Erosion impact on slurry pump behavior and productive life: An experimental and Numerical investigation

ABSTRACT Normally, the characteristics of the main parts of a slurry pump that may be suffer from erosion under two-phase flow circumstances have been extensively and thoroughly researched. Whereas, the effect of particle properties on pump behavior or performance has been the subject of several studies; however, the current research focused on various methods for reducing slurry erosion utilizing recent research methods. Thus, the analysis and investigation for various pressure distributions, velocity, erosion-rate, and vortex structure were carefully demonstrated in this study. In addition, the slurry pump’s wear or erosion characteristics were carefully examined, and it was found that as the flow rate increases, the wear of the suction surface worsens. As a result, the key findings of this research might offer the ideal guidance for optimum design and the right strategies for erosion protection for any slurry flow through centrifugal pumps.


Introduction
According to the principles of physics, a slurry pump is a type of centrifugal pump that raises the pressure of a combination of liquid and solid particles through a revolving impeller and transforms electrical energy into slurry potential and kinetic energy (Bulletin, 2005)., Additionally, centrifugal pumps typically cost less to run, own, and maintain than other types of pumps (Bachus & Custodio, 2003).Additionally, slurry is essentially a blend of liquids and solids, and its physical properties depend on a number of factors, including the size and distribution of the particles, the concentration of solids in the liquid, the amount of turbulence, the temperature, and the dynamic viscosity of the fluid flow.The presence of solid particles or slurry obviously reduces the head and efficiency of centrifugal pumps.Due to the solids impact, which reduces the clear water head and efficiency, choosing a pump's operating range is challenging.For instance, a few percent of the pump head curve reduction might result in significant changes to flow and efficiency (Kumar, 2017)., Additionally, the slurry flow centrifugal pump, which is widely employed in power plants, pumping stations, mines, and other fossil energy fields, might be categorized as vital equipment for conveying fluids.Given that the medium being conveyed is a two-phase solid-liquid flow, the wear characteristics and hydraulic performance of the slurry pump are key determining factors.As a result, numerous studies were conducted to enhance the performance of slurry pumps, including the following, Wang, Zhao, Zou, & Hu, 2012, who investigated how particle concentration affected slurry pump performance using the Eulerian multiphase model.They discovered that friction loss is mostly responsible for the decline in pump performance at high concentrations (Khalil, Kassab, Naby, & Azouz, 2013); it was tested how well the pumps performed when the fluid concentrations were varied.Also, it was discovered how the head reduction was affected by the solid concentration, specific gravity, and particle size.Through experimentation in (Kumar, Gandhi, & Mohapatra, 2014), the performance of the slurry pump was compared to the viscosity of the conveying fluid.The outcome showed that the head and efficiency of slurry pumps continuously drop as the viscosity of the conveying fluid declines.Duarte, de Souza, & dos Santos, 2015 examined the erosion feature of a two-phase flow of solids and liquids in an elbow.They demonstrated that when the particle concentration is higher than 20%, the growth efficiency of tube wall wear gradually declines as the particle concentration increases as a result of the buffer effect.The impact of particle size and solid concentration on the performance of slurry pumps operating was examined by (Salim, Bajawi, & Suhaibani, 2015) at various speeds.The results showed that as particle size, specific gravity, and solid concentration increase; the head and efficiency gradually decline while the input power steadily rises.
The effects of three different particle sizes on the functionality of slurry pumps using the sliding grid method was investigated in (Tarodiya & Gandhi, 2019).They discovered that particles with high specific gravities have just a minimal impact on the head and efficiency.Xiao et al., 2019 examined the impact of various fluid flow parameters on erosion by tracking particles in the Lagrangian frame.They discovered that differences in the geometry of the flow components are the primary cause of the flow characteristics and the kind of erosion (Peng, Huang, Zhou, Zhou, & Zhou, 2020).The Euler-Euler method was used to examine how well slurry pumps performed when subjected to varying particle concentrations and low flow rates.The outcome demonstrated that the internal flow field was unstable and local wear was severe when the slurry pump was operating under part-load flow conditions.In addition, the Newtonian glass bead-water (GBW) and non-Newtonian kaolin water (KW) slurry flows were used as the analysis medium in studying the impact of slip factor variations on the head of centrifugal pumps.The results showed that GBW experienced more severe slip factor degradation than KW (Abdolahnejad, Moghimi, & Derakhshan, 2021), under various particle concentrations, the pump's head and efficiency were examined experimentally.The drop in efficiency amplitude is greater than the reduction in head amplitude, according to the results, when the weight concentration of solid particles in the conveying fluid exceeds 40%.Optimization of the vane and blade geometry parameters of the slurry pump using the response surface methodology was explained by (Alawadhi, Alzuwayer, Mohammad, & Buhemdi, 2021).Also, (Tarodiya and Gandhi., 2021) integrated an erosion model to simulate the impeller and volute's wear and analyze the results.The outcome showed that variations in flow rate and solid particle size were mostly responsible for the increased erosion zone and rate of removal of surface material (Wang et al., 2021); based on a CFD-DEM coupling algorithm, the effect of particle migration characteristics on the flow and wear of the pump was investigated; they discovered that increasing particle diameter increases the intensity and scale of the vortex.

Experimental work
Complete experimental setup of the test rig which used to evaluate the main performance parameters of centrifugal pump with slurry flow is illustrated in Figure 1.It comprises of an open circuit test loop with a 3 inch pipe diameter.Additionally, an appropriate functioning gate valve that is situated close to the pump's delivery flange allows for a wide range of flow rate adjustment.Moreover, slurry entering the delivery line first passes via a graded measurement tank, then to the mixing tank through a pipe equipped with a ball valve.The measuring tank about 300 liters which is provided with a graduated 2 inches Plexiglas transparent pipe to indicate slurry level in it.The rise in the level of slurry in the measuring tank could therefore be measured over a lengthy period of time with an accuracy of (±1 mm) to determine the flow rate.On the other hand, two calibrated bourdon-type pressure gauges with an accuracy of (±0.025 kg f /cm 2 ) are used to measure the suction and delivery heads of the pump.In addition, the two pressure gauges are positioned at the same level.In contrast, a D.C. swinging motor with variable speed (5 HP) is directly attached to the pump.A tachometer is used to measure the motor speed, with an error measurement of (±2%).Moreover, using a calibrated torque meter with a (±2%) error reading, the torque applied to the pump is determined.Now, after the completion of the tests for pump with clear water, a pre-calculated amount of solid material for a predetermined solid concentration was slowly added to the water in the maxing tank with the stirrer and pump in operation.The slurry was kept in circulation in the test loop for approximately (15) minutes for through mixing before starting any measurements.Finally, the slurry flow material used is coarse sand glass material, where its grain size is about 350 micron.The sieve analysis of dry test sample is made before experimental work procedures.The average particle size distribution of sand glass and the physical properties are as follows: (distribution parameter (Z = d85/d15), where (d85=> 0.645 mm) and (d15=> 0.228 mm) are the sieve diameters for which (85%) and (15%) of the particles are passed, respectively.So, Z = d85/d15 = 2.83 < 10 i.e it defines narrow size distribution, while values larges than (10) denotes broad grading.Therefore, the sand glass have narrow size distribution of Properties of the solid material used.

Hydraulic parameters evaluation
For all types of water and slurry flow, a full range of data were taken at various discharge values, from shutoff to fully open delivery valve.However, to ascertain hydraulic performance under various circumstances, flow rate, suction and delivery pressure heads, power consumption, and overall efficiency are measured and computed.Plots of the (H-Q), (η-Q), and (P-Q) curves are also used to demonstrate the impact of pump performance on both water and slurry flow, as illustrated in Figures 2 & 3 and 4, respectively, at 1500 rpm.
• Thus, 0.5% concentration of slurry was selected for comparing with behavior of water flow.• From the efficiency comparison curve for water and slurry flow at 1500 rpm, it could be noticed the following aspects: (a) The efficiency values of water flow is higher than the values of slurry flow.Thus, because that the slurry flow as usual, facing more resistance in movement and transmitting.(b) The efficiency reduces by 10% when using water with slurry at the point 0f 10 L/s flow and 1500 rpm.
-From the power comparison curve for water and 0.5% concentration slurry flow at 1500 rpm, we achieved that: (a) The measured power is increased by 5% at same point i.e. for the same value of Q.(b) Whereas, the power at low speed has a higher deviation between the water and slurry flow due to the blocking effect of slurry at the low values of the flow while, the resistance of flow transmitting is increased.

Modeling formulation
Fluent Discrete Phase Model (DPM) is used to investigate slurry flow in a centrifugal pump model field.Two-way coupling for mixing the liquid and solid phases is considered; this means that the effect in both directions between the carrier and the particles.The coupled manner is used to solve the particle trajectory and carrier phase equations.The coupling is obtained by the momentum exchange between the phases.On the other hand, including a source term in the carrier phase momentum equation has an effect on the coupling.Following equation give the particle momentum exchange.Where: Fdrag The drag force per unit mass of particle m.pThe mass flow rate of the particle Ñt The time step Saffman's lift force can also be included in the exchange term after the drag force.For every solved computation of the continuous phase flow field, this momentum exchange turns out to be a momentum sink in the balance of continuous phase momentum.The carrier phase equations are changed to the nondimensional form shown below.
Where Fy and Fx the momentum exchange term as nondimensional components.
u and v non dimensional velocity component of carriers phase.
P pressure of the fluid ρ density of the fluid μr viscosity of the fluid Re reynolds number Thus, the slurry flow governing equations and Lagrangian-Eulerian approach with using DPM are investigated mathematically by two-way coupling.SIMPLE algorithm is applied to solve the governing equations for the DPM slurry flow.First order upwinding and Standard k -e model are used for modeling turbulence and discretization, respectively.For the flow equations of the carrier phase, the particle trajectory equation is determined twice per 20 iterations.For flow equations, the residual convergence of the carrier and discrete phase equations is 106 with first order up-winding.A first order up-winding in momentum and pressure-velocity coupling SIMPLE algorithm is used with turbulence dissipation rate and kinetic energy.There is an automatic mesh using ANSYS mesh modeler with cell size 1 mm to generate number of nodes 1,120,000.Also, fluent under ANSYS R20 is used to solve the model.

Numerical results
The centrifugal pump's performance is monitored by observing the pressure and velocity distribution for the centrifugal pump model field.On the other hand, the effect of slurry on the pressure, velocity and erosion rate is observed using the discrete phase model contour for the previous parameters.Moreover, validation of the numerical model is carried out by comparing the experimental and numerical performance curve of the centrifugal pump.The following Figure 5 demonstrates the change of the velocity distribution with and without using slurry in the fluid entering the model.The velocity distribution of the fluid has a normal gradient from the inlet to the outlet plane, and the value of the velocities remains constant at the fixed layer in the fluid field.Deformation of the gradient and distribution for the velocity field is observed when the slurry enters the fluid field of the pump model.As an example to show the deformation in the velocity distribution, a histogram of the velocity distribution in the impeller outlet face is presented in Figure 6.The histogram shows that the distribution of the velocity around the face that the flow leave the impeller is completely changed due to using slurry because of changing in the density of the mixed flow after slurry add to the water.Now, changing in the fluid properties of the inlet condition during add slurry to the water also effect on the pressure distribution around the fluid field of the pump model.Figure 7 shows that the pressure is decreased at all boundary of the fluid field.As an example, the static pressure is decreased from 18 to 16.5 psi with and without slurry, respectively.Using slurry also has an important effect on the metal erosion rate as mentioned above.The model that constructed with 1% slurry added to the water estimate the rate of erosion around the wall of the pump model.Figure 8 presents that the erosion occurs at the wall boundary of the impeller.At the impeller inlet, the erosion rate is observed at the suction side of the blade tip with value reached to 0.09 gm/m2.s.Also, the erosion is clearly showed at the volute case wall in Figure 9 with rate of 0.01 gm/m2.s.

Conclusions & recommendations
The current work uses both computational and experimental methods to demonstrate the impact of slurry flow on a centrifugal pump's performance.Furthermore, the laboratory test rig is constructed to use the slurry inter to the pump with maximum diameter of slurry reach 1 mm.On the other hand, the main results showed that the hydraulic head is reduced by 23.48% at the point of 10 L/s flow but it is reduced by 22.47% as average value for all points or Q values.Moreover, the results showed that the efficiency is reduced by 5% at the point of 10 L/s flow.Whereas, the power especially at the low values of flow has a high reducing effect due to the blocking of the particles.A complete three-dimension model with discreet phase is simulated using CFD software to present the effect of the water, which carry the particles, on the performance and erosion rate of the domain surfaces that reached the maximum value of 0.09 gm/m 2 .s.Then, It's urgent to state some important issues to be recommended as follows: 1. Normally, to decrease erosion rate as possible it's so urgent: • To decrease the slurry particle sizes (decreasing particle diameter) for decreasing the intensity and scale of the vortex, then decreasing erosion rate as possible.

Figure 1 .
Figure 1.Test rig setup for evaluating water and slurry pump performance.

Figure 2 .
Figure 2. (H-Q)exp.Comparison curve for water and of slurry flow with different concentrations.
(a) The values of H increased with decreasing of Concentration values of Slurry so, H is inversely proportional to slurry concentration, therefore, H water values are greater than all slurry concentrations.(b) The 0.5% concentration slurry flow is closed to water (H-Q) curve because of the almost equal

Figure 3 .
Figure 3. Power curve comparison of water and 0.5% concentration slurry flow at 1500 rpm.

Figure 4 .
Figure 4. Efficiency curve comparison for water and 0.5% concentration slurry flow at 1500 rpm.

Figure 5 .
Figure 5.The velocity contours for operating point and 0.5% concentration slurry flow at 1500 rpm.

Figure 6 .
Figure 6.Histogram of the velocity distribution at impeller outlet for operating point and 0.5% concentration slurry flow at 1500 rpm.

Figure 7 .
Figure 7. Distribution of static pressure contours for operating point and 0.5% % concentration slurry flow at 1500 rpm.
WATER SCIENCE• power especially, must be at the low values of flow has a high reducing effect due to the blocking of the particles 2. Research on the centrifugal slurry pump's performance characteristics under cavitation and non-cavitation circumstances at varied pump speeds is urgently needed.3.Experimental and Numerical Investigation ofSlip Factor Reduction in Centrifugal Slurry Pump have to be studied clearly.Comparison between different erosion studies such as studying the effect of fine, medium, and large size of slurry flow grains on pump hydraulic performance and various pumping operation conditions must be investigated.