bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental investigation of the flow characteristics of small orifices and valves in water hydraulics
Authors: Bikai Zhu , Yan Huang , Tiehua Zhang , Zhuangyun Li
Published: August 2003

This paper describes an experimental investigation of the flow characteristics of water passing through small sharp-edged cylindrical orifices and valves of different shapes in water hydraulics. The test results using orifices with aspect ratios, l/d, of 1–15 and diameters of 0.8-3 mm show that the flow coefficients in the case of non-cavitating flow are larger than those of flow with cavitation and decrease with increase in the aspect ratio. However, the flow coefficients of flow with cavitation tend to be of constant value close to the contraction coefficient, Cc at small aspect ratios. Orifices with large aspect ratios have the effect of suppressing cavitation. Experimental results concerning the spool valve illustrate that the sharp-edged valve is less cavitation stricken at large opening than at small opening. Throttles with a triangular notch have better anticavitation ability than those with a square notch. The flow of the throttle with a square notch is significantly affected by the flow direction and the shape of the flow passage.
Fire-induced failure of a propane tank: Some lessons to be learnt
Authors: Tan D M , Xu J , Venart J E S
Published: August 2003

This paper presents the failure analysis of a 1000 US gallon, horizontal, propane tank, which suddenly circumferentially separated at its central section while being radiantly heated. Thermo-hydraulic analyses of the tank and its contents, as well as finite element analysis of its possible thermal stress states coupled with other evidence show that the reasons for the catastrophe were complex—weld defects, low melting point fittings, placement, and fire fighting—and all contributed to the failure. Recommendations are made in order to prevent future similar accidents.
Modelling ductile failure propagation during blowdown under localized jet fire attack
Authors: Falope G B O , Mahgerefteh H
Published: August 2003

A rigorous mathematical model for determining the failure mode of pressurized vessels exposed to localized jet-fire impingement during rapid depressurization or blowdown is presented. Accounting for the thermodynamic trajectory of the two-phase hydrocarbon inventory, the method of separation of variables for non-homogenous heat conduction is used to determine the transient radial temperature gradient across the heated section of the vessel wall. The resulting temperature profile in conjunction with the appropriate vessel geometry stress equations are then used to simulate the transient triaxial thermal and pressure stress yield propagation. Failure is assumed to occur when any of the total stresses exceed the ultimate tensile strength of the vessel wall material. The application of the model to a real cylindrical vessel under localized jet fire attack in the vapour space reveals catastrophic failure involving rapid propagation of a tear along the major axis of the vessel wall due to severe thermal stress loading.
Some aspects of the mathematical modelling of fireballs
Authors: Novozhilov V
Published: August 2003

The development of large-scale fireballs is a typical result of explosions associated with accidental fuel releases in the oil and process industries. The two major mechanisms that lead to fireball formation are vapour cloud explosions and boiling liquid expanding vapour explosions (BLEVEs). An ability to model fireballs is extremely important from the point of view of safety and risk analysis. The present paper provides a state-of-the-art review of the computational techniques available for the mathematical modelling of fireballs. The emphasis is placed on computational fluid dynamics (CFD) modelling, based on Reynolds-averaged Navier—Stokes (RANS) equations for reactive flow. The results of calculations and estimations of fireball hazards are compared with available experimental data. New results are presented for problems that are usually given less attention in fireball studies. These concern estimations of air entrainment rates into fireballs and potential strategies for fireball suppression.
Development of a piezoelectric force sensor for a chip refiner
Authors: Siadat A , Bankes A , Wild P M , Senger J , Ouellet D
Published: August 2003

Chip refiners are used to separate individual fibres from the wood matrix through the application of cyclic compressive and shear forces. The work presented here deals with the development of a two-axis piezoelectric force sensor to measure these cyclic forces in directions normal and tangential to the motion of refiner bars. The sensor consists of a small probe tip that replaces a portion of a refiner bar and is supported on four piezoelectric elements inside a housing. Stresses applied to pulp and wood material, at the surface of the probe, are thus transmitted to the piezoelectric elements, which respond by producing voltage signals. Signals from two of the four piezoelectric elements are used to determine forces in the normal and tangential directions during refining. A prototype sensor was tested in an atmospheric-discharge laboratory refiner. Impacts from individual bar crossings could clearly be discerned even at the maximum operating speed of the refiner. At low refiner speed, detailed measurements of the magnitude of the normal and tangential forces throughout a bar crossing were obtained. However, resonant vibrations of the sensor made it difficult to obtain such information when running the refiner at maximum speed. A number of design modifications are discussed, with the aim of improving the sensor performance for applications in larger-scale commercial refiners.
Pharmaceutical process validation: An overview
Authors: Aleem H , Zhao Y , Lord S , McCarthy T , Sharratt P
Published: August 2003

Drugs are critical elements in health care. They must be manufactured to the highest quality levels. End-product testing by itself does not guarantee the quality of the product. Quality assurance techniques must be used. In the pharmaceutical industry, process validation performs this task, ensuring that the process does what it purports to do. It is also a regulatory requirement. This paper presents an introduction and general overview of this process, with special reference to the requirements stipulated by the US Food and Drug Administration (FDA).
Interior air flow simulation in railway rolling stock
Authors: Berlitz T , Matschke G
Published: August 2003

For the thermal comfort of passengers in modern trains thermodynamic parameters such as pressure, temperature and relative humidity are important, but also technical features such as location, velocity and direction of the air supplied to the compartment must not be neglected. By applying computational fluid dynamics (CFD) to the simulation of the interior air flow, time- and cost effectiveness can be increased significantly: in an early development phase, where influencing the design and the concept is still possible with low additional effort, air conditioning can be optimized in a very cost- and time-effective way. Thus, by exceeding the normative requirements the passenger's needs are met more closely and more easily. After validation of the method and numerical model by full-scale measurements, a powerful and sound tool for parameter variations and the design and construction of air-conditioning facilities is obtained. The interior air flow in the first-class compartment of a regional train was simulated numerically. Thermodynamic and aerodynamic parameters were measured in a full-scale test train for the validation. The results show the ability of CFD to deal with parameter variations and the prediction of thermal comfort. Benefits and drawbacks and the limits of the application of CFD have been worked out.
A study of the phenomenon of wheel climb derailment: Results of basic experiments using model bogies
Authors: Nagase K , Wakabayashi Y , Sakahara H
Published: August 2003

Wheel climb derailment sometimes occurs when a train passes through a steep curve on a railway track at low speeds. The authors conducted experiments on the phenomenon of wheel climb derailment using model bogies and a model track. The Nadal formula (Nadal limit) is used to evaluate the risk of derailment. Because the friction coefficient between the rail and the wheel has a considerable influence on the critical values to be calculated using the Nadal formula, it is inappropriate to evaluate the risk of derailment by using the Nadal formula alone. The risk of derailment can be determined in a straightforward way by measuring the wheel vertical displacement. In this study, to measure the wheel vertical displacement accurately, a high-precision laser displacement sensor was used. The experimental results revealed that a wheel both slips downwards and climbs up simultaneously and that vertical displacement of the wheel occurs when the degree of wheel climb-up exceeds the degree of wheel slip-down. Although the friction coefficient between the rail and the wheel is a primary factor responsible for causing wheel climb derailment, measurement of the friction coefficient is difficult to achieve. Therefore, a model slipping adhesion bogie was used to measure the adhesion coefficient instead of the friction coefficient. The data obtained from the experiments were analysed in order to verify the relationship between the adhesion coefficient and the wheel climb-up behaviour. As a result, it was found that the adhesion coefficient has a major influence on the occurrence of wheel climb derailment.
Surface cracks and wear of rail: A full-scale test on a commuter train track
Authors: Olofsson U , Nilsson R
Published: August 2003

Damage mechanisms such as surface cracks and wear on a rail can reduce the service life of a railway track. The purpose of this investigation was to study the development of these two damage mechanisms on new and 3-year-old rails in a commuter railway track over a period of 2 years. Four curves were studied with radius between 303 and 616m. In two of the curves, two different kinds of rail steel grade (UIC 900A grade with ultimate strength 900N/mm2 and UIC 1100 grade with ultimate strength 1100N/mm2) were used in each curve. In the other two curves, only the lower-strength rail was used. Four pieces of new rail, each 20m long, were inserted in the two curves with both UIC 900A and UIC 1100 grade rail. Lubrication was applied on the high rail of one of the curves with both UIC 900A and UIC 1100 grade rail and on one of the curves with only UIC 900A grade rail. The two remaining curves were not lubricated. Surface cracks in the form of headchecks could be noted on the surface of the new 1100 grade rails after 1 month of traffic. By contrast, the surface of the UIC 900A grade rails showed visible surface cracks in only two of four curves and that after approximately 2 years of traffic. Both materials seemed to be similarly sensitive to crack initiation but the 1100 grade rail was more sensitive to crack propagation and also more sensitive to the formation of headcheck cracks. Lubrication, as expected, reduced the profile change. A less expected outcome was that lubrication also reduced the rate of crack propagation; however, the lubricated UIC 1100 grade rail was as sensitive to crack initiation as the unlubricated UIC 1100 grade rail. By comparing the wear depth in the headcheck zone with the crack length, equilibrium between these two damage mechanisms was found for the lubricated UIC 1100 grade rail. Both the crack length and the wear depth showed low values. By using a lubricant with friction modifiers the stresses was low enough to prevent crack propagation; at the same time, the rail was hard enough to reduce the wear rate. This is probably the most favourable state in terms of rail maintenance cost.
Contact stress variations near the insulated rail joints
Authors: Chen Y. C. , Kuang J. H.
Published: August 2003

The effect of an insulated rail joint (IRJ) on the contact stress variation near wheel-rail contact zones was simulated by employing three-dimensional finite element models. Three linear elastic IRJ materials, i.e. epoxy-fibreglass, polytetrafluoroethylene (PTFE) and Nylon-66, were investigated. Contact elements were used to simulate the interaction between the wheel and rail contact points. Numerical results showed that the presence of IRJ might significantly affect the wheel-rail contact stress distributions. Results also indicated that the traditional Hertzian contact theory is no longer available to predict the contact stress distribution around the rail joints.
Improvements in railway switches
Authors: Bugarín M. R. , Díaz-de-Villegas J-M García
Published: August 2003

This article deals with the reason for the impact on the axles of a railway vehicle on a straight switch rail when crossing the deflecting device of a main track turnout. This phenomenon has been studied by means of the development of a dynamic model, whose theoretical basis is also explained. The dynamic model allows the axle movement on crossing the deflecting device to be represented and provides extremely interesting data relating to speed, acceleration and guiding forces. Finally, the article describes two types of deflecting device modifications (the FAKOP and the CATFERSAN) that will result in improved movement across the deflecting device. A proposal is made for the modification of the geometry of the straight stock rail, known as CATFERSAN, which prevents the phenomenon described above. This modification can be easily incorporated into both new deflecting device designs and those already in use on the tracks, causing them to be inoperative during a short period of time.
Modification of a generalized inverse simulation technique for rotorcraft flight
Authors: Anderson D
Published: August 2003

Inverse simulation techniques have been employed for several years to analyse the manoeuvrability, operational suitability and conceptual design of helicopters. Much of the published work has used specially constructed (algebraic) models of the aircraft. Recently, integration methods have been used successfully with conventional simulation models, although with some important simplifying assumptions made regarding the dynamics of the main rotor, principally the omission of coupled lead/lag and rotorspeed degrees of freedom. This paper will present the current state-of-theart in helicopter inverse simulation—inserting a complete, validated, rigid-body rotorcraft model inside an integration-based algorithm. It is found that the additional rotor dynamics destabilize the inverse algorithm, resulting in severe oscillations in certain unconstrained states, most notably body pitch and roll angles. Analysis of the dynamics of the inverse system shows that these oscillations are manifest by lack of robustness in the inverse algorithm. Several new modifications to the inverse algorithm are shown to reduce these instabilities considerably.
Bifurcation analysis of inertia coupled roll manoeuvres of airplanes
Authors: Sinha N K , Ananthkrishnan N
Published: August 2003

The extended bifurcation analysis (EBA) technique has been recently proposed for the bifurcation analysis of dynamical systems with constrained equilibrium states. In this paper, the EBA technique is used to investigate non-linear behaviour of an aircraft in constrained roll manoeuvres. A comparative performance analysis of the aircraft in three roll manoeuvres, viz. zero sideslip roll, velocity vector roll, and roll manoeuvre with a linear aileron-rudder interconnect (ARI), has been carried out. Selective numerical simulations are carried out to supplement the information obtained from bifurcation analysis.
Operating temperatures of oil-lubricated medium-speed gears: Numerical models and experimental results
Authors: Long H , Lord A A , Gethin D T , Roylance B J
Published: August 2003

This paper investigates the effects of gear geometry, rotational speed and applied load, as well as lubrication conditions on surface temperature of high-speed gear teeth. The analytical approach and procedure for estimating frictional heat flux and heat transfer coefficients of gear teeth in high-speed operational conditions was developed and accounts for the effect of oil mist as a cooling medium. Numerical simulations of tooth temperature based on finite element analysis were established to investigate temperature distributions and variations over a range of applied load and rotational speed, which compared well with experimental measurements. A sensitivity analysis of surface temperature to gear configuration, frictional heat flux, heat transfer coefficients, and oil and ambient temperatures was conducted and the major parameters influencing surface temperature were evaluated.
The principle of unidirectional collinearity of angular momenta
Authors: Rimrott F P J
Published: August 2003

The principle of unidirectional collinearity of angular momenta - in short the collinearity principle - is a physical law governing the behaviour of gyroscopic systems and valid for spinning single-body and multi-body spacecraft, for planetary systems, for galaxies, and possibly on the microscopic scale for atomic systems. In the present paper the collinearity principle is stated and its origin, history and applications are discussed.
Finite element analysis in spine research
Authors: Fagan M J , Julian S , Mohsen A M
Published: August 2003

Finite element analysis is a widely accepted tool used in many industries and research activities. It allows new designs to be thoroughly ‘tested’ before a prototype is even manufactured, components and systems which cannot readily be experimented upon to be examined, and ‘diagnostic’ investigations to be undertaken.

Finite element models are already making an important contribution to our understanding of the spine and its components. Models are being used to reveal the biomechanical function of the spine and its behaviour when healthy, diseased or damaged. They are also providing support in the design and application of spinal instrumentation.

The spine is a very complex structure, and many of the models are simplified and idealized because of the complexity and uncertainty in the geometry, material properties and boundary conditions of these problems. This type of modelling simplification is not peculiar to spinal modelling problems. Indeed, the idealization is often a strength when there is such uncertainty and variation between one individual and another, allowing cause-effect relationships to be isolated and fully explored, and the inherent variability of experimental tests to be eliminated.

This paper reviews the development of finite element analysis in spinal modelling. It shows how modelling provides a wealth of information on our physiological performance, reduces our dependence on animal and cadaveric experiments and is an invaluable complement to clinical studies. It also leads to the conclusion that, as computing power and software capabilities increase, it is quite conceivable that in the future it will be possible to generate patient-specific models that could be used for patient assessment and even pre- and inter-operative planning.
Patient-specific spine models. Part 1: Finite element analysis of the lumbar intervertebral disc—a material sensitivity study
Authors: Fagan M J , Julian S , Siddall D J , Mohsen A M
Published: August 2003

If patient-specific finite element models of the spine could be developed, they would offer enormous opportunities in the diagnosis and management of back problems. Several generic models have been developed in the past, but there has been very little detailed examination of the sensitivity of these models' characteristics to the input parameters. This relationship must be thoroughly understood if representative patient-specific models are to be realized and used with confidence. In particular, the performance of the intervertebral discs are central to any spine model and need detailed investigation first.

A generic non-linear model of an intervertebral disc was developed and subjected to compressive, flexion and torsional loading regimes. The effects of both material and geometric non-linearities were investigated for the three loading schemes and the results compared with experimental data. The basic material properties of the fibres, annulus and nucleus were then varied and the effects on the stiffness, annulus bulge and annulus stresses analysed.

The results showed that the non-linear geometry assumption had a significant effect on the compression characteristics, whereas the non-linear material option did not. In contrast, the material non-linearity was more important for the flexural and torsional loading schemes. Thus, the inclusion of non-linear material and geometry analysis options in finite element models of intervertebral discs is necessary to predict in vivo load-deflection characteristics accurately.

When the influence of the material properties was examined in detail, it was found that the fibre properties did not have a significant effect on the compressive stiffness of the disc but did affect the flexural and torsional stiffnesses by up to ±20 per cent. All loading modes were sensitive to the annulus properties with stiffnesses varying by up to ±16 per cent. The model also revealed that for a particular compressive deformation or flexural or torsional rotation, the disc bulge was not sensitive to any of the material properties over the range of properties considered. The annulus stresses did differ significantly as the material properties were varied (up to 70 per cent under a compressive load and 60 per cent during disc flexion).
Finite element analysis of stress around a sternum screw used to prevent sternal dehiscence after heart surgery
Authors: Jutley R S , Watson M A , Shepherd D E T , Hukins D W L
Published: August 2003

The sternum screw has been proposed as a means of preventing sternal dehiscence, following heart surgery, by increasing the contact area between the wire used to close the median sternotomy and the surrounding bone; as a result, the contact stress is reduced. A finite element model was constructed of a cylindrical wire or screw passing through a block of sternum which consisted of cancellous bone sandwiched within a cortical shell. The thickness of the cortical shell and the material properties of bone were varied between reasonable values. The stress distribution in the sternum was calculated for each model when the wire was subjected to a tension (250 N) which would be required for six wires to withstand a strong cough (40kPa). Results were validated by comparison with a simple analytical model in which the bone and wire were considered incompressible. They show that the screw reduces the contact stress to almost one-seventh of its value when wire is used alone. Contact stresses are especially high if the cortical shell is thin. The high stress in the bone around a screw falls off within a few millimetres. As a result, no problems are anticipated in placing six screws in each half-sternum so that the sternotomy may be closed with the usual six wires.
Recovery of distal hole axis in intramedullary nail trajectory planning
Authors: Zhu Y , Phillips R , Griffiths J G , Viant W , Mohsen A , Bielby M
Published: August 2003

In intramedullary nail (IMN) surgical operations, one of the main efforts for surgeons is to find the axes of two distal holes. Two distal holes on an IMN, which are inside the intramedullary canal of a patient's femur, can only be seen in a lateral X-ray view. For the standard surgical procedure, the localization of the distal hole axes is a trial-and-error process which results in a long surgical time and large dose of X-ray exposure. In this paper, an algorithm to derive the three-dimensional position and orientation of the distal hole axis was developed. The algorithm first derives the nail axis through two X-ray images. Then the distal hole axis is calculated through projecting back the hole boundary on the X-ray image from a lateral view to three-dimensional space. A least-squares method is used to determine the centres of the front hole and the back hole through iteration. The algorithm has been tested with real data and it was robust.
The calculation of a human lumped-mass model from acceleration and force-plate data
Authors: Shippen J
Published: August 2003

This paper describes a technique for the calculation of a lumped-mass representation of a human based on acceleration of body locations, typically obtained from a three-dimensional motion tracking system, and external forces and torques, typically measured from a force plate. The inverse problem of solving for lumped masses is presented, which results in a mass model of the individual subject via a fast, fully automated approach. This method can be used to obtain the mass model per se for the identification of growth deformities or together with a kinematic model for inverse and forward dynamics. Furthermore the mass model and acceleration trajectories subsequently can be used to calculate the contact forces between the floor and the subject at locations remote to a force plate.
The influence on strain shielding of material stiffness of press-fit femoral components
Authors: Simões J A , Vaz M A
Published: August 2003

The investigation and development of hip prostheses that can provoke identical strain patterns with those of the intact femur (physiological strains) are challenging design problems that have been addressed by several researchers. The modification of the physiological femoral strain pattern provokes adverse tissue biological reactions such as bone hypertrophy, as well as possible mechanical failure of the bone-implant construction. Investigators have used numerical and experimental methods to study the influence of the prosthesis material and geometry on physiological strain deviation. Within the present study, same geometry femoral components composed of different materials have been analysed using strain gauges. The effect of stem stiffness on the strain deviation relatively to those obtained with the intact femur was assessed. Five similar Freeman's prostheses made of different materials (steel, aluminium, composite and polyurethane) at the proximal and middle distal regions were manufactured and tested. The results revealed that only at the proximal lateral and proximal medial aspects of the femur were some differences observed between the strain patterns of the prostheses studied.
Mechanical testing of the wire clamping characteristics of the Fixclip™ internal fixation system
Authors: Vadivelu R , Baker A S , Chetwynd D G
Published: August 2003

Stainless steel wires (Kirschner's wires) have been used for over 60 years to fix internally a wide range of osteotomies and fractures in bones. Fixclips™ (Corifix, Cirencester, UK) shaped like winged washers have been used to clamp pairs of K wires of diameters ranging from 0.8 to 3.0mm to standard orthopaedic screws and to fix bones internally in more than 400 patients. The system has proved to be biologically and mechanically very effective. This paper describes the design and some biomechanical test results of the Fixclip™. Preliminary strength tests conducted using a Hounsfield Tensometer show that the pull-out force, reflecting the grip of the clip on the wire, is dependent on the wire size and, throughout the clinically relevant range, increases linearly with increasing screw torque. Changing the surface finish of the clip did not confer any advantage over the existing polished clip in terms of grip strength.
Noise characteristics of turbines for wave power conversion
Authors: Takao M , Setoguchi T , Kaneko K , Raghunathan S , Inoue M
Published: August 2003

A variety of designs of self-rectifying air turbines for wave power conversion have been proposed over the last decade. However, the noise characteristics of the turbines have not been presented so far. In order to clarify the noise characteristics of the turbines, experimental investigations have been performed under steady flow conditions in this study. As a result, it is found that the noise characteristics of impulse-type turbines are superior to those of Wells-type turbines. Moreover, the noise characteristics have been discussed from the viewpoint of the specific noise level, a term used widely in engineering.
Performance of the once-through multistage flash desalination process
Authors: Ettouney H , El-Dessouky H , Al-Juwayhel F
Published: August 2003

The brine circulation multistage flash desalination process (MSF) dominates the thermal desalination market, while the once-through multistage flash desalination process (MSF-OT) remains to be found on a limited scale. This is because the MSF-OT process has no control on the temperature of the feed sea water. For non-equatorial regions, where the sea water temperature drops to 5 — 15°C during winter operation, the MSF-OT performance deteriorates unless the volume of the low-temperature stages is drastically increased to allow for reduction in the brine reject temperature to lower values. Another approach to solving this problem is to use the brine mixing (MSF-M) technique to control the feed sea water temperature. Irrespective of this, the MSF-OT process should be considered the optimum choice for large-scale thermal desalination in equatorial regions, where the sea water temperature remains constant throughout the year at 28°C. This study focuses on design and performance features of the MSF-OT process. Results are presented in terms of variations in the process thermal performance ratio, the specific heat transfer area and the conversion ratio as a function of the top brine temperature, the number of flashing stages and the feed sea water temperature. The performance of the MSF-OT process is identical to the MSF process as long as the feed sea water temperature remains above 25°C. Evaluation of the MSF-M system and comparison with the performance of the MSF and MSF-OT processes is presented.
Application of a three-dimensional viscous transonic inverse method to NASA rotor 67
Authors: Tiow W. T. , Zangeneh M
Published: August 2003

The development and application of a three-dimensional inverse methodology in which the blade geometry is computed on the basis of the specification of static pressure loading distribution is presented. The methodology is based on the intensive use of computational fluid dynamics (CFD) to account for three-dimensional subsonic and transonic viscous flows. In the design computation, the necessary blade changes are determined directly by the discrepancies between the target and initial values, and the calculation converges to give the final blade geometry and the corresponding steady state flow solution. The application of the method is explored using a transonic test case, NASA rotor 67. Based on observations, it is conclusive that the shock formation and its intensity in such a high-speed turbomachinery flow are well defined on the loading distributions. Pressure loading is therefore as effective a design parameter as conventional inverse design quantities such as static pressure. Hence, from an understanding of the dynamics of the flow in the fan in relation to its pressure loading distributions, simple guidelines can be developed for the inverse method in order to weaken the shock formation. A qualitative improvement in performance is achieved in the redesigned fan. The final flowfield result is confirmed by a well-established commercial CFD package.
Influence of fuel volatility on combustion and emission characteristics in a gas turbine combustor at different inlet pressures and swirl conditions
Authors: Sharma N. Y. , Som S. K.
Published: August 2003

The practical challenges in research in the field of gas turbine combustion mainly centre around a clean emission, a low liner wall temperature and a desirable exit temperature distribution for turboma-chinery applications, along with fuel economy of the combustion process. An attempt has been made in the present paper to develop a computational model based on stochastic separated flow analysis of typical diffusion-controlled spray combustion of liquid fuel in a gas turbine combustor to study the influence of fuel volatility at different combustor pressures and inlet swirls on combustion and emission characteristics. A κ-ɛ model with wall function treatment for the near-wall region has been adopted for the solution of conservation equations in gas phase. The initial spray parameters are specified by a suitable probability distribution function (PDF) size distribution and a given spray cone angle. A radiation model for the gas phase, based on the first-order moment method, has been adopted in consideration of the gas phase as a grey absorbing-emitting medium. The formation of thermal NO x as a post-combustion reaction process is determined from the Zeldovich mechanism.

It has been recognized from the present work that an increase in fuel volatility increases combustion efficiency only at higher pressures. For a given fuel, an increase in combustor pressure, at a constant inlet temperature, always reduces the combustion efficiency, while the influence of inlet swirl is found to decrease the combustion efficiency only at higher pressure. The influence of inlet pressure on pattern factor is contrasting in nature for fuels with lower and higher volatilities. For a higher-volatility fuel, a reduction in inlet pressure decreases the value of the pattern factor, while the trend is exactly the opposite in the case of fuels with lower volatilities. The NOx emission level increases with decrease in fuel volatility at all combustor pressures and inlet swirls. For a given fuel, the NOx emission level decreases with a reduction in combustor pressure and an increase in inlet swirl number.
Study on the natural air cooling of electronic equipment casings: Effects of the outlet vent and the power heater locations on the cooling capability
Authors: Ishizuka M , Peng G , Kitamura Y
Published: August 2003

This paper is concerned with the natural cooling of electronic equipment casings. Effects of the size and the location of the outlet vent as well as the relative distance from the outlet vent location to the power heater position on the flow resistance have been investigated experimentally by using a simple model casing simulated for practical natural air cooled electronic equipment casings. The result shows that the mean temperature rise inside the casing increases with increase in the heater input power, but decreases linearly with increase in the vent porosity coefficient in logarithmic coordinates. As the heater approaches the outlet vent, the temperature rise increases linearly in the logarithmic scale.

By defining a new dimensionless parameter called the equivalent Reynolds number, involving the Reynolds number and the porosity coefficient, the flow resistance coefficient is found to have a close logarithmic linear correlation, K = kxχ−1.5, with the equivalent Reynolds number. Its validation has been proved by the good agreement with experimental results. The result indicates that the relative distance from the outlet vent to the heat dissipation unit can be considered as a chimney height in the practical engineering design. Although further more detailed validations are needed, a useful correlation between the flow resistance coefficient, the Reynolds number and the porosity coefficient has been presented for the design application of natural cooling electronic casings.
A model for predicting the yearly load in district heating systems
Authors: Jónsson G. R.
Published: August 2003

This paper presents a model that can be used to predict the yearly load in district heating systems some years ahead. To demonstrate the model, data from Reykjavik, Iceland, were used in the analysis. The model is based on the three main factors affecting the consumption. The first factor is the increase in the number of houses, called the connected volume, that need to be heated. The trend in the volume during the last decade forms the basis for predicting future values using regression analysis. The second factor is the climate, which is an important factor since approximately 85-90 per cent of the hot water consumption is weather dependent. The estimated variability in the weather is based on data for the period from 1949 to 1999 using bootstrap techniques. The third factor is the behaviour of the consumers, which is analysed by looking at past consumption values after isolating the effect of the first two factors from the consumption. A prediction of the consumption is obtained given some values of each of the three factors. This process is repeated several hundred times, and from those values an estimate of the expected consumption is obtained. Furthermore, the two-sided (100 — α) per cent confidence interval for the consumption is determined by cutting off α/2 per cent of the lowest and highest predicted consumption values.
Analysis of the Vading concept-a new rotary-piston compressor, expander and engine principle
Authors: Ertesvåg I. S.
Published: August 2003

A novel concept for rotary machines is described. A rotor is positioned acentrically in a cylindrical cavity. One or more (typically, three or four) vanes slide radially in slots in the rotor. The vanes are connected to an axle such that the tip of a vane follows the internal surface of the housing without touching it. It is shown how the concept can be utilized in the design of compressors, expanders, and internal combustion engines. A thermodynamic model is formulated for the engine process, and calculations for a chosen set of geometrical data are presented. It is concluded that the machine can be described mathematically, and that it can work as claimed by the inventor, Kjell Vading. Some potential advantages over other concepts are discussed.
Dropwise condensation theory and experiment: A review
Authors: Rose J. W.
Published: August 2003

The paper reviews progress in dropwise condensation research from 1930 to the present. Particular attention is given to heat transfer measurements, theory, transition and effects of surface material. Although it has been known since the 1930s that heat transfer coefficients for dropwise condensation of steam are much higher than those for film condensation, there were, until the 1960s, wide discrepancies between the results of different investigators. Subsequently, more accurate measurements have shown good consistency and the mechanism and theory of the dropwise condensation have become better understood. There has been considerable controversy over the magnitude of the so-called ‘constriction resistance’ and the effect of the surface thermal conductivity on the heat transfer coefficient. The balance of evidence suggests that this is only significant at very low heat fluxes and for very small condensing surfaces. Measurements have also been made with sufficiently high cooling intensities to cover the range of dropwise to filmwise condensation transition. The detailed mechanism of transition is still not fully understood. Perhaps most importantly, the practical problem of promoting lasting dropwise condensation under industrial conditions remains to be solved despite considerable effort spanning more than 70 years.
Integration of solid oxide fuel cells into gas turbine power generation cycles. Part 1: Fuel cell thermodynamic modelling
Authors: Pangalis M. G. , Martinez-Botas R. F. , Brandon N. P.
Published: August 2003

The development of a detailed thermodynamic model of a fuel cell is presented. This model predicts the performance of a gas turbine and fuel cell systems integrated together in hybrid power generation cycles. The achievement of this goal involved the independent modelling of each component (prereformer, internal reformer, active area, combustion zone and fuel preheating) using numerical methods in the form normally required by cycle calculations used in gas turbine design. The fuel cell model was based on the principle of operation of the Westinghouse tubular solid oxide fuel cell (SOFC) design, involving internal reforming and prereforming of methane. Its performance was examined under a wide range of operating conditions leading to exhaust temperatures in the range 370–935°C.

Fuel cell system efficiencies as high as 56 per cent were predicted at low current densities (150mA/cm2), while the efficiency dropped to 38.7 per cent at high current densities (600mA/cm2) owing to the irreversibilities developed. Pressurized operation of the fuel cell was assessed in the range 1–25 atm; high-pressure operation leads to an increased power output, particularly at high current densities, but it also produces a significant decrease in electrical efficiency (from 55 to 37 per cent). Pressurized operation should only be contemplated when the fuel cell is integrated with a gas turbine, as shown in Part 2 of this paper, where the hybrid configuration will be shown to give an impressive 76.4 per cent maximum electrical efficiency.
Integration of solid oxide fuel cells into gas turbine power generation cycles. Part 2: Hybrid model for various integration schemes
Authors: Cunnel C , Pangalis M. G. , Martinez-Botas R. F.
Published: August 2003

The second part of this paper deals with modelling gas turbine cycles integrated with a fuel cell model to produce hybrid cycles. The main objectives were to develop an understanding of the integration options and to determine the theoretical optimum configuration. Six different realistic cycles are analysed and discussed. The fuel cell model is detailed in Part 1 of this paper. The gas turbine cycles considered included intercooling, reheat and recuperation.

The choice of hybrid configuration will depend on the application, but from this analysis it is shown that a recuperated gas turbine cycle with a fuel cell ahead of the combustor is a good choice for power generation at small/medium scale. This cycle achieved a thermal efficiency of 64.1 per cent at a relatively low pressure ratio of 14; the specific power, although lower than that of other configurations explored, was found to be reasonable at 520 kW/kgs. The addition of an intercooler to this cycle indicated a further increase in efficiency at 69.6 per cent and a considerable increase in specific power; the corresponding pressure ratio was 30, which would lead to a significantly different gas turbine. The maximum efficiency of all cases was found for a cycle containing a primary fuel cell (ahead of the combustor) and a reheat fuel cell (in-between the high-pressure and low-pressure turbine) with a numerical value of 76.4 per cent at a low pressure ratio but leading to a much reduced power (200 kW/kgs); a peak specific power of 489 kW/kgs was found but at much higher pressure ratios.
A generalized object-oriented computational method for simulation of power and process cycles
Authors: Chakraborty N , Chakraborty S
Published: August 2003

A flexible computational model, based on a generalized object-oriented iterative algorithm is developed for the analysis of power and process cycles. Each component of the plant is identified as an object, and the interlinking between various objects is achieved through an appropriate node connectivity. Subsequently, ‘iteration loops’ are activated, consistent with the number of primary unknowns, until a converged solution is achieved. Simulation results are presented that correspond to the heat balance analysis of a typical cogeneration cycle of a process plant.
Two-dimensional mathematical model of a packed bed dryer and experimentation
Authors: Basirat-Tabrizi H , Saffar-Avval M , Assarie M. R.
Published: August 2003

A comprehensive heat and mass transfer model, based on the Eulerian two fluid model (TFM), developed for a packed-bed-drying process. The temperature and moisture content in a particle was considered with the conjugate effects between the gas and particles in a packed bed. Numerical study of the model was carried out on two-dimensional, axi-symmetrical cylindrical coordinates in order to investigate the effects of the different parameters such as particle size, variation of inlet gas temperature on the moisture content, and temperature of solid and gas outlet. For experimental observations, an experimental apparatus was designed and utilized. The theoretical results were then compared to the experimental data, which indicated good agreement.
Performance simulation of scroll compressors
Authors: Lee G. H.
Published: August 2003

The scroll compressor is widely used in air conditioning and heat pump plant because it combines high efficiency and reliability with low noise and vibration. This paper describes a simulation model for estimating the performance of such machines. The model includes consideration of both the compression process and the dynamic behaviour of the moving parts. The compression process is modelled on the assumption of the working chamber as a control volume to which the equations of conservation of mass and energy are applied, allowing for radial and flank leakage and suction refrigerant heating. The derived output from the model includes a pressure-volume diagram of the compression process together with the resultant forces on the components, friction losses within the machine and temperatures of the main components within the compressor. Estimates of the volumetric, adiabatic and mechanical efficiencies of the scroll compressor are then obtained directly from this. Performance estimates thus obtained may be used for the development of the package air conditioning system.
Axial compressor performance modelling with a quasi-one-dimensional approach
Authors: White N. M. , Tourlidakis A , Elder R. L.
Published: August 2003

This paper describes a technique for the numerical modelling of axial compressors using the simplest form of representation—a mean-line one-dimensional method. Although this type of flow analysis is a gross simplification of a complex three-dimensional system, which can now be modelled more accurately by many of today's computational fluid dynamics (CFD) packages, it does offer the advantages of simple input requirements and fast convergence times. These factors were major considerations when choosing a prediction method to be employed within an optimization program developed at Cranfield for the optimization of stator vane stagger angles, where detailed stage data were not required. The objective was to develop a technique capable of simply modelling the flow in multistage compressors to provide performance data including overall pressure ratio, efficiency and flow range at various speeds, as well as providing interblade data so that restaggering of blades could be accounted for. The salient issues presented here deal firstly with the construction of the compressor model and its incorporation into a FORTRAN program. A discussion of the results then follows, where four very different compressors have been modelled. Finally, the stability limit (or surge point) prediction methods are reviewed.

Results have shown that consistent agreement can be obtained with such a performance prediction model, providing the loss and deviation correlations used are applicable to the blade profiles. It was also apparent that the two simplistic methods of surge prediction, which relied upon either stage or overall characteristic gradients, gave better agreement than the more rigorous discrete stage-to-stage model. This was thought to be a result of the continuous nature of the empirical rules utilized, which predict a smooth stage characteristic and hence falsely delay the estimated instability point.