416018-1R0 Oil-Water Sampling Mixer (002)

ALDEN Solving Flow Problems Since 1894
ALDEN Research Laboratory, Inc.
30 Shrewsbury Street
Holden, MA 01520
ALDEN Solving Flow Problems Since 1894
ALDEN Research Laboratory, Inc.
30 Shrewsbury Street
Holden, MA 01520
COMPUTATIONAL ANALYSIS OF
WESTFALL’S 2800 SINGLE AND DUPLEX MIXER
FOR SAMPLING FROM OIL PIPELINE CONTAINING
WATER
Alden Report No:
416018-1R0
By:
Kimbal Hall, PE
Submitted to:
Bob Glanville
Westfall Manufacturing Co.
15 Broad Common Road
Bristol, RI 02809-2721
Issued on:
April 25, 2016

Kimbal Hall, PE
Phone: (508)829-6000 x6486
Email: khall@aldenlab.com
Westfall’s 2800 Single / Duplex Mixer
Oil / Water Pipeline Sampling Mixer
COMPUTATIONAL MODEL
ALDEN
416018-1R0
REPORT
Page 2 of 11
2
Table of Contents
Introduction.........................................................................................................................................................3
Model Description ...............................................................................................................................................3
Results..................................................................................................................................................................7
List of Figures
Figure 1: Water Concentration at the Pipe Wall Between the Flow Model Inlet and the Single 2800 Mixer
..............................................................................................................................................................................4
Figure 2: Single 2800 Mixer (top) and Duplex Mixer (bottom) ......................................................................5
Figure 3: CoV of Water in Oil.............................................................................................................................8
Figure 4: Range of Water Concentrations at Various Locations Downstream of the Mixer ..........................8
Figure 5: Contours of Water Volume Fraction at 2 Diameter Increments....................................................10
Figure 6: Pathlines colored by Water Volume Fraction ..................................................................................11
List of Tables
Table 1 CFD Solver Information ........................................................................................................................3
Table 2: Process Flow Information....................................................................................................................4
Table 3: Pressure Loss Results...........................................................................................................................7
Table 4: Minimum and Maximum Water Fractions and Water CoV ...............................................................9

Kimbal Hall, PE
Phone: (508)829-6000 x6486
COMPUTATIONAL MODEL
ALDEN
416018-1R0
REPORT
Page 3 of 11
3
Introduction
Alden Research Laboratory Inc. (Alden) was contracted by Westfall Manufacturing Inc. (Westfall) to
analyze the level of mixing and head loss that can be expected from installing a single 2800 mixer or a
duplex mixer in a oil pipeline with up to 0.6% vol water.
The objective of the mixer is to create a homogenous oil/water mixture downstream of the mixer so that a
sample can be taken from a single point, which will be representative of the oil/water mixture in the
pipeline.
Model Description
The computational model geometry was developed using the commercially available three-dimensional
CAD and mesh generation software, GAMBIT V2.4.6. The computational domains generated for the
model consisted of approximately 7 million tetrahedral and hexahedral cells.
Alden used the CFD software package ANSYS-Fluent v15.0 to calculate the full-scale, three-dimensional,
incompressible, turbulent flow through the pipe and mixer. A stochastic, two-equation realizable k-
model was used to simulate the turbulence. Detailed descriptions of the physical models employed in
each of the Fluent modules are available from ANSYS-Fluent. CFD solver information is presented in
Table 1.
Table 1 CFD Solver Information
The flow model consisted of a stratified oil/water mixture flowing in a 36” diameter pipeline. The total
liquid flow rate was set at 400 MBD, which equates to an average velocity of 3.68 ft/s (Table 2).
Water, being denser than oil, was introduced at the bottom of the pipe such that the total volume fraction
of water in the pipeline was 0.59%. The mixer was placed 10 pipe diameters downstream of the model
inlet (Figure 1).

Kimbal Hall, PE
Phone: (508)829-6000 x6486
COMPUTATIONAL MODEL
ALDEN
416018-1R0
REPORT
Page 4 of 11
4
Table 2: Process Flow Information
Figure 1: Water Concentration at the Pipe Wall Between the Flow Model Inlet and the
Single 2800 Mixer

Kimbal Hall, PE
Phone: (508)829-6000 x6486
COMPUTATIONAL MODEL
ALDEN
416018-1R0
REPORT
Page 5 of 11
5
Two mixer designs were considered. First, the single 0.8 Beta 2800 mixer was investigated as shown in
Figure 2. Next, a duplex mixer was considered, which consists of two mixers that are separated by 2 pipe
diameters, and offset by 90°.
Figure 2: Single 2800 Mixer (top) and Duplex Mixer (bottom)
The flow model extends for 20 pipe diameters downstream of the mixer, so that the coefficient of
variation (CoV) of water in the oil can be calculated over a range of downstream distances.

Kimbal Hall, PE
Phone: (508)829-6000 x6486
COMPUTATIONAL MODEL
ALDEN
416018-1R0
REPORT
Page 6 of 11
6
Oil and water are immiscible. Instead of mixing into a solution, they are always separated by an
interfacial layer. If left to sit with minimal shear stress, the oil and water will collect into stratified layers.
When shear stress is applied to the interfacial layer, the water and oil will break up into smaller drops – in
this case water drops within the continuous oil phase. The shear needs to be high enough to overcome
the surface tension forces around the water droplets, which increase as the droplet gets smaller and the
radius of curvature of the droplet shrinks. With modest amounts of shear, the water will break into
droplets that are fine enough that a macroemulsion is formed, where the water droplets have diameters
on the order of microns, and are dispersed throughout the oil – this is the goal of the mixer.
Without any stabilizing agent such as a surfactant, and when kinetic energy is no longer applied through
agitation, the emulsion will return to its stratified state through coalescence of water droplets as they
bump into each other. This process generally takes place over a period of minutes, which is much longer
than the residence time between the mixer and the sampling port. As such, coalescence is neglected in the
flow model
The CFD model is made up of cells with a length scale of approximately 0.5-inches, so the water droplets
are much smaller than the size of the cells. The size disparity between the water droplets and the
computational cells is such that surface tension forces are not important for the bulk mixing of the fluids,
and are not included in the flow model. Since the two fluids are immiscible, the binary mass diffusivity of
water in oil was set to zero.

Kimbal Hall, PE
Phone: (508)829-6000 x6486
COMPUTATIONAL MODEL
ALDEN
416018-1R0
REPORT
Page 7 of 11
7
Results
The coefficient of variation (CoV) was measured at 1 diameter increments downstream of both the single
2800 mixer and the duplex mixer for a total length of 20 diameters (Figure 3, Table 4).
CoV is a measure of uniformity, which is measured as the standard deviation of the concentration across
the pipeline at a given plate, divided by the average concentration. A CoV of zero indicates that the flow is
perfectly mixed.
Another useful measure for a sampling mixer is the range of water concentrations in the pipeline that
could be taken from the sample port. To address this question, the minimum and maximum water
volume fraction was also reported at 1 diameter increments downstream of the mixer, and is presented in
Figure 3, and Table 4. In the plot, the shaded area between the minimum and maximum curves indicates
the range of concentrations that could be measured at a sample location a given distance downstream of
the mixer.
The mixers also incur some pressure loss in the pipeline. The pressure loss for the 400 MBL case is
calculated for each mixer, along with a k-value that can be used to calculate the pressure loss at any other
flow rate using the following equation in consistent units:
Where:
P = pressure
ρ = fluid density
V = average fluid velocity in the pipeline
The pressure loss and mixer k-value is presented below in Table 3.
Table 3: Pressure Loss Results
The duplex mixer mixes better than the single mixer, but at the cost of a higher pressure loss. Both mixers
reach CoV values below 0.05 within 12 diameters of the mixer outlet.
For best results, the sampling location for both mixers should be placed approximately 10 pipe diameters
downstream of the mixer.
Contours of water volume fraction and pathlines of flow through the mixer are included in Figure 5 and
Figure 6 respectively.

Kimbal Hall, PE
Phone: (508)829-6000 x6486
COMPUTATIONAL MODEL
ALDEN
416018-1R0
REPORT
Page 8 of 11
8
Figure 3: CoV of Water in Oil
Figure 4: Range of Water Concentrations at Various Locations Downstream of the Mixer

Kimbal Hall, PE
Phone: (508)829-6000 x6486
COMPUTATIONAL MODEL
ALDEN
416018-1R0
REPORT
Page 9 of 11
9
Table 4: Minimum and Maximum Water Fractions and Water CoV

Kimbal Hall, PE
Phone: (508)829-6000 x6486
COMPUTATIONAL MODEL
ALDEN
416018-1R0
REPORT
Page 10 of 11
10
Figure 5: Contours of Water Volume Fraction at 2 Diameter Increments
for Single 2800 Mixer (top) and Duplex Mixer (bottom)

Kimbal Hall, PE
Phone: (508)829-6000 x6486
COMPUTATIONAL MODEL
ALDEN
416018-1R0
REPORT
Page 11 of 11
11
Figure 6: Pathlines colored by Water Volume Fraction
for Single 2800 Mixer (top) and Duplex Mixer (bottom)

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