D.A. Paterson

Simulation of flow past a cube in a turbulent boundary layer

This paper considers the flow over a surface-mounted cube placed in a turbulent boundary layer. The flow is considered to be incompressible and one face of the cube is set perpendicular to the approach flow direction. This flow is simulated on computer by the solution of the Reynolds equation and continuity equation with the help of a k−ϵ model of turbulence. Computed predictions are compared with experimental measurements. A very good level of agreement is obtained for mean pressures and velocities in the vicinity of the cube, and adequate agreement is obtained for velocity fluctuations.

Holistic model for atmospheric corrosion: Part 2 - Experimental measurement of deposition of marine salts in a number of long range studies

Abstract This paper is the second in a series looking at understanding the factors controlling and predicting marine aerosol concentration on land. It looks at results from three transects across the Australian continent. In each transect, the airborne salinity was measured, using the wet candle method at distances from 10 m to 40-300 km from the coast. The positions of the transects were selected to give a significant variation in the factors controlling salt production and transport. For example, one transect in South Australia was established where both high whitecap activity is likely to promote salt production and flat terrain and prevailing winds are likely to favour transport. Another, in Queensland, was established where calm seas will limit salt production and very seasonal winds and high relative humidity and rainfall will limit transport. On the basis of this experimental study, the general validity of the fundamental concepts put forward in Part 1 is assessed. Further, the feasibility of building a mathematical model to predict salinity is determined and the main factors causing variations in salinity on land are outlined. The results are then used to assist in the interpretation of previous work in the literature.

Holistic model for atmospheric corrosion Part 6 – From wet aerosol to salt deposit

Abstract This paper is the sixth paper outlining a holistic model of atmospheric corrosion. Previous papers outline how airborne salinity could be estimated at any given location and how the deposition onto a surface could be modelled. This paper investigates the initial reactions of raindrops or deposited marine aerosols on metal surfaces (zinc, galvanised steel, aluminium and gold). It combines short term field exposures with a series of controlled laboratory experiments. Surface changes to the metal upon field exposure are characterised by the nature and distribution of corrosion nodules, oxide films and retained salts. Eleven distinct forms of surface change are observed. The conditions promoting each pattern of surface changes were estimated by comparison with laboratory tests with a variety of deposition modes. Laboratory tests included deposition of saline droplets in three size ranges. A strategy to use the results in a holistic model of corrosion is proposed.

Holistic model for atmospheric corrosion Part 4 – Geographic information system for predicting airborne salinity

Abstract This paper is the fourth in a series of five papers addressing the factors controlling and predicting marine aerosol concentrations on land. It outlines the procedures used to develop a geographic information system (GIS) model of airborne salinity across Australia. The basic mathematical formulae have been presented previously, and this paper outlines how these formulae are applied in a GIS system. While the basic formulae are based on models of the processes controlling the formation and distribution of marine aerosols, some constants have been determined empirically. These constants are established by regression analysis using data derived and presented previously from a long range study of atmospheric salinity levels in a transect across the Australian State of South Australia. The model was then tested with databases of airborne salinity measurements throughout Australia and was shown to possess a high level of accuracy. It was then used to predict the salinity across Australia, with a salinity map of Australia being produced. A number of features of the map are discussed. Lastly, the model is used to illustrate the role of coastal forms in controlling salinity in adjacent regions.

Using wastewater and high-rate algal ponds for nutrient removal and the production of bioenergy and biofuels

This paper projects a positive outcome for large-scale algal biofuel and energy production when wastewater treatment is the primary goal. Such a view arises partly from a recent change in emphasis in wastewater treatment technology, from simply oxidising the organic matter in the waste (i.e. removing the biological oxygen demand) to removing the nutrients - specifically nitrogen and phosphorus - which are the root cause of eutrophication of inland waterways and coastal zones. A growing need for nutrient removal greatly improves the prospects for using new algal ponds in wastewater treatment, since microalgae are particularly efficient in capturing and removing such nutrients. Using a spreadsheet model, four scenarios combining algae biomass production with the making of biodiesel, biogas and other products were assessed for two of Australias largest wastewater treatment plants. The results showed that super critical water reactors and anaerobic digesters could be attractive pathway options, the latter providing significant savings in greenhouse gas emissions. Combining anaerobic digestion with oil extraction and the internal economies derived from cheap land and recycling of water and nutrients on-site could allow algal oil to be produced for less than US

Computation of rain falling on a tall rectangular building

1 per litre.

Computation of wind flow over topography

A computational study has been conducted to evaluate raindrop trajectories, rain intensities and angles of impact of raindrops on various surfaces of a CAARC standard building. In the first stage, the pressure distribution around the building is calculated from a 3-D computational fluid dynamics (CFD) program. The surface mean pressures are then compared with those obtained from a wind tunnel investigation. In the second stage, raindrops of various sizes are introduced into the airstream above and upwind of the building and allowed to hit the building. A Monte-Carlo simulation, based on the computed turbulence timescale, is used to account for turbulent buffeting of raindrops by wind gusts. The resulting rain impact data are presented here.

Experimental studies of salts removal from metal surfaces by wind and rain

Abstract Computer models of wind flow over topography are run to establish appropriate values of Topographic Multipliers for both gust wind speeds and mean wind speeds at and above ground level. The work was initially undertaken to test the rules in the Australian Standard [1]. It is found that the rules are too lax for peak multipliers for two-dimensional escarpments, embankments and ridges in neutrally stratified boundary layers.

Experimental studies on dependence of surface temperatures of exposed metal plates on environmental parameters

Abstract This paper outlines an experimental programme aimed at determining the mechanisms of salt removal from metallic surfaces by wind and rain. The paper provides data and process understanding that will be integrated into a holistic model of atmospheric corrosion. Experiments are reported in which fine salt crystals were deposited either wet (as fine droplets of seawater) or dry onto a surface. The surfaces were then placed in a wind tunnel and salt loss was determined as a function of wind speed. In another experiment, the motion of simulated raindrops falling onto metal plates was determined. Finally, in a third series of experiments, video footage of simulated rain on metal surfaces was studied in order to determine both the subsequent motion of rain and its cleaning efficiency. The efficiency of surface cleaning by wind and rain, as determined by these experiments, was then related to Australian climatic conditions. A future paper will present mathematical models of the processes defined in this paper.

AIRLIFE - TOWARDS A FLEET MANAGEMENT TOOL FOR CORROSION DAMAGE

Abstract The present study reports on an investigation into the dependence of the surface temperature of metal plates on environmental parameters. Monitored plates were exposed at three locations (one coastal and two inland) in southern Australia. The following parameters were monitored: surface temperature, surface wetness, wind speed, ambient relative humidity, air temperature and lifting condensation level. (The lifting condensation level is the height at which a parcel of air rising from the ground will reach saturation.) An analysis was undertaken of the temperature difference between the exposed plate surfaces and ambient air. It was found that the maximum temperature difference during the day depended on season, wind speed and, to a lesser extent, the lifting condensation level. The maximum undercooling during the night showed a relatively limited range and a weak dependence on wind speed. The rate of rise in temperature difference after sunrise was found to be only slightly dependent on season, but highly dependent on whether the surface was wet or dry. If the surface was dry, the rise in temperature difference depended on the wind speed and lifting condensation level. The relevance of these findings to moisture formation and evaporation from surfaces, and thus to corrosion processes, is discussed.