A so-called blockage geometry consisting of a rod with a fin positioned concentrically within a pipe is used to asses the capabilities of numerical turbulent flow and mass transfer models to predict the turbulent mass transfer coefficients. Measurements of the mass transfer coefficient have been performed for a range of fin diameters and flow rates. The limiting diffusion current measurements were performed using the ferri-ferrocyanide system and nickel electrodes. Different mass transfer turbulence models are used for the calculations and the results are compared with the measurements. The influence of flow rate and fin diameter on the mass transfer rate is examined.

The local and averaged forced-convective heat transfer coefficients were estimated from measured local and averaged mass transfer coefficients in a model slagging-gasifier hearth pool using the Chilton-Colburn analogy. A solution of ferri/ferrocyanide and buffer with addition of CMC (carboxymethylcellulose) was used for the electrochemical mass transfer measurements. This solution had similar properties to those of the slag in the real gasifier. The influence of natural convection due to the differences in temperatures in the hearth was also estimated. Values of heat transfer coefficient similar to those estimated by British Gas for the prototype Westfield gasifier were found using the mass transfer modelling method.

Summary The flower of Brassica napus L. appears to be typically zoophilous (suited to animal pollination) because of its visually attractive petals, robust stigma and nectaries. Pollination by wind is feasible, however, and its likely effectiveness is not immediately foreseeable because of the complexity of interactions between objects and windborne particles. Computational fluid dynamics (CFD) and wind‐tunnel experiments were used to investigate the aerodynamic interactions between the flower and a windborne suspension of its pollen. The flower's petals handicapped wind pollination by reducing the target efficiency of the upwind‐facing stigma. For downwind‐facing flowers, pollen reception was negligible. Several aspects of the plant's architecture (floral structure, pollen cohesiveness, inflorescence structure) are uncompromisingly zoophilous. Estimates of the amount of wind pollination suggest that it is unlikely to be important for the long‐distance dispersal of B. napus genes such as those from genetically modified varieties. This study illustrates how CFD may become a powerful tool in future analyses of wind pollination.

This paper presents the findings of a detailed investigation to determine the performance effects of a diesel engine when the inert nitrogen (N(2)) in air is replaced by carbon dioxide (CO(2)). The requirement for a diesel engine to operate in such a manner is access to free air being prohibited, as is the case with a submarine power generation unit. Numerous projects have investigated non-air-breathing diesel engine systems. The more recent ones have concentrated on strategies whereby the recirculated non-air mixture maintains the thermodynamic properties of free air such that engine performance is not compromised. This has led to the addition of argon and other inert gases. However, systems utilizing purely fuel, oxygen and carbon dioxide mixtures have not been investigated since the 1960s, and owing to the confidentiality of defence-related work little public data have been made available.A Perkins T4.236 truck engine has been configured to operate on a mixture of 70 mol % CO(2) and 30 mol % O(2) when preheated to a temperature of 150 degrees C. Performance results show that under such inlet conditions the rated brake power of the engine las defined by fuelling rate) degrades by 20-23 per cent with a subsequent increase in brake specific fuel consumption of 23-28 per cent. In-cylinder observations in relation to ignition delay and exhaust oxygen concentrations lead to the hypothesis that the carbon dioxide is seriously affecting both pre-and post-ignition processes by slowing down reaction rates. Investigations were also carried out to assess the capability of an existing diesel engine model, based on the filling and emptying technique, suitably modified such that it could be used to simulate non-air performance. The modifications to the model to allow parametric comparisons to be undertaken of non-air brake performance indicators were found to be within 5 per cent of experimental values.

Studies of combined natural and forced convection in a vertical parallel plate electrochemical cell in laminar conditions in cases of opposing and aiding flow are reported. In an ongoing project it was necessary to identify conditions in which natural convection had no significant influence on mass transfer rates at the cell walls so that data could be validly compared with purely laminar flow computational models. For the different electrode lengths investigated, natural convection dominated at low Reynolds number and there was no Reynolds number dependence. At high Reynolds number the data approached the laminar flow solution. At intermediate Reynolds number, however, there existed a distinct region where free and forced convection were significant. At high electrolyte concentrations data did not merge with laminar flow equations until Re=1000 and low electrolyte concentration data for the large plate could not be compared with numerical predictions below Re of 250. An attempt was made to compare the data with those of other workers on combined forced and natural convection heat and mass transfer.

An expert rule-based control system is presented which has been applied to a 1 MW coal-fired chain-grate stoker. The goal of the control scheme is to achieve efficient carbon burnout while meeting a specified load demand schedule and simultaneously achieving statutory emissions levels in the face of random disturbances to the feed and quality of both the coal and the air supply.

Experimental measurements have been made of cylinder pressure, crank angle, ignition delay, exhaust-gas temperature and fuel consumption for a 3.9-litre diesel engine operating on air and on mixtures of oxygen, carbon dioxide, argon and helium. The performance of the engine was evaluated over the available load range at speeds of 1600, 1800 and 2000 min(-1), and also under maximum load conditions at various speeds. Results show that the ratio of heat capacities of the gas at the point of fuel injection is the major factor in determining the performance in comparison with natural air operation. A mixture of oxygen, carbon dioxide, argon and helium was prepared which gave an engine performance close to that for operation on air. The measured engine output characteristics did not appear to be influenced by any factor that could unambiguously be attributed to chemical effects of the components of the mixtures.

The combustion of coal on a chain-grate stoker presents a complex problem to the control engineer. Although such rigs can operate continuously with a minimum of supervision emission requirements and the need for greater fuel efficiency are leading to a review of operating practice. The principal problems that are being addressed are the variation in the coal feed quality and distribution, and unscheduled secondary air. The variations that these cause in both the heat and emissions output of the boiler are in need of regulation. In an attempt to bring modern control theory to the problem a new general control system is being designed for chain-grate stoker rigs in a collaborative project between Exeter University and CRE Group Ltd. The control of chain-grate stokers is made difficult by the imbalance between the complex and distributed process on the one hand, and the relatively few measurements available on commercial plants on the other. The control system must reflect this. However it is both expensive and possibly hazardous to carry out this development on-line. Another vehicle on which to develop the control system is required

Collaborative investigators in the UK and in Canada have undertaken both experimental and modelling strategies on nonair diesel engine performance. The results of preliminary simulation strategies reported in this paper indicate that existing air-breathing models can be suitably modified to predict nonair brake performance indicators to within 5% of experimental results. However, nonair ignition delay and heat release models will provide even greater accuracy and the preliminary development of such models is also reported

The control of coal combustion on chain-grate stokers is a complex problem which is of importance to environmental concerns. Producing efficient combustion in spite of material and feed disturbances is a difficult task, allying this to the meeting of stringent emissions criteria even more so. A mathematical model has been used to develop a control scheme, some simulation results of which are shown.

The defence, commercial and scientific communities are all aware of the strategic importance that the oceans hold. Future underwater operations are under evaluation using autonomous ocean-ranging submersibles of the unmanned variety. Such vessels are commonly termed autonomous underwater vehicles (AUVs), and the search for suitable power systems that are able to provide high reliability coupled with long underwater durations has intensified over the last decade. This paper presents a review of those power systems that are under consideration, design and development, mainly for the AUV application. No attempt is made by the authors to directly compare individual systems, as this can only be effectively undertaken once a well-defined vehicle and associated mission profile has been defined.

This paper reports an electrochemical study of local mass transfer behaviour in decaying annular swirl flow. Initially, flow visualisation experiments were conducted to observe the general behaviour of the flow. It was found that the swirl angle decays exponentially along the tube. Measurements of pressure drop across the vaned swirl generators were correlated in terms of the inverse of the square of the tangent of the vane angle and approximately the square of the mean fluid velocity for vane angles of 30° and over. Measurements of the axial distribution of local mass transfer coefficient for the inner rod were carried out using the electrochemical limiting diffusion current technique and results were correlated for each swirl generator, in the Reynolds number range 3300–50000. It was found that the relative enhancement of mass transfer in swirl flow increases as the vane angle increases and Reynolds number decreases.

Density, viscosity, and diffusivity data have been obtained for equimolar ferri and ferro-cyanide (0.01–0.2 M) in 0.5 M aqueous sodium hydroxide solutions in the temperature range 10 to 90°C. For the determination of the diffusivity of the ferricyanide ion, limiting currents were measured by means of a rotating disc electrode, and the apparent diffusivities calculated from these measurements were corrected taking into account the migration term which became significant at high concentration. All data have been presented both graphically and as second order polynominals.