Steam system network synthesis using process integration

Steam boilers are used to generate steam in order to meet cold process heat requirements. The most common heat exchanger network layout associated with the boiler is a completely parallel design. This observation suggests that the flowrate of steam needed for the system can be reduced, while maintaining the required duty, simply by changing the layout of the network. Phase change of saturated steam to saturated liquid plays a vital role in the targeting method as well as the design of the network layout. A hybrid graphical and mathematical technique for targeting and network synthesis is presented. The main objective of the technique is to reduce steam flowrate without compromising duty requirements of the process heat exchangers. In order to assess the advantage of a hybrid technique, a case study is used where steam savings of 29.6% is obtained. A complete mathematical technique to demonstrate the advantage of the graphical targeting concept in solution time improvement is further presented.Dissertation (MEng)--University of Pretoria, 2008.Chemical Engineeringunrestricte

Development of the learning programme management and evaluation scale for the South African skills development context

Research purpose: The present study developed and tested the construct validity and reliability of the learning programme management and evaluation (LPME) scale. Motivation for the study: The LPME scale was developed to measure and enhance the effectiveness of the management and evaluation of occupational learning programmes in the South African skills development context. Currently no such instrument exists in the South African skills development context; hence there is a need for it. Research design, approach and method: This study followed a quantitative, non-experimental, cross-sectional design using primary data. The LPME scale was administered to a sample of 652 skills development practitioners and learners or apprentices drawn from six organisations representing at least five economic sectors in South Africa. Data were analysed using SPSS and Rasch modelling to test the validity and reliability of the new scale. Main findings: The findings show that the LPME scale is a valid and reliable 11-dimensional measure comprising 81 items. Practical/managerial implications: In view of the seriousness of the skills shortage challenge facing South Africa, this study provides a solid base upon which skills development practitioners can effectively manage and evaluate occupational learning programmes. Furthermore, the newly developed LPME scale provides a basis for further human resource development research in the quest for a solution to the skills shortage challenge. Contribution/value-add: This study contributes by developing a new scale and testing its validity and reliability. As a valid and reliable measure, the LPME scale can be applied with confidence in various South African workplaces.Industrial and Organisational Psycholog

Degradation of insecticides used for indoor spraying in malaria control and possible solutions

BACKGROUND: The insecticide dichloro-diphenyl-trichloroethane (DDT) is widely used in indoor residual spraying (IRS) for malaria control owing to its longer residual efficacy in the field compared to other World Health Organization (WHO) alternatives. Suitable stabilization to render these alternative insecticides longer lasting could provide a less controversial and more acceptable and effective alternative insecticide formulations than DDT. METHODS: This study sought to investigate the reasons behind the often reported longer lasting behaviour of DDT by exposing all the WHO approved insecticides to high temperature, high humidity and ultra-violet light. Interactions between the insecticides and some mineral powders in the presence of an aqueous medium were also tested. Simple insecticidal paints were made using slurries of these mineral powders whilst some insecticides were dispersed into a conventional acrylic paint binder. These formulations were then spray painted on neat and manure coated mud plaques, representative of the material typically used in rural mud houses, at twice the upper limit of the WHO recommended dosage range. DDT was applied directly onto mud plaques at four times the WHO recommended concentration and on manure plaques at twice WHO recommended concentration. All plaques were subjected to accelerated ageing conditions of 40°C and a relative humidity of 90%. RESULTS: The pyrethroids insecticides outperformed the carbamates and DDT in the accelerated ageing tests. Thus UV exposure, high temperature oxidation and high humidity per se were ruled out as the main causes of failure of the alternative insecticides. Gas chromatography (GC) spectrograms showed that phosphogypsum stabilised the insecticides the most against alkaline degradation (i.e., hydrolysis). Bioassay testing showed that the period of efficacy of some of these formulations was comparable to that of DDT when sprayed on mud surfaces or cattle manure coated surfaces. CONCLUSIONS: Bioassay experiments indicated that incorporating insecticides into a conventional paint binder or adsorbing them onto phosphogypsum can provide for extended effective life spans that compare favourably with DDT’s performance under accelerated ageing conditions. Best results were obtained with propoxur in standard acrylic emulsion paint. Similarly, insecticides adsorbed on phosphogypsum and sprayed on cattle manure coated surfaces provided superior lifespans compared with DDT sprayed directly on a similar surface.The Bill & Melinda Gates Foundation through the Grand Challenges Exploration Initiative.http://www.malariajournal.com

Degradation of insecticides used for indoor spraying in malaria control and possible solutions

BACKGROUND: The insecticide dichloro-diphenyl-trichloroethane (DDT) is widely used in indoor residual spraying (IRS) for malaria control owing to its longer residual efficacy in the field compared to other World Health Organization (WHO) alternatives. Suitable stabilization to render these alternative insecticides longer lasting could provide a less controversial and more acceptable and effective alternative insecticide formulations than DDT. METHODS: This study sought to investigate the reasons behind the often reported longer lasting behaviour of DDT by exposing all the WHO approved insecticides to high temperature, high humidity and ultra-violet light. Interactions between the insecticides and some mineral powders in the presence of an aqueous medium were also tested. Simple insecticidal paints were made using slurries of these mineral powders whilst some insecticides were dispersed into a conventional acrylic paint binder. These formulations were then spray painted on neat and manure coated mud plaques, representative of the material typically used in rural mud houses, at twice the upper limit of the WHO recommended dosage range. DDT was applied directly onto mud plaques at four times the WHO recommended concentration and on manure plaques at twice WHO recommended concentration. All plaques were subjected to accelerated ageing conditions of 40°C and a relative humidity of 90%. RESULTS: The pyrethroids insecticides outperformed the carbamates and DDT in the accelerated ageing tests. Thus UV exposure, high temperature oxidation and high humidity per se were ruled out as the main causes of failure of the alternative insecticides. Gas chromatography (GC) spectrograms showed that phosphogypsum stabilised the insecticides the most against alkaline degradation (i.e., hydrolysis). Bioassay testing showed that the period of efficacy of some of these formulations was comparable to that of DDT when sprayed on mud surfaces or cattle manure coated surfaces. CONCLUSIONS: Bioassay experiments indicated that incorporating insecticides into a conventional paint binder or adsorbing them onto phosphogypsum can provide for extended effective life spans that compare favourably with DDT’s performance under accelerated ageing conditions. Best results were obtained with propoxur in standard acrylic emulsion paint. Similarly, insecticides adsorbed on phosphogypsum and sprayed on cattle manure coated surfaces provided superior lifespans compared with DDT sprayed directly on a similar surface.The Bill & Melinda Gates Foundation through the Grand Challenges Exploration Initiative.http://www.malariajournal.com

n Histories-, argeologiese ondersoek na die funksies van die stadspoort gedurende die Yster II-typerk met spesifieke verwysing na Khirbat Al-Mudaiyina

Verhandeling (B.D.) -- Universiteit van Stellenbosch, 1997.Full text to be digitised and attached to bibliographic record