Pulsation Amplitude Research Articles

Intensification of absorption rate of carbon dioxide and ammonia in a simulated packed (Stephens–Morris) column using pulsed gas phase under optimized parametric conditions

BackgroundReducing gas emissions is a significant challenge in our ecosystem. Gas-liquid absorption is used in chemical industry to remove components from gas streams. Stephens–Morris tube, known for liquid-liquid and gas-liquid systems, has gained attention for gas absorption columns utilizing disc-shaped packing elements to improve mass transfer by creating tortuous flow path. MethodsThis investigation focuses on physical absorption of CO2 and NH3 in gas-liquid systems based on various process parameters vis. liquid flow rate (0.24–0.60 L/min), gas flow rate (6–60 L/min), pulsation frequency (0–9.06 Hz), pulsation amplitude (0–26 mm), effect of solute gas concentration (0–100 %), and effect of varying the number of discs in the disc column (15, 20, 25, 33). Response Surface Methodology (RSM) was used to predict maximum absorption efficiency under optimized conditions. Significant FindingsPulsation frequency and amplitude proportionally increased absorption coefficient, while liquid flow rate affected it differently in pulsed and unpulsed absorption. In gas film-controlled system, mass transfer coefficient was proportional to the gas flow rate. RSM yielded R2 of 0.975 while relative error and dwill was 0.097 and 0.96, respectively. Understanding system characteristics and operations at optimal pulsation frequencies and amplitudes can maximize absorption effectiveness, particularly for low-solubility gases dominated by liquid phase resistance.

Numerical simulation on the mixing behavior of double-wave screw under speed sinusoidal pulsating enhancement induced by differential drive

Abstract A novel speed sinusoidal pulsating system is designed by applying differential drive, which is loaded on the plasticizing screw in an extruder or in an injection molding machine. With the CFD software ANSYS POLYFLOW 19.2, this paper builds simplified physical and mesh models for the double wave screw unit, carries out numerical simulation by using particle tracing manner, and finally analyses comparatively the mixing behavior of the wave screw mixing unit with and without sinusoidal pulsating field. It is found that the mixing screw unit with the superimposed excitation field takes on lower transportation efficiency and a descending melt pressure, while there are different reactions on the various pulsating amplitude and frequency for the max shear rate and mixing index. On the other hand, the introducing pulsating field can strengthen the shear field and gain a higher mixing efficiency. The results are of great importance and reference for improving the plasticizing performance and engineering application of the speed pulsating system.

Experimental analysis of pulsatile flow effects on flow structure in transitional-type cavity

Studies combining flow separation and pulsatile flow phenomena are inherent in the field of biomedicine and have many engineering and biomedical applications. In this study, the pulsatile flow structure is investigated experimentally based on a transitional-type cavity with a length-to-depth ratio of 8 using a microparticle image velocimetry system. A pulsatile flow is generated by pulsating the inlet pressure in sinusoidal pulses using a pressure control unit. Stationary flow and four sets of pulsatile parameters are investigated: two pulsation amplitudes (A = 0.15 and 0.60) and two pulsation frequencies (f = 0.5 and 1 Hz) in the Reynolds range of 50–2000. The recirculation flow dynamics in a cavity are analyzed by investigating the effect of pulsations on the flow structure and statistical flow parameters such as vorticity, shear rate, and turbulence intensity. The analysis shows that the effect of the pulsation amplitude on the recirculation zone dynamics is more prominent than that of the pulsation frequency. The magnitude of the recirculation zone reduction achieved by the pulsatile flow is inversely proportional to the pulsation amplitude. A reduction in the recirculation zone length decreases the shear rate distribution along the cavity. Additionally, an analysis into the turbulence intensity shows that effect of pulsations is negligible when the flow approaches the turbulent flow regime.

A retinal imaging system for combined measurement of optic nerve head vascular pulsation and stimulated vasodilation in humans

Vascular pulsation at the optic nerve head (ONH) reflects vessel properties. Reduction in the stimulated retinal vasodilatory capacity has been reported in diabetes, but its relation with vascular pulsation is unknown. Here we report a new retinal imaging system for correlative assessment of ONH vascular pulsation and stimulated retinal vasodilation. Retinal reflectance images were acquired before and during light flicker stimulation to quantify arterial and venous vasodilation (DAR, DVR) in subjects with and without diabetic retinopathy (N = 25). ONH vascular pulsation amplitude and frequency (PA, PF), were quantified by curve fitting of periodic intensity waveforms acquired in retinal vasculature (RV) and ONH tissue (ONHT) regions. The relationships between pulsation metrics, heart rate (HR), intraocular pressure (IOP), and vasodilatory responses were evaluated. Pulsation metrics were not significantly different between regions (p ≥ 0.70). In RV, inter-image variabilities of PA and PF were 10% and 6%, whereas inter-observer variabilities were 7% and 2% respectively. In both regions, PF was correlated with HR (p ≤ 0.001). PA was associated with DAR in both regions (p ≤ 0.03), but only with DVR in RV (p ≤ 0.05). Overall, ONH vascular pulsation was associated with stimulated retinal vasodilation, suggesting diabetes may have concomitant effects on retinal vasculature compliance and neurovascular coupling.

Numerical study on active droplet generation governed by pulsatile continuous‐phase flow

AbstractPrecise control on the droplet generation is an important issue for the application of droplet microfluidics. Passive formation of droplets depends on multiparameters. The droplet size and generation frequency highly correlate to each other, raising the control difficulty. In comparison, the active method through external perturbations is more flexible. In this work, the droplet generation governed by pulsatile continuous‐phase flow is numerically studied. The effects of the pulsation amplitude and frequency, as well as the velocity and viscosity of the discrete fluid are investigated. Different modes of droplet generation (viz., sub‐periodic, period‐1, and period‐n modes) are identified, the underlying mechanisms are interpreted. This method may be applied in various droplet microfluidic/microreactor systems to improve the droplets control and manipulations.

Experimental investigation on the combustion characteristics and thermoacoustic instability of liquid spray flame with blended fuel

This study experimentally investigates the combustion characteristics and thermoacoustic instability of two fuels, ethanol and RP-3, at five different blending ratios. The flame images, root temperature of blended fuel flame and pollutant emissions were photographed and tested. The experimental results indicate that high-pressure pulsation amplitude and airflow disturbance can enhance droplets’ evaporation and combustion processes, resulting in a reduction in flame length. Lower evaporation temperature ensures a higher temperature of the flame root while increasing the blend ratio of RP-3 and increasing the global equivalence ratio can increase the temperature level inside the combustion chamber. The root temperature of ethanol flame can reach over 1400 K. Fuel characteristics and burner structure can influence the coupling between pressure pulsation and flame heat release pulsation, leading to differences in the amplitude of combustion instability. The shorter the outlet length of the burner, the wider the stability range of the flame. Moreover, the increase in total burner length results in a shift of the oscillation dominant frequency towards lower frequencies. Emission characteristic curves reveal that high-pressure pulsation amplitude can improve the combustion efficiency of blended RP-3 fuel but are unfavorable for the complete combustion of ethanol. Meanwhile, under the dilution effect of the airflow, the emissions of NOx and CO at the outlet gradually decrease as the airflow increases.

Optimization of Guide Vane Centrifugal Pumps Based on Response Surface Methodology and Study of Internal Flow Characteristics

The methodologies of computational fluid dynamics (CFD) and response surface method (RSM) were integrated to uncover the optimal correlational framework for intricate hydraulic geometric parameters of guide vane centrifugal pumps. Parameters such as blade number, blade wrap angle, blade outlet angle, and relative axial distance between the guide vane and impeller, as well as radial distance, are embraced as optimization design variables. Meanwhile, pump head and efficiency were chosen as responsive variables. An analysis of 46 sets of hydraulic performance data was carried out by using the Box–Behnken experimental design method. Subsequently, response surface approximation models were established between hydraulic parameters and the efficiency, as well as the head. The optimal design point was predicted and a simulation of the hydraulic characteristics for the optimal scheme was conducted; the errors were 0.846% for head and 0.256% for efficiency between the simulation results with predicted results from RSM. The optimized model demonstrates noteworthy enhancements in hydraulic performance in comparison to the original model. By analyzing the internal flow of the optimized model under transient conditions, it was found that, as the internal flow of the flow passage components is relatively disordered at small flow rates, the amplitude of pressure pulsation is affected a lot. At other flow rates, the inside pressure pulsation waveform exhibits pronounced periodicity, and the primary causes of pressure pulsation in various flow components are not the same. Wall dissipation and turbulent dissipation emerge as significant contributors to the entropy generation in this centrifugal pump. The magnitude of entropy generation is correlated with the flow rate and the structural configuration of the pump’s components. High-entropy regions concentrate around the leading and trailing edges of the blades.

Steady-State Amplitude of Nonlinear Pulsations of a Gas Bubble in Liquid under the Action of Periodic External Pressure in Resonance

Steady-State Amplitude of Nonlinear Pulsations of a Gas Bubble in Liquid under the Action of Periodic External Pressure in Resonance

Analysis of impact of rotation speed changes on pressure pulsation of positive displacement pump

The paper presents the results of experimental research on the impact of changes in the rotation speed of a hydraulic external gear pump on pressure pulsation in the discharge line for a constant value of pressure. The analyses were performed in the time domain (analysis of peak-to-peak pressure) and frequency domain (analysis of changes in frequency and pulsation amplitude). The results of experimental studies have shown that the change of the pump’s rotation speed influences changes in the course of pressure pulsation (peak-to-peak pressure and amplitude), in some cases significantly increasing the parameters mentioned. The obtained test results can be used to develop recommendations for designing hydraulic and hydrotronic systems equipped with a variable-speed pump drive.

Energy loss analysis of transition simulation for a prototype reversible pump turbine during load rejection process

The dynamic behavior of a reversible pump turbine (RPT) during the load rejection process was investigated through numerical simulation and experimental testing. The study focused on various parameters, such as the operation of guide vanes, torque, flow, head, and runner forces. The pressure fluctuations at different monitoring points were analyzed using the time-frequency method, specifically the continuous wavelet transforms (CWT). The results revealed significant pressure pulsation amplitudes in the vaneless region. Additionally, the entropy production rate was employed to quantify energy loss in different domains, including direct dissipation, turbulent dissipation, and wall shear stress. Moreover, the study utilized the vorticity transport equation to examine vortex characteristics and transport in the stay vanes, guide vanes, and runner flow channels. The vortex characteristics were classified into relative vortex stretching (RVS), Coriolis force (CORF), and viscous diffusion (VISD). The findings highlight significant energy loss in flow patterns associated with high RVS and CORF regions. This study provides valuable insights into the transition process and energy loss of RPTs during load rejection, serving as a basis for future research aiming to enhance the safety and reliability of RPTs under load rejection conditions.

Numerical investigation of clocking effect on unsteady fluid flow in vicinity of tongue for centrifugal pump with vaned diffuser

In order to investigate the clocking effect on unsteady flow distortion in the vicinity of the tongue and hydraulic loss in the volute, experiments and numerical simulations were conducted with four different relative angular positions between the vane and tongue. Numerical results were validated against experimental data, which included measurements of pressure pulsation at the tongue and downstream of the tongue. The radial and circumferential velocities near the tongue at the diffuser-volute clearance were depicted by expanding the rotating surface, and comparisons were made under different diffuser positions to reveal the flow distortion affected by the clocking effect. Shear stress rates and total pressure distributions at the volute exit pipe were also depicted to study the flow loss in the volute affected by the flow pattern from the tongue. The findings show that the pressure fluctuation at the tongue and downstream of the tongue is significantly affected by the diffuser mounting position. The amplitude and intensity of pressure pulsation under θ d1 are clearly smaller than those at other diffuser positions. As the vane trailing edge approaches the tongue, the pressure gradient becomes very large, leading to the formation of a vortex at the tongue that promotes crowding effects and reverse flow occurring in the exit pipe. This, in turn, leads to deflection of the main flow in the volute, high velocity gradients, and subsequently large shear stress rates and hydraulic losses. When the diffuser is installed at θ d4, the flow distortion and flow loss are improved.

Multi-objective optimization of multi-channel cold plate under intermittent pulsating flow by RSM and NSGA-Ⅱ for thermal management of electric vehicle lithium-ion battery pack

The heat transfer and energy consumption characteristics are the most important performance parameters of cold plate for thermal management of electric vehicle lithium-ion battery pack. In this work, in order to address the issue about multi-objective optimization of multi-channel cold plate under intermittent pulsating flow, RSM (Response Surface Methodology) and Non-dominated Sorting Genetic Algorithm II (NSGA-II) is combined to make a trade-off between the average heat transfer coefficient and energy consumption of multi-channel cold plate under intermittent pulsating flow. Box-Behnken design is used to arrange a series of numerical investigations using the steady flow velocity vin, pulsation amplitude A, and pulsation frequency e as design variables and the average heat transfer coefficient have and energy consumption W as objective functions. Regression models are created in the form of quadratic polynomials, and the significance of each term in the model is determined by analysis of variance (ANOVA). Results show that the linear term of vin has the greatest effect on have and W. According to the Pareto optimal solution obtained from NSGA-II, the optimal objective functions are have = 394.7012 W m−2 °C−1, W = 0.1086 J, and the corresponding design variables are vin = 0.02392 m/s, A = 0.1778 and e = 3.1846 Hz.

Increasing Performance of Spiral-Wound Modules (SWMs) by Improving Stability against Axial Pressure Drop and Utilising Pulsed Flow.

Spacer-induced flow shadows and limited mechanical stability due to module construction and geometry are the main obstacles to improving the filtration performance and cleanability of microfiltration spiral-wound membranes (SWMs), applied to milk protein fractionation in this study. The goal of this study was first to improve filtration performance and cleanability by utilising pulsed flow in a modified pilot-scale filtration plant. The second goal was to enhance membrane stability against module deformation by flow-induced friction in the axial direction ("membrane telescoping"). This was accomplished by stabilising membrane layers, including spacers, at the membrane inlet by glue connections. Pulsed flow characteristics similar to those reported in previous lab-scale studies could be achieved by establishing an on/off bypass around the membrane module, thus enabling a high-frequency flow variation. Pulsed flow significantly increased filtration performance (target protein mass flow into the permeate increased by 26%) and cleaning success (protein removal increased by 28%). Furthermore, adding feed-side glue connections increased the mechanical membrane stability in terms of allowed volume throughput by ≥100% compared to unmodified modules, thus allowing operation with higher axial pressure drops, flow velocities and pulsation amplitudes.

Numerical analysis of wake field and unsteady forces on submarine propeller with twisted rudders

A twisted submarine rudder was designed to reduce the unsteady force on and improve the propulsion efficiency of the propeller. The twisted rudder not only switches the wake in the pre-rotation state in the direction opposite to the propeller rotation but also increases the mismatch between the circumferential phase-angle distribution characteristics of the wake peak and propeller profile at each radius. To investigate the influence of this rudder on the submarine's flow field and the propeller's hydrodynamic performance, the shear stress transport (SST) k−ω turbulence model was used to calculate and compare the resistance characteristics and flow field at the aft of the submarine without a propeller when the ordinary and twisted rudders were installed, as well as the wake field of and unsteady force on the propeller with the propeller. The circumferential velocity in the propeller wake was significantly reduced, and the propulsion efficiency was improved by approximately 7.31%. In addition, the pulsation amplitude of the unsteady force was significantly reduced. The main blade-passing frequency (1BPF) amplitudes of the force and torque decreased by more than 40% and 35%, respectively, which significantly reduced the hull vibration caused by the unsteady force on the propeller.

Cross influence of rotational speed and flow rate on pressure pulsation and hydraulic noise of an axial-flow pump

Axial-flow pumps may experience significant pressure pulsation and high hydraulic noise when deviating from design conditions, and this article investigates the cross influence of rotational speed and flow rate on inlet pressure pulsation and hydraulic noise of an axial-flow pump based on coherence theory through physical model experiments. The energy amplitude of pressure pulsation is directly proportional to rotational speed and inversely proportional to flow rate, as rotational speed increases, the energy distribution of the blade passage frequency (fBPF) within different frequency bands of pressure pulsation improves. Pressure pulsation and the overall natural frequency of the pump device work together to define the primary and secondary frequencies of the sound pressure level, as rotational speed increases, these frequencies eventually move toward 2fBPF, and the coherence coefficient at frequencies of fBPF and 2fBPF is above 0.9. To reduce hydraulic noise, both pressure pulsation and natural frequency should be given sufficient attention.

Performance and unsteady flow characteristic of forward-curved impeller with different blade inlet swept angles in a pump as turbine

As an economical energy recovery device, a pump as turbine (PAT) is widely used in micro hydropower and energy recovery fields. Compared with an original impeller, a special impeller with forward-curved blades can dramatically enhance a PAT's efficiency and broaden its high-efficiency range because the blade angles created by the latter more effectively match the PAT's operating mode. The shape of blade curve and sweep has obvious influence on the performance of a PAT. To investigate how the inlet swept angle of forward-curved blade influences the performance of PAT, five different forward-curved impellers with different inlet swept angle blades were designed and numerically investigated based on a verified computational fluid dynamics (CFD) method. The effects of blade inlet swept angles on the external characteristics, energy loss and unsteady characteristics of PAT are analyzed. Compared with the blade whose inlet swept angle is 0°, the maximum efficiency of back-swept PAT with swept angle of −8° increases by 0.58% while the head decreases by 0.49 m. However, the efficiency of forward-swept PAT of 8° reduces by 0.9%, and the head increases by 0.68 m. The maximum reduction rates of the main frequency amplitude of pressure pulsation in the volute, impeller and draft tube of back-swept PAT are 35.2%, 45.47% and 67.24%, respectively, indicating that the back-swept blade can contribute to improve the operation stability of PAT. Moreover, the vortex in PAT with back-swept blade is greatly improved under partial and design flow rate, which can improve the unsteady flow characteristics of PAT.

Influence of Blade Trailing-Edge Filing on the Transient Characteristics of the Centrifugal Pump during Startup

During the startup process of a centrifugal pump, the vibration and noise problems caused by unsteady flow are the focus of attention, and pressure pulsation is one of the main reasons for this problem. In the current research, a special impeller with blade pressure side trimming was proposed to reduce the strong pressure pulsation phenomenon during the startup process of centrifugal pumps. This article uses numerical simulation methods to simulate three typical blade trailing edges: original trailing edge (OTE), pressure side long linear (LLPS), and pressure side short linear (SLPS), and verifies them with experimental results. The results indicate that although the head of the centrifugal pump after filing has been reduced, its efficiency has been improved to a certain extent. Thirteen monitoring points were set up near the impeller outlet circumference and volute tongue to analyze the changes in pressure pulsation, verifying that blade trimming has a significant inhibitory effect on pressure pulsation during the startup of centrifugal pumps. The average maximum pressure pulsation amplitude of all monitoring points decreased by 32.23%, and the maximum pressure pulsation amplitude decreased by 56%. Blade trimming can affect the internal flow field distribution of centrifugal pumps. By analyzing the static pressure distribution, velocity streamline distribution, and vorticity distribution at the middle interface of three different impellers during startup, it was verified that there is a close relationship between pressure pulsation and unsteady flow structure during startup. The final conclusion is that blade trimming has a significant inhibitory effect on the pressure pulsation of the centrifugal pump during startup, and the impeller outlet vorticity is significantly reduced. The scheme proposed in this study has far-reaching prospects in the design of low noise centrifugal pumps.

Role of Cx43 in iPSC-CM Damage Induced by Microwave Radiation.

The heart is one of the major organs affected by microwave radiation, and these effects have been extensively studied. Previous studies have shown that microwave-radiation-induced heart injury might be related to the abnormal expression and distribution of Cx43. In order to make the research model closer to humans, we used iPSC-CMs as the cell injury model to investigate the biological effect and mechanism of iPSC-CM injury after microwave radiation. To model the damage, iPSC-CMs were separated into four groups and exposed to single or composite S-band (2.856 GHz) and X-band (9.375 GHz) microwave radiation sources with an average power density of 30 mW/cm2. After that, FCM was used to detect cell activity, and ELISA was used to detect the contents of myocardial enzymes and injury markers in the culture medium, and it was discovered that cell activity decreased and the contents increased after radiation. TEM and SEM showed that the ultrastructure of the cell membrane, mitochondria, and ID was damaged. Mitochondrial function was aberrant, and glycolytic capacity decreased after exposure. The electrical conduction function of iPSC-CM was abnormal; the conduction velocity was decreased, and the pulsation amplitude was reduced. Wb, qRT-PCR, and IF detections showed that the expression of Cx43 was decreased and the distribution of Cx43 at the gap junction was disordered. Single or composite exposure to S- and X-band microwave radiation caused damage to the structure and function of iPSC-CMs, primarily affecting the cell membrane, mitochondria, and ID. The composite exposure group was more severely harmed than the single exposure group. These abnormalities in structure and function were related to the decreased expression and disordered distribution of Cx43.

Cooling Strategies for Heated Cylinders Using Pulsating Airflow with Different Waveforms

Pulsate flow is an effective technique applied for cooling several engineering systems depending on their pulsate frequency. One very sound external flow pulsation application is heat transfer over heated bodies. In present work, an experimental design and numerical model of controlled pulsating flow according to generated pulsating frequency and wave shape around a heated cylinder were performed. The effects of pulsating frequency, amplitude, and mean velocity on the fluid flow and heat transfer characteristics over a heated cylinder were studied. The wave frequency varied from 2 to 12 Hz, and the amplitude varied from 0.2 to 0.8 m/s. Moreover, different waveforms were investigated to determine their effect on wall cooling. For constant wave frequency and amplitude, the most efficient wave in cooling was the sawtooth wave, with the average wall temperature after 30 s was 1.6 °C cooler than that of the forced convection case, followed by the triangular wave at 1.2 °C less. The heat transfer rate and the flow field were drastically influenced by the variations of these parameters. Optimization was conducted for each wave type to find the optimum wave frequency and amplitude. The optimizing showed that, the most efficient wave was the sawtooth with 12°C temperature reduction compared with that of the forced convection case, followed by the triangular. Furthermore, regression analysis was conducted to estimate the relationships between these variables and surface temperature. It was found that the wave amplitude had a greater role in cooling than that of the frequency

Multi-Objective Parameter Optimization of Submersible Well Pumps Based on RBF Neural Network and Particle Swarm Optimization

In order to improve the hydraulic performance of a submersible well pump, steady and transient simulations were carried out based on ANSYS CFX software. The head and efficiency of the submersible well pump under standard operating conditions were taken as the optimization objectives, and the impeller outlet placement angle, outlet width, and vane wrap angle were selected as the optimization variables using the Plackett-Burman experimental design method. The RBF neural network training samples were constructed using the uniform experimental design method to build a hydraulic performance prediction model for the submersible well pump, and a multi-objective particle swarm optimization was used to solve the model and obtain the Pareto optimal solution set. Using the head and efficiency of the initial model as the boundary, the Pareto optimal solution and the corresponding structural parameters are sought. After the optimization, the head of the individual with the better head is increased by about 2.65 m, and the efficiency of the individual with the better efficiency is increased by about 2.3 percentage points compared with that of the initial model. The pressure gradient in the impeller flow channel is more obvious, the work capacity is significantly improved, the vortex area of the spatial guide vane is smaller, the flow line is more regular, and the pressure pulsation amplitude at the inlet and outlet of the impeller and the spatial guide vane is significantly reduced.