bluuebunny/crossref_metadata_2025_split huggingface dataset:
ELECTROPHYSIOLOGICAL STUDY OF VAGAL AFFERENT AND EFFERENT UNITS IN CONSCIOUS SHEEP
Authors: Rousseau J. P. 
Published: December 2014

Crossed‐nerve anastomoses were performed to record activity of vagal efferents and afferents during regurgitation and eructation in conscious sheep. Following anastomoses of the central end of a vagus nerve to the peripheral end of a phrenic nerve, discharges in units of the diaphragm reinnervated by vagal efferent neurones were associated with contractions of the caudal oesophagus and of the rumen. During regurgitation in the course of rumination, discharges in oesophageal efferents consisted of a characteristic pattern of two bursts in a constant association with the additional phase of the reticular contraction and the more forceful inspiratory effort. Discharges in two types of units bore a temporal relation with the motor gastric cyles. Early units are interpreted as innervating pillars of the rumen and late units its dorsal wall. Regular patterns of discharge were recorded during successive A sequences of rumen contractions. In contrast, there was a variability of pattern of activity of efferents during B sequences: a constant time relationship was not observed between discharges of both types of units. During B sequences accompanied by eructation, the most characteristic pattern in gastric and oesophageal units had the following features: the impulses in the early units increased in frequency, outlasted the discharge in the late units by 1 s and ended when a brief discharge was recorded in an oesophageal unit at the time of eructation. It is suggested from the patterns of discharge observed in both gastric and oesophageal efferents that the orderly sequence which achieves regurgitation and eructation results from the central co‐ordination of efferent output.Following anastomoses of the central root of the nodose ganglion to the peripheral end of the accessory nerve, discharges in units of the mastoido‐humeral muscle reinnervated by vagal afferent axons were associated with contractions of the oesophagus and movements of the larynx during swallowing and regurgitation. Discharges in oesophageal afferents coming from the caudal oesophagus were coincident with discharges observed in the vagal efferent fibres innervating this part of the oesophagus. Afferents from the pharynx and the larynx were active at the same time as the nasopharynx and the glottis were demonstrated to be closed. Thus the major characteristic of the afferents the traffic of which has been recorded in cross‐sutured sheep in the course of rumination is that their discharges are occurring at the same time as motor events are developing. It has been concluded that in the complex motor events during regurgitation there is a significant afferent input which contributes to the central nervous regulation of their course at any time.
ROLE OF ACTIVITY‐INDUCED THERMOGENESIS IN TWENTY‐FOUR HOUR ENERGY EXPENDITURE OF LEAN AND GENETICALLY OBESE (OB/OB) MICE
Authors: Dauncey M. J. , Brown D. 
Published: December 2014

The contribution made by spontaneous physical activity to 24 h energy expenditure has been assessed in lean and ob/ob mice living at 28°C. Measurements were made in young animals when the ob/ob mice were the same body weight as their lean littermates, and again when they were adult and the ob/ob mice were twice as heavy as their littermates.In the young ob/ob mice, not only was 24 h heat production lower than in their lean littermates (P 〈 0·005) but so also was motor activity (P 〈 0·01). In adults, total 24 h heat production was similar in lean and obese animals, and thus on the basis of metabolic body size it was considerably lower in the obese adults (P 〈 0·005). The obese adults were also significantly less active than their lean littermates (P 〈 0·05). Differences between genotypes were particularly marked during the night. Partition of 24 h energy expenditure into the two components of rest and activity showed that in the young ob/ob mice the lower heat production occurred because they expended 31% less energy on rest and 47% less on activity than did their lean littermates. In the obese adults, the lower heat production per unit metabolic body size was accounted for by 16% less energy being expended on rest and 74% less on activity than in the lean mice. It is concluded that differences in motor activity between lean and ob/ob mice could account, at least in part, for the development and maintenance of obesity in these animals.
Experimental Evaluation of a Metal Mesh Bearing Damper
Authors: Zarzour Mark , Vance John 
Published: December 2014

Metal mesh is a commercially available material used in many applications including seals, heat shields, filters, gaskets, aircraft engine mounts, and vibration absorbers. This material has been tested by the authors as a bearing damper in a rotordynamic test rig. The test facility was originally used to support the design of a turboprop engine, developing squirrel cages and squeeze film dampers for both the gas generator and power turbine rotors. To design the metal mesh damper, static stiffness and dynamic rap test measurements were first made on metal mesh samples in a specially designed nonrotating test fixture. These property tests were performed on samples of various densities and press fits. One sample was also tested in an Instron machine as an ancillary and redundant way to determine the stiffness. Using the stiffness test results and equations derived by a previous investigator, a spreadsheet program was written and used to size metal mesh donuts that have the radial stiffness value required to replace the squirrel cage in the power turbine. The squirrel cage and squeeze film bearing damper developed for the power turbine rotor was then replaced by a metal mesh donut sized by the computer code.
Coast down tests were conducted through the first critical speed of the power turbine. The results of the metal mesh tests are compared with those obtained from previous testing with the squeeze film damper and Show that the metal mesh damper has the same damping as the squeeze film at room temperature but does not lose its damping at elevated temperatures up to 103 °C. Experiments were run under several different conditions, including balanced rotor, unbalanced rotor, heated metal mesh, and wet (with oil) metal mesh. The creep, or sag, of the metal mesh supporting the rotor weight was also measured over a period of several weeks and found to be very small. Based on these tests, metal mesh dampers appear to be a viable and attractive substitute for squeeze film dampers in gas turbine engines. The advantages shown by these tests include less variation of damping with temperature, ability to handle large rotor unbalance, and the ability (if required) to operate effectively in an oil free environment. Additional testing is required to determine the endurance properties, the effect of high impact or maneuver loads, and the ability to sustain blade loss loads (which squeeze films cannot handle).
A Perspective on Future Directions in Intelligent Health Control of Gasturbines and Auxiliaries
Authors: Eftekhari Shahroudi K. 
Published: December 2014

Despite their seemingly impressive claims, current products for Condition Monitoring, Diagnostic and Decision Support Systems (CMD&D) do not provide the reliable bottom line information that end users and operators need. Instead they confuse the issue with gigabytes of logged trends, complex cause-effect matrices, fault signatures etc. The term “Intelligent Health Control” here refers to the next generation of such systems which provide usable information on:
• the existence and severity of faults;
• how their severity will progress with utilization;
• how this progress can be influenced or controlled.
In this paper the fundamental shortcomings of current approaches are discussed prior to introducing the basics of Intelligent Health Control in terms of fault models and how they can be used to close the diagnostic, prognostic and intelligent control triangle.
The industry will unavoidably shift towards an “information centric” view from the currently predominant “data centric” view. Gigabytes of performance trends will no longer be relevant. Instead, reliable bottom line information will be required on how to minimize or control the costs associated with machinery health degradation or faults. In order to keep the discussion real, the current state of the art of enabling technologies are discussed, including:
• Open Information Buses;
• Adding real time data server functionality to the control system;
• Computational Steering, Human-in-the-Loop Optimization (or semi-automatic problem solving);
• Fault Models;
• Faster than real time simulation;
• Neural Nets.
Thermodynamic and Techno-Economic Analyses of a Combined Cycle Power Plant With a Simple Cycle Gas Turbine, the Bottoming Air Turbine Cycle and the Reverse Brayton Cycle
Authors: Shnaid Isaac 
Published: December 2014

The modem combined cycle power plants achieved thermal efficiency of 50–55% by applying bottoming multistage Rankine steam cycle. At the same time, the Brayton cycle is an attractive option for a bottoming cycle engine. In the author’s US Patent No. 5,442,904 is described a combined cycle system with a simple cycle gas turbine, the bottoming air turbine Brayton cycle, and the reverse Brayton cycle.
In this system, air turbine Brayton cycle produces mechanic power using exergy of gas turbine exhaust gases, while the reverse Brayton cycle refrigerates gas turbine inlet air. Using this system, supercharging of gas turbine compressor becomes possible.
In the paper, thermodynamic optimization of the system is done, and the system techno-economic characteristics are evaluated.
The Combination of SOFC and Microturbine for Civil and Industrial Cogeneration
Authors: Campanari Stefano , Macchi Ennio 
Published: December 2014

Recent studies have shown the possibility of obtaining extremely high electric efficiencies in distributed electric power generation with small capacity advanced plants based upon the combined technologies of solid oxide fuel cells and microturbines. This paper investigates the potential energy savings achievable by the application of this novel technology to cogeneration.
Due to the high electrical efficiency of these systems (approaching 65% LHV), their heat/electricity ratio is unusually low. The addition of a heat pump can dramatically increase the heat/electricity ratio as well as add flexibility to the system. The application of these systems to distributed electricity generation connected to residential heating is discussed. Detailed results are presented, in terms of annual energy balances; they indicate high primary energy savings and reduction in emissions of carbon dioxide.
Effects of Stator Pressure Field on Upstream Rotor Performance
Authors: Graf M. B. , Greitzer E. M. , Marble F. E. , Sharma O. P. 
Published: December 2014

Effects of stator pressure field on upstream rotor performance in a high pressure compressor stage have been assessed using three-dimensional steady and time-accurate Reynolds-averaged Navier-Stokes computations. Emphasis was placed on: (1) determining the dominant features of the flow arising from interaction of the rotor with the stator pressure field, and (2) quantifying the overall effects on time averaged loss, blockage, and pressure rise. The time averaged results showed a 20 to 40% increase in overall rotor loss and a 10 to 50% decrease in tip clearance loss compared to an isolated rotor. The differences were dependent on the operating point and increased as the stage pressure rise, and amplitude of the unsteady back pressure variations, was increased.
Motions of the tip leakage vortex on the order of the blade pitch were observed at the rotor exit in all the unsteady flow simulations; these were associated with enhanced mixing in the region. The period of the motion scaled with rotor flow-through time rather than stator passing.
Three steady flow approximations for the rotor-stator interaction were assessed with reference to the unsteady computations: an axisymmetric representation of the stator pressure field, an inter-blade row averaging plane method, and a technique incorporating deterministic stresses and bodyforces associated with stator flow field. Differences between steady and unsteady predictions of overall rotor loss, tip region loss, and endwall blockage ranged from 5 to 50% of the time average, but the steady flow models gave overall rotor pressure rise and flow capacity within 5% of the time averaged values.
Combustion Instabilities in Industrial Gas Turbines — Measurements on Operating Plant and Thermoacoustic Modelling
Authors: Hobson David E. , Fackrell John E. , Hewitt G. 
Published: December 2014

Measurements of vibration and combustion chamber dynamic pressures have been taken on a number of 150MW industrial gas turbines operating on pre-mixed natural gas, both during long periods of base-load operation and during short duration load-swings. The data has been analysed in terms of the frequency and bandwidth of the principle peak in the vibration and pressure spectra as a function of load and other operating parameters. It is observed that bandwidth, which is a measure of the damping of the resonant mode of the combustion chamber’s acoustic resonance, decreases towards zero as the machines approach their combustion stability limits.
A theoretical model of the thermoacoustic behaviour of the combustion system has been developed to see to what extent the observed behaviour on the operational machines can be explained in terms of an acoustic model of the ductwork and a flame characterised simply by a time-delay. This time delay is obtained from the frequency response function of the flame in response to unsteady perturbations in inlet velocity and is calculated using computational fluid dynamics.
The model has also been used to illustrate the importance of fuel supply system design in controlling combustion stability. It is shown that stability can be a strong function of the acoustic impedance of the fuel supply and that this can lead to enhanced or reduced stability depending on the flame characteristics.
Investigation of Ignition Probability in a Gas Turbine Combustor Using Laser Ignition
Authors: Hicks R. A. , Wilson C. W. , Sheppard C. G. W. , Woolley R. , Wyatt J. 
Published: December 2014

For an aircraft gas turbine engine, the ignition performance is usually expressed in terms of the range of flight conditions over which stable combustion can be established. At present, the size of an aircraft’s gas turbine combustor is governed predominately by its altitude relight performance and is principally derived from existing empirical design rules. These indicate the volume required to give adequate primary zone airodynamic loading to achieve the desired relight performance. A possible means of improving altitude relight performance is to relocate the point of ignition away from the combustor wall to a more favourable location within the combustion chamber. One way of achieving this is through the use of laser ignition. Reported in the paper is an initial programme of work in which the possibility of using laser ignition has been investigated in a gas turbine research combustor operating at several inlet conditions. Comparative results show that, when sited at the same location, laser ignition gave no noticeable improvement in ignition performance when compared to a standard surface discharge igniter (SDI). However, by using laser ignition to locate the ignition site away from the combustor wall, the range of combustor mass flow and AFR at which ≥75% ignition probability could be achieved was increased by approximately 33%.
In conjunction with the experimental study, an ignition probability model, based on the local magnitude of a Karlovitz stretch factor, has been developed to identify suitable regions within the combustor in which to apply laser ignition. The Karlovitz parameter gives an indication as to whether or not a flame kernel will propagate successfully and has been used in conjunction with flow field and scalar distributions generated by Computational Fluid Dynamics (CFD) to yield a 2D map of ignition probability. However, the sensitivity shown by the model to the accuracy of the CFD predictions meant that reliable estimates of optimum ignition sites could only be obtained using experimental fuel and turbulence intensity distributions.
Energy Comparison Among Load Following, Hydro Storage and Two-Shift Operation Strategies for Intermediate Fossil Fuel Power Units
Authors: Bianchi M. , Gadda E. , Peretto A. 
Published: December 2014

During the night hours, to match the lowest load demand by a power generation system, many different strategies can be employed: unit load following, unit shutdown and hydro storage. Obviously, the utilized strategy influences the power production (gas turbines, hydro turbines, etc.) during the peak load demand.
In this paper, the energy comparison among the above different strategies is carried out as a function of the load demand, the heat rate of the peaking units, the hydro storage total efficiency and the hydro stored energy.
In particular, two sets of intermediate load fossil fuel power units (conventional and advanced) are considered.
For the sets considered and relatively to the variable costs, the two-shift operation proved to be the most convenient strategy.
Reliable Rotor Dynamic Design of High-Pressure Compressors Based on Test Rig Data
Authors: Wagner Norbert G. 
Published: December 2014

The overall design of high-pressure centrifugal compressors is largely influenced by rotordynamic aspects. Rotor instability may restrict operating speed and/or maximum discharge pressure if the destabilizing effects have not been considered accurately during the design phase.
A test rig for high pressures has been designed and operated successfully in order to achieve dynamic labyrinth seal coefficients through simulation of original conditions in every aspect. Details are given of the full-scale test rig, which uses active magnetic bearings as a key feature, as well as results from the comprehensive test program.
Later on, these results are employed for the design of a compressor for very high pressures, demonstrating the complexity of this design task. Validation of the labyrinth test data and the rotor dynamic analysis is provided by the results from a PTC class I test on a reinjection compressor. During shop testing, this machine has been run with and without swirl brakes and the test results agree very well with the predictions.
An Algebraic Model for High Intensity Large Scale Turbulence
Authors: Ames F. E. , Kwon O. , Moffat R. J. 
Published: December 2014

An algebraic turbulence model, which has been developed based on the dynamics of ν′ spectra of external turbulence near a surface, is presented in this paper. The model provides an accurate method of predicting the influence of large-scale high intensity turbulence on heat transfer and boundary layer development in turbomachinery. The model has been developed to predict both laminar and turbulent boundary layer development and heat transfer. The laminar boundary layer model has been tested against boundary layer data taken in a low speed cascade. The model produces accurate velocity and eddy diffusivity distributions. The turbulent boundary layer model is composed of inner and outer layer models combined with an intermittency function. The inner model is written in the form of a conventional mixing length model; while the outer layer model is expressed in terms of the external turbulence characteristics. Predictions of boundary layer profiles and heat transfer distributions are shown for both turbulent and laminar boundary layers.
Vane Stanton number predictions were made for inlet turbulence levels ranging from one to thirteen percent for a chord Reynolds number of 800,000. Predictions agreed with experimentally determined levels within 6 percent on the pressure surface but were underpredicted by up to 15 percent in the stagnation region. Levels of heat transfer predicted in the turbulent region of the suction surface agreed with the data within 10 percent.
Channel Height Effect on Heat Transfer and Friction in a Dimpled Passage
Authors: Moon H. K. , O’Connell T. , Glezer B. 
Published: December 2014

The heat transfer enhancement in cooling passages with dimpled (concavity imprinted) surface can be effective for use in heat exchangers and various hot section components (nozzle, blade, combustor liner, etc.), as it provides comparable heat transfer coefficients with considerably less pressure loss relative to protruding ribs. Heat transfer coefficients and friction factors were experimentally investigated in rectangular channels which had concavities (dimples) on one wall. The heat transfer coefficients were measured using a transient thermochromic liquid crystal technique. Relative channel heights (H/d) of 0.37, 0.74, 1.11 and 1.49 were investigated in a Reynolds number range from 12000 to 60000.
The heat transfer enhancement (NuHD) on the dimpled wall was approximately constant at a value of 2.1 times that (Nusm) of a smooth channel over 0.37≤H/d≤1.49 in the thermally developed region. The heat transfer enhancement ratio Nu¯HD/Nusm was invariant with Reynolds number. The friction factors (f) in the aerodynamically fully developed region were consistently measured to be around 0.0412 (only 1.6 to 2.0 times that of a smooth channel). The aerodynamic entry length was comparable to that of a typical turbulent flow (Xo/Dh = 20), unlike the thermal entry length on dimpled surface which was much shorter (xo /Dh<9.8). The thermal performance Nu¯HD/Nusm/f/fsm1/3≅1.75 of dimpled surface was superior to that 1.16<Nu¯HD/Nusm/f/fsm1/3<1.60 of continuous ribs, demonstrating that the heat transfer enhancement with concavities can be achieved with a relatively low-pressure penalty.
Neither the heat transfer coefficient distribution nor the friction factor exhibited a detectable effect of the channel height within the studied relative height range (0.37≤H/d≤1.49).
The Superposition Approach to Local Heat Transfer Coefficients in High Density Ratio Film Cooling Flows
Authors: Gritsch Michael , Baldauf Stefan , Martiny Moritz , Schulz Achmed , Wittig Sigmar 
Published: December 2014

The present paper reports on the use of the superposition approach in high density ratio film cooling flows. It arises from the linearity and homogeneity of the simplified boundary layer differential equations. However, it is widely assumed that the linearity does not hold for variable property flows. Therefore, theoretical considerations and numerical calculations will demonstrate the linearity of the heat transfer coefficient with the dimensionless coolant temperature θ as long as identical flow conditions are applied. This makes it necessary to perform at least two experiments at different θ but with the coolant to main flow temperature ratio kept unchanged.
A comprehensive set of experiments is presented to demonstrate the capability of the superposition approach for determining heat transfer coefficients for different film cooling geometries. These comprise coolant injection from two dimensional tangential slots, single holes, and rows of cylindrical holes. Particularly, two dimensional local distributions of the heat transfer coefficient will be addressed.