In this work, a model of gas leakage through nonmetallic gaskets was developed in order to predict leakage rate of gasket sealing connections. The model was verified by the leakage experiments on two types of gaskets...In this work, a model of gas leakage through nonmetallic gaskets was developed in order to predict leakage rate of gasket sealing connections. The model was verified by the leakage experiments on two types of gaskets： compressed non-asbestos fiber gasket and flexible graphite gasket reinforced with tanged metal sheet. The coefficients in the leakage rate formula were obtained by regression of experimental data for each type of gasket, The model was also validated against the experimental leakage data by other researchers and shown to produce accurate predications. Furthermore, the model was applied to a bolted flanged connection in service in order to assess the tightness of the connection.展开更多
An electromagnetic calculation and the parameters of the magnet system of the magnetically confined plasma rocket were established. By using ANSYS code, it was found that the leakage rate depends on the current intens...An electromagnetic calculation and the parameters of the magnet system of the magnetically confined plasma rocket were established. By using ANSYS code, it was found that the leakage rate depends on the current intensity of the magnet and the change of the magnet position.展开更多
This paper addresses the issue of reciprocating compressors staggered labyrinth seal structure. The internal flow field of sealed structure, the displacement of cylinder and piston for different tooth profile angles a...This paper addresses the issue of reciprocating compressors staggered labyrinth seal structure. The internal flow field of sealed structure, the displacement of cylinder and piston for different tooth profile angles are analyzed synchronously using FLUENT software, and the effects of fluid-structure interaction on the performance of the labyrinth seal are revealed. The results indicate that with the growth of tooth profile angle, the leakage rate of labyrinth seal tends to decrease first, and then increase. The results of fluid-structure interaction analysis are close to those of actual engineering. The effect of fluid-structure interaction makes tiny deformation in calculation mesh of piston and cylinder structure, and the coupling interaction affects the performance of the labyrinth seal.展开更多
A fundamental analysis of helium-gas coolant leakage rate through first-wall cracks in Tokamak fusion reactors was made. Criteria for ascertaining the correct flow models were thoroughly investigated. After testing th...A fundamental analysis of helium-gas coolant leakage rate through first-wall cracks in Tokamak fusion reactors was made. Criteria for ascertaining the correct flow models were thoroughly investigated. After testing the criteria, it was determined that the correct model is the compressible choked flow for the helium-gas coolant under the normal operating conditions in the Tokamak fusion reactors. The upper bound leakage rates through metallic wall for two crack sizes were calculated. The calculated maximum numbers of allowable cracks through metallic and silicon-carbon composite wall were also reported. The experimental data of specimen S-23 (the small crack size), checked with the predicted or calculated leakage rate. But the experimental data of specimen S-4 (the large crack size, which is only 4.4 times larger than the crack size of specimen S-23) were two orders of magnitude higher than the calculated value. This is probably due to the many through-cracks undetected and therefore, not reported in the experiment, and not due to the difference in crack sizes. It should be noted that since there are only two test data points, it is recommended that more testing or experimental data will be needed. The results of two previous investigations about the calculated leakage values, their equations used, and their flow models employed were also reviewed. It is concluded that the correct model for the analysis is the compressible choked flow, and that helium can be as an effective coolant for fusion power reactors. Several recommendations are also made. Specifically, more experiments for helium, and similar analysis and experiments for lithium and water coolant are needed; and should be encouraged.展开更多
Since the beginning of the 20th century, many researches on the sealing characteristic of mechanical seals were carried out broadly and in depth by various methods and some leakage models were built. But due to the la...Since the beginning of the 20th century, many researches on the sealing characteristic of mechanical seals were carried out broadly and in depth by various methods and some leakage models were built. But due to the lack of the way to characterize the main factors of influence on the leakage, most of the early researches were based on the assumptions that the seal faces topography and the frictional conditions were invariant. In the early built models, the effect of the surface topography change of the seal face on the leakage rate was neglected. Based on the fractal theory, the contact of end faces of the rotary and stationary rings was simplified to be the contact of a rough surface and an ideal rigid smooth surface, and the contact interface＇s cavity size-distribution function as well as the fractal characteristic of the cavity profile curve was discussed. By analyzing the influence of abrasion on the seal face topography and the leakage channel, the time-correlation leakage prediction model of mechanical seals based on the fractal theory was established and the method for predicting the leakage rate of mechanical seals with parallel plane was proposed. The values of the leakage rate predicted theoretically are similar to the measured values of the leakage rate in the model test and in situ test. The experimental results indicate that the leakage rate of mechanical seals is a transient value. The surface topography of the end faces of the seal tings and its change during the frictional wear of mechanical seals can be accurately characterized by the fractal parameters. Under the work conditions of changeless frictional mechanism, the fractal parameters measured or calculated based on the accelerated testing equation can be used to predict the leakage rate of mechanical seal in service. The proposed research provides the basis for determining the leakage state and predicting working life of mechanical seal.展开更多
Spiral groove dry gas seal(S?DGS), the most widely used DGS in the world, encounters the problem of high leakage rate and inferior film stability when used in high?speed machinery equipment, which could not be well so...Spiral groove dry gas seal(S?DGS), the most widely used DGS in the world, encounters the problem of high leakage rate and inferior film stability when used in high?speed machinery equipment, which could not be well solved by optimization of geometrical parameters and molded line of spiral groove. A new type of bionic cluster spiral groove DGS(CS?DGS) is proved to have superior film stability than S?DGS at the condition of high?speed and low?pressure numerically. A bionic CS?DGS is experimentally investigated and compared with common S?DGS in order to provide evidence for theoretical study. The film thickness and leakage rate of both bionic spiral groove and common spiral groove DGS are measured and compared with each other and with theoretical values under different closing force at the condition of static pressure, high?speed and low?pressure, and the film stiffness and stiffness?leakage ratio of these two face seals are derived by the relationship between closing force and film thickness at the steady state. Experimental results agree well with the theory that the leakage and stiffness of bionic CS?DGS are superior to that of common S?DGS under the condition of high?speed and low?pressure, with the decreasing amplitude of 20% to 40% and the growth amplitude of 20%, respectively. The opening performance and stiffness characteristics of bionic CS?DGS are inferior to that of common S?DGS when rotation speed equals to 0 r/min. The proposed research provides a new method to measure the axis film stiffness of DGS, and validates the superior performance of bionic CS?DGS at the condition of high?speed and low?pressure experimentally.展开更多
This work is focused on the theoretical investigation of internal leakage of a newly developed pi lotscale fluid switcherenergy recovery device （FSERD） for reverse osmosis （RO） system. For the purpose of in creasi...This work is focused on the theoretical investigation of internal leakage of a newly developed pi lotscale fluid switcherenergy recovery device （FSERD） for reverse osmosis （RO） system. For the purpose of in creasing FSERD efficiency and reducing the operating cost of RO, it is required to control the internal leakage in a low level. In this work, the internal leakage rates at different leakage gaps and retentate brine pressures are investigated by computational fluid dynamics （CFD） method and validating experiments. It is found that the internal leak age has a linear relationship with the retentate brine pressure and a polynomial relationship with the scale of leakage gap. The results of the present work imply that low internal leakage and high retentate brine pressure bring benefits to achieve high FSRD efficiency.展开更多
When the variable geometry hypersonic inlet is sealed with ceramic wafers,the cavity flows inside the sealing chamber can be affected by the boundary layer near the side wall.To study the influence of the boundary lay...When the variable geometry hypersonic inlet is sealed with ceramic wafers,the cavity flows inside the sealing chamber can be affected by the boundary layer near the side wall.To study the influence of the boundary layer thickness near the side wall on the flow and leakage characteristics in sealing chamber,the numerical calculation of the cavity flow in the sealing chamber under different inflow boundary layer thicknesses is carried out.The results show that three-dimensional cavity flow structures are close to being asymmetric,and the entrance pressure of the leakage path can also be affected by asymmetry;with the increase of the thickness of the boundary layer,the pressure at the cavity floor and the seal entrance decreases.Finally,the existing leakage prediction model is modified according to the distribution rule of the cavity floor and the flow properties in the leakage path.展开更多
The high-pressure electro-pneumatic servo valve(HESV)is a core element of the high-pressure pneumatic servo system.The annular clearance and the rounded corner of the spool-sleeve can cause the leakage at null positio...The high-pressure electro-pneumatic servo valve(HESV)is a core element of the high-pressure pneumatic servo system.The annular clearance and the rounded corner of the spool-sleeve can cause the leakage at null position,thereby affecting high-precision control and stability of the servo system.This paper investigates the effects of the clearance structure on leakage behavior at null position of the HESV.A numerical approach was employed to evaluate the effects,and then a mathematical model was established to obtain the variation law of leakage flow rate at null position.The results indicate that the leakage flow rate at null position varies linearly with supply pressure and rounded corner radius,and is nonlinear as a quadratic concave function with annular clearance.The leakage flow rate of the annular clearance and the rounded corner varies with the valve opening in an invariable−nonlinear−linear trend.A test rig system of leakage behavior at null position of the HESV was built to confirm the validity of the numerical model,which agrees well with the conducted experimental study.展开更多
The coupling effect among the flow of fluid film, the frictional heat of fluid film and the thermal deformation of sealing rings is inherent in mechanical seals. The frictional heat transfer analysis was carded out to...The coupling effect among the flow of fluid film, the frictional heat of fluid film and the thermal deformation of sealing rings is inherent in mechanical seals. The frictional heat transfer analysis was carded out to optimize the geometrical parameters of the sealing rings, such as the length, the inner radius and the outer radius. The geometrical parameters of spiral grooves, such as the spiral angle, the end radius, the groove depth, the ratio of the groove width to the weir width and the number of the grooves, were optimized by regarding the maximum bearing force of fluid film as the optimization objective with the coupling effect considered. The depth of spiral groove was designed to gradually increase from the end radius of spiral groove to the outer radius of end face in order to decrease the weakening effect of thermal deformation on the hydrodynamic effect of spiral grooves. The end faces of sealing rings were machined to form a divergent gap at inner radius, and a parallel gap will form to reduce the leakage rate when the thermal deformation takes place. The improved spiral groove mechanical seal possesses good heat transfer performance and sealing ability.展开更多
The loads acting on the sealing elements of balanced mechanical seals are analyzed. When the balance factor approaches the back pressure factor, the spring pressure will become main part of the face pressure. The leak...The loads acting on the sealing elements of balanced mechanical seals are analyzed. When the balance factor approaches the back pressure factor, the spring pressure will become main part of the face pressure. The leakage model of balanced mechanical seals is established on the base of M-B model for rough surface. Several GY-70 type balanced mechanical seals are tested. The influences of the spring pressure both on the leakage rate and on the friction characteristic of balanced mechanical seals are investigated. The research results indicate that as spring pressure increases, both the clear-ance between two end faces and the leakage rate will decrease, and the friction will be more serious because lubrication medium between the rotating ring and the stationary ring reduces, though the increase of the spring pressure may not be enough to change the face friction state of mechanical seals. There exists an optimum spring pressure for mechanical seal operation. Under this spring pres-sure, not only leakage rate is small, but also the seal end surfaces have a fine friction characteristic. Under different operating conditions, identical type mechanical seals may possess different spring pressure. Appropriate selection of spring pressure is valuable to realize long-period and small leakage rate operating of balanced mechanical seals.展开更多
In order to investigate the sealing performance variation resulted from the thermal deformation of the end faces, the equations to calculate the fluid film pressure distribution, the bearing force and the leakage rate...In order to investigate the sealing performance variation resulted from the thermal deformation of the end faces, the equations to calculate the fluid film pressure distribution, the bearing force and the leakage rate are derived, for the fluid film both in parallel gap and in wedgy gap. The geometrical parameters of the sealing members are optimized by means of heat transfer analysis and complex method. The analysis results indicate that the shallow spiral grooves can generate hydrodynamic pressure while the rotating ring rotates and the bearing force of the fluid film in spiral groove end faces is much larger than that in the flat end faces. The deformation increases the bearing force of the fluid film in flat end faces, but it decreases the hydrodynamic pressure of the fluid film in spiral groove end faces. The gap dimensions which determine the characteristics of the fluid film is obtained by coupling analysis of the frictional heat and the thermal deformation in consideration of the equilibrium condition of the bearing force and the closing force. For different gap dimensions, the relation- ship between the closing force and the leakage rate is also investigated, based on which the leakage rate can be controlled by adjusting the closing force.展开更多
[Objective] The research aimed to study the effects of reducing the concentrations of Mn2＋, Cu2＋ or Zn2＋ in nutrient solution on the contents of Mn, Cu and Zn of grafted cucumber leaves as well as on the SOD and is...[Objective] The research aimed to study the effects of reducing the concentrations of Mn2＋, Cu2＋ or Zn2＋ in nutrient solution on the contents of Mn, Cu and Zn of grafted cucumber leaves as well as on the SOD and isozymes activities and the rate of electrolytic leakage under cold stress. [Method] Nutrient solution containing low concentrations of Mn2＋, Cu2＋ or Zn2＋ were used for cultivating the grafted cucumber seedlings for the cold treatment. [Result] The results indicated that reducing the concentrations of Mn2＋, Cu2＋ or Zn2＋ in nutrient solution had declined the SOD activities in grafted cucumber leaves and increased the rates of electrolytic leakage. Mn2＋ had shown the maximum influences, followed by Cu2＋, and Zn2＋ had shown the minimum influences. [Conclusion] Cold resistance of cucumber can be improved by changing the contents of Mn2＋, Cu2＋ or Zn2＋ in nutrient solution.展开更多
The injury tolerance of cell plasma membrane and the correlative enzymes activities of plasma-membrane protection system in the Ulmuspumila leaves treated by nine concentrations （0.3%, 0.6%, 0,9%, 1,2%, 1.5%, 1.8%, 2...The injury tolerance of cell plasma membrane and the correlative enzymes activities of plasma-membrane protection system in the Ulmuspumila leaves treated by nine concentrations （0.3%, 0.6%, 0,9%, 1,2%, 1.5%, 1.8%, 2,1%, 2.4%, 3.0%） of Na2CO3 and NaHCO3 mixtures were studied in a greenhouse of Northeast Forestry University, Harbin, China. The rate of electrolyte leakage （REL） and SOD （Superoxide dismutase） activity in leaves of different samples were determined. Results showed that the REL in leaves of U. pumila presented a slowly increasing trend at the salt concentrations less than 1.5%, which indicated that cell plasma membrane of U. pumila leaves had rather strong resistance to the injury of salt ion, and had a significant increase at the salt concentrations more than 1.5%. The SOD activities in leaves of U, pumila presented an increased trend at salt concentrations less than 1.5%, the growth of seedlings did not decline, and tress and leaves had no symptom of injury, while the salt concentrations exceeded 1.5%, SOD activities sharply decreased and REL increased promptly.展开更多
The vacuum system for HL-2A was built in 2003. The test results indicated that this system is feasible. It consists of three main parts: a pumping system, a pumping divertor and a glow discharge cleaning (GDC) system....The vacuum system for HL-2A was built in 2003. The test results indicated that this system is feasible. It consists of three main parts: a pumping system, a pumping divertor and a glow discharge cleaning (GDC) system. For the pumping system, there are three main functions: (1) evacuating the vacuum vessel thus to produce an ultra high vacuum, (2) removal of impurities released during baking and (3) pumping during GDC. The pumping divertor controls the particles at the plasma edge and the GDC system provides a clean wall conditioning. During the first campaign of physical trial experiment on HL-2A, the ultimate pressure reached 4.6 × 10-6 Pa, and the total leakage and outgassing rate in 12 hours was 1.8 × 10-5 Pa·m3/s, which is close to that of ASDEX.展开更多
The localised leakage in shield tunnels that mainly occurs at segment joints may induce other defects,which threatens operational safety.To obtain a universal solution for the sealant performance of gasketed joints,we...The localised leakage in shield tunnels that mainly occurs at segment joints may induce other defects,which threatens operational safety.To obtain a universal solution for the sealant performance of gasketed joints,we proposed a novel analytical model based on the multiscale contact and percolation theories,in which the obtained percolation pressure and interfacial separation can be utilized to derive the critical water leakage pressure and leakage rate.The evolutionary process of leakage was divided into three stages(i.e.,the percolation,leakage and breakdown),which explicitly reveal the progressive hydraulic deterioration of gasketed joints.The gaskets still own partial waterproof capacity until the end of the leakage stage due to the remaining contact pressure at surface asperities.The proposed model was first verified by several sets of experimental data,based on which the determination of three key model parameters(i.e.,self-sealing slope,sealing coefficient,and expel pressure)were discussed in detail.The parametric study indicates that the waterproof capacity is significantly affected by the joint opening,offset,and the surface roughness of the gaskets.The variation in waterproof capacity with joint opening is mainly due to the nonlinearity of the gasket’s modulus and self-sealing slope.The increase in joint offset can result in a lower waterproof capacity as well as a larger leakage rate.Gasket’s surface roughness affects the percolation pressure and interfacial separation,which contributes to the long-term sealant performance.展开更多
The honeycomb seal is a vital component to reduce the leakage flow and improvethe system stability for the turbomachines. In this work, a three-dimensional model is established for the interlaced hole honeycomb seal ...The honeycomb seal is a vital component to reduce the leakage flow and improvethe system stability for the turbomachines. In this work, a three-dimensional model is established for the interlaced hole honeycomb seal (IHHCS) and the non-interlaced hole honeycombseal (NIHHCS) to investigate its leakage and rotordynamic characteristics by adopting computational fluid dynamics (CFD). Results show that the hole arrangement patterns have littleimpact on the pressure drop and turbulence kinetic energy distribution for the seals, and theIHHCS possesses a slightly lower leakage flow rate than the NIHHCS. Moreover, the numericalresults also show that the NIHHCS possesses a better rotordynamic performance than theIHHCS at all investigated conditions. Both seals show a larger k and a lower Ceff with the increase of the positive preswirl ratios and rotational speeds, while the negative preswirl ratioswould reduce the k and improve the Ceff. The NIHHCS possesses a higher absolute value ofFt for all operating conditions, this could explain the distinction of Ceff for both seals atdifferent working conditions.展开更多
Pneumatic cryogenic control valves(PCCV)are designed to meet the special requirements for the large cryogenic helium refrigeration system.Polychlorotrifluoroethylene(PCTFE)is adopted as the flat seal material of the v...Pneumatic cryogenic control valves(PCCV)are designed to meet the special requirements for the large cryogenic helium refrigeration system.Polychlorotrifluoroethylene(PCTFE)is adopted as the flat seal material of the valve seat.The leakage rates and compressive strain of the PCTFE gasket with different sealing stress are tested at both room temperature(293 K)and liquid nitrogen temperature(77 K).After 300 open/close cycles,the experimental results show that the sealing properties of the PCTFE gasket are improved.The leakage rates are about 10-8(293 K)and 10-4(77 K)Pam3 s-1 respectively.Finally,the effects of working pressure on sealing characteristics are discussed.The working pressure has little effect on compressive strain but it has a great influence on leakage rate.The leakage rate is linear with the working pressure of inlet at room temperature,but at liquid nitrogen temperature the leakage rate is linear with the square of the working pressure.展开更多
A flow gas low-pressure multi-wire proportional chamber（LPMWPC） with an active area of 180 mm× 80 mm has been developed for the flying time test of the recoil nuclei on super heavy nuclear experiments. The LPMW...A flow gas low-pressure multi-wire proportional chamber（LPMWPC） with an active area of 180 mm× 80 mm has been developed for the flying time test of the recoil nuclei on super heavy nuclear experiments. The LPMWPC detector can be operated in single as well as double step operational modes. In the case of double step operational mode with a high gas amplification factor, signals from α-particles reside well above the electronic noise. The gas leakage rate and time resolution obtained from the α239Pu source are shown and discussed at the condition of 3 mbar Isobutane gas. It was shown that the time resolution was better than 2.9 ns at the best work condition, and the detecting efciency was larger than 98% at the low energy α particles. So the LPMWPC is fit to measure the flying time in the super heavy nuclear fragments experiment.展开更多
Whether the transitions between 6s5d 3D and 5d6p 3F can be used for laser cooling of barium heavily depends upon the transition probabilities of 5d6p 3F-5d2 3F. Taking the transition 6s5d 3D3-5d6p 3F4 as a scale, the ...Whether the transitions between 6s5d 3D and 5d6p 3F can be used for laser cooling of barium heavily depends upon the transition probabilities of 5d6p 3F-5d2 3F. Taking the transition 6s5d 3D3-5d6p 3F4 as a scale, the leakage rate of 5d6p 3Fa-5d2 3F was used to evaluate the transition probabilities. 706 nm laser pulses with different durations were applied to a barium atomic beam for 6s5d 3D3-5d2 3F4 optical pumping, and the remaining percentages in 6s5d 3D3 were measured. After exponential fitting, the transition probability of 5d6p 3F4-5d2 3F3,4 was determined to be 2.1（4） ~ 104 s-1, which is in agreement with theoretical calculations using the scaled Thomas-Fermi-Dirac method.展开更多
基金Supported by the Funds for Outstanding Scientists of Jiangsu Province of China (No.2005-6).
文摘In this work, a model of gas leakage through nonmetallic gaskets was developed in order to predict leakage rate of gasket sealing connections. The model was verified by the leakage experiments on two types of gaskets： compressed non-asbestos fiber gasket and flexible graphite gasket reinforced with tanged metal sheet. The coefficients in the leakage rate formula were obtained by regression of experimental data for each type of gasket, The model was also validated against the experimental leakage data by other researchers and shown to produce accurate predications. Furthermore, the model was applied to a bolted flanged connection in service in order to assess the tightness of the connection.
基金the Fund of Knowledge Innovation Program of Chinese Academy of Sciences(No.KJCX2-SW-N19)
文摘An electromagnetic calculation and the parameters of the magnet system of the magnetically confined plasma rocket were established. By using ANSYS code, it was found that the leakage rate depends on the current intensity of the magnet and the change of the magnet position.
基金the Science and Technology Projects of Liaoning Province(No.2012219020)the China Postdoctoral Science Foundation(No.2013M541249)
文摘This paper addresses the issue of reciprocating compressors staggered labyrinth seal structure. The internal flow field of sealed structure, the displacement of cylinder and piston for different tooth profile angles are analyzed synchronously using FLUENT software, and the effects of fluid-structure interaction on the performance of the labyrinth seal are revealed. The results indicate that with the growth of tooth profile angle, the leakage rate of labyrinth seal tends to decrease first, and then increase. The results of fluid-structure interaction analysis are close to those of actual engineering. The effect of fluid-structure interaction makes tiny deformation in calculation mesh of piston and cylinder structure, and the coupling interaction affects the performance of the labyrinth seal.
文摘A fundamental analysis of helium-gas coolant leakage rate through first-wall cracks in Tokamak fusion reactors was made. Criteria for ascertaining the correct flow models were thoroughly investigated. After testing the criteria, it was determined that the correct model is the compressible choked flow for the helium-gas coolant under the normal operating conditions in the Tokamak fusion reactors. The upper bound leakage rates through metallic wall for two crack sizes were calculated. The calculated maximum numbers of allowable cracks through metallic and silicon-carbon composite wall were also reported. The experimental data of specimen S-23 (the small crack size), checked with the predicted or calculated leakage rate. But the experimental data of specimen S-4 (the large crack size, which is only 4.4 times larger than the crack size of specimen S-23) were two orders of magnitude higher than the calculated value. This is probably due to the many through-cracks undetected and therefore, not reported in the experiment, and not due to the difference in crack sizes. It should be noted that since there are only two test data points, it is recommended that more testing or experimental data will be needed. The results of two previous investigations about the calculated leakage values, their equations used, and their flow models employed were also reviewed. It is concluded that the correct model for the analysis is the compressible choked flow, and that helium can be as an effective coolant for fusion power reactors. Several recommendations are also made. Specifically, more experiments for helium, and similar analysis and experiments for lithium and water coolant are needed; and should be encouraged.
基金supported by China Postdoctoral Science Foundation (Grant No. 20070410323)Jiangsu Provincial Planned Projects for Postdoctoral Research Funds of China (Grant No. 0701001C)Jiangsu Provincial Planned Projects for Fostering Talents of Six Scientific Fields of China (Grant No. 07-D-027)
文摘Since the beginning of the 20th century, many researches on the sealing characteristic of mechanical seals were carried out broadly and in depth by various methods and some leakage models were built. But due to the lack of the way to characterize the main factors of influence on the leakage, most of the early researches were based on the assumptions that the seal faces topography and the frictional conditions were invariant. In the early built models, the effect of the surface topography change of the seal face on the leakage rate was neglected. Based on the fractal theory, the contact of end faces of the rotary and stationary rings was simplified to be the contact of a rough surface and an ideal rigid smooth surface, and the contact interface＇s cavity size-distribution function as well as the fractal characteristic of the cavity profile curve was discussed. By analyzing the influence of abrasion on the seal face topography and the leakage channel, the time-correlation leakage prediction model of mechanical seals based on the fractal theory was established and the method for predicting the leakage rate of mechanical seals with parallel plane was proposed. The values of the leakage rate predicted theoretically are similar to the measured values of the leakage rate in the model test and in situ test. The experimental results indicate that the leakage rate of mechanical seals is a transient value. The surface topography of the end faces of the seal tings and its change during the frictional wear of mechanical seals can be accurately characterized by the fractal parameters. Under the work conditions of changeless frictional mechanism, the fractal parameters measured or calculated based on the accelerated testing equation can be used to predict the leakage rate of mechanical seal in service. The proposed research provides the basis for determining the leakage state and predicting working life of mechanical seal.
基金Supported by National Natural Science Foundation of China(Grant No.51575490)National Key Basic Research Development Plan(973 Plan,Grant No.2014CB046404)+1 种基金Key Program of Zhejiang Provincial Natural Science Fund Project(Grant No.LZ15E050002)Zhejiang Provincial Natural Science Foundation of Youth Fund(Grant No.LQ17E050008)
文摘Spiral groove dry gas seal(S?DGS), the most widely used DGS in the world, encounters the problem of high leakage rate and inferior film stability when used in high?speed machinery equipment, which could not be well solved by optimization of geometrical parameters and molded line of spiral groove. A new type of bionic cluster spiral groove DGS(CS?DGS) is proved to have superior film stability than S?DGS at the condition of high?speed and low?pressure numerically. A bionic CS?DGS is experimentally investigated and compared with common S?DGS in order to provide evidence for theoretical study. The film thickness and leakage rate of both bionic spiral groove and common spiral groove DGS are measured and compared with each other and with theoretical values under different closing force at the condition of static pressure, high?speed and low?pressure, and the film stiffness and stiffness?leakage ratio of these two face seals are derived by the relationship between closing force and film thickness at the steady state. Experimental results agree well with the theory that the leakage and stiffness of bionic CS?DGS are superior to that of common S?DGS under the condition of high?speed and low?pressure, with the decreasing amplitude of 20% to 40% and the growth amplitude of 20%, respectively. The opening performance and stiffness characteristics of bionic CS?DGS are inferior to that of common S?DGS when rotation speed equals to 0 r/min. The proposed research provides a new method to measure the axis film stiffness of DGS, and validates the superior performance of bionic CS?DGS at the condition of high?speed and low?pressure experimentally.
基金Supported by the Research and Development Programs of Tianjin(10JCYBJC04700,10ZCKFSH02100)
文摘This work is focused on the theoretical investigation of internal leakage of a newly developed pi lotscale fluid switcherenergy recovery device （FSERD） for reverse osmosis （RO） system. For the purpose of in creasing FSERD efficiency and reducing the operating cost of RO, it is required to control the internal leakage in a low level. In this work, the internal leakage rates at different leakage gaps and retentate brine pressures are investigated by computational fluid dynamics （CFD） method and validating experiments. It is found that the internal leak age has a linear relationship with the retentate brine pressure and a polynomial relationship with the scale of leakage gap. The results of the present work imply that low internal leakage and high retentate brine pressure bring benefits to achieve high FSRD efficiency.
基金supported by the Opening Foundation of National State Key Laboratory of High Temperature Gas Dynamics(No.2021KF07)。
文摘When the variable geometry hypersonic inlet is sealed with ceramic wafers,the cavity flows inside the sealing chamber can be affected by the boundary layer near the side wall.To study the influence of the boundary layer thickness near the side wall on the flow and leakage characteristics in sealing chamber,the numerical calculation of the cavity flow in the sealing chamber under different inflow boundary layer thicknesses is carried out.The results show that three-dimensional cavity flow structures are close to being asymmetric,and the entrance pressure of the leakage path can also be affected by asymmetry;with the increase of the thickness of the boundary layer,the pressure at the cavity floor and the seal entrance decreases.Finally,the existing leakage prediction model is modified according to the distribution rule of the cavity floor and the flow properties in the leakage path.
基金Project(51705164)supported by the National Natural Science Foundation of China。
文摘The high-pressure electro-pneumatic servo valve(HESV)is a core element of the high-pressure pneumatic servo system.The annular clearance and the rounded corner of the spool-sleeve can cause the leakage at null position,thereby affecting high-precision control and stability of the servo system.This paper investigates the effects of the clearance structure on leakage behavior at null position of the HESV.A numerical approach was employed to evaluate the effects,and then a mathematical model was established to obtain the variation law of leakage flow rate at null position.The results indicate that the leakage flow rate at null position varies linearly with supply pressure and rounded corner radius,and is nonlinear as a quadratic concave function with annular clearance.The leakage flow rate of the annular clearance and the rounded corner varies with the valve opening in an invariable−nonlinear−linear trend.A test rig system of leakage behavior at null position of the HESV was built to confirm the validity of the numerical model,which agrees well with the conducted experimental study.
文摘The coupling effect among the flow of fluid film, the frictional heat of fluid film and the thermal deformation of sealing rings is inherent in mechanical seals. The frictional heat transfer analysis was carded out to optimize the geometrical parameters of the sealing rings, such as the length, the inner radius and the outer radius. The geometrical parameters of spiral grooves, such as the spiral angle, the end radius, the groove depth, the ratio of the groove width to the weir width and the number of the grooves, were optimized by regarding the maximum bearing force of fluid film as the optimization objective with the coupling effect considered. The depth of spiral groove was designed to gradually increase from the end radius of spiral groove to the outer radius of end face in order to decrease the weakening effect of thermal deformation on the hydrodynamic effect of spiral grooves. The end faces of sealing rings were machined to form a divergent gap at inner radius, and a parallel gap will form to reduce the leakage rate when the thermal deformation takes place. The improved spiral groove mechanical seal possesses good heat transfer performance and sealing ability.
基金This project is supported by Provincial Natural Science Foundation of Educa-tion Office of Jiangsu, China (No. 04KJD530090)Innovating Founda-tion for Doctoral Dissertation of Nanjing University of Technology, China (No. BSCX200510).
文摘The loads acting on the sealing elements of balanced mechanical seals are analyzed. When the balance factor approaches the back pressure factor, the spring pressure will become main part of the face pressure. The leakage model of balanced mechanical seals is established on the base of M-B model for rough surface. Several GY-70 type balanced mechanical seals are tested. The influences of the spring pressure both on the leakage rate and on the friction characteristic of balanced mechanical seals are investigated. The research results indicate that as spring pressure increases, both the clear-ance between two end faces and the leakage rate will decrease, and the friction will be more serious because lubrication medium between the rotating ring and the stationary ring reduces, though the increase of the spring pressure may not be enough to change the face friction state of mechanical seals. There exists an optimum spring pressure for mechanical seal operation. Under this spring pres-sure, not only leakage rate is small, but also the seal end surfaces have a fine friction characteristic. Under different operating conditions, identical type mechanical seals may possess different spring pressure. Appropriate selection of spring pressure is valuable to realize long-period and small leakage rate operating of balanced mechanical seals.
文摘In order to investigate the sealing performance variation resulted from the thermal deformation of the end faces, the equations to calculate the fluid film pressure distribution, the bearing force and the leakage rate are derived, for the fluid film both in parallel gap and in wedgy gap. The geometrical parameters of the sealing members are optimized by means of heat transfer analysis and complex method. The analysis results indicate that the shallow spiral grooves can generate hydrodynamic pressure while the rotating ring rotates and the bearing force of the fluid film in spiral groove end faces is much larger than that in the flat end faces. The deformation increases the bearing force of the fluid film in flat end faces, but it decreases the hydrodynamic pressure of the fluid film in spiral groove end faces. The gap dimensions which determine the characteristics of the fluid film is obtained by coupling analysis of the frictional heat and the thermal deformation in consideration of the equilibrium condition of the bearing force and the closing force. For different gap dimensions, the relation- ship between the closing force and the leakage rate is also investigated, based on which the leakage rate can be controlled by adjusting the closing force.
基金Supported by Shandong Provincial Outstanding Young Scientist Research Award Fund(BS2009NY016)National Natural Science Foundation(30571271)~~
文摘[Objective] The research aimed to study the effects of reducing the concentrations of Mn2＋, Cu2＋ or Zn2＋ in nutrient solution on the contents of Mn, Cu and Zn of grafted cucumber leaves as well as on the SOD and isozymes activities and the rate of electrolytic leakage under cold stress. [Method] Nutrient solution containing low concentrations of Mn2＋, Cu2＋ or Zn2＋ were used for cultivating the grafted cucumber seedlings for the cold treatment. [Result] The results indicated that reducing the concentrations of Mn2＋, Cu2＋ or Zn2＋ in nutrient solution had declined the SOD activities in grafted cucumber leaves and increased the rates of electrolytic leakage. Mn2＋ had shown the maximum influences, followed by Cu2＋, and Zn2＋ had shown the minimum influences. [Conclusion] Cold resistance of cucumber can be improved by changing the contents of Mn2＋, Cu2＋ or Zn2＋ in nutrient solution.
文摘The injury tolerance of cell plasma membrane and the correlative enzymes activities of plasma-membrane protection system in the Ulmuspumila leaves treated by nine concentrations （0.3%, 0.6%, 0,9%, 1,2%, 1.5%, 1.8%, 2,1%, 2.4%, 3.0%） of Na2CO3 and NaHCO3 mixtures were studied in a greenhouse of Northeast Forestry University, Harbin, China. The rate of electrolyte leakage （REL） and SOD （Superoxide dismutase） activity in leaves of different samples were determined. Results showed that the REL in leaves of U. pumila presented a slowly increasing trend at the salt concentrations less than 1.5%, which indicated that cell plasma membrane of U. pumila leaves had rather strong resistance to the injury of salt ion, and had a significant increase at the salt concentrations more than 1.5%. The SOD activities in leaves of U, pumila presented an increased trend at salt concentrations less than 1.5%, the growth of seedlings did not decline, and tress and leaves had no symptom of injury, while the salt concentrations exceeded 1.5%, SOD activities sharply decreased and REL increased promptly.
文摘The vacuum system for HL-2A was built in 2003. The test results indicated that this system is feasible. It consists of three main parts: a pumping system, a pumping divertor and a glow discharge cleaning (GDC) system. For the pumping system, there are three main functions: (1) evacuating the vacuum vessel thus to produce an ultra high vacuum, (2) removal of impurities released during baking and (3) pumping during GDC. The pumping divertor controls the particles at the plasma edge and the GDC system provides a clean wall conditioning. During the first campaign of physical trial experiment on HL-2A, the ultimate pressure reached 4.6 × 10-6 Pa, and the total leakage and outgassing rate in 12 hours was 1.8 × 10-5 Pa·m3/s, which is close to that of ASDEX.
基金financially supported by the National Natural Science Foundation of China(Grant No.52278407)the Fundamental Research Funds for the Central Universities(Grant No.22120210573).
文摘The localised leakage in shield tunnels that mainly occurs at segment joints may induce other defects,which threatens operational safety.To obtain a universal solution for the sealant performance of gasketed joints,we proposed a novel analytical model based on the multiscale contact and percolation theories,in which the obtained percolation pressure and interfacial separation can be utilized to derive the critical water leakage pressure and leakage rate.The evolutionary process of leakage was divided into three stages(i.e.,the percolation,leakage and breakdown),which explicitly reveal the progressive hydraulic deterioration of gasketed joints.The gaskets still own partial waterproof capacity until the end of the leakage stage due to the remaining contact pressure at surface asperities.The proposed model was first verified by several sets of experimental data,based on which the determination of three key model parameters(i.e.,self-sealing slope,sealing coefficient,and expel pressure)were discussed in detail.The parametric study indicates that the waterproof capacity is significantly affected by the joint opening,offset,and the surface roughness of the gaskets.The variation in waterproof capacity with joint opening is mainly due to the nonlinearity of the gasket’s modulus and self-sealing slope.The increase in joint offset can result in a lower waterproof capacity as well as a larger leakage rate.Gasket’s surface roughness affects the percolation pressure and interfacial separation,which contributes to the long-term sealant performance.
基金This study was co-supported by the National Natural Science Foundation of China(No.51875361)the Natural Science Foundation of Shanghai(No.20ZR1439200).
文摘The honeycomb seal is a vital component to reduce the leakage flow and improvethe system stability for the turbomachines. In this work, a three-dimensional model is established for the interlaced hole honeycomb seal (IHHCS) and the non-interlaced hole honeycombseal (NIHHCS) to investigate its leakage and rotordynamic characteristics by adopting computational fluid dynamics (CFD). Results show that the hole arrangement patterns have littleimpact on the pressure drop and turbulence kinetic energy distribution for the seals, and theIHHCS possesses a slightly lower leakage flow rate than the NIHHCS. Moreover, the numericalresults also show that the NIHHCS possesses a better rotordynamic performance than theIHHCS at all investigated conditions. Both seals show a larger k and a lower Ceff with the increase of the positive preswirl ratios and rotational speeds, while the negative preswirl ratioswould reduce the k and improve the Ceff. The NIHHCS possesses a higher absolute value ofFt for all operating conditions, this could explain the distinction of Ceff for both seals atdifferent working conditions.
基金supported by the fund of the State Key Laboratory of Technologies in Space Cryogenic Propellants (Grant No. SKLTSCP1210)
文摘Pneumatic cryogenic control valves(PCCV)are designed to meet the special requirements for the large cryogenic helium refrigeration system.Polychlorotrifluoroethylene(PCTFE)is adopted as the flat seal material of the valve seat.The leakage rates and compressive strain of the PCTFE gasket with different sealing stress are tested at both room temperature(293 K)and liquid nitrogen temperature(77 K).After 300 open/close cycles,the experimental results show that the sealing properties of the PCTFE gasket are improved.The leakage rates are about 10-8(293 K)and 10-4(77 K)Pam3 s-1 respectively.Finally,the effects of working pressure on sealing characteristics are discussed.The working pressure has little effect on compressive strain but it has a great influence on leakage rate.The leakage rate is linear with the working pressure of inlet at room temperature,but at liquid nitrogen temperature the leakage rate is linear with the square of the working pressure.
基金Supported by NNSFG-CAS Joint Fund for Research Based on Large-scale Scientific Facilities(10979064)Major State Basic Research Development Program of China(973 Program)(2010CD834204)National Natural Science Foundation of China(11205221)
文摘A flow gas low-pressure multi-wire proportional chamber（LPMWPC） with an active area of 180 mm× 80 mm has been developed for the flying time test of the recoil nuclei on super heavy nuclear experiments. The LPMWPC detector can be operated in single as well as double step operational modes. In the case of double step operational mode with a high gas amplification factor, signals from α-particles reside well above the electronic noise. The gas leakage rate and time resolution obtained from the α239Pu source are shown and discussed at the condition of 3 mbar Isobutane gas. It was shown that the time resolution was better than 2.9 ns at the best work condition, and the detecting efciency was larger than 98% at the low energy α particles. So the LPMWPC is fit to measure the flying time in the super heavy nuclear fragments experiment.
文摘Whether the transitions between 6s5d 3D and 5d6p 3F can be used for laser cooling of barium heavily depends upon the transition probabilities of 5d6p 3F-5d2 3F. Taking the transition 6s5d 3D3-5d6p 3F4 as a scale, the leakage rate of 5d6p 3Fa-5d2 3F was used to evaluate the transition probabilities. 706 nm laser pulses with different durations were applied to a barium atomic beam for 6s5d 3D3-5d2 3F4 optical pumping, and the remaining percentages in 6s5d 3D3 were measured. After exponential fitting, the transition probability of 5d6p 3F4-5d2 3F3,4 was determined to be 2.1（4） ~ 104 s-1, which is in agreement with theoretical calculations using the scaled Thomas-Fermi-Dirac method.
