ICWES15 - The Study of two Phase Flow Wall Erosion using a Generalized Computational Fluid dynamics Prediction Model. Presented by Ms Dorina Ionescu, Johannesburg, SAfrica

THE STUDY OF TWO PHASE FLOW WALL EROSION

USING A GENERALIZED COMPUTATIONAL FLUID

DYNAMIC MODEL

Dorina Ionescu

Department of Mechanical Engineering Technology

Faulty of Engineering; South Africa

WALL EROSION THEORY

According to Mazumder et al (2004) and (2003)

1. Solid particle erosion is the mechanical process by which material is removed from a solid surface due to the impact of small solid particles on the metal surface.

• For ductile materials, erosion is caused by localized plastic strain and fatigue in the metal surface.

• In brittle materials the impact of solid particles can cause surface cracks and chipping of micro-size metal pieces.

2. Among all the various factors, the particle impact velocity has the greatest influence in erosion.

15th International Conference for Women Engineers and Scientists

GENERALIZED EROSION PREDICTION MODELS

Most of the erosion prediction models are based on empirical

data and can only be applied to operating conditions that are

similar to the experimental conditions, and cannot be generalized

to other flow condition.

1. The CFD based erosion models, take into account details of the flow effect and pipe geometry.

2. For dilute phase loading of less than 10% particles interactions can be neglected and a single phase model can be used to represent the mixture.

1. The multiphase modelling in the present research was done through Discrete Phase Model (DPM), sub-modelling capability Erosion / Accretion


RELATION BETWEEN EROSION, PRESSURE DROP AND BEND GEOMETRY

1. The effects of a bend in a pneumatic conveying pipeline are twofold:

• it causes a loss of energy which results in an additional pressure drop;

• can cause product attrition or pipeline wear, or both.

2. The research work done in the field resulted in conflicting conclusions:

• Marcus et al (1984) stated that the short radius bends cause the least pressure drop,

• Mills & Mason (1985) find short radius bends better in some circumstances while long radius bends were better in other.

• In the research conducted at the University of Johannesburg it was observed that bends with a larger radius induce less pressure drop and wall erosion, than the bends with a shorter radius.

• However for large radius bends there are two maximum erosion areas and only one for the short radius bends.


EROSION PREDICTION

Reference volumes 1. The CFD reference volume shown in figures 1 and 2 were generated from

a horizontal 50 mm internal diameter pipe volume for a length of 800 mm, followed by the bend and a short vertical portion of 200 mm after the bend.

Fig. 1 - Volume 1 Fig. 2 – Volume 3

vertical upward bend R/D = 2,5 vertical downward bend R/D = 2,5

R= bens radiusD= pipe diameter


EROSION PREDICTION

2. The CFD reference volume shown in figures 3 and 4 were generated from a horizontal 50 mm internal diameter pipe volume for a length of 800 mm, followed by the bend and a short vertical portion of 200 mm after the bend.


vertical upward bend R/D = 5 vertical downward bend R/D

= 5


Location of maximum pipe erosion in bends with a R/D ratio of 2,5

1. In the present study, according to the CFD modelling the erosion in the elbow is more significant for a vertical upward bend than for a vertical downward, (contrary to Deng et al-2005) conclusion.

2. Figures 5 and 6 show a detail of the maximum erosion and the points where it occurs, (volumes 1 and 3).


vertical upward bend R/D = 2, 5 vertical downward bend R/D = 2, 5


Maximum erosion of 4,36e- 07 kg/m2 -ssituated at 420 from the material entrance

Maximum erosion of 2,69e - 07 kg/m2 -s situated at 420 from the material entrance

Location of maximum pipe erosion in bends with a R/D ratio of 5

3. Figures 7 shows a detail of the maximum erosion and the points where it occurs, (volume 2).

Fig. 7 - Volume 2 vertical upward bend R/D = 5


Maximum erosion of 3,61e – 07 kg/m2 - s situated at 350 and 750 from the material entrance in the bend

Location of maximum pipe erosion in bends with a R/D ratio of 5

4. Figures 8 shows a detail of the maximum erosion and the points where it occurs, (volume 4).

Fig. 8 - Volume 4 vertical downward bend R/D = 5


Maximum erosion of 2,21e – 07 kg/m2-s situated at 400 and 850 from the material entrance in the bend

EROSION REDUCTION - UNIVERSITY OF JOHANNESBURG RESEARCH

1. To reduce the wall erosion in the bend via flow velocity control, the reference volumes were modified by subtracting a spiral shaped volume of 1,5 turns , rectangular cross section of 12 mm depth x 10 mm width and a pitch of 100 mm. The starting point of the spiral shaped volume is at 600 mm from the beginning of the horizontal section, and ends at 750 mm along the horizontal.

2. Four modified volumes were created i.e. Volume 1-S, Volume 2-S, Volume 3-S and Volume 4-S.

3. The maximum velocities recorded were as follows:


Control volumes Modified volumes

Velocity decrease in modified volumes as compared to the reference volumes

Volume 1 = 32, 8 m/s;

Volume 2 = 30, 1 m/s;

Volume 3 = 32, 5 m/s;

Volume 4 = 30, 1 m/s;

Volume 1 - S = 28,6 m/s;

Volume 2 - S = 28,3 m/s;

Volume 3 - S = 28,8 m/s;

Volume 4 – S = 28,5 m/s;

12,8 % (R/D=2,5)

6,0 % (R/D=5)

11,4 % (R/D=2,5)

5,3 % (R/D=5)


Figure 9 shows the velocity path lines defined by velocity magnitude in the

bend area for the modified volumes.

Volume 1-S, Bend velocity 2,86e + 01 m/s Volume 2-S, Bend velocity 2,83e + 01m/s

Volume 3-S, Bend velocity 2,88e + 01 m/s Volume 4-S, Bend velocity 2,85e + 01 m/s

Fig. 9 – Velocity path lines defined by velocity magnitude in the modified volumes


Wall erosion reduction in the Modified volumes due to velocity decrease

1. Figure 10 shows the maximum and average erosion values, in the modified volume 1 - S.

Fig. 10 - Volume 1-S - DPM Erosion (auto range) horizontal / vertical upward bend, R/D = 2, 5


Volume 1-S: Average erosion 1, 49 e - 07 kg/m2 - s

Volume 1-S: Maximum erosion 2, 71e - 07 kg/m2 - s



Fig. 11 - Volume 3 - S - DPM Erosion (auto range) horizontal / vertical downward bend, R/D = 2,5


Volume 3-S: Maximum erosion 2, 71e - 07 kg/m2-s

Volume 3-S: Average erosion 1, 22e - 07 kg/m2 - s



Fig. 12 - Volume 2-S - DPM Erosion (auto range) horizontal / vertical upward bend, R/D =5





4. Figure 13 shows the maximum and average erosion values, in the modified volume 4- S.

Fig. 13 - Volume 4-S - DPM Erosion (auto range) horizontal / vertical upward bend, R/D = 5




Calculation of mass loss through erosion and the installation life expectancy1. The erosion area considered was half the pipe circumference

(0, 0785 m) multiplied by 1/3 of the bend length (0, 0783 m), resulting in an erosion area of approximately 6, 146 x 10-3 m2.

2. The pipe wall thickness was 3,91 mm.

3. The mass loss for reference volumes was calculated using the maximum erosion values recorded.

4. As the maximum erosion points in the modified volumes (1-S, 2-S, 3-S and 4-S) are very few, the mass los was calculated using the average erosion values.

5. The life expectancy was calculated considering that the installation is fully operational for 4 hours per day.


Calculation of mass loss through erosion and the installation life expectancy

6. Tables 1 lists the values for the reference volumes 1, 2, 3 and 4

Table 1


Volume 1 Volume 2 Volume 3 Volume 4

Overall static pressure

17,08 kPa 17,34 kPa 17,56 kPa 17,765kPa

Maximum velocity 32,8 m /s 30,1 m /s 32,5 m /s 30,1 m /s

Maximum mass loss through erosion

4,36 x 10-7

[kg/m2 – s]

3,61 x 10-7

[kg/m2 – s]

2,69 x 10-7

[kg/m2 – s]

2,21 x 10-7

[kg/m2 – s]

Installation life expectancy

30 days 36,3 days 49 days 59,3 days

Calculation of mass loss through erosion and the installation life expectancy

7. Tables 2 lists the values for the modified volumes 1 - S, 2 - S, 3 - S and 4 - S

Table 2


Volume 1-S Volume 2-S Volume 3-S Volume 4-S

Overall static pressure 22,5 kPa 28,4 kPa 29,1 kPa 28,6 kPa

Maximum velocity 28, 6 m/s 28, 3 m/s 28, 8 m/s 28, 5 m/s

Maximum mass loss through erosion

1, 49 x 10-7

[kg/m2 – s]

0, 906 x 10-7

[kg/m2 – s]

1, 22 x 10-7

[kg/m2 – s]

1, 17 x 10-7

[kg/m2 – s]

Installation life expectancy

88 days 144, 7 days 107,4 days 112 days

Installation life expectancy increase compared to control volumes

293 % 399 % 219 % 189 %

CONCLUSIONS

1. The DPM modelling of the reference volumes show a heavy erosion concentrated on a well defined area in the bend. This will result in complete penetration after a minimum of 30 days (120 hours) for volume 1 and a maximum of 59,3 days (237 hours) for volume 4.

2. The modified volumes show a dramatic increase of installation life expectancy ranging from a minimum of 88 days (325 hours) for volume 1-S to a maximum of 112 days (578, 8 hours) for volume 2-S.

3. All volumes showed a sever pressure drop ranging from 17,08 kPa for volume 1 to a maximum of 29, 1 kPa for volume 3-S.

4. For all volumes the particle velocities are within comparable values all being above saltation velocity.

5. Careful consideration should be given to the pressure drop as there is the risk of pipe clogging.


ICWES15 - The Study of two Phase Flow Wall Erosion using a Generalized Computational Fluid dynamics Prediction Model. Presented by Ms Dorina Ionescu, Johannesburg, SAfrica

Technology

erosion models

maximum erosion areas

solid particle erosion

scientistsmaximum erosion

wall erosion theory

erosion reduction university

phase flow wall erosion

vertical downwardbend