Analysis of Timing Effect on Flow Field and Pulsation in Vertical Axial Flow Pump

Vertical axial flow pump device has the characteristics of large flow and low head, which is widely used in pumping station projects with head of 3–9 m. In order to study the influence of the timing effect of the impeller relative flow channel and guide vane on the flow field and pulsation in the axial flow pump device, the whole flow channel of the vertical axial flow pump device was taken as the research object. The reliability of the numerical simulation was verified by physical model test. The flow field characteristics and pressure pulsation characteristics of the inlet and outlet regions of the impeller, the guide vane and the campaniform inlet conduit at different timing positions of the impeller under different flow rates were analyzed. The results show that the pressure coefficient distribution of the impeller inlet of the vertical axial flow pump device presents four high-pressure areas and four low-pressure areas with the rotation of the impeller. The pressure pulsation at the inlet and outlet of the impeller is mainly affected by the rotation of the impeller, and the main frequency is 4 times the rotation frequency amplitude of pressure pulsation decreases with the increase of flow rate. When the flow rate increased from 0.8 Qbep to 1.2 Qbep, the average velocity circulation at the guide vane outlet decreased by 12%; there is an obvious negative value region of the internal regularized helicity of the guide vane. When the flow rate increases from 0.8 Qbep to 1.2 Qbep, the amplitude of the pressure pulsation coefficient at the outlet of the guide vane decreases gradually, with a decrease of 94%. When the flow rate is 1.2 Qbep, the main frequency and the secondary frequency of the pressure pulsation are both low-frequency, with obvious low-frequency pulsation characteristics. Under the small flow condition of 0.8 Qbep, the outlet flow fluctuation of seven guide vane was 18.9% on average, and the flow variation of each guide vane was large. Under the optimal flow condition of 1.0 Qbep and large flow condition of 1.2 Qbep, the outlet flow fluctuation of 7 guide vane is 4.7% and 0.56% on average, and the flow change of each guide vane is stable. The outlet flow of the guide vane is mainly concentrated in two guide vane slots of the guide vane, and the flow ratios are 30.56%, 30.14% and 29.16% under three flow conditions, respectively. The research results provide a scientific basis for the optimization design and stable operation of vertical axial flow pump device.

An Electrochemical Platform for the Carbon Dioxide Capture and Conversion to Syngas

We report on a simple electrochemical system able to capture gaseous carbon dioxide from a gas mixture and convert it into syngas. The capture/release module is implemented via regeneration of NaOH and acidification of NaHCO3 inside a four-chamber electrochemical flow cell employing Pt foils as catalysts, while the conversion is carried out by a coupled reactor that performs electrochemical reduction of carbon dioxide using ZnO as a catalyst and KHCO3 as an electrolyte. The capture module is optimized such that, powered by a current density of 100 mA/cm2, from a mixture of the CO2–N2 gas stream, a pure and stable CO2 outlet flow of 4–5 mL/min is obtained. The conversion module is able to convert the carbon dioxide into a mixture of gaseous CO and H2 (syngas) with a selectivity for the carbon monoxide of 56%. This represents the first all-electrochemical system for carbon dioxide capture and conversion.

Outflow adjustment coefficient for the design of storage facilities using the rain envelope method applied to Brazilian state capitals

Detention devices are often used as alternative measures for stormwater control. The Envelope Curve Method is widely used in Brazil to estimate detention device volumes. This method estimates the storage volume based on inlet and outlet balance, where the inlet is obtained by the Rational Method and the outlet by orifice bottom discharge. Usually, the outlet flow is adopted as a constant and equivalent to the maximum allowed, and this procedure can cause reservoir undersizing. This paper evaluates detention control measures’ hydraulic behavior for the Envelope Curve Method and proposes the inclusion of an outflow adjustment coefficient (Cout), seeking to compensate for the adoption of constant outlet flow simplification. Values for this coefficient were estimated for several Brazilian state capitals, ranging from 0.62 up to 0.65. The undersizing hypothesis due to the adoption of constant outlet flow was confirmed, as the simulations showed the need for an increase between 8.4% to 16.8% in the device size. This undersizing may be compensated for by applying the outflow adjustment coefficient (Cout). Keywords: adjustment coefficient, detention facilities, envelope curve, hydrologic design outflow adjustment coefficient.

Effect of Emissary Vein on Hemodynamics of the Transverse- Sigmoid Sinus Junction

Objective: To investigate the effect of the blood flow direction and afflux location of emissary veins (EVs) on the hemodynamics of the transverse-sigmoid sinus (TS-SS) junction.Methods: A patient-specific geometric model was constructed using computed tomography venography (CTV) and 4D flow MR data from a venous pulsatile tinnitus (PT) patient. New EV models were assembled with the afflux at the superior, middle and inferior portions of the SS from the original model, and inlet and outlet directions were applied. Computational fluid dynamics (CFD) simulation was performed to analyze the wall pressure and flow pattern of the TS-SS junction in each condition.Results: Compared to the model without EVs, the wall pressure was greatly increased in models with inlet flow and greatly decreased in models with outlet flow. The more closely the EV approached the TS-SS, the larger the pressure in models with inlet flow, and the smaller the pressure in models with outlet flow. The flow streamline in the lateral part of the TS-SS junction was smooth in all models. The streamlines in the medial part were regular spirals in outlet models and chaotic in inlet models. The streamlines showed no obvious changes regardless of afflux location. The velocity at the TS-SS junction of inlet models were uniform, medium-low flow rate, while in control and outlet models were the lateral high flow rate and the central low flow rate.Conclusion: The flow direction and afflux location of EVs affect the hemodynamics of the TS-SS junction, which may influence the severity of PT.

Optimization of the Outlet Flow Ratio of Mini-Hydrocyclone Separators Using the Full Factorial Design Method to Determine the Separation Efficiency

Cyclone separators are widely used to eliminate particles flowing through pipelines in equipment from various industrial processes. Unlike general filters, cyclone separators can constantly and effectively eliminate foreign substances present in the fluid flowing through the equipment. In this study, we fabricated mini-hydrocyclone separators using the 3D printing method for application in the steam and water analysis system (SWAS) in a thermal power plant instead of the conventional strainer filter. The gravimetric method was used to measure the separation efficiency of the hydrocyclone separators and compare the weights of the sludge discharged from the underflow and overflow outlets. The outlet flow ratio was optimized by adjusting the diameters of the spigot and vortex finder of the separators, which influenced the outlet flow rate. To apply the gravimetric method more objectively, the optimum values of the diameters of the vortex finder and spigot with an outlet flow ratio of 1 were determined using full factorial design (FFD) in the design of experiments (DOE). The obtained values were verified through numerical analysis using the ANSYS Fluent software. Furthermore, after fabrication of the mini-hydrocyclone separators using an SLA-type 3D printer, we conducted a numerical analysis, and the results were compared with that of the actual experiment. It was observed that the use of FFD can effectively optimize the desired outlet flow ratio in the mini-hydrocyclone separator. In addition, the changes in the outlet flow ratio do not affect the separation efficiency of the cyclone separators.

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

The casing-wall static pressure of the centrifugal compressor behaves the double-peak distribution in the circumference at small flow rates but the single-peak distribution at large flow rates. 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 large flow rates, 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 small flow rates 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.

Design and Testing of a Pneumatic Oscillating Chinese Wolfberry Harvester

A pneumatic oscillating Chinese wolfberry harvester was designed to improve the efficiency of manual harvesting and minimize fruit damage by mechanical harvesting. The shedding model of Chinese wolfberry under pneumatic forces was established based on kinetic analysis, and the flow field characteristics were investigated using computational fluid dynamics (CFD). The position and shape of the fan outlet were determined by comparing the effects of a linear reduction outlet and a Laval reduction outlet on the outlet airflow rate. The size of the oscillating mechanism was optimized with nonlinear constraints to achieve uniform oscillation of the airflow. A three-factor, three-level orthogonal test was conducted on the NingQi 7 wolfberry variety. The flow rate at the outlet, the oscillation frequency, and the outlet distance were the test factors, and the net harvesting rate of ripe fruits, the harvesting rate of green fruits, and the damage rate of ripe fruits were the test indices. The results showed that the net harvesting rate of ripe fruits was 85.21% at an outlet distance of 10 cm, an outlet flow rate of 70 m·s−1, and an oscillation frequency of 2 Hz. This study provides references for the design of pneumatic harvesters for Chinese wolfberry.

Experimental assessment of the rotor outlet flow in a twin-entry radial turbine by means of Laser Doppler Anemometry

The current paper presents the validation of some hypotheses used for developing a one-dimensional twin-entry turbine model with experimental measurements. A Laser Doppler Anemometry (LDA) technique has been used for measuring the axial Mach number and for counting the number of particles downstream of the rotor outlet. These measurements have been done for different mass flow ratio (MFR) and reduced turbocharger speed conditions. The flow coming from each turbine entry does not fully mix with the other within the rotor since, downstream of the rotor, they can still be differentiated. Thus, the hypothesis of studying twin-entry turbines as two separated single-entry turbines in one-dimensional models is corroborated. Moreover, the rotor outlet area corresponding to each flow branch has linear trends with the MFR value. Therefore, the rotor outlet effective area used for one-dimensional models should vary linearly with the MFR value.

High Resolution 2.5D PIV Measurements of the Flow Fields Generated by Small Fans

The free jets of an axial and a centrifugal fan have been scanned by a specialized particle image velocimetry (PIV) set-up, which allows for volumetric scans of the time-averaged velocity field. Both of these fans have similar dimensions of approximately 70 mm x 70 mm x 25 mm. A classic PIV set-up was combined with a precise linear stage to move the fans through the laser fan beam in small steps, creating a dense array of measurement planes. Two components of the time-averaged velocity field are captured by the first 2.5D scan. Another scan, with the fan rotated by 90° about its outlet surface normal, captures the missing third velocity component. This article describes the details of the measurement set-up, and mentions measures concerning seeding, reflections, and calibration. In the signal processing stage, two independent sets of gathered image data have to be processed, producing two sets of velocity image frames. These are subsequently combined using gridded interpolation in order to obtain a 3D velocity field. Specifically devised software tools allow for a CFD-like analysis and visualization of the flow field. Typical parameters of the generated jets, like the spreading and rotation rates, are calculated from the measurement data and details of the outlet flow fields are investigated. The interpolated data are also used to analyze the influence of an assumed coarser measurement grid resolution on the results for the obtained outlet flow fields.