Rainer Haldenwang

Evolution of rheological properties of highly concentrated emulsions with aging —Emulsion-to-suspension transition

The effect of aging on the rheological properties and physical structure of highly concentrated water-in-oil emulsions with dispersed phase of 82–90v% is the subject of this study. It was proven by various experimental techniques that aging leads to the emulsion-to-suspension transition. Significant shift of rheological properties to the solid-like behavior is the result of the emulsions aging, which shows itself as an increase of the storage modules with time as well as Newtonian viscosity measured in the upward sweeping shear rate mode. Comparison of flow curves measured in the upward and downward sweeping shear rate modes shows that the rheopectic effect at low stresses is observed for both fresh and aged emulsions. Viscosity measurements in the downward mode demonstrate transition to the elastic-like behavior at low stresses with appearance of strongly pronounced yield stress. Dependencies of the characteristic rheological parameters on aging have been investigated by using different analytical method...

Optimisation of Pulsed Ultrasonic Velocimetry system and transducer technology for industrial applications.

Pulsed Ultrasonic Velocimetry, commonly referred to as Ultrasonic Velocity Profiling (UVP) in research and engineering applications, is both a method and a device to measure an instantaneous one-dimensional velocity profile in opaque fluids along a measurement axis by using Doppler echography. Studies have suggested that the accuracy of the measured velocity gradient close to wall interfaces need to be improved. The reason for this is due to distortion caused by cavities situated in front of ultrasonic transducers, measurement volumes overlapping wall interfaces, refraction of the ultrasonic wave as well as sound velocity variations (Doppler angle changes). In order to increase the accuracy of velocity data close to wall interfaces and solve previous problems a specially designed delay line transducer was acoustically characterised and evaluated. Velocity profiles measured using the delay line transducer, were initially distorted due to the effect of finite sample volume characteristics and propagation through the delay line material boundary layers. These negative effects were overcome by measuring physical properties of the ultrasonic beam and implementing a newly developed deconvolution procedure. Furthermore, custom velocity estimation algorithms were developed, which improved the time resolution and penetration depth of the UVP system. The optimised UVP system was evaluated and compared to standard transducers in three different straight pipes (inner diameters of 16, 22.5 and 52.8mm). Velocity data obtained using the optimised UVP system showed significant improvement close to wall interfaces where the velocity gradients are high. The new transducer technology and signal processing techniques reduced previously mentioned problems and are now more suitable for industrial process monitoring and control.

Experimental procedure and database for non-Newtonian open channel flow

Unlike Newtonian open channel flow, not much work has been done to study the flow behaviour of non-Newtonian fluids in open channels.A scarcity of water worldwide has forced design engineers to increase the solid concentrations when designing flumes. With this increase in concentration, the fluids become more non-Newtonian in behaviour. Very little data have been available to test some of the design protocols that have been proposed by various authors (Kozicki and Tiu, 1967;Wilson, 1991; De Kee et al., 1990). Limited amount of data have been published by some authors (Coussot, 1994; Naik, 1983) to test their own protocols. Haldenwang (2003) at the Flow Process Research Centre of the Cape Peninsula University of Technology created a large experimental database for non-Newtonian open channel flow. The experiments were carried out in three rectangular tilting flumes of different widths varying from 75 to 300 mm. The tests were conducted on three fluids: bentonite and kaolin suspensions and carboxymethylcellulose solutions, all at various concentrations. Rheological characterisation of the fluids were conducted in an inline tube viscometer with three different diameter tubes. This paper will describe the methodology behind how the data were obtained for the database. It is hoped that the database will be of use to researchers working in the area of non-Newtonian open channel flow.

Experimental database for non-Newtonian flow in four channel shapes

The database for non-Newtonian flow in rectangular open channels developed by the Flow Process Research Centre at the Cape Peninsula University of Technology was recently extended to include the testwork on non-Newtonian flow in open channels of semi-circular, triangular and trapezoidal cross-sections. As for flow in rectangular open channels, the flow of carboxymethylcellulose solutions and aqueous kaolin and bentonite suspensions was investigated in these open channels at angles varying from 1° to 5°. The flow curve data for these three fluids were best represented by the power law, Bingham plastic and Herschel–Bulkley models, respectively. The research methodology in the use of this extended database to study laminar, transitional and turbulent non-Newtonian open channel flows is described. It is hoped that this database will be a useful resource to researchers working in the field of non-Newtonian open channel flow.

Laminar and Turbulent Flow of Non-Newtonian Fluids in Open Channels for Different Cross-Sectional Shapes

AbstractNew models for the prediction of laminar and turbulent flow of non-Newtonian fluids in open channels of different cross-sectional shapes are proposed. These models are compared with three previously published models for laminar flow and five previously published models for turbulent flow using a recently extended experimental database for non-Newtonian flow in open channels of different cross-sectional shapes. Flow of three different fluids (aqueous carboxymethylcellulose solutions and kaolin and bentonite suspensions) was investigated in open channels of four different cross sections (rectangular, semicircular, trapezoidal, and triangular) at slopes varying from 1 to 5°. The new laminar model gave a closer fit to the data than those from the previously published models. However, the presence of the yield stress still presents a problem that makes flow prediction in laminar flow for such fluids not very accurate. The new model for turbulent flow gave the best fit to the flow data compared with the...

Determining the viscous behavior of non-Newtonian fluids in a flume using a laminar sheet flow model and Ultrasonic Velocity Profiling (UVP) system

The flow of non-Newtonian fluids in rectangular open channels has received renewed interest over the past number of years especially as large flumes are being used to transport tailings in countries like Chile. The effect of yield stress on the flow behavior is complex and not yet fully understood. The Ultrasonic Velocity Profiling (UVP) technique has been used to construct velocity profiles of non-Newtonian fluids flowing in a 10 m by 300 mm wide tilting flume. The contour maps were integrated to show that the velocity profiles were indeed correct. The thin film flow models available in the literature have been tested in terms of flow depth and Reynolds number. The measured profiles also show the influence of the side walls on the general flow features as the distance from the centre increases. The results reported herein span the laminar, transition and turbulent flow regions. As far as can be ascertained, it is the first time that this technique has been used to measure velocity profiles in opaque non-Newtonian fluids for open channel flow. It is shown here that, under appropriate conditions, the velocity profile and flow depth can be used to obtain the viscous properties of the fluids tested. Excellent correspondence between the rheological parameters inferred from the velocity profile measurements and that from the tube viscometry was obtained.

Sustainable housing financing model to reduce South Africa housing deficit

Purpose This study aims to identify and establish effective housing financing concepts to be adopted by government in achieving its mandate of providing sustainable affordable housing for the poor to decrease the building of shacks, as well as proposing solutions to the housing deficit in South Africa. A rise in demand and shortage in supply of housing calls for the need to address issues of affordable housing in South Africa, and developing countries in general, to ensure a stable and promising future for poor families. Design/methodology/approach Literature has revealed that the South African government, at all levels, accorded high priority to the provision of low-cost housing. Thus, government has adopted subsidy payment as a method of financing affordable housing to ensure that houses are allocated free to the beneficiaries. This also addresses the historically race-based inequalities of the past, but unfortunately, this has not been fully realised. This study uses a sequential mixed method approach, where private housing developers and general building contractors were the research participants. The qualitative data were analysed using a case-by-case analysis, and quantitative data were analysed using a descriptive statistical technique on SPSS. Findings The results of the qualitative analysis reveal a gross abuse of the housing subsidies system by the beneficiaries of government-funded housing in South Africa. This is evident from illegal sale of the houses below market value. This has led to a continual building of shacks and an increased number of people on the housing waiting list instead of a decrease in the housing deficit. The results from quantitative analysis affirm the use of “Mortgage Payment Subsidies, Mortgage Payment Deductions, Down-Payment Grant and Mortgage Interest Deductions” as viable alternatives to subsidy payment currently in use to finance affordable housing projects by the South African Government. Practical implications At the moment, the focus of the South African National Government is continual provision of free housing to the historically disadvantage citizens, but the housing financing method being used encourages unapproved transfer of ownership in the affordable housing sector. This study thus recommends the use of an all-inclusive housing financing method that requires a monetary contribution from the beneficiaries to enable them take control of the process. Originality/value The relational interface model proposed in this study will reduce pressure on government budgetary provision for housing and guarantee quick return of private developers’ investment in housing. Government must, as a matter of urgency, launch a continuous awareness programme to educate the low-income population on the value and the long-term benefits of the housing.

Construction approaches to enhance sustainability in affordable housing in developing countries

The responsiveness of the construction industry to the preservation of natural resources for the benefits of future generation has been very poor in developing countries. This is unconnected to the demand for sustainable shelters to house the growing population and meeting the demand for supporting infrastructure to provide better living standards for the people. Building energy efficient houses does not only contribute to better living conditions, but also a better environment thereby culminating into creating sustainable communities. The existing literatures reveal the existence of much discussion about sustainable development, but this is not matched with much action. This paper aims to provide a new approach upon which housing development for low and middle income population in developing countries could be constructed to enhance sustainability. The study employs the use of quantitative methods for data gathering and construction professionals within South African construction industry were the research participants. The data were analysed using descriptive statistical techniques. The research highlights four construction methods and factors which affect the construction methods that enhance sustainability in housing. Eliminating material wastage and complexities in housing processes are the core factors which when achieved will reduce construction cost to a minimum, reduce negative impact of construction on the environment while maintaining high quality in the housing constructed.

Flow Rate Measurement of Non-Newtonian Fluids through Sharp Crested Notches

AbstractSharp crested notches, particularly rectangular and V-shaped ones, have been used to measure the flow rate of water in open channels for a long time. However, they have not been used to measure the flow rate of non-Newtonian fluids. The aim of this work is to explore the possibility of extending their range of application to non-Newtonian fluids, especially for rectangular and V-shaped notches. An experimental facility in the flow process research laboratory was used to perform the extensive tests reported herein. The notches and an in-line tube viscometer were calibrated using water. The in-line tube viscometer was used to determine the fluid rheology. Three different types of non-Newtonian fluids [namely, aqueous solution of carboxymethyl cellulose (CMC) solutions and water-based suspensions of kaolin and bentonite] were used as model test fluids. The experimental values of the coefficient of discharge (Cd) were plotted against three different definitions of the Reynolds number denoting differen...

Integration of project management skills to manage a fourth year research project

Civil engineering students at the Cape Peninsula University of Technology generally find the final year research project very daunting. In most cases it is the first time that they are not “learning” passively by sitting in lectures, receiving notes and worked out examples, memorising the material and then writing an examination to demonstrate their “competency”. Suddenly learning comes by doing, and they are faced with the challenge of executing a significant research project. For students who do not have good management skills, this becomes a very difficult task. To address this problem, staff have, over the past decade, integrated project management with the research project to the extent that it has now become one subject with two final year credits. This means that students learn how to use project management skills to manage the research project, which runs over one year. Project management skills integrated with a rigid structure, complemented by lecturer support in a web‐based e‐learning environment, has been developed to assist students in completing the research project. This has proved to be very successful and students have commented that without the newly acquired project management skills, they would not have been able to complete the projects on time. The results indicate that the integration of project management skills can relieve the role reversal entrapment problem. However, interventions to prepare the students more adequately must be considered over the first three years of study. The paper presents the historical background to the problem, an overview of how the revised methodology is being implemented, and it indicates how e‐learning is used to manage the course.