Analysis of body force effects on flow boiling and condensation with finite inlet quality

This study explores flow boiling pressure drop of FC-72 in a rectangular channel subjected to single-side and double-sided heating for vertical upflow, vertical downflow, and horizontal flow with positive inlet quality. Analysis of temporal records of pressure transducer signals is used to assess the influences of orientation, mass velocity, inlet quality, heat flux, and single-sided versus double-sided heating on magnitude of pressure drop oscillations, while fast Fourier transforms of the same records are used to capture dominant frequencies of oscillations. Time-averaged pressure drop results are also presented, with trends focusing on the competing influences of body force and flow inertia, and particular attention paid to the impact of vapor content at the test section inlet and the rate of vapor generation within the test section on pressure drop. Several popular pressure drop correlations are evaluated against the present pressure drop database. Predictions are presented for subsets of the database corresponding to low and high ranges of inlet quality and mass velocity. The correlations are ranked based on mean absolute error, overall data trends, and data spread. While most show general success in capturing the data trends, they do so with varying degrees of accuracy. Further, this study concerns the development of a set of mechanistic criteria capable of predicting the flow conditions for which gravity independent flow condensation heat transfer can be achieved. Using FC-72 as working fluid, a control-volume based annular flow model is solved numerically to provide information regarding the magnitude of different forces acting on the liquid film and identify which forces are dominant for different flow conditions. Separating the influence of body force into two components, one parallel to flow direction and one perpendicular, conclusions drawn from the force term comparison are used to model limiting cases, which are interpreted as transition points for gravity independence. Experimental results for vertical upflow, vertical downflow, and horizontal flow condensation heat transfer coefficients are presented, and show that, for the given test section, mass velocities above 425 kg/m2s ensure gravity independent heat transfer. Parametric evaluation of the criteria using different assumed values of mass velocity, orientation, local acceleration, and exit quality show that the criteria obey physically verifiable trends in line with those exhibited by the experimental results. As an extension, the separated flow model is utilized to provide a more sophisticated approach to determining whether a given configuration will perform independent of gravity. Results from the model show good qualitative agreement with experimental results. Additionally, analysis of trends indicate use of the separated flow model captures physics missed by simpler approaches, demonstrating that use of the separated flow model with the gravity independence criteria constitute a powerful predictive tool for engineers concerned with ensuring gravity independent flow condensation heat transfer performance

Thermal Storage for High-Power Small Satellites

As the power levels and sizes of small satellites grow, new capabilities become possible along with new challenges for thermal control. Greater amounts of heat must be transported across longer distances, making it more difficult to control component temperatures using simple, passive systems. This paper describes the performance of an innovative thermal storage technology for small satellite thermal control systems. The thermal storage unit helps maintain temperature stability by efficiently incorporating a solid/liquid phase-change material (PCM). This paper describes the results of an analysis and testing program that proved the feasibility of the PCM thermal storage concept. We formulated a simple model for a high-power small satellite in an orbital thermal environment. We found that proper selection of the PCM depends on the thermal environment, thermal control system characteristics, and characteristics of the thermal load. The model shows that a properly designed thermal storage system can dramatically reduce temperature variation. We designed and built a sub-scale PCM thermal storage unit and measured its performance with a heat pipe under conditions that simulate operation in a small satellite thermal control system. Results of these tests demonstrate the capability of the thermal control system to reduce temperature variation during transient operation

Finishing the euchromatic sequence of the human genome

The sequence of the human genome encodes the genetic instructions for human physiology, as well as rich information about human evolution. In 2001, the International Human Genome Sequencing Consortium reported a draft sequence of the euchromatic portion of the human genome. Since then, the international collaboration has worked to convert this draft into a genome sequence with high accuracy and nearly complete coverage. Here, we report the result of this finishing process. The current genome sequence (Build 35) contains 2.85 billion nucleotides interrupted by only 341 gaps. It covers ∼99% of the euchromatic genome and is accurate to an error rate of ∼1 event per 100,000 bases. Many of the remaining euchromatic gaps are associated with segmental duplications and will require focused work with new methods. The near-complete sequence, the first for a vertebrate, greatly improves the precision of biological analyses of the human genome including studies of gene number, birth and death. Notably, the human enome seems to encode only 20,000-25,000 protein-coding genes. The genome sequence reported here should serve as a firm foundation for biomedical research in the decades ahead

Experimental Investigation and Modeling of Key Design Parameters in Flow Boiling and Condensation

In order to better understand and quantify the effect of instabilities in systems utilizing flow boiling heat transfer, the present study explores dynamic results for pressure drop, mass velocity, thermodynamic equilibrium quality, and heated wall temperature to ascertain and analyze the dominant modes in which they oscillate. Flow boiling experiments are conducted for a range of mass velocities with both subcooled and saturated inlet conditions in vertical upflow, vertical downflow, and horizontal flow orientations. High frequency pressure measurements are used to investigate the influence of individual flow loop components (flow boiling module, pump, preheater, condenser, etc.) on dynamic behavior of the fluid, with fast Fourier transforms of the same used to provide critical frequency domain information. Conclusions from this analysis are used to isolate instabilities present within the system due to physical interplay between thermodynamic and hydrodynamic effects. Parametric analysis is undertaken to better understand the conditions under which these instabilities form and their impact on system performance. Several prior stability maps are presented, with new stability maps provided to better address contextual trends discovered in the present study. Further, this study utilizes experimental results for vertical upflow boiling of FC-72 in a rectangular channel with finite inlet quality to investigate Density Wave Oscillations (DWOs) and assess their potential impact on design of two-phase systems for future space missions. Highspeed flow visualization image sequences are presented and used to directly relate the cyclical passage of High and Low Density Fronts (HDFs and LDFs) to dominant low-frequency oscillations present in transient pressure signals commonly attributed to DWOs. A methodology is presented to determine frequency and amplitude of DWO induced pressure oscillations, which are then plotted for a wide range of relevant operating conditions. Mass velocity (flow inertia) is seen to be the dominant parameter influencing frequency and amplitude of DWOs. Amplitude of pressure oscillations is at most 7% of the time-averaged pressure level for current operating conditions, meaning there is little risk to space missions. Reconstruction of experimental pressure signals using a waveform defined by frequency and amplitude of DWO induced pressure fluctuations is seen to have only moderate agreement with the original signal due to the oversimplifications of treating DWO induced fluctuations as perfectly sinusoidal in nature, assuming they occur at a constant frequency value, and neglecting other transient flow features. This approach is nonetheless determined to have potential value for use as a boundary condition to introduce DWOs in two-phase flow simulations should a model be capable of accurately predicting frequency and amplitude of oscillation. Additionally, this study presents a new mechanistic model for Density Wave Oscillations (DWOs) in vertical upflow boiling using conclusions drawn from analysis of flow visualization images and transient experimental results as a basis from which to begin modeling. Counter to many prior studies attributing DWOs to feedback effects between flow rate, pressure drop, and flow enthalpy causing oscillations in position of the bulk boiling boundary, the present instability mode stems primarily from body force acting on liquid and vapor phases in a separated flow regime leading to liquid accumulation in the near-inlet region of the test section, which eventually departs and moves along the channel, acting to re-wet liquid film along the channel walls and re-establish annular, co-current flow

1-Year Outcomes of Transcatheter Tricuspid Valve Repair

BACKGROUND: Surgical management of isolated tricuspid regurgitation (TR) is associated with high morbidity and mortality, thereby creating a significant need for a lower-risk transcatheter solution. OBJECTIVES: The single-arm, multicenter, prospective CLASP TR (Edwards PASCAL TrAnScatheter Valve RePair System in Tricuspid Regurgitation [CLASP TR] Early Feasibility Study) evaluated 1-year outcomes of the PASCAL transcatheter valve repair system (Edwards Lifesciences) to treat TR. METHODS: Study inclusion required a previous diagnosis of severe or greater TR and persistent symptoms despite medical treatment. An independent core laboratory evaluated echocardiographic results, and a clinical events committee adjudicated major adverse events. The study evaluated primary safety and performance outcomes, with echocardiographic, clinical, and functional endpoints. Study investigators report 1-year all-cause mortality and heart failure hospitalization rates. RESULTS: Sixty-five patients were enrolled: mean age of 77.4 years; 55.4% female; and 97.0% with severe to torrential TR. At 30 days, cardiovascular mortality was 3.1%, the stroke rate was 1.5%, and no device-related reinterventions were reported. Between 30 days and 1 year, there were an additional 3 cardiovascular deaths (4.8%), 2 strokes (3.2%), and 1 unplanned or emergency reintervention (1.6%). One-year postprocedure, TR severity significantly reduced (P \u3c 0.001), with 31 of 36 (86.0%) patients achieving moderate or less TR; 100% had at least 1 TR grade reduction. Freedom from all-cause mortality and heart failure hospitalization by Kaplan-Meier analyses were 87.9% and 78.5%, respectively. Their New York Heart Association functional class significantly improved (P \u3c 0.001) with 92% in class I or II, 6-minute walk distance increased by 94 m (P = 0.014), and overall Kansas City Cardiomyopathy Questionnaire scores improved by 18 points (P \u3c 0.001). CONCLUSIONS: The PASCAL system demonstrated low complication and high survival rates, with significant and sustained improvements in TR, functional status, and quality of life at 1 year

The complete sequence of a human Y chromosome.

The human Y chromosome has been notoriously difficult to sequence and assemble because of its complex repeat structure that includes long palindromes, tandem repeats and segmental duplications1-3. As a result, more than half of the Y chromosome is missing from the GRCh38 reference sequence and it remains the last human chromosome to be finished4,5. Here, the Telomere-to-Telomere (T2T) consortium presents the complete 62,460,029-base-pair sequence of a human Y chromosome from the HG002 genome (T2T-Y) that corrects multiple errors in GRCh38-Y and adds over 30 million base pairs of sequence to the reference, showing the complete ampliconic structures of gene families TSPY, DAZ and RBMY; 41 additional protein-coding genes, mostly from the TSPY family; and an alternating pattern of human satellite 1 and 3 blocks in the heterochromatic Yq12 region. We have combined T2T-Y with a previous assembly of the CHM13 genome4 and mapped available population variation, clinical variants and functional genomics data to produce a complete and comprehensive reference sequence for all 24 human chromosomes