Recycling of carbon fibre composites

A clear case for carbon fibre recovery and reuse exists on environmental grounds due to the high cost and energy use of virgin fibre production. On a specific energy basis, carbon fibres can be recovered at around 10% of the energy required to manufacture virgin fibres but the scale of the recovery process can make a large difference to overall cost effectiveness. This study will describe the technical and economic challenges associated with the recycling of carbon fibres, the state of the art in recycling technologies and the re-use of fibres in high performance composites

Stator and rotor vent modelling in a MVA rated synchronous machine

An investigation into the solution dependence of a conjugate heat transfer computational fluid dynamics (CFD) model of a synchronous generator, with respect to meshing, has been carried out. Utilising CFD as a tool for investigating the airflow and thermal performance of electrical machines is increasing. Meshing is a vital part of the CFD process, but its importance is often misunderstood or overlooked in the context of electrical machine analyses; partly due to the relative mesh independency of the finite element analysis (FEA) numerical method. This paper demonstrates how a relatively complex, aircooled generator CFD model can be considerably influenced by changes in the mesh. Flow rate, velocity and windage effects are assessed as a function of the mesh adopted. Mesh changes have been shown to affect the mass flow rate through a single vent by up to 55% and the associated heat transfer coefficient by 128%

Fluid flow and heat transfer analysis of TEFC machine end regions using more realistic end-winding geometry

In this paper a typical small low voltage TEFC motor (output power ~10 kW) has been studied using computational fluid dynamics. The complexity of the end winding geometries, often consisting of several insulated copper strands bound together, provides a challenge to the modelling and analysis of heat transfer and fluid flow phenomena occurring in the end region which typically is an area of most interest for thermal management. Approximated geometries are usually employed in order to model the end windings to reduce analysis time and cost. This paper presents a comparison of two cases, a typical simplified geometry and a more realistic geometry of end windings and uses these cases to highlight the challenges and impact on predicted heat transfer. A comparison of the two models indicate that the different representations of end winding geometries can affect the heat dissipation rate through the outer housing by up to 45%

Numerical investigations of convective phenomena of oil impingement on end-windings

A novel experimental rig for analysing intensive liquid cooling of highly power-dense electrical machine components has been developed. Coupled fluid flow and heat transfer has been modelled, using computational fluid dynamics (CFD), to inform the design of a purpose-built enclosure for optimising the design of submerged oil jet cooling approaches for electrical machine stators. The detailed modelling methodology presented in this work demonstrates the value in utilising CFD as a design tool for oil-cooled electrical machines. The predicted performance of the final test enclosure design is presented, as well as examples of the sensitivity studies which helped to develop the design. The sensitivity of jet flow on resulting heat transfer coefficients has been calculated, whilst ensuring parasitic pressure losses are minimised. The CFD modelling will be retrospectively validated using experimental measurements from the test enclosure

A simplified wood combustion model for use in the simulation of cooking fires

Paper presented at the 5th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 1-4 July, 2007.Wood combustion was studied with the intention of developing a simplified model of fuel burn-rate in small cooking fires, for inclusion in a CFD model of a whole cook-stove. The investigation included collecting experimental data on fuel burn-rate, model development and comparison of experimental and simulation results. In the experimental phase, regular blocks of wood were arranged in a lattice or crib with a range of volumes, void fractions and specific surface areas. The burning cribs yielded 3-40 kW fires. The simplified model assumed an unreacted core of virgin wood surrounded by char. It included considerations of heat transfer through the fuel by conduction; thermal decomposition of the virgin fuel into char and volatile gases, limited by the supply of heat to the pyrolysis region; the surface combustion of char limited by the diffusion of oxygen through the species boundary layer and impeded by the counter-flow of volatile gases. The model predicted the change of burn-rate with crib volume, porosity and surface area shown by experimental data, though it does incur significant errors, due to the assumption of one-dimensional behaviour within the crib, and neglecting spatial and temporal variations in boundary conditions. It was concluded that accuracy of the model could be improved by developing it to two or three dimensions, and that the easiest way to do this was through CFD. The model was sufficiently accurate to be used as a source of wood volatiles when modelling small fires in cookstoves, with the aim of investigating the effect of design changes on stove efficiency.cs201

Numerical investigations of convective phenomena of oil impingement on end-windings

A novel experimental rig for analysing intensive liquid cooling of highly power-dense electrical machine components has been developed. Coupled fluid flow and heat transfer has been modelled, using computational fluid dynamics (CFD), to inform the design of a purpose-built enclosure for optimising the design of submerged oil jet cooling approaches for electrical machine stators. The detailed modelling methodology presented in this work demonstrates the value in utilising CFD as a design tool for oil-cooled electrical machines. The predicted performance of the final test enclosure design is presented, as well as examples of the sensitivity studies which helped to develop the design. The sensitivity of jet flow on resulting heat transfer coefficients has been calculated, whilst ensuring parasitic pressure losses are minimised. The CFD modelling will be retrospectively validated using experimental measurements from the test enclosure

Thermal management of a high speed permanent magnet machine for an aeroengine

The paper describes the mechanical and thermal design of a high speed, high power density synchronous permanent magnet machine for an aero engine starter generator system with a power rating of 150 kW and maximum speed of 32,000 rpm. As both mechanical and thermal aspects have a direct impact on machine overall performance and weight reduction, a critical design optimisation was carried out. Intensive cooling is guaranteed by direct liquid oil-cooling of stationary components; a stator sleeve is also introduced into the airgap to prevent excessive windage. Thermal investigations were carried out by the means of Computational Fluid Dynamics (CFD) and Lumped Parameter Thermal Network (LPTN) analyses. Experimental validation also allowed the identification of most critical machine temperatures and the validation of the models developed. Finite Element Analysis(FEA) is used for the static structural analyses of the statorsleeve

Effect of fiber suspension jet stability on alignment quality of discontinuous carbon fiber tapes

A hydrodynamic alignment process has been developed for converting discontinuous random carbon fibers into tapes with a highly aligned orientation distribution to greatly improve the applicability of recovered fibers to composite parts. In hydrodynamic alignment processes short fibers are aligned by the velocity gradient along the flow direction in a convergent nozzle. Thereafter the jet of fiber suspension is deposited on a nylon mesh and the now redundant dispersion medium is drained away to leave an aligned fiber tape. The fundamental physical principles at work in the process have not been widely studied and are shown in the present work to greatly influence the properties of the resulting materials. In this work, the influence of suspension jet stability on the fiber orientation distribution was examined and the liquid jet break-up regime was determined. To explore the factors which can affect the suspension jet stability, different nozzle geometries, viscosities of dispersion media, fiber lengths and Reynolds numbers were applied in experimental work. The shear rate profiles inside different nozzles were simulated by Computational Fluid Dynamics methods and the results described in this paper

Developmental dyslexia: predicting individual risk

Background: Causal theories of dyslexia suggest that it is a heritable disorder, which is the outcome of multiple risk factors. However, whether early screening for dyslexia is viable is not yet known. Methods: The study followed children at high risk of dyslexia from preschool through the early primary years assessing them from age 3 years and 6 months (T1) at approximately annual intervals on tasks tapping cognitive, language, and executive-motor skills. The children were recruited to three groups: children at family risk of dyslexia, children with concerns regarding speech, and language development at 3;06 years and controls considered to be typically developing. At 8 years, children were classified as 'dyslexic' or not. Logistic regression models were used to predict the individual risk of dyslexia and to investigate how risk factors accumulate to predict poor literacy outcomes. Results: Family-risk status was a stronger predictor of dyslexia at 8 years than low language in preschool. Additional predictors in the preschool years include letter knowledge, phonological awareness, rapid automatized naming, and executive skills. At the time of school entry, language skills become significant predictors, and motor skills add a small but significant increase to the prediction probability. We present classification accuracy using different probability cutoffs for logistic regression models and ROC curves to highlight the accumulation of risk factors at the individual level. Conclusions: Dyslexia is the outcome of multiple risk factors and children with language difficulties at school entry are at high risk. Family history of dyslexia is a predictor of literacy outcome from the preschool years. However, screening does not reach an acceptable clinical level until close to school entry when letter knowledge, phonological awareness, and RAN, rather than family risk, together provide good sensitivity and specificity as a screening battery

Continuous photo-oxidation in a vortex reactor: efficient operations using air drawn from the laboratory

We report the construction and use of a vortex reactor which uses a rapidly rotating cylinder to generate Taylor vortices for continuous flow thermal and photochemical reactions. The reactor is designed to operate under conditions required for vortex generation. The flow pattern of the vortices has been represented using computational fluid dynamics, and the presence of the vortices can be easily visualized by observing streams of bubbles within the reactor. This approach presents certain advantages for reactions with added gases. For reactions with oxygen, the reactor offers an alternative to traditional setups as it efficiently draws in air from the lab without the need specifically to pressurize with oxygen. The rapid mixing generated by the vortices enables rapid mass transfer between the gas and the liquid phases allowing for a high efficiency dissolution of gases. The reactor has been applied to several photochemical reactions involving singlet oxygen (1O2) including the photo-oxidations of α-terpinene and furfuryl alcohol and the photodeborylation of phenyl boronic acid. The rotation speed of the cylinder proved to be key for reaction efficiency, and in the operation we found that the uptake of air was highest at 4000 rpm. The reactor has also been successfully applied to the synthesis of artemisinin, a potent antimalarial compound; and this three-step synthesis involving a Schenk-ene reaction with 1O2, Hock cleavage with H+, and an oxidative cyclization cascade with triplet oxygen (3O2), from dihydroartemisinic acid was carried out as a single process in the vortex reactor