Influence of Pre-Swirl and Eccentricity in Smooth Stator/Grooved Rotor Liquid Annular Seals, Measured Static and Rotordynamic Characteristics

Circumferential grooves are machined into the rotor surface of liquid annular seals to reduce leakage. Analyses in the literature regarding rotordynamic coefficients for smooth stator/grooved rotor (SS/GR) seals are scarce, and measured results are absent despite the significant effect of these annular seals on pump rotordynamics. Furthermore, few annular seal test rigs can impose and measure pre-swirl. Consequently, this study aims to quantify the effect of pre-swirl and operating static eccentricity on measured static and dynamic characteristics of the SS/GR seal. The test seal has a nominal minimum radial clearance of Cr = 203.2 µm (8 mil) and the length-to-diameter ratio of L/D = 0.5. The rotor surface has 15 square grooves with a depth of 1.524 mm (60 mils). This geometry is based on measured dimensions in an Electrical Submersible Pump. The author conducts tests at speeds of 2, 4, 6, and 8 krpm, axial pressure drops of 2.07, 4.14, 6.21, and 8.27 bar (30, 60, 90, and 120 psi), and eccentricity ratios up to ε0 = 0.80. Pre-swirl is imposed and varied over low, medium, and high values. The lubricant is ISO VG 2 oil at 46.1⁰C (115⁰F) to ensure turbulent flow at all operating conditions. Measured grooved seal results are compared to results of a smooth seal of equal length, diameter, and nominal clearance. Note that no published predictions for this seal exist, precluding measurement-versus-prediction comparisons. Static measurements include leakage rate, applied static load, eccentric position, pre-swirl ratio (PSR), and outlet swirl ratio (OSR). At 2 krpm and 8.27 bar, the SS/GR seal leakage rate is lower than the smooth seal by a factor of 0.7 for a total reduction of 19 LPM. However, at high speeds and low pressures, grooved seal leakage is 0.8 to 0.9 times that of the smooth seal with reductions in leakage rate on the order of 2 LPM. Consequently, adding rotor grooves to restrict leakage is more advantageous at high pressure drops and low speeds. Outlet swirl is measured for the first time in a liquid-annular-seal test rig. Contrary to expectation, measured OSR is generally lower than 0.5, possibly due to the axial and radial location of the pitot tube within the outlet chamber. Dynamic measurements include rotor-stator relative displacement, stator acceleration, and applied dynamic excitations. The author calculates dynamic-stiffness values, rotordynamic coefficients, whirl frequency ratio, and effective damping. Most notable of the dynamic results is the negative direct stiffness of the SS/GR seal. Negative direct stiffness would have a detrimental effect on pump rotordynamics, lowering both the natural frequency and the onset speed of instability. Calculated whirl frequency ratio is generally high (≥0.5) with values up to 1.2 for the grooved seal. Finally, effective damping is lower for the grooved seal than the smooth seal indicating that the SS/GR seal has worse stability characteristics than a comparable SS/SR seal. Overall, increases in PSR have a detrimental effect on SS/GR seal rotordynamic performance leading to modest decreases in direct stiffness, increases in the magnitude of cross-coupled stiffness, and increases in whirl frequency ratio. Additionally, operation at high eccentricity ratios for the SS/GR seal has negative effects. Leakage increases, and direct stiffness decreases as eccentricity ratios approach 0.80

Toward an Empirical Concept of Group

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/93537/1/j.1468-5914.1993.tb00543.x.pd

Outcome measurements in scleroderma: Results from a Delphi exercise

Objective. To obtain a consensus on the minimal clinically relevant treatment effect in various scleroderma disease outcome measures to be used in future clinical trials

Technological Change Around The World: Evidence From Heart Attack Care

International audience"Supply side" incentives to curtail health care spending are closely linked with trends in the use of costly treatments. by the Technological Change in Health Care (TECH) Research Network ABSTRACT: Although technological change is a hallmark of health care worldwide , relatively little evidence exists on whether changes in health care differ across the very different health care systems of developed countries. We present new comparative evidence on heart attack care in seventeen countries showing that technological change-changes in medical treatments that affect the quality and cost of care-is universal but has differed greatly around the world. Differences in treatment rates are greatest for costly medical technologies , where strict financing limits and other policies to restrict adoption of intensive technologies have been associated with divergences in medical practices over time. Countries appear to differ systematically in the time at which intensive cardiac procedures began to be widely used and in the rate of growth of the procedures. The differences appear to be related to economic and regulatory incentives of the health care systems and may have important economic and health consequences. H ea lt h c ar e is an i ndu st ry that is becoming part of a global economy. Biomedical knowledge and technologies are already "global" in the sense that leading physicians in all developed countries read the same journals and electronic reviews and participate in international consortia to encourage best practices. For the most part, the same drugs and devices are available worldwide, at least within a few years of each other. Leading clinical researchers and experts collaborate internationally; leading drug and biotechnology firms think globally. As worldwide policy interest in quality of care continues to rise, international comparisons of health care systems are becoming common. Yet health care also remains a local industry, with care delivered by physicians influenced by their local peers, practice settings, and health care policies

The Relationship Between Health Policies, Medical Technology Trends and Outcomes: A Perspective from the TECH Global Research Network

International audienceThe goal of this paper is to present new comparative evidence on heart attack care in 17 countries showing that changes in medical treatments are universal, but have differed greatly. We have collected a large body of comparable information that show how countries differ in treatment rates and why these differences are relatively marked. Countries appear to differ systematically in the time at which intensive cardiac procedures began to be widely used and in the rate of growth of the procedures. Our results show that differences in treatment rates are greatest for expensive medical technologies. Also strict financing limits and regulatory policies have affected the adoption of intensive technologies. These differences may have important economic and health consequences