Pulsation Rate Research Articles

The Influence of Angle Parameters on Pulsation Characteristics of Elastomer Rotor Pump

In view of the poor sealing performance of elastomer rotor profile and the defect of particle sticking in the tip of rotor, the pulsation characteristics of rotor cavity under 5°, 8°, 11°, 15° and 18° conditions are studied by transient calculation of the whole flow field of rotor pump based on CFX immersion solid technology and RNG k − ξ turbulence model. When the wrap angle increases, the instantaneous mass pulsation rate decreases. When the wrap angle increases, the cavitation possibility at the inlet meshing point increases, and the pressure at the outlet meshing point increases. In order to improve the periodic impact of liquid on the elastomer and prevent the adhesion surface from falling off, the elastomer rotor should adopt the structure of small wrap angle under the condition of ensuring the width of sealing at the top of rotor.

Numerical investigation of the pulsation frequency of the flow rate effect on the mixing efficiency of the active T-shaped micromixer

Flow patterns and mixing efficiency of fluids with different inlet flow rate pulsation frequencies in T-shaped micromixer were numerically investigated at Reynolds numbers Re = 100 and Re = 180. The flow rate pulsations were set sinusoidal with different frequencies of 0; 1; 10 and 50 Hz. The relative mixing efficiency means the mixing efficiency of active mixer regarding the mixing efficiency of an identical passive mixer without pulsations at the input; it was considered as the main value. The dependences of such value on the pulsation frequencies were obtained. It was found that active micromixers are much more efficient than the passive ones. Herewith, in the engulfment regime, the mixing efficiency increases twofold regarding the passive mixer, and in the region, before the onset of the engulfment regime, the mixing efficiency increases by about 170 times. In addition, it was found that the increase in mixing efficiency is almost independent of the frequency of pulsations.

Machine milking parameters for Murciano-Granadina breed goats

In dairy ruminants, the combination of milking parameters must ensure good milking performance without harming udder conditions. Commonly, milking conditions for goats are established without having checked the admissible limits for optimal and fast milking. The aim of this study was to establish a limit combination of machine milking parameters that improves machine milking performance without altering milkability or udder status. To this end, we studied the effect of 2 combinations (42 kPa, 120 cpm, 60% vs. 44 kPa, 120 cpm, 60% in terms of kilopascals of vacuum level, cycles per minute of pulsator rate, and percentage of pulsator ratio, respectively) on milk production and composition, milk fractioning during milking, SCC, teat tissue thickness variation after milking, and the milk emission kinetics parameters throughout 1 lactation period (6 mo). The 42 and 44 kPa measured at the vacuum gauge level became average values of 37.5 and 39.3 kPa, respectively, measured at the teat sphincter level during milking. Milk flow significantly increased and total milking time decreased 25 s with the elevation of the vacuum level from 42 to 44 kPa without any adverse effect on milk fractioning at milking. However, the use of 44 kPa also showed an increase in tissue thickness above 5%, and we observed a tendency of average conductivity of milk to increase, although without any adverse effect on SCC. It seems that 44 kPa, 120 cpm, 60% is a possible limit combination of parameters to improve milking performance without altering milkability or udder conditions. We concluded that this combination can be used for milking Murciano-Granadina breed goats in conditions similar to those of this study (mid-level milking system and 1 milking/d), although further studies are necessary to verify its application in the case of 2 milkings/d.

Development and Control of an Electro-Hydraulic Actuator System for an Exoskeleton Robot

Exoskeleton robots have been developed in various fields and are divided into electric and hydraulic exoskeletons according to the actuator type. In the case of hydraulic robots, because a unidirectional pump is applied, there are limitations to the wearer’s walking. In addition, robot systems are complicated, because a directional control valve is required to change the direction of the actuator. To solve these problems, we designed the electro-hydraulic actuator (EHA) system which has both the hydraulic and electric advantages. The EHA system consists of a hydraulic bidirectional pump, a motor, a hydraulic cylinder, and various valves. For the development of the piston pump, we analyzed the gait cycle and considered the flow rate and pulsation rate. In order to reduce the size and weight of the EHA system, the valves were made from one manifold, and the hydraulic circuit was simplified. We verified that the developed EHA system is applicable to robots through position and force control experiments. Because the hydraulic system is nonlinear, we designed a sliding mode control (SMC) and compared it with the proportional integral derivative (PID) controller.

Unity and Diversity of Yellow Hypergiants Family

We summarize the results of long-term spectral monitoring of yellow hypergiants (YHGs) of northern hemisphere with a R$\ge$60000 resolution. The spectra of these F-G stars of extremely high luminosity, compactly located at the top of the Hertzsprung-Russell diagram revealed a variety of spectral features: various types of H$\alpha$ profile, the presence (or absence) of forbidden and permitted emissions, as well as circumstellar components. Variability of spectral details of various nature is studied. Absolute luminosity, circumstellar envelope expansion rate and amplitude of pulsations are determined. The reliability of the YHG status for V1427 Aql is reliably confirmed; manifestations of a significant dynamic instability of the upper layers of the atmosphere of $\rho$ Cas after the 2017 ejection and stratification of its gas envelope are registered; the lack of companion in the system of the V509 Cas hypergiant is proven; a conclusion is made that the V1302 Aql hypergiant is approaching to the low-temperature boundary of the Yellow Void.

Optimization of Suction Chamber Structure in a Scroll Refrigeration Compressor

In order to improve the suction performance of the scroll compressors, five modification models are proposed by reducing or enlarging the area of the suction flow passage based on a scroll refrigeration compressor. The three-dimensional numerical simulation model is established using the commercial software PumpLinx to calculate the flow field and the performance of every modified model. The comparison and analyses has been done based on the simulation results. The results indicated that the enlargement of the suction passage only improve the volumetric efficiency a little while the shrink of the suction passage can improve it effectively. The mass flow rate pulsation when the modification angle is 270° is much higher than that of the original model, but it decreases with the modification angle. As the modification angle increases, the volume of inner suction passage and the back flow rate from the inner suction passage decrease and less fluid from suction chamber 2 flows back to the suction port, so the average mass flow rate increases and the mass flow rate pulsation decreases. The Model 5 has the maximum volumetric efficiency and lower mass flow pulsation, but the tangential and radial forces on the orbiting scroll are the highest.

Bulk tank somatic cell count and total bacterial count are affected by target practices and milking machine features in dairy sheep flocks in Castilla y León region, Spain

To study the effect of main flock target practices and milking machine features on the variation of bulk tank milk (BTM) somatic cell count (SCC) and total bacterial count (TBC) in dairy sheep flocks, a total of 3458 records of BTM SCC and TBC, corresponding to 340 audited flocks from the Consorcio de Promoción del Ovino of Castilla y León region (Spain), were collected throughout 12 months before testing the technical features of their milking machines. Average values were established for flock size (485.6 ewes), replacement rate (21.1%), parlor capacity (35.7 places), number of milking units (13.8), milking vacuum (36.2 kPa), pump air capacity at 50 and 36 kPa (106.4 and 158.3 L/min per milking unit), manual reserve (122.3 L/min per milking unit), air, milk and milking unit system consumptions (8.0 to 12.5 L/min per milking unit), internal diameters of the main air and milk pipes (5.9 mm and 4.2 mm per milking unit), pulsation rate and ratio (161.1 c/min and 57.4%), age and time since the last revision of the milking installation (16.3 years and 48.1 months), BTM temperature (3.4 °C) and washing water temperature at water-heater outlet (62.1 °C). Antibiotic dry therapy, time since last milking machine revision, and warm water temperature were critical factors influencing BTM SCC and TBC variation. Optimised BTM quality was also obtained for flocks with a greater size and foreign breeds, confined and post-dipped, with daily bedding maintenance, a low-level milk pipeline system, the presence of pulsation airline, greater manual reserve, smaller milk system consumption, and greater main air and pulsation pipe diameters. Greater milk pipe diameters and pulsation rates ≥180 c/min were associated with smaller SCC, but greater TBC, whereas pulsation ratios ≥60% increased SCC, but decreased TBC. Overall, results will allow for the optimisation of educational and risk management programs in the dairy sheep sector to improve flock mammary health and BTM hygiene.

Experimental and numerical investigation of controlled disturbances development from two sources in supersonic boundary layer

The paper presents the experimental results and the results of direct numerical simulation of the development and interaction of two wave trains from two point sources of controlled disturbances in a supersonic boundary layer on a flat plate with an incident flow Mach number of 2.5. Sources were located parallel to the leading edge of the model. For the introduction of controlled disturbances into the boundary layer, the normal component of the mass flow rate was varied in the calculations. In the experiment, periodic glow discharges at a frequency of 20 kHz were used. In both cases, the disturbances sources worked synchronously. Mass flow rate pulsations were measured and recorded in sections, parallel to the leading edge of the model, near the maximum of disturbances along the boundary layer. In the experiment, a constant-temperature hot-wire anemometer was used. After performing a discrete Fourier transform, the spatial distributions of disturbances, the beta-spectra were determined, and the wave characteristics of the development of disturbances downstream were estimated. In addition, direct numerical simulation of the downstream development of disturbances from a single source was performed. The work presents a comparison of experimental and theoretical calculated data. The paper discusses the effects inherent in the interaction of unstable traveling controlled disturbances from two sources operating synchronously.

Study on Unstable Characteristics of Centrifugal Pump under Different Cavitation Stages

In order to reveal the regularity of unsteady flow of centrifugal pump under different cavitation stages, a visual closed test-bed is built to collect signals such as the distribution of cavitation bubbles at the impeller inlet and external characteristics, etc. in the process of cavitation of centrifugal pumps. Combined with the shape and distribution of bubbles captured by high-speed photography, the cavitation stage of the centrifugal pump is divided. In addition, the variation of vorticity distribution, pressure pulsation and radial force of centrifugal pump under different cavitation stages are studied using the standard k-e turbulence model and the Kunz cavitation model. Main contributions are as follows: The cavitation bubbles can absorb the energy of vortex core to a certain extent and increase the volume of vortex core. Cavitation bubbles can also block the flow-path and induce the distortion of the internal flow field, resulting in unstable pressure waves that cause a significant increase in pressure pulsation rate. Besides, with the development of cavitation, the radial force on the impeller tends to remain invariable first and then decrease, and trajectory of the radial force changes from closed to open.

Influence of the Manifold Configuration of Pulsating Heat Pipes on Their Performance

The performance characteristics of three air-to-air pulsating heat pipes with R1233zd as a working fluid for cooling an electronic cabinet are presented. Each of these pipes comprises two coolers staked in one unit of dimension 36 × 19 × 5 cm3, constructed with extruded multiport tubes and louvered fins brazed together. These pipes differ from each other only in their manifold configuration achieved by having fluid distribution plates at the evaporator and condenser manifolds to provide a serial connection of the flow paths. The experiments were performed with PHPs of only one type, composed of two coolers in stack and turned through 90° on their narrow side. A new parameter, representing the rate of pressure pulsations in a PHP, was introduced into consideration, and it is shown that this parameter correlates with the PHP performance.

Transient Simulation for a Pumped Storage Power Plant Considering Pressure Pulsation Based on Field Test

In this study, fast Fourier transform and inverse transform are adopted for noise reduction filtering the data of load rejection pressure of a single unit in a one-tube, four-unit pumped storage power station. Five-spot triple smoothing method is used to extract the time-average and pulsation value of the water hammer pressure of the spiral case and draft tube inlet. The reasonable correction formula is put forward, and the pulsating pressure rise rate of the spiral case (4.44%) and the draft tube inlet (−1.22%) are obtained. A mathematical model is also established for the transition process of the water conveyance and power generation system of the pumped storage power station, and the field single-unit load rejection condition is simulated. The simulation results are consistent with the measurements, and the accuracy of the calculation model in predicting the time-average pressure of water hammer is verified. Thus, the extreme successive load rejection conditions can be simulated based on the proposed model. Combining with the pulsating pressure rise rate of unit, the actual extreme value of extreme working condition is reasonably calculated. The conclusion shows that the pressure of spiral case and draft tube inlet after considering pressure pulsation can meet the control requirements, avoid the damage caused by extreme working condition test to unit, and ensure the operation safety of unit.

An approach of calculation and analysis of pulsating flow rate of single-sided ventilation due to unsteady wind pressure

Natural ventilation of buildings has received considerable attention aiming to reduce the energy consumption and CO2 emissions. The flow rate of a single-sided ventilation building due to unsteady wind pressure consists of two elements: mean ventilation rate and fluctuating ventilation rate. To design an efficient ventilation system, an accurate model that is capable of considering the variation of fluctuating flow needs to be developed. In this paper, a novel and simple model was developed that can predict the fluctuating ventilation rate due to the pulsating flow of single-sided, wind-driven natural ventilation in buildings. The model of the pulsating ventilation rate is derived based on the theory of wind engineering, the air compressibility, and inertia of air at the opening. The indoor and outdoor fluctuating wind pressure was constructed using a transfer function. It is found that there was an acceptable relative error of 13.9% compared with Haghighat’s model, which proved that the calculation method is reasonable. Finally, the model had also been used to analyze the effect of influencing parameters such as opening area, room volume, mean wind speed, turbulence intensity of the wind, and power spectrum density analysis on the pulsating ventilation rate.

The approach on reducing the pressure pulsation and vibration of seawater piston pump through integrating a group of accumulators

Seawater piston pump is a key power component for underwater equipment. Low pressure pulsation and vibration have become the key requirements of high quality seawater piston pump in the interest of improving the stability, reliability and stealth of underwater equipment. A new type crankshaft seawater piston pump was studied in this paper. The kinematics of the pistons was analyzed and a simulation model was established. The simulation results indicated that its pressure pulsation rate was as high as 17%. Fortunately, after integrating accumulators and optimizing the precharge pressures, the pressure pulsation rate can be reduced below 5% in the working range. The pump possessed better performance when the accumulators were precharged with optimized multiple pressures than with a single pressure. In addition, experimental analysis was conducted through measuring the pressure pulsation and vibration acceleration under different conditions. The experiment results of the pressure pulsation well agreed with the simulation results. Besides, the vibration acceleration of the seawater piston pump was obviously reduced in wide working range when the accumulators were precharged with the optimized combination multiple parameters. In conclusion, integrating accumulators into pump and optimizing the precharge parameters can reduce the pressure pulsation and vibration acceleration in the working range.

Pressure characteristics of a novel double rotor hydraulic transformer

The hydraulic transformer is the core component when it works with the common pressure rail system, which integrates the functions of the pump and the motor, and thus possesses sensitive pressure characteristics. The rotating speed has significant influence on the pressure characteristics of a hydraulic transformer while it has not been considered previously. In this study, aimed at improving the working performance, a novel double rotor hydraulic transformer is proposed and a comprehensive mathematical model considering the dynamic characteristics of the cylinder block is established. At the same time, a prototype is made and the experiment is conducted. The test results show that the robust rotor structure enables a larger pressure range, and the numerical results exhibit a good match with the test results. The parameter sensitivity study shows that the delivery pressure is mainly subject to the valve plate control angle δ and, under the effects of the resistance torques, pressure loss will occur especially under a large control angle and a high rotating speed. The magnitude of the instantaneous angular velocity fluctuation increases sharply when the speed is lower than 400 r/min, which is the main reason for the serious pressure pulsation at a low speed. As a result of the improved low-speed stability and output flow uniformity, the pressure pulsation rate of the double rotor hydraulic transformer is greatly reduced. However, the pulsation rate is still high at an extremely low speed. In addition, when the rotating speed exceeds the capability of the damping grooves, the pressure undershoot becomes serious at the A-T transition region around the control angle of −30°. Consequently, from the perspective of pressure characteristics, the limitation on the rotating speed under small control angles is suggested for the design of the double rotor hydraulic transformer controller.

Numerical and experimental studies on flow performances and hydraulic radial forces of an internal gear pump with a high pressure

Unbalanced radial force is one of the most urgent issues for internal gear pumps (IGPs) working at high working pressures. A numerical model for the prediction of the unbalanced radial force is essential for the structural design of gear pumps, facing the challenges of gear engagement description, dynamic mesh method, and so on. In this work, a three-dimensional computational fluid dynamics model of an IGP with a high working pressure was established based on the 2.5-dimensional dynamic mesh method, with cavitation and gear engagements included. The flow behavior and the hydraulic radial force of the high-pressure IGP were studied, and experiments for pump performances were conducted for comparisons. Results indicated that the numerical model could provide a reasonable solution of the flow rate and pressure pulsation for the high-pressure IGP, verified by the experimental data. The circumferential pressure distribution of the pump does not increase linearly, but presents a stepped increase. The hydraulic radial force fluctuates with gear rotation, and its value increases with the working pressure.

Growth, Coenosarc Pulsations, and Hydroplasm Movement in the Colonial Hydroid Dynamena pumila (L., 1758) Placed in Flow-Through and Nonflow Cuvettes

The coenosarc pulsations of the stolon and hydroplasmic flows (HFs) in the colonial hydroid Dynamena pumila (L., 1758) have been recorded in flow-through and nonflow, shallow cuvettes via time-lapse video microscopy. The water in the flow-through cuvette was refreshed during every 24 s. Each episode was video recorded for 2 h. Eleven indicators were used to compare hydroid reactions to maintenance in flowing and nonflowing water: the period and amplitude of pulsations of the stolon growing tip; the hourly stolon growth; the period and amplitude of transverse coenosarc pulsations; the period of unidirectional HF rate pulsations; the maximum velocity of HFs to and from the stolon tip; the distance of particle transfer per act of unidirectional HF; the volume of displaced hydroplasm per HF; and the percentage of the rest ratio in coenosarc pulsations and hydroplasm movement. On the whole, no significant changes in the coenosarc pulsations or in the growth and displacement of the hydroplasm were detected when they were compared sequentially in the same colonies in nonflowing and flowing water. At the same time, there were no changes in the growth, the frequency and amplitude of the transverse pulsations of the coenosarc, or the activity and extent of the hydroplasm currents. However, it was found that the period of growth pulsations increases by 20% in the regime with water exchange in comparison with the previous regime without flowing water. The period of HFs in the stolon increases by 42%, and the maximum current velocity decreases by 20% in flowing water. As a result, the calculated volume of moved hydroplasm in the stolon for one HF decreased by 30% in flow conditions.

Design of the Hydrostatic Thrust Spherical Bearing with Restrictors (Fitted Type)

The hydrostatic bearings are broadly observed in industrial applications owing to their potential characteristics of low running friction, high load-carrying capacity, high stiffness and small viscous dissipation. Spherical bearings have advantages over other configurations of bearings because of their self-aligning property and also their capacity to accept both radial and thrust loads. Operation of the spherical bearings is unaffected by angular miss-alignment. They are mainly used in machine tools, precision measuring instruments, hydraulic piston pumps and motors, gyroscope gimbals, telescopes, radar tracking units, air craft engines and rotary drum of centrifugal separator for enriched uranium. The main objective of this part of study is to handle the fitted bearing design taking into consideration the combined effects of rotational inertia, surface roughness and the fluid film viscosity variability. The mathematical expressions derived in part 2 for this type of bearings with its different configurations (with and without recess; hemispherical and partial hemispherical seats) have been used in the detailed bearing design. Improving the previous design through developing some mathematical expressions, a new conception is adopted to reveal the bearing consistency showing how the fluid flow rate pulsation or intermittent could be prevented. The detailed design procedures show the advantages of this method to get the central pressure ratio mathematically through maximizing the flow rate with minimizing the supply pressure which means minimum pump power to get maximum discharge. This design showed very high mean static stiffness of all the bearing configurations and an acceptable temperature rise for a heavy duty bearing without the need to a use a cooling system.

Heat transfer and turbulent characteristics in a pulsating flow

Heat transfer coefficient was experimentally estimated in the separation region behind a spanwise rib in a channel with forced flow pulsations. The same channel but without the rib was used for SIV measurements of dynamics of flow velocity vector fields that yielded in variations of normalized turbulent energy production, diffusion and dissipation over the flow rate pulsation period. High sensitivity of convective heat transfer, turbulent production, diffusion and dissipation to the forced flow pulsations have been revealed.

Experimental investigation of the influence of flow rate pulsations on the rivulet flow regime

The influence of flow rate pulsations on the rivulet flow regime has been investigated. The experiments were carried out on the underside of a smooth polyethylene plate. The investigation has shown that the influence of flow rate pulsations on the stream patterns is determined by flow peculiarities in the steady-state regime. Disturbances arising from pulsations of liquid flow rate can affect the stream liquid pattern of the rivulet. Such disturbance can cause the development of latent instability at individual points situated along the length of rivulet. The greatest effect on the stream structure is observed for the flow rate pulsation at liquid discharge with the ambiguity of rivulet regime. If the flow rate pulsations affect periodically the meandering rivulet, then it is possible to reduce the degree of meandering and convert the stream into the straight rivulet. In the regime of unstable meandering, it is impossible to identify correctly the effects caused by the flow rate pulsations at the initial area of the rivulet because of great self-acting pulsations of flow rate appearing in different sections along the rivulet.

Heat transfer of laminar pulsating flow in a rectangular channel

Pulsating flow has been found to both enhance and reduce heat transfer, although the explicit conditions that deliver heat transfer enhancement have yet to be identified. The current work builds on experimental and theoretical hydrodynamic analyses of earlier studies to investigate the effect of flow rate pulsations on the driving temperature difference for the case of constant heat flux, using a novel analytical solution to the energy equation in a rectangular channel. It is found that the oscillating temperature profiles are formed primarily as a result of fluid displacement against the temperature gradient, although diffusion at low frequencies and low Prandtl numbers obscures the mechanism. The temperature gradient at the wall is fixed for the case of constant heat flux, despite enhanced velocity gradients at the wall. The overall time-averaged change in Nusselt number with respect to steady flow is universally negative due to an enhanced axial heat flow towards the channel entrance, in agreement with similar studies in pipes. However, analysis of the time-dependent bulk temperature predicts that heat transfer is enhanced over the second half-cycle, where the flow rate is below it’s mean value. Hence, future work should investigate heat transfer enhancement using truncated sinusoidal flow rates.