Top Clearance Research Articles

Experimental investigation on short-time and long-time tribological performance of Fischer-Tropsch fuel compared with fossil diesel

ABSTRACT The Fischer-Tropsch (F-T) fuel, as an alternative fuel for internal combustion engines, can cause undesired wear issues on engine components mainly due to its almost zero sulfur content. In order to explore a conveniently accessible additive to improve the lubricity of the F-T fuel, this study conducted both short-time and long-time tribological performance experiments of the F-T fuel added with 200 ppm lubrication improver Infineum R655 and compared with commercial fossil diesel. A four-ball wear test machine was used to perform fuel anti-wear and load-carrying properties tests. Two four-cylinder fuel pumps with top clearance and flat top two types of plungers were, respectively, operated with the F-T fuel and diesel for 300 hours. The parameters characterizing the tribological performance of the fuel pump plunger couples before and after the durability test were measured, including roundness, straightness, depth of parallelism, line profile, sealing time, and fuel delivery amount. The anti-wear property test results show that the wear scar diameter of the metal ball is 0.59 mm for the F-T fuel, which is 7.8% decreased than that of diesel. The results of fuel load-carrying capacity experiment exhibit that the maximum nonseizure load of the F-T fuel is 246 N, which is better than that of diesel. Regarding the fuel pump bench 300-hour operating results, wear of the fuel pump plunger components was acceptable using the F-T fuel with the lubrication improver, without any modification of fuel pumps. Additionally, the improvement brought by this additive is applicable to the two common types of plunger components mentioned above. The results of this study reveal that the desired tribological performance of the F-T fuel can be achieved by adding the lubrication improver additive evaluated in this work.

The Influence of Lobe Top Clearance on the Performance of High-Speed Centrifugal Pumps

High-speed centrifugal pumps are widely used in several industries due to their high efficiency and small footprint. In actual applications, there are issues such as low operational efficiency and a small high-efficiency flow interval; particularly, the leakage occurring in the impeller channel gap presents a significant barrier to the pump’s performance and stability. This study takes the fully open impeller miniature high-speed centrifugal pump as the object and uses a numerical simulation calculation method. The objective of this research endeavor is to analyze the effects of different flow conditions on a high-speed centrifugal pump’s external characteristics, flow field characteristics, and energy loss. The findings indicate that lobe top clearance exerts a substantial impact on the efficiency of high-speed centrifugal pumps. Increasing the lobe top clearance will result in a reduction in pump head and efficiency, particularly under high flow conditions. The lobe top clearance has a significant impact on the complexity of the flow in the impeller, particularly the flow close to the suction surface of the impeller, according to an analysis of the flow field characteristics. The energy loss analysis further confirms the importance of reducing lobe top clearance for improving pump performance and reducing energy loss. These results provide valuable guidance for optimizing centrifugal pump designs with lobe top clearance.

P42: Effect of impeller number and design variation on the hemolysis performance of magnetically levitated centrifugal pumps

Background: Hemolysis is linked to an increase in the length of exposure to high shear stress in addition to the degree of shear stress. Turbulence is also a significant cause of blood injury. In the maglev ventricular assist device blood is only in contact with the pump housing and impeller. So, it is vital that decreasing NPSS, reducing exposure time, and the suppression of disturbed flow are incorporated into the optimization design for blood pump. The blood pump must also deliver enough pressure head and flow rate to sustain clinical circulation. The purpose of this study is to analyze the effects of different number of blades, number of splitters, blade length, blade angle and its distribution on pressure head, hemolysis and platelet activation. Firstly, computational fluid dynamics was used to analyze the effects of the above characteristics on scalar shear force, velocity distribution, hemolysis, and then the validity of the numerical analysis was verified by combining with in vitro hemolysis experiments, and finally the best impeller design was selected. Methods: In this study, three rotors with different number of vanes were developed. Compared to the CentriMag with curved vanes, all three variants have straight vanes to improve the pump efficiency and the passability in the pump. The inlet and outlet edges of the vanes are chamfered to reduce the shear stress area. In order to avoid excessive axial force makes the whole rotor in the rotation process floating, in the back cover plate position designed to raise the structure, in order to increase the surface area, reduce the axial force to stabilize the leaf top clearance, the three new design of the rotor back cover plate raised degree is also different. In order to balance the number of blades and the impeller’s hydraulic performance, the outer diameter of the impeller is also designed. 6-blade rotor consists of 3 blades and 3 spliters, the outer diameter of the impeller is 43.5mm; 8-blade rotor consists of 4 blades and 4 spliters, the outer diameter of the impeller is 43mm; 9-blade rotor consists of 3 blades and 6 spliters, the outer diameter of the impeller is 43mm. The 9-blade rotor consists of 3 blades and 6 splitters, with a minimum impeller outside diameter of 42.5mm. Results: By CFD simulation, the 9-blade maglev impeller outperformed several other impellers in terms of shear force, shear area, and passability, and the NIH in in vitro experiments was <0.0016g/100L Conclusion: The 9-vane magnetically levitated rotor developed in this study improves pump passability and reduces the occurrence of hemolysis in the pump by reducing the vane shear forceFigure 1. Independently developed magnetic levitation hemolysis platformFigure 2. Newly designed 3-bell bladeFigure 3. Computational fluid dynamics analysis of different impellers

Effect of blade top clearance on semi-open fuel pump performance and leakage vortex

Effect of blade top clearance on semi-open fuel pump performance and leakage vortex

Optimal Design of Double Stage Internal Loop Air-Lift Bioreactor

Biorefinery systems play a critical role in the transition towards a sustainable bioeconomy, and bioreactors are a key component in these systems. While mechanically stirred reactors have been extensively studied, there is a lack of research on pneumatically driven systems like air-lift reactors (ALRs). This study aims to address this gap by examining the hydrodynamic behavior of a double draft tube airlift bioreactor using Computational fluid dynamics simulations. Ten different geometric configurations were investigated, with variations in draft tube placement, liquid height, distance between draft tubes and draft tube diameters. Results showed that the placement of the draft tubes heavily influenced hydrodynamic behavior, with smaller distances between draft tubes and a funnel configuration leading to higher velocities. Stable downcomer velocities were achieved by maintaining a consistent distance between the bottom clearance and the sum of the distance between draft tubes and the bottom clearance on the top clearance. The model was validated against literature experimental data. This study provides insight into the optimal design of ALRs, which can contribute to the development of more efficient and effective bioreactor systems. The findings can be used to forecast the most optimal configurations of airlift bioreactors and have significant value for the development of more efficient biorefining concepts in light of the increasing importance of studying biorefineries and their components in the shift towards a biomass-based economy.

A new way to evaluate thrombotic risk in failure heart and ventricular assist devices

Thrombosis is one of the main complications in patients implanted with ventricular assist device (VAD). The complicated structure and disturbed flow field within failure heart and blood pump play an important role in thrombosis formation. In this study, the influence of Left ventricular (LV) volumes on flow field contributing to thrombosis formation within failure heart and VAD was investigated. Computational Fluid Dynamics (CFD) methods were employed to investigate the effect of different LV volumes on the thrombogenic potential of failure heart and VAD. Lagrangian methods were utilized to obtain information on platelet voyage trajectories. The concepts of mean and threshold of stress accumulation and residence time were introduced to accurately assess the likelihood of thrombus. Eulerian methods were used to identify thrombus-prone locations. CFD results showed that residence time (RT) was the main cause of thrombus formation in the failure heart, and the percentage of platelet trajectories above the RT threshold increased significantly with increasing LV volume. The RT in the left atrial appendage and LV increased significantly with LV volume increasing, which indicated that thrombus is prone to form there. Compared with the failure heart, non-physiological shear stress (NPSS)-caused platelet activation is the main reason for thrombus formation within VAD. The narrow zones (top clearance and secondary flow passage) within VAD have a high incidence of thrombus generation. In VAD patients, the LV volume has an important impact on thrombosis probability within failure heart, in which the larger size of the LV volume is, the higher risk of thrombosis will be. The size of LV volume has little effect on the thrombosis formation probability of VAD, where the NPSS plays the leading role in thrombosis formation. The finding of this study can be utilized to guild the clinical treatment and VAD structure optimization design for reducing the thrombosis risk.

Fracture Evolution between Blasting Roof Cutting Holes in a Mining Stress Environment

The problem of strong ground pressure caused by thick and hard roofs in coal mine stopes has become more prominent. Blasting roof cutting and pressure relief are effective technical ways to solve this engineering problem. The key to achieving roof cutting and pressure relief is the evolution and penetration of cracks between blasting roof cutting holes in a mining stress environment. To solve this problem, research on the evolution of cracks between blasting roof cutting holes in a mining stress environment is being conducted. Along with specific engineering examples, the mechanical effect of blasting dynamic load in the surrounding rock medium between holes in a mining stress environment is analyzed using the research methods of field investigation, blasting simulation, and mechanical analysis. The fracture evolution law between blasting roof cutting holes under the conditions of different hole diameters and spacings, confining pressure environments, and rock mass strengths is analyzed using the univariate comparative analysis method. The research shows that the superposition effect of blasting dynamic load between adjacent blastholes in the transmission process leads to the “X” type penetration evolution of surrounding rock fracture area and fracture area between blastholes. Among them, the blasting effect of a hole diameter of 70 mm and a hole spacing of 0.8 m is best. When designing the blasting roof cutting scheme, we should pay attention to the key factors such as hole diameter and hole spacing. The hole spacing is particularly critical to the effect of roof cutting and crack formation, whereas the confining pressure and rock mass strength have little impact on the expansion and development of blasting cracks, which can be listed as secondary factors for comprehensive analysis in design. According to the transmission law of blasting dynamic load between holes, the critical criterion of blasting top clearance penetration under mining stress environment is deduced. Four important factors affecting blasting top cutting effect are simulated and studied for optimizing the design of roof cutting scheme. Practical engineering application results show that the blasting roof cutting scheme achieves a good seam- forming effect and creates good initial conditions for thick and hard roof cutting. It can serve as a reference for the decision making of blasting top caving technology under similar engineering conditions.

Hydraulic Optimization of Closed Transformation of Open Sump for the Water Treatment Pumping Station

Taking the closed modification of an open sump of a water treatment pump station as the research background, the hydraulic design criteria for the closed modification of the sump are put forward by combining numerical simulation, model test. Based on CFD technology, a water pumping station including closed sump, bellmouth, impeller, guide vane, elbow and outlet sump is simulated, and the hydraulic performance of the schemes under different parameters is analyzed and compared. The top floor clearance, width, back wall distance, and floor clearance of the sump are optimized hydraulically, and the hydraulic design criteria of the closed sump are obtained. The results show that when the recommended optimization parameters of the closed sump in this study are that the top floor height HD is 0.9 DL, the width B is 3.0 DL, the back wall distance T is from 0.4 DL, and the floor clearance C is 0.75 DL, the internal flow pattern and hydraulic of the closed sump is better. (DL is the diameter of bellmouth of water pumping station). The model test was set up to compare the hydraulic performance of the pumping station between CFD and the test. The results showed that the CFD data is in good agreement with the experimental data.

Research on the Adjustable Guide Vane in a Compressor Sector Cascade

In order to simulate the inlet flow angle and Mach number of the tested blade, a row of guide vanes is set before the tested blade during the sector cascade experiment. In this paper, a kind of adjustable guide vane (AGV) is designed, which can rotate continuously and change the inlet flow angle of the tested blade conveniently and quickly. The variation rule of the clearance between the AGV and the end wall is introduced. The influence of the clearance on the flow field structure under different Mach number and incidence angle is studied by numerical and experimental methods. It is found that the clearance of the leading edge is small at the top and the root, and the leakage vortex is mixed with the passage vortex. The interaction between the leakage vortex and the passage vortex in the trailing edge results in the decrease of Mach number and the increase of flow angle at the AGV outlet. The clearance has little effect on the span of 20% - 80%. At the same incidence angle condition, with the increase of Mach number, the influence range of leakage vortex is expanded, and the variation magnitude of flow angle and Mach number at the top and root position is increased; At the same Mach number condition, with the decrease of the AGV rotation angle from positive to negative, the top clearance is increased gradually, and the root clearance is decreased gradually. The separation range at the top is expanded gradually, which results in the variation magnitude of flow angle and Mach number is increased, but the effect is opposite at the root of the AGV.

Influences of top clearance and liquid throughput on the performances of an external loop airlift slurry reactor integrated mixing and separation

Abstract A new developed external loop airlift slurry reactor, which was integrated with gas–liquid–solid three-phase mixing, mass transfer, and liquid–solid separation simultaneously, was deemed to be a promising slurry reactor due to its prominent advantages such as achieving continuous separation of clear liquid from slurry and cyclic utilization of solid particles without any extra energy, energy-saving, and intrinsic safety design. The principal operating parameters, including gas separator volume, handling capacity, and superficial gas velocity, are systematically investigated here to promote the capabilities of mixing, mass transfer, and yield in the pilot external loop airlift slurry reactor. The influences of top clearance and throughput of the clear liquid on flow regime and gas holdup in the riser, liquid circulating velocity, and volumetric mass transfer coefficient with a typical high solid holdup and free of particles are examined experimentally. It was found that increasing the gas separator volume could promote the liquid circulating velocity by about 14.0% at most. Increasing the handling capacity of the clear liquid from 0.9 m3·h−1 to 3.0 m3·h−1 not only could increase the output without any adverse consequences, but also could enhance the liquid circulating velocity as much as 97.3%. Typical operating conditions investigated here can provide some necessary data and guidelines for this new external loop airlift slurry reactor to upgrade its performances.

Heat transfer simulation in cavity of twin screw compressor under coupling of clearance leakage-heat by utilizing fuzzy beamlet finite element model

In order to optimize structure of twin screw compressor, and improve the working efficiency of twin screw refrigeration compressor, the heat transfer rules of cavity in twin screw refrigeration should be obtained correctly. Because the coupling of clearance leakage flow and heat transfer has a significant effect on heat transfer of cavity medium of twin screw refrigeration compressor, the heat transfer model of cavity medium under clearance leakage-heat coupling is constructed. To promote the computation accuracy and efficiency, the fuzzy beamlet finite element model is constructed by considering fuzzy affecting parameters and taking beamlet transform as interpolating function of element. The heat transfer laws of medium in cavity are obtained based on the theoretical an experimental analysis. Based on the simulation results, the computation error of fuzzy beamlet finite element method has least computation error and diversity than the other two methods for comparison, and the running time of fuzzy beamlet finite element method is least. Heat transfer analysis of medium in cavity under three conditions is carried out, and results show that temperature of cavity medium of twin screw refrigeration compressor is highest when the clearance leakage-heat coupling is considered and agrees better with reality; therefore, the proposed method has higher computing precision and efficiency than selected numerical methods according to computing results and running time. The impact of different clearances on heat transfer of medium in cavity is analyzed based on fuzzy beamlet finite element method, results show that the temperature of cavity medium increases accordingly as tooth top clearance, clearance between teeth, suction end clearance and exhaust end clearance increase, and the suction end clearance and exhaust end clearance have less effect on temperature of cavity medium.

Investigation of the performance of double-layer diverging combustion chamber in a single-cylinder diesel engine

Double-layer diverging combustion chamber (DLDC chamber) was designed for the diesel engine to increase the in-cylinder air utilization and change the fuel–air mixing process by diverging the fuel spray into two layers. A 135-type diesel engine was selected to find out the DLDC chamber performance characteristics and compare the DLDC chamber performance with the re-entrant chamber. The influence of the injection parameters on the DLDC chamber performance showed that the injection timing affected the chamber performance more significantly than the injection pressure; advancing the injection timing decreased the BSFC; postponing the injection timing showed the potential to decrease the exhaust emissions simultaneously and decreasing the injection pressure showed the potential to decrease the NOx without worsening the BSFC. The comparison results showed that the DLDC chamber had lower BSFC and provided less soot with specific injection timings, while the DLDC chamber obtained higher NOx; the DLDC chamber had a longer ignition delay with a higher maximum in-cylinder pressure and higher heat release rates during the premixed combustion phase. The investigation suggested that the injection parameters affected the fuel–air mixing and combustion in different layers and made the DLDC chamber obtain different engine performance; making more fuel spray flow into the upper layer and the top clearance reduced the BSFC of the DLDC chamber but sometimes increased the soot; diverging the fuel spray into the two layers improved the fuel–air mixing process and increased the heat release rates of the premixed combustion phase but still resulted in some inhomogeneous mixture distribution.

Influence of Top Clearance Height in Airlift Reactor on the Aerobic Granular Formation

Conventional active sludge is the technology that is usedcommonly in wastewater treatment. However, this technology has thedisadvantage, its relatively low settling speed causing a large landrequirement. One technology that can be used to overcome this deficiencyis aerobic granular. In this study aerobic granular is formed in acontinuous flow system of airlift reactor with a 12 (twelve) hourshydraulic retention time. Aeration is carried out for 24 hours at a rate of 2liters per minute (lpm). The height variation of top clearance (ht) is usedto determine its effect on the aerobic granular formation. The ht variationused is 15 cm, 20 cm, and 30 cm. The height of top clearance at the airliftreactor affects the circulation and superficial gas velocity which thenaffect the hydrodynamic shear force. The larger the hydrodynamic shearforce, the better the granular quality will be. The granular quality isdetermined based on physical characteristics including Sludge VolumeIndex (SVI), sludge density index (SDI), settling velocity, size, and aspectratio. The result shows that the height of top clearance affects the granularquality that formed. However, the effect is not linear. The non-linearity ofthe relationship between the top clearance height and granular formationcan be due to the sizeable superficial gas velocity and biomass washout. The ht variation that provides the best granular quality is achieved at 15cm, followed by 30 cm, and finally 20 cm. The ht variation of 15 cmreaches an optimum result with the value of SVI is 50 ml/g, settlingvelocity 39,4 m/hour, SDI 2.02 g/ml, size 3.5 mm, the aspect ratio of 0.86, and organic removal efficiency reaches 87.2%.

Visualization Investigation of the Influence of Chamber Profile and Injection Parameters on Fuel Spray Spreading in a Double-Layer Diverging Combustion Chamber for a DI Diesel Engine

The double-layer diverging combustion chamber (DLDC chamber) aims to improve the fuel–air mixing formation and promote in-cylinder air utilization by changing fuel spray spreading characteristics. In order to investigate how the DLDC chamber profile and injection parameters affect the fuel spray spreading, visualization of fuel injection and impingement tests were carried out on two different DLDC chambers with different fuel injection parameters. The visualization test results showed that double-layer fuel spray spreading was obtained in the two DLDC chambers and the peripheral top clearance of each chamber was utilized efficiently. The DLDC chamber with a 50% upper layer volume provided a larger fuel spray distribution region after the start of injection. The DLDC chamber with a 70% upper layer volume obtained a larger fuel spray distribution region with better top clearance utilization at the later stage of injection. The injection parameters mentioned in this research showed significant effects on the fuel spray spreading in the DLDC chamber. Increasing the injection pressure provided a larger fuel spray distribution area at the beginning of injection. Decreasing the nozzle hole diameter had a positive influence on obtaining a larger fuel spray distribution. Advancing the injection timing enabled the enlarging of the fuel distribution region.

Update on Conflict and Diplomacy

This update summarizes bilateral, multilateral, regional, and international events affecting the Palestinians and Israel 16 February-15 May 2018. U.S. president Donald Trump's December pronouncement to move the U.S. embassy from Tel Aviv to Jerusalem overshadowed the quarter. Trump son-in-law and chief negotiator, Jared Kushner, lost his top secret security clearance on 16 February, calling into question his longevity in the White House and his ability to negotiate a deal. U.S. and Israeli officials prepared for the opening of the new U.S. embassy in Jerusalem on 14 May 2018. The Israelis welcomed the embassy move, but were focused on the ongoing investigation into corruption allegations against Israeli prime minister Benjamin Netanyahu. An assassination attempt on Palestinian Authority prime minister Rami Hamdallah complicated the already stalled Palestinian national reconciliation process. With conditions in Gaza worsening and the seventieth anniversary of the 1948 Nakba approaching, Palestinians in Gaza embarked on a mass protest movement dubbed the Great March of Return, to demand the internationally guaranteed right of return for Palestinian refugees and raise awareness about the catastrophic humanitarian situation there. The Israeli army countered the protests with sharpshooters, maiming protesters in their hundreds, and killing journalists, aid workers, medical personnel, and children. The violence was the worst since Operation Protective Edge, Israel's fifty-day war on Gaza in the summer of 2014.

Hydrodynamics and mass transfer in an internal airlift slurry reactor for process intensification

By combining the prominent advantage of directional fluid flow in an internal airlift loop reactor with the cheap cost of liquid-solid separation in a hydrocyclone, a new slurry reactor for process intensification integrating solid catalytic reactions with liquid-solid separation for clear liquid products is proposed and designed to cut down the capital and operating costs. The reactor can be operated properly when the superficial gas velocity is above 0.0108 m/s, and the solid particles of aluminum oxide are all retained in the slurry reactor if the particle diameter is larger than 57.9 μm. The influences of superficial gas velocity and top clearance on the performance of hydrodynamics and mass transfer in the gas-liquid two-phase and the gas-liquid-solid three-phase systems are measured and discussed systematically, and some data base for the rational design, optimization and scaling-up of this type of promising reactor is provided.

가변 사판식 압축기의 탑 클리어런스 측정 방법 및 신뢰성 확보에 관한 연구

가변 사판식 압축기의 탑 클리어런스 측정 방법 및 신뢰성 확보에 관한 연구

Aeration and mass transfer optimization in a rectangular airlift loop photobioreactor for the production of microalgae

Effects of superficial gas velocity and top clearance on gas holdup, liquid circulation velocity, mixing time, and mass transfer coefficient are investigated in a new airlift loop photobioreactor (PBR), and empirical models for its rational control and scale-up are proposed. In addition, the impact of top clearance on hydrodynamics, especially on the gas holdup in the internal airlift loop reactor, is clarified; a novel volume expansion technique is developed to determine the low gas holdup in the PBR. Moreover, a model strain of Chlorella vulgaris is cultivated in the PBR and the volumetric power is analyzed with a classic model, and then the aeration is optimized. It shows that the designed PBR, a cost-effective reactor, is promising for the mass cultivation of microalgae.

Improving performance of flat-plate photobioreactors by installation of novel internal mixers optimized with computational fluid dynamics

A novel mixer was developed to improve the performance of flat-plate photobioreactors (PBRs). The effects of mixer were theoretically evaluated using computational fluid dynamics (CFD) according to radial velocity of fluid and light/dark cycles within reactors. The structure parameters, including the riser width, top clearance, clearance between the baffles and walls, and number of the chambers were further optimized. The microalgae culture test aiming at validating the simulated results was conducted indoor. The results showed the maximum biomass concentrations in the optimized and archetype reactors were 32.8% (0.89gL−1) and 19.4% (0.80gL−1) higher than that in the control reactor (0.67gL−1). Therefore, the novel mixer can significantly increase the fluid velocity along the light attenuation and light/dark cycles, thus further increased the maximum biomass concentration. The PBRs with novel mixers are greatly applicable for high-efficiency cultivation of microalgae.

Mixing Characteristics and Bubble Behavior in an Airlift Internal Loop Reactor with Low Aspect Ratio

The present study summarizes the results of macro- and micro-mixing characteristics in an airlift internal loop reactor with low aspect ratio (H/D≤5) using the electrolytic tracer response technique and the method of parallel competing reactions respectively. The micro-mixing has never been investigated in airlift loop reactors. The dual-tip electrical conductivity probe technique is used for measurement of local bubble behavior in the reactor. The effects of several operating parameters and geometric variables are investigated. It is found that the increase in superficial gas velocity corresponds to the increase in energy input, liquid circulation velocity and shear rate, decreasing the macro-mixing time and segregation index. Moreover, it is shown that top clearance and draft diameter affect flow resistance. However, the bubble redistribution with a screen mesh on the perforated plate distributor for macro-mixing is insignificant. The top region with a high energy dissipation rate is a suitable location for feeding reactants. The analysis of present experimental data provides a valuable insight into the interaction between gas and liquid phases for mixing and improves the understanding of intrinsic roles of hydrodynamics upon the reactor design and operating parameter selection.