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Heat transfer in two and three-dimensional single span greenhouses

  • Authors: Kruger, S. , Pretorius, L.
  • Date: 2016
  • Subjects: Greenhouse , Natural ventilation , Computational fluid dynamics
  • Language: English
  • Type: Conference proceedings
  • Identifier: http://hdl.handle.net/10210/214272 , uj:21260 , Citation: Kruger, S & Pretorius, L. 2016. Heat transfer in two and three-dimensional single span greenhouses.
  • Description: Abstract: The purpose of this paper is to investigate the heat transfer in two-dimensional and three-dimensional cavities representing a single span greenhouse. This investigation is conducted numerically using Computational Fluid Dynamics (CFD). The heat transfer and temperature fields driven by buoyancy forces are investigated. The research commences with the validation of a few fundamental geometries used as the building blocks for a large commercial greenhouse. The first fundamental geometry is a square filled with air. The CFD results for a square cavity are first evaluated against experimental results found in the literature for both two and three dimensional cavities. The heat transfer inside the cavities is then investigated and compared to those found in the literature. A reasonably good comparison between the numerical CFD results and the experimental results was found for both the two- and three-dimensional cavities. Based on the validated CFD models, two three-dimensional single span greenhouses containing a pitched roof were investigated to determine the effect of design alterations on the heat transfer within the cavity. The results were also compared to two-dimensional greenhouses with a 30 and 45 degree roof angle respectively. Results found that there are significant differences between the two and three-dimensional cases when the average Nusselt number is considered, especially for a greenhouse containing a roof angle of 45 degrees. Temperature distributions were also found to vary significantly throughout the three-dimensional greenhouses.
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Effect of benches on the natural convection in a single-span three-dimensional greenhouse

  • Authors: Kruger, S. , Pretorius, L.
  • Date: 2019
  • Language: English
  • Type: Conference proceedings
  • Identifier: http://hdl.handle.net/10210/399195 , uj:33261 , Citation: Kruger, S. & Pretorius, L. 2019. Effect of benches on the natural convection in a single-span three-dimensional greenhouse.
  • Description: Abstract: Greenhouses present a sustainable solution for food production in areas unfavorable for year round cultivation. In order to use the space within these structures efficiently, the maximum amount of growing area must be achieved. The main objective of the research conducted in this paper is determine the effect of stacked benches on the indoor climate and convective heat transfer of a single span greenhouse. Both a closed and a ventilated greenhouse will be investigated. This is achieved by utilizing a numerical method, namely CFD. The initial greenhouse considered is a greenhouse with a zero degree roof angle and no roof vents. The three-dimensional CFD model is validated with experimental results based on this greenhouse. The numerical greenhouse model is then modified to contain a 45 degree roof and stacked benches. The CFD simulation provides results in terms of graphs and parametric contour plots to illustrate the temperature and velocity flow fields around the bench arrangements. The results may be useful for small greenhouse growers to enable efficient crop production.
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Effects of culture on project management contributing to the success of managing culturally diverse engineering teams in a global environment

An integrated systems approach to risk management within a technology-driven industry, using the design structure matrix and fuzzy logic

  • Authors: Barkhuizen, W.F. , Pretorius, J.H.C. , Pretorius, L.
  • Date: 2012
  • Subjects: Fuzzy logic thinking , Risk management
  • Type: Article
  • Identifier: uj:4661 , ISSN 2224-7890 , http://hdl.handle.net/10210/10034
  • Description: Risk interactions exist within a system and its sub-systems, between functional and physical elements in various dimensions such as spatial interaction, information exchange, material transfer, and energy exchange. These interactions are of a multi-dimensional complexity, and thus are not sufficiently interpreted using conventional management tools. Alternative system representation and analysis techniques are proposed – in particular the design structure matrix (DSM) and fuzzy logic thinking – to quantify the risk management effort necessary to deal with uncertain and imprecise interactions. A cement grinding plant case study is used to elaborate on the risk management methodology
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The effect of geometrical electrical cable configurations on heat transfer in cable ducts

An approach to innovation in risk systems

  • Authors: Barkhuizen, W.F. , Pretorius, J.H.C. , Pretorius, L.
  • Date: 2011
  • Subjects: Risk interactions , Fuzzy logic thinking
  • Type: Article
  • Identifier: uj:6043 , http://hdl.handle.net/10210/10449
  • Description: Risk interactions exist between functional and physical elements within a system and its sub-systems in various ”dimensions” such as spatial interaction, information exchange, material transfer, energy exchange etc. The interactions are of a multi-dimensional complexity that cannot be sufficiently interpreted using conventional management tools (PERT, Gantt and CPM methods). Alternative system representation and analysis techniques are proposed, in particular the design structure matrix (DSM), and fuzzy logic thinking to quantify the risk management effort necessary to deal with uncertain and imprecise interactions. A Cement Grinding Plant case study is utilized to elaborate on the risk management methodology.
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A systematic approach for the implementation of an effective management model for gland service

  • Authors: Robinson, G.S. , Pretorius, J.H.C. , Pretorius, L.
  • Date: 2016
  • Language: English
  • Type: Conference proceedings
  • Identifier: http://hdl.handle.net/10210/93285 , uj:20327 , Citation: Robinson,G.S., Pretorius, J.H.C. & Pretorius, L. 2016. A systematic approach for the implementation of an effective management model for gland service.
  • Description: Abstract:The aim of the research was to develop an Effective Management Model (EMM) for a Gland Service System (GSS). The Systematic Approach to Engineering Design focuses on the optimisation of the GSS which is a fundamental pillar for the functionality of the slurry pumps in a tailings plant. The EMM was considered for a wide variety of mining applications to innovatively create a method for the correct design, implementation, control and maintenance of a Gland Service System. A Production Performance Model (PPM) was created utilising the Overall Equipment Effectiveness (OEE) Theory to provide an indication of the production capacity of a tailings plant. The subsystem of the PPM was the EMM, its core focus was on the optimisation of the Gland Service System, which in turn directly relates the improved performance of the tailings plant which ultimately results in the improved capability of the mines production process. Simulink was used to incorporate the optimisation inputs of the GSS, thus forming a model from Qualitative and Quantitative feedback as well as the Experimentation with regard to water quality and its effect on the GSS. By using these data sets, triangulation of the data sampling systems was used. The combination of non-probability sampling, and purpose sampling systems formed the basis of the triangulation system.
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Investigating the effect of team grouping principles on project success : a case study

  • Authors: Coetzee, Jacques , Pretorius, J.H.C , Pretorius, L.
  • Date: 2011
  • Subjects: Project management , Self Perception Inventory , Project success , Project teams
  • Type: Article
  • Identifier: uj:4717 , http://hdl.handle.net/10210/10966
  • Description: Time is money, an expression very often used these days. As we know, deadlines and budgets form a critical part of any project. It is for this reason that the researcher decided to investigate the effect that project team composition has on project success. The reality however is that project teams are formed randomly or by availability of personnel and not with due regard to individual competency and the efficiency of team roles. This often leads to project failure. The research aim was to identify and apply various methods used to compose an optimal project team. One of the factors that influences teamwork within the project team is the behaviour of team members. Dr. R. Meredith Belbin developed a Self Perception Inventory (SPI) which is a tool used to determine the preferred team role for every team member. This SPI was applied to the chosen sample and the outcome, which is a report of the individual's preferred team role, was compared to the actual role these individuals performed in one of their unsuccessful projects. The result of the study showed that when individuals are not applied within their preferred team roles it could have a negative effect on the chances for project success.
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A systems dynamic approach to channel management

  • Authors: Dirker, H.G. , Pretorius, L. , Pretorius, J.H.C.
  • Date: 2009
  • Subjects: Distribution channels management , Control and instrumentation products , Systems dynamic modelling , Channel management
  • Type: Article
  • Identifier: uj:6206 , ISSN 0-9815817-2-2 , http://hdl.handle.net/10210/5290
  • Description: The purpose of this paper is to explore from a systems dynamic modelling approach ways in which to manage distribution channels in the control and instrumentation product market. In this market multi-faceted product lines, technological knowledge and the position of the product in its life cycle play important roles in the manner in which these products are diffused into the market. Due to the fast pace of emerging technologies, it is becoming increasingly difficult for manufacturers to keep their routes to the markets aligned to ensure profitability and customer satisfaction. Aims of the paper include the following: to asses whether driving factors identified by way of preliminary research case studies, qualitative methods and inductive reasoning are realistic and how the identified factors could be used within a systems dynamic modelling approach to understand the value additions derived from a distribution channel for the various types of product lines. In conducting the research, unlike many studies using qualitative methods, this paper additionally employs system dynamics simulation to develop an analysis of different scenarios that can be used by manufacturers in their channel management approach. This paper contributes to the field of technology business strategies and planning by introducing a systems dynamic model that can be of assistance to technology manufacturers to ascertain the appropriate route to market for their various product lines.
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