A starved feed reactor (SFR) is a semi-batch polymerization reactor where initiator and monomer are fed slowly into a fixed amount of solvent. The polymerization is carried out isothermally at elevated temperatures. T...A starved feed reactor (SFR) is a semi-batch polymerization reactor where initiator and monomer are fed slowly into a fixed amount of solvent. The polymerization is carried out isothermally at elevated temperatures. The added initiator decomposes instantaneously and the added monomer polymerizes immediately. The molecular weight (MW) and molecular weight distribution (MWD) of the product polymer can be effectively controlled by the feed ratio of monomer to initiator. This paper presents a study on the MWD of styrene polymerization in a SFR. The MWD model parameters are regressed with experimental data. Although the solids fraction in the SFR is high (higher than 50%), viscosity is not too high and the 'gel effect' is weak due to the low molecular weight of the products. It is found that the termination rate constant is a power function of molecular weight, radicals terminate via 100% combination, the thermal initiation can be neglected even at high reaction temperature studied. And calculated results indicate that in the SFR, the validity of the long chain assumption becomes doubted. It appears that other alterative assumption should be found for an improved model.展开更多
The performance of gas diffusion porous electrode starved of electrolyte solution can be significantly increased by decreasing the thickness of uneven liquid film covering the catalyst agglomerates.
When the oil supply is not adequate to maintain the ideal lubrication,angular contact ball bearing will enter into the starved lubrication regime resulting in the potential performance degradation and consequently the...When the oil supply is not adequate to maintain the ideal lubrication,angular contact ball bearing will enter into the starved lubrication regime resulting in the potential performance degradation and consequently the severe failures.To study the effects of starved lubrication on the performance of angular contact ball bearing,this paper first proposes a multi-degree-of-freedom(DOF)tribo-dynamic model by introducing five-DOF inner ring,six-DOF balls,and six-DOF cage.The model considers the starved lubrication in the ball-raceway contact and the full multi-body interactions between the bearing components.With different ball-raceway starvation degrees being analyzed,the effects of starved lubrication on the bearing tribo-dynamic performance are first revealed.By comparison,it is found that the oil film thickness,the skidding performance,and the traction forces in the ball-raceway contact are significantly influenced by the starvation degrees.It is also found that the starvation-induced change of the ball-pocket contact force is dramatical under combined loads,and the maximum contact force under this load condition increases with the increasing starvation degrees.展开更多
人生本已苦短,短而并不能得到多少安宁。本文的一句话,不仅让笔者的心悲凉起来:There are very few times in a woman's life when somethingdoesn't Interfere with her sleep(在女人的一生中没有什么事情能干扰她的睡眠的时间...人生本已苦短,短而并不能得到多少安宁。本文的一句话,不仅让笔者的心悲凉起来:There are very few times in a woman's life when somethingdoesn't Interfere with her sleep(在女人的一生中没有什么事情能干扰她的睡眠的时间,是非常有限的)。作为一个即将达到"而立之年"的女性,正是在夜半时分无法入眠时,起床上网浏览,正巧读到此文,产生的共鸣之强烈,你们也许可以想象。不过,此文给我的帮助很大,尤其是以下一段,也许,今后我的睡眠会好起来,我愿意将本文推荐给贵刊的女性读者,不,也包括男性读者,希望能够从中受益。文章写道:展开更多
失眠,睡眠不足,一直以来,似乎是男性的健康问题。本文却揭示了这样一个铁的事实:women are two times more likely to have insomnia thanare men.(女性的失眠问题可能是男性的两倍)。健康专家在本文亮出了一个新颖的观点:Sleep should ...失眠,睡眠不足,一直以来,似乎是男性的健康问题。本文却揭示了这样一个铁的事实:women are two times more likely to have insomnia thanare men.(女性的失眠问题可能是男性的两倍)。健康专家在本文亮出了一个新颖的观点:Sleep should be up there with diet and exercise as necessary for goodhealth.(睡眠问题应该和食物、运动并列为健康之必须)。如何才能提高睡眠质量?文章提出了可以借鉴的观点和方法:using the bedroom for sleep and sexonly(no television);restricting sleep time to six and a half hours so the person isa little tired but not sleep deprived,enabling her to sleep better the next night;eliminating caffeine;having small frequent meals and exercising early in the day.(卧室仅为睡眠和性生活所用,无电视。限制睡眠时间为六个半小时,使稍感疲劳,而非“睡眠剥夺”,如此令晚上的睡眠更好些,拒绝咖啡因,少食多餐,早起锻炼)。展开更多
Surface texturing has been proven to be an effective method for improving the lubrication characteristics and tribological behavior of tribo-pairs under various operating conditions.Inspired by the unique Swiss cheese...Surface texturing has been proven to be an effective method for improving the lubrication characteristics and tribological behavior of tribo-pairs under various operating conditions.Inspired by the unique Swiss cheese-like leaves of Monstera riedrichsthalii,eight bionic texture patterns were introduced.The influence of vein features,such as costal vein angles(45°and 60°),vein symmetry(symmetric,asymmetric),and elliptical holes,on the tribological and vibration characteristics of rolling bearings was investigated under starved lubrication through a wear test rig and time‒frequency domain vibration signal analysis.The results show that the average coefficients of friction and wear losses of the Monstera riedrichsthalii bionictextured groups are generally lower than those of the smooth reference.The amplitudes and parameters(i.e.,peak value,root mean square(RMS),and crest factor)of the time-domain vibration signals of the textured groups are greater than those of the smooth group in the early stages,but the vibration parameters of most textured groups are lower than those of the smooth bearings in the later stages,especially those of the groups with elliptical holes.The amplitudes and power spectral density(PSD)curves of the frequency-domain vibration signals exhibit similar variations to those of the time-domain signals.Compared with the smooth reference,the Monstera riedrichsthalii bionictextured group with a combination of 45°secondary-vein angle,asymmetry,and elliptic holes can provide excellent tribological and vibration performance.Its well-lubricating period,average coefficient of friction(CoF),and mass loss can be effectively prolonged or reduced by 37.4%,7.3%,and 43.9%,respectively.展开更多
Water is one of the most significant causes of lubrication failure.There is little research on the direct observation of the impact of water on lubrication properties.In this study,the influence of water on oil replen...Water is one of the most significant causes of lubrication failure.There is little research on the direct observation of the impact of water on lubrication properties.In this study,the influence of water on oil replenishment under different elastohydrodynamic(EHD)lubricating conditions is evaluated using optical interferometry and infrared microscopy,and a dimensionless criterion when water influences the film thickness is proposed.Evidence shows that the scour displacing effect and emulsification of water/oil are the main reasons for the reduction in film thickness.Once a water droplet enters an oil reservoir around the critical contact zone,it hardly moves away.This aggravates starvation,reduces the center film thickness of the contact,and leads to lubrication failure of the mechanical components.展开更多
An experimental investigation was performed for investigating the tribological performance of micro-dimple surface texture patterns on a cylindrical surface in a realistic operating environment of starved lubrication....An experimental investigation was performed for investigating the tribological performance of micro-dimple surface texture patterns on a cylindrical surface in a realistic operating environment of starved lubrication. Micro-dimples were generated by a dual-frequency surface texturing method, in which a high-frequency (16.3 kHz) three-dimensional (3D) vibration and a low-frequency (230 Hz) one-dimensional (1D) vibration were applied at the tool tip simultaneously, resulting in the generation of the hierarchical micro-dimples in a single step. Rotating cylinder-on-pin tribological tests were conducted to compare the tribological performance of the non-textured reference specimen and micro-dimple samples. The effect of surface textures generated with various shape parameters (long drop and short drop), dimension parameters (length and surface texture density), and operation parameters (load and sliding velocity) on the tribological performance was evaluated. Stribeck curves indicate that the hierarchical micro-dimples exhibit a lower coefficient of friction than the reference specimen in the high contact-pressure regions. It is also observed that variation in the length of a micro-dimple, the shape effect, is the major factor affecting the friction response of the textured surfaces. The generation of additional hydrodynamic pressure and lift effect by hierarchical structures is the main reason for the improved performance of hierarchical micro-dimple surfaces.展开更多
The load-bearing behaviour of lubricated contacts depends primarily on the normal force,the relative velocity,and the geometry.Thus,with the aid of the Stribeck curve,it is usually well possible to characterize whethe...The load-bearing behaviour of lubricated contacts depends primarily on the normal force,the relative velocity,and the geometry.Thus,with the aid of the Stribeck curve,it is usually well possible to characterize whether hydrodynamics,mixed friction,or boundary friction is more likely to be present.The fact that the load regime can also depend on the fluid quantity is obvious,but has hardly been systematically investigated so far.Especially for contacts with microscopic roughness,the defined application of a very small amount of fluid is a very challenging requirement.In this paper,a very fundamental study shows how a pin-on-disc tribometer can be used to achieve the transition from dry friction via mixed friction to predominant hydrodynamics by the amount of supplied fluid.The experiments are carried out on samples filed with different coarseness.In addition,the simultaneous influence of partial filling and normal force as well as relative velocity is also shown.Very good reproducibility has been practically reached over the entire range of the tests.Regarding the quantities for the coefficient of friction(COF),it was concluded that close to full filling,a reduction of the fluid quantity has a similar effect on the COF as the reduction of the velocity.This property goes along with the common theory of starved lubricated systems.Such behaviour was not observed to the same extent for the normal force.In the vicinity of smaller fluid quantities,the COF increases very rapidly with further reduction in fluid quantity,far more disproportionately than that with reduction in velocity.With a deeper understanding of this problem,various practical issues such as idling or the run-up process in bearings can also be studied in a more focused manner.展开更多
基金Supported by the State Key Polymerization Reaction Engineering Laboratory of Zhejiang University.
文摘A starved feed reactor (SFR) is a semi-batch polymerization reactor where initiator and monomer are fed slowly into a fixed amount of solvent. The polymerization is carried out isothermally at elevated temperatures. The added initiator decomposes instantaneously and the added monomer polymerizes immediately. The molecular weight (MW) and molecular weight distribution (MWD) of the product polymer can be effectively controlled by the feed ratio of monomer to initiator. This paper presents a study on the MWD of styrene polymerization in a SFR. The MWD model parameters are regressed with experimental data. Although the solids fraction in the SFR is high (higher than 50%), viscosity is not too high and the 'gel effect' is weak due to the low molecular weight of the products. It is found that the termination rate constant is a power function of molecular weight, radicals terminate via 100% combination, the thermal initiation can be neglected even at high reaction temperature studied. And calculated results indicate that in the SFR, the validity of the long chain assumption becomes doubted. It appears that other alterative assumption should be found for an improved model.
文摘The performance of gas diffusion porous electrode starved of electrolyte solution can be significantly increased by decreasing the thickness of uneven liquid film covering the catalyst agglomerates.
基金This work was supported by the National Natural Science Foundation of China(Grant Nos.52130502 and 51875344)the Research Project of State Key Laboratory of Mechanical System and Vibration(Grant No.MSVZD202107)。
文摘When the oil supply is not adequate to maintain the ideal lubrication,angular contact ball bearing will enter into the starved lubrication regime resulting in the potential performance degradation and consequently the severe failures.To study the effects of starved lubrication on the performance of angular contact ball bearing,this paper first proposes a multi-degree-of-freedom(DOF)tribo-dynamic model by introducing five-DOF inner ring,six-DOF balls,and six-DOF cage.The model considers the starved lubrication in the ball-raceway contact and the full multi-body interactions between the bearing components.With different ball-raceway starvation degrees being analyzed,the effects of starved lubrication on the bearing tribo-dynamic performance are first revealed.By comparison,it is found that the oil film thickness,the skidding performance,and the traction forces in the ball-raceway contact are significantly influenced by the starvation degrees.It is also found that the starvation-induced change of the ball-pocket contact force is dramatical under combined loads,and the maximum contact force under this load condition increases with the increasing starvation degrees.
文摘人生本已苦短,短而并不能得到多少安宁。本文的一句话,不仅让笔者的心悲凉起来:There are very few times in a woman's life when somethingdoesn't Interfere with her sleep(在女人的一生中没有什么事情能干扰她的睡眠的时间,是非常有限的)。作为一个即将达到"而立之年"的女性,正是在夜半时分无法入眠时,起床上网浏览,正巧读到此文,产生的共鸣之强烈,你们也许可以想象。不过,此文给我的帮助很大,尤其是以下一段,也许,今后我的睡眠会好起来,我愿意将本文推荐给贵刊的女性读者,不,也包括男性读者,希望能够从中受益。文章写道:
文摘失眠,睡眠不足,一直以来,似乎是男性的健康问题。本文却揭示了这样一个铁的事实:women are two times more likely to have insomnia thanare men.(女性的失眠问题可能是男性的两倍)。健康专家在本文亮出了一个新颖的观点:Sleep should be up there with diet and exercise as necessary for goodhealth.(睡眠问题应该和食物、运动并列为健康之必须)。如何才能提高睡眠质量?文章提出了可以借鉴的观点和方法:using the bedroom for sleep and sexonly(no television);restricting sleep time to six and a half hours so the person isa little tired but not sleep deprived,enabling her to sleep better the next night;eliminating caffeine;having small frequent meals and exercising early in the day.(卧室仅为睡眠和性生活所用,无电视。限制睡眠时间为六个半小时,使稍感疲劳,而非“睡眠剥夺”,如此令晚上的睡眠更好些,拒绝咖啡因,少食多餐,早起锻炼)。
基金the financial support from the Natural Science Foundation of Liaoning Province(No.2023-MS-234)the Scientific Research Fund of Liaoning Provincial Education Department(No.LJKMZ20220800)+1 种基金the“Da Biao Li Xiang”Project of Shenyang University of Chemical Technology(No.512000001185)the National Natural Science Foundation of China(No.52275156).
文摘Surface texturing has been proven to be an effective method for improving the lubrication characteristics and tribological behavior of tribo-pairs under various operating conditions.Inspired by the unique Swiss cheese-like leaves of Monstera riedrichsthalii,eight bionic texture patterns were introduced.The influence of vein features,such as costal vein angles(45°and 60°),vein symmetry(symmetric,asymmetric),and elliptical holes,on the tribological and vibration characteristics of rolling bearings was investigated under starved lubrication through a wear test rig and time‒frequency domain vibration signal analysis.The results show that the average coefficients of friction and wear losses of the Monstera riedrichsthalii bionictextured groups are generally lower than those of the smooth reference.The amplitudes and parameters(i.e.,peak value,root mean square(RMS),and crest factor)of the time-domain vibration signals of the textured groups are greater than those of the smooth group in the early stages,but the vibration parameters of most textured groups are lower than those of the smooth bearings in the later stages,especially those of the groups with elliptical holes.The amplitudes and power spectral density(PSD)curves of the frequency-domain vibration signals exhibit similar variations to those of the time-domain signals.Compared with the smooth reference,the Monstera riedrichsthalii bionictextured group with a combination of 45°secondary-vein angle,asymmetry,and elliptic holes can provide excellent tribological and vibration performance.Its well-lubricating period,average coefficient of friction(CoF),and mass loss can be effectively prolonged or reduced by 37.4%,7.3%,and 43.9%,respectively.
基金This work was financially supported by the National Natural Science Foundation of China(Grant Nos.51805505,52075514,and 51605460).
文摘Water is one of the most significant causes of lubrication failure.There is little research on the direct observation of the impact of water on lubrication properties.In this study,the influence of water on oil replenishment under different elastohydrodynamic(EHD)lubricating conditions is evaluated using optical interferometry and infrared microscopy,and a dimensionless criterion when water influences the film thickness is proposed.Evidence shows that the scour displacing effect and emulsification of water/oil are the main reasons for the reduction in film thickness.Once a water droplet enters an oil reservoir around the critical contact zone,it hardly moves away.This aggravates starvation,reduces the center film thickness of the contact,and leads to lubrication failure of the mechanical components.
文摘An experimental investigation was performed for investigating the tribological performance of micro-dimple surface texture patterns on a cylindrical surface in a realistic operating environment of starved lubrication. Micro-dimples were generated by a dual-frequency surface texturing method, in which a high-frequency (16.3 kHz) three-dimensional (3D) vibration and a low-frequency (230 Hz) one-dimensional (1D) vibration were applied at the tool tip simultaneously, resulting in the generation of the hierarchical micro-dimples in a single step. Rotating cylinder-on-pin tribological tests were conducted to compare the tribological performance of the non-textured reference specimen and micro-dimple samples. The effect of surface textures generated with various shape parameters (long drop and short drop), dimension parameters (length and surface texture density), and operation parameters (load and sliding velocity) on the tribological performance was evaluated. Stribeck curves indicate that the hierarchical micro-dimples exhibit a lower coefficient of friction than the reference specimen in the high contact-pressure regions. It is also observed that variation in the length of a micro-dimple, the shape effect, is the major factor affecting the friction response of the textured surfaces. The generation of additional hydrodynamic pressure and lift effect by hierarchical structures is the main reason for the improved performance of hierarchical micro-dimple surfaces.
基金German Research Foundation for funding this project(No.390252106,“Fundamental Studies on Tribological Contacts with Partially Filled Gaps”).
文摘The load-bearing behaviour of lubricated contacts depends primarily on the normal force,the relative velocity,and the geometry.Thus,with the aid of the Stribeck curve,it is usually well possible to characterize whether hydrodynamics,mixed friction,or boundary friction is more likely to be present.The fact that the load regime can also depend on the fluid quantity is obvious,but has hardly been systematically investigated so far.Especially for contacts with microscopic roughness,the defined application of a very small amount of fluid is a very challenging requirement.In this paper,a very fundamental study shows how a pin-on-disc tribometer can be used to achieve the transition from dry friction via mixed friction to predominant hydrodynamics by the amount of supplied fluid.The experiments are carried out on samples filed with different coarseness.In addition,the simultaneous influence of partial filling and normal force as well as relative velocity is also shown.Very good reproducibility has been practically reached over the entire range of the tests.Regarding the quantities for the coefficient of friction(COF),it was concluded that close to full filling,a reduction of the fluid quantity has a similar effect on the COF as the reduction of the velocity.This property goes along with the common theory of starved lubricated systems.Such behaviour was not observed to the same extent for the normal force.In the vicinity of smaller fluid quantities,the COF increases very rapidly with further reduction in fluid quantity,far more disproportionately than that with reduction in velocity.With a deeper understanding of this problem,various practical issues such as idling or the run-up process in bearings can also be studied in a more focused manner.
