spatial distribution, Sauter mean diameter, and distribution index with pressure differential clearly show the presence of droplets collision and its adverse effects on droplet size uniformity. The spray outline, droplet mass spatial distribution, and droplet size spatial distribution, droplets dispersion and collision in the process of atomization provide a great insight into the processes of atomization and spray development, which are key information for fuel injector design and quality control. The visualizations of spray pattern and droplet size spatial distribution with variations of pressure differential for pressure swirl atomizer are key issues in swirl cup or internally staged airblast fuel injectors because pressure swirl atomizer provides primary atomization or pilot spray which affects the quality of air/fuel mixing in lean-burn combustion. Moreover, a well-defined and complete database regarding the isothermal hollow cone spray is provided for validation of spray model.
Article
The work presents effervescent atomizer with air stone aerator. The aerator used air stone AS30 by Tetratec. porous stone with fine pores gives small resistance and allow to use the full power of the aerator. Measurements of the pressure drop and droplets sizes and spray angle produced by an effervescent twin-fluid atomizer with air stone aerator were carried out using the microphotography method. The tests were conducted from 0.05 to 0.3 (m3/h) and for liquid of 10 to 50 (l/h). The results showed that the drop of pressure increases with the rise of the gas flow rate and liquid flow rate. The discharge coefficient depends on the relation of the mass gas flow rate and the mass liquid flow rate. The spray angle increased with an increase in gas Reynolds number and with a decrease in liquid Reynolds number. Dimensionless equations were proposed that described the discharge coefficient and the spray angle. The obtained data is very important for atomizers designing, especially including some of twin-fluid atomizers.
Article
Oxy-fuel combustion of heavy oil can be applied to oil field steam injection boilers, allowing the utilization of both heavy oil and CO2 resources. The present study investigated the oxy-fuel combustion characteristics of heavy oil under different conditions, including the flame, temperature, and pollutant emission characteristics. The results showed that heavy oil combustion was stable at O2 concentrations of 29%, as the O2 concentration was increased, the flame began to brighten gradually, becoming shorter and thicker, while the temperature gradient became higher and the high temperature zone moved closer to the burner exit. The overall temperature and the combustion rates in O2/CO2 atmospheres were below those seen in O2/N2 atmospheres. The volume of NO emitted in the flue gas was almost unaffected by the change in O2 concentrations in atmospheres containing high concentrations of CO2, but it increased rapidly with increasing O2 concentration in O2/N2 atmospheres.
Article
The air core formed in the pressure-swirl atomizer has been experimentally and theoretically investigated. The experiments were implemented from the pressure of 0.1 MPa–1.4 MPa at the room temperature. Five types of atomizers with different swirl chamber length and five types of mixture of the glycerol and water with different liquid viscosity were employed for discussing effects of the swirl chamber length and the liquid viscosity on the air core size. In addition, a semi-theoretical prediction correlation of the air core size was derived by establishing a control-volume model based on the angular momentum theorem in the particles system, and then was verified with the experimental results. It is found that the air core size increases with the decrease of the swirl chamber length and the decrease of the liquid viscosity. The air core will disappear when the swirl chamber length is greater than a critical length or the ejected liquid viscosity exceeds a threshold if other parameters are unchanged. The critical swirl chamber length decreases with an increase of the liquid viscosity and the viscosity threshold decreases with an increase of the swirl chamber length. Compared with some available correlations proposed in the literatures, predictions by the new correlation derived in the present paper roughly show better agreement with the experimental results at a wide range of liquid viscosity.
Article
An experimental study is performed to study the effect of inner and outer injection pressure on spray characteristics and the detailed structure of interacted liquid sheets of a coaxial swirl injector. A high speed camera is used to visualize the transition merging process of the coaxial swirling liquid sheet. A laser reflection system is set up to analyze the wave frequency of liquid sheet. A Malvern RTSizer is used to measure the droplet size of the coaxial spray. It is found that the structure of the interacted spray is considerably different from the individual spray, the interaction between the inner and outer liquid film promoted the breakup. At the same injection pressure, the temporal instability of a liquid sheet does not change spatially. For both individual and coaxial spray, the wave frequency increase as the injection pressure increase. The individual inner spray is more unstable and easier to breakup. Furthermore, the relationship between the surface instability and the droplet size distribution of the coaxial liquid spray is investigated quantitatively. For both individual spray and coaxial sprays, the Sauter Mean Diameter (SMD) decrease as the inner injection pressure increase. The inner spray has a higher weighing factor that influences the SMD of the coaxial spray. For coaxial spray at low inner injection pressure, the liquid film thickness would be the dominate factor to the SMD.
Article
Experimental study on the effects of the geometric ratios of pressure swirl atomizers on the spray characteristics such as spray cone angle and _SMD_ has been conducted. Twelve atomizers of different geometric configurations have been used for this purpose. The atomizers have been divided into three groups, each containing four nozzles, based on the variation in three geometric ratios i.e. _D__s__/D__o_, _L__o__/D__o_ and _L__s__/D__s_.These ratios have been varied from 3 to 7.5, 0.81 to 2.69 and 1.25 to 5.0 respectively for the examination of their influence on the spray cone angle and _SMD_. Spray cone angle was measured through high speed camera while _SMD_ was measured by using Malvern instruments. The experiments were performed at two injection pressures of 0.8 MPa and 1.2 MPa by using water as the test liquid. The results show that the spray cone angle continuously decreases with the increase in ratio _D__s__/D__o_, however, an optimal value 3.75 of this ratio has been recognized during the measurements of _SMD_. Furthermore, _SMD_ has been observed to continuously increase with the increase in _L__o__/D__o_, while an optimal value 1.44 of this ratio has been identified during the measurements of spray cone angle. Similarly, an optimal value 3.75 of the ratio _L__s__/D__s_ has also been determined from the experimental measurements of spray cone angles and _SMD_.