Small Flow Rate Research Articles

A Model of Coupled Flow in Impeller and Volute of a Single Stage Centrifugal Pump with Interaction of Impeller-Tongue Gap Flow

The impeller-volute interaction flow in centrifugal pump is influenced by the flow in impeller-tongue gap. In order to completely understand the mechanism of interaction between impeller-volute flow and impeller-tongue gap flow, a transient three-dimensional numerical simulation of the flow in a single stage centrifugal pump was carried out by applying sliding mesh approach and the standard k-ε turbulence model in CFD, and the derived transient flow data were time-averaged over a period of one blade passing the tongue. The analysis of the flow in the pump revealed that under off-design conditions, a reversed flow with lower pressure at small flowrates below the dutypoint or a stagnation region with higher pressure at high flowrates above the dutypoint appeared in the near tongue region in volute, which enhanced the asymmetric flow in impeller channels. It was consequently considered that the flow in impeller-tongue gap was a superposition of a drag flow by impeller and a pressure leakage flow driven by pressure difference between two sides of the tongue, and the pressure difference was zero at design condition, but increased with the deviation degree of the flow in impeller from the dutypoint. Under smaller flowrates, the gap leakage flow has direction opposite to that at higher flowrates, and affects much the volute flow. In the end, based on the analytical results, a semi-empirical model for the volute flow was deduced by one-dimensional flow continuity, and it may supply a reference for optimizing the flow in volute.

Hydrodynamics and mass transfer of Taylor bubbles flowing in non-Newtonian fluids in a microchannel

The paper presents a study on the mass transfer of Taylor bubbles flowing in non-Newtonian fluids (slug flow) using an oxygen-sensitive colorimetric method, for the bubble formation and flow stages. The effects of fluid rheology on the operation range, bubble length and bubble shape are first presented, showing that they can be well described by the effective viscosity. The concentration distribution and kLa are also altered by the fluid rheology. Such effect highly depends on the flow rates, leading to distinct phenomena under small and high flow rates. Nevertheless, for all the fluid systems the mass transfer can be described by three parts, the transfer through the caps, through the lateral film and the film-slug exchange. A mass transfer model is proposed accordingly, which shows a larger contribution of the film (20%-60%) in shear-thinning fluids than that in the Newtonian fluid (10%-25%).

Numerical Study of the Air Ingress Accident of the HTR-PM and Possible Mitigation Measures

The double-ended guillotine break (DEGB) of the horizontal coaxial gas duct of a high-temperature gas-cooled reactor is an extremely hypothetical accident, which could cause the air to enter into the primary circuit and react with graphite in the reactor core. The performance of the HTR-PM plant under this extremely hypothetical accident has been studied by the system code TINTE in this work. The results show that the maximum fuel temperature will not reach the temperature design limitation, and the graphite oxidation will not cause unacceptable consequences even under some conservative assumptions. Moreover, nitrogen and helium injected from the fuel charging tube were studied as the possible mitigation measures to further alleviate the consequences of this air ingress accident. The preliminary results show that only the flow rate of nitrogen injected reaches a certain value, which can effectively alleviate the consequences, while for helium injection, both high and small flow rate can prevent or cut off the natural circulation and alleviate the consequences. The reason is that helium is much lighter than nitrogen, and the density difference between the coolant channel and the reactor core is small when helium is injected. Considering the injection velocity, the total usage amount, and the start time of gas injection, helium injected with a small flow rate is suggested.

Design Analysis of Micro Gas Turbines in Closed Cycles

The problems faced by designers of micro-turbines are connected with a very small volume flow rate of working media which leads to small blade heights and a high rotor speed. In the case of gas turbines this limitation can be overcome by the application of a closed cycle with very low pressure at the compressor inlet (lower than atmospheric pressure). In this way we may apply a micro gas turbine unit of accepted efficiency to work in a similar range of temperatures and the same pressure ratios, but in the range of smaller pressure values and smaller mass flow rate. Thus, we can obtain a gas turbine of a very small output but of the efficiency typical of gas turbines with a much higher power. In this paper, the results of the thermodynamic calculations of the turbine cycles are discussed and the designed gas turbine flow parts are presented. Suggestions of the design solutions of micro gas turbines for different values of power output are proposed. This new approach to gas turbine arrangement makes it possible to build a gas turbine unit of a very small output and a high efficiency. The calculations of cycle and gas turbine design were performed for different cycle parameters and different working media (air, nitrogen, hydrogen, helium, xenon and carbon dioxide).

In-situ gradient formation by direct solid addition of buffer components

Buffer preparation and storage requires a significant facility footprint in large scale bioprocessing and together with the costs of supply chain management can have a substantial economic impact. In-line buffer mixing in chromatography is commonly performed by blending different buffer solutions using at least two pumps and a static or dynamic mixer. We developed a device for an in-line gradient delivery of buffering agents directly from solids to be applied for chromatographic separation processes. A solid feeding device with a screw conveyor and a hold tank for the solids was designed and a miniaturized system was 3D printed. The coefficient of variation for the precision of the solid feeding of 5 different buffering agents was below 5% even for very small solid flow rates necessary for lab-scale chromatography. Stability was demonstrated by a constant linear solid feed at a very low dosing rate of 0.05 g.min−1 over 24 hours. We demonstrated the suitability for chromatography by directly connecting the system to a standard chromatography workstation for protein chromatography. The solids were fed into a miniaturized continuously stirred tank reactor connected to an ÄKTA purification system. The performance of the in-line gradient delivery of buffering agents directly from solids was compared to conventional in-line buffer mixing. We were able to achieve highly linear gradients for elution using only one pump of a chromatographic system, generating the gradient by the direct addition of solids avoiding the necessity of additional pumps and hold tanks. By direct conditioning of buffers and the addition of solids a simple, just in time, at site preparation of buffers was possible. The design of the feeding unit for solid addition for buffer preparation is easily scalable and adaptable to work with or as a replacement for already existing in-line dilution or conditioning units.

Numerical Investigation on the Transient Flow of a Boiler Circulating Pump Based on the Shear Stress Transport Turbulence Model

Based on the shear stress transport (SST) turbulence model, the influence of different outlet pipe angles on the head and efficiency of a boiler circulating pump was analyzed. When the outlet pipe angle changed from 115° to 130°, the head and efficiency of the pump reduced significantly. The boiler circulating pump with 115° outlet pipe angle was selected as the further research object, and the reliability of the numerical simulation was verified by experiments. The transient flow of the prototype pump under the design flow rate condition (1.0Qd) and four other flow rate conditions (0.6Qd, 0.8Qd, 1.2Qd, and 1.4Qd) was studied. The results show that, under the conditions of design flow and large flow rate (1.0Qd, 1.2Qd, and 1.4Qd), the centrality and regularity of radial force distribution are obviously better than those of small flow rate (0.6Qd, 0.8Qd). The leakage of the rear seal ring is less than that of the front seal ring under five flow rate conditions. As the flow rate increases, the leakage of front and rear seal rings decreases, and the leakage ratio of front and rear seal rings increases. The energy loss of the rear cover plate is greater than the energy loss of the front cover plate under five flow rate conditions. With the increase in flow rate, the total loss energy of the prototype pump decreases first and then increases, and the energy loss of the disc becomes larger and larger.

Numerical and experimental investigation of solar air collector with internal swirling flow

Swirling flow was introduced into the solar air collector (SAC) with the purpose of thermal performance improvement. Numerical simulation was carried out to analyze the parameters that affect the thermal performance. The internal flow and heat transfer characteristics were compared between the basic and swirling-flow collectors in order to explain their difference in performance. The sensitivity study shows that the parameters of the swirling type, the swirling state and the swirling intensity all have significant influence on thermal performance of SAC. The numerical results show that the active swirling flow can yield better improvement than passive swirling flow. The maximum thermal efficiency growth rate (TEGR) of active swirling flow and passive swirling flow are 23.83% and 16.03%, respectively, compared with the basic model in the calculation. An experimental model was built to verify the effectiveness of swirling flow in thermal performance enhancement of SAC. The TEGR can be increased by up to 13.24% under small flow rate in the experiment. However, the improvement is not significant when the flow state is turbulent and the Reynolds number is high. This paper provides a new idea for the performance improvement of flat-plate solar air collectors.

Experimental and simulated optimization study on dynamic heat discharge performance of multi-units water tank with PCM

The water tank is most commonly a crucial energy storage device of a solar heating system. However, few existing studies have focused on the quantitative analysis of the heat discharge process of a square water tank. In this paper, a multi-units water tank with phase change material (MWT-PCM) was proposed. The dynamic heat discharge performances of the MWT-PCM and the conventional water tank both with 235.8 dm 3 were compared experimentally. A validated mathematical model was established to optimize the configuration of the MWT-PCM. Results demonstrated that: (1) The water temperature of both tanks had a sharp decline at the initial stage of the heat discharge process. (2) The instantaneous residual effective heat and the instantaneous heat supply of the WMT-PCM were 127% and 45.6% higher than that of the conventional water tank on average, respectively. (3) Due to the PCM, the effective heat discharge time could be prolonged by about 90 min. (4) When the PCM was arranged in a multi-unit manner, a small flow rate operation was recommended. However, the effect of changes in the total mass of the PCM was not obvious, and thus, for the given total mass, a smaller pipe diameter was recommended.

Distribution of condensation droplets in the last stage of steam turbine under small flow rate condition

The parameter variation, condensation and distribution of wet steam are very complicated when the steam turbine works under small flow rate condition. In this paper, the two-phase fluid model, the homogeneous nucleation model and the droplet growth model are combined to study the parameter variation in the last stage flow field, the condensation and distribution rule of wet steam and the interaction among them under small flow rate condition. The results show that the condensation location of wet steam, the number and size of droplets are influenced greatly by the location of vortex and the parameters of flow field. The droplet is mainly distributed on the side of pressure surface and the downstream of trailing edge of rotor blade. And the distribution of droplet corresponds to the distribution of the vortex. At 5%THA condition, the flow angle fluctuates violently, and the velocity triangle presents a distribution of “X“ shape. Besides, the vortex at corresponding locations is obvious, which corresponds to the distribution of droplets. The larger the droplet number, the larger the droplet size is.

Effect of Blade Outlet Angle on Radial Force of Marine Magnetic Drive Pump

To research the effects of the blade outlet angle on the performance and the radial force of the marine pump, the unsteady numerical simulation of the four different models is carried out. The radial forces on the impeller and the blades are obtained under different flow rate conditions. The time and frequency domain characteristics of radial resultant force on the impeller and the blades are analyzed and those of the impeller torque are researched. The results show that the radial forces of the impeller and the blades increase with the increase of the blade outlet angle at the same flow rate. With the same blade outlet angle, the radial forces decrease with the increase of the flow rate. The roundness of radial force vector diagram becomes more obvious with the decrease of the blade outlet angle. The root mean square (RMS) of radial force on the blades is about 30% of that on the impeller. The main frequency of radial force on the impeller and the blades is the axial passing frequency (APF), and that of impeller torque is the blade passing frequency (BPF), and there are peaks at the blade frequency multiplier. At the same flow rate, the main frequency and maximum fluctuation amplitudes on the impeller and the blades increase with the increase of the blade outlet angle. Meanwhile, the impeller torque increases with the increase of the blade outlet angle. With the same blade outlet angle, the main frequency, maximum fluctuation amplitudes, and the impeller torque decrease with the increase of the flow rate. The amplitude difference decreases with the increase of the flow rate. The blade outlet angle has an obvious greater influence on the radial forces and fluctuation at the small flow rate. The vibration test shows that the vibration intensities of model 25 and model 35 are less than 2.5 mm/s, and the vibration intensity of model 25 is about 0.2 mm/s less than that of model 35.

Design and characteristics of a triple-cathode cascade plasma torch for spheroidization of metallic powders

Arc plasma torch is an effective tool for spheroidization of metallic powders. However, as most conventional plasma torches were not specifically designed for plasma spheroidization, they may exhibit the disadvantages of the radial injection of powders, large fluctuations in the arc voltage, large gas flow rate, and disequilibrium between multiple plasma jets during the spheroidization process. Therefore, this paper presents a triple-cathode cascade plasma torch (TCCPT) for plasma spheroidization. Its structural design, including three cathodes, a common anode, and three sets of inter-electrodes, are detailed to ensure that powders can be inserted into the plasma jet by axial injection, the arc voltage fluctuations are easily maintained at a low level, and the plasma torches can work at a relatively small gas flow rate. Experimental results showed that the proposed TCCPT exhibits the following characteristics: (1) a relatively small arc voltage fluctuation within 5.3%; (2) a relatively high arc voltage of 75 V and low gas flow rate range of 10–30 SLM; (3) easy to be maintained at the equilibrium state with the equilibrium index of the three plasma jets within 3.5 V. Furthermore, plasma spheroidization experiments of SUS304 stainless steel powers were carried out using the proposed TCCPT. Results verified that the proposed TCCPT is applicable and effective for the spheroidization of metallic powders with wide size distribution.

Comparison of Swing and Tilting Check Valves Flowing Compressible Fluids.

Although check valves have attracted a lot of attention, work has rarely been completed done when there is a compressible working fluid. In this paper, the swing check valve and the tilting check valve flowing high-temperature compressible water vapor are compared. The maximum Mach number under small valve openings, the dynamic opening time, and the hydrodynamic moment acting on the valve disc are chosen to evaluate the difference between the two types of check valves. Results show that the maximum Mach number increases with the decrease in the valve opening and the increase in the mass flow rate, and the Mach number and the pressure difference in the tilting check valve are higher. In the swing check valve, the hydrodynamic moment is higher and the valve opening time is shorter. Furthermore, the valve disc is more stable for the swing check valve, and there is a periodical oscillation of the valve disc in the tilting check valve under a small mass flow rate.

Tube-Based DBD Plasma Treatment for Improving the Performance of the Slippery Coating Layers on Medical Catheters

This work develops a tube-based dielectric barrier discharge (DBD) plasma treatment for improving the performance of the slippery coating layers on medical catheters. The raw materials of the polymer catheters usually exhibit hydrophobic surface property and need a hydrophilic slippery coating layer for reducing the friction during catheter insertion. However, the high friction force may cause an uncomfortable feeling or even the infective or thrombosis injuries on the epithelium. This study develops an atmospheric tube-based DBD plasma for treating the surface of the plastic catheter for enhancing the coating performance of the slippery layer coating on medical catheters. The tube-based DBD plasma system is a semiclose and co-axial concentric circles system composed of a glass tube as the DBD layer and the inner supporting hook for catheter production as the center electrode for DBD discharges. The treatment for the inner and outer catheter tube can be achieved simultaneously with a small carrier flow rate of 30–100 sccm. Results show that the contact angles of these catheter tubes are significantly reduced after plasma treatment and the hydrophilicity of the treated surface maintains 57% for more than 30 min after the treatments. The catheters with different plasma treatments are coated with the commercial slippery layer and tested the kinetic friction under the ASTM D1894 standard. The kinetic friction test indicates that the catheters with plasma treatment exhibit lower kinetic friction force, indicating that lower friction during catheter medical insertion operations. The experimental results have shown that the medical catheter treated by the developed tube-based DBD plasma can be effectively modified and facilitated in the subsequent coating process.

Selective Diffusion of CO2 and H2O through Carbon Nanomembranes in Aqueous Solution as Studied with Radioactive Tracers.

Nanometer-thin carbon nanomembranes (CNMs) are promising candidates for efficient separation processes due to their thinness and intrinsic well-defined pore structure. This work used radioactive tracer molecules to characterize diffusion of [3H]H2O, [14C]NaHCO3, and [32P]H3PO4 through a p-[1,1',4',1″]-terphenyl-4-thiol (TPT) CNM in aqueous solution. The experimental setup consisted of two microcompartments separated by a CNM-covered micropore. Tracers were added to one compartment and their time-dependent increase in the other compartment was monitored. Occurring concentration polarization and outgassing effects were fully considered using a newly developed mathematical model. Our findings are consistent with previous gas/vapor permeation measurements. The high sensitivity toward a small molecule flow rate enables quantification of diffusion through micron-sized CNMs in aqueous solution. Furthermore, the results allow unambiguous distinction between intact and defective membranes. Even for extremely small membrane areas, this method allows detailed insight into the transmembrane transport properties, which is crucial for the design of 2D-separation membranes.

Dynamics of bubble formation at micro-orifices under constant gas flow conditions

Fine gas dispersion into a liquid is requested in a number of industrial applications. One way to achieve fine gas dispersion is to downsize the openings from which gas bubbles are generated. Accordingly, we have investigated the dynamics of bubble formation from submerged orifices ranging from 0.04 to 0.8 mm at a comprehensive range of gas flow rates for a system of air and deionized water. In this range of orifice size, we observe a different mechanism of bubble formation compared with millimeter-range orifices. We discuss the observations on the basis of temporal change of the bubble shape, bubble base expansion, and detachment criteria. At submillimeter orifices, the mechanism of bubble formation is highly influenced by the capillary pressure and the gas kinetic energy. The latter results in congregation of small bubbles in the vicinity of the orifice, even at very small gas flow rates. Moreover, we studied the evolution of individual forces applied to the surface of bubbles during their formation. We have found that the formation of bubbles at submillimeter orifices cannot be described with a quasi-static force balance. Finally, we present a bubbling regime map using relevant dimensionless numbers.

Using Artificial Potential Field Theory for a Cooperative Control Model in a Connected and Automated Vehicles Environment

Artificial potential field (APF) theory has been extensively applied in traffic path planning as an efficient method to avoid collision. However, studies in collision avoidance based on APF theory only considered the movement of single vehicle. In this paper, a vehicle cooperative control model for avoiding collision in the connected and autonomous vehicles (CAVs) environment is presented, using APF theory. The proposed model not merely guarantees the travel safety of vehicles in avoiding collision, but also promotes driving comfort and improves traffic efficiency. To verify the cooperative control model, simulations of four scenarios are designed and compared with the human driving environment. Five indicators are selected to evaluate the results, that is, time–space diagram, time mean speed (TMS), the rate of large deceleration time (large deceleration is that deceleration larger than –2 m/s2), the inverse time-to-collision ([Formula: see text]), and lane-changing times. According to the simulation results, the cooperative control model could alleviate the capacity drop and increase the TMS to improve traffic efficiency, reduce the rate of the large deceleration time to promote driving comfort, and decrease [Formula: see text] to promote safety in small and large input flow rates. The results reveal the proposed model is significantly superior to the human driving environment whether in free or congested situations, except for the lane-change times, which are slightly larger.

Study on improvement of hydraulic performance and internal flow pattern of the axial flow pump by groove flow control technology

When an axial flow pump operates at small flow rates, rotating stall may occur, which seriously restricts the pump performance and poses a great threat to the safe and stable operation of the whole system. The present work proposed a new groove flow control technology for the axial flow pump and studied its improvement effect and mechanism under stall conditions by numerical simulation. Results show that the groove flow control technology can significantly improve the hydraulic performance of the axial flow pump under stall conditions, with the pump head increment as high as 85.55% and the unstable region on the hydraulic performance curve was completely eliminated. In the inlet pipe region, it can effectively improve the bad flow state near the inlet of the impeller by increasing the axial velocity component and decreasing the velocity circulation dramatically. In the impeller region, the flow separation on the blade surface was improved and the cross-passage vortexes were suppressed, and the reasons were explained by analyzing the flow fields and pressure distributions in the representative grooves. In addition, compared with the diagonal groove (DG) scheme, the axial groove (AG) scheme showed better performance.

Correlation of the leakage flow rate with pressure changes in a clearance-sealed piston prover

Leakage flow rate is one of the most important contributions to the measurement uncertainty when measuring small gas flow rates with a clearance-sealed piston prover. Our previous study has shown that the systematic effects related to the change of the gas viscosity can be successfully corrected, whereas the effects related to the reproducibility of the leakage flow rate are poorly understood. This paper focuses on the interpretation and correction of the reproducibility related effects by analysing experimentally identified variations of the leakage flow rate and the gas pressure in the inclined piston prover. Small changes of the leakage flow in the inclined piston prover indicate that the position of the piston relative to the cylinder remains approximately the same. The obtained relationship between the leakage flow rate and the gas pressure below the piston led to the pressure-based correction of the leakage flow rate.

Effects of water flow rate and surface cover plant density on the growth of duckweed (Lemna minor L.)

Globally, agriculture sector is facing unprecedented challenges in producing fertilizers and increasing the amount of fertilizer production without having negative impact on the environment. Thus, the organic fertilizers are needed to be produced as they do not give any damages to the environment. Duckweed plant has a lot of potentials that can be used in the agriculture sector. This plant can breed in approximately 16-48 hours by splitting. The water needs and its breeding speed ability are the basis for conducting this research. The research objective was to determine the effect of water flow rate and surface cover plant density on the growth and yield of duckweed plants. This research was conducted in November–December 2018 in Cangkringan District, Sleman, Special Region of Yogyakarta, Indonesia. The experiment was arranged in a split plot design. The main plot was irrigation water flow rate, consisting of two levels, namely large water flow rate (0.336 L.second-1) and small water flow rate (0.085 L.second-1). The subplot was the density of the duckweed plant surface cover, consisting of 10%, 20%, 40% and 60%. The results of this study indicated there was no effect of water flow rate on the plant growth, yield, and yield quality of duckweed plants. The C/N ratio of the duckweed plants fulfilled the requirement to be used as green manure.

Design method for flow tube structure of electromagnetic water meter with shrunk measurement tube based on pressure loss-flow restriction

Due to the low flow rate measurement demand for battery-powered electromagnetic water meter, shrunk measurement tubes (such as circular section transition to square section) are often used to enhance flow velocity and measurement performance at small flow rate. However, this will also result in an increase in sensor pressure loss, even exceeding the pressure loss limit. Therefore, it is necessary to study a flow tube structure design method based on pressure loss-flow restriction, and design a flow tube structure which can not only maximize the induced voltage, but also meet the actual pressure loss requirement. Because there are many unknown variables in the formula of pressure loss mechanism, it cannot be directly used in structural design. Therefore, taking DN100 sensor as an example, based on finite element software, the variation of pressure loss with the length, width and height of rectangular section is obtained by orthogonal test method, and the numerical model of pressure loss is established. According to the requirements of industry and induced voltage enhancement, the optimal rectangular section size is found with the established pressure loss numerical model, and the structure of flow tube transition section is further optimized to reduce pressure loss. Finally, the prototype is made according to the optimized structure. Pressure loss experiment shows that the error between simulated value and measured value is within ±2.68% (±0.4 KPa). It means the pressure loss-flow restriction based design method for flow tube structure of electromagnetic water meter with shrunk measurement tube is effective and reliable.