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A heat transfer correlation of flow boiling in micro-finned helically coiled tube

  • Authors: Cui, Wenzhi , Li, Longjian , Xin, Ming-dao , Jen, Tien-Chien , Chen, Qinghua , Liao, Quan
  • Date: 2006
  • Subjects: Convective boiling , Heat transfer , Helically coiled tubes , Nucleate boiling
  • Type: Article
  • Identifier: uj:5275 , http://hdl.handle.net/10210/14944
  • Description: Two main mechanisms, nucleate boiling and convective boiling, are widely accepted for in-tube flow boiling. Since the active nuclei on the heated wall are dominant for nucleate boiling and flow pattern governs the convective boiling, the heat transfer coefficient is strongly influenced by the wall heat flux, mass flux and vapor quality, respectively. In practical industrial applications, for example, the evaporators in refrigeration, forced convective evaporation is the dominant process and high heat transfer efficiency can be obtained under smaller temperature difference between wall and liquid. Therefore, it is of importance to develop a correlation of convective boiling heat transfer with a good accuracy. In this paper, a new kind of micro-finned helically coiled tube was developed and the flow boiling heat transfer characteristics were experimentally studied with R134a. Based on the analysis of the mechanisms of flow boiling, heat transfer correlations of the specific micro-finned helically coiled tubes are obtained.
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Alkaline leaching of nickel bearing ammonium jarosite precipitate using KOH, NaOH and NH4OH in the presence of EDTA and Na2S

An ANN approach for the prediction of uniaxial compressive strength, of some sedimentary and igneous rocks in Eastern KwaZulu-Natal

  • Authors: Ferentinou, Maria , Muhammad, Fakir
  • Date: 2017
  • Subjects: Uniaxial Compressive Strength , Point Load Index , Brazilian Tensile Strength
  • Language: English
  • Type: Conference proceedings
  • Identifier: http://hdl.handle.net/10210/240483 , uj:24738 , Citation: Ferentinou, M. & Muhammad, F. 2017. An ANN approach for the prediction of uniaxial compressive strength, of some sedimentary and igneous rocks in Eastern KwaZulu-Natal.
  • Description: Abstract: The Uniaxial Compressive Strength (UCS) of intact rocks is an essential index of strength in rock engineering. Laboratory based direct compressive strength estimation may be problematic, as obtaining fresh samples is not always feasible. Thus, the aim of indirect methods index test such as point load index test, and empirical correlations with UCS of indexes like the Brazilian indirect tensile strength test, serve as an alternative for many geotechnical engineering projects. The aim of this paper is to propose a relationship between UCS and indirect tests or indexes for some sedimentary and igneous rocks in KwaZulu-Natal using the technology of artificial intelligence. These tests include the point load index (Is (50)) test and Brazilian Tensile Strength (σt), test. Block samples were collected in KwaZulu Natal, among these include sedimentary rocks (sandstones, siltstone, tillite) and igneous rocks (granitoids and dolerite). A back propagation artificial neural network was developed and trained in order to predict UCS. The input parameters were unit weight γ, (Is (50)), (σt), and lithology. The lithology was introduced in the neural network as a qualitative input parameter, in order to indirectly incorporate in the model the mineralogical content. Training results returned, R value of 0.99% for the training set, and R = 0.92% for the test set, which is conveying to the conclusion that the approach is valid and could be used, as an alternative indirect approach to UCS estimation.
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An experiment study of flow pattern and pressure drop for flow boiling inside microfinned helically coiled tube

  • Authors: Cui, Wenzhi , Li, Longjian , Xin, Ming-dao , Jen, Tien-Chien , Liao, Quan , Chen, Qinghua
  • Date: 2008
  • Subjects: Flow boiling , Pressure drop , Helically coiled tubes , Microfin tubes , Flow patterns , Finned tubes
  • Type: Article
  • Identifier: uj:5278 , http://hdl.handle.net/10210/14947
  • Description: In this paper, flow patterns and their transitions for refrigerant R134a boiling in a microfinned helically coiled tube are experimentally observed and analyzed. All the flow patterns occurred in the test can be divided into three dominant regimes, i.e., stratified-wavy flow, intermittent flow and annular flow. Experimental data are plotted in two kinds of flow maps, i.e., Taitel and Dukler flow map and mass flux versus vapor quality flow map. The transitions between various flow regimes and the differences from that in smooth straight tube have also been discussed. Martinelli parameter can be used to indicate the transition from intermittent flow to annular flow. The transition from stratified-wavy flow to annular or intermittent flow is identified in the vapor quality versus mass flux flow map. The flow regime is always in stratified-wavy flow for a mass flux less than 100 kg/m2 s. The two-phase frictional pressure drop characteristics in the test tube are also experimentally studied. The two-phase frictional multiplier data can be well correlated by Lockhart–Martinelli parameter. Considering the corresponding flow regimes, i.e., stratified and annular flow, two frictional pressure drop correlations are proposed, and show a good agreement with the respective experimental data.
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An investigation into the governance of information technology projects in South Africa

Assessing the effectiveness of a biological recovery of nickel for tailing dumps management

Assessment of progress towards universal health coverage for people with disabilities in Afghanistan : a multilevel analysis of repeated cross-sectional surveys

  • Authors: Trani, Jean-Francois , Kumar, Praveen , Ballard, Ellis , Chandola, Tarani
  • Date: 2017
  • Language: English
  • Type: Articles
  • Identifier: http://hdl.handle.net/10210/241510 , uj:24865 , Citation: Trani, J.F. 2017. Assessment of progress towards universal health coverage for people with disabilities in Afghanistan : a multilevel analysis of repeated cross-sectional surveys
  • Description: Abstract: Background Since 2002, Afghanistan has made much effort to achieve universal health coverage. According to the UN Sustainable Development Goal 3, target eight, the provision of quality care to all must include usually underserved groups, including people with disabilities. We investigated whether a decade of international investment in the Afghan health system has brought quality health care to this group. Methods We used data from two representative household surveys, one done in 2005 and one in 2013, in 13 provinces of Afghanistan, that included questions about activity limitations and functioning difficulties, socioeconomic factors, perceived availability of health care, and experience with coverage of health-care needs. We used multilevel modelling and tests for interaction to investigate factors associated with differences in perception between timepoints and whether village remoteness affected changes in perception. Findings The 2005 survey included 334 people, and the 2013 survey included 961 people. Mean age, employment, and asset levels of participants with disabilities increased slightly between 2005 and 2013, but the level of education decreased. Formal education and higher asset level were associated with improved availability of health care and positive experience with coverage of health-care needs, whereas being employed was only associated with the latter. Perceived availability of health care and positive experience with coverage of health-care needs significantly worsened in 2013 compared with in 2005 (227 [69%] perceived that services were available in 2005 vs 405 [44%] in 2013, p<0·0001; 255 [78%] perceived a positive experience in 2005 vs 410 [45%] in 2013, p<0·0001). Village remoteness increased in 2013 (no connectivity by paved road 186 [57%] in 2005 vs 797 [87%] in 2013, p<0·0001; mean time to reach health-care facility 64·3 min [SD 167·7] vs 84·4 min [107·7], p<0·0001) and negatively affected perception of health-care availability. Interpretation Perceived availability of health care and experience with health-care coverage have not greatly improved for people with disabilities in Afghanistan, particularly in remote areas. Health policy in Afghanistan will need to address attitudinal, social, and accessibility barriers to health care.
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Bagasse energy cogeneration potential in the Zimbabwean sugar industry

  • Authors: Mbohwa, Charles
  • Date: 2003
  • Subjects: Bagasse - Zimbabwe , Energy cogeneration - Zimbabwe , Sugar trade - Zimbabwe
  • Type: Article
  • Identifier: uj:5205 , http://hdl.handle.net/10210/14448
  • Description: The cogeneration of steam and electricity has become the norm in the sugarcane industry worldwide. This process has been taken further to a stage where sugar companies can export a substantial amount of energy to the grid. Mauritius and Reunion Islands have implemented state of the art technology in bagasse energy cogeneration. It is on this basis that the potential for cogeneration in Zimbabwe’s sugar industry is being examined. The findings indicate that it is technically feasible to implement such a project. A full economic and financial feasibility study would still need to be done. Two plants of 105 MW each can be put in place, providing about 517 GWh of clean bagasse firm power to the Zimbabwe Electricity Supply Authority.
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Barriers to successful implementation of sustainable construction in the Ghanaian construction industry

  • Authors: Ametepey, Ofori , Aigbavboa, Clinton , Ansah, Kwame
  • Date: 2015
  • Subjects: Sustainable construction - Ghana , Sustainable construction - Ghana - Management
  • Type: Article
  • Identifier: uj:5298 , http://hdl.handle.net/10210/15052
  • Description: Sustainable construction efforts in some countries have been unsuccessful due to numerous barriers to its successful implementation. This study identifies and priorities likely barriers to successful implementation of sustainable construction in the Ghanaian construction industry and measures to overcome potential barriers. A multiple research approach involving semi-structured interviews and a questionnaire survey was adopted for the study. Interviews were carried out amongst purposively selected 18 contractors and 16 consultants whereas questionnaire survey was conducted among 100 randomly selected practitioners (58 Architects, 37 Quantity Surveyors and 5 Structural Engineers) to examine the relevance of the identified factors in the Ghanaian context. The factors identified as barriers to successful implementation of sustainable construction and measures to overcome potential barriers to sustainable construction were evaluated and ranked according to their mean scores. The five strongest barriers to the implementation of sustainable construction in Ghana are ranked as cultural change resistance, lack of government commitment, fear of higher investment costs, lack of professional knowledge, and lack of legislation respectively. Factor analysis using the SPSS Version 16 package enabled the barriers identified to be grouped under six components as 1) Financial barriers, 2) Political barriers, 3) Management/ Leadership barriers, 4) Technical barriers, 5) Socio-cultural barriers, 6) Knowledge/ Awareness barriers. The results of this study would enable the Ghanaian construction industry to be successful in its quest to implement sustainable construction. This will be possible through the implementation of the measures suggested to remove potential barriers to the implementation of sustainable construction. Identification of barriers and measures to overcome potential barriers are steps towards successful implementation of the sustainability concept in the Ghanaian construction industry.
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Challenges relating to the inter-facility transport of high acuity paediatric cases

  • Authors: Vincent-Lambert, Craig , Wade, Geraldine
  • Date: 2018
  • Language: English
  • Type: Article
  • Identifier: http://hdl.handle.net/10210/260570 , uj:27441 , Citation: Vincent-Lambert, C. & Wade, G. 2018. Challenges relating to the inter-facility transport of high acuity paediatric cases. African Journal of Emergency Medicine 8 (2018) 29–33. , DOI: https://doi.org/10.1016/j.afjem.2017.12.001
  • Description: Abstract: Introduction: The motivation for this study came from anecdotal reports and observations that there was a potential need for improvement to the systems that support inter-facility transfers of high acuity paediatric cases between referring and receiving facilities in Johannesburg, South Africa. In this exploratory study, we formally document and describe challenges being experienced by members of the healthcare team in facilitating the interfacility transport of high acuity paediatric cases. Methods: A qualitative, explorative design was applied, making use of interviews with purposefully-identified role players involved in paediatric transportation and care. Verbatim transcripts from audio recorded interviews underwent content analysis to allow for the identification of common categories. Results: Participants described a number of challenges, which included time delays, lack of qualified ambulance personnel, poor communication between role players, and lack of appropriate equipment. Discussion: There are significant challenges experienced by members of the healthcare team with regard to interfacility transport of high acuity paediatric and neonatal cases in Johannesburg, South Africa. Whilst we acknowledge the African context and resource constrained setting, health systems managers need to explore the feasibility of establishing dedicated and suitably resourced retrieval teams who specialise in the transfer of high acuity paediatric and neonatal patients in order to improve quality of care and overall patient outcomes in this population.
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Circular economy ownership models : a view from South Africa industry

Comparison of metastable phases induced by heat treatment of unmilled and milled cobalt powders

Critical pedagogies of place : educators' personal and professional experiences of social (in)justice

  • Authors: Perumal, Juliet Christine
  • Date: 2014
  • Subjects: Teacher identity , Social justice , Teachers - Cross-cultural studies
  • Type: Article
  • Identifier: uj:5449 , http://dx.doi.org/10.1016/j.tate.2014.09.004 , http://hdl.handle.net/10210/13189
  • Description: Participating in the education system of a foreign country, or within a new political dispensation presents various challenges for teachers. Understanding the challenges that teachers face as a result of relocation to new geographical and political contexts urges analyzing the contexts, which influence teachers' personal and pedagogic identities. Drawing on Buell's (1995) insights on place and identity; and Fraser's (2008) conceptions of social justice, this paper explores how teachers from South Africa, India, Zimbabwe and the Democratic Republic of Congo reinvent their identities in order to enact their professional and personal lives within different geo-political and socio-cultural contexts.
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Developing fluid flow and heat transfer in a channel partially filled with porous medium

  • Authors: Jen, Tien-Chien , Yan, T. Z.
  • Date: 2005
  • Subjects: Heat transfer , Fluid flow , Porous mediums
  • Type: Article
  • Identifier: uj:5264 , http://hdl.handle.net/10210/14933
  • Description: A three-dimensional computational model is developed to analyze fluid flow in a channel partially filled with porous medium. In order to understand the developing fluid flow and heat transfer mechanisms inside the channel partially filled with porous medium, the conventional Navier–Stokes equations for gas channel, and volume-averaged Navier–Stokes equations for porous medium layer are adopted individually in this study. Conservation of mass, momentum and energy equations are solved numerically in a coupled gas and porous media domain along a channel using the vorticity–velocity method with power law scheme. Detailed development of axial velocity, secondary flow and temperature field at various axial positions in the entrance region are presented. The friction factor and Nusselt number are presented as a function of axial position, and the effects of the size of porous media inside the channel partially filled with porous medium are also analyzed in the present study.
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Development of bio fuels in South Africa : challenges and opportunities

  • Authors: Pradhan, Anup , Mbohwa, Charles
  • Date: 2014
  • Subjects: Biofuels , Biofuels - South Africa
  • Type: Article
  • Identifier: uj:4807 , ISSN 1364-0321 , http://hdl.handle.net/10210/12205
  • Description: Biofuels have a potential to extend and diversify South Africa’s energy supply, thus reducing dependence on imported fuels and pollution levels. Despite several biofuel policies and mandates, biofuel develop- ment in South Africa has stalled in the legislative process and no large scale commercial biofuel project has materialized yet. Developing biofuels, especially using food grains, is a big challenge to the government of South Africa due to issues related to food security, commodity prices, economic and social concerns, and impacts of land use changes on the environment. The production cost of feedstock and employment creation opportunities from agricultural production play a vital role in selecting suitable feedstock for the region. Since considerable investment and infrastructure will be required for continued supply of feedstock and efficient biomass conversion technologies, rigorous research and comprehensive studies are required to identify feedstock and technologies best suited for the successful establishment of biofuel industry in South Africa.
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Dry-out CHF correlation for R134a flow boiling in a horizontal helically-coiled tube

  • Authors: Chen, C.-N. , Han, J.-T. , Jen, T.-C. , Shao, L.
  • Date: 2011
  • Subjects: Critical heat flux , Helically coiled tubes , Heat transfer
  • Type: Article
  • Identifier: uj:5286 , http://hdl.handle.net/10210/14955
  • Description: An experimental study was carried out to investigate the R134a dry-out critical heat flux (CHF) characteristics in a horizontal helically-coiled tube. The test section was heated uniformly by DC high-power source, and its geometrical parameters are the outer diameter of 10 mm, inner diameter of 8.4 mm, coil diameter of 300 mm, helical pitch of 75 mm and valid heated length of 1.89 m. The experimental parameters are the outlet pressures of 0.30–0.95 MPa, mass fluxes of 60–500 kg m 2 s 1, inlet qualities of 0.36–0.35 and heat fluxes of 7.0 103–5.0 104 Wm 2. A method based on Agilent BenchLink Data Logger Pro was developed to determine the occurrence of CHF with a total of 68 T-type thermocouples (0.2 mm) set along the tube for accurate temperature measurement. The characteristics of wall temperatures and the parametric effect on dry-out CHF showed that temperature would jump abruptly at the point of CHF, which usually started to form at the front and offside (270 and 90 ) of the outlet crosssection. The CHF values decrease nearly linearly with increasing inlet qualities, while they decrease more acutely with increasing critical qualities, especially under larger mass flux conditions. The mass flux has a positive effect on CHF enhancement, but the pressure has negative one. A new dimensionless correlation was developed to estimate dry-out CHF of R134a flow boiling in horizontal helically-coiled tubes under current experimental conditions and compared to calculated results from Bowring and Shah correlations.
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Effect of thermal treatment on mechanically milled cobalt powder

Effects of construction projects schedule overruns : a case of the Gauteng Province, South Africa

  • Authors: Mukuka, Mulenga , Aigbavboa, Clinton , Thwala, Wellington Didibhuku
  • Date: 2015
  • Subjects: Construction industry , Construction projects
  • Language: English
  • Type: Article
  • Identifier: http://hdl.handle.net/10210/68913 , uj:17795 , Citation: Mukuka, M., Aigbavboa, C. & Thwala, W. 2015. Effects of construction projects schedule overruns : a case of the Gauteng Province, South Africa
  • Description: Abstract: Construction schedule overruns are not uncommon on construction projects world over and the South African construction industry has not escaped the challenges of failing to deliver projects on time. In order to find mitigation measures of schedule overruns, the first step is to identify the causes of these overruns. This paper assesses the effects of construction projects schedule overruns in the Gauteng – South African construction industry. The data used in this paper were derived from both primary and secondary sources. The secondary data was collected via a detailed review of related literature. The primary data was collected through a well-structured questionnaire which was distributed to construction professionals, who include: Architects, quantity surveyors, civil engineers, construction mangers and project managers. Out of the 200 questionnaires sent out, 146 were received back representing a 73% response rate. Data received from the questionnaires was analysed using descriptive statistics procedures. Findings from the study revealed that extension of time, cost overruns, loss of profit, disputes, poor quality of work due to hurrying the project, creates stress to the client, acceleration losses, bad reputation with contraction team, claims and delay in getting profit by the client were the major effects of construction projects schedule overruns in Gauteng, South Africa. The study contributes to the body of knowledge on the subject of the effects of construction project schedule overruns in Gauteng, South Africa.
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Effects of processing parameters on the corrosion properties of dissimilar friction stir welds of aluminium and copper

  • Authors: Akinlabi, Esther Titilayo , Anthony, Andrews , Akinlabi, Stephen A.
  • Date: 2013
  • Subjects: Aluminium alloy , Copper , Corrosion , Friction stir welding
  • Type: Article
  • Identifier: uj:5019 , http://hdl.handle.net/10210/13159
  • Description: The influence of friction stir welding processing parameters on dissimilar joints conducted between aluminium alloy (AA5754) and commercially pure copper (C11000) was studied. The welds were produced by varying the rotational speed from 600 to 1200 r/min and the feed rate from 50 to 300 mm/min. The resulting microstructure and the corrosion properties of the welds produced were studied. It was found that the joint interfacial regions of the welds were characterized by interlayers of aluminium and copper. The corrosion tests revealed that the corrosion resistance of the welds was improved as the rotational speed was increased. The corrosion rates of the welds compared to the base metals were improved compared with Cu and decreased slightly compared with the aluminium alloy. The lowest corrosion rate was obtained at welds produced at rotational speed of 950 r/min and feed rate of 300 mm/min which corresponds to a weld produced at a low heat input.
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Electricity from bagasse in Zimbabwe

  • Authors: Mbohwa, Charles , Fukuda, Shuichi
  • Date: 2003
  • Subjects: Electric power production - Zimbabwe , Energy cogeneration - Zimbabwe , Bagasse - Zimbabwe
  • Type: Article
  • Identifier: uj:5203 , http://hdl.handle.net/10210/14446
  • Description: Zimbabwe has suffered electrical power shortages resulting in electrical energy imports rising to between 40% and 50% of total energy needs. Electricity generation capacity has stagnated at around 2000 Megawatts (MWe) since 1985, when two thermal units totaling 440 MWe were completed at Hwange. The e.ective capacity is 1:75 GWe. The current plan is to increase capacity by installing 600 MWe at Hwange at a cost of at least US $ 600 million. Raising this level of capital is difficult hence over the last 15 years there has been a failure to increase capacity. This article is based on a study of bagasse cogeneration in Zimbabwe and Mauritius conducted over a two-year period
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