Engineering

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A flux-correct Green element model of quasi three-dimensional multiaquifer flow.
(American Geophysical Union, 2000-12) Taigbenu, A.E.; Onyejekwe, Okey O.
Transient flow in multiply layered aquifers, separated by connecting layers of aquitards which provide hydraulic interactions between the aquifers, is solved by the Green element method (GEM) in a manner that reveals one of its strengths of being able to correctly model the leakage flux without resorting to adjusting the grid representing the one-dimensional (l-D) flow in the aquitards, as done in the finite element method (FEM). The hydraulic approach of approximating the flow is adopted so that flow in the aquifer takes place in two dimensions and that in the aquitards takes place in the one-dimensional vertical direction. The 1-D Green element (GE) model earlier developed for transient diffusion and referred to as the transient GE (TGE) formulation [Taigbenu and Onyejekwe, 1999] is used in modeling the flow in the aquitards, while the 2-D GE model developed for linear and nonlinear transient diffusion [Taigbenu and Onyejekwe, 1998] is used for calculating the flows in the confined and unconfined aquifers. Both models are coupled to solve regional flow problems in multiaquifer systems of arbitrary geometry which receive point and distributed recharge of arbitrary strengths. The solution procedure, which is iterative, provides information on the hydraulic heads and fluxes in the aquifers and aquitards at various specified times. Because GEM is founded on the singular integral theory, singularities that arise from water abstractions at wells (point recharge) are naturally captured in the singular Green's function, thereby making it possible to use a more coarse grid for problems in which there exist active wells. Furthermore, the implementation procedure of GEM achieves sparsity of the coefficient matrix so that less amount of computing resources is required for its decomposition. The superiority of the current approach over FEM in predicting the leakage flux through the aquitards and achieving comparable accuracy for well problems with coarser grid is demonstrated
Scheduling linearly deteriorating jobs on parallel machines: a simulated annealing approach
(2001) Hindi, K.S.; Mhlanga, S.
Scheduling deteriorating jobs on parallel machines is an NP-hard problem, for which heuristics would be the ®rst solution option. Two variants of linearly deteriorating jobs are considered. The ®rst is that with simple linear deterioration, i.e. where there is a deterioration rate only, which is meaningful only if the jobs are assumed to be available at a positive time t0 . In the second variant, there is a basic processing time and a deterioration rate and all jobs are available at time t ˆ 0. In both cases, we seek to minimize the makespan. Starting from simple heuristics, both steepest descent search and simulated annealing are designed and implemented to arrive at optimal or near-optimal solutions. Computational results for randomly generated problem instances with diåerent job/machine combinations are pre sented.
A postal survey of effluent generation and disposal in the Zimbabwean dairy industry
(Water research commision, 2002-04-02) Masiiwa, Husiel; Ikhu-Omoregbe, Daniel IO
Water is a major utility in the dairy industry, which results in significant effluent volumes being generated, hence the challenge of its disposal cannot be ignored. In Zimbabwe, industry generally is not made to pay the full cost of managing industrial effluents, which inadvertently encourages environmental pollution. This paper presents the results of a postal survey of effluent generation and disposal by the dairy industry. A total of 30 questionnaires were sent out to various milk processors around the country out of which 15 were returned. The useful respondents receive and process 56% of the total milk produced in the country. The data obtained indicated that while some of the plants discharge their effluents into the municipal sewers, others discharge theirs by means of land irrigation. This latter method has the consequence of groundwater pollution. Respondents’ knowledge of effluent characteristics was generally low, which is not surprising as there are no stringent penalties for polluting.
A time-dependent Green’s function-based model for stream-unconfined aquifer flows
(Water research commision, 2004-07-01) Taigbenu, A.E.
A numerical formulation that is based on the Green element method (GEM), which incorporates a time-dependent Green’s function, is used to solve transient two-dimensional flows of stream-unconfined aquifer interaction. The Green’s function comes from the fundamental solution to the linear diffusion differential operator in two spatial dimensions. In classical boundary element applications, this Green’s function has found use primarily in linear heat transfer and flow problems; its use here for the nonlinear stream-unconfined aquifer flow problem represents the computational flexibility that is achieved with a Green element sense of implementing the singular integral theory. The nonlinear discretised element equations obtained from numerical calculations are linearised by the Picard and Newton-Raphson methods, while the global coefficient matrix, which is banded and sparse, is readily amenable to matrix solution routines. Using four numerical examples, the accuracy of the current formulation is assessed as against an earlier one that incorporates the Logarithmic fundamental solution. It is observed that comparable accuracy is achieved between both formulations, indicating that the current formulation is a viable numerical solution strategy for the stream-aquifer flow problem.
Performance analysis of immigration operation by discrete event modelling and simulation
(2009) Gandure, J.; Mhlanga, S.
Discrete event modelling and simulation were used to analyse the performance of immigration operation in Botswana. The relationships between length of queues of immigrants, queuing time, service time and engagement of duty officer were investigated. Data collected by direct observation and clock-timing of processing immigrant request at an inland office on a normal working day was used to determine whether to increase or reduce the number of serving officers to balance the operations. The findings indicated that the system of operation was balanced or fairly matched by 75 % utilization of the officer, average immigrant queuing time of 4.2 min, and required no changes. The pilot study could be replicated at other boarder posts and airports prior to the expected influx of tourists during the 2010 World Cup Football Competition in South Africa.
Air pollution control techniques for the cement manufacturing industry: A case study for Zimbabbwe
(2012) Zimwara, D.; Mugwagwa, L.; Chikowore, T.R.
Technological advancement has resulted in cement making companies being able to produce higher volumes compared to the past. However the higher production levels have also been largely labelled as the leading cause of pollution. The main sources of air pollution in the industry include excavation activities, dumps, tips, conveyer belts, crushing mills and kiln emissions. Harnessing appropriate technology for use in the cement industry could go a long way towards minimising on-site wastes and pollution. This review examines various options in practice for reducing pollution at cement manufacturing companies, which help ensure legislative compliance. By adoption of appropriate technology and computer modelling, industry will not only reduce production waste but also comply with legislation to do with environmental protection. The paper examines certain methods of pollution control used for air and looks at how computer modelling can be adopted for the classification, quantification and control of particulate matter; and how efficient energy use can contribute to better air quality. An analysis of gas stack emissions was done for a cement manufacturing company in Zimbabwe where compliance was investigated. Emissions samples were randomly selected at various points within the company and concentration of various emission constituents were analysed.
Implementation Of A Computerized Balanced Scorecard (BSC) System In A Manufacturing Organisation In Zimbabwe
(2013) Gwangwava, N.; Mhlanga, S.; Goriwondo, W.
This modern era’s high technological improvements present manufacturers and other organizations with a plethora of Management Information Systems (MISs) which makes them face challenges when choosing a corporate information system. High initial investment in setting up the information systems make it very difficult for companies to adopt new systems as they come into market before realizing a reasonable return from the previous system. In line with these concerns, a methodology for building a Balanced Scorecard module as a strategic management platform that can be integrated smoothly into already existing information system such as MRP/ERP is presented. The paper uses a case study of a manufacturing company based in Zimbabwe. Various manufacturing based metrics are reviewed with the main intent of showing how these can be tracked in a computerized platform. Sample data extracted from the production system is used to test the built system. The paper shows a methodology for software design, setting up and adopting a BSC system. The proposed approach is used to design a computerized BSC system for the case study company, which incorporates a BSC dashboard for the four main perspectives derived from various operational metrics.
Cost of Quality as a Driver for Continuous Improvement - Case Study – Company X
(2013) Zimwara, D.; Mugwagwa, L.; Maringa, D.; Mnkandla, A.; Mugwagwa, L.; Ngwarati, T.T.
In the manufacturing, metal casting industry is one of the oldest basic principal and most important industries. The casting process is hindered by the occurrence of various defects. High casting reject levels and customer returns have a considerable adverse effect on productivity, delivery performance, customer satisfaction and employee morale. In addition excessive rejection reduces yield, wastes valuable raw materials and involves management time in problem solving. All foundry processes generate a certain level of rejection that is closely related to the type of casting, the processes used and the equipment available. This paper seeks to establish the extent to which cost of quality can impact on continuous improvement of the products and the relationship with the customers of the organization. To determine the cost of quality (COQ) at casting company X, the researchers used existing company records, publications and historical evidence of the company. The researchers utilized techniques such as, bar charts and tables in presenting and interpreting data. The above techniques have the ability to provide methods for collecting, presenting, and analysis and meaningfully interpret data. The research findings estimated the COQ to be 6.6% of sales revenue.
Design of a Dual Operating Mode Sheet Folding Machine.
(2013) Gwangwava, N.; Mugwagwa, L.; Ngoma, S.
A sheet folding machine that can be operated through hydraulics by two hydraulic cylinders or manually (with the cylinders disengaged) was designed. The design need emanated from the strained national electrical grid system that has recently seen industrialists and households in Zimbabwe experiencing major power cuts. The machine enables manufacturers to shedule heavier jobs during periods when power supply is up and lighter jobs during power cut periods hence run their workshops throughout the daily production shifts. The two hydraulic cylinders can be disengaged from the machine’s folding beam so that manual operation can be done through a manual clamping lever system. The folding force at full capacity is 294.6 KN (29.46 Ton), total bending length of 1.8 m and working height of 1 m. The folding force decreases significantly in manual operating mode to 500 N, considering that on average an operate can manually exert that force. A student version of Simulation X 3.5 was used to simulate the hydraulic operation of the machine
Soft Computing Methods for Predicting Environmental Quality: A Case Study of the Zimbabwe Sugar Processing Industry
(2013) Zimwara, D.; Mugwagwa, L.; Nherera, K.
Sugarcane growing and processing is associated with environmental degradation and pollution. The impact that sugar processing industries have on the environment affects the ecosystem. Methods of soft computing that is fuzzy logic, neural networks, and genetic algorithms can be adopted for environmental protection, particularly in the developing countries. Soft computing techniques, particularly neural networks and fuzzy logic, have been used to predict and sometimes control air quality. This paper looks at how fuzzy logic can be adopted for predicting air quality. The common environmental impacts associated with sugarcane production are water and air pollution. This paper focuses on air pollution. The major waste streams are identified and the extent of air pollution is predicted by classifying the air quality as poor, ordinary, very good, and excellent. This paper presents a fuzzy rule base that can be used to classify the pollutants and predict the air quality based on the amount of the specific pollutant in the air. The Mamdani fuzzy inference system is used to build the rule base, with the membership functions being non-intersecting and triangular. The adoption of fuzzy logic techniques will help sugar processing industries to be aware of the impact their operations have on the environment.
Academic staff development strategies in engineering fields of study: case study of Zimbabwe
(2013-06) Mhlanga, Samson; Matope, Stephen; Mugwagwa, Lameck; Phuthi, Nduduzo; Moyo, Vincent S.
Higher education is the basic instrument of economic growth and technological advancement in any society. The economic meltdown in Zimbabwe which climaxed 2008 with an inflation level of 231million % exacerbated the brain drain. After the economic meltdown, Zimbabwe is in the process of rebuilding the quality of staff and the staffing levels in its higher education institutions. The challenge has been the decision on the mode of study: whether to go via taught masters or masters by research; where to allow the faculty members to study: in the region, or beyond; on a fulltime or on a part-time basis or on a split-site basis. These challenges have been due to the need to have a quick but quality programme of staff development, while maximising on the resources available for staff development. A survey was undertaken of the engineering related departments in Zimbabwe universities focusing on the existing staffing levels, their qualifications, current numbers undergoing study and their levels. The challenges faced by each institution from the administrative side and from the staff side are summarised. Recommendations on staff development strategies are given in conclusion.
Academic staff development strategies in engineering fields of study: case study of Zimbabwe
(2013-06) Mhlanga, S.; Matope, S.; Mugwagwa, L.; Phuthi, N.; Moyo, V. S.
Higher education is the basic instrument of economic growth and technological advancement in any society. The economic meltdown in Zimbabwe which climaxed 2008 with an inflation level of 231million % exacerbated the brain drain. After the economic meltdown, Zimbabwe is in the process of rebuilding the quality of staff and the staffing levels in its higher education institutions. The challenge has been the decision on the mode of study: whether to go via taught masters or master's by research; where to allow the faculty members to study: in the region, or beyond; on a fulltime or on a part-time basis or on a split-site basis. These challenges have been due to the need to have a quick but quality programme of staff development, while maximising on the resources available for staff development. A survey was undertaken of the engineering related departments in Zimbabwe universities focusing on the existing staffing levels, their qualifications, current numbers undergoing study and their levels. The challenges faced by each institution from the administrative side and from the staff side are summarised. Recommendations on staff development strategies are given in conclusion.
INVESTIGATION OF THE EFFECTS OF LUBRICANT FAT CONTENT ON DRAWN COPPER WIRES
(2013-07) Chiduwa,A.C.; Nyanga, L.; Mhlanga, S.; van der Merwe, A.F.; Kanyemba, G.
The Lean Manufacturing goal of reducing waste and increasing productivity has made it a necessity to produce good quality products in manufacturing industries at a low cost. In the cable manufacturing companies this can be achieved by optimising the wire drawing process. One way to meet the desired quality of the drawn wires is to improve lubricant efficiency through installation of an automatic, continuous lubricant fat content control system on the drawing machine. The paper shows a method of finding the optimum lubricant concentration for producing good quality copper wires using Taguchi experiments. Taguchi experiments are employed to analyse the effects of different lubricant fat content levels on the tensile strength and lubricant temperature. The results from the experiments indicated that the tensile strength of the wire is affected by low lubricant fat content. The lower the lubricant fat content: the lower the tensile strength drawing lubricant resulting in numerous wire breakages that affect the quality of the final product, namely the cable
Understanding the Poor Performance of Urban Sewerage Systems:A Case of Coldstream High Density Suburbs, Chinhoyi, Zimbabwe
(UPDR, 2013-09) Chinyama, Annatoria; Toma, Tendai
The population of Coldstream High Density Suburbs in Chinhoyi, Zimbabwe is increasing and the sewerage system shows signs of poor performance. The frequency of reported sewerage system blockages in the suburb increased from 43 per month to 65 per month between April 2012 and March 2013. The suburb has also been experiencing water shortages. An increasing population and low water supply versus overflowing sewage is a potential health risk. The main objective of this paper was to investigate the causes of the sewer system poor performance. This was achieved by assessing the sewer system infrastructure as well as the operation of the system. The impact of the behaviour of residents on the performance of the system was also discussed. The main components of the infrastructure (manholes and sewers) were physically checked for soundness. The operation of the system was assessed by a hydraulic analysis of discharge, depth of flow and velocity of flow in the sewers. Questionnaires were used to investigate the impact of the behaviour of residents on the performance of the sewer system. It was found that 4% of the components of the sewer system infrastructure were below standard and the collector main sewer was the one mainly affected. 68% of the sewers along the collector main had velocity of flow below 0.6m/s and all the sewers had depth of flow below 50%. Of the residents interviewed, 90% dumped solid wastes in the sewers and 43% did so because they were unaware of the impact. It was concluded that the sewer system failed to meet standard because the sewer system fails to self-cleanse the solid waste dumped by residents in the sewers due to water shortages. It is recommended that the municipality raises awareness among residents and some of the infrastructure should be rehabilitated.
Recovery of Lead from Lead Laden Cupels by a Simultaneous Leaching and Electrowinning Process in a Methanesulphonic acid bath
(Sphinx Knowledge House, 2014) Mangunda, Cledwyn T.; Kuipa, Olga; Sithole, Tapuwa R.; Kuipa, Pardon K.
Cupels are generated by mines during the fire assaying of precious group metals. The cupels contain lead which is a known environmental hazard hence the need to recover it. This work illustrates how leaching and electrowinning processes can be combined to produce a hybrid lead recovery process. Bench scale tests were conducted for the hybrid leaching and electro winning process using Methane Sulfonic Acid (MSA) as a leaching solvent at a concentration of 200g MSA per litre of water. A glass electrowinning cell fitted with a 9cm × 4cm pure lead cathode and 9cm × 4cm graphite anode with inter electrode gap of 15cm and a magnetic stirrer bar was used. Lead laden cupels (containing 30g lead) were subjected to simultaneous leaching and electrowinning and lead recovery after a period of 80 minutes was found to be 98%. The hybrid process was found to require about 20% less solvent than that required for the convectional leaching process which requires multiple stages to reduce the concentration of the solute in the raffinate to the same extent.
Imaging Ellipsometry Study on the effect of Electrolyte on the drainage of an Aqueous Film trapped between a Plane Hydrophilic Silica Surface and an approaching Organic droplet
(Sadguru publications, 2014) Kuipa, Olga; Kuipa, Pardon K.
An imaging ellipsometer is used to study the drainage of an aqueous film trapped between a hydrophilic silica equilateral prism surface and a heptane or butylacetate droplet. The interfacial droplet profile on approach to the hydrophilic silica surface is such that the droplet is dimpled at its center with the periphery of the droplet (the barrier ring) being the region of closest approach to the hydrophilic silica surface. The time it takes for these drops to either achieve an equilibrium film thickness at the barrier ring or to coalesce with the macroscopic hydrophilic silica surface was experimentally determined; drainage time increases whilst equilibrium film thickness decreases with increasing salt concentration in the continuous phase. The increase in drainage time is attributed to hindered drainage of the aqueous film due probably to an increase in the aqueous film viscosity, which should translate into a decrease in the film elasticity. Compression of the double layer may also qualitatively explain the observed decrease in equilibrium film thickness at the barrier ring as the salt concentration increases. When aluminum chloride is used as the electrolyte the equilibrium film thickness is relatively constant (around 90 ± 10 nm) for the range of concentrations studied. This may be due to the fact that the aluminum ion has a valence of three and may screen electrostatic interactions between the oil droplet and the hydrophilic silica surface at relatively lower aluminum chloride concentrations.
Towards the implementation of e-manufacturing: design of an automatic tea drying control system.
(2014) Mabvuu, N.; Nyanga, L.; van der Merwe, A. F.; Matope, S.; Mhlanga, S.
Many of the production costs for producing tea are attributable to the process of drying the tea. E-manufacturing can assist companies to reduce these production costs by making crucial information available to decision-makers so that they can make informed decisions. This paper presents an application of e-manufacturing to the design of an automatic tea drying control system. This control system will ensure that the multiple drying parameters such as temperature, dryer-exit tea moisture content, and fuel consumption are maintained at optimal states during the course of the drying of tea. The additional aim of this system is to balance the cost of production and the quality of the final product. Using the Guggenheim-Anderson-De Boer (GAB) model, the optimum drying temperature was found to be 100-110°C, while maintaining a dryer-exit tea moisture content of 3 to 3.12 per cent, at a drying rate of 3 per cent per minute. A Barix control application to control the system’s activities, using the web user interface (WUI), was also developed.
Removal of Cr(VI) from Aqueous Solutions Using Powder of Potato Peelings as a Low Cost Sorbent
(Hindawi Publishing Corporation, 2014-06) Mutongo, F.; Kuipa, Olga; Kuipa, Pardon K.
Potato peels which are a low cost, renewable agroindustry by-product were used for the removal of hexavalent chromium from aqueous effluents. Batch experiments were carried out with an artificial effluent comprising of potassium dichromate in deionised water. The effects of the initial hexavalent chromium concentration, dose of biosorbent, and removal kinetics were explored. An adsorbent dosage of 4 g/L was effective in complete removal of the metal ion, at pH 2.5, in 48 minutes. The kinetic process of Cr(VI) adsorption onto potato peel powder was tested by applying pseudo-first-order and pseudo-second-order models as well as the Elovich kinetic equation to correlate the experimental data and to determine the kinetic parameters. The adsorption data were correlated by the Langmuir and Freundlich isotherms. A maximum monolayer adsorption capacity of 3.28 mg/g was calculated using the Langmuir adsorption isotherm, suggesting a functional group limited adsorption process. The results confirmed that potato peels are an effective biosorbent for the removal of hexavalent chromium from effluent.
Development of a condition based maintenance system for a sugar producing company
(2014-07-14) Chindondondo, B.; Nyanga, L.; Merwe, A. V.; Mupinga, T.; Mhlanga, S.
With globalisation taking centre stage in almost every market; traditionally monopolistic manufacturing companies in Zimbabwe are struggling to compete with international companies whose operations are optimised. This paper focuses on maintenance practises of a Zimbabwean sugar manufacturer with an aim to improve the company’s asset care plans. The company’s current maintenance philosophy and its shortcomings on certain equipment in the plant were identified together with the associated annual maintenance costs. A Pareto analysis on the equipment’s breakdown history was used to determine the conditions that can be monitored using Condition Based Maintenance (CBM); and experiments to establish the feasibility of monitoring these conditions were done. The paper then recommends and proposes a CBM system replete with its three main elements of data acquisition, data processing and maintenance decision making to reduce breakdowns on the subject equipment by at most 76%.
Treatment of Low Turbidity Water Using Poly-Aluminium Chloride (PAC) and Recycled Sludge: Case study Chinhoyi
(Zimbabwe Journal of Science & Technology, 2015) Jowa, Taurai; Mguni, Liberty L
Coagulation of low turbidity water using PAC and recycled sludge was studied using a bench scale sedimentation jar test operated at ambient temperature and pressure. Tests were done on low turbidity raw water samples from the river Manyame in Chinhoyi. The coagulants tested were aluminium sulphate (control), PAC and recycled sludge. The effects of the coagulants on the final physical properties of treated water (pH, conductivity, floc quality and most importantly turbidity) were analysed. It was observed that for 60 mg/L dosages, final pH was in the 8.2-8.4 range with an average of 0.24 unit change for PAC and 0.12 for aluminium sulphate, changes in conductivity were less than 20 μScm-1for both coagulants and PAC was more efficient in turbidity removal at all dosages. The higher efficiencies of PAC where due to the poly-ions formed during hydrolysis. An improvement to the coagulating system was attempted by using settled sludge from clarifiers. At a constant 30 mg/L PAC dosage, the maximum turbidity removal efficiency, 73%, was observed at 6 ml sludge dosage.

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