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21.04.2008
Individual Project ENGD3000, 2008
Leycroft RSV Simulation
W. Shipway P04125213 A. Lees
CONTENTS
Course:
Title:
Student:
Supervisor:
Abstract: Rotary Spin Vane separators (RSV’s) are used in Walkers Crisp Factories
throughout the UK to separate the water and potato particulate from the flow in a pipe.
The system of pipes is known as a Leycroft Turbo Air Sweep System. It has been
proposed to install this system in other locations, including India and the USA, but the
factories are not large enough to accommodate it. This paper is written to find the design
requirements of the Rotary Spin Vane separator with regards to the length of piping pre
and post-RSV.
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CONTENTS
1. ASSIGNMENT OUTLINE................................................................................... 1
2. AIM ....................................................................................................................... 2
3. SUMMARY OF OBJECTIVES. .......................................................................... 2
4. CHALLENGES .................................................................................................... 2
5. RESEARCH .......................................................................................................... 9
5.1 – Walkers Crisp Factory ..................................................................................... 9
5.2 – Fluid Dynamics................................................................................................. 10
5.2.1 – Fluid Dynamics – Fluid Flow ........................................................... 12
5.2.2 – Fluid Dynamics – Flow Through a Bend........................................... 14
5.3 – Air Conditioning .............................................................................................. 14
5.4 – RSV Operation ................................................................................................. 15
5.5 – Applications ..................................................................................................... 15
5.5.1 – Food Industry .................................................................................... 15
5.5.2 – Oil Industry ....................................................................................... 16
5.5.3 – Space Industry ................................................................................... 16
5.5.4 – Other Applications ............................................................................ 17
5.6 – Manufacturers ............................................................................................ 17
6. DESIGN CHANGES ............................................................................................ 18
7. ENGINEERING DRAWINGS ............................................................................. 18
8. RSV BODY .......................................................................................................... 19
9. FAN MODEL ....................................................................................................... 21
10. PROCEDURE ..................................................................................................... 25
11. MEASUREMENTS ............................................................................................ 25
12. DISCREPANCIES BETWEEN THE SYSTEMS .............................................. 26
13. RESULTS ........................................................................................................... 26
14. INTERPRETATION ...........................................................................................32
15. HYPOTHESIS .................................................................................................... 33
16. SUMMARY OF HYPOTHESIS ........................................................................ 34
16.1 – Test 2 Variables ............................................................................................. 36
17. TEST 2 ................................................................................................................ 37
17.1 – Parameters ................................................................................................ 37
17.2 – Process and Results................................................................................... 38
Page
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18. DISCUSSIONS ................................................................................................... 43
18.1 – Potential Errors ........................................................................................ 43
18.2 – Test 1 ........................................................................................................ 45
18.2.1 – Limits of Post-RSV Pipe Length .................................................... 45
18.2.2 – Liquid Flow Pattern ........................................................................ 45
18.2.3 – RSV Frictional Coefficient ............................................................. 46
18.2.4 – Centrifugal Impingement ................................................................ 47
18.2.5 – Introducing a Bend in the Pipe Work ............................................. 47
18.2.6 – Decreasing of Increasing the Pressure ............................................ 48
18.3 – Test 2 ........................................................................................................ 49
18.3.1 – Stream of Water .............................................................................. 50
18.3.2 – Vertical RSV’s and the Inlet Pipe ................................................... 51
18.3.3 – Rotational (Radial) Flow Inside the Pipe ........................................ 51
18.4 – Boundary Layer and Surface Finish ........................................................ 52
18.5 – Applications of Newtonian Fluid Flow ....................................................52
18.6 – Further Testing ......................................................................................... 53
19. CONCLUSIONS ................................................................................................ 53
20. NONCLEMATURE ........................................................................................... 56
21. REFERENCES ................................................................................................... 57
22. APPENDIX ......................................................................................................... 58
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1. ASSIGNMENT OUTLINE
As part of the Walkers crisp process raw potato chips are cleansed and then water
particulate is removed from the chips by a suction process, before the chips are fried.
The reason for this removal of water pre-frying is to reduce the moisture content of the
potato chips and hence lower the gas consumption of the fryer when cooking the crisps.
The system used to remove the moisture (named the Leycroft Turbo Air Sweep System)
is shown in Figure 1. There are two systems, one passing above the chip conveyor belt,
and the other passing below the belt. The system under investigation passes below the
belt, and is located at the Leicester Walkers Crisp Factory.
More specific to the project, once the water droplets are removed from the potatoes it is
transported through the pipe work into the atmosphere through a funnel exiting the
building on the roof. At the exit point on the roof there should only be air in the pipe
work system. To remove the moisture exit before it enters the atmosphere a Rotary Spin
Vane Separator (RSV) has been introduced to the system, approximately half way along
the pipe work, in-line. The RSV separates the water and chip particulate from the air,
and only lets air continue the route to the exit. The particulate is trapped in the RSV and
removed through a drain pipe, settling in a catch box.
The problem with the current Leycroft Turbo Air Sweep system is that it is too
large in length to be implemented in other factories, and as such design changes
must be made to the pipe work to allow installation. It is investigated here whether
any changes made to the system affect the functionality of the RSV.
The manufacturer (PepsiCo) would like to know whether vertical ductwork can join at a
90 degree angle to the separator ductwork. This, along with varying pipe work lengths
pre and post separator will be subject to investigation by experimental process.
The current system shows that there is no debris (no potato chips or water) exiting at the
roof, and as such there should be no debris after any design changes have been
implemented. It is presumed, although not stated, that the reason for no water/potato
debris exiting at the roof is due to environmental regulations.
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2. AIM
The aim of the project is to investigate how to separate liquid and solid particulate from
an air stream (3-phase flow). A Rotary Spin Vane separator (RSV) is designed for such
a task, and hence exclusively this paper will investigate the parameter of the RSV and
how they affect the flow pre and post-RSV. These are considered with the overall aim
of decreasing the length of the Leycroft Turbo Air Sweep System installed at Walkers
Crisp Factory.
3. SUMMARY OF OBJECTIVES
To achieve the aim the objective are outlined in chronological order: -
1) Research fluid dynamics and any related principles that may apply.
2) Research RSV’s and their operation, the manufacturers, and their
applications.
3) Produce a physical model of the Walkers RSV and Leycroft System of
ducting.
4) Test the model to the same parameters of the Leycroft System, and test the
proposed design changes (to the length of the ducting).
5) Examine the results and extract applicable information to the operation of
the RSV.
4. CHALLENGES
The project is not designed to challenge any fundamental laws, and as such any
theoretical investigations will be considered purely academic, and as a possible source
of improvement to the current system. Any such hypothetical improvements will be
empirically validated.
Therefore the logical approach to investigating the effects of changing the pipe work is
to build an accurate model of the current system, and test this model by simulating the
actual system. Then, by changing the pipe work the effects can be observed and
proposed onto the real system.
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The pipe-work system (shown in Figure 1) will been re-scaled for modelling purposes,
and the pipe would need to be out-sourced. For this reason all proportions are subject to
this size (namely the diameter of the pipe). The overall system will be scaled down and
a one off prototype will be manufactured.
The project plan is outlined in Figure 3, the Gantt chart. The main task involved is
physically modelling the separator, and applying it to an external fan. Appropriate pipe
lengths will be installed in-line with the RSV and the fluid/solid flow (3-phase,
consisting of air/water/potato) will be observed. Then appropriate design changes will
be applied to the model and the experiment will be repeated and observed with
reference to the base results found in the first experiment.
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Figure 1. Overview of the Turbo Air Sweep System (Leycroft System). Note the system is either situated above or below the chip transport belt, not both.
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PREVIEW
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WEEK: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32
OBJECTIVES
submit project outline
submit interim report
submit 2 copies of final report
oral presentation
1 outline project
2 initial research
2.1 Rresearch RSV and fluids
3 build a model
3.1 source materials
3.2 order materials
3.3 scale down drawings
3.4 model fan
3.6 produce RSV body
3.6 check scale
3.7 assemble
4 test
4.1 check data for parameters
4.2 outline testing variables
4.3 outline testing procedure
4.4 test model
5 evaluate results
5.1 interpret results
5.2 form conclusions of results
5.3 conclusions/correlations
6 (Potential) re-test
6.1 outline new investigation
6.2 outline new procedure
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6.3 re-test model
7 evaluate results
7.1 interpret results
7.2 form conclusions of results
7.3 conclusions/correlations
8 theoretical interpretation
8.1 produce a CAD model
8.2 apply CFD to model
8.3 compare results/evidence
9 formulate correlation
9.1 verify concludions
10 write report
Figure 3. Gantt Chart
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P&ID Reference
Point
Pipe Work Internal
Diameter in mm CSA in m 2 Air Flow at
Reference Point in
m3/min
Air Speed at
Reference Point in
m/sec
1 150 0.017679 28.32 26.69
2 200 0.031429 56.63 30.03
3 200 0.031429 56.63 30.03
4 250 0.049107 56.63 19.22
5 250 0.049107 113.26 38.44
6 600 0.282857 113.26 6.67
7 600 0.282857 113.26 6.67
8 350 0.096250 113.26 19.61
9 300 0.070714 113.26 26.69
System Pipework Air Speeds @ Nominal Air Flow Specification of 113.26 m3/min (4000 CFM)
V
9
Title: Leycroft L2 Turbo Air Sweeps P&ID Diagram
Sheet: 2 of 2
Drawn: Mark Timmins
Date: 9 July 2007
Version: A
Item Length in mm Diameter in mm CSA in m 2
Hole N/A 3.0 0.000007071428571
Slot 46.0 3.0 0.000138000000000
Total Slot CSA 0.000145071428571
No. of Slots per Plenum 115
Total Plenum (x1) CSA in m2 0.016683214
No. of Plenums 2
Total Plenum (x2) CSA in m2 0.033366429
Air flow rate in m3/min though each plenum slot 0.49
Air speed in m/sec through each Plenum Slot 56.57
System Plenum Air Speeds @ Nominal Air Flow Specification of 113.26 m3/min (4000 CFM)
P&ID Reference
Point
Pipe Work Internal
Diameter in mm CSA in m 2 Air Flow at
Reference Point in
m3/min
Air Speed at
Reference Point in
m/sec
1 150 0.017679 28.32 26.69
2 200 0.031429 56.63 30.03
3 200 0.031429 56.63 30.03
4 250 0.049107 56.63 19.22
5 250 0.049107 113.26 38.44
6 600 0.282857 113.26 6.67
7 600 0.282857 113.26 6.67
8 350 0.096250 113.26 19.61
9 300 0.070714 113.26 26.69
System Pipework Air Speeds @ Nominal Air Flow Specification of 113.26 m3/min (4000 CFM)
V
99
Title: Leycroft L2 Turbo Air Sweeps P&ID Diagram
Sheet: 2 of 2
Drawn: Mark Timmins
Date: 9 July 2007
Version: A
Title: Leycroft L2 Turbo Air Sweeps P&ID Diagram
Sheet: 2 of 2
Drawn: Mark Timmins
Date: 9 July 2007
Version: A
Item Length in mm Diameter in mm CSA in m 2
Hole N/A 3.0 0.000007071428571
Slot 46.0 3.0 0.000138000000000
Total Slot CSA 0.000145071428571
No. of Slots per Plenum 115
Total Plenum (x1) CSA in m2 0.016683214
No. of Plenums 2
Total Plenum (x2) CSA in m2 0.033366429
Air flow rate in m3/min though each plenum slot 0.49
Air speed in m/sec through each Plenum Slot 56.57
System Plenum Air Speeds @ Nominal Air Flow Specification of 113.26 m3/min (4000 CFM)
Figure 4. Air speed and air flow rate at different sections of the Leycroft system.
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To build the model schematic drawings of the RSV have been provided by PepsiCo,
shown in Figure 2. These drawings will be used to produce a scale model of the RSV.
The static fan also needs to be prototyped, and it has been suggested that rapid
prototyping by Stereo-Lithography would be appropriate. Therefore the fan design
needs to be modelled with CAD, using Pro-Engineer. The fan design will be drawn for
scaling and modelling purposes.
Note: “static” in this interpretation means the rotors do not rotate, rather there is a
velocity forced upon the rotors from the main turbine (see Figure 1).
Once the drawings have been manufactured the model system needs to be assembled,
with the location constrained to the availability of a main turbine. This will therefore be
assembled at the university laboratories in Queens building, Leicester university. The
experiments on the model will be carried out as described in Section 10 - Procedure.
5. RESEARCH
5.1 – Walkers Crisp Factory
The Walkers Crisp Factory under investigation is located in Leicester, address: -
Walkers Snack Foods
Bursom Road
Leicester
LE4 1BS
The Factory is one of many located across the UK. The process of making crisps (with
relevance to this paper) is outlined below.
3 4
5
6
8
1 2
7
Figure 5. The relevant process of making the crisp, with steps numbered 1 to 8.
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The process is: -
1. Cut potato chips are moved along a belt (green arrow).
2. The belt moves through water to clean the chips (green arrow).
3. The chips fall off the belt into the fryer (green arrow).
4. Water and potato particulate are sucked off the potato chips as they move
towards the fryer. The plenums are located at point 4 (blue-grey arrow).
5. The 3-phase flow passes into the Rotary Spin Vane Separator (RSV).
6. Clean air only (single phase) exits the RSV (blue arrow).
7. The suction is caused by the fan located at point 7.
8. Clean air exits the system at the roof.
The RSV in situ is shown in Figure 6 below.
Figure 6. The RSV at Leicester’s Walkers Factory.
5.2 – Fluid Dynamics
The RSV basic principles operate on a combination of fluid (multi-phase) travelling
through a vessel of pressure P, and at velocity V. At some point along the vessel a
device is used to remove one or more of the phases. Therefore fluid mechanics should
apply to this operation. The pressure and velocity at any stage of the system is
proportional (in a linear fashion) to each other, as per Newtonian physics (known as the
ideal gas law, PV = mRT, where R is a physical gas constant, equivalent to Boltzmann’s
constant).
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IN THIS PREVIEW
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5.2.1 – Fluid Dynamics – Fluid Flow
The flow of a fluid with constant density can be described using Bernoulli’s equation,
which states
ghPV
2
2
= constant
where V = velocity
g = gravitational constant
h = height of the fluid flow above ground level
P = pressure
ρ = density of the fluid
Considering that the equation is constant for a section of fluid flow, it can now used to
suggest what will happen when a change to the pipe is introduced, as is shown in Figure
7.
UNAVAILIBLE
Figure 7. A pipe with varying diameter and height
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Bernoilli’s equation can be stated for a variation of any of the variables, including
gravity if the height were large enough, and so it takes the form,
22
2
21
1
2
1
22gh
PVgh
PV
The above statements are only generalisations, and can be applied to predict the
approximate flow on application. The assumptions made in the above statements is that
the fluid is incompressible (constant density, ρ), the flow type is steady (as opposed to
turbulent flow), and the fluid is frictionless. But, of course friction does occur in fluid
flow, which brings us nicely to the next research subject.
Whenever a fluid passes over a stationary object the fluid that touches the object
experiences high shear stress, due to the fluid “sticking” to the surface. This point of
high shear stress creates a layer of fluid, where the fluid has low velocity. This is layer
of high shear due to friction is called the boundary layer, and can be diagrammatically
represented as in Figure 8 and 9.
UNAVAILIBLE
Figure 8. A slab of fluid moving over a solid object
For a pipe this can be reversed, as shown
UNAVAILIBLE
Figure 9. A slab of fluid moving through a pipe. The fluid is decelerated due to friction
on the wall.
Ref: [13] to [15]
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5.4 – RSV Operation
The operation of an RSV (Rotary Spin Vane separator) is designed to separate
contaminants from a gas flow. The gas and contaminants must be contained within a
closed system, usually consisting of duct-work (referred to above as a vessel). Certain
separators deal with the process of separation through what is known as gravity
segregation, with the heaviest fluid sinking to the bottom of the vessel through
gravitational force. These types of separators are not discussed in this paper (it is
outside of the scope).
It is known that as the multi-phase flow enters RSV the fan sends it off in a trajectory
towards the separator wall. The liquid droplets then drain off the wall, with the gas flow
continuing through and past the RSV. In this way there may be many phases in the
flow, and limitations to the quantity of the phases with regards to the RSV’s ability to
separate them.
As previously stated there is no direct references found relevant to phase separation, and
as such the principles behind the operation cannot be disclosed here. However, as
previously stated this paper is not intended to challenge or validate any fundamental
laws.
Ref: [22] to [24]
5.5 - Applications
The main applications for the RSV are listed below: -
5.5.1 - Food industry
The application of RSV technology in the food industry is due to the necessity to clean
the food before it is processed and packaged. Due to the relative importance of hygiene
in the food industry it is necessary to remove contaminants from a system, as in all
instances these contaminants (water/other cleaning liquid, or solid particulate) will
contain bacteria. Also it is sometimes necessary to remove a discharge of droplets in
chimney fitting, before it enters the atmosphere. This is of course the application that
this paper is based on.
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It is also noted that the use of separators in the food processing industry can be applied
to remove liquids from solids, such as the wine, beer and milk industry. Although the
direct application of RSV’s does not apply, the main process of directing liquids into a
wall applies. By spinning a barrel containing the liquid and solid, the liquid is separated
by centrifugal forces. The machine is commonly known as a mist separator, or
centrifugal separator. However, separators of this nature will not work on solid removal,
as it either lets the solids pass through, or disrupts the machine.
Ref: [25] to [27]
5.5.2 - Oil industry
In all instances in the oil industry oil is removed from the ground. Whether the oil is
located deep in the ground on terra firma or underneath the sea is not of consequence
with regards to the application of RSV technology. The oil erected from the ground is
never pure, and always contains both water and solid particulate (earth). Indeed a well
stream is often used to procure the oil from its location, and as such liquid is purposely
imposed on the oil. Therefore RSV’s are applied due to a need to separate the oil from
the water and gas. This is due to the necessity to use pure oil in all it applications, e.g.
for burning or lubrication. Also it is necessary to separate it to protect downstream
equipment like compressors.
The process of separating the oil is done in multiple stages, firstly from gravity
segregation (as previously touched on), then from a vane separator, then to remove the
remaining liquid (typically less then 2%) from the gas, a gas scrubber is used. The
latter, gas scrubbing, is a process of gases coming into intense contact with a liquid to
remove the remaining small volume of liquid. As such it is not further investigated, as
the process is different.
Ref [28] to [32]
5.5.3 - Space industry
A phase separator is used in the space industry for life support, thermal management
and power conversion. All air in space stations/shuttles is man made (i.e. through water
electrolysis and from storage tanks), and as such it is important to separate the gas from
liquid in an efficient manner. However, due to the lack of gravity in space the process is
slightly different, and this is referred to later in the paper.
Ref: [33] to [35]
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5.5.4 – Other Applications
Other than the above described processes, it is obvious from these descriptions above
that RSV technology is applicable to any industry where contaminants may prove
detrimental to the industry’s process. This is usually considerate to specific equipment
in the industry, such as sensitive equipment, or highly contaminant fluid in the relative
atmosphere, which may corrode the equipment. As such the application is used to
protect the equipment. Such British Standards apply to the safety of machinery by
evaluation of the efficiency of the removal of air borne hazardous substances. This is
outlined in BS EN 1903, but applies mostly to air-conditioners.
As stated in the Food Industry the operation of separation can be achieved by spinning a
barrel. This also applies to the waste industry, and the pharmaceutical industry.
They can also be used to recapture valuable liquids (such as solvents), although in most
instances gas scrubbers are the preferred method.
It is of course debatable as to which industry is the main user of separators. It is likely
that the food industry is the main user; however, the main economic profit would lie
within the oil and space industry. It is of relevance to note that the oil industry as a
whole represents the largest £ value industry.
Ref: [36] to [40]
5.6 – Manufacturers
The main manufacturers of vane separators are listed below,
Munters, UK – for use in the process industry – www.munters.co.uk
Mikropor, Istanbul – Air, gas and liquid purification -
www.mikroporamerica.com/
However, it seems that the majority of separators consist of either knock out drum
types, where they remove free liquid from gas streams, and the phase flow passes
through a meshing pad; gas scrubbers, where the flow comes into intense contact with
liquid; and finally gravity segregation, which has previously been discussed.
Ref: [41]
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6. DESIGN CHANGES
The proposed design changes made by PepsiCo involve using a 90 degree bend pre
separator and variable lengths of pipe-work pre and post separator. These are the
experimental variables, along with different air-flow velocities.
If during the experiment it becomes clear there are uncertainties in particular areas, or it
is appropriate to test another variable, then these will be tested and justified.
7. ENGINEERING DRAWINGS
The pipe work has been outsourced from the following manufacturer -
www.pipecenter.co.uk. This has a diameter of 100mm, 3mm, made from Acetyl
material. This provides adequate strength in case the velocity and pressure change cause
appreciable stress on the walls and could potentially buckle the pipe.
Drawings D001 to D003 are shown at the end of this paper, and are used to manufacture
the model. Drawing D001-1 has been scaled to 1:100/616. This is because the outside
diameter of the pipe work in the actual system is 616mm, and the out-sourced pipe work
has an outside diameter of 100mm, with 3mm thickness.
Drawing D001-2 and D001-3 has been scaled to 1:90/610. This is because as explained
a shell needed to be created around the fan of 2mm thickness. The fan needs to be
placed inside the pipe. The internal diameter of the actual pipe is 610mm, and the inside
of the model pipe is 94mm (100mm external diameter of 3mm thickness). With the shell
having an external diameter of 94mm to mate to the pipe, it leaves the blades (D001-3)
and diverter (D001-2) of external diameter 94mm – 2mm – 2mm = 90mm.
Drawing D002 shows the Leycroft system; with scaled dimensions to enable the model
to be assembled at the correct proportions.
Drawing D003 shows the proposed design changes, as outlined in section 6.
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8. RSV BODY
The main body of the RSV, as designed in drawing D001-1, will be manufactured by
vacuum forming. This is the best manufacturing technique, as it wastes little material.
Techniques like injection moulding are not available, due to costs and machine
availability. The costing would not be justified, and the time to manufacturer would not
be adequate for the project. The other technique possible would be turning; however
this would waste a lot of material. Hence vacuum forming has been employed. This was
done by turning a piece of low cost material (subject to its heat resistance) into half of
the RSV body. This mould was then placed in a vacuum forming machine, and a sheet
of plastic was heated above it. The plastic was then lowered onto the turned mould, and
negative pressure was forced inside the area between the mould and plastic. This causes
the plastic to form over the mould.
The plastic was then bolted to a CNC machine, where an outline was modelled in Pro
Engineer, and an appropriate file was created to cut out the waste material. Holes were
also added for the other half. This is shown in Figures 10 to 12. The two halves were
then loosely bolted together, slotted over the piping, and tightened.
Figure 10. The CNC machine, with the model bolted down inside.
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Figure 11. The model after the waste material has been cut.
Figure 12. One half of the final RSV body.
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9. FAN MODEL
The fan will be manufactured using a rapid prototyping technique, stereo-lithography.
This uses a vat of resin and a laser to solidify the liquid resin. A moveable bed drops
down by a certain amount and the laser then solidifies the next “plane”. Due to the
brittleness of the resin the manufacturer of the fan was consulted on the production of
the fan. It was proposed that it would be possible to make, but an accurate scale of the
thickness of the blades would not be possible. Also the blades would be vulnerable due
to their length. It was suggested that a shell was placed around the whole component to
give structural rigidity. The thickness of the shell and blades was suggested to be 2mm.
The fan was modelled as shown below in Figure 13, and then an .stl file was sent to the
Innovation Centre at DeMontfort University, where the model was manufactured. It
takes approximately 12 hours to manufacture, and photos are shown in Figures 16 and
17.
Figure 13. The fan modelled in Pro Engineer, for rapid prototyping.
Some concern was raised as to the dimensions of the blades. Figure 2 shows the original
blade and diverter (the section in the middle). But, when this was modelled in Pro
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Engineer it did not seem to fit correctly. This was raised with PepsiCo, and as such they
provided us with a revised drawing of the blades. This is shown in Figure 14. However
this schematic also proved to be inadequate. Hence the overall model of the Leycroft
System was assembled in Pro Engineer, to the dimensions of the drawings D001 to
D003 (see section 7 – Engineering Drawings). The fan component was then added to
the assembly in Pro Engineer and re-modelled so that it fits. This component was then
sent to the Rapid Prototyping Centre as a .stl file.
Figure 14. The revised blade design, provided by PepsiCo.
Figure 15. The overall assembly of the test rig, as modelled in Pro Engineer.
It is also appropriate to model this assembly in case any Computational Fluid Dynamics
can be applied. This model also provides a visual representation of the system in 3D. As
such it can be used to analyse any potential problems with the assembly, however, none
came up.
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Figure 16. The fan, .stl file (top left), structure stability (top right), and the model.
These pictures above are of the finished static fan, and complement the photos of the
stereo-lithography machine. The picture top left shows the digital model, from which
the laser takes its co-ordinates from, and the highlighted red sections are added for
structural rigidity. These are broken away when the component has been baked and is
solid, of which one segment is shown top right.
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Figure 17. The resin bath, which the fan is made in
One such parameter of the RSV is the interaction between the potato
particulate/air/water and the blades. It is necessary to ensure the model was of a similar
surface finish to the actual fan. The fan is made by welding cut to shape sheets of steel,
as is needed in the food industry, and is shown in Figure 18 below. An appropriately
smooth material is needed for the model, to simulate the steel. But, the rapid
prototyping technique for manufacturing the fan is primarily used for high geometrical
accuracy and good surface finish, and hence is appropriate.
Figure 18. a section of the fan, showing the blades.
Ref: [42] to [44]
Resin bath
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12. DISCREPANCIES BETWEEN THE SYSTEMS
1. The drawings provided by PepsiCo (Figures 1 and 2) show inconsistencies with the
location of the fan in the RSV, and the orientation of the RSV. In Figure 1 the fan in the
RSV is shown to be after the main body of the RSV (i.e. closer to the main turbine).
This would cause the RSV to not function properly, as the 3-phase flow would pass
through the RSV body before hitting the fan.
2. The position of the fan blades is inconsistent with convention. Convention states the
fan blade should be angled behind the diverter. That is, the blades should sweep back
from the centre, but the fan situated at the Leicester Factory protrudes in the opposite
direction to the 3-phase flow. This however will be researched to ensure that the logic
here is correct.
13. RESULTS - TEST 1
The velocity of air flow is quoted as 6.7m/s at the inlet of the RSV; see Appendix -
Turbo Air Sweeps Modelling URS Version 0.2, page 11, at P&ID reference point 6. A
smoke machine was obtained to run the test (taken from a aero-dynamics test rig.),
which was placed in front of the system, and allowed to warm up for 15 minutes.
Test 1.1: Initial Test – Base results – 03/01/2008
Velocity at input, V = 6.7 m/s
Pipe Length pre-RSV, L1 = 0.36 m
Pipe Length post-RSV, L2 = 0.95 m (see drawing D002)
This test involved using a smoke machine to observe the flow through the pipe work. It
proved unsuccessful due to the colour and density of the smoke making it hard to
observe accurately. Consequently minute adjustments were made to try and improve the
visibility of the flow. Eventually it was conceived that we needed to apply the smoke
stream over a single blade. This proved successful by the fact that a vortex stream was
observed to flow through the separator, although any similarities to the actual system
were reduced at each adjustment (the flow placement at the inlet, the velocities, and
density of flow).
Outcome: UNSUCCESSFUL – unable to observe
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Figure 19. A smoke machine has been put in front of the input opening, to visualise the
fluid flow. But, as stated in Test 1.1 it was not successful, as it was not possible to
observe the flow accurately. It was also inaccurate by the fact it was just one phase (air).
It was previously stated that the 2 potential ways to model the 3 phase flow included
using a smoke machine and to use a sprayer to physically inject water into the system.
Due to the former being inadequate for testing purposes (as described in test 1.1) a
water sprayer was used to simulate a 2-phase flow. The sprayer was filled with water,
and dye was added to help observe the dynamics of the water droplets.
Test 1.2: Initial Test Attempt 2 – Base results – 10/01/2008
Velocity at input, V = 6.7 m/s
Pipe Length pre-RSV, L1 = 0.36 m
Pipe Length post-RSV, L2 = 0.95 m (see drawing D002)
This test involved using a pressurised water sprayer to force feed a 2-phase flow (air
and water droplets) at the inlet. It proved successful in both visually observing the flow,
and in simulating the actual system. There was an observed 2-phase flow before the
RSV and 1-phase (air) flow after. The saturation pre and post-RSV is unknown.
Outcome: SUCCESSFUL – Base parameters set
The test was recorded to better analyse the experiment, and images of the clip are shown
in Figures 20 to 23.
Test 1.3: Introducing a 90 degree bend at the input – 10/01/2008
V = 6.7 m/s
L1 = 0.36 m
Smoke machine
RSV body
Main Turbine Input
aperture RSV body
Fan
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was an observed 2-phase flow before the RSV and 1-phase flow after. The saturation
pre and post-RSV is unknown.
Outcome: SUCCESSFUL – decreasing the pipe length considerably had no adverse
effects on the RSV’s purpose. Please see Figure 22 and 23.
Test 1.6: Adjusting the pipe length before and after the RSV – 10/01/2008
V = 6.7 m/s
L1 = 0.19 m
L2 = 0.36 m
The pipe lengths were changed to 0.19m before and 0.36m after the RSV as shown in
Drawing D003. The water sprayer was applied at the input. The changes to the pipe
lengths gave no major change in particulate separation by the RSV. There were
observed water droplets along the pipe section after the RSV but only approximately
1% of the total quantity sprayed, and the water flow stopped approximately 150mm
after the RSV. No water entered the fan. The saturation pre and post-RSV is unknown.
Outcome: SUCCESSFUL – changing the length of the pipe work after the RSV does
affect the phase content post separator. An appropriate length needs to be applied post
separator to ensure no water reaches the fan.
It was noted in all tests that the hole in the bottom of the RSV did not operate
sufficiently. The pressure difference between inside the system and that of atmospheric
caused the water to remain in the bottom of the RSV. If left to fill too much the water
overflowed into the pipe port RSV.
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Figure 20. The initial test, using red ink dye and water. There was no water after the
RSV.
Figure 21. Introducing the pipe introduces a larger boundary layer for the flow to
decrease in velocity.
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Figure 22. For test 1.5 a 0.19m pipe was assembled pre-RSV.
Figure 23. For test 1.5 a concentrated jet of water was also applied.
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14. INTERPRETATION
Section 13 shows that none of the suggested design changes as described in Section 6
gave undesirable results. The limitations of the test were the amount of fluid the RSV
was subject to, the maximum velocity of the fan (i.e. its power output), and the amount
of variations in pipe length.
The amount of fluid used was assumed to be more than the actual system, and as such is
adequate for modelling purposes.
The maximum velocity of the fan was a restriction with regards to finding the
limitations of the RSV, but to solve the problem presented by PepsiCo it is not an issue,
as the stated velocity is 6.7m/s, as shown in Figure 4. Indeed it would be better to lower
the fan speed, as this would decrease the power consumption of the fan. This is
contradicting to knowledge given by a consultant that the optimum fan speed is 9.5m/s
(as described in Test 1.4). Also, decreasing the fan speed will increase the amount of
water left on the potato chips, and so increase gas consumption of the fryer. This
association suggests that there is a compromise and therefore a theoretical optimum fan
speed and fryer temperature (gas consumption). But the gas consumption for given chip
surface moisture content is outside of the scope of this project, and it would also require
more information from PepsiCo with regards to the fryer and chip production.
The variations in pipe length pre and post-RSV were constrained to the resources
available, as there was only a finite amount of pipe to work with.
Test 1.5 involved changing the pipe pre separator, and had no adverse effects. Test 6
involved changing the pipe pre and post separator, and although there was a minimal
amount of liquid after the separator, it was observed that some liquid did pass the RSV.
Therefore there are limitations with respect to the pipe length post-RSV. This is the
main outcome of the test. However the amount of water in the bottom of the RSV did
affect the liquid quantity post-RSV. As Test 1.6 progressed the amount of liquid
observed post-RSV increased, but at the start of the test there was only a small amount.
It is suggested that the increase is not due to a certain amount passing through the RSV
in a linear fashion (i.e. the longer the test progressed the more water passed through in a
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16. SUMMARY OF HYPOTHESIS
Referring to Section 14 and 15 the main parameters of the RSV is hypothesised to be
1. The length of the pipe work post-RSV. A limit has been suggested that 0.19 m
length post-RSV is the limit for the functionality of the RSV, but it was not
tested past this length.
2. The geometry of the fan blades. Specifically the angle and surface area in
contact with the phase flow.
3. The diametric ratio of the RSV. The diameter to length of the RSV will have a
limit to which it can no longer separate the phases.
4. The material and surface finish of the inside of the RSV. If the surface frictional
coefficient were too low then the water and some particulate would simply
follow the path of the air, and not be caught in the RSV
5. The speed of the fluid flow.
6. The insert inside the RSV, where the pipe work protrudes into the RSV slightly.
This is shown below in Figure 24. The protrusion (insert) is there to ensure no
water/particulate enters the other side of the pipe work. It does this by simple
means of physically blocking the outskirts of the pipe work.
UNAVAILIBLE
Figure 24. Detail of the section that protrudes into the RSV
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A second test is hence conducted. Of the above parameters number 3 is investigated.
This has been deduced in the following manner: -
Regarding number 1: It would be appropriate to change the length of the pipe work
post-RSV to find the limit of length before the water was sucked past the RSV into the
fan, but as previously highlighted, there is only a finite amount of pipe-work, and so this
test is not possible. The length of the pipe work has already been investigated to a good
degree as well.
Regarding number 2: It would be possible, and indeed it would likely have a
considerable amount of difference to the RSV, however the stereo lithography process
is quite expensive, and it would take too long a time to make another. The process
previously involved booking the machine some weeks in advance, making the model,
and acquiring funding for it. It was quoted by the manufacturer that the fan would cost
approximately £150.
Regarding number 4: As described later, increasing the frictional coefficient is possible,
but once this is done the model can no longer be used for such a wide variety of
experiments, as the coating would be permanent. Also, colleagues are using the system
for their own investigations, and this may be disadvantageous to their experiments.
Regarding number 5: This has already been investigated in Test 1.
Regarding number 6: It is relatively obvious that decreasing the protrusion (as in Figure
xx above) will decrease the RSV functionality, but increasing it may provide some more
insight.
Also the main purpose of investigating the RSV is to decrease the length of the Leycroft
System. This directly does that, and the only other parameter that considers this is the
pipe work length post-RSV.
Ref: [45] to [47]
16.1 – Test 2 Variables
It is therefore proposed that changing the length of the RSV at the larger diameter
section and then running a test should provide more data and help to find out what the
limitations of the system are. In this sense it will help to find what the main design
requirements are for the RSV. To do this the RSV is cut along its diameter at one end,
to make the RSV adjustable. This is shown in Figure 26. The interface must be tight to
ensure there is no pressure drop. It is calculated geometrically as in Figure 25.
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UNAVAILIBLE
Figure 25. The trigonometric drawing of the RSV cut.
Figure 26. A photo of the RSV cut.
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which did not continue along the pipe towards the main turbine, but remained where it
was. Figure 26 shows a picture of the RSV and pipe after the RSV.
Figure 26. x = 0.14m. An insignificant amount of water was observed post-RSV.
Test 2.2: x = 0.12m – 02/04/2008
The test was conducted as in Test 1, with the fan switched on, the water sprayer was
sprayed into the inlet, with coloured water to observe the flow pre and post-RSV.
Outcome: SUCCESSFUL – the observed flow was exactly the same as in Test 2.1.
Only a small amount of water (less than 1%) was observed along the pipe post-RSV,
which did not continue along the pipe towards the main turbine, but remained where it
was. Figure 27 shows a picture of the RSV and pipe after the RSV. It was observed that
a stream of water formed in the pipe before the RSV. This is shown in Figure 28.
Figure 27. x = 0.12. Only a small amount of water (less than 1%) passed into the pipe
post-RSV.
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Figure 28 (a). x = 0.12m. A stream formed in the pipe
Figure 28 (b). x = 0.12m. A stream formed at in the pipe before the RSV
Test 2.3: x = 0.1m – 02/04/2008
The test was conducted as in Test 1, with the fan switched on, the water sprayer was
sprayed into the inlet, with coloured water to observe the flow pre and post-RSV.
Outcome: SUCCESSFUL – the observed flow was exactly the same as in Test 2.1.
Only a small amount of water (less than 1%) was observed along the pipe post-RSV,
which did not continue along the pipe towards the main turbine, but remained where it
was. Figure 29 shows a picture of the RSV and pipe after the RSV. It was observed that
there was no water in the extension section. This is highlighted in Figure 30.
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Figure 29. x = 0.1m. Only a small amount of water (less than 1%) passed into the pipe
post-RSV.
Figure 30. x = 0.1m, notice there is no water in the circled area.
Test 2.4: x = 0.08m – 02/04/2008
The test was conducted as in Test 1, with the fan switched on, the water sprayer was
sprayed into the inlet, with coloured water to observe the flow pre and post-RSV.
Outcome: SUCCESSFUL – It was observed that there was a considerable amount of
water in the pipe after the RSV. This is highlighted in Figure 31.
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18. DISCUSSIONS
Please see sections 14 - Interpretation, and 15 - Hypothesis for a discussion on test 1.
This is because the outcomes of this test dictated the variables for test 2. They are
however further discussed in section 18.2 – Test 1, and summarised in 19 -Conclusions.
18.1 - Potential Errors
The amount of fluid removed from the system is quoted as 80-100 l/min, from the
Turbo Air Sweeps Modelling URS Version 0.2, page 6. To compare the amount of
liquid Test 1 and test 2 removed from the system the water sprayer has been tested. This
was conducted by pressurising the sprayer by the same amount as was done in the test,
and spraying water into a beaker for 10 seconds. The outcome was that the sprayer
dispersed 110 ml. comparatively this is 0.66 l/min.
This gives rise to 2 concerns. Firstly, the model is to a particular scale, and as such the
flow rate needs to be multiplied by this scale factor to yield accurate comparisons.
Secondly, after conducting test 1 and 2 and observing the flow rate and quantity of
liquid, the water separation rate seems very high for the Leycroft System.
Problem 1 is tackled first. The internal diameter of the Leycroft System and the model
is 610mm and 94mm respectively (taking into account the thickness of the material, as
this is the area that the fluid flows through). The x-sectional area is then
2m 3109464
209402
A Model,
2m304
2610
4
2
1A System,Leycroft
..π
..ππd
By taking the scale factor A1/A2 the flow rate of liquid for the model is
l/min528660310946
30660
2
1Model of Rate Flow ...
..
A
A
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The high separation rate is evaluated by knowing a few parameters. The flow rate is
nominally 6.7m/s, and the quantity of liquid separated is 80 to 100 l/min. The flow of
liquid can be calculated as,
m/s
4
35
)2(m 30
/s)3(m310671
)2
(m2
610
/s)3
(m3
1060
100
area sectional-x
(l/min)100 .
.
-.
.
π
This calculation assumes that 100 litres of fluid travels through a pipe of 0.3 m2 x-
section every second. As such there are no other phases (air or particulate) present, i.e.
100% of the x-sectional area is covered by the liquid at any instant in time. This shows
that it is possible, as the actual flow rate is defined as 6.7 m/s, and hence the quantity of
air and particulate can occupy 26.4% of the x-sectional area at any one instant in time.
This is applicable to all lengths of the pipe work, assuming the fluid flow is not that of
the slug/plug type.
2 or multiple phase flow patterns can arrange themselves in a variety of configurations.
With slug flow large gas bubbles followed varyingly with slugs of liquid form the
majority of the flow pattern. Please see Figure 33 for an appreciable description. The
changes in flow pattern are a function of either gas-liquid interface, or geometry
changes.
Figure 33. Varying 2 phase flow types along a pipe [48]
The 3rd
phase flow of potato particulate was not tackled, due to limitations of the
experimental technique, i.e. it was not possible to simulate a similar flow of particulate.
However, as described in the hypothesis, having a phase flow of greater density would
only separate easier from the main flow pattern.
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18.2.3 – RSV Frictional Coefficient
After test 1 was conducted it was hypothesised that a higher frictional coefficient inside
the RSV would be beneficial to the removal of the water/particulate. This could simply
be applied as a coating inside the RSV, instead of making a new system. However it is
also suggested that it could be detrimental to the overall operation of the system. Whilst
the RSV specifically is used to remove water and potato particulate, this is superseded
by the operation of removing water from the potatoes on the belt. Having a higher
frictional coefficient at the RSV would cause the air to also lower its velocity when
entering the RSV. This may prove to be detrimental to the sucking operation at the
plenum chambers, as regardless of the pressure difference pre and post-RSV the fluid
velocity would be lower when the frictional coefficient is higher. This is a law of
classical physics. A simple analogy is that more force is required to push a brick over a
rough surface than a smooth surface.
It is not suggested that having a very smooth surface finish would also prove to be
beneficial to the RSV operation. Having what is known as “cold welding” between two
interfacing surfaces occurs when two surfaces are of such a mechanical smoothness that
they adhere to each other, and is dependant on the molecular force of the material. As
such this smoothness would not be achieved easily, and it may not provide such a high
coefficient as a rough surface.
Irrespective of the above statement, having a higher coefficient of friction will cause all
fluid flow to decrease. This may or may not prove to be detrimental to the suction
power at the plenums. It is suggested that the fluid velocity would decrease overall for a
given fan speed for a higher frictional coefficient inside the RSV, and hence would
require more power to suck the same amount of water off the potatoes. But, this
decrease in velocity may only be minimal, and not enough to be considered. As stated at
the start of this paper this hypothesis would need to be experimentally proven, and
indeed not only proven but shown to have such an effect that it should be considered
beneficial enough to the system to stop the chip manufacture whilst the coating were
applied. Indeed, the cost effectiveness should be analysed. It should be decided how
long it would take to dismantle, apply the coating, and re-assemble the RSV, which
would be offset by the increase in performance of the RSV with regards to its cost
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effectiveness. Then it would be decided whether this capital loss would be greater than
the benefits discussed. However, this is not decided here due to a few reasons. Firstly
there is not enough information with regards to the economics; secondly it is beyond the
scope. The test is not done due to the limit in time; also by applying a coating it would
not be possible to see the whole process, only the outcome post-RSV. Whilst this is
adequate for that particular experiment it would disturb the model in such a way that
any future testing would not be possible, even if it is only very small.
18.2.4 – Centrifugal Impingement
As described in section 15 – hypothesis, the operation of the RSV relies on the density
of the other phases (water/potato). The RSV turns the axial flow pattern into a radial
flow, and the liquid and solid particulate is thrown off by centrifugal forces, whilst the
air remains in this radial flow pattern. The liquid and particulate then drain off the inner
wall of the RSV. This is also validated by the fact that space applications have to pursue
different techniques to achieve this phase separation. By definition, in space the
respective weight (force) of a liquid particle travelling through a vessel of ducting will
be zero, due to the lack of gravity. As such what is known as a vortex separator is being
researched elsewhere and applied to space technology. The basic physics fundamental
to the success of this vortex separator is that a force is applied to the phase flow by use
of a vortex, creating an induced centrifugal force (simulating gravity).
18.2.5 – Introducing a Bend in the Pipe Work
A radius of curvature of approximately 300mm is used for the pipe bend in test 1.3, and
the velocity was not shown to decrease to any extent. Therefore, it is suggested that
boundary layer separation did not occur (see section 5.2.2 – Flow Through a Bend), and
hence a pipe should be used with a radius of curvature of 1.9m (by scaling up to size) in
the Leycroft System, assuming a linear relationship. It is not known if this is the limit of
the radius of curvature, as other pipe bends were not tested. If bends are applied the
velocities around these locations should be checked, and the turbine should be adjusted
accordingly. But, this gives rise to a problem. It is necessary to note that a bend can
cause turbulence due to boundary layer separation, and hence the velocity in the bend is
not uniform. It has been calculated that the laminar velocity be measured at a point
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along the pipe 12 to 14 times the diameter of the pipe [49], and must be considered
when measuring velocities at this point.
If the pipe bend radii of 1.9m, then curved guide vanes could be suggested. An example
is shown in Figure 34. Even though the boundary layer surface is increased, the losses
due to separation are greatly reduced. Further information of flow through a bend is
found in Ref. [50] and [51].
UNAVAILIBLE
Figure 34. Curved guide vanes for small bends. [52]
18.2.6 – Decreasing or Increasing the Pressure
In test 1.4 the velocity of the main turbine was increased to a maximum of 8.5m/s. As
explained in section 5 – Research, this is used to force a pressure change between one
vessel and another. But, as experimentally found an increase in pressure difference
(represented by the fan speed) had no adverse effects on the operation of the RSV. If the
pressure change were decreased (the fan speed slowed down) however, it may cause
problems. As previously described the liquid impinge onto the RSV by applying a radial
flow pattern. If the fan speed was decreased then the radial centrifugal force would
decrease, and the point of separation from the flow would also decrease. There should
consequently be a theoretical limit to the fan speed. Also, more importantly, if the fan
speed was decreased then suction of liquid from the potatoes would decrease.
There would also likely be a limit to the increase in speed of the main turbine. If the
velocity were too high it could suck the water from the RSV, particularly further away
from the fan. This problem could be solved by the application of another “static” fan.
This is shown below in Figure 35. The RSV main body would have to be increased in
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length to a certain extent, to allow sufficient room for the second fan, and allow the 2nd
flow of liquid to impinge on the wall. An example is shown below. This is not discussed
further though as there are many variables to consider, like the specific location, the
length of the blades, the orientation of the blades, the angle of the blades, introducing a
2nd
rotational flow etc...
UNAVAILIBLE
Figure 35. An RSV with 2 fans, for high flow velocity.
Ref: [53] to [58]
18.3 – Test 2
Test 2 involved changing the length of the RSV. It was found that the limit to the length
of the RSV is 0.08m. This potentially shows a limitation with regards to the length of x.
At x = 0.08m there was a considerable amount of water passing through the RSV and
into the pipe. The cause may be that the RSV no longer functions at this length, and as
such a limit has been reached. This limitation has to consider hypothesis number 3, the
diameter to length ratio (see section 16 - Summary of Hypothesis), as a smaller/larger
diameter will change the operation. The limits may be considered then for diameter to
length ratio of 2.2.
But, as stated in test 1 the drainage hole did not function properly due to the pressure
difference. This is applicable to test 2 as well, and as such it was observed that if left to
fill too much it overflowed into the pipe post-RSV. More specifically, a description of
the process at this stage is that the suction from the fan caused a turbulent formation of
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fluid (both water and air) at the bottom of the RSV. When filled to a certain amount this
turbulence causes some of the liquid to spill over into the pipe post-RSV. This amount
can be calculated as a function of the length of x, the diameter of the RSV and the time
it took to cause this turbulence. But it is not necessary as this does not occur in the
Leycroft System, i.e. there is a pump in situ of the drain that counter acts the pressure
difference. However, the variables of this function can predict that a decrease in x will
also decrease the time it takes to cause this turbulent overflow, hence it would happen
quicker the shorter x was. Indeed, it was observed to occur very quickly for x = 0.08m
and below. This may account for the observed liquid post-RSV, rather than a deficit in
the function of the RSV at x = 0.08m and below.
It was noticed in test 2.3 that there was no water at the extended part of the RSV (when
x decreased). This observation confirms that the RSV is a closed system at this point,
and that no water escapes through a gap at the interface. This ensures the tests are not
invalid due to a change in the RSV design. Also, it was noted that adjusting the length
of x whilst the fan was ON required considerably more force than with the fan OFF.
This is due to the attempted change in length increases the volume for a constant
pressure (set by the main turbine). The result of this is due to a tight fit of the RSV,
suggesting that the cut did indeed produce a close model to the original RSV, with no
decrease in pressure, and more importantly no gaps for the water escape from.
18.3.1 – Stream of Water
The observed stream of water pre-RSV suggests that the air flow does not carry 100%
of the water droplets. Some of the water that was sprayed into the pipe was carried
along to the RSV, at which point it separated in the normal manner. However, when the
stream of water made contact with the RSV fan, the quantity of water inside the RSV
dramatically increased. However, this did not change the operation of the RSV, as it
was still able to separate the phases. Absolutely, this is described to occur in the
Leycroft Turbo Air Sweeps System, see Appendix Turbo Air Sweeps Modelling URS
Version 0.2 – page 18. This describes “a continuous stream of water flowing into the
separator belly from the main ductwork – this was expected”. This stream is associated
with keeping the separator clean. For the model to also formulate this stream it
demonstrates an accurate simulation, and as such the results are more convincing.
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Student: W. Shipway
Figure 36. The droplets are dispersed in an angular formation.
18.4 – Boundary Layer and Surface Finish
Please refer to section 5.2.1 – Fluid Dynamics - Fluid Flow for the theory of a boundary
layer.
When the liquid comes into contact with the surface of the blades, it creates a boundary
layer of high shear stress, and will create a layer of liquid on the blades. Therefore it is
not necessary to consider the surface finish of the blades as part of the design, as the
blade will be covered with this boundary layer of liquid. However, as found by
experimentation, the liquid does not cover the inside of the RSV completely at any
instant in time, and hence the roughness of the inside should be considered. The extent
of the difference this will make is not known, and, it is also not known whether the
boundary layer will consist of only liquid or gas, or a mixture. Theoretically, if the
velocity is zero then by definition there would be no change. However, “high shear
stress” does not mean zero velocity, but “low” relative velocity. When the gas passes
over the liquid on the blades it may also affect the boundary layer.
18.5 – Applications of Newtonian Fluid Flow
It is shown that the principles of fluid dynamics do obey Newtonian Physics, and hence
could be used to predict the flow pattern and radial velocity for separation. However,
the flow pattern is not known, and would be subject to the quantity of air, water and
potato sucked in from the plenums, and is of course variable considering the
manufacturing technique. Therefore, it is not appropriate to model the RSV with
principles proposed by D. Bernoulli, Navier-Stoke, Rankine, and Reynolds, as the
θ
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practical variables are not known. As such there is no analytical correlation covering the
separation of phases in a vessel, but it was not found to be necessary for the project.
However it would have been excellent to measure the variables at the plenum and
develop an analytical technique.
Note: water and air obey Newtonian Fluid mechanics, i.e. the relationship is linear with
respect to rises in temperature and hence velocity and pressure. But the relationships of
a solid in a fluid flow are not known.
18.6 – Further Testing
To further test the system:- a) the flow rate would be increased to a proportionate value
of 2.3 l/min b) the application of a simplistic pressure drop with respect to the inside of
the pipe at the bottom of the RSV to remove the liquid would be needed, i.e. a pump.
This may validate or null test 2. c) the pipe inlet and outlet locations could be changed
to see the effects. d) the fan could be flipped so see if it makes a difference in the correct
orientation. e) smaller bend radii of pipe could be applied. f) two fans could be applied
to see if there are any effects on the operation.
19. CONCLUSIONS
The Rotary Spin Vane separator (RSV) is found to rely on the density of the
other phases (water/potato). The RSV fan turns the axial flow pattern into a
radial flow, and the liquid and solid particulate is thrown off by centrifugal
forces, whilst the air remains in this radial flow pattern. The liquid and
particulate then drain off the inner wall of the RSV.
The limit of the length of the pipe post-RSV has been experimentally found as
4m for the Leycroft System (taking into account the scale of the model). It is
hypothesised that this limit is due to the boundary layer associated with flow
through a pipe. However, the turbulent liquid at the bottom of the RSV may
have been the cause of the observed liquid.
The turbulent liquid in the bottom of the RSV was observed better in test 2. The
hole in the bottom of the RSV did not serve its purpose, as the negative pressure
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inside the RSV with respect to atmospheric cause a vacuum in the RSV, and as
such the liquid did not exit the system until the main turbine was switched off.
If pipes with bends were introduced, it is suggested that boundary separation
(and hence velocity flow losses) will not occur for a radius of curvature of 1.9m
for the Leycroft System.
By increasing the flow velocity the separation rate of liquid would increase, as
the centrifugal force acting tangential would increase. There is a limit to this on
the operation of the RSV however, as a high velocity would cause the liquid to
be taken off the inner wall and back into the stream further along the RSV body.
As the RSV is applied horizontally in the Leycroft System the inlet pipe can be
pulled out by approximately 154mm. This would decrease the overall length of
the system, but not by much comparatively. However, the fan is orientated
incorrectly in the Leycroft System, and as such any other system would need to
take into account the fan blades being 5 degrees less than the RSV slope, with
respect to the horizontal axis. This is to ensure the liquid and particulate does not
impinge on the slope of the RSV body.
The limit of the RSV body length is found experimentally to be 0.5m for the
Leycroft System. However, this limit may be subject to the turbulent flow in the
bottom of the RSV, as aforementioned
High shear stress at the interface between the blades and fluid/solid flow will
cause a boundary layer at the surface of the fan blades, and hence the surface
finish of the blades is insensitive to the RSV operation. However, the interface
of solid particulate and gas may disrupt the boundary layer, and so this surface
of liquid may not be constant.
The surface finish of the RSV body would cause a change in the separation rate,
due to the frictional coefficient. However, it is not known whether it would be
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Title: Leycroft RSV Simulation
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detrimental to the flow velocity, and indeed whether the change would be
noticeable.
If the blade angle was to shallow (to the horizontal axis) then it would not cause
enough centrifugal force, and so the liquid and solid would not separate from the
radial flow. Conversely, if the angle were too large, it would be detrimental to
the flow velocity, as it would act as a blockage.
The diametral ratio to length of the RSV body is found to be 2.2. Associated
with the above statement, if the diameter is too small then the radial flow pattern
would not sufficiently materialise, and the liquid/solid would not separate. Also,
the liquid would more easily return to the flow. If the diameter is too large then
the separated liquid may not impinge on the wall at a great velocity and hence
may return to the flow, particularly at the top most part of the RSV inner wall.
Note: all geometry stated assumes that the flow velocity and water separation rate is
linear. It is assumed that the solid particulate would separate from the radial flow easier
than the liquid proportionately to the respective increase in density. This is in following
with Newton’s 2nd
law of Motion.
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20. NONCLEMATURE
Symbol Description Units Section
PL Pressure, inside the Leycroft System N.A.
5.2
PF Pressure, behind the fan N.A.
5.2
P1 Pressure, of pipe for use in Bernoulli’s equation N.A. 5.2
P2 Pressure, of pipe for use in Bernoulli’s equation N.A. 5.2
V Velocity N.A. 5.2
V1 Velocity, of pipe for use in Bernoulli’s equation N.A. 5.2
V2 Velocity, of pipe for use in Bernoulli’s equation N.A. 5.2
h1 Height, of pipe with reference to a ground level N.A. 5.2
h2 Height, of pipe with reference to a ground level N.A. 5.2
ρ Density, of fluid N.A. 5.2
A1 Area, of the Leycroft System m2
18
A2 Area, of the model m2
18
x Length, of the RSV larger diameter m 17
y Length, of the pipe inside the RSV m 17
θ Angle, of droplet formation after the RSV degrees 18
Θ Angle, of RSV body slope degrees 16
d Diameter, outside of RSV body (model) mm 16
d1 Diameter, outside of pipe (model) mm 16
a Length, of opposite side of triangle mm 16
b Length, of adjacent side of triangle mm 16
c Length, of hypotenuse of triangle mm 16
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21. REFERENCES
[1], [17], [52] B. S. Massey, 1989, Mechanics of Fluids, 6th
Ed., Chapman & Hall, London
[2], [48] S. W. Yuan, 1970, Foundations of Fluid Mechanics, SI Unit Edition, Prentice Hall,
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[3], [49] R. J. Goldstein, 1983, Fluid Mechanics Measurements, Hemisphere, London
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[5] T. Schwenk, 1965, Sensitive Chaos, Rudolph Stiener, London
[6] S. Levy, 1999, Two Phase Flow in Complex Systems, Wiley & Sons, Chichester
[7] W. Schowalter, 1978, Mechanics of Non-Newtonian Fluids, Pergamon, Oxford
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[20] W. P. Jones, 1980, Air Conditioning Applications & Design, Edward Arnold, London
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[23] www.glossary.oilfield.slb.com/Display.cfm?Term=separator, Schlumberger Ltd., 2008
[24] www.glossary.oilfield.slb.com/Display.cfm?Term=two-phase%20separator, Schlumberger Ltd.,
2008
[25] www.foodprocessing-technology.com/contractors/separator/westfalia/, SPG Media Ltd., 2007
[26] www.munters.co.uk – See DS8000 series, and DV270, Munters AB, Sweden
[27] www.misteliminators.org/separators/index.html
[28] http://process- equipment.globalspec.com/LearnMore/Manufacturing_Process_Equipment
/Air_Quality/Scrubbers, GlobSpec., 2008
[29] http://en.wikipedia.org/wiki/Scrubber, last modified 10.02.2008
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Netherlands, 2008
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[34] www.scribd.com/doc/388135/Aerospace-systems, 2007
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Title: Leycroft RSV Simulation
Student: W. Shipway
[35] X. deFerrán, 1991, ISO Project, ESA Directorate for Scientific Programmes, ESTEC,
Noordwijk, Netherlands
[36] www.luwa.co.uk/luwa/product%20files/Waste%20Sep.html, LUWA (UK) Ltd.,
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[38] www.chemplast.co.uk/gas-liquid-separators/gas-liquid-separators.htm
[39] www.biotage.com/DynPage.aspx?id=25351
[40] http://products.ihs.com/bs-seo/gbm13_28.htm
[41] B. Kalis, 2004, We need a mist eliminator in that knockout drum! Can we add one without
overhauling the vessel?, Amistico
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[44] www.stereolithography.com/slainfo.php
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[50] H. Ito, 1959, Friction Factors for Turbulent flow in Curved Pipes, J. Basic Engng 81D
[51] H. Ito, 1960, Pressure Losses in Smooth Pipe Bends, J. Basic Engng 82D
[53] http://hyperphysics.phy-astr.gsu.edu/hbase/frict.html#rou, R Nave
[54] http://hyperphysics.phy-astr.gsu.edu/hbase/frict2.html, R Nave
[55] R. L. Childers, E. R. Jones, 1993, Contemporary College Physics, 2nd Ed, Addison-Wesley,
USA
[56] http://en.wikipedia.org/wiki/Factor_of_adhesion, last modified 03.03.2008
[57] http://en.wikipedia.org/wiki/Drag_%28physics%29, last modified 26.02.2008
[58] http://en.wikipedia.org/wiki/Coefficient_of_friction, last modified 27.02.2008
Discussions with:
Dr. Rajakaruna - Thermodynamics, contacted for applications of Fluid Dynamics
Mr A. Lees - Chartered Engineer, Mechanics and Design, Project Leader
Prof. Goman - Computational Methods for aerodynamics, contacted for applications of
CFD
22. APPENDIX
The Turbo Air Sweeps Modelling Specification is shown in the following pages.
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