1,678 research outputs found
Measurements of mixed convective heat transfer to low temperature helium in a horizontal channel
A horizontal 2.85 m long, 19 mm i.d. stainless steel heated circular channel was employed to measure coefficients of heat transfer to low temperature helium flow. Experimental parameters range from 6.5 to 15 K, from 0.12 to 0.3 MPa at heat fluxes up to 1000 W/m square and Reynolds numbers from 9,000 to 20,000. A significantly nonuniform distribution of heat transfer coefficients over the tube periphery is observed. Difference between temperatures on the upper and lower surfaces of the stainless steel channel wall was found to reach 9 K. It was noted that the highest temperature on the wall outer surface is displaced from its uppermost point. Measurements of local flow temperatures revealed vortical structure of the flow. The displacement of the point with the highest temperature is attributable to the effect of vortices. The relationships for calculating local and averaged coefficients of heat transfer are proposed
Some heat transfer and hydrodynamic problems associated with superconducting cables (SPTL)
To study some effects of thermogravitation on (CIIK-SPTL) systems, a heated tube experiment was set up at Krzhizhanovsky Power Engineering Institute Moscow, U.S.S.R. Heat transfer data were taken with fluid helium flowing through a 2.85 m, 19 mm diameter uniformly heated horizontal tube. Temperatures were measured on the top and bottom of the tube at six axial locations with three other circumferential measurements made at (X/L) =57. Typical temperature profiles show significant variations both axially and circumferentially. The data are grouped using reduced Nusselt number (NuR) and the bulk expansion parameter for each axial location. The average data for 0.26 less than or equal to X/L less than or equal to 0.76 follow a power law relation with the average expansion parameter. System instabilities are noted and discussed. Future work including heat transfer in coaxial cylinders is discussed
Flows in Pinned Arrays Simulating Brush Seals
Flows through idealized pin arrays were investigated using an unstructured grid finite difference model and the simplified Ergun model to predict leakage flows and pressure drops in brush seals. The models are in good agreement in the laminar region with departures in the laminar-turbulent transition region defined by the simplified Ergun model. No local disturbances in the velocity or pressure fields, symptomatic of turbulence were found in the numerical results. The simplified model failed to predict the pressure drop of a 32-pin anisotropic array. Transitional and anisotropic behavior require
Sensitivity of CryoSat-2 Arctic sea-ice freeboard and thickness on radar-waveform interpretation
Variability in splanchnic tissue oxygenation during preterm red blood cell transfusion given for symptomatic anaemia may reveal a potential mechanism of transfusion-related acute gut injury
Background There is increasing evidence indicating an association between red blood cell (RBC) transfusions and necrotising enterocolitis (NEC) in preterm infants, especially late-onset NEC. This phenomenon is referred to as transfusion-related acute gut injury (TRAGI). One theory as to a pathophysiological mechanism is that transfusion may result in an ischemia-reperfusion injury to intestinal tissue. We tested the hypothesis that there is significantly greater variability during transfusion in splanchnic tissue oxygen saturation (SrSO2) than in cerebral tissue oxygen saturation (CrSO2). Materials and methods This was a prospective, observational study using near-infrared spectroscopy to monitor SrSO2 and CrSO2in preterm neonates undergoing RBC transfusion for symptomatic anaemia. Mean, standard deviation, highest and lowest SrSO2 and CrSO2 values during each transfusion were determined. The greatest difference in SrSO2 and CrSO2 during each transfusion was calculated, along with the coefficient of variation. Results
We studied 37 subjects. Throughout all transfusions, the mean SrSO2 was 45.6% ±13.8 and the mean CrSO2 was 65.4% ±6.9 (p\u3c0.001). The variability of SrSO2 was significantly greater than that of CrSO2. Averaging data from all subjects, the greatest difference in SrSO2 was 43.8% ±13.4 compared with 23.3% ±7.6 for CrSO2 (p\u3c0.001). The mean coefficient of variation in all transfusions was 20.5% for SrSO2and 6.0% for CrSO2 (p\u3c0.001). Increasing post-conceptional age did not affect SrSO2 variability (R2=0.022; p=0.379), whereas CrSO2 variability during transfusion decreased with increasing post-conceptional age (R2=0.209; p=0.004). Discussion In preterm infants, there is a large degree of tissue oxygenation variability in splanchnic tissue during RBC transfusion and this does not change with increasing maturity. We speculate that these findings, combined with lower average tissue oxygenation, may demonstrate susceptibility of the preterm gut to TRAGI
High-Risk Corneal Graft Rejection in the Setting of Previous Corneal Herpes Simplex Virus (HSV)-1 Infection
Acknowledgments The authors thank M. Robertson and R. Fordyce for technical support during the duration of the study. The work performed in Aberdeen was supported by grant from Action Medical Research UK (SP4328; London, England, UK), NHS Grampian Endowment grant (12/49; Aberdeen, Scotland, UK), and Saving Sight in Grampian (Charity No.SC002938; Aberdeen, Scotland, UK). The work performed in Pittsburgh was supported by a Fight for Sight Post-Doctoral Award (JEK; New York, NY, USA); unrestricted grants from the Western Pennsylvania Medical Eye Bank Foundation (Pittsburgh, PA, USA), Research to Prevent Blindness (New York, NY, USA), and the Eye and Ear Foundation of Pittsburgh (RLH; Pittsburgh, PA, USA); and National Institutes of Health Grants P30EY08098 (RLH; Bethesda, MD, USA) and EY10359 (RLH).Peer reviewedPublisher PD
Simulation of brush insert for leading-edge-passage convective heat transfer
Current and proposed high speed aircraft have high leading edge heat transfer (to 160 MW/sq m, 100 Btu/sq in/sec) and surface temperatures to 1370 K (2000 F). Without cooling, these surfaces could not survive. In one proposal the coolant hydrogen is circulated to the leading edge through a passage and returned to be consumed by the propulsion system. Simulated flow studies and visualizations have shown flow separation within the passage with a stagnation locus that isolates a zone of recirculation at the most critical portion of the passage, namely the leading edge itself. A novel method is described for mitigating the flow separation and the isolated recirculation zones by using a brush insert in the flow passage near the leading edge zone, thus providing a significant increase in heat transfer
Global Atmospheric Aerosol Modeling
Global aerosol models are used to study the distribution and properties of atmospheric aerosol particles as well as their effects on clouds, atmospheric chemistry, radiation, and climate. The present article provides an overview of the basic concepts of global atmospheric aerosol modeling and shows some examples from a global aerosol simulation. Particular emphasis is placed on the simulation of aerosol particles and their effects within global climate models
Quantification of Gear Tooth Damage by Optimal Tracking of Vibration Signatures
This paper presents a technique for quantifying the wear or damage of gear teeth in a transmission system. The procedure developed in this study can be applied as a part of either an onboard machine health-monitoring system or a health diagnostic system used during regular maintenance. As the developed methodology is based on analysis of gearbox vibration under normal operating conditions, no shutdown or special modification of operating parameters is required during the diagnostic process. The process of quantifying the wear or damage of gear teeth requires a set of measured vibration data and a model of the gear mesh dynamics. An optimization problem is formulated to determine the profile of a time-varying mesh stiffness parameter for which the model output approximates the measured data. The resulting stiffness profile is then related to the level of gear tooth wear or damage. The procedure was applied to a data set generated artificially and to another obtained experimentally from a spiral bevel gear test rig. The results demonstrate the utility of the procedure as part of an overall health-monitoring system
The MESSy aerosol submodel MADE3 (v2.0b): description and a box model test
We introduce MADE3 (Modal Aerosol Dynamics model for Europe, adapted
for global applications, 3rd generation; version: MADE3v2.0b), an
aerosol dynamics submodel for application within the MESSy framework
(Modular Earth Submodel System). MADE3 builds on the predecessor
aerosol submodels MADE and MADE-in. Its main new features are the
explicit representation of coarse mode particle interactions both
with other particles and with condensable gases, and the inclusion
of hydrochloric acid (HCl) / chloride (Cl) partitioning
between the gas and condensed phases. The aerosol size distribution
is represented in the new submodel as a superposition of nine
lognormal modes: one for fully soluble particles, one for insoluble
particles, and one for mixed particles in each of three size ranges
(Aitken, accumulation, and coarse mode size ranges).
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In order to assess the performance of MADE3 we compare it to its
predecessor MADE and to the much more detailed particle-resolved
aerosol model PartMC-MOSAIC in a box model simulation of an
idealised marine boundary layer test case. MADE3 and MADE results
are very similar, except in the coarse mode, where the aerosol is
dominated by sea spray particles. Cl is reduced in MADE3 with
respect to MADE due to the HCl / Cl partitioning that
leads to Cl removal from the sea spray aerosol in our test
case. Additionally, the aerosol nitrate concentration is higher in
MADE3 due to the condensation of nitric acid on coarse mode
particles. MADE3 and PartMC-MOSAIC show substantial differences in
the fine particle size distributions (sizes ≲ 2 μm) that could be relevant when simulating climate effects on
a global scale. Nevertheless, the agreement between MADE3 and
PartMC-MOSAIC is very good when it comes to coarse particle size
distributions (sizes ≳ 2 μm), and also in terms
of aerosol composition. Considering these results and the
well-established ability of MADE in reproducing observed aerosol
loadings and composition, MADE3 seems suitable for application
within a global model
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