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For a direct dry cooling system, the turbine back pressure fluctuates with the meteorological conditions. Moreover, the operation of axial flow fans plays an important role in the cooling performance of air‐cooled condensers (ACC). It is of significant use to study the operation strategies of axial flow fans under various ambient conditions. Based on typical 2 × 660MWdirect dry cooling power generating units, the ACC model coupled with the turbine thermodynamic characteristics is developed, by which the thermo‐flow performances of the ACC are predicted in the dominant wind direction, and then the standard coal consumption is calculated. The results show that the increased ambient temperature and wind speed, or the reduced fan rotational speed leads to the high turbine back pressure. At the low ambient temperature and wind speed, the standard coal consumption rate of the unit can be reduced by reducing the speed of axial flow fans appropriately, with the maximum drop in coal consumption rate reached 0.734 g/(kWh) when the ambient temperature is 10°C without wind. If the wind speed exceeds 12 m/s or the ambient temperature reaches 25°C, 110% of the rated fan rotational speed is recommended. [ABSTRACT FROM AUTHOR]

As the progress of the high‐speed performance requirement for porous gas journal bearings continuing, the aerodynamic effect, which plays a key role in the state of lubrication, causes the porous gas journal bearings being gradually to be used as hybrid bearings. This paper firstly presents a theoretical analysis on the lubrication mechanism of the hybrid bearings. The gas flow in the porous and clearance is modelled by using the mass continuity equation. Two experimental test rigs are designed to systematically test the static and dynamic characteristics of the hybrid bearings. The numerical results are corroborated by the experimental data. Results show that there is optimal clearance for hybrid bearings to obtain maximum load capacity. The load capacity of the hybrid bearings is increased by the aerodynamic effect to be higher than that of pure aerostatic bearings especially at higher rotational speed and larger eccentric ratio. However, due to the occurrence of the aerodynamic effect, the hybrid bearings show clear cross‐coupling dynamic coefficients, which may lead to bearing instability. It is interesting to note that the direct dynamic stiffness and damping coefficients are both influenced by the aerodynamic and aerostatic effects. Higher rotational speed and external supply pressure will result in higher direct dynamic coefficients. [ABSTRACT FROM AUTHOR]

Inertia friction welding (IFW) is a solid‐state welding technology that avoids defects associated with molten weld processes; however, this process has rarely been used to weld ultrahigh‐strength steel (UHSS). Herein, 32CrMnSi2Ni6MoV UHSS is joined successfully via IFW. The mechanical properties after welding at different rotational speeds and the microstructure at 2800 rpm are studied in detail. The temperature distributions in the peripheral and central areas are modeled according to the temperature at the weld zone. The microstructural transformation is analyzed for different temperature intervals, and the microstructural characteristics of each interval correspond to the actual microstructure of the welded joint according to the temperature distribution model. High‐strength martensite forms at the weld zone, and the thermomechanical‐affected zone (TMAZ) in the peripheral region is divided into phase transformation zone, partial recrystallization zone, and plastic deformation zone, whereas the TMAZ in the central region includes only the partial recrystallization and pure plastic deformation zones. This difference is due to the higher frictional heat caused by the higher peripheral linear velocity during rotation. A tensile test shows that fracture occurs in the base metal (BM) region, and the yield strength, tensile strength, and elongation are 805 MPa, 1064 MPa, and 13.88%, respectively. [ABSTRACT FROM AUTHOR]

This study considers the design of surface‐mounted permanent magnet electrical machines for high‐speed applications and proposes a methodology to determine the maximum achievable power density. Power density is usually improved by increasing rotational speed. At high speed, a mechanical retaining system for the rotor magnets must be considered. As the speed increases, the thickness of the retaining sleeve becomes larger, reducing torque capability. There will be an optimal speed at which the output power will be maximised. Both structural and electromagnetic design must be considered simultaneously to properly address this design problem. To simplify the design procedure, static finite‐element simulations are used for the electromagnetic analysis and analytical formulae are employed for retaining sleeve sizing. The procedure is aided by multi‐objective optimisation algorithms. A case study based on the specification of an aeronautical actuator is presented. The performances that can be obtained using different iron cores, high‐grade silicon steel, and cobalt iron steel are compared. Finally, results obtained from transient finite‐element electromagnetic and structural analysis are presented to validate the feasibility of the proposed procedure. [ABSTRACT FROM AUTHOR]

This study is concerned with the unified analytical solution of rotor strength for the segmented permanent magnet (PM) rotor retained by the carbon‐fibre sleeve and non‐magnetic alloy sleeve in high‐speed surface‐mounted permanent magnet synchronous machine. Considering the influence of different densities and coefficients of thermal expansion of PMs and pole fillers on rotor stress, the analytical solution for rotor strength was proposed based on displacement method and stress potential method in polar coordinate. The proposed analytical solution was validated by the finite‐element method (FEM) and experiment, respectively, and the influences of rotational speed, retaining sleeve thickness and interference fit between the retaining sleeve and PMs on rotor strength were further investigated based on the analytical solution proposed. It is shown that the results calculated by the proposed analytical solution and the FEM are in good agreement with each other, and the analytical solution can accurately predict the stress distributions of the segmented PM rotor retained by the carbon‐fibre sleeve and non‐magnetic alloy sleeve. The difference in density and coefficient of thermal expansion between PM and pole filler, rotational speed and operating temperature have great effects on rotor strength. [ABSTRACT FROM AUTHOR]

This Letter presents an amplitude modulation method of the rotating‐based mechanical antenna that does not require the change in the rotational speed of the permanently polarised material as in frequency modulation, hence overcoming the mechanical design challenges. A mechanical‐based modulator is designed to control the attenuation of the radiation field in specific polarisation direction, and the signal reception in different polarisation directions is realised by using two‐axis orthogonal coils. The underlying physics is discussed and simulated using the basic electromagnetic theory, the design of transmitters is described, and a prototype is built to verify the effectiveness of the modulation method. [ABSTRACT FROM AUTHOR]

Aim To compare the shaping ability of four different nickel-titanium rotary instruments during the preparation of curved root canals in extracted teeth. Methodology A total of 80 root canals with curvatures ranging between 25° and 39° were divided into four groups of 20 canals. Based on radiographs taken prior to instrumentation, the groups were balanced with respect to the angle and the radius of canal curvature. Canals were prepared to a final apical size of 40 using Mtwo, Pro Taper Universal, Pro Taper NEXT and BT- Ra Ce. Using pre- and post-instrumentation radiographs, straightening of the canal curvatures and canal transportation were determined with a computer image analysis programme. Preparation time and instrument failures were also recorded. The data were analysed statistically using anova and Student- Newman- Keuls test. Results The use of BT- Ra Ce files resulted in significantly more straightening during instrumentation compared to Mtwo ( P < 0.05), whilst the differences between all other instruments were not significant ( P > 0.05). No significant differences were obtained between all four instruments regarding canal transportation ( P = 0.429). Instrumentation with Pro Taper NEXT files was significantly faster than with all other instruments ( P < 0.05). During the preparation of the curved canals, one BT2 instrument fractured, whilst no fracture occurred when using the other instruments ( P > 0.05). Conclusions Within the parameters of this study, all instruments maintained root canal curvature well and were safe. However, care should be taken when using the BT2 instrument due to its unique cylindrical design. [ABSTRACT FROM AUTHOR]

Aim To develop a method to evaluate the cutting behaviour of nickel-titanium ( Ni Ti) coronal flaring instruments. Methodology Bio Ra Ce BR0 ( BR), Hy Flex CM 1 ( HY), Pro File OS No. 2 ( PF) and Pro Taper Sx ( PT) instruments were used in simulated coronal flaring using a lateral action against bovine dentine blocks, at 250 and 500 rpm. Cutting efficiency was assessed by three methods: first, areas of notches produced by instruments were directly measured under a stereomicroscope. Second, dentine specimens were then analysed by surface profilometry to determine the maximum cutting depth and finally by microcomputed tomography to assess the volume of removed dentine. Data were compared using parametric tests with the significance level set at 0.05. Results For all three methods, HY and PF were the most and the least cutting-efficient instruments, respectively ( P < 0.05). Significant differences were detected between 250 and 500 rpm for HY and PT (area); for BR, HY and PT (depth); and for BR and HY (volume). There were strong positive correlations between the results obtained with those three different methods with r-values ranging from 0.81 to 0.92. Conclusion Measuring the amount of material removed in a specific time under stereomicroscopy is a simple and rational way to assess the cutting behaviour of Ni Ti rotary instruments in lateral action. Hy Flex, manufactured with thermomechanically treated Ni Ti wire, was the most efficient instrument, and increased rotational speed was associated with increased cutting efficiency. [ABSTRACT FROM AUTHOR]

Aim To evaluate the effect of rotational speed on cyclic fatigue of Mtwo nickel-titanium files. Methodology A total of 120 new Mtwo rotary instruments sizes 10, 0.04 taper; 15, 0.05 taper; 20, 0.05 taper; and 25, 0.06 taper were randomly divided into three groups on the basis of the rotational speed used to shape nine standardized simulated canals: group A = 350 rpm; group B = 250 rpm; group C = 150 rpm. Each group consisted of 40 instruments, 10 for every size. The average preparation time (in seconds) and the average correlated numbers of cycles to instrument ( NCI) the nine standardized canals were recorded for each file. The resistance to cyclic fatigue was determined by counting numbers of cycles to failure ( NCF) with a rotational speed of 300 rpm in a 60° curve with a 5-mm radius. Data were analysed by two-way anova. Results Preparation time was significantly longer at 150 rpm than at 250 or 350 rpm. The average number of cycles needed for each file to instrument nine standardized canals was significantly higher at 350 and 250 rpm, than at 150 rpm. There were no significant differences in the NCF ( P > 0.05) between A, B and C groups for instruments of the same size. Conclusions Speed did not affect the cyclic fatigue of Mtwo instruments with the same size and taper. Preparation time was shorter at 350 or 250 rpm rather than at 150 rpm. However, there was no significant difference between 350 and 250 rpm rotational speed, neither in the preparation time of simulated canals nor in the resistance to fatigue fracture. [ABSTRACT FROM AUTHOR]

The residence time distribution (RTD) of a model particulate–fluid mixture (potato in starch solution) in the ohmic heater in a continuous sterilization process was measured using a radio frequency identification (RFID) methodology. The effect of solid concentration and the rotational speed of the agitators on the RTD were studied. The velocity of the fastest particle was 1.62 times the mean product velocity. In general, particle velocity was found to be greater than the product bulk average velocity. Mean particle residence time (MPRT) increased with an increase in the rotational speed of the agitators ( P < 0.05), and no particular trend was observed between the MPRT and the solid concentration. The distribution curves E (θ) were skewed to the right suggesting slow moving zones in the system. [ABSTRACT FROM AUTHOR]

Experimental studies on the effects of scaling on the performance of centrifugal blood pumps were conducted in a closed-loop test rig. For the prototype, eight different impellers of the same outer diameter of 25 mm were tested at 1,500, 2,000, and 2,500 revolutions per minute (rpm) using blood analog as fluid medium. This corresponds to Reynolds numbers (Re) of 25,900, 34,500, and 43,200, respectively. The results indicated that the nondimensional pump characteristic is a function of Re. This is understandable since the typical operating Re for centrifugal blood pumps is less than 100,000. Thus, the effects of scaling cannot be ignored for centrifugal blood pumps. Experiments on a 5× scaled-up model have also indicated that the scaled-up model is more efficient than the prototype model. Our results showed that in the range of Re tested, the nondimensional head versus flow curve is a function of Re to the power of approximately 0.25. It is observed that the nondimensional head versus flow is a function of diameter ratio to the power of 0.2. [ABSTRACT FROM AUTHOR]

Abstract Aim The purpose of this study was to evaluate the influence of rotational speed, torque, and operator experience on the incidence of locking, deformation, and separation of instruments when using a specific Ni–Ti rotary instrumentation technique in extracted human teeth. Methodology Greater Taper Ni–Ti rotary instruments (GT) were used in a crown-down technique. In one group (rotational speed evaluation) of canals (n = 300) speeds of 150, 250 and 350 r.p.m. (subgroups 1, 2 and 3) were used. Each one of the subgroups included 100 canals. In a second group (evaluation of torque) (n = 300) torque was set at 20, 30 and 55 Ncm (subgroups 4, 5 and 6). In the third group (evaluation of operator proficiency) (n = 300) three operators with varying experience (subgroups 7, 8 and 9) were also compared. Each subgroup included the use of 10 sets of GT rotary instruments and 100 canals of extracted human molars. Each set of instruments was used in up to 10 canals and sterilized before each case. NaOCl 2.5% was used as an irrigant. The number of locked, deformed, and separated instruments was recorded for each group. Statistical analysis was carried out with pairwise comparisons using Fisher’s exact tests for each of the failure type. Results When the influence of rotational speed was evaluated, instrument deformation and separation did not occur in subgroups 1 (150 r.p.m.), 2 (250 r.p.m.), and 3 (350 r.p.m.). Instrument locking occurred in subgroup 3 only. Statistical analysis demonstrated a significant difference between the 150 and 350 r.p.m. groups and between the 250 and 350 r.p.m. groups with respect to instrument locking. In torque evaluation, neither separation, deformation nor locking occurred during the use of the instruments, at 150 r.p.m., and at the different torque values. When the operators were compared, although two instruments were separated in canals prepared by the least experienced operator, Fisher’s exact tests did not... [ABSTRACT FROM AUTHOR]

Abstract Aim The purpose of this study was to evaluate the influence of rotational speed, torque, and operator experience with a specific Ni–Ti rotary instrumentation technique on the incidence of locking, deformation and separation of instruments. Methodology ProFile Ni–Ti rotary instruments (PRI) sizes 40–15 with a 6% taper were used in a crown-down technique. In one group of canals (n = 300) speeds of 150, 250 and 350 rpm (subgroups 1, 2 and 3) were used. Each one of the subgroups included 100 canals. In a second group (n = 300) torque was set at 20, 30 and 55 Ncm (subgroups 4, 5 and 6). In the third group (n = 300) three operators with varying experience (subgroups 7, 8 and 9) were also compared. Each subgroup included the use of 10 sets of PRI and 100 canals of extracted human molars. Each set of PRI was used in up to 10 canals and then sterilized before each case. NaOCl 2.5% was used as an irrigant. The number of locked, deformed, and separated instruments for the different groups, and within each part of the study was analysed statistically for significance with chi-squared tests. Results In group 1 only one instrument was deformed in the 150-rpm group and no instruments separated or locked. In the 250-rpm group instrument separation did not occur, however, a high incidence of locking, deformation and separation was noted in the 350-rpm group. In general, instrument sizes 30–15 locked, deformed and separated. Chi-squared statistics showed a significant difference between the 150 and 350 rpm groups but no difference between the 150 and 250 rpm groups with regard to instrument separation. Overall, there was a trend toward a higher incidence of instrument deformation and separation in smaller instruments. Locking and separation occurred during the final passage of the instruments, in the last (tenth) canal in each subgroup. In the second group, neither separation nor deformation and locking occurred during the use of the ProFile... [ABSTRACT FROM AUTHOR]

Aiming at a high‐speed‐impeller mechanical seal structure that plays a significant role in the oxidant turbopump of cryogenic rocket systems, the computational fluid dynamic approach is introduced to analyze its working performance, including the phase distribution in the flow channel, the cooling effect of the frictional element, and the sealing function as well as the power consumptions of the impellers. The established periodic 3D model, which could simultaneously account for the turbulent flow, coupled heat transfer, cavitation, and evaporation, as well as the change of thermophysical properties, was successfully verified by the experimental data. The results show that the sealing ability of a totally liquid‐filled impeller would increase with increasing rotational speed, blade size, and density of the working fluid. After the rotational speed increasing over a certain value (14,000 r/min in this case), a dynamically steady gas–liquid interface would be maintained at the Impeller II's blades, which indicates the completely effective sealing of liquid. Meanwhile, the friction surface could be effectively cooled by this two‐stage leakage cooling scheme, and its maximum temperature could be stably controlled at the rated speed. Based on the good sealing performance and effective cooling, this high‐speed‐impeller seal structure was proved to be feasible and available for cryogenic rocket systems. [ABSTRACT FROM AUTHOR]

Abstract Martín B, Zelada G, Varela P, Bahillo JG, Magán F, Ahn S, Rodríguez C. Factors influencing the fracture of nickel-titanium rotary instruments. International Endodontic Journal , 36 , 262–266, 2003. Aim To evaluate the effect of rotational speed and the angle and radius of curvature of root canals on the fracture of two types of nickel-titanium rotary instruments: K3® and ProTaper® . Methodology A total of 240 root canals of extracted human maxillary and mandibular molars were divided into two groups of 120, according to the angle of the canal curvature (group A: <30°, group B: >30°). Each group was then divided into two subgroups of 60 canals in order to perform instrumentation using K3® and ProTaper® rotary instruments at three different rotational speeds: 150, 250 and 350 r.p.m. (20 canals at each rotational speed). Each instrument was used a maximum of 20 times and at one rotational speed only. The angle and radius of canal curvature were measured in the only group in which fractures actually took place (group B). Results There were a total of 22 instrument fractures; all of these occurred in canals with curves >30°. In a multivariate analysis, it was demonstrated that the files used at a rotational speed of 350 r.p.m. were more likely to fracture than those used at 250 r.p.m. (OR: 1113.88; 95% CI: 2.36–526420.05) and than those used at 150 r.p.m. (OR: 13531.33; 95% CI: 5.37–34120254.00). A decrease in the angle of curvature of the canal also significantly reduced the likelihood of fracture (OR: 0.2083; 95% CI: 0.068–0.6502). These relationships remained significant after being adjusted for the potential interactions between the remaining variables. No significant differences were found between the files or the radii of the canals. Conclusions Instrument fracture was associated with rotational speed and the angle of curvature of the canal. [ABSTRACT FROM AUTHOR]