Large Flow Rate Research Articles

A piezoelectric micro gas compressor with parallel-serial hybrid chambers

A piezoelectric micro gas compressor with parallel-serial hybrid chambers (PMGCPS) is presented, which consists of two compression stages of stage I and stage II. The stage I is composed of two piezoelectric driving units connected in parallel, while stage II is composed of a piezoelectric driving unit, forming an integral tower compression structure. Based on the tower compression structure, the PMGCPS owns the dual advantages of large flow rate and high output pressure. The prototype of PMGCPS is designed and manufactured. The driving frequency and voltage characteristics of PMGCPS are experimented. Under the driving frequency of 300 Hz and the driving voltage of 300 Vpp, the maximum flow rate and output pressure of PMGCPS is 795.6 mL/min and 13.4 kPa, respectively. PMGCPS provides new ideas for the further development of piezoelectric micro gas compressor.

Flow Stability in a Miniature Centrifugal Pump under the Periodic Pulse Flow

The flow behavior inside a miniature centrifugal pump, under a periodic pulse flow rate, was studied by means of numerical simulation. For a given incoming periodic pulse flow with a sine wave, the performance of the centrifugal pump was investigated in the section with increasing flow and the section with decreasing flow, and the special points of the flow rate and the periodic flow were identified. Further, the energy gradient method and the Q-criterion were adopted to analyze the internal vertical structure and flow stability. It was found that the regions with large variations in velocity and total pressure were mainly located at the leading edge of the suction surface and the middle area of the pressure surface of the blades. Irregular pressure fluctuation frequency under the periodic pulse flow was shown; this was mainly concentrated in the low-frequency zones close to the impeller’s rotational frequency. In addition, for the same flow rate in the periodic pulse flow, the pressure frequency fluctuation for the increasing flow rate section was higher than that observed for the decreasing flow rate section. It was found that the most unstable sections appeared in the first half-period of the flow rate variation (large flow rate), according to the distributions of the Q criteria of the vortex and the energy gradient function K. In this section, motions of strong vortices led to large gradients of the mechanical energy.

A Numerical Simulation on the Leakage Event of a High-Pressure Hydrogen Dispenser

For the sake of the increasing demand of hydrogen fuel cell vehicles, there are more concerns on the safety of hydrogen refueling stations. As one of the key pieces of equipment, the hydrogen dispenser has drawn attention on this aspect since it involves massive manual operations and may be bothered by a high probability of failure. In this paper, a numerical study is conducted to simulate the possible leakage events of the hydrogen dispenser based on a prototype in China whose working pressure is 70 MPa. The leakage accident is analyzed with respect to leakage sizes, leak directions, and the time to stop the leakage. It is found that, due to the large mass flow rate under such high pressure, the leak direction and the layout of the components inside the dispenser become insignificant, and the ignitable clouds will form inside the dispenser in less than 1 s if there is a leakage of 1% size of the main tube. The ignitable clouds will form near the vent holes outside the dispenser, which may dissipate quickly if the leakage is stopped. On the other hand, the gas inside the dispenser will remain ignitable for a long time, which asks for a design with no possible ignition source inside. The results can be useful in optimizing the design of the dispenser, regarding the reaction time and sensitivity requirements of the leakage detector, the size and amount of vent holes, etc.

Aerodynamic characteristics analysis of quadrangle inlet and exhaust grille for embedded ventilation cooling system of aircraft

Adding grilles at the inlet and exhaust of the aircraft ventilation cooling system helps to improve the aerodynamic characteristics and electromagnetic shielding characteristics of the whole system. Taking the X-47B aircraft as the research object, the quadrilateral open inlet and exhaust ducts and their grilles of the ventilation and cooling system embedded in the fuselage are designed. Based on CFD method, the influence of four design parameters of intake and exhaust grille: diversion angle, grille thickness, aperture shape and aperture size on flow resistance characteristics of the pipeline system is analyzed. The results show that the flow resistance characteristics are better when the grille diversion angle of inlet and outlet is smaller and closer to the conventional inlet and outlet. For the inlet, the rectifier effect is better when the grille thickness is larger, and the outlet of the exhaust duct needs a suitable thickness of the grille to balance the rectification and exhaust resistance. Besides, the circular hole grille shows good effect in the inlet and exhaust port. The small flow rate of inlet needs to use small aperture grilles to increase the rectification effect and suppress the internal and external flow interference, while the small flow rate of exhaust channel uses large aperture grilles, and the large flow rate uses small aperture grilles to improve the mixing rectification efficiency of internal flow to external flow.

Simultaneous quantification of anthraquinone glycosides, aglycones, and glucuronic acid metabolites in rat plasma and tissues after oral administration of raw and steamed rhubarb in blood stasis rats by UHPLC-MS/MS.

Rhubarb is a widely used herbal medicine. To achieve different effects, rhubarb is usually steamed with rice wine (steamed rhubarb). This steaming treatment increases the blood-activating and stasis-removing effects of rhubarb. A specific and accurate ultra high performance liquid chromatography with tandem mass spectrometry method was established for simultaneous determination of anthraquinone glycosides, aglycones, and glucuronic acid metabolites in plasma and tissues after administration of raw rhubarb and steamed rhubarb in blood stasis rats. Chromatographic separation was performed on ACQUITY UPLC BEH Shield RP 18 column using the mobile phase consisting of water and acetonitrile both containing 0.1% formic acid. Satisfactory linearity, precision, accuracy, extraction recovery, and matrix effect have been achieved. From pharmacokinetic study, it showed that glucuronic acid metabolites were found abundantly in plasma as bioactive components. The lower area under concentration-time curve, maximum concentration, and higher apparent volume of distribution (P<0.01), body clearance (P<0.01) values in steamed rhubarb showed that most components of steamed rhubarb have lower bioavailability in plasma compared with raw rhubarb. But it found these components were mainly distributed in spleen and liver with large blood flow and perfusion rates. The pharmacokinetics and tissue distribution studies of anthraquinone components will provide helpful information for clinical application of steamed rhubarb and raw rhubarb.

Effect of an impinging jet on the flow characteristics and thermal performance of mainstream in battery cooling of hybrid electric vehicles

The novel concept of impinging jet cooling, i.e., an active-passive air cooling strategy, was proposed to achieve improved battery thermal management in hybrid vehicles, and this method is supported by excess high pressure discharged air. To comprehensively realize the active-passive combined cooling behavior, a rectangular channel with a jet impingement hole was utilized to experimentally and numerically study the flow characteristics and thermal performance of the joint cooling mechanism. The numerical results were confirmed by the experimental data in this work, the maximum deviations of the offset and Nusselt numbers are 18.8% and 7.5%, respectively. The thermal transport performs much better under the interaction between the mainstream and impinging jet, i.e., the average Nusselt number and maximum Nusselt number can be increased by 0.43-16.55, 5.73-34.42, respectively, at inlet pressures of the impinging jet in the range of 1–6 bar. The values of Nu/Nu0/(f/f0) 1/3 are improved by 1.52–3.33. The jet fluid was deflected under the influence of the mainstream and a vortex can be induced, which is beneficial for the heat transfer performance. The jet fluid closely reached the heated plane at a relatively large volume flow rate and the heat transfer performance was excellent once the jet fluid touched the heated plane. The thermal boundary layer becomes thinned under the impact of the impinging jet but the magnitude of the reduction is relatively slight.

Numerical simulation of the effects of sandy water on regulator labyrinth channel in micro-sprinkler systems

Abstract The effects of sandy water on the W-shaped labyrinth channel of micro-sprinkler irrigation systems with large flowrate were investigated using Computational Fluid Dynamics (CFD). Using ANSYS FLUENT software and different inflow conditions (e.g., pressure, velocity, sediment concentration, and sand particle diameter), internal turbulent multiphase flow and sand deposition were simulated by the Eulerian multiphase flow model. Particle erosion in the labyrinth channel was calculated by the Discrete Phase Model (DPM). The results show that vortex movements and shear actions at the boundary layer cause self-flushing in the channel. The location of sand particle deposits and the turbulent dissipation rate are related to the operating pressure, which is optimal at 300 kPa. The erosion rate of the channel wall is proportional to the inflow sediment concentration but has no obvious relationship with inflow velocity. Based on the movement regulation of sand particles in the labyrinth channel, recommendations on filtration requirements and operating pressure of irrigation systems are proposed.

Stratified-to-annular gas-liquid flow patterns transition in a horizontal pipe

Air-water flow in a 20 mm horizontal pipe is studied using side-view visualization with a background image and Brightness-Based Laser-Induced Fluorescence technique. The investigation is focused on the transition from stratified to annular flow patterns. Stratified flow is organized at the pipe inlet, and the dynamics of liquid lifting up the pipe walls is investigated. During the transition to annular flow, the liquid film is spread over the pipe walls in a stable and gradual manner; the spreading begins before the disturbance waves are formed. Two transition regimes are identified. At large gas and low liquid flow rates, the film is spread up the pipe walls reaching a stable height unaffected by the passing waves. At low gas and large liquid flow rates, the liquid can be lifted by the large-scale waves, but it promptly drains downwards between the waves. Secondary flow in the gas phase is considered the main mechanism of liquid lifting and the only mechanism able to create a stable annular film. The processes of formation and development of disturbance waves are qualitatively the same as previously observed in vertical pipes. Namely, the disturbance waves are formed due to the coalescence of high-frequency initial waves appearing near the inlet; the disturbance waves undergo coalescence and grow in amplitude and speed. Quantitatively, the disturbance wave formation occurs at larger distances from the inlet compared to the vertical flow, and the acceleration rate is much lower. An estimation of circumferential shear stress due to secondary flow is made based on the roughness of the liquid film surface at the bottom of the pipe. An increase in this shear stress increases the height of the liquid film on the pipe walls.

Plasma-catalytic oxidation of volatile organic compounds with honeycomb catalyst for industrial application

Efficiently processing volatile organic compounds (VOCs) with nonthermal plasma and honeycomb catalyst for practical industrial applications presents a sizable challenge. An attempt has been made to generate a large volume of uniform plasma at atmospheric pressure in a practical-scale honeycomb catalyst. H-ZSM-5, a type of zeolite, was washcoated on a commercial bare honeycomb monolith as the catalyst-supporting material, after which the monolith was impregnated with Pd. The plasma discharge power can be controlled by controlling the humidity in the feed gas, metal content, applied voltage, and total flow rate of the feed gas. The plasma was characterized by the voltage and current waveforms, and optical emission spectroscopy (OES). In this study, 85% of dilute toluene (15ppm) was successfully removed from an airstream at a large flow rate of 60L/min with an energy density of 84J/L. Under this condition, the selectivity of CO2 was 76%. This investigation demonstrated the practical applicability of the plasma-honeycomb catalytic reactor to process a fast-flowing feed gas without resulting in a significant large pressure drop, which can hardly be achieved with typical packed-bed plasma reactors.

In-situ investigation on methane hydrate decomposition characteristics under variational seawater flow process

Natural gas hydrates (NGHs) are a form of natural gas widespread in the seafloor, and the realization of commercial exploitation is of great significance to solve the energy problem. There must be large amount of seawater and gas migration during the hydrate exploitation process. Studies have shown that seawater flow at a constant flow rate will enhance hydrate exploitation, especially at high flow rates. However, the seawater flow rate varies as a result of different seawater saturation in different areas of hydrate reservoir. There is little research on the effects of variational flow rate on hydrate decomposition characteristics. In this study, the effects of step-up flow rate and step-down flow rate modes on hydrate decomposition were investigated using the magnetic resonance imaging (MRI) system. The experimental results showed that the flowing seawater filled the pores that were occupied by free gas or generated by hydrate decomposition, which is beneficial to maintain the hydrate reservoir stability during the exploitation process. Through comprehensive comparison, the energy consumption of the variational flow rate mode was more than 60% less than that of the constant flow rate mode. For low hydrate saturation (22.5%), large seawater flow rate maintained a large driving force (fugacity difference) for hydrate decomposition, the efficiency of step-down flow rate mode was 131.1% greater than the efficiency of step-up mode; for high hydrate saturation (36.5%), low seawater flow rate made the mass transfer between seawater and hydrate more sufficient, the efficiency of step-up mode was 40.6% greater than that of step-down mode.

Energy consumption, flow characteristics and energy-efficient design of cup-shape blade stirred tank reactors: Computational fluid dynamics and artificial neural network investigation

Developing high-efficient and green energy-saving stirred tank reactors is of vital importance in liquid-liquid processing industries. Therefore, this work revealed the energy consumption, flow characteristics, and explored the energy-saving strategies of novel-designed Cup-shape Blade (CB) stirred tank reactors characterized by easy fabrication, low energy consumption and large pumping flow rate. Computational Fluid Dynamics (CFD) and Artificial Neural Network (ANN) were conducted to investigate the influences of geometrical parameters on liquid-liquid power number (NP), flow number (NQ) and flow patterns. The improved method for hyper-parameter specification indicates that the Bayesian regulation training algorithm and the two-hidden-layer scheme possess the best performance. Back Propagation Neural Network (BPNN) presents the best predictive accuracy for NP and NQ, and Learning Vector Quantization (LVQ) network shows the best classification capability of flow patterns. Analyses based on the ANN modeling and the “Local Interpretable Model-agnostic Explanations” method show the joint and complicated effects of geometrical parameters on energy consumption and flow characteristics. Procedures were proposed to ascertain the energy-efficiency blade configuration based on ANN.

Experimental and numerical study of upward flame spread and heat transfer over expanded polystyrene at different altitudes

Experimental and numerical study on upward, vertical flame spread was carried out on expanded polystyrene (EPS) at two different altitudes of 50 m and 3658 m to understand the effect that altitude has on flame spread of melted material. The experiments show that, with the altitude increase, the flame spread rate would decrease. At low altitude, the flame spread rate accelerated at later time, while at high altitude, the stagnant stage of pyrolysis front was formed. The numerical simulation could well give the trend of pyrolysis front evolution and the different flame spread behaviors with altitudes. It was found that, at low altitude, Raxincreased slowly in the turbulent period with relatively large entrainment air flow rate, mainly due to the increased and then decreased mass loss rate in the wall fire zone. While, at high altitude, the simulated increasing entrainment air flow rate, combined with the larger preheating length δf and the smaller flame heat flux qf", resulted in the stagnancy of pyrolysis front easily. It was hypothesized that extinction occurred eventually at high altitude due to competition between flame spread rate νf and preheating length δf.

Operation characteristics of open-cathode proton exchange membrane fuel cell with different cathode flow fields

Open-cathode proton exchange membrane fuel cell (PEMFC) is considered as a promising power source for unmanned aerial vehicles and portable applications due to its simple structure and low parasitic power. In this study, the operating condition effects of the open-cathode PEMFC with different cathode flow fields (parallel, pin-type, and metal foam) are investigated experimentally. Polarization curve and electrochemical impedance spectroscopy (EIS) are tested to characterize the cell performance and electrochemical impedance, respectively. The results show that the cell with the metal foam flow field has better performance than that with the other flow fields in the baseline conditions. Although increasing the fan voltage could provide adequate reactant gas and remove excess water, too large air flow rate could reduce membrane water content and decrease temperature that is bad for the cell performance. Increasing the operating temperature would improve the cell performance, but the increase of ohmic resistance caused by higher water evaporation rate cannot be neglected. The cell performance does not increase significantly with increasing the anode backpressure in the low current density region, but decreases with increasing the anode backpressure in the high current density region.

Varicose-whipping instabilities transition of an electrified micro-jet in electrohydrodynamic cone-jet regime

A cone-jet regime in electrohydrodynamic atomization (EHDA) is widely applied into printing, electro-spinning, spray-coating, and biological mass spectrometry. Regulating different instabilities of jet is crucial for optimizing its operating parameters. In present work, an atypical, hemispherical capillary with inner diameter of 0.40 mm and cap size of 6.20 mm was employed as atomization nozzle, through which a steady cone-jet regime was confirmed versus suitable feeding liquid flow rate and electric potential. A permanent and highly charged jet emits from a Taylor cone apex and further disintegrates into fine highly charged drops in the form of varicose or whipping instabilities. The results indicate that a steady cone-jet is observed in the specific ranges of the feeding liquid flow rate, electric potential and conductivity. The typical breakup instabilities including varicose and whipping are clearly observed with an increase in liquid flow rate for a fixed electric potential for most of liquids, and the transition from varicose to whipping instability easily occurs. For a steady cone-jet, the jet breakup instabilities usually depends on the competition between interfacial forces on the electrified jet. The transition process involving a low-viscosity jet with a large flow rate is observed, and the general parameter G=Γ2δμ0.52 is calculated to account for surface charge, surface tension, and viscosity effects, where Γ is the electric force to surface tension ratio and δμ is the inertia to viscous force ratio. Finally, the varicose, transition regime, and whipping are classified with first and second critical threshold values G = 40 and G = 102, respectively. Meanwhile, as the electrified jet transforms from varicose to whipping instabilities, the jet breakup length shows a trend of increasing first and then decreasing.

Differences in Formation Mechanism of Static Pressure Circumferential Distribution of Centrifugal Compressor Under Different Operating Conditions

Abstract The casing-wall static pressure of the centrifugal compressor behaves the double-peak distribution in the circumference at small flow rates (SM) but the single-peak distribution at large flow rates (LM). A previous study shows that the double-peak distribution is induced by the redistribution of impeller outlet flow rates. In this paper, by using the similar simplified method of directly imposing pressure boundary to the diffuser outlet, the original reason for the formation process difference of pressure distribution in the circumference at different operating conditions is further investigated. The results show that at LM, under the combined action of the specific downstream pressure distribution and the flow performance of the compressor itself, alternating low/high velocity airflow zones similar to those at SM cannot be established in the diffuser when the impeller outlet flow rates are redistributed. Therefore, the static pressure can only express the single-peak distribution in the circumference. In fact, whether the static pressure exhibits the double-peak or single-peak distribution in the circumference depends on whether the impeller outlet flow mutation can destroy the original flow balance. When the flow mutation is dominant, the double-peak distribution is created, whereas when the original flow balance is prevailing, the single-peak distribution is formed.

Оптимизация обратных направляющих аппаратов высокорасходных центробежных компрессорных ступеней CFD-методами

Calculations performed with modern computer fluid dynamics (CFD) programs aid in optimizing the flow path of a centrifugal compressor. The characteristics of the stator elements of the flow path, calculated by CFD methods, are considered to be quite accurate. Optimization of three-stage reverse-directing devices with a large flow rate (0.15) and different theoretical head coefficients (0.45; 0.60; 0.70) has been carried out. For optimizing return channels a parameterized model was created. Optimization was performed with MOGA (Multi-Objective Genetic Algorithm) optimization method in the Direct Optimization program of the ANSYS software package. The optimization goal was to achieve the minimum loss factor at the design point. In the optimization process, the following parameters were varied: the number of and the inlet angle of the vanes, the height of the vanes at the inlet, external and internal radii of curvature of the U-bend. For the return channel with a minimum loss coefficient, the dependences of this parameter on the flow coefficient were calculated. Comparison with the characteristics of the initial variant showed that the optimized return channels are more efficient over the entire flow range. Optimization allowed reducing the loss factor by 20%.

Key Optimization Technology of Intelligent Layered Water Injection with Hydraulic Control in Bohai Oilfield

Conventional hydraulic control intelligent layered water injection technology has shortcomings such as low accuracy of allocation, limited layered number, unsatisfying the requirement of slim hole and inability of monitoring of water injection downhole data. Based on the problems exposed in the application of in Bohai Oilfield, technical optimization research was carried out. A digital decoder is developed, the number of adjustment stages of flow control valve is increased, the large flow rate downhole flowmeter based on vortex street test principle is matched, and the layered allocation scheme is optimized. Thus the key optimization technology of intelligent layered water injection technology with hydraulic control in Bohai oilfield are formed. The optimized hydraulic control intelligent separate injection process can implement the maximum layer number of 6 layers, and the different size of flow control valves regulation stage are increased to 11 and 7 stages respectively. It can also meet the application requirements of 82.55 mm slim hole water injection well, and realize real-time monitoring of downhole data on the surface. After optimization, the system has been applied in 20 wells in Bohai Oilfield, which has stable and reliable operation, flexible nozzle adjustment, and real-time downhole data upload, accuracy more than 95%. Single well allocation cycle is cut down to 1 day. The application effect is good.

Leaf surface characteristics affect the deposition and distribution of droplets in rice (Oryza sativa L.)

We studied the effects of leaf surface characteristics on canopy droplet behaviour using two rice cultivars with similar leaf shapes but significantly different leaf surface characteristics: Jia58 (glabrous rice; smooth leaf surface and no burrs) and Yongyou12 (hairy-leaved rice; rough leaf surface covered with burrs). The plants were subjected to spray tests with different spray pressures and nozzle apertures. The results showed that the deposition amount per unit leaf area was significantly higher in the Yongyou12 canopy than in the Jia58 canopy. The diameter, volume median diameter, number median diameter, and coverage of droplets were significantly higher in Yongyou12 than in Jia58, while the coverage density of droplets was significantly lower. The proportion of small droplets of Jia58 is higher than that of Yongyou12. Thus, a larger amount of large-sized droplets could retain on the leaf surface of hairy-leaved rice, and a larger number of small-sized droplets were retained on the leaf surface of glabrous rice. Smaller pressure and larger flow nozzle were conducive to the retention of the Jia58, while Yongyou12 required larger pressure and larger flow nozzles. Ultrastructural analyses revealed that the leaf surface of glabrous rice had no trichomes and more wax than hairy-leaved rice, and the critical surface tension was lower, resulting in the retention of mainly small droplets on its leaf surface and a lower deposition amount. Therefore, in order to increase the deposition of pesticide droplets on the leaf surface in production, glabrous rice should choose nozzles with smaller spray pressure and large flow rate.

Numerical Investigation on the Evaporation Performance of Desulfurization Wastewater in a Spray Drying Tower without Deflectors

The desulfurization wastewater evaporation technology with flue gas has been widely applied to dispose of desulfurization wastewater. This paper investigates the effect of flue gas flow rate and temperature, wastewater flow rate and initial temperature, and droplet size on the evaporation performance of the desulfurization wastewater in a spray drying tower without deflectors. The results show that the flue gas flow rate and temperature affect the evaporation performance of desulfurization wastewater. The larger flow rate and higher temperature of flue gas correspond to the faster evaporation speed and the shorter complete evaporation distance of the wastewater droplet. Decreasing the flow rate and increasing the initial temperature of the desulfurization wastewater is advantageous to enhance the evaporation speed and shorten the complete evaporation distance of the wastewater droplet. Reducing the droplet size is beneficial to improve the evaporation performance of the desulfurization wastewater. The orthogonal test results show that the factors affecting droplet evaporation performance are ranked as follows: flue gas flow rate &gt; wastewater flow rate &gt; flue gas temperature &gt; wastewater initial temperature &gt; droplet size. Considering the evaporation ratio and the complete evaporation distance, the optimal setting is 14.470 kg/s for flue gas flow rate, 385 °C for flue gas temperature, 0.582 kg/s for wastewater flow rate, 25 °C for wastewater initial temperature, and 60 μm for droplet size. These studied results can provide valuable information to improve the operational performance of the desulfurization wastewater evaporation technology with flue gas.

A Novel Stacked Rotary Cup Atomizer Toward Efficient Centrifugal Granulation of Molten Blast Furnace Slag

Atomizer is one of the most important facilities in molten slag centrifugal granulation heat recovery system, which concerns the heat recovery rate of the system as well as the quality of slag particles. Aim to large slag flow rate in industrial application, a novel stacked rotary cup atomizer (SRCA) is proposed to achieve high‐quality centrifugal granulation performance. The authentic molten slag is adopted as working medium and the centrifugal granulation phenomena are visually investigated including the molten slag fragmentation on the surface of atomizer and the impacting of slag droplets on the water cooled wall. A film perforation fragmentation mode is found in the experiments under high slag flow rate. The granulated particle size distribution, average particle size, and slagging mass fraction produced by the atomizer are obtained. Moreover, the granulation performances of the SRCA with divergent structures are tested. The results demonstrate that the SRCA has excellent granulation performance in large slag flow rate to produce smaller particles and suppress slagging. Comparing with the typical rotary cup atomizer, the largest decrement in average particle size and slagging mass fraction for the SRCA is ascertained as 28.1% and 71.1%, respectively.