Balance Holes Research Articles

The Influence of Balance Hole Position of Water Pump on Axial Force and External Characteristics

The method of balancing the axial force of water pump by balance hole is taken as a research object. Based on the combined CFD technology and experimental research, the relationship between the radial position of balance hole and the effect of axial force, external characteristics of the pump is studied in-depth. Research shows that, the effect of balance hole location on the axial force and the external characteristics have certain law, which effect is significant in balancing the interior pressure; with the increase of radial radius of the balance hole location, the overall balance of interior pressure is increased, the greater the axial force is; the smaller radial radius is, the better the effect of axial force balance is, but leakage may increase and the stroke and efficiency is decreased slightly.

Application of the balancing holes on the turbine stage discs with higher root reaction

The influence of the flow area of balancing holes in the discs of a steam turbine on its thermodynamic efficiency is examined for turbine stages operating in the increased root reaction regime. The interstage seal flooding with steam is modelled. The impact is given on stage reaction changes, on mass flow adjustments, and on overpressure operating in the rotor disc.

Acridine modified dibenzothiophene derivatives as high triplet energy host materials for blue phosphorescent organic light-emitting diodes

Acridine modified dibenzothiophene derivatives were synthesized as host materials of imidazole ligand based Ir emitters for blue phosphorescent devices. The shallow energy levels of the acridine based host materials by the strong electron donating acridine moiety were well matched with the energy levels of Ir blue triplet emitter derived from imidazole. Additionally, strong electron transporting character of the acridine moiety could increase hole density in the emitting layer and balance holes and electrons. The energy level matching between the host and dopant materials and increased hole density in the emitting layer provided a very high external quantum efficiency of 27.8% in the blue phosphorescent organic light-emitting diodes.

Effect of impeller reflux balance holes on pressure and axial force of centrifugal pump

The size of impeller reflux holes for centrifugal pump has influence on the pressure distribution of front and rear shrouds and rear pump chamber, as well as energy characteristics of whole pump and axial force. Low specific-speed centrifugal pump with Q=12.5 m3/h, H=60 m, n=2950 r/min was selected to be designed with eight axial reflux balance holes with 4.5 mm in diameter. The simulated Q-H curve and net positive suction head (NPSH) were in good agreement with experimental results, which illustrated that centrifugal pump with axial reflux balance holes was superior in the cavitation characteristic; however, it showed to little superiority in head and efficiency. The pressure in rear pump chamber at 0.6 times rate flow is 29.36% of pressure difference between outlet and inlet, which reduces to 29.10% at rate flow and 28.33% at 1.4 times rate flow. As the whole, the pressure distribution on front and rear shrouds from simulation results is not a standard parabola, and axial force decreases as flow rate increases. Radical reflux balance holes chosen to be 5.2 mm and 5.9 mm in diameter were further designed with other hydraulic parts unchanged. With structural grids adopted for total flow field, contrast numerical simulation on internal flow characteristics was conducted based on momentum equations and standard turbulence model (κ-ɛ). It is found that axial force of pump with radical reflux balance holes of 5.2 mm and 5.9 mm in diameter is significantly less than that with radical reflux balance holes of 4.5 mm in diameter. Better axial force balance is obtained as the ratio of area of reflux balance holes and area of sealing ring exceeds 6.

Numerical Study of Centrifugal Fan with Slots in Blade Surface

When the airfoil is working, the geometry of the channel that the fluid flows through changes with the airfoil profile. It makes the magnitude and direction of the velocity change, and resulting in flow separation. The impact produced by flow separation causes the loss of the flow's energy. This paper takes the blade of G4-73No.8D centrifugal fan as the research object. The flow and aerodynamic characteristics of the blades under different incidence angles are analyzed and researched by means of CFD. The slotted technique on centrifugal fan blade with slots cut along the blades pressure side to suction side is adopted. And slotted blade models data are compared with generic models. The results show that the method to create a slot in blade can control the stall of centrifugal fan flow passage availably. And under the appropriate parameters, slotted model can decrease the blade surface resistance and increase lift force effectively. Slotted model also has a role of control and mitigation of boundary layer separation, improving blade aerodynamic performance observably. The slot plays a similar role as the balancing hole, and make the high pressure low speed fluid flow into low-pressure side where the fluid is accelerated and has no extra energy be consumed. The research shows that slotted technique on centrifugal fan blade is useful to improve the characteristics of blade surface flow field, resulting in significant energy saving.

Effect of heteroatoms substitution on electronic, photophysical and charge transfer properties of naphtha [2,1-b:6,5-b′] difuran analogues by density functional theory

Heteroatoms substitution technique was used and nitrogen (N) and sulpher (S) were doped to design new analogues of naphtha [2,1-b:6,5-b′] difuran (DPNDF) by replacing carbon (C) and hydrogen (H) atoms. The molecular structures of all analogues have been optimized at the ground (S0) and first excited (S1) states using density functional theory (DFT) and time-dependent density functional theory (TD-DFT), respectively. Then highest occupied molecular orbitals (HOMOs), the lowest unoccupied molecular orbitals (LUMOs), photophysical properties, adiabatic/vertical electron affinities (EAa)/(EAv), adiabatic/vertical ionization potentials (IPa)/(IPv) and hole/electron reorganization energies λh/λe have been investigated. The effect of doping has been studied on the transfer integral, mobility and photostability. The photostability enhanced by increasing the number of nitrogen atoms. We obtained the high hole mobility as 0.96cm2V−1s−1 for analogue “a”. The reorganization energies, transfer integrals and mobilities revealed that the “b” would be electron transporter, “d” balance hole as well as electron transporter, whereas the “a”, “c” and “e” may be good hole transport materials.

The Real Role of 4,4'-Bis[N-[4-{N,N-bis(3-methylphenyl)amino}phenyl]-N-phenylamino] biphenyl (DNTPD) Hole Injection Layer in OLED: Hole Retardation and Carrier Balancing

We explored interfacial electronic structures in indium tin oxide (ITO)/DNTPD/N,N'-diphenyl-N,N'-bis(1-naphthyl)-1,1'-biphenyl-4,4'-diamine (NPB) layer stack in an OLED to clarify the real role of an aromatic amine-based hole injection layer, DNTPD. A hole injection barrier at the ITO/DNTPD interface is lowered by 0.20 eV but a new hole barrier of 0.36 eV at the DNTPD/NPB is created. The new barrier at the DNTPD/NPB interface and its higher bulk resistance serve as hole retardation, and thus those cause the operation voltage for the ITO/DNTPD/NPB to increase. However, it improves current efficiency through balancing holes and electrons in the emitting layer.

Investigation of CFD calculation method of a centrifugal pump with unshrouded impeller

Currently, relatively large errors are found in numerical results in some low-specific-speed centrifugal pumps with unshrouded impeller because the effect of clearances and holes are not accurately modeled. Establishing an accurate analytical model to improve performance prediction accuracy is therefore necessary. In this paper, a three-dimensional numerical simulation is conducted to predict the performance of a low-specific-speed centrifugal pump, and the modeling, numerical scheme, and turbulent selection methods are discussed. The pump performance is tested in a model pump test bench, and flow rate, head, power and efficiency of the pump are obtained. The effect of taking into consideration the back-out vane passage, clearance, and balance holes is analyzed by comparing it with experimental results, and the performance prediction methods are validated by experiments. The analysis results show that the pump performance can be accurately predicted by the improved method. Ignoring the back-out vane passage in the calculation model of unshrouded impeller is found to generate better numerical results. Further, the calculation model with the clearances and balance holes can obviously enhance the numerical accuracy. The application of disconnect interface can reduce meshing difficulty but increase the calculation error at the off-design operating point at the same time. Compared with the standard k-ɛ, renormalization group k-ɛ, and Spalart-Allmars models, the Realizable k-ɛ model demonstrates the fastest convergent speed and the highest precision for the unshrouded impeller flow simulation. The proposed modeling and numerical simulation methods can improve the performance prediction accuracy of the low-specific-speed centrifugal pumps, and the modeling method is especially suitable for the centrifugal pump with unshrouded impeller.

Numerical Simulation of 3D Solid-Liquid Turbulent Flow in a Low Specific Speed Centrifugal Pump: Performance Comparison of Four Geometric Models

For numerically simulating 3D solid-liquid turbulent flow in low specific speed centrifugal pumps, there exist several problems including how to design geometrical shape of the calculation model to represent the real pump and how to predict pump performance accurately to guide the design of pump. To solve these problems, four kinds of geometric models were designed. The performance of a low specific speed solid-liquid centrifugal pump was predicted, and the results showed that the improved prediction methods are more accurate than the traditional method. Moreover, the simulation results of the entire flow field of the geometric model including balance holes and the lateral clearances of impeller in which liquid rotates with half speed of impeller are closer to the real situation.

Controlling the influence of Auger recombination on the performance of quantum-dot light-emitting diodes

Development of light-emitting diodes (LEDs) based on colloidal quantum dots is driven by attractive properties of these fluorophores such as spectrally narrow, tunable emission and facile processibility via solution-based methods. A current obstacle towards improved LED performance is an incomplete understanding of the roles of extrinsic factors, such as non-radiative recombination at surface defects, versus intrinsic processes, such as multicarrier Auger recombination or electron-hole separation due to applied electric field. Here we address this problem with studies that correlate the excited state dynamics of structurally engineered quantum dots with their emissive performance within LEDs. We find that because of significant charging of quantum dots with extra electrons, Auger recombination greatly impacts both LED efficiency and the onset of efficiency roll-off at high currents. Further, we demonstrate two specific approaches for mitigating this problem using heterostructured quantum dots, either by suppressing Auger decay through the introduction of an intermediate alloyed layer, or by using an additional shell that impedes electron transfer into the quantum dot to help balance electron and hole injection.

Conversion efficiency improvement mechanisms of polymer solar cells by balance electron–hole mobility using blended P3HT:PCBM:pentacene active layer

To improve the power conversion efficiency of polymer solar cells, the blended P3HT:PCBM:pentacene active layer was used to balance hole–electron mobility and roughen surface. Using space-charged-limited current model to analyze the hole-only devices and the electron-only devices, the P3HT:PCBM:pentacene (weight ratio=1:0.8:0.09) active layer exhibited balance hole–electron mobility. Compared with the power conversion efficiency of 3.46% of the conventional polymer solar cells using P3HT:PCBM (1:0.8) active layer, the power conversion efficiency of 4.42% was obtained. In other words, the power conversion efficiency was improved about 27.5%.

Model of Flow in the Side Chambers of an Industrial Centrifugal Pump for Delivering Viscous Oil

A series of experiments has been conducted to identify the effects of both fluid viscosity and wear-rings gap on the performance of a low specific speed industrial centrifugal pump of type 65Y60 for transporting viscous oils by the author group. Unfortunately, the experimental results remained unexplained on a fluid dynamics base. To remedy this problem, a highly viscous oil flow model and computational method in the side chambers in that pump were proposed based on the existing theoretical and experimental results. The flow coupling between the chambers and the gaps of the wear-rings and/or the balance holes was realized. The model was validated by making use of the existing experiment data in the chamber between a rotating disk and the walls of a stationary cylindrical container. Then the flow model was applied into the two side chambers in that pump when the wear-rings clearances and liquid viscosity were changed. The results demonstrated that the flow model is sensitive to wear-rings gap, liquid viscosity, the roughness of the wet walls of the chambers, and leakage flow rate. For this pump, an enlarged clearance can improve the mechanical efficiency, but the increment in the efficiency is unable to compensate for the considerable drop in the volumetric efficiency, causing the gross efficiency not be improved, especially at a high viscosity.

The Study on Released Holes of Flameproof Submersible Pump with Inner Motor for Coal Mine

The ANSYS ICEM was used to build the meshes in the impeller, volute, the sealing rings clearance and the other whole flow field of the flameproof submersible pump with inner motor for coal mine BQW50-70×5-132/N for further simulation, and two outlets were set here and the inner flow character of the pump was simulated. The axial force was numerical analyzed with the changing of the sealing rings gap and the changing of the area of balance hole. Finally, three balance holes, with a total area of 2400mm2, 0.2mm sealing rings gap are taken based on this study.

전산유체역학을 이용한 워터펌프 축력 저감

Computational Fluid Dynamics (CFD) method has been used to investigate the axial force of automotive water pump. As the excessive axial force can make some unexpected problems like impeller interference and coolant leakage we have focused on finding the cause of axial force and its reduction in this paper. First, we have tested the closed type water pump with and without balance hole by the calculation methods. By examining the pressure contour around the impeller, we have found that the axial force arises not only from the pressure difference around shroud but also from the pressure difference around hub. So we have tested two impellers - one is normal open type impeller and the other is open type impeller with modified hub. The results show that the axial force reduction is about 150~200N for normal one and 700N@3000RPM for modified impeller. And the hydraulic efficiency which is important in aspect of engine fuel efficiency is reduced about 6.5% for normal one but increased 4%@3000RPM for modified impeller.

Topology optimization of actuator arms in hard disk drives for reducing bending resonance-induced off-tracks

The objective of this work is to find an optimal actuator arm configuration in hard disk drives (HDD's) for sufficiently small arm bending-induced off-track error by maximizing the fundamental eigenfrequency of arm bending modes subject to a constraint on the mass moment of inertia of arms. By applying the topology optimization method for the purpose, an arm configuration having two balancing holes instead of a single balancing hole in conventional designs was obtained. It is numerically shown that an optimized arm configuration substantially increases the arm bending resonant frequency with little change in the mass moment of inertia of arms in comparison with conventional designs having a single balancing hole. Finally, the performance of an optimized actuator arm is verified by showing that the eigenfrequencies associated with arm bending modes are increased by about 100 Hz and the off-track error by measuring the position error signal (PES) from actual sample drives can be reduced by as much as 25%.

The Impact of Balance Hole Radial Position of Centrifugal Pump on Axial Force and External Characteristics

In this paper, the method of balancing the axial force with balance hole is studied based on the combination of CFD and experimental research. The relationship between the radial position of balance hole and the effect of axial force and external characteristics of the pump is in-depth studied. Research shows that, there are certain laws for the effect of the balance hole location to the axial force and the external characteristics: the overall pressure of the balance chamber and the axial force decrease with the decrescence of the balance hole radial location, which could get good effect on balancing axial force. But the head and efficiency decreased.

69.2: High Efficiency Red‐Emission Phosphorescent Polymer Lighting Emitting Diodes Based on Ir(piq)3 Derivatives

AbstractIn this paper, several kinds Ir(piq)3 derivatives are used as dopants in polyfluorene to fabricate high performance pure red emission phosphorescent polymer light‐emitting‐diodes. Electron injection/hole blocking layer Cs2CO 3 is inserted between light emitting polymer layer and Al cathode. By modulating the electron injection ability from cathode using Cs2CO3 nano‐thick layer, electron current can be controlled precisely to balance hole current. Peak efficiencies of 16.9 cd/A and 17.6 lm/W at 220cd/m2 is achieved.

Improving organic light-emitting devices by modifying indium tin oxide anode with an ultrathin tetrahedral amorphous carbon film

The characteristics of organic light-emitting devices based on tris-(8-hydroxyqunoline) aluminum with an ultrathin tetrahedral amorphous carbon (ta-C) film on indium tin oxide have been investigated. The device with a 1.0-nm ta-C layer has the highest current and power efficiency. The current efficiency of a device with a ta-C layer thickness of 1.0nm is 3.7cd∕A at 20mA∕cm2, however, the current efficiency of a standard device without a ta-C layer is 2.56cd∕A at the same current density. The current efficiency is improved by 46% compared to the standard device. Although there is a 1.2-V increase in driving voltage for 100-cd∕m2 luminance, the power efficiency is still improved by 22% compared to that of the standard device. The improvement of the efficiency is due to smoothing indium tin oxide surface, blocking hole injection from anode and balancing hole and electron currents. The optimal thickness of ta-C layer for hole injection mechanics can be understood by tunneling.

The role of NDE in the life management of steam turbine rotors

The rotors of steam turbines are subject to life limitations due to creep and thermal fatigue. Creep occurs during steady-state operation due to the centrifugal stresses sustained at high temperature, while thermal fatigue arises from cyclic thermal stresses set up during start-up and shut-down. The most serious threat to the safety of these rotors arises from the possibility that, near the bore, creep cracks may initiate and grow to a size which could result in a brittle fracture of the rotor during a cold start. Initiation may be assisted by any pre-existing forging defects in the near-bore region and growth may be assisted by fatigue due to the thermal and mechanical stresses applied during starting. Creep cracking can also occur at blade root fixings, leading eventually to the loss of blades and possibly substantial consequential damage to the turbine. Creep, thermal fatigue, and additionally stress corrosion cracking can occur at other stress-concentrating features such as balance holes and changes of section; the effect of any cracking at such features is dependant upon the local stress levels. The detection, classification and sizing of flaws is therefore critical to life extension of steam turbine rotors.

Development of the Floating Centrifugal Pump by Use of Non Contact Magnetic Drive and Its Performance

This article focuses on the impeller construction, non contact driving method and performance of a newly developed shaftless floating pump with centrifugal impeller. The drive principle of the floating impeller pump used the magnet induction method similar to the levitation theory of the linear motor. In order to reduce the axial thrust by the pressure different between shroud and disk side, the balance hole and the aileron blade were installed in the floating impeller. Considering the above effect, floating of an impeller in a pump was realized. Moreover, the performance curves of a developed pump are in agreement with a general centrifugal pump, and the dimensionless characteristic curve also agrees under the different rotational speed due to no mechanical friction of the rotational part. Therefore, utility of a non contacting magnetic‐drive style pump with the floating impeller was made clear.