Benefits of Installing Restrictive Orifice Plates On the Suction of Reciprocating Pumps:1D Pulsation and CFD Studies

Case Stud

Benefits of Installing Restrictive Orifice Plates on the Suction of Reciprocating Pumps: 1D Pulsation and CFD Studies

Case StudiesIt is well understood that static pressure at the inlet of reciprocating pumps, quantified typically by Net Positive Suction Head Available (NPSHA), must be sufficient to avoid cavitation in the pump suction manifold and chamber. In an effort to conserve NPSHA, pump designers generally rely on rules of thumb that resist the addition of pressure drop elements such as restrictive orifice plates, choke tubes and line-size reductions to the inlet piping of all pumps, including reciprocating pumps. Another design consideration of reciprocating pumps is the generation of pressure pulsations due to pump piston and valve motion. Uncontrolled pulsations can result in cavitation and vibration-related fatigue failures. In many cases, pressure drop elements are required to control pressure pulsations. Can there be a balance between the pulsation control benefits of pressure drop elements and the need to meet NPSHA? This paper is of interest to designers and engineers working with reciprocating pump installations. It aims at challenging industry resistance to using pressure drop elements in the suction piping of reciprocating pumps by, first, outlining the virtues achieved in terms of pulsation and vibration control, and second, presenting results from numerical simulations (one-dimensional pulsation and detailed CFD modelling). Recent field data from a quintuplex pump installation were used to validate the 1-D pulsation model. The results show that well-designed orifice plates, and other pressure drop elements, are beneficial for reducing pulsations and cavitation risks; and can be used in the suction piping of reciprocating pumps

New Approach to Designing Centrifugal Compressor Surge Control Systems

TutorialMany facilities employ two or more centrifugal compressors, operated in either series or parallel configurations. An accurately designed surge control system that includes multiple compressors with the associated piping systems is a vital element of a facility’s design and ongoing operational integrity. The design must ensure compressors are not subjected to damaging fast dynamic events leading to large capital costs and significant down time for operators. Examples of such fast dynamic events are those following emergency shutdown (ESD) of fast stop of one or all compressor units in a station. Typical studies are not accurate enough to capture the complex interactions leading to catastrophic events, especially for complicated system arrangements. This paper introduces three methods of surge control analysis that can be conducted to assess the effectiveness of any surge control system design to prevent the compressor from surge. The first method utilizes the perturbation theory to relate the compressor deceleration and the resulting drop in its flow and head to determine the elapsed time that the compressor can stay out of surge before the surge control system brings about enough positive flow to prevent the unit from undergoing deep surge. The second method is simpler, and is based on a dimensionless number, called the inertia number, which combines the salient parameters from the dynamic equation between the fluid energy and that of the compressor rotor inertia to determine, as a first cut check, if the surge control system is adequate. The third method, which is always recommended, and is based on solving the full gas dynamic partial differential equations (PDEs) in spatial and temporal domain, which describe the true dynamic characteristics of the flow through the various piping elements, the compressor itself, to provide much more accurate predictions of surge control system behavior during fast transient events. Comparisons are made to field measurements to provide model validations, and an example application (Case Study) of three units operating in parallel. The first two (Units 6 and 7) were existing in a compressor station, while the third (Unit 8) was an add-on. The addition of Unit 8 meant a number of station layout modifications, which included: re-wheeling of Units 6 and 7 (i.e., change the compressor impellers); adding after gas cooling; and relocating the anti-surge valves downstream of the coolers to allow for both hot (fast stop) and cold recycle (anti-surge) capabilities. Due to the addition of equipment and significant reconfiguration of station piping and valves, a dynamic surge analysis on Units 6, 7, and 8 was required to determine whether the existing anti-surge and fast stop valves were adequately sized and whether the anti-surge valves could be relocated downstream of the gas coolers. A new fast stop recycle system was added along with Unit 8, which also needed to be adequately sized. Further complications arose from the fact that Unit 6’s anti-surge valve configuration differs from that of Unit 7 and that Unit 6 has twin recycle valves jointly serving as anti-surge valves with a single fast stop valve while Unit 7 has a single antisurge valve and a single fast stop valve

Centrifugal Compressor Surge Control Systems - Fundamentals of a Good Design

LectureLecture 2: Many facilities employ two or more centrifugal compressors, operated in either series or parallel configurations. An accurately designed surge control system that includes multiple compressors with the associated piping systems is a vital element of a facility’s design and ongoing operational integrity. The design must ensure compressors are not subjected to damaging fast dynamic events leading to large capital costs and significant down time for operators. Examples of such fast dynamic events are those following emergency shutdown (ESD) or fast stop of one or all compressor units in a station. Typical studies are not accurate enough to capture the complex interactions leading to catastrophic events, especially for complicated system arrangements. This paper introduces three methods of surge control analysis that can be conducted to assess the effectiveness of any surge control system design to prevent the compressor from surge. The first method utilizes the perturbation theory to relate the compressor deceleration and the resulting drop in its flow and head to determine the elapsed time that the compressor can stay out of surge before the surge control system brings about enough positive flow to prevent the unit from undergoing deep surge. The second method is simpler, and is based on a dimensionless number, called the inertia number, which combines the salient parameters from the dynamic equation between the fluid energy and that of the compressor rotor inertia to determine, as a first cut check, if the surge control system is adequate. The third method, which is always recommended, and is based on solving the full gas dynamic partial differential equations (PDEs) in spatial and temporal domain, which describe the true dynamic characteristics of the flow through the various piping elements, the compressor itself, to provide much more accurate predictions of surge control system behavior during fast transient events. Comparisons are made to field measurements to provide model validations, and an example application (Case Study) of three units operating in parallel. The first two (Units 6 and 7) were existing in a compressor station, while the third (Unit 8) was an add-on. The addition of Unit 8 meant a number of station layout modifications, which included: re-wheeling of Units 6 and 7 (i.e., change the compressor impellers); adding after gas cooling; and relocating the anti-surge valves downstream of the coolers to allow for both hot (fast stop) and cold recycle (anti-surge) capabilities. Due to the addition of equipment and significant reconfiguration of station piping and valves, a dynamic surge analysis on Units 6, 7, and 8 was required to determine whether the existing anti-surge and fast stop valves were adequately sized and whether the anti-surge valves could be relocated downstream of the gas coolers. A new fast stop recycle system was added along with Unit 8, which also needed to be adequately sized. Further complications arose from the fact that Unit 6’s anti-surge valve configuration differs from that of Unit 7 and that Unit 6 has twin recycle valves jointly serving as anti-surge valves with a single fast stop valve while Unit 7 has a single anti-surge valve and a single fast stop valve

Complete Genome Sequences of Paenibacillus Larvae Phages BN12, Dragolir, Kiel007, Leyra, Likha, Pagassa, PBL1c, and Tadhana

We present here the complete genomes of eight phages that infect Paenibacillus larvae, the causative agent of American foulbrood in honeybees. Phage PBL1c was originally isolated in 1984 from a P. larvae lysogen, while the remaining phages were isolated in 2014 from bee debris, honeycomb, and lysogens from three states in the USA

BCL-2 Inhibition Targets Oxidative Phosphorylation and Selectively Eradicates Quiescent Human Leukemia Stem Cells

SummaryMost forms of chemotherapy employ mechanisms involving induction of oxidative stress, a strategy that can be effective due to the elevated oxidative state commonly observed in cancer cells. However, recent studies have shown that relative redox levels in primary tumors can be heterogeneous, suggesting that regimens dependent on differential oxidative state may not be uniformly effective. To investigate this issue in hematological malignancies, we evaluated mechanisms controlling oxidative state in primary specimens derived from acute myelogenous leukemia (AML) patients. Our studies demonstrate three striking findings. First, the majority of functionally defined leukemia stem cells (LSCs) are characterized by relatively low levels of reactive oxygen species (termed “ROS-low”). Second, ROS-low LSCs aberrantly overexpress BCL-2. Third, BCL-2 inhibition reduced oxidative phosphorylation and selectively eradicated quiescent LSCs. Based on these findings, we propose a model wherein the unique physiology of ROS-low LSCs provides an opportunity for selective targeting via disruption of BCL-2-dependent oxidative phosphorylation

Oceanic Residual Depth Measurements, the Plate Cooling Model and Global Dynamic Topography

Convective circulation of the mantle causes deflections of the Earth's surface that vary as a function of space and time. Accurate measurements of this dynamic topography are complicated by the need to isolate and remove other sources of elevation, arising from flexure and lithospheric isostasy. The complex architecture of continental lithosphere means that measurement of present-day dynamic topography is more straightforward in the oceanic realm. Here, we present an updated methodology for calculating oceanic residual bathymetry, which is a proxy for dynamic topography. Corrections are applied that account for the effects of sedimentary loading and compaction, for anomalous crustal thickness variations, for subsidence of oceanic lithosphere as a function of age, and for non-hydrostatic geoid height variations. Errors are formally propagated to estimate measurement uncertainties. We apply this methodology to a global database of 1,936 seismic surveys located on oceanic crust and generate 2,297 spot measurements of residual topography, including 1,161 with crustal corrections. The resultant anomalies have amplitudes of ±1 km and wavelengths of ∼1,000 km. Spectral analysis of our database using cross-validation demonstrates that spherical harmonics up to and including degree 30 (i.e. wavelengths down to 1,300 km) are required to accurately represent these observations. Truncation of the expansion at a lower maximum degree erroneously increases the amplitude of inferred long-wavelength dynamic topography. There is a strong correlation between our observations and free-air gravity anomalies, magmatism, ridge seismicity, vertical motions of adjacent rifted margins, and global tomographic models. We infer that shorter wavelength components of the observed pattern of dynamic topography may be attributable to the presence of thermal anomalies within the shallow asthenospheric mantle.This research is supported by a BP-Cambridge collaboration

Guidelines for the use and interpretation of assays for monitoring autophagy (3rd edition)

In 2008 we published the first set of guidelines for standardizing research in autophagy. Since then, research on this topic has continued to accelerate, and many new scientists have entered the field. Our knowledge base and relevant new technologies have also been expanding. Accordingly, it is important to update these guidelines for monitoring autophagy in different organisms. Various reviews have described the range of assays that have been used for this purpose. Nevertheless, there continues to be confusion regarding acceptable methods to measure autophagy, especially in multicellular eukaryotes. For example, a key point that needs to be emphasized is that there is a difference between measurements that monitor the numbers or volume of autophagic elements (e.g., autophagosomes or autolysosomes) at any stage of the autophagic process versus those that measure fl ux through the autophagy pathway (i.e., the complete process including the amount and rate of cargo sequestered and degraded). In particular, a block in macroautophagy that results in autophagosome accumulation must be differentiated from stimuli that increase autophagic activity, defi ned as increased autophagy induction coupled with increased delivery to, and degradation within, lysosomes (inmost higher eukaryotes and some protists such as Dictyostelium ) or the vacuole (in plants and fungi). In other words, it is especially important that investigators new to the fi eld understand that the appearance of more autophagosomes does not necessarily equate with more autophagy. In fact, in many cases, autophagosomes accumulate because of a block in trafficking to lysosomes without a concomitant change in autophagosome biogenesis, whereas an increase in autolysosomes may reflect a reduction in degradative activity. It is worth emphasizing here that lysosomal digestion is a stage of autophagy and evaluating its competence is a crucial part of the evaluation of autophagic flux, or complete autophagy. Here, we present a set of guidelines for the selection and interpretation of methods for use by investigators who aim to examine macroautophagy and related processes, as well as for reviewers who need to provide realistic and reasonable critiques of papers that are focused on these processes. These guidelines are not meant to be a formulaic set of rules, because the appropriate assays depend in part on the question being asked and the system being used. In addition, we emphasize that no individual assay is guaranteed to be the most appropriate one in every situation, and we strongly recommend the use of multiple assays to monitor autophagy. Along these lines, because of the potential for pleiotropic effects due to blocking autophagy through genetic manipulation it is imperative to delete or knock down more than one autophagy-related gene. In addition, some individual Atg proteins, or groups of proteins, are involved in other cellular pathways so not all Atg proteins can be used as a specific marker for an autophagic process. In these guidelines, we consider these various methods of assessing autophagy and what information can, or cannot, be obtained from them. Finally, by discussing the merits and limits of particular autophagy assays, we hope to encourage technical innovation in the field