Pump Inlet Pressure Research Articles

Effect of different startup modes on the cavitation performance in Rotary lobe pump

This present paper therefore used the dynamic mesh of FLUENT, RNG k-ε turbulence model and Z-wart-Gerber-Belamri cavitation model are used to simulate a rotary lobe pump with unsteady method. Meanwhile the instantaneous flow field distribution and its internal cavitation of rotary lobe pump are analyzed. We also gave the judgment of incipient cavitation. At the same time the cavitation area and the inlet pressure of the lobe pump are determined under the conditions of incipient cavitation, critical cavitation, developing cavitation and complete cavitation. The results show that the bubble occurs firstly in the rotor meshing of the suction cavity, and with the rotation of the rotor, the cavitation is brought into the adjacent transition region, forming the attached cavitation bubble. In different linear startup modes, it can be seen that with the increase of rotational speed, it is easier to form a local low-pressure region at the meshing gaps between two rotors and the pump cavity. When the startup time is 0.1s, the diffusion of the low-pressure region of the inlet section is effectively suppressed, so the volume of the bubble is obviously reduced. Moreover, the critical NPSHc of the lobe pump is 3.59m and the critical cavitation point flow rate is 20.85m3/h, which is in good agreement with the experimental data.

Model Predictive Control with Adaptive Strategy Applied to an Electric Submersible Pump in a Subsea Environment

An automatic control of Electric Submersible Pumps (ESPs), employed for artificial lift oil production, is desired in order to ensure safe operation while satisfying pump and well constraints. In this context, the use of an advanced control strategy, such as model predictive control (MPC), can be beneficial in order to deal with the process constraints, variables coupling and optimal operation. In this paper, a linear MPC strategy was applied to an ESP model in order to keep the pump inlet pressure in a desired reference value, minimizing the pump power and respecting the variables constraints. Model adaptation based on homotopic transition between models was proposed for plant nonlinear response regions broadening the range of control.

Erosion-corrosion effect of nanocoolant on actual car water pump

In automobile cooling system, water and ethylene glycol are usually used as coolant. For many years, nanofluid has been reported to enhance thermal properties of conventional heat transfer fluid due to dispersion of solid particles which exhibit superior thermal conductivity. Many past researchers found improvement of heat transfer rate in automobile cooling system by using nanofluid as coolant. However, there are very few reported on drawback such as tribological impact on components in automobile cooling system. Hence, this paper focused to determine erosion-corrosion effect of nanofluid on aluminium impeller in Perodua Kancil D37 water pump. Working parameters such as inlet pressure, coolant temperature and rpm of pump were in line with ASTM D2809-09 standard. Testing coolants were made up of corrosive water, ethylene glycol and graphene nanoplatelets. Each pump surface profile was inspected using 3D imaging microscope after undergoing 100 hours of testing continuously. Also, precise weight measurement was carried out before and after testing to determine total material loss. It was observed that corrosion effect was about the same for both base coolant and nanocoolant. Erosion-corrosion effect increased material loss when nanocoolant was used instead of base coolant. Based on ASTM 2809-09 standard, erosion-corrosion damage on impeller was found to be minimal and scored high rating in evaluation. Thus, both coolants can be considered to be incorporated in future cooling system.

Transient temperature and pressure calculation model of a wellbore for dual gradient drilling

During deep-water oil and gas explorations, the dual gradient drilling (DGD) technology provides solutions to problems caused by the narrow density window and the shallow gas by controlling the pressure profile in the wellbore. A transient temperature calculation model is established with consideration of the heat generated by the pump in the specific processes of the DGD systems. Besides, the momentum equation is modified by considering the lift force of the pump on the drilling mud in the pressure calculation. An iterative scheme for the coupled temperature and pressure calculations is developed. Besides, the transient temperature and pressure are analyzed for a deep-water well in South Sea. It is shown that the bottom-hole pressure varies significantly with the transient temperature in the wellbore, and the change of the bottom-hole pressure in the case of the DGD (626 kPa) is larger than that in case of the conventional drilling (115 kPa) due to the constant inlet pressure of the subsea pump. With this fact in mind, an adequate safety margin is strongly recommended to be considered during the hydraulic parameter design of the DGD. Our results further show that the DGD can significantly extend the operation range of the drilling fluid density, and the advantage becomes more obvious in a deep water.

Performance Analysis of Transcritical Carbon Dioxide Rankine Cycle with Regenerator

Transcritical carbon dioxide Rankine cycle (TCRC) has a potential to convert low grade heat source into power. Thus, the objective of this paper is to evaluate TCRC performance based on the first and the second law of thermodynamics for wide and different operating conditions. To address this, TCRC thermal efficiency, exergetic efficiency, utilization ratio and the exergy destruction of the components are analyzed parametrically. Engineering Equation Solver (EES) is used to solve the set of equations and to evaluate the working fluid properties at the given conditions. For the analysis compressor efficiency, turbine efficiency and effectiveness of the regenerator are assumed to be 0.9, 0.9 and 0.95, respectively. The pump inlet pressure was assumed to be 6.2 MPa. It is found that at 10 MPa turbine inlet pressure 240°C is the optimal turbine inlet temperature operating condition. The percentage of exergy destructions at 240°C turbine inlet temperature are 0.94, 4.53, 9.55, 41.23, and 43.74 by the pump, turbine, condenser, heater and regenerator, respectively. Hence, the highest and the smallest exergy destructions are in the regenerator and the pump. This study will help to select the potential component for further improvement.

A Novel Multi-objective Physiological Control System for Rotary Left Ventricular Assist Devices.

Various control and monitoring algorithms have been proposed to improve the left-ventricular assist device (LVAD) therapy by reducing the still-occurring adverse events. We developed a novel multi-objective physiological control system that relies on the pump inlet pressure (PIP). Signal-processing algorithms have been implemented to extract the required features from the PIP. These features then serve for meeting various objectives: pump flow adaptation to the perfusion requirements, aortic valve opening for a predefined time, augmentation of the aortic pulse pressure, and monitoring of the LV pre- and afterload conditions as well as the cardiac rhythm. Controllers were also implemented to ensure a safe operation and prevent LV suction, overload, and pump backflow. The performance of the control system was evaluated in vitro, under preload, afterload and contractility variations. The pump flow adapted in a physiological manner, following the preload changes, while the aortic pulse pressure yielded a threefold increase compared to a constant-speed operation. The status of the aortic valve was detected with an overall accuracy of 86% and was controlled as desired. The proposed system showed its potential for a safe physiological response to varying perfusion requirements that reduces the risk of myocardial atrophy and offers important hemodynamic indices for patient monitoring during LVAD therapy.

Application of the semi-analytical cavitation model to flows in a centrifugal pump

Visualization experiments are carried out to investigate the cavitating flows in a centrifugal pump at different flow rates. The cavity lengths under different pump inlet pressure are obtained. The semi-analytical cavitation model is improved since it is not suitable for predicting large cavities full of vapor. The improved cavitation model is used to numerically study the steady and rotating cavitation in the centrifugal pump. Compared with the Zwart cavitation model, the numerical results predicted by the semi-analytical model agree much better with the experiments, especially for large cavities. The cavity lengths at the suction side are overestimated during the simulations, especially by using the Zwart model. At low flow rates, the prediction of the rotating cavitation effect is weaker and the cloud shedding frequency is smaller than those in the experiments.

The characteristics investigation under the unsteady cavitation condition in a centrifugal pump

Numerical simulation and experimental method are combined to investigate the pump inlet and outlet pressure fluctuations, the vibration characteristics and the internal flow instabilities under the unsteady cavitation condition in a centrifugal pump. It is found that the unsteady cavitation starts to generate as the NPSHa is lower than 5.93 m. Apparent asymmetric and uneven cavity volume distribution on each blade and in the impeller can be observed as the NPSHa decreases from 4.39 m to 1.44 m, which includes the cavitation develops from cavitation surge, rotating cavitation to asymmetric cavitation. The flow vortexes in each blade channel are produced in the cavity trailing edges by the shedding and collapse of cavitation, which interfere with each other and aggravate the flow instabilities. The dominant frequencies of the pump inlet and outlet pressure fluctuations are the shaft frequency and blade passing frequency under the unsteady cavitation conditions, respectively. Broadband pulses are obtained from both the pump inlet and outlet pressure pulsations, which results from the random shedding and collapse of unsteady cavitation bubbles. Obvious corresponding relationship between the root mean squares of the vibration measured in different positions and the suction performance curve is found under both the non-cavitation and unsteady cavitation conditions.

Fluid-hammer induced pressure oscillations in a cryogenic feed line

A transient, thermodynamic flow model is developed to simulate pressure oscillations in cryogenic fluid occurring due to sudden closing of valves, a phenomenon commonly known as fluid-hammering. The effects of line dimensions and flow rate changes on amplitude and frequency of these oscillations are investigated using numerical analysis. The model is validated with in-house experimental data and literature based on MOC solution for fluid-hammer. Current study is significant for understanding pressure oscillations during valve operation in launch vehicle cryogenic engine. Very low pressures caused due to fluid-hammer could lead to reduction in pump inlet pressure below saturation level, resulting in pump cavitation. Pressure oscillations also cause fluctuations in propellant flow rate, resulting in undesirable variations in thrust output from the engine. Computational analysis shows that increase in line diameter and reduction in the rate of change of flow rate reduce the peak amplitude of pressure oscillations.

A Physiological Controller for Turbodynamic Ventricular Assist Devices Based on Left Ventricular Systolic Pressure.

The current article presents a novel physiological feedback controller for turbodynamic ventricular assist devices (tVADs). This controller is based on the recording of the left ventricular (LV) pressure measured at the inlet cannula of a tVAD thus requiring only one pressure sensor. The LV systolic pressure (SP) is proposed as an indicator to determine the varying perfusion requirements. The algorithm to extract the SP from the pump inlet pressure signal used for the controller to adjust the speed of the tVAD shows robust behavior. Its performance was evaluated on a hybrid mock circulation. The experiments with changing perfusion requirements were compared with a physiological circulation and a pathological one assisted with a tVAD operated at constant speed. A sensitivity analysis of the controller parameters was conducted to identify their limits and their influence on a circulation. The performance of the proposed SP controller was evaluated for various values of LV contractility, as well as for a simulated pressure sensor drift. The response of a pathological circulation assisted by a tVAD controlled by the introduced SP controller matched the physiological circulation well, while over- and underpumping events were eliminated. The controller presented a robust performance during experiments with simulated pressure sensor drift.

New, Virtually Wall-less Cannulas Designed for Augmented Venous Drainage in Minimally Invasive Cardiac Surgery.

Inadequate venous drainage during minimally invasive cardiac surgery becomes most evident when the blood trapped in the pulmonary circulation floods the surgical field. The present study was designed to assess the in vivo performance of new, thinner, virtually wall-less, venous cannulas designed for augmented venous drainage in comparison to traditional thin-wall cannulas. Remote cannulation was realized in 5 bovine experiments (74.0 ± 2.4 kg) with percutaneous venous access over the wire, serial dilation up to 18 F and insertion of either traditional 19 F thin wall, wire-wound cannulas, or through the same access channel, new, thinner, virtually wall-less, braided cannulas designed for augmented venous drainage. A standard minimal extracorporeal circuit set with a centrifugal pump and a hollow fiber membrane oxygenator, but no in-line reservoir was used. One hundred fifty pairs of pump-flow and required pump inlet pressure values were recorded with calibrated pressure transducers and a flowmeter calibrated by a volumetric tank and timer at increasing pump speed from 1500 RPM to 3500 RPM (500-RPM increments). Pump flow accounted for 1.73 ± 0.85 l/min for wall-less versus 1.17 ± 0.45 l/min for thin wall at 1500 RPM, 3.91 ± 0.86 versus 3.23 ± 0.66 at 2500 RPM, 5.82 ± 1.05 versus 4.96 ± 0.81 at 3500 RPM. Pump inlet pressure accounted for 9.6 ± 9.7 mm Hg versus 4.2 ± 18.8 mm Hg for 1500 RPM, -42.4 ± 26.7 versus -123 ± 51.1 at 2500 RPM, and -126.7 ± 55.3 versus -313 ± 116.7 for 3500 RPM. At the well-accepted pump inlet pressure of -80 mm Hg, the new, thinner, virtually wall-less, braided cannulas provide unmatched venous drainage in vivo. Early clinical analyses have confirmed these findings.

New Dual Lumen Self-Expanding Catheter Design Requiring Less Suction.

Contribution of venovenous extracorporeal membrane oxygenation (v-v ECMO) to gas transfer is flow dependent. Catheter design is a key factor for optimal pressure/flow rate relationship. This study was designed for the assessment of a new self-expanding dual lumen catheter design versus the current standard. Outlet pressure/flow rate and inlet pressure/flow rate for a new Smart catheter with self-expanding dual lumen design constricted to 27 F with 5 mm long constrictor corresponding to the percutaneous path versus Avalon 27 F catheter (control) were compared on a flow bench with a Biomedicus centrifugal pump. Flow, pump inlet pressure and outlet pressure were determined at 500, 1,000, 1,500, 2,000, and 2,500 revolutions per minute (RPM). At 500 RPM and with a 5 mm long constrictor (1,000; 1,500; 2,000; and 2,500 RPM), catheter outlet pressure values were -0.13 ± 0.07 mm Hg (-2.55 ± 0.06; -7.38 ± 0.14; -15.03 ± 0.44; -26.46 ± 0.39) for self-expanding versus -2.93 ± 0.23* (-10.60 ± 0.14; -22.74 ± 0.34; -38.43 ± 0.41; -58.25 ± 0.40)*: p < 0.0001* for control. The flow values were 0.61 ± 0.01 L/min (1.64 ± 0.03, 2.78 ± 0.02; 4.07 ± 0.04; 5.37 ± 0.02) for self-expanding versus 1.13 ± 0.06*; (2.19 ± 0.04; 3.30 ± 0.03; 4.30 ± 0.03; 5.30 ± 0.03)*: p < 0.0001* for control. The corresponding catheter inlet flow rates of the self-expanding catheter were slightly more than that of the control. For the given setup, our evaluation demonstrated that the new dual lumen self-expanding catheter requires lower catheter outlet pressures for higher flows as compared to the current standard.

Novel design and operational control of integrated ultrafiltration — Reverse osmosis system with RO concentrate backwash

A novel design for a reverse osmosis (RO) desalination system directly integrated with an ultrafiltration (UF) pre-treatment unit was developed. The integration involves direct RO feed from the UF filtrate and UF backwash using the RO concentrate. This alignment reduces overall plant footprint, while the use of RO concentrate for UF backwash allows 100% UF recovery and implementation of flexible backwash strategies. The present system design utilizes a control scheme, whereby RO productivity can be prescribed independently of the UF system which self-adjusts to provide the RO system with its required feed flow rate at the specified RO pump inlet pressure. UF backwash, achieved via direct RO concentrate flow from the RO system provided a continuous flow for sequential UF backwash which was additionally integrated with pulse backwash using a hydraulic accumulator. Seawater desalination field studies with a UF–RO pilot system of 12,000gal/day permeate production capacity successfully demonstrated the advantage of RO concentrate UF backwash that was triggered based on a membrane resistance threshold. The above self-adaptive UF backwash strategy significantly extended the projected UF operation period (by a factor of nine) to the threshold of required chemical cleaning.

Research on the noise induced by cavitation under the asymmetric cavitation condition in a centrifugal pump

An experimental investigation has been carried out to research the noise induced by cavitation under the asymmetric cavitation (AC) condition in a centrifugal pump. The acoustic pressure signals at the pump inlet and outlet were measured respectively during the development of cavitation in a closed hydraulic test rig. It could be found that both the pump inlet and outlet acoustic pressures changed obviously with the development of cavitation. The time domain and the power spectrum density of the pump inlet and outlet acoustic pressure pulsations were analyzed. The broadband pulses of the acoustic pressure pulsations were found and the reasons for the phenomenon were given.

Experiment and numerical simulation of cavitation performance for a double suction centrifugal pump

The energy and cavitation performances of a double suction centrifugal pump are tested on a standard experiment rig. The influence of condensation coefficient of the mass transport cavitation model on numerical simulation is analyzed by using the RNG k-e turbulence model and the mass transport cavitation model. As a result, the condensation coefficient mostly regulates the cavity length in the impeller. According to the calculation result, the value of condensation coefficient is modified. The calculated variation of pump head and efficiency with pump inlet pressure decrease agrees well with the experimental data. The results demonstrate that the numerical model and method can accurately predict the cavitation flows in a double suction centrifugal pump. The flow field analysis indicates that the cavitation firstly appears at suction side of blade near the leading edge and then extend to the outlet of impeller with the further reduction of pump inlet pressure. Due to the influence of asymmetric volute structure, the vapor distribution in different flow passages is not uniform.

Influence of blade angle distribution along leading edge on cavitation performance of a centrifugal pump

The influence of blade angle distribution along leading edge on cavitation performance of centrifugal pumps is analysed in the present paper. Three sets of blade angle distribution along leading edge for three blade inlet angles are chosen to design nine centrifugal pump impellers. The RNG k-ϵ turbulence model and the Zwart-Gerber-Belamri cavitation model are employed to simulate the cavitation flows in centrifugal pumps with different impellers and the same volute. The numerical results are compared with the experimental data, and the comparison proves that the numerical simulation can accurately predict the cavitation performance of centrifugal pumps. On the basis of the numerical simulations, the pump head variations with pump inlet pressure, and the flow details in centrifugal pump are revealed to demonstrate the influence of blade angle distribution along leading edge on cavitation performances of centrifugal pumps.

Numerical simulation and analysis of cavitation flows in a double suction centrifugal pump

Cavitation is an unsteady phenomenon, which is nearly inevitable in pumps. It would degrade the pump performance, generate vibrations and noises, and even erode pump flow passage components. The double suction centrifugal pump at design flow rate and large flow rate is numerically simulated using the k-ω turbulence model and the mass transport cavitation model. As a result, the calculated variation of pump head with pump inlet pressure agreed well with the experimental data. The results demonstrate that the numerical model and method can accurately predict the cavitation flows in a double suction centrifugal pump. The cavitation characteristics are analysed in great details. In addition, based on the calculation results, the reason that the plunge of pump head curve is revealed. It is found that the steep fall of pump head happens when the cavity reaches the blade to blade throat and the micro-vortex group appears at the back of the blade suction side. At the same time, this practice can provide guidance for the optimal design of double suction pumps.

Numerical and experimental investigation on the development of cavitation in a centrifugal pump

Concerning the development of cavitation in a centrifugal pump, numerical simulations and experimental investigations have been carried out in a closed hydraulic test rig. The internal flow characteristics and pressure pulsation at pump inlet and outlet have been analyzed during the process of cavitation development. The results of the research reveal the occurrence and development of cavitation in the centrifugal pump which has been confirmed through experiments and numerical simulation. The degree of pump cavitation could be monitored through pump inlet and outlet pressure pulsation. Compared with pump outlet pressure pulsation, pump inlet pressure pulsation is more sensitive to the change of cavitation. According to the results of the investigation, the typical frequency of pump inlet pressure pulsation could be regarded as around 30 Hz in the severe cavitation conditions. Meanwhile, the pump head dropped by 0.77% from noncavitation conditions which could be regarded as a symbol of incipient cavitation.

A monitoring and physiological control system for determining aortic valve closing with a ventricular assist device

Real-time monitoring of the aortic valve function and the loading state of the left ventricle (LV) during mechanical circulatory support is essential. Therefore, we developed a system that determines accurately the aortic valve closing moment based on integrals derived from the pump inlet pressure and the pump power [pressure-power area (PPA)]. A Deltastream diagonal pump was implanted in 10 healthy Rhoen sheep. Changes in ventricular volume and pressure in different assist levels were measured by a conductance catheter placed in the LV and were correlated with intrinsic pump signals, motor power, voltage and current. Measurements were obtained in the state of normal as well as decreased left ventricular contractility induced by β-blockers. Complete datasets were obtained in seven animals. The PPA-feedback signal reached its maximum at the speed of aortic valve closing. This was validated by pressure-volume (PV)-catheter measurements both at the baseline and in the state of decreased contractility. In both cases, zero-crossing occurred at the point of aortic valve closing speed. With this trial, we deliver the experimental basis for the development of an automatic feedback controller that would allow periodic speed changes in accordance with the loading state of the native ventricle and the opening state of the aortic valve. This would deliver real-time data to treating physicians and enable the establishment of a standard weaning protocol.

Caval collapse during cardiopulmonary bypass: a reproducible bench model

During open heart surgery, so-called atrial chatter, a phenomenon due to right atria and/or caval collapse, is frequently observed. Collapse of the cava axis during cardiopulmonary bypass (CPB) limits venous drainage and may result downstream in reduced pump flow on (lack of volume) and upstream in increased after-load (stagnation), which in turn may both result in reduced or even inadequate end-organ perfusion. The goal of this study was to reproduce venous collapse in the flow bench. In accordance with literature for venous anatomy, a caval tree system is designed (polyethylene, thickness 0.061 mm), which receives venous inflow from nine afferent veins. With water as medium and a preload of 4.4 mmHg, the system has an outflow of 4500 ml/min (Scenario A). After the insertion of a percutaneous venous cannula (23-Fr), the venous model is continuously served by the afferent branches in a venous test bench and venous drainage is augmented with a centrifugal pump (Scenario B). With gravity drainage (siphon: A), spontaneously reversible atrial chatter can be generated in reproducible fashion. Slight reduction in the outflow diameter allows for generation of continuous flow. With augmentation (B), irreversible collapse of the artificial vena cava occurs in reproducible fashion at a given pump speed of 2300 ± 50 RPM and a pump inlet pressure of -112 mmHg. Furthermore, bubbles form at the cannula tip despite the fact that the entire system is immersed in water and air from the environment cannot enter the system. This phenomenon is also known as cavitation and should be avoided because of local damage of both formed blood elements and endothelium, as well embolization. This caval model provides a realistic picture for the limitations of flow due to spontaneously reversible atrial chatter vs irreversible venous collapse for a given negative pressure during CPB. Temporary interruption of negative pressure in the venous line can allow for recovery of venous drainage. This know-how can be used not only for testing different cannula designs, but also for further optimizing perfusion strategies.