bluuebunny/crossref_metadata_2025 huggingface dataset:
Collagen-calcium phosphate composites
Authors: Lawson A C , Czernuszka J T
Published: October 2002

There is a widespread clinical need for bone augmentation and replacement. The major solid phases of bone are collagen and calcium phosphate and a bone analogue based on these two constituents should have some useful properties. In this review this theme is developed and the properties of natural and naturally based composites are compared. Composites have been produced by the precipitation of calcium phosphates on to collagen and a summary of the methods and results from mechanical testing and scanning electron microscopy are presented. Composites with mechanical properties intermediate between cancellous and cortical bone have been produced. The review concludes by explaining some of the mechanical properties of the composites, using knowledge of the hierarchical architecture of bone and results from microscopical examination of the fractured composites.
Biomaterials and cardiovascular devices
Authors: Macnair R , Underwood M J , Angelini G D
Published: October 2002

In the field of cardiovascular surgery there is presently a lack of biomaterials possessing essential characteristics of the native tissue or organ which is to be replaced. This paper describes various biomaterials that have been introduced into the circulatory system and the complex reactions that subsequently occur. The risk of infection is also discussed as well as prevention and treatment regimes that can be used. Examples of future biomaterial development are outlined in an attempt to achieve biocompatibility.
Theoretical estimates of cruciate ligament forces: Effects of tibial surface geometry and ligament orientations
Authors: Imran A , O'Connor J J
Published: October 2002

A mathematical model of the knee in the sagittal plane was used to analyse the effect of tibial surface geometry and ligament orientations on the estimates of cruciate ligament forces.

An elementary mechanical analysis was used to calculate the ligament forces L during a simulated antero-posterior (A-P) laxity test (passive test), and during isometric quadriceps contraction (IQE). Three sets of anatomical parameters (sites of bony attachments and lengths of the ligaments) were used from the literature. Flat, concave and convex shapes were considered for the tibial plateau articulating with a compatible convex femoral condyle. Also, the effects of position and posterior tilt of the tibial plateau were analysed for the concave and flat surfaces. The analysis showed that the ligament forces rose steeply as they approached collinearity with the contact force, C. For a flat tibia, the direction of C remained independent of flexion angle or position of the tibial plateau. For the concave tibia, the direction of C varied with flexion as well as with position of the centre of curvature, O, of the tibial plateau. C had an anterior component synergistic with the posterior cruciate ligament (PCL) when the point of contact, F, was anterior to O. On the other hand, C had a posterior component synergistic with the anterior cruciate ligament (ACL) when F was posterior to O. Also, posterior tilt of the flat or concave surfaces resulted in an increase in the anterior component of C. The effects of the convex tibial surface were opposite to those of the concave surface.

During the A-P laxity test, the ligament forces arising from the concave tibia were very sensitive to the A-P position of O and to the posterior tilt of the plateau which allowed C and L to approach collinearity. Proximo-distal movement of O had a relatively insignificant effect on the ligament force. Similarly, compared to the concave surface, the posterior tilt of the flat tibia had a lesser effect on the ligament forces.

Compared to the passive test, use of the muscle forces during IQE resulted in larger ligament forces, though the trends in force behaviour over the flexion range remained the same.

The analysis emphasizes the importance of correct graft placement during ligament reconstruction, and the need to avoid steep inclination (more than 70° to tibial plateau). Increasing the inclination from 70 to 80° doubles the ligament force. Further, the analysis suggests that, in bicompartmental knee replacement, the efficacy of concave surfaces in replacing cruciate ligament function depends critically on the horizontal placement of the tibial component and its orientation about the mediolateral axis.
A prototype model for renal vasculature and its application in haemodialyser miniaturization
Authors: Waugh H V , Addlesee A J
Published: October 2002

At present, little information and few models are available to describe either renal haemodynamics or the structure of the kidney. By modelling renal haemodynamics, more information about flow behaviour and efficiency can be obtained, thus leading to the modelling of the human kidney and enabling comparisons with dialysis haemodynamics to be made. This paper examines a prototype model of renal vasculature and remarks upon comparisons drawn from data from human kidneys, as an introduction to those interested in replicating the functions of the kidney by using a miniature haemodialyser.
Computer aided design and fabrication of models for in vitro studies of vascular fluid dynamics
Authors: Chong C K , Rowe C S , Sivancsan S , Rattray A , Black R A , Shortland A P , How T V
Published: October 2002

An integrated computer aided design/computer aided manufacture system has been used to model the complex geometry of blood vessel anastomoses. Computer models are first constructed with key dimensions derived from radiological images of bypass grafts, and from casts of actual blood vessel anastomoses. Physical models are then fabricated in one of two ways: the surface geometry data can be used to control the movement of a three-axis milling machine; alternatively, the same data can be exported in a form that can be interpreted by a stereolithography apparatus. Both methods produce geometrically defined solid investments that can be used in a multistep casting process that yields high-quality physical models for vascular fluid dynamic studies. This technique is useful for parametric studies.
Press-fit acetabular cup fixation: Principles and testing
Authors: Macdonald W , Carlsson L V , Charnley G J , Jacobsson C M
Published: October 2002

Pre-clinical testing of the fixation of press-fit acetabular components of total hip prostheses relies on cadaver or synthetic bone, but the properties and geometry of bone models differ from those of physiological bone. Cup designs use varied mechanisms for initial stability in bone; therefore, using different analogues and tests is appropriate.

Press-fit cup stability was tested in the following: firstly, polyurethane (PU) foam modelling can-cellous support; secondly, glass-fibre reinforced epoxide (GFRE) tubes modelling acetabular cortical support; thirdly, cadaveric acetabula. Three commercial cups [Harris-Galante II (H-G II), Zimmer; Optifix, Smith & Nephew, Richards; porous coated anatomic (PCA), Howmedica] and an experimental cup with enhanced rim fixation were tested in three modes: direct pull-out, lever-out and axial torque.

The fixation stabilities measured in the PU and the GFRE models showed trends consistent with those in cadaver bone, differing in the oversizing and cup geometry. The experimental cup was significantly more secure in most modes than other cups; the H-G II and Optifix cups showed similar stabilities, lower than that of the experimental cup but greater than that of the PCA cup (analysis of variance and Tukey's highly significant difference test; p < 0.001). The stabilities measured in cadaver bone more closely approximated those in GFRE. The use of several bone analogues enables separation of fixation mechanisms, allowing more accurate prediction of in vivo performance.
Three-dimensional morphometry in ultrasound
Authors: Linney A D , Deng J
Published: October 2002

The clinical use of three-dimensional (3D) ultrasound has rapidly spread to many specialities over the last ten years. The reason is easy to see, namely that single two-dimensional (2D) scans are often difficult to interpret and the mental correlation of multiple 2D scans to form a 3D image of anatomical morphology is taxing and uncertain. The rapid development of techniques for the realtime tracking of the spatial position and orientation of ultrasound probes and the development of computer graphics techniques for the presentation of anatomical images have made 3D ultrasound a realistic diagnostic tool. The authors describe the range of methods of data acquisition and display and provide illustrations of some current clinical applications.
Comparison of flow in numerical and physical models of a ventricular assist device using low- and high-viscosity fluids
Authors: König C S , Clark C , Mokhtarzadeh-Dehghan M R
Published: October 2002

The flows in a model of a ventricular assist device (VAD) were investigated numerically and experimentally for two different Newtonian test fluids. These were a blood analogue fluid and a much higher viscosity fluid. A finite volume method was employed to solve the governing equations for a three-dimensional unsteady laminar flow on a transient grid. The numerical solutions were compared with experimental results from an identical physical model. The experimental flows were investigated by flow visualization and by laser Doppler velocity measurements at selected points in the flow field. The validation was based on comparisons of flow patterns and of one-component velocity-time histories. The maximum Reynolds numbers in the inflow tube of the model VAD were approximately 460 and 3300 using the high- and low-viscosity fluids respectively. The investigation showed that the flow patterns were better predicted for the high-viscosity fluid. However, the agreement between the velocity-time histories was found to be slightly better for the low-viscosity fluid. The discrepancies in the flow patterns may be due to intermittent turbulence with a further contribution from numerical diffusion.
Optimizing the configuration of cement keyholes for acetabular fixation in total hip replacement using Taguchi experimental design
Authors: Mburu G , Aspden R M , Hutchison J D
Published: October 2002

Cement fixation of the acetabular component is increasingly recognized as a common site of loosening when hip replacements fail. Cement keyholes drilled into the acetabulum have been recommended to improve this fixation but little is known of the optimum positions or sizes of these holes. This study investigates the diameter, depth and number of keyholes to be drilled to maximize the failure torque in a model system. A Taguchi experimental design was used to identify the most significant factors and to predict the best configuration of keyholes within the constraints of the experimental test rig. One hole at each of the pubic, iliac and ischial sites, of 12 mm diameter and 6 mm depth, was found to be the optimum configuration. The failure torque was most strongly dependent on the hole diameter in the pubic region, decreased with increasing hole depth and was not sensitive to the number of holes.
Development of a ten-station, multi-axis hip joint simulator
Authors: Goldsmith A A J , Dowson D
Published: October 2002

Joint simulators are now used extensively to evaluate the performance of materials and designs of total replacement hip and knee joints. In this Technical Note a new ten-station hip joint simulator with biaxial rotational articulation synchronized to a physiological loading cycle is described. The current simulator manufactured by ProSim Limited (Manchester, UK) is a development of a first generation machine designed and built in-house at DePuy International Limited (Leeds, UK). The use of this new form of ten-station hip simulator to evaluate the performance of 22 mm zirconia femoral heads and ultra-high molecular weight polyethylene acetabular cups over some 7 million loading cycles is described elsewhere [1].
The influence of continuous sliding and subsequent surface wear on the friction of articular cartilage
Authors: Forster H , Fisher J
Published: October 2002

Reciprocating motion friction tests were conducted upon cartilage-on-metal contacts while subjected to a constant load. Initial friction coefficients were compared with repeat friction coefficients following a sufficient load removal period. The repeat friction coefficients were marginally higher than the initial values and both were primarily dependent on the loading time. It was concluded that while a wear component had been identified, which modestly increased friction coefficients, the overriding parameter influencing friction was loading time. The authors postulate that fluid phase load carriage (being dependent on loading time) within the articular cartilage is largely responsible for low friction coefficients in the mixed and boundary lubrication regimes. This mechanism has been referred to as biphasic lubrication. Both synovial fluid and Ringer's solution were used as lubricants. Over the assessed 120 min loading time friction coefficients rose from 0.005 (for both lubricants) after 5 s to 0.50 and 0.57 for synovial fluid and Ringer's solution respectively. Synovial fluid was found to significantly reduce friction coefficients compared to Ringer's solution over broad ranges of the assessed loading times (p<0.05). Stylus and non-contacting laser profilometry were successfully employed to provide reliable, quantitative and accurate measures of surface roughness. Laser profilometry before and after a continuous sliding friction test revealed a significant increase in surface roughness from Ra = 0.8(±0.2) μm to Ra = 2.1 (±0.2) μm, (p < 0.0005); confirming that surface wear was occurring. Scanning electron microscopy (SEM) revealed the typical highly orientated collagen fibres of the superficial tangential zone. Environmental SEM (ESEM) of fully hydrated cartilage specimens provided largely featureless images of the surface which suggested that sample preparation for conventional SEM was detrimental to the authenticity of the cartilage surface appearance using SEM. Two distinct acellular, non-collagenous surface layers were identified using ESEM and transmission electron microscopy (TEM); respectively referred to as the boundary layer and surface lamina. The phospholipid/glycoprotein based boundary layer will provide boundary lubrication during intimate contact of opposing cartilage surfaces. The surface lamina, being a continuum of the proteoglycan interfibrillar matrix, is present to prevent fibrillation of the underlying collagen fibres. Both layers may contribute to the time dependent frictional response of articular cartilage. Although laser profilometry did reveal surface wear which was consistent with a small increase in friction, the primary variable controlling the friction coefficient was the period of loading.
Engines versus electrons: The future of power production
Authors: Winterbone D E
Published: October 2002

The demands for energy are increasing as countries become richer, and if all mankind achieved the per capita energy consumption of the United States then the total energy consumption of the world would rise by a factor of about 4.5. This would make a large demand on fuel supplies and probably increase pollution beyond a sustainable level. This paper examines the limits to the theoretical efficiency of power generation, including both heat engines and fuel cells, and demonstrates that thermal efficiencies of above 60 per cent are achievable in each case if combined plants are used. It is shown that the fuel cell has benefits over the heat engine when the plant operates for a significant time at low load.
Proposal for a highly intermittent heating law for discontinuously occupied buildings
Authors: Fraisse G , Virgone J , Menezo C
Published: October 2002

This article presents an intermittent heating controller which is designed for calculating the supply temperature of hot-water-radiator heating systems. This controller uses a new heating law which has been obtained by inverting a simplified model for calculating the internal temperature of a building in relation to the external temperature, as well as the supply temperature of the distribution circuit and the temperature of the structure. The latter is used to determine the thermal state of the building, which is an important parameter in the evaluation of energy needs when a building is heated in an intermittent mode. During non-occupancy periods, the parameters of the model are automatically modified by a recursive least-squares routine. A second law optimizes the heating restart time during non-occupancy periods; this law also incorporates a learning mechanism.

The controller's performance is analysed, and the results are compared with those of a controller using a classical heating law which does not take into account the thermal state of building. Numerical simulations demonstrate that the new heating controller leads to performances comparable with those obtained by classical methods, but for a higher degree of intermittence. This means that the comfort obtained is similar, but that the energy consumption is lower. The new heating law also proves to be advantageous in other ways; it provides faster learning, much better lower temperature control and a reduction in instances of overheating during inter-season periods, when little heating is needed.
Exergy analysis for a combined system of steam-injected gas turbine cogeneration and multiple-effect evaporation
Authors: Huang Y-C , Hung C-I , Chen C-K
Published: October 2002

An exergy analysis has been used for a combination of steam-injected gas turbine cogeneration system and forward-feed triple-effect evaporation process, with and without vapour recompression. The fuel utilization efficiency, power—heat ratio and second-law efficiency are examined for evaluation of the thermal system performance. It is shown that the interaction between the combustion irreversibility and the exhaust exergy losses is dominant in governing the system efficiency with various steam injection ratios and feedstock mass flowrates. The compressor and gas turbine losses are shown to have a relatively small influence.
Cooling and heating rate limits of a reversed reciprocating ericsson cycle at steady state
Authors: Blank D A , Wu C
Published: October 2002

The optimal cooling and heating rates for the reversed reciprocating Ericsson cycle with ideal regeneration are determined for heat pump operations. These limiting rates are based on the upper and lower thermal reservoir temperature bounds and are obtained using time and entropy minimization procedures from irreversible thermodynamics. Use is made of time symmetry (a second law constraint) to minimize cycle time. This optimally allocates the thermal capacitances of the cycle and minimizes internal cycle entropy generation. Although primarily a theoretical work, a very practical and extensive parametric study using several environmentally friendly working fluids (neon, nitrogen and helium) is included. This study evaluates the relative contributions of various system parameters to rate-optimized design. The coefficient of performance (COP), and thus the quantity of cooling or heating for a given energy input, is the traditional focus; instead this work aims at the rate of cooling or heating in heat pumps under steady state conditions and using ideal gases as their working substances. The results obtained provide additional criteria for use in the study, design and performance evaluation of employing Ericsson cycles in refrigeration, air conditioning and heat pump applications. They give direct insight into what is required in designing a reversed Ericsson heat pump to achieve maximum heating and cooling rates. The choices of working fluids and pressure ratios were found to be very significant design parameters, together with selection of regenerator and source—sink heat transfer parameters. The parameter most influencing both the heating and cooling mode COPs and the heat transfer rates was found to be the heat conductance of the thermal sink.
The design and analysis of pipe diffusers for centrifugal compressors
Authors: Bennett I , Tourlidakis A , Elder R L
Published: October 2002

The geometry of the region between the impeller tip and diffuser throat is accepted as being very influential, little understood and crucial to the performance of centrifugal compressors. This paper presents an experimental investigation of the flow in this region where the diffusing section of the compressor is of the ‘pipe diffuser’ configuration. The results are presented with an emphasis on design-type correlations. The principal features under investigation were the size of the diffuser throat and the influence of the number of diffuser passages.
Instability in lean premixed combustors
Authors: Dowling A. P. , Hubbard S
Published: October 2002

A generalized acoustic equation is used to identify the mechanisms driving combustion instability. The relationship between the unsteady rate of heat release and the flow is found to influence significantly the frequency of oscillation. A kinematic flame model is reviewed and used to describe the unsteady combustion in a premixed ducted flame and in a typical lean premixed industrial gas turbine. Comparison is made between theory and experiment.
Laser imaging of fuel injection systems and combustors
Authors: Greenhalgh D. A.
Published: October 2002

The control of NO x, stability and re-light in combustors is strongly influenced by the patternation of the fuel and its subsequent mixing with air. This paper reviews imaging approaches to two-phase flow and fuel vapour. The two main methods discussed are laser-induced fluorescence (LIF) for the imaging of volume fraction of fuel vapour or the volume fraction of liquid fuel and laser sheet drop-sizing (LSD) for the imaging of fuel droplet size. A range of practical applications is presented to illustrate the techniques, these include a 1 atm lean prevaporized premixed (LPP) combustor, a study of the pilot zone of a double annular system and the study of spray patternation and droplet size for a variety of fuel injectors.
Ultra-low NOx via catalytic combustion
Authors: Schlatter J. C.
Published: October 2002

The potential for achieving ultra-low NOx levels (below 3 ppmv) in a gas turbine combustor via catalytic combustion has been recognized for more than 20 years [1]. However, the challenging environment in the combustor has until recently thwarted efforts to develop catalysts for this application. Development of the technology described below began 10 years ago with a recognition of the fundamental characteristics of Nx production in high-temperature environments and an analysis of approaches to catalytic combustion that were tried unsuccessfully in other laboratories. Starting from these early assessments, Catalytica devised and developed a new approach that has resulted in successful application of catalytic combustion to an operating gas turbine. The essential features of that technology and recent experiences in its application are the subject of this paper.
Design and rating of dedicated mechanical-subcooling vapour compression refrigeration systems
Authors: Khan J-ur-R , Zubair S. M.
Published: October 2002

Subcooling of the refrigerant at the exit of the condenser in a vapour compression refrigeration system allows the refrigerant to enter the main cycle evaporator with a lower quality and thus allows the refrigerant to absorb more heat in the evaporator, thereby improving the coefficient of performance (COP) of the system. In a dedicated mechanical-subcooling vapour compression refrigeration system, the subcooling is performed by utilizing a small dedicated vapour compression refrigeration cycle. This cycle is coupled to the main cycle at the exit of the condenser. In this paper, thermodynamic models of the dedicated mechanical-subcooling systems are developed to simulate the actual performance of the system, particularly with respect to the subcooler saturation temperature in addition to the heat exchanger areas. It is demonstrated that the performance of the overall cycle is improved over the corresponding simple cycle and this improvement is found to be related to the refrigerant saturation temperature of the subcooler. The models are also used to predict an optimum distribution of the total heat exchanger area between the evaporator and condenser.
A novel supervisory control approach to switching operations for hybrid wind/diesel/battery/mains energy systems
Authors: Gu T , Keerthipala W W L , Islam S M , Nayar C V
Published: October 2002

Hybrid energy systems, integrating renewable energy technologies with diesel generators, batteries and inverters, can provide 24 h grid quality power to remote communities. Work in the Centre for Renewable Energy Systems Technology Australia (CRESTA) has been carried out to develop a new hybrid/wind/diesel/battery/mains energy system. In the system, the switching operations of different modes play an important role in the proper running of the system. From the view of discrete event dynamic systems, a novel supervisory control approach for the switching operations of modes has been explored, in which the switching actions are defined as events, switching modes as states and events take the system from one state to another. The supervisory controller for a prototype of the hybrid wind/diesel/battery/mains energy system has been designed and it has been simulated in PSCAD/EMTDC. The results reveal that this technique could facilitate the analysis and design of supervisory controllers for switching operations, particularly in the complicated hybrid energy systems.
Modelling of cogeneration systems. Part 1: Historical perspective
Authors: O'Brien J I , Bansal P K
Published: October 2002

This paper presents a brief review of cogeneration plant models that have been developed to fulfil different modelling requirements. Three types of models are readily available in the literature, namely the static, part-load and optimization models. The static models are simple design-point models which have found wide application for quickly predicting plant performance and providing data for preliminary economic analysis. However, these models are unable to predict performance of the plant at off-design conditions. To predict the performance of the cogeneration plant away from design conditions, part-load models have been developed. These models use fundamental engineering equations to predict plant performance at part-load conditions but these complex packages are expensive. The optimization models use operations research techniques to optimize the operation of utility plants to minimize operating cost or to maximize revenue. Many of these models are developed using a regression analysis of measured data and use linear functions to simulate components. The models use simplifying assumptions to analyse the thermodynamic performance of the plant but these are usually sufficient for the optimization studies conducted. The method used is dependent on the objective of the modelling process and each type is suited to different applications.
Performance prediction of an industrial centrifugal compressor inlet guide vane system
Authors: Coppinger M , Swain E
Published: October 2002

Variable inlet guide vanes (VIGVs) can significantly extend the stable operating range of industrial centrifugal compressors as a result of imparting swirl to the inlet flow. Typical setting angles range from −20° to +80°; therefore the vanes are normally made from flat plate. An undesirable consequence of the large setting angles required by the vanes is a pressure loss, leading to a decrease in the overall stage efficiency. An ideal inlet guide vane system will therefore induce large swirl angles in the inlet flow with a low associated pressure loss.

Efforts have been made to determine the performance characteristics of an existing VIGV design using both an experimental test facility and numerical techniques. The results obtained from these techniques are far more comprehensive than earlier full-scale performance testing. Validation of the performance of the existing design using these techniques has led to the development of a new vane design and potential improvements to the inlet ducting geometry.

The test techniques and resulting analyses of the existing design are presented here together with some analyses and predictions of the performance of the improved VIGV system design.
Water spray cooling of gas turbine cycles
Authors: Ritchey I , Fisher E H , Agnew G D
Published: October 2002

Aerodervative gas turbines intercooled by water spray injection systems have recently entered service. A calculation framework is presented which permits the effect of water spray injection for both intercooling and inlet chilling to be evaluated and compared with conventional cooling techniques for a range of cycles. The calculations are based on representative performance maps for compressors and turbines, focusing upon the actual performance benefits that can be realized from existing turbomachinery. The principal conclusions are that

spray intercooling can give a greater power boost than conventional intercooling for a given compressor operating envelope spray inlet chilling can give performance benefits comparable with absorption chilling and intercooling is more attractive at ambient temperatures below 15°C, whereas inlet chilling is preferable at higher temperatures.
The design and performance results of simple flat plate low solidity vaned diffusers
Authors: Engeda A
Published: October 2002

Vaned diffusers for centrifugal compressors have decades of development history, but most of it is of a proprietary and empirical nature. Centrifugal compressor designers are continuously searching for a diffuser system that combines the good qualities of vaneless and vaned diffuser systems. Vaneless diffusers are known to possess wide operating range with relatively low efficiency while current conventional vaned diffusers have narrow range and high efficiency. The low solidity vaned diffuser (LSVD) has shown good performance from both range and efficiency standpoints. Its relatively high efficiency and wide flow range potentials are strong current factors, leading the compressor manufacturer to seriously consider it as the best compromise diffuser that has been sought through the years. This paper discusses the design and experimental performance results of eight flat plate LSVDs. These diffusers had a solidity of 0.9, 0.8, 0.7 and 0.6. Eight low solidity vaned diffusers (LSVD1 to LSVD8) and for comparison purposes two vaneless diffusers (VNL1 and VNL2) and a conventional vaned diffuser (CVND) were all tested downstream of the same impeller at three speeds.
Experimental database for a cogeneration gas engine efficiency prediction
Authors: Dupleac R , Tazerout M , Mahieu V , Rousseau S , Leduc B
Published: October 2002

A total of 115 operating test points have been investigated on a cogeneration industrial 200 kWe gas engine at Ecole des Mines de Nantes, with load varying between 50 and 100 per cent, spark advance between 8° and 20° crank angle and air excess in the range 1.3-1.7. The analysis provides a mathematical correlation giving the influence of load variation and other parameters on the thermal power, the natural gas inlet power, the electrical efficiency and the global efficiency with an accuracy better than 2 per cent.
Experimental performance evaluation of a 99.0 mm radial inflow nozzled turbine with varying shroud profiles
Authors: Doran W. J. , Spence S. W T. , Artt D. W.
Published: October 2002

In addition to the experimental data already presented by Spence, Doran and Art in 1999, further comprehensive performance tests were carried out on the same 99.0 mm radial turbine using four different shroud profiles with three nozzles of varying sizes. Efficiency maps are presented for each of 12 different turbine configurations tested. For the largest stator size giving the highest flowrate the turbine efficiency is shown to vary by over 3.5 per cent with different shroud profiles. An examination of the effect of shroud profile with respect to rotor incidence angle revealed that a larger radius of shroud curvature was better for positive incidence while a smaller shroud radius was most efficient for negative incidence.
Three-dimensional flow field downstream of an embedded stator in a multistage axial flow compressor: Part 2: Deterministic stress and heat flux distribution and average-passage equation system
Authors: Suryavamshi N , Lakshminarayana B , Prato J
Published: October 2002

The results from the area traverse measurements of the unsteady velocity and total temperature downstream of the second stator of a three-stage axial flow compressor have been correlated to derive various deterministic stress and heat flux terms. These terms are consistent with those arising from the average-passage equation system of Adamczyk. The deterministic periodic stress and heat flux terms were found to be larger than the aperiodic terms for both the normal and the shear components. Consequently the terms involving the aperiodic components in the average-passage equations could be neglected for stator exit and rotor inlet flow modelling. The deterministic periodic normal and shear stresses were seen to be most significant in the stator wakes away from the end-wall regions. The most significant shear stress correlation was between the axial and the tangential velocity components. Since the correlations involving the radial component were small, it is postulated that the dominant mechanism for mixing (in the radial direction) is due to the steady deterministic radial velocity. All three components of deterministic heat flux were found to be significant in this flow field, especially in the wakes. The dominant terms in the average-passage equation system away from the end walls were due to the tangential gradient compared with the radial gradient terms and both the terms were found to be of equal importance in the hub and casing end-wall regions.
The influence of inlet flow distortion on the performance of a centrifugal compressor and the development of an improved inlet using numerical simulations
Authors: Kim Y , Engeda A , Aungier R , Direnzi G
Published: October 2002

The performance of centrifugal compressors can be seriously affected by inlet flow distortions due to the unsatisfactory nature of the inlet configuration and the resulting inlet flow structure. Experimental tests have been carried out for the comparison of centrifugal compressor stage efficiency with two different inlet configurations, one of which is straight with constant cross-sectional area and the other a 90° curved pipe with nozzle shape. The comparative test results indicated significant compressor stage performance difference between the two different inlet configurations and the details are discussed to understand the performance behaviour of the compressor exposed to the distorted flow from the bend inlet configuration. The experimental investigation motivated the need for a new inlet design as well as a clear picture of the detailed flow field in the existing inlet design using numerical simulations. Two design approaches are reported in this paper, one of which is the location of vanes and the other the length of the curvature radius. For a more effective design method, a generalized formula is developed for the optimum position and number of vanes in such a way that each divided flow passage with vanes shares the same pressure gradient in radial direction. Numerical simulation results are presented and discussed in terms of mass-averaged parameters and flow structures, based on the comparison of flow properties at the pipe exit cross-sectional area of each design. Finally, new designs of different inlet systems are proposed to reduce the secondary flow and to provide flow as uniform as possible for a compressor.
Analysis of the dynamic behaviour of regenerative gas turbines
Authors: Kim J. H. , Kim T. S. , Ro S. T.
Published: October 2002

In this study, a model to simulate the dynamic operation of regenerative gas turbines is described and the transient behaviour of a small engine equipped with a stationary recuperator is presented. The mathematical model of each component consisted of unsteady one-dimensional governing equations and steady state component characteristics. The equation set derived was solved by using a fully implicit numerical method. A realistic control unit model for speed control was likewise introduced to simulate the operation of real engines. Special emphasis was given to the thermal inertia of the recuperator metal that governs the dynamic characteristics of the engine. The dynamic characteristics were examined for a couple of load change modes such as stepwise and periodic load variations. Characteristic transient responses were then investigated and the dependence of transient response on the frequency of load variation was demonstrated.
Performance of integrated gasification combined cycle power plants integrated with methanol synthesis processes
Authors: Carapellucci R , Cau G , Cocco D
Published: October 2002

Base-load integrated gasification combined cycle (IGCC) power plants can perform load-following service by integration with a methanol synthesis process. The methanol, produced from a portion of the coal gas and stored in liquid phase, can be used for matching intermediate and peak-load demand.

In this paper, the load modulation capabilities of IGCC power plants for the coproduction of electricity and methanol have been investigated. Referring to a conventional duty cycle, the main performance of power plants combining slurry-feed entrained-bed gasification and gas or liquid phase methanol synthesis has been assessed, for two different peaking electric power generation solutions. Moreover, the flexibility of these plants has been evaluated for different operating conditions, some remote from design conditions.

The results of the study show that IGCC power plants combining electric power generation and methanol synthesis offer considerable scope for enhancing operating flexibility and load modulation capabilities of coal gasification power plants. The plants designed for advanced liquid phase methanol synthesis process performed best in terms of overall efficiency, plant layout and operating flexibility.
A study of slip factor and velocity components at the rotor exit of forward-curved squirrel cage fans, using laser Doppler anemometry
Authors: Montazerin N , Damangir A , Fard A. Kazemi
Published: October 2002

Velocity profiles outside the rotor of four squirrel cage fans are measured in order to calculate their local slip factors. They show that the fluid exit angle from the rotor and the blade outlet angle of such fans are very different. Inlet configuration and volute spread angle both affected the direction of the flow out of the rotor and hence the slip factor. The general understanding in centrifugal turbomachines is that more energy transfer per unit mass is equivalent to a larger tangential component of velocity and therefore a larger slip factor. In squirrel cage fans a small slip factor results from a large radial velocity component out of the rotor. This gives a larger volumetric flowrate with no sensible head loss. The advantages of a large incidence angle and a large deviation mean that flow adherence to the blades is not always a prime design criterion in such fans.
A new slip factor for centrifugal impellers
Authors: Paeng K. S. , Chung M. K.
Published: October 2002

A new simple but accurate correlation for the slip factor of centrifugal impellers is developed. The functional form of the correlation is obtained by investigating the radius of a relative eddy inscribed by two adjacent vanes and the exit circle of a flow channel in the impeller. Two functions are introduced to correct the slip factor obtained by the present relative eddy model with reference to previous analytical results of Visser, Brouwers and Badie and experiments. The proposed correlation is a function of the number of vanes (Z), vane exit angle (β'2) and the inlet-exit radius ratio (r1/r2).
Optimization of multistage turbines using a through-flow code
Authors: Petrovic M. V. , Dulikravich G. S. , Martin T. J.
Published: October 2002

Fast and accurate flow calculation and performance prediction of multistage axial flow turbines at design and off-design conditions were performed using a compressible steady state inviscid through-flow code with high fidelity loss and mixing models. The code is based on a stream function model and a finite element solution procedure. A new design system has been developed which optimizes hub and shroud geometry and inlet and exit flow field parameters for each blade row of a multistage axial flow turbine. Optimization was performed using a hybrid constrained optimization code that switches among the modules automatically in order to avoid local minima and to accelerate design convergence rate. By automatically varying a relatively small number of geometric variables per turbine stage it is possible to find an optimal radial distribution of flow parameters at the inlet and outlet of every blade row. Thus, an optimized meridional flow path can be found that is defined by the optimized shape of the hub and shroud while keeping blade shapes intact. The multistage design optimization system has been demonstrated using an actual two-stage axial gas turbine as an example. The comparison of computed performance of an already very high efficiency initial design and its optimized design demonstrates more than 1 per cent improvement in the turbine efficiency at design and significant off-design conditions. The entire design optimization process is feasible on a typical single-processor computer workstation or a personal computer.
Analysis of flow velocities within the impeller and the vaneless diffuser of a radial flow pump
Authors: Wuibaut G , Dupont P , Bois G , Caignaert G , Stanislas M
Published: October 2002

Two-dimensional particle image velocimetry has been used in order to analyse the flow in the outlet part of a centrifugal pump (impeller and vaneless diffuser). Tests have been carried out in air. The paper first describes the main characteristics of the centrifugal pump and the associated test facilities. An analysis of the main results in design operating conditions of the SHF (Société Hydro-technique de France) impeller is then proposed.
Time-resolved vane-rotor-vane interaction in a transonic one-and-a-half stage turbine
Authors: Miller R. J. , Moss R. W. , Ainsworth R. W. , Harvey N. W.
Published: October 2002

This paper describes the effect of both an upstream and a downstream vane on the time-resolved surface pressure field around a high-pressure rotor blade. The geometry of the downstream vane considered is a large low aspect ratio vane located in a swan-necked diffuser duct, similar to those likely to be used in future engine designs. Two test geometries are considered: firstly, a high-pressure turbine stage coupled with a swan-necked diffuser exit duct; secondly, the same high-pressure stage but with a vane located in the downstream duct. Both tests were conducted at engine-representative Mach and Reynolds numbers, and experimental data were acquired using fast response pressure transducers mounted on the mid-height streamline of the high-pressure rotor blades. It is shown that the potential field of the downstream vane causes a relatively large static pressure fluctuation on the late rotor suction surface but that the early suction surface and pressure surface are unaffected by the presence of the vane. In addition to the two main interaction mechanisms (upstream vane-rotor and downstream vane-rotor interactions) a third interaction is identified. This is shown to be caused by the interaction, within the rotor passage, between the flowfield associated with the upstream vane and the potential field associated with the downstream vane. This new interaction mechanism is shown to cause static pressure fluctuations on the late rotor suction surface at a frequency corresponding to the difference in the numbers of upstream and downstream vanes.
Power from marine currents
Authors: Fraenkel P. L.
Published: October 2002

This paper describes the rationale and the engineering approach adopted for the development of technology for converting the kinetic energy in marine currents for large-scale electricity generation. Although the basic principles involved are relatively straightforward and well understood, being similar to those of a wind turbine, a practical and cost-effective large-scale system designed to extract the kinetic energy of flowing water has yet to be developed. This paper describes the research and development being undertaken through an industrial consortium with the aim of achieving this goal for the first time, i.e. to achieve the world's first commercially viable systems for delivering power from marine currents.
Trend prediction from steam turbine responses of vibration and eccentricity
Authors: Sinha B. K.
Published: October 2002

Condition monitoring of machines with data sampled from time-dependent variations has been elucidated. Passive diagnostic approaches have been examined particularly for prognostic parameters. Trend predictions using truncated power series and autoregressive moving average methods have been compared. Necessary background information for modelling with respect to measured data acquired over a period of 2 years on a specific case has been provided. The repair effected on the basis of trend forecasting exemplifies an important application of condition monitoring.
Status of and experience with NOx reduction in coal-fired power plants
Authors: Stöhr M , Schütz H , Krüger H
Published: October 2002

Power plant operators in Germany, Europe and other countries are reducing flue gas NOx emissions of large and small power plants to meet air quality regulations for the population and the environment. Beginning with the environmental impact, the use of different techniques for NOx reduction and experience with these techniques is given.
Nox emission control in gas turbines for combined cycle gas turbine plant
Authors: Moore M J
Published: October 2002

The increase, in recent years, in the size and efficiency of gas turbines burning natural gas in combined cycle has occurred against a background of tightening environmental legislation on the emission of nitrogen oxides. The higher turbine entry temperatures required for efficiency improvement tend to increase NOx production. First-generation emission control systems involved water injection and catalytic reduction and were relatively expensive to operate. Dry low-NOx combustion systems have therefore been developed but demand more primary air for combustion. This gives added incentive to the reduction of air requirements for cooling the combustor and turbine blading. This paper reviews the various approaches adopted by the main gas turbine manufacturers which are achieving very low levels of NOx emission from natural gas combustion. Further developments, however, are necessary for liquid fuels.