Measuring contact pressure distributions under elastohydrodynamic point contacts

Circular point contact EHD pressure distributions were investigated under various operating conditions using a thin film piezo-resistive pressure transducer. A series of controlled experiments, in which the active element of the transducer is positioned at various contact cross-sections, was carried out. The results are analysed and presented in the form of isobars. The pressure distribution closely describes the Hertzian pressure profile with a secondary pressure peak appearing prior to and near the exit constriction.     

Experimental study on deep penetrated laser welding under local subatmospheric pressure

Unlike the normal vacuum chamber that a workpiece is put inside, a new vacuum chamber was designed to put on the welding zone of a workpiece, which has no size limit with this chamber, so that a large and thick plate could be welded with laser under low pressure. In this new vacuum chamber, a local subatmospheric pressure on the welding zone was achieved with side draught by a vacuum pump. A series of spot welding experiments were performed with fiber laser under subatmospheric pressure, normal atmospheric pressure with and without shielding gas side-blowing, respectively. The feature of weld surfaces and cross-section profiles for above different conditions were compared. A high-speed camera was applied to observe the behavior of plasma plume. The results indicated that the deeper welding penetration and narrower weld bead width could be obtained under subatmospheric pressure. The characteristics of spot weld bead under local subatmospheric pressure were quite different from the one under normal atmospheric pressure with shielding gas side-blowing method. The plasma plume was suppressed more effectively by local subatmospheric pressure than that by shielding gas side-blowing. Additional experiments of continuous laser welding under local subatmospheric pressure were tried and sound welds could be obtained.     

Inter-laboratories comparison at 100 GΩ and 1 TΩ level to evaluate the traceability transfer from INRIM in the field of high dc resistance

A National inter-laboratories comparison of dc resistance at 100 GΩ and 1 TΩ among the National Institute of Metrological Research (INRIM) and eight Secondary Electrical Calibration Laboratories was carried out in 2010. All the involved Laboratories made their measurements with a method based on a Multifunction Calibrator (MFC) and on a digital multimeter (DMM), both used in their dc voltage function.These and other Secondary Electrical Laboratories are traceable to National Standards by means of the calibration at INRIM of a complete set of primary standards or, alternatively, by means of the calibration of a high accuracy DMM or of a Multifunction Transfer Standard (MTS) or of few primary standards. All the relative differences between each Laboratory’s value and its reference value obtained in the comparison were within their relative expanded uncertainties. This result showed that the traceability transfer methods from INRIM to Electrical Secondary Laboratories lead to satisfactory results in the field of high dc resistance.     

Novel characterization of the large water discharge

Measurement of water discharges is important in chemical engineering and pharmacy. However, high-accuracy measurements of the large water discharge are difficult due to long operational periods and large total water discharge. Here is reported a novel device for the highly accurate, continuous measurement of large water discharge at atmospheric pressure. The device is composed of two identical water discharge measurement subsystems. The computer-controlled system automatically switches the subsystems alternate operation to provide continuous, accurate measurements. Each subsystem used a slender glass tube 2300?mm in length, a pressure transducer, and a solenoid valve. After static calibration, the pressure transducer accurately measures the volume of water in the tube based on the pressure difference in the liquid levels. Moreover, the dynamic error caused by the fluidity of water was characterized. Comparison of simulations and measurements were used to characterize and reduce the dynamic error. Continuous large water discharge measurements were performed. The results show that the device is accurate, stability, and not limited by the measurement time, allowing continuous operation for extended intervals.     

Highly precise experimental device for determining the heat capacity of liquids under pressure

An experimental device for making isobaric heat capacity measurements of liquids under pressure is presented. The device is an adaptation of the Setaram micro-DSC II atmospheric-pressure microcalorimeter, including modifications of vessels and a pressure line allowing the pressure in the measurement system to be set, controlled, and stabilized. The high sensitivity of the apparatus combined with a suitable calibration procedure allows very accurate heat capacity measurements under pressure to be made. The relative uncertainty in the isobaric molar heat capacity measurements provided by the new device is estimated to be 0.08% at atmospheric pressure and 0.2% at higher levels. The device was validated from isobaric molar heat capacity measurements for hexane, nonane, decane, undecane, dodecane, and tridecane, all of which were highly consistent with reported data. It also possesses a high sensitivity as reflected in its response to changes in excess isobaric molar heat capacity with pressure, which were examined in this work for the first time by making heat capacity measurements throughout the composition range of the 1-hexanol+n-hexane system. Finally, preliminary measurements at several pressures near the critical conditions for the nitromethane+2-butanol binary system were made that testify to the usefulness of the proposed device for studying critical phenomena in liquids under pressure.     

A study on the manufacturing conditions of metal matrix composites by low pressure infiltration process

Metal fiber preform reinforced aluminum alloy composite as made by the infiltration of molten metal under low pressure casting process. The infiltration behavior of filling pattern and the velocity profile with low-pressure casting process was investigated. The thermocouple was inserted into the preform in order to observe the infiltration behavior. The infiltration of applied pressure time, 1, 2 and 5 s under constant pressure of 0.4 MPa was completely filled during 0.4 s. In these conditions, molten aluminum alloy has successfully infiltrated to FeCrSi metal fiber preform by low-pressure casting process. It was observed the porosity of composites for reliability of composites. The automobile piston was developed with FeCrSi reinforced aluminum alloy that is 0% porosity by the optimal applied pressure and applied pressure time.     

A table for experimental study of mechanoluminescent pulse pressure transducers

The procedure and results of experimental study of mechanoluminescent pressure transducers converting mechanical stress into an optical signal are described. A prototype of the mechanoluminescent pulse pressure transducer and a mechanical shock table for laboratory study of it are presented. The developed table allows one not only to fix and evaluate the output luminous flux of the transducer, but also to quantitatively determine the mechanical loading value. Comparison of recorded oscillograms of energy-emittance pulses of the transducer and results of numerical calculations demonstrates the adequacy of the used mathematical model of mechanoluminescent conversion.     

Hydrostatic and central venous pressure measurement by the IVAC 560 infusion pump

The IVAC Variable Pressure Volumetric Pump, Model 560, was evaluated for hydrostatic and central venous pressure (CVP) measurement. In bench tests, 4 per cent of IVAC systems failed a +/- 2 mm Hg accuracy test. When measurements were inaccurate, errors were small (SD = 0.49 mm Hg). In simultaneous clinical measurements with a standard electronic transducer system, the correlation coefficient between the IVAC and transducer measurements was 0.95. A potential drawback of the IVAC 560 for CVP measurement is the lack of waveform display. The IVAC system is simple to operate and less expensive per use than the standard electronic system.     

Plugging criteria for thinned high-pressure feedwater heater tubes considering pressure and thermal loading

When heat exchanger tubes have critical thinning which could cause unsafe conditions, it is general practice to plug the tubes so that they are out of service to prevent rupture failure at the thinnest location. Plugging criteria for the high-pressure feedwater heater tubes of fossil power plant were studied. Tubes in the desuperheating zone were considered due to their high internal pressure and the high temperature difference across the tube wall. Theoretical analysis of uniform thinning and eccentric thinning of the tube was conducted to determine the stress conditions at the thinnest location under internal/external pressure and thermal gradient across the tube. The minimum required tube thickness was determined using the maximum shear stress criterion (Tresca theory). Accuracy and effectiveness of the analytic solutions of the stresses were verified by comparing the results obtained with those obtained from finite element analysis. Using finite element analysis, the stresses for eccentric thinning were determined. Thermal loading due to temperature difference across the wall was considered even though the contribution of pressure loading to the stress of the tube was known to be higher than that of the thermal loading. As case studies, the tube plugging criteria of three high pressure feedwater heaters were determined using actual temperature and design pressure industry data. The procedure used in this study can be applied to different pressure and temperature operating conditions, and different tube materials.     

Zero stability of disposable and reusable pressure transducers

Zero stability tests were performed on contrasting, commercially available, blood pressure-transducer systems. One system was based on a brand of disposable transducer. The others employed one brand of reusable transducer with and without samples of two different brands of compatible disposable domes. Drift was measured at atmospheric pressure over 3-hr periods. Drifts with the disposable transducers and with the bare reusable transducers were small, ranging from -2 to +2 mm Hg over 3 hr. However, the drifts of the reusable transducers with domes were significantly greater, ranging from -11 mm to +5 mm Hg. The disposable transducers did not drift significantly after the first half hour, although the reusable transducers with domes continued to drift. In addition, one brand of disposable dome produced inaccurate calibrations with the reusable transducer. The methodology of drift measurement and analysis should be practical and useful in other settings and with other brands of transducers. In general, the results indicate that periodic zeroing is still a clinically important procedure, and it is a worthwhile effort prior to treatment decisions based on pressure readings.     

The smart-orifice meter: a mini head meter for volume flow measurement

Differential pressure based flow meters generally consist of a flow restriction element which generates a differential pressure and a pressure transducer, externally piped to the restriction, which measures the flow related differential pressure. The smart-orifice mini head meter presented takes advantage of silicon technology by incorporating a differential pressure microsensor. In contrast to conventional head meters, it represents a single compact and economic device for general flow meter applications, in particular where small size is of concern. Computational fluid dynamics analyses were applied to develop a non-standard orifice design and prototypes of the smart-orifice were fabricated. The performance of the mini head meter in water flow measurement was determined in a computer supported test bench facility. It was compared to the results predicted by the simulation, as well as to a conventional head meter arrangement with externally mounted pressure transducer, including measurements with water at elevated temperature and different absolute line pressures. The results are very promising and verify the competitiveness of the smart-orifice as a mini head meter.     

In situ pressure measurements in dimpled elastohydrodynamic sliding contacts by Raman microspectroscopy

In situ pressure measurements within dimples formed in glass-steel point contacts under various sliding conditions were performed using Raman microspectroscopy. Experiments were conducted using a ball-on-disc type apparatus in which a circular contact is formed between a rotating glass disc and a rotating steel ball. Film thickness distributions were measured by duochromatic optical interferometry. Polyphenyl ether oil (5P4E) which has a high pressure-viscosity coefficient was used to produce a dimple in the contact area. Experimental results show that the pressure increases locally in the dimple zone and the pressure profile changes, accompanying the changes of the dimple location as a function of the slide-to-roll ratio. The maximum pressure is located downstream the maximum height of the dimple. The rheological response of the oil film under dimple occurrence conditions is discussed.     

Ultrasound Measurement of Two-Filler Concentrations in Polypropylene Compounds. Part 1: Static Calibration

Ultrasound waves are used to measure the concentration levels of mica and glass, simultaneously, in polypropylene polymer compounds. A test chamber was designed to accommodate a 1 MHz ultrasound transducer for static calibration of the system response to various levels of glass and mica concentration in the polymer blend. Temperature and pressure calibrations of the transducer response were also performed under controlled experiments. Attenuation and time-of-flight measurements of ultrasound waves propagating through the polymer blend were used to determine the relative concentrations of the fillers. The experimental results show that the system is capable of measuring the filler concentration of mica and glass fibres within _0.5% and _1.0%, respectively.     

Cylinder pressure reconstruction based on complex radial basis function networks from vibration and speed signals

Methods to measure and monitor the cylinder pressure in internal combustion engines can contribute to reduced fuel consumption, noise and exhaust emissions. As direct measurements of the cylinder pressure are expensive and not suitable for measurements in vehicles on the road indirect methods which measure cylinder pressure have great potential value. In this paper, a non-linear model based on complex radial basis function (RBF) networks is proposed for the reconstruction of in-cylinder pressure pulse waveforms. Input to the network is the Fourier transforms of both engine structure vibration and crankshaft speed fluctuation. The primary reason for the use of Fourier transforms is that different frequency regions of the signals are used for the reconstruction process. This approach also makes it easier to reduce the amount of information that is used as input to the RBF network. The complex RBF network was applied to measurements from a 6-cylinder ethanol powered diesel engine over a wide range of running conditions. Prediction accuracy was validated by comparing a number of parameters between the measured and predicted cylinder pressure waveform such as maximum pressure, maximum rate of pressure rise and indicated mean effective pressure. The performance of the network was also evaluated for a number of untrained running conditions that differ both in speed and load from the trained ones. The results for the validation set were comparable to the trained conditions.     

动压气浮马达轴承间隙测量设备

动压气浮陀螺马达轴承间隙尺寸是决定其运转性能的重要指标。为提高轴承间隙测量的精度和自动化程度,并实现快速批量测量,研制了一台动压气浮陀螺马达轴承间隙自动测量设备。采用外部加力方式,使转子体与定子产生相对位移,从而将内部气膜间隙转化为外部微位移。设备整体结构采用模块化设计理念,包括夹持模块、自动施力模块和位移测量模块。夹持摸块实现被测动压马达定子在两轴端的固定,采用柔性支撑方式有利于保护被测件和保证施加力的平顺性;自动施力模块主要由三维精密位移平台集成三轴测力传感器构成,测量时转子体与力传感器通过夹指连接,位移平台使转子体与定子产生相对位移,三轴测力传感器则实现施加力的精确控制和定子的调中心控制;测量模块由二维精密位移平台集成双电感测头构成,基于相对测量原理实现微小位移测量。实验表明:设备测量精度在0.3μm以内。该设备可以实现外力的可控连续加载,适用于批量测量。     

Pressure measurements in laboratory-scale blast wave flow fields

The present study examines the effects that temporal and spatial averagings due to finite size and finite response time of pressure transducers have on the pressure measurements in blast wave flow fields generated by milligram charges of silver azide. In such applications, the characteristic time and length scales of the physical process are of the same order of magnitude as the temporal and spatial characteristics of the transducer. The measured pressure values will then be spatially and temporally averaged, and important parameters for the assessment of blast effects may not be properly represented in the measured trace. In this study, face-on and side-on pressure transducer setups are considered. In the experiments, face-on and side-on readings at the same distance from the charge as well as time-resolved optical visualization of the whole flow field are obtained simultaneously for the same explosive event. The procedure of data extraction from the experimental pressure traces is revisited and discussed in detail. In the numerical modeling part of the study, numerical blast flow fields are generated using an Euler flow solver. A numerical pressure transducer model is developed to qualitatively simulate the averaging effects. The experimental and numerical data show that the results of pressure measurements in experiments with small charges must be used with great caution. The effective averaging of the pressure signal may lead to a significant underestimation of blast wave intensities. The side-on setup is especially prone to this effect. The face-on setup provides results close to those obtained from optical records only if the pressure transducer is sufficiently remote from the charge.     

System for gas pressure measurements in the arc plasma environment

Developed measurements system for evaluation of gas pressure value in direct vicinity of switching arc plasma was described in this paper. The system is resistant to heavy duty conditions present inside the MV switch quenching chamber and its functionality was verified during large scale functional tests. In this paper results of gas pressure measurements performed for a current interrupter equipped with an arc quenching system based on combination of forced air flow and gassing material ablation were presented. Gas pressure was measured by means of developed system, for several values of capacitive load current at 12/24 kV supplying voltage.     

A study on correlation between pressure variations and augmentation of heat transfer in acoustic fields

The present paper investigated the correlation between the acoustic pressure variations and the augmentation of heat transfer in the ultrasonic induced acoustic fields. The augmentation ratios of heat transfer coefficient were experimentally measured and were compared with the profile of the pressure distribution in the acoustic fields predicted by numerical analysis. For numerical analysis, a coupled finite element-boundary element method (coupled FE-BEM) was applied. The results of the present study reveal that the acoustic pressure is higher near two ultrasonic transducers than other points where no ultrasonic transducer was installed. The augmentation trend of heat transfer is similar with the profile of the acoustic pressure distribution. In other words, as the acoustic pressure increases, the higher augmentation ratio of heat transfer is obtained. Numerical and experimental studies clearly show that the acoustic pressure variations are closely related to the augmentation of heat transfer in the acoustic fields.     

Uncertainty analysis of the high pressure closed loop gas flow standard facility in NIM

High pressure air flow standard facilities, including the pVTt facility, sonic nozzle facility and closed loop facility were built in NIM at the end of 2014. The high pressure closed loop gas flow facility was the first closed loop facility in China. The system has 4 sets of 100 mm diameter turbine meters for the reference meters with a flow range of (40–1300) m³/h and a pressure range of (190–2500) kPa. To avoid uncertainties introduced during installation, the reference meters were designed to be calibrated in situ using the sonic nozzle facility. The uncertainty in the pressure measurement was reduced by installing an absolute pressure transducer in the manifold upstream of the reference meters, with differential pressure transducers used to measure the pressure drops across the reference flow meter and the test flow meter. The relative expanded uncertainty for the test meter can reach 0.20% (k = 2) as verified by comparison the sonic nozzle facility and the closed loop facility measurements.     

Buckling analysis of filament-wound thick composite cylinder under hydrostatic pressure

Underwater vehicles that operate in deep waters require a pressure hull to maintain the sufficient strength and stiffness against external hydrostatic pressure. We investigated the validity of the finite element method (FEM) that is applied to a buckling analysis of the filament-wound composite cylinder, subjected to an external hydrostatic pressure. Two methods were suggested for the buckling analysis of a filament-wound thick composite cylinder under hydrostatic pressure: using the equivalent properties of the composite, and using stacking sequence. The hydrostatic pressure test was conducted to verify the FEA. Test results were compared with the previous results obtained by FEM on the buckling of a filament-wound composite cylinder under hydrostatic pressure. FEM analysis results were in good agreement with the test results. The difference between FEM results and the test results was approximately 1∼5%.