Annular Seals of High Energy Centrifugal Pumps: Presentation of Full Scale Measurement

Prediction of rotordynamic behavior for high energy concentration centrifugal pumps is a challenging task which still imposes considerable difficulties. While the mechanical modeling of the rotor is solved most satisfactorily by finite element techniques, accurate boundary conditions for arbitrary operating conditions are known for journal bearings only. Little information is available on the reactive forces of annular seals, such as neck ring and interstage seals and balance pistons, and on the impeller interaction forces. The present focus is to establish reliable boundary conditions at annular seals. For this purpose, a full scale test machine was set up and smooth and serrated seal configurations measured. Dimensionless coefficients are presented and compared with a state of the art theory

Rotordynamic coefficients and leakage flow of parallel grooved seals and smooth seals

Based on Childs finite length solution for annular plain seals an extension of the bulk flow theory is derived to calculate the rotordynamic coefficients and the leakage flow of seals with parallel grooves in the stator. Hirs turbulent lubricant equations are modified to account for the different friction factors in circumferential and axial direction. Furthermore an average groove depth is introduced to consider the additional circumferential flow in the grooves. Theoretical and experimental results are compared for the smooth constant clearance seal and the corresponding seal with parallel grooves. Compared to the smooth seal the direct and cross-coupled stiffness coefficients as well as the direct damping coefficients are lower in the grooved seal configuration. Leakage is reduced by the grooving pattern

Selective P2X7 receptor antagonists for chronic inflammation and pain

ATP, acting on P2X7 receptors, stimulates changes in intracellular calcium concentrations, maturation, and release of interleukin-1β (IL-1β), and following prolonged agonist exposure, cell death. The functional effects of P2X7 receptor activation facilitate several proinflammatory processes associated with arthritis. Within the nervous system, these proinflammatory processes may also contribute to the development and maintenance of chronic pain. Emerging data from genetic knockout studies have indicated specific roles for P2X7 receptors in inflammatory and neuropathic pain states. The discovery of multiple distinct chemical series of potent and highly selective P2X7 receptor antagonists have enhanced our understanding of P2X7 receptor pharmacology and the diverse array of P2X7 receptor signaling mechanisms. These antagonists have provided mechanistic insight into the role(s) P2X7 receptors play under pathophysiological conditions. In this review, we integrate the recent discoveries of novel P2X7 receptor-selective antagonists with a brief update on P2X7 receptor pharmacology and its therapeutic potential

Mechanical Behavior of an Industrial Gas Turbine under Fault Conditions, a Case History

The resolve of journal bearing field problems and the full vibrational assessment of an industrial gas turbine, simple cycle rotor train, ABB’s GTllN2 is presented. Three units experienced several times damage of the journal bearings on the compressor end. The analysis of the damage, including tests, indicated that insufficient jacking oil flow was the cause. The jacking concept was corrected and starting history has proven reliable operation, resulting in not one additional failure

Improved Hydraulic Design Lowers Cavitation Erosion And Vibrations Of A Water Transport Pump

Lecturepg. 81In this case history, the successful application of well-known tools for hydraulic design changes and cavitation erosion prediction is presented. A description of the tools can be found in many publications and will not be repeated here. However, the application of the tools in a difficult field situation with unfavorable hydraulic boundary conditions is outlined and the resulting successful solution is presented. There are six pumping stations in the Rio Colorado Tijuana Aqueduct (water pipeline), which crosses northern Baja California in Mexico. The planning of the construction work did not adequately consider all the necessary hydraulic boundary conditions for the pipeline pumps; i.e., some of the suction reservoirs were built with a relatively small elevation relative to their pumping stations. Consequently, the existing available net positive suction head (NPSH) for the pumps of some stations is very low and marginal for satisfactory operation. Therefore, impellers are experiencing premature wear (repair/replacement after less than a year of operation), caused by cavitation erosion. Construction changes to the pipeline to increase the NPSH available were cost prohibitive. Hence, to extend the life expectancy of impellers, the customer placed an order with the OEM to develop an improved hydraulic design with respect to cavitation erosion. As nothing but the pump hydraulic could be changed, the new design would have to work under the existing, far less than optimum pipeline conditions, and compromises had to be found which would normally not be desirable for a new pipeline layout. Preliminary testing was to be done on the test bed and final testing was subject to a joint effort of the manufacturer and the user of the prototype pump installed and operating in the pipeline. A new impeller, with slightly modified rated flow conditions to adapt to effective plant conditions, and a steeper head – a capacity characteristic to avoid runout on the curve, was developed. Pump case changes were introduced at the inlet splitters and at the volute tips. Cavitation noise level to estimate erosion rates was measured as described by Guelich and Pace [1] and Guelich [2]. The original impeller’s life with respect to cavitation was estimated. A 65 to 70 percent probability of a 16,000 hr life was determined based on data from the new configuration, both on the test bed and in the pipeline, allowed the expected impeller life to be quantified. A guarantee to reach at least double the original time span for the worst operating conditions possible, at max flow, i.e., single pump operation, could be given. More than three years could be guaranteed for operation at plant design conditions and the chance to reach 4.5 years was estimated to be about 80 percent. The extrapolated life has been verified through a prorate erosion rate during a field inspection after almost 3000 hrs of operation. Vibration levels were significantly lowered due to the new hydraulic design with staggered impeller vanes. The comparison of old design and new design pump vibrations, taken during pipeline operation at the same station, indicate the clearly higher safety margin for the mechanical integrity of the upgraded machines. Additionally, as a byproduct, the efficiency has been increased by about two percent, as the pump best efficiency flow had been adjusted to the effective operating flow in the pipeline

Aerodynamic Performance Measurements of a Film Cooled Turbine Stage.

ABSTRACT Modem high performance gas turbine engines utilize film cooling to reduce the heat load on high-pressure turbine stage components, thereby increasing the maximum turbine inlet temperature at which the cycle can operate. However, increased turbine inlet temperature comes at the expense of a reduction in turbine efficiency. The objective of this research is to measure the aerodynamic performance of a film cooled turbine stage and to quantify the loss caused by film cooling. An un-cooled turbine stage was first fabricated with solid blading and tested using a newly developed short duration measurement technique. The stage was then modified to incorporate vane, blade and rotor casing film cooling. The film-cooled stage was then tested over a range of coolant-to-mainstream mass flow and temperature ratios for the same range of operating conditions (pressure ratios and corrected speeds) as the un-cooled turbine. This paper presents the experimental results for these two series of tests